AXIAL FIELD OF VIEW dimensions of a slice through the TOMOGRAPHIC VOLUME parallel to and including the SYSTEM AXIS Note 1 to entry: In practice it is specified only by its axial dimensio
General
All measurements must be conducted with the PULSE AMPLITUDE ANALYSER WINDOW configured as outlined in Table 1 Additional measurements may be taken using alternative settings recommended by the manufacturer Prior to measurements, the tomographic system should be calibrated according to the manufacturer's standard procedure for installed units, without any special adjustments for specific parameters If a test cannot be executed precisely as specified in the standard, the reasons for the deviation and the exact conditions of the test must be clearly documented.
Table 1 – R ADIONUCLIDES and ENERGY WINDOWS to be used for performance measurements
NOTE Because the characteristics of a GAMMA CAMERA may change noticeably between 122 keV ( 57 Co) and
141 keV ( 99m Tc), the former is not included as a suitable RADIONUCLIDE However, it may be useful in some circumstances, e.g for quality control
Unless otherwise specified, each DETECTOR HEAD in the system shall be characterized by a full data set
SPECT characterization will be provided for an acquisition that includes the minimum rotation necessary to gather a complete data set, typically 120° for a three-headed system Additionally, if the tomograph operates in a non-circular orbiting mode that affects performance parameters, test results for this mode must also be reported.
Unless otherwise specified, measurements shall be carried out at COUNT RATES not exceeding
Planar imaging
S YSTEM SENSITIVITY
System sensitivity is a crucial parameter that defines how effectively a system can detect radiation from a radioactive source, particularly at low activity levels where count losses are minimal The count rate measured for a specific activity and radionuclide is influenced by various factors, including the detector's material, size, and thickness, as well as the radioactive source's dimensions, shape, and its absorption and scattering characteristics Additionally, the instrument's dead time, energy thresholds, and collimator also play significant roles in determining the overall detection efficiency.
The purpose of this measurement is to determine the detected rate of events per unit of
ACTIVITY for a standard volume source of given dimensions and a specified COLLIMATOR
The SYSTEM SENSITIVITY test involves placing a known amount of ACTIVITY from a specified RADIONUCLIDE within the GAMMA CAMERA's DETECTOR FIELD OF VIEW to measure the resulting COUNT RATE, which is used to calculate SYSTEM SENSITIVITY Accurate assays of ACTIVITY, typically measured with a dose calibrator or well counter, are crucial for this test; however, achieving an absolute calibration better than ±10% is challenging For applications requiring higher accuracy, it is advisable to use absolute reference standards of the relevant RADIONUCLIDE.
The RADIONUCLIDE used for this measurement shall be appropriate for the COLLIMATOR energy specification and chosen from Table 1
The cylindrical phantom made of polymethylmethacrylate, as illustrated in Figure 2, will be utilized The source cuvette, depicted in Figure 3, must be filled with the designated radionuclide and positioned within the cylindrical hole specified in Figure 2 The remaining space in the hole will be occupied by a cylindrical insert, with dimensions also provided in Figure 2 Finally, the entire phantom, along with the source, will be positioned on the front face of the collimator.
(distance d = 0) and centred on the COLLIMATOR AXIS
Measurements of system sensitivity can be conducted without scatter by positioning the source cuvette, as shown in Figure 3, at a distance of 10 cm from the front face of the collimator.
To ensure accurate data collection, a minimum of 200,000 counts must be acquired using the ENERGY WINDOW setting outlined in Table 1 The recorded data acquisition time will be utilized to calculate the COUNT RATE \( C_s \) for all events captured in the image.
The ACTIVITY in the phantom shall be corrected for decay to determine the average ACTIVITY,
A ave , during the data acquisition time interval, T acq , by the following equation
A cal is the ACTIVITY measured at time T cal ;
T 0 is the acquisition start time;
T 1/2 is the RADIOACTIVE HALF-LIFE of the RADIONUCLIDE
The SYSTEM SENSITIVITY S for the COLLIMATOR used shall then be found by
Material: polymethylmethacrylate and shall be expressed in counts ⋅ s –1 ⋅ MBq –1
Report the SYSTEM SENSITIVITY together with the COLLIMATOR and the RADIONUCLIDE used.
S PATIAL RESOLUTION
Spatial resolution is crucial for an imaging system's ability to accurately depict the spatial distribution of a radionuclide within an object This measurement can be conducted using line sources in air, which assesses intrinsic spatial resolution without a collimator, and with a collimator and scattering material, which evaluates system spatial resolution The system spatial resolution measurement, which accounts for scatter, provides a more realistic representation of clinical scenarios when imaging patients, while intrinsic spatial resolution focuses on the detector head's performance without the influence of a collimator.
The purpose of this measurement is to describe the ability of the camera to characterize small objects
For all systems, the SPATIAL RESOLUTION shall be measured in IMAGE PLANES parallel to the
The characterization of the COLLIMATOR FRONT FACE involves measuring the width of the LINE SPREAD FUNCTIONS using LINE SOURCES This width is quantified by the FULL WIDTH AT HALF MAXIMUM (FWHM) and the EQUIVALENT WIDTH (EW) For precise measurement, the FWHM of the LINE SPREAD FUNCTION must cover a minimum of ten PIXELS in the test image.
Gamma cameras equipped with detectors made of multiple crystals may struggle to achieve ten pixels in the full width at half maximum (FWHM) in test images In such instances, it is essential to specify the matrix used for testing and to apply and document appropriate interpolation methods.
For the measurement of SYSTEM SPATIAL RESOLUTION the RADIONUCLIDE for the measurement shall be chosen from Table 1 according to the COLLIMATOR used For the measurement of
INTRINSIC SPATIAL RESOLUTION the RADIONUCLIDE shall be 99m Tc
For the measurement of SYSTEM SPATIAL RESOLUTION, a LINE SOURCE shall be prepared by placing a solution containing the selected RADIONUCLIDE in a tube with an inner diameter of
1 mm and length at least equal to the longer detector axis
For the measurement of INTRINSIC SPATIAL RESOLUTION, a multiple slit transmission phantom shall be used as shown in Figure 4
NOTE 1 Slit width 1,0 mm ± 0,05 mm
NOTE 2 Slit straightness ± 0,05 mm over any 30 mm length
NOTE 3 Slit centre separation 30,0 mm ± 0,05 mm
The phantom should be positioned at the center of the detector's field of view, with the collimator removed Additionally, a point source must be placed in front of the detector's center, ensuring it is at least five times the maximum linear dimension away.
DETECTOR FIELD OF VIEW (Figure 5)
D = Appropriate size and shape for different camera fields of view and larger thanDETECTOR FIELD OF VIEW
Lead shield prevents uncontrolled scatter
Figure 5 – Source arrangement for intrinsic measurements
4.2.2.6.1 S YSTEM SPATIAL RESOLUTION (with scatter)
The GAMMA CAMERA will be fitted with the COLLIMATOR being analyzed The LINE SOURCE will be positioned with its axis perpendicular to the COLLIMATOR AXIS and aligned parallel to either the X- or Y-axis at the measurement depth in water or a water-equivalent material that covers the entire field of view Additionally, the air gap between the COLLIMATOR FRONT FACE and the scattering medium's surface must be less than 5 mm.
The COLLIMATOR AXIS will measure a total of 200 mm, with assessments conducted across three parallel planes These measurements will be taken with the source positioned at distances of 50 mm, 100 mm, and 150 mm.
The measurement of the collimator front face must be conducted with the source aligned parallel to the other electronic axis Data collection requires a pixel size that is equal to or less than 10% of the full width at half maximum (FWHM) at the measurement depth Additionally, a minimum of 10,000 counts should be gathered at the peak point of each line spread function.
The slit transmission phantom shall be placed on the GAMMA CAMERA, with the COLLIMATOR removed Two sets of data shall be obtained The orientation of the slit transmission phantom
(5 × ) m ax l inear di m ens ion of F O V
≈ 2 FOV shall be adjusted until its slit axis is aligned parallel to the X- or Y-axis, respectively At least
1 000 counts shall be collected in the peak point of each LINE SPREAD FUNCTION
4.2.2.7.1 Data processing for SYSTEM SPATIAL RESOLUTION
The SYSTEM SPATIAL RESOLUTION profiles, with a width of 30 mm ± 5 mm, must be measured at right angles to the LINE SOURCE The lateral extension of these profiles should continue until the measured quantity reaches 5% of the maximum value or until the edge of the DETECTOR FIELD OF VIEW, depending on which is smaller Additionally, the profiles must abut each other.
4.2.2.7.2 Data processing for INTRINSIC SPATIAL RESOLUTION
For the INTRINSIC SPATIAL RESOLUTION profiles of width 30 mm ± 5 mm shall be obtained at right angles to the direction of the slit The profiles shall abut each other
The Full Width at Half Maximum (FWHM) is calculated through linear interpolation between neighboring pixels at half the maximum pixel value, representing the peak of the response function (refer to Figure 6) The resulting values are then converted to millimeter units by multiplying with the corresponding pixel size.
A and B are the points where the interpolated curve cuts the line of half maximum value
EQUIVALENT WIDTH (EW) shall be measured from the corresponding response function EW is calculated from the formula (see Figure 7)
∑ i C i is the sum of the counts in the profile between the limits defined by 1/20 C m on either side of the peak;
C m is the maximum PIXEL value;
PW is the PIXEL width in millimetres (see Figure 7)
H al f m ax im um v al ue M ax im um v al ue
NOTE EW is given by the width of the rectangle having the area of the LINE SPREAD FUNCTION and its maximum value C m
The PIXEL width PW is x i+1 – x i
The areas shaded differently are equal
Figure 7 – Evaluation of equivalent width (EW)
The measured LINE SPREAD FUNCTIONS yield essential data, including the calculated MODULATION TRANSFER FUNCTION (MTF) displayed as linear scaling graphs for the central profile Additionally, the analysis provides the FULL WIDTH AT HALF MAXIMUM (FWHM), FULL WIDTH AT TENTH MAXIMUM (FWTM), and EQUIVALENT WIDTH (EW) for each measurement.
The LINE SPREAD FUNCTION was measured, and for each source-to-COLLIMATOR distance, the indices were calculated and averaged in both the x- and y-directions Ultimately, the x- and y-indices were combined to determine the SPATIAL RESOLUTION specifications.
M ax im um v al ue C m
From the measured LINE SPREAD FUNCTIONS (4.2.2.6.2) the FWHM and EW shall be calculated as described in 4.2.2.8.1
The spatial resolution of each collimator, including scatter, must be reported as Full Width at Half Maximum (FWHM), Full Width at Tenth Maximum (FWTM), and Effective Width (EW) as a function of the source-to-collimator distance Additionally, graphs illustrating the corresponding modulation transfer functions should be provided, along with the reported pixel size.
The INTRINSIC SPATIAL RESOLUTION, expressed as FWHM and EW, according to 4.2.2.6.2 shall be reported.
S PATIAL NON - LINEARITY
Spatial linearity describes the ability of the system to reproduce the geometric properties of the object
SPATIAL NON-LINEARITY measurements provide information about the geometric distortion of a straight line
To assess SPATIAL NON-LINEARITY in all systems, measurements should be conducted in an IMAGE PLANE that is parallel to the detector's front face This involves analyzing the deviations from a straight line in the image produced by the slit phantom.
NOTE For pixelized detectors this method also applies
For the measurement of SPATIAL NON-LINEARITY the RADIONUCLIDE shall be 99m Tc
To measure spatial non-linearity, a multiple slit transmission phantom is utilized, as illustrated in Figure 4 This phantom encompasses the entire detector field of view and is positioned at the center of the detector face with the collimator removed Additionally, a point source is placed in front of the detector's center, ensuring it is at least five times the maximum linear dimension of the detector field of view, as shown in Figure 5.
The data acquired in the measurement of INTRINSIC SPATIAL RESOLUTION (4.2.2.6.2) shall be analysed
Profiles will be derived from two sets of data using slices that are oriented perpendicular to the slit axis, extending up to 30 mm along this axis These slices will be positioned adjacent to one another.
The position of each peak in the profiles is identified based on Figure 6 (position E) Distances between adjacent peak locations are calculated, and the differential non-linearity for the detector field of view is determined by the standard deviation of all measured distances from the two data sets (X and Y oriented).
Absolute non-linearity will be assessed through least squares fitting of equally spaced parallel lines for each data set, oriented in both X and Y directions It is defined as the maximum displacement, measured in millimeters, between the observed and fitted lines across the detector's field of view.
The differential non-linearity for the DETECTOR FIELD OF VIEW shall be reported according to 4.2.3.8.1 for X and Y
Absolute non-linearity shall be reported according to 4.2.3.8.2 for X and Y.
N ON - UNIFORMITY OF RESPONSE
Uniformity describes the ability of an imaging system to reproduce the object with a local sensitivity which is constant all over the DETECTOR FIELD OF VIEW
The measurement involves imaging a uniform flux directed at the GAMMA CAMERA in air without a COLLIMATOR to assess intrinsic non-uniformity of response, and with a COLLIMATOR using scattering material to evaluate system non-uniformity of response.
The system non-uniformity of response, which includes scatter, better reflects the clinical scenario when assessing a patient In contrast, the intrinsic non-uniformity of response defines the performance of the detector head in the absence of a collimator and the effects of scatter.
The purpose of this measurement is to characterize the ability of the camera to reproduce a uniform input signal without random local changes in count density
The uniformity of an image produced by a uniform photon flux is characterized by assessing differential non-uniformity, integral non-uniformity, and non-uniformity distribution The test measures the maximum deviation from the average count density both locally, through differential non-uniformity, and across the entire detector field of view, via integral non-uniformity Furthermore, a three-class histogram of pixel deviations is provided to illustrate the non-uniformity distribution.
To measure the system non-uniformity of response, select the radionuclide from Table 1 based on the collimator utilized For assessing intrinsic non-uniformity of response, the radionuclide 99m Tc should be used.
NOTE In addition other than the nuclides listed can be used
4.2.4.5.1 Measurement of INTRINSIC NON - UNIFORMITY OF RESPONSE
A source holder and source shall be positioned as shown in Figure 5
4.2.4.5.2 Measurement of SYSTEM NON - UNIFORMITY OF RESPONSE
The measurement shall be performed using a PARALLEL HOLE COLLIMATOR appropriate to the
RADIONUCLIDE used The source configuration shown in Figure 8, with a RADIONUCLIDE selected from Table 1, shall be placed as close as possible to the COLLIMATOR FRONT FACE
4.2.4.6.1 Measurement of INTRINSIC NON - UNIFORMITY OF RESPONSE
Areas beyond the detector's field of view must be protected with lead shielding The pixels used in the system will be square in shape, with a size that is equal to or less than twice the intrinsic spatial resolution, measured by the full width at half maximum (FWHM) Additionally, the average count per pixel will be specified.
10 000 ± 10 % The COUNT RATE shall not exceed 40 000 counts per second
4.2.4.6.2 Measurement of SYSTEM NON - UNIFORMITY OF RESPONSE
The photon flux reaching the COLLIMATOR FRONT FACE shall be uniform within ± 1 %, measured over areas of 1 cm 2
The PIXELS must be square and their size should be equal to or less than the SYSTEM SPATIAL RESOLUTION, which is measured in terms of FWHM at a distance of 50 mm from the COLLIMATOR FRONT FACE Additionally, the average number of counts per PIXEL should exceed 10,000, with a tolerance of ± 10%.
NOTE For a low energy PARALLEL HOLE COLLIMATOR the count density specified corresponds to approximately
Before evaluating the measurements outlined in sections 4.2.4.6.1 and 4.2.4.6.2, it is essential to calculate the mean number of counts per pixel within a square area, where each side measures 75% of the shortest dimension of the detector's field of view Subsequently, pixels will be chosen for inclusion in the analysis based on this calculation.
First, all PIXELS at the edge that contain less than 75 % of the mean number of counts shall be set to zero
Pixels with at least one directly adjacent neighbor that has a zero count will be excluded from the analysis and set to zero The analysis will then focus on the remaining non-zero data.
PIXELS) obtained from the image of the uniform flux shall be smoothed once by convolution with a nine-point filter function of the following weights:
In those cases where a PIXEL with zero count was included in the smoothing operation, the normalization coefficient shall be adjusted accordingly
The evaluation of non-uniformity across the detector field of view involves several key steps First, calculate the percentage of non-zero pixels where the count deviates by 10% or more from the mean count per pixel Next, determine the percentage of non-zero pixels with a count deviation of 5% to less than 10% from the mean Finally, assess the percentage of non-zero pixels that deviate by 2.5% to less than 5% from the mean count per pixel.
The maximum and minimum value of all non-zero PIXELS shall be determined From these data the integral non-uniformity shall be calculated using the following equation:
The uniform flux image will be analyzed as distinct rows and columns Each horizontal line in the X direction will be processed by beginning at one end and evaluating a group of five.
PIXELS including the first PIXEL , and noting the PIXELS with the maximum and minimum counts The differential non-uniformity shall be calculated using the following equation:
The set is advanced by one pixel, and the differential non-uniformity is calculated by examining the five pixels This procedure is repeated until the outermost pixel is reached Subsequently, all other horizontal lines undergo the same processing, with the differential non-uniformity represented as the maximum absolute value.
This process is repeated for all vertical lines (Y direction) independently Then the averages of both X and Y values are reported
Each COLLIMATOR must report the SYSTEM NON-UNIFORMITY OF RESPONSE, which includes non-uniformity distribution (4.2.4.8.1), integral non-uniformity (4.2.4.8.2), and differential non-uniformity (4.2.4.8.3) Additionally, the PIXEL size utilized for the analysis should be clearly specified.
The same data have to be reported for the INTRINSIC NON-UNIFORMITY OF RESPONSE.
I NTRINSIC ENERGY RESOLUTION
Energy resolution describes the ability of the detector to properly identify the energy of the detected photons
The INTRINSIC ENERGY RESOLUTION is measured to characterize the ability of a GAMMA CAMERA to separate photons with different energies
Measure an energy spectrum in low scatter configuration using a uniform irradiation of the
DETECTOR FIELD OF VIEW to yield an average energy resolution
The source shall be 99m Tc
A source holder and a source shall be positioned as in Figure 5 The COUNT RATE shall not exceed 20 000 counts per second
To achieve an accurate pulse height spectrum, it is essential to use a channel width that is 5% or less of the expected photopeak full width at half maximum (FWHM) Additionally, the peak channel must contain more than 10,000 counts to ensure reliable data.
The channel number shall be expressed in terms of energy by calibrating the GAMMA CAMERA with an additional RADIONUCLIDE
The INTRINSIC ENERGY RESOLUTION shall be the FWHM of the full energy absorption peak expressed as a percentage of this energy
The INTRINSIC ENERGY RESOLUTION shall be reported.
Intrinsic MULTIPLE WINDOW SPATIAL REGISTRATION
MULTIPLE WINDOW SPATIAL REGISTRATION is a measure of the ability of a GAMMA CAMERA to accurately position photons of different energies when imaged through different photopeak
The purpose of the test is to determine the energy dependence of the source localization in the image which may result in an energy dependent spatial scaling
Measurements shall be made at nine specified points on the entrance plane of the scintillation camera
The RADIONUCLIDE used to measure MULTIPLE WINDOW SPATIAL REGISTRATION shall be 67 Ga The
ENERGY WINDOW settings for each of the three 67 Ga photopeaks shall be set as specified in Table 1 The COUNT RATE shall not exceed 10 000 counts per second through each photopeak
A lead-lined source holder will collimate the 67 Ga source through a cylindrical hole measuring 5 mm in diameter and 25 mm in length The design, illustrated in Figure 9, shows the 67 Ga source positioned within the holder To reduce side wall penetration, the source height is specified to be 5 mm.
NOTE 1 Drawing not to scale
NOTE 2 See 4.2.6.5 and 4.2.8.5 for recommended values for d and t
Figure 9 – Small shielded liquid source
Images will be captured using a collimated 67 Ga source positioned at nine specific points on the detector's surface, including the central point, four points along the X-axis, and four points along the Y-axis The off-center points will be located at 0.4 and 0.8 times the distance from the central point to the edge of the camera's field of view (FOV) Separate images will be obtained through distinct energy windows corresponding to the 67 Ga photopeaks at each source location, with a maximum pixel size of 2.5 mm For cameras with two energy windows, images will be taken at each point using the 93 keV and 300 keV photopeaks If the camera has three or more energy windows, the 184 keV photopeak will also be included A minimum of 1,000 counts must be recorded in the peak pixel of each photopeak image.
The displacement of count centroids in the X and Y directions will be assessed for each measurement point's photopeak images To analyze the individual photopeak images, a square region of interest (ROI) will be centered on the maximum count pixel associated with each image.
The square ROI should have pixel dimensions roughly four times the anticipated FWHM of the image count profile being analyzed Each image will be integrated along the Y direction to obtain the X count profile, and along the X direction to derive the Y count profile The centroid of counts in both the X and Y directions will be calculated for each image based on the respective count profiles using the method outlined below.
The maximum difference in position of the centroid of counts acquired from each photopeak shall be determined The largest PIXEL displacement shall then be converted to millimetres
To determine the centroid of counts in the X and Y directions for the count profiles in each photopeak, identify the maximum count pixel in the integrated X or Y profile Then, calculate the centroid of counts using the specified formula.
L j is the calculated centroid location for energy window where j can equal 1,2 or 3;
X i is the X or Y count profile pixel at the i th location;
C i are the counts at the X i or Y i location;
The sum, denoted as ∑ = n i 1, is calculated over the profile pixels centered on the pixel with the maximum count The total number of pixels involved in this calculation is influenced by the Full Width at Half Maximum (FWHM) of the count profile and the size of the pixels It is essential that the minimum number of pixels included in this sum encompasses both the left and right half maximum counts.
The displacement D ij between ENERGY WINDOWS i and j is then:
The maximum displacement is simply the largest D ij
The MULTIPLE WINDOW SPATIAL REGISTRATION will be documented as the maximum variation in spatial positions across different ENERGY WINDOWS, measured in either the X or Y direction of the photopeak count centroids for the nine assessed points Results will be presented in millimeters.
C OUNT RATE performance
The performance of COUNT RATE is intricately influenced by the spatial distribution of ACTIVITY and scattering materials, necessitating simulations that reflect clinical imaging scenarios Consequently, tests are performed using a COLLIMATOR along with scattering materials.
COUNT RATE performance includes: a) the relationship between registered COUNT RATE and ACTIVITY, i.e the COUNT RATE CHARACTERISTIC;
The COUNT RATE CHARACTERISTIC indicates the stability of GAMMA CAMERA sensitivity across varying ACTIVITY levels, significantly influenced by the measurement setup Additionally, it serves as a verification for address errors resulting from ADDRESS PILE UP.
The ADDRESS PILE UP results in spatial distortion in the image and is highly dependent on the set-up of the measurement conditions
This procedure aims to assess the deviations from the linear relationship between COUNT RATE and ACTIVITY due to COUNT LOSSES, as well as to evaluate image distortions at high COUNT RATES, particularly those that result in spatially misplaced events.
Measurements of the COUNT RATE are performed at various ACTIVITY levels The variation of
ACTIVITY is normally achieved by radioactive decay No correction is made for COUNT LOSSES and scatter Each measured count shall be taken into account only once
The RADIONUCLIDE for the measurement shall be 99m Tc with ENERGY WINDOW setting according to Table 1
A cylindrical phantom as described in 4.2.1.5 and Figure 2 shall be used The air gap d between the surface of the phantom and the COLLIMATOR FRONT FACE shall not be more than
A COUNT RATE CHARACTERISTIC (measured COUNT RATE versus incident COUNT RATE or ACTIVITY) is to be measured by acquiring a series of images over time (e.g frames) The variation of
ACTIVITY is accomplished by radioactive decay with measurements continuing over approximately 10 RADIOACTIVE HALF-LIVES The time per frame shall be less than one-half of the
Radioactive half-life refers to the time required for half of the radioactive atoms in a sample to decay In experiments, the initial activity must be set to ensure that the count rate exceeds saturation levels Additionally, the final measurement should be taken when the count loss is below 1%.
A background acquisition shall be performed
The total counts acquired in each image shall be processed Background correction shall be performed for all frames
The average of the decaying ACTIVITY , A ave,i, during the data acquisition interval for time frame i, T acq,i, shall be determined by the following equation:
A cal is the ACTIVITY measured at time T cal ;
T 0,i is the acquisition start-time of the time frame i;
T 1/2 is the RADIOACTIVE HALF-LIFE of the RADIONUCLIDE in use
From the above measurements, plot the COUNT RATE CHARACTERISTIC (i.e measured COUNT RATE versus ACTIVITY)
To determine the conversion factor between ACTIVITY and COUNT RATE without COUNT LOSS, it is essential to average the values obtained from the three frames with the lowest ACTIVITY Additionally, sufficient counts must be acquired in these frames to achieve a statistical precision of 1% or better.
The measured COUNT RATE, which corresponds to 80 % of the TRUE COUNT RATE, shall be read from the graph and stated
To identify address errors resulting from ADDRESS PILE UP, profiles will be generated in both the X and Y directions at the center of the source image for chosen images This includes one pair of profiles measured at a COUNT RATE of around 5,000 counts per second, along with an additional pair at a different measured rate.
COUNT RATE of approximately 20 000 counts per second, and one pair at the maximum measured COUNT RATE
The ACTIVITY shall be specified as the total amount of ACTIVITY within the phantom
Report the graph showing the COUNT RATE CHARACTERISTIC and the ACTIVITY level at 20 %
The profiles in the X- and Y-direction were reported at the center of the source, with one pair of profiles recorded at a count rate of approximately 5,000 counts per second.
COUNT RATE of approximately 20 000 counts per second and one pair at the maximum measured COUNT RATE.
Shield leakage test
The DETECTOR SHIELD prevents the detection of unwanted photons originated from outside the entrance field of view of the COLLIMATOR
The purpose of this test is to identify the locations of the highest leakage and its magnitude
The entire surface of the DETECTOR SHIELD, including the joints, must be thoroughly examined using a collimated source to identify the highest leakage count rates at both the rear and side of the shield.
DETECTOR SHIELD and the joints (particularly the joint between the COLLIMATOR and the
The RADIONUCLIDE is selected from Table 1 according to the COLLIMATOR under study
A small collimated source, as illustrated in Figure 9, with d not larger than 20 mm and t not less than 10 mm, totally filled with the RADIONUCLIDE
To ensure accurate measurements, the source must be positioned against the external surface of the DETECTOR SHIELD and its joints It is essential to sweep the entire surface of the DETECTOR SHIELD and record the COUNT RATES.
The reference COUNT RATE shall be measured with the source placed on the COLLIMATOR AXIS at
100 mm distance from the COLLIMATOR FRONT FACE
The maximum leakage count rates at both the rear and side of the detector shield must be documented, along with the highest leakage count rate observed at the joints in the shield.
Express the ratios of the three maximum leakage COUNT RATES as a percentage of the reference COUNT RATE
The three maximum leakage ratios shall be reported
The RADIONUCLIDE and the COLLIMATOR used shall be stated.
Wholebody imaging
Scanning constancy
For wholebody image creation with a PLANAR WHOLEBODY IMAGING EQUIPMENT the speed of the relative movement of the GAMMA CAMERA and the object shall be constant
The purpose of this measurement is to test the constancy of GAMMA CAMERA motion in the scanning direction
A gamma camera equipped with a radioactive source on its detector head generates whole-body images that maintain a consistent count per unit of axial distance, assuming a constant scanning speed.
The RADIONUCLIDE to be employed for this measurement shall be 99m Tc
A small source will be positioned at the center of the detector's field of view, attached to the collimator The activity of this source will be calibrated to achieve a count rate of approximately [insert specific count rate].
10 000 counts per second, through a 20 % PULSE AMPLITUDE ANALYSER WINDOW, in the
The scan speed and acquisition matrix must adhere to the clinically recommended range Additionally, two scans should be conducted over the entire scanning length \( L \) as illustrated in Figure 10.
MANUFACTURER using different speeds The image of the source shall be recorded
Dimensions in millimetres a) Source position for resolution measurement parallel to the direction of motion b) Source position for resolution measurement perpendicular to the direction of motion
L full wholebody scanning length (as specified by the manufacturer)
Figure 10 – Source positions for scanning constancy for wholebody imaging
A profile is created based on the source image aligned with the motion direction This profile must have a width ranging from 20 mm to 30 mm, perpendicular to the motion, and should include a minimum of 10,000 counts for each profile bin.
The analysis will focus on the length L, omitting 20 mm from each end of the profile Within this analysis region, the mean value M of the counts per profile bin will be calculated Additionally, the percent deviation from M will be assessed for each bin, with the maximum percent deviation from M being identified.
Any deviation greater than ± 4 standard deviations of M (assuming Poisson statistics) is indicative of non-uniform scanning motion The locations of such deviations and their values shall be noted
The report must feature a graph illustrating the percent deviation from the mean value of counts, along with the maximum percent deviation from this mean Additionally, any deviations exceeding ± 4 standard deviations should be clearly indicated.
The COLLIMATOR and the scan speeds used in performing the measurements shall be also reported.
S PATIAL RESOLUTION without scatter
Spatial resolution is crucial for an imaging system's capability to accurately depict the spatial distribution of a radionuclide within an object This measurement is conducted by imaging line sources in air using a collimator It is assumed that the motion during a whole-body scan does not impact the spatial resolution of the final image.
The purpose of this test is to validate the consistency of SPATIAL RESOLUTION in wholebody scans
SPATIAL RESOLUTION without scatter shall be measured parallel and perpendicular to the direction of motion, and expressed as FULL WIDTH AT HALF MAXIMUM (FWHM) of the LINE SPREAD FUNCTION
The RADIONUCLIDE to be employed for this measurement shall be 99m Tc
The sources shall consist of capillary tubes, each having an inside diameter of less than or equal to 1 mm and a length of at least 120 mm
The sources will be calibrated to achieve a COUNT RATE between 3,000 and 10,000 counts per second, utilizing a PULSE AMPLITUDE ANALYSER WINDOW as specified in Table 1, while ensuring that both capillary tubes are within the DETECTOR FIELD OF VIEW.
The sources shall be placed on the wholebody scanning table on a flat support with low attenuation
To measure resolution in the direction of motion, both capillary tubes must be positioned at the center of the scanned field of view, oriented perpendicular to the motion Additionally, the second source should be aligned parallel to the first at a specified distance of at least.
100 mm as shown in Figure 10a
To measure resolution perpendicular to the motion direction, both capillary tubes must be positioned within the scanned field of view, aligned parallel to the motion The second source should be placed parallel to the first at a minimum distance of 100 mm, as illustrated in Figure 10b.
NOTE It may be possible to position four sources simultaneously in the DETECTOR FIELD OF VIEW of the GAMMA CAMERA and to combine the two measurements into one scan
The scan speed must adhere to clinical recommendations, with scans conducted both above and below the table at the specified source positions The camera should be placed 100 mm from the sources to the collimator front face, and the pixel size must not exceed 20% of the full width at half maximum (FWHM) of the spatial resolution.
COLLIMATOR being used The scan range shall be at least three times the axial length of the detector and shall cover all sources
Profiles of width 30 mm ± 5 mm shall be obtained at right angles to the direction of each LINE SOURCE The profiles shall abut each other
The FWHM shall be calculated for each profile using a Gaussian fit method Additionally, for each LINE SOURCE the corresponding peak position shall be calculated from the profile
For both pairs of LINE SOURCES and each detector head the PIXEL size shall be determined from the known LINE SOURCE spacing and the corresponding peak positions
The FWHM values will be averaged for tubes oriented both parallel and perpendicular to the direction of motion, with measurements taken above and below the table These values will be reported in millimeters.
The FWHM values shall be reported separately for the measurements above and below the table and in the directions parallel and perpendicular to the direction of motion The
COLLIMATOR and scan speed used in performing the measurements shall be reported.
Tomographic imaging (SPECT)
Test of PROJECTION geometry
The reconstruction of SPECT data sets requires a precise knowledge of the geometry of the
PROJECTIONS In particular all lines of response must be perpendicular to the axis of rotation
The consistency of the geometry of acquired projections is primarily influenced by four key factors: the accuracy of the center of rotation, the tilt of the detector head, the alignment of the collimator holes, and the co-registration of multiple heads.
Accurate reconstruction necessitates understanding the position of the projection of the COR within the Xp, Yp coordinate system for each projection angle of the slice In an ideal system with circular detector rotation, the projection of a slice is essential for error-free reconstruction.
POINT SOURCE at the COR will be at the same position X' p in the PROJECTION matrix for all angles of PROJECTION (see Figure 1)
An error-free reconstruction requires that the direction of the COLLIMATOR holes is orthogonal to the SYSTEM AXIS for each angle of PROJECTION Deviations from this requirement are called
If all holes of a PARALLEL HOLE COLLIMATOR are parallel, the OFFSET is constant for all source positions within the measuring volume, assuming linearity of the positioning electronics
For multiple-head systems, it is crucial that all detectors are matched to image the same volume, ensuring they have identical pixel sizes, offsets, and z-direction coordinates Specifically, the offsets of the individual detector heads must be properly aligned with one another.
To assure the consistency of the geometry of acquired PROJECTIONS
The tests shall be performed for all COLLIMATORs For multiple-head systems all angular
DETECTOR HEAD configurations and all COLLIMATOR combinations shall be tested
The RADIONUCLIDE for the measurement shall be 99m Tc with ENERGY WINDOW setting according to Table 1
4.4.1.5.1 C ENTRE OF ROTATION (COR) and DETECTOR HEAD TILT
Three POINT SOURCES locations are required The sources shall be positioned radially at least
5 cm from the SYSTEM AXIS The axial location (Z) shall be at the centre of the DETECTOR FIELD
OF VIEW and the other two, ± 1/3 of the AXIAL FIELD OF VIEW from the centre If more than one
When utilizing a POINT SOURCE, it is essential to carefully select the location of each source to ensure that the centroid of its PROJECTION can be independently assessed.
A point source will be positioned at each intersection of an orthogonal grid in the X, Z plane, effectively covering the entire field of view The grid lines will be spaced 10 cm apart.
For each DETECTOR HEAD a minimum of 32 PROJECTIONS equally spaced over 360° are acquired and displayed as a SINOGRAM The RADIUS OF ROTATION shall be set to 20 cm or higher
At least 10 000 counts per view shall be acquired The PIXEL size shall be less than 4 mm
To calculate the centroid \( X_p(\theta) \) of the source in the \( X_p \) direction, 50 mm wide strips will be utilized in the \( Y \) direction, centered around the \( Y_p \) position of each source This process will be repeated for each projection angle \( \theta \).
When a detector head is tilted, the image of the point source shifts in both the X and Y directions To isolate the X movement from the Y movement under reasonable head tilt conditions, the centroid is calculated using a 50 mm wide strip The subscript "p" denotes the projection space, as illustrated in Figure 1.
The DETECTOR HEAD TILT is determined by calculating the centroid Y p (θ) of the image of one
POINT SOURCE in the Y p direction, using the data full field-of-view in the X p direction This calculation shall be done for each PROJECTION ANGLE
The centroids X p (θ) and Y p (θ) are calculated according to 4.4.1.7.1 and 4.4.1.7.2, respectively
A sine function is fitted to the calculated centroids X p (θ) for each source position i
X p,i (θ) = A i sin(θ + ϕ i ) + C i (9) where θ is the PROJECTION ANGLE;
A i is the amplitude of the sine function for source position i; ϕ i is the phase shift of the sine function for source position i;
C i is the base shift of the sine function for source position i
Then the OFFSET is calculated as the average of the C i over the three source positions
In addition, the difference between fit and data shall be plotted (showing the error) as a function of θ The maximum difference for each axial position shall be determined
One source is selected for the evaluation of DETECTOR HEAD TILT
A sine function is fitted to the calculated centroid Y p (θ) for the selected source
Y p (θ)= B sin(θ + ψ) + D (10) where θ is the PROJECTION ANGLE;
B is the amplitude of the sine function for the selected source; ψ is the phase shift of the sine function for the selected source
D is the base shift of the sine function for the selected source
The head tilt angle value a is calculated as a = arcsin B/A, where A is the amplitude for the selected source as obtained in 4.4.1.8.1
In addition the difference between fit and data shall be plotted (showing the error) as a function of θ
The following analysis is performed for all source positions i
A sine function is fitted to the calculated centroids X p,i (θ)
X p,i (θ) = A i sin(θ + ϕ i ) + C i (11) where θ is the PROJECTION ANGLE;
A i is the amplitude of the sine function for source position i; ϕ i is the phase shift of the sine function for source position i;
C i is the base shift of the sine function for source position i
The mean value of all C i , (which are the local hole misalignments in X p -direction) shall be calculated and the maximum deviation from this mean value identified
A sine function is fitted to the calculated centroid Y p,i (θ)
Y p,i (θ)= B i sin(θ + ψ i ) + D i (12) where θ is the PROJECTION ANGLE;
B i is the amplitude of the sine function for source position i; ψ i is the phase shift of the sine function for source position i
D i is the base shift of the sine function for source position i
The local hole misalignment in the Y p -direction a i is calculated as a i = arcsin B i /A i
The mean value of all a i shall be calculated and the maximum deviation from this mean value identified
The DETECTOR HEAD and COLLIMATOR used shall be stated For multiple head systems the configuration of the DETECTOR HEADs shall be reported
The PIXEL size used shall be reported
Report the OFFSET of the CENTRE OF ROTATION as calculated according to 4.4.1.8.1 in millimetres
Plot the difference between fitted sine function and the locations of the centroids as a function of θ for each axial position
The maximum difference for each axial position shall be reported in millimetres
The head tilt angle value α shall be reported
Plot the difference between fitted sine function and the locations of the centroids as a function of θ
The mean values of all C i and all A i and the corresponding maximum deviations from these mean values shall be reported
Report all C i and A i values and their positions.
Measurement of SPECT SYSTEM SENSITIVITY
The DETECTOR POSITIONING TIME, along with the selected acquisition time, affects the portion of total acquisition time that is ineffective for data collection, thereby impacting the sensitivity of a tomographic device This effect is particularly significant for rotating detectors operating in "step and shoot" mode.
This test provides a measure to determine the idle time of the system during the acquisition that is not used for data acquisition
The result of the test is based on a standard SPECT acquisition
The RADIONUCLIDE for the measurement shall be 99m Tc with ENERGY WINDOW setting according to Table 1
A POINT SOURCE of 99m Tc shall be placed at the CENTRE OF ROTATION in air
The COUNT RATE must exceed 1,000 counts per second (cps) Two 360° tomographic acquisitions will be conducted, one with a minimum of 60 PROJECTIONS and the other with at least 120 PROJECTIONS, each having an acquisition time of 10 seconds per PROJECTION The subscript j indicates either "low" or "high," reflecting the respective number of PROJECTIONS The total time T j, from the beginning of the first PROJECTION to the conclusion of the last, will be recorded Following the tomographic acquisition, a static acquisition of the same duration T j will be performed, with data corrected for decay based on the different starting times.
The total DETECTOR POSITIONING TIME T pos shall be calculated according to:
N total is the sum of the counts in all PROJECTIONS;
N static is the number of counts in the static acquisition
The mean DETECTOR POSITIONING TIME per PROJECTION ∆T pos is then calculated by dividing T pos by the number of transitions between PROJECTION steps actually used
The correction factor c j for the calculation of the VOLUME SENSITIVITY is then given by j j j j T T c T pos, acq, acq,
The correction factor c j shall be calculated for the subscript j with corresponding acquisition times per PROJECTION∆T acq,j of 20 s (low) and 10 s (high), respectively
The correction factor \( c_j \) should be documented for the subscript \( j \) along with the associated acquisition times per PROJECTION \( \Delta T_{acq,j} \) of 20 seconds for low and 10 seconds for high This setup reflects a common clinical scenario with a total acquisition time of 30 minutes.
The VOLUME SENSITIVITY of a SPECT system may only provide an indirect measure of the clinical performance of a SPECT system
The test determines the VOLUME SENSITIVITY and relates it to the AXIAL FIELD OF VIEW
A standard SPECT acquisition of a uniform phantom is used to calculate the NORMALIZED VOLUME SENSITIVITY
The RADIONUCLIDE for the measurement shall be 99m Tc with ENERGY WINDOW setting according to Table 1
The measurement will utilize a cylindrical phantom with an outer diameter of 200 mm ± 3 mm, a wall thickness of 3 mm ± 1 mm, and an inner length of 190 mm ± 3 mm, uniformly filled with a 99m Tc water solution.
The activity concentration, expressed in kBq/cm³, must be precisely measured by counting a minimum of two samples from the solution using a calibrated well counter Additionally, the results should be adjusted for radioactive decay to reflect the time of measurement, specifically at the midpoint of the acquisition interval.
Accurate assays of radioactivity, measured with a dose calibrator or well counter, are crucial for the test's reliability Maintaining absolute calibration with these devices is challenging, often achieving accuracies no better than 10% For applications requiring greater precision, it is advisable to use absolute reference standards with suitable γ-emitters.
Position the phantom so that its long axis aligns with the SYSTEM AXIS, maintaining proximity to it The RADIUS OF ROTATION (R) should be set to 20 cm For each COLLIMATOR routinely utilized in SPECT imaging, ensure that at least one million counts are acquired in static imaging mode, and document the acquisition time (T).
To analyze the phantom image, the number of counts \( N_{ROI} \) within a rectangular region of interest (ROI) must be calculated The ROI should have a maximum width of 240 mm to encompass the cylinder's diameter, while its length must be at least 150 mm in the axial direction and centered on the phantom.
The NORMALIZED VOLUME SENSITIVITY S norm is then calculated by dividing the number of counts
The ROI is determined by the average activity concentration, acquisition time, and axial length, multiplied by the correction factor, as described in the equation provided in section 4.4.2.1.8.
ROI norm j cps/ kBq/cm a l c T a
NOTE For a given phantom set-up and PARALLEL HOLE COLLIMATOR , the NORMALIZED VOLUME SENSITIVITY and the
SYSTEM SENSITIVITY measured according to 4.2.1 are related by a fixed ratio and the correction factor c j
The values shall be specified and stated for the subscript j of low and high respectively.
Scatter measurement
The scattering of primary gamma rays can lead to inaccuracies in radiation source localization Different designs and implementations of emission tomographs result in varying sensitivities to scattered radiation This procedure aims to quantify the relative system sensitivity to scattered radiation, represented by the scatter fraction.
(SF), as well as the values of the SCATTER FRACTION in each slice (SF i )
Unscattered events are expected to be found within a strip that is 2 × FWHM wide, centered on the LINE SOURCE image in each SINOGRAM This width is selected because the scatter value remains largely unaffected by the precise dimensions of the region, and very few unscattered events occur beyond one FWHM from the line image.
The scatter response function's width enables a simplified analysis approach By employing linear interpolation between the intersection points of the scatter tails and the edges of a 2 × FWHM wide strip, we can estimate the scatter amount within the strip The estimated scatter is determined by the area under the interpolation line, along with contributions from outside the strip.
Estimates of the SCATTER FRACTION for uniform source distributions are made under the assumption of its low radial dependence Under this assumption, the measure of SCATTER
The FRACTION for a LINE SOURCE on-axis is applied to a cross-sectional area with a radius of 22.5 mm For a LINE SOURCE 45 mm off-axis, the SCATTER FRACTION is applied to an annulus between 22.5 mm and 67.5 mm, while the SCATTER FRACTION for a LINE SOURCE 90 mm off-axis is applied to an annulus between 67.5 mm and 100 mm The three SCATTER FRACTION values are weighted by their respective areas, resulting in a weighted average, with the annular areas in the ratios of 1:8:10.75.
NOTE The mounting plate replaces the cover of the cylindrical phantom
The source holders consist of tubes of lengths sufficient to fill the inside length of the cylindrical phantom
In addition, the drawing shows the weighting areas (bounded by the dashed lines) for the scatter measurement
Figure 12 – Phantom insert with holders for the scatter source
The RADIONUCLIDE for the measurement shall be 99m Tc with ENERGY WINDOW setting according to Table 1, with an ACTIVITY less than that at which the percent dead-time losses exceed 5 %
The test phantom must be filled with non-radioactive water to serve as a scatter medium The LINE SOURCE of the test phantom should be inserted parallel to the cylinder's axis at radial distances of 0 mm, 45 mm, and 90 mm, ensuring the phantom is centered axially for tomographic assessments.
22,5 with an AXIAL FIELD OF VIEW greater than 165 mm, the phantom shall be centred within the AXIAL FIELD OF VIEW
Measurements will be conducted by imaging a single line source at three distinct radial positions within a water-filled test phantom This will utilize the collimator designed for SPECT imaging, following a circular orbit with a radius of rotation of 200 mm.
Data collection will occur at specified radial distances from the tomograph's long axis, with SINOGRAM data acquired for each radial location of the LINE SOURCE A minimum of 200,000 counts per slice is required for each slice within the AXIAL FIELD OF VIEW or the central 165 mm, depending on which is smaller.
Data shall not be corrected for scatter or ATTENUATION
All SINOGRAMS from slices at least 10 mm away from either end of the phantom will be processed For tomographs with an AXIAL FIELD OF VIEW of less than 165 mm, every slice will be processed.
In the SINOGRAM, all PIXELS located more than 120 mm from the center are set to zero For each PROJECTION ANGLE, the center of the LINE SOURCE is identified by locating the PIXEL with the highest value, which is then aligned with the central PIXEL row of the SINOGRAM Following this realignment, a sum PROJECTION is generated The counts at the left and right edges of the 2 × FWHM wide strip, denoted as C L,i,k and C R,i,k, are extracted from the sum PROJECTION Linear interpolation is applied to determine the count levels at ±1 × FWHM from the central PIXEL of the PROJECTION The average of C L,i,k and C R,i,k is multiplied by the fractional number of PIXELS between the edges of the strip, and this product is added to the counts in the PIXELS outside the strip to calculate the scattered counts C s,i,k for slice i and source position k The total counts, C tot,i,k, represent the sum of scattered and unscattered counts across all PIXELS in the sum PROJECTION.
NOTE In the summed PROJECTION the scatter is estimated by the counts outside the 2 × FWHM wide strip plus the area of the LSF below the line C L,i,k – C R,i,k
Figure 13 – Evaluation of scatter fraction
The average activity, denoted as \$A_{ave,k}\$, during the data acquisition period \$T_{acq,k}\$ for the line source at position \$k\$ is determined by applying a decay correction, with each midpoint of the time intervals \$T_{acq,k}\$ linked to a common starting time.
The SCATTER FRACTION SF i for each slice, i, due to a uniform source distribution shall be calculated as follows:
SF i i i i i i i (17) where the subscripts 1, 2 and 3 refer to LINE SOURCES at radial distances 0 mm, 45 mm and 90 mm, respectively
For each processed slice, the corresponding value of SF i will be recorded Additionally, the average SF of all SF i values will be presented as the system's SCATTER FRACTION for uniform sources.
SPECT SYSTEM SPATIAL RESOLUTION
The SPECT SYSTEM SPATIAL RESOLUTION characterizes the ability of the SPECT system to identify small details and high contrasts
SPECT acquisition and reconstruction of a set of POINT SOURCES
The RADIONUCLIDE selected from Table 1
The IEC cylindrical phantom (see Figure 11) shall be used with the mounting plate according to Figure 12
Three point sources, made from a radionuclide specified in Table 1 and not exceeding 2 mm in any dimension, must be positioned within a water-filled cylinder The cylinder's axis should align with the system axis The first point source is to be placed along the cylinder's axis at the central plane, as illustrated in Figure 12.
The second point source will be positioned 45 mm radially and -50 mm along the Z direction from the central plane The third point source will also be placed at a specified radial position.
90 mm and +50 mm from the central plane in the Z direction
To assess the spatial resolution of the SPECT system, align the phantom's axis with the system axis, ensuring that the two off-center point sources intersect either the X or Y axis of the reconstructed transverse slice Conduct measurements with a radius of rotation of 200 mm, unless otherwise specified; if the system cannot achieve this, use the maximum possible radius and document it Data should be collected with a pixel size that is equal to or less than 30% of the system's full width at half maximum (FWHM) at 200 mm from the collimator's face, utilizing at least 120 equally spaced projection angles over a 360° acquisition A minimum of 250,000 counts must be recorded in each reconstructed slice.
The analysis will focus on three slices positioned to encompass the center of the phantom and extend ± 50 mm along its axis The TRANSVERSE POINT SPREAD FUNCTIONS for each reconstructed slice will be evaluated in both the X and Y directions, providing insights into PIXEL size, RADIAL, and TANGENTIAL RESOLUTION Additionally, from the coronal or sagittal slice that includes the three POINT SOURCES, the POINT SPREAD FUNCTIONS will be assessed in the Z direction to determine PIXEL size and AXIAL RESOLUTION.
Three transverse slices, 10 mm ± 3 mm thick shall be reconstructed using filtered backprojection a ramp filter with a cut-off at the Nyquist frequency as determined by the acquisition PIXEL size
The analysis of the measured point spread functions will yield essential data, including the radial resolution (FWHM and EW) for each position in the radial direction, as detailed in section 4.4.4.6 and illustrated in Figures 6, 7, and 14 Additionally, the tangential resolution (FWHM and EW) will be determined for each position in the tangential direction, also based on the measurements from section 4.4.4.6 and represented in Figures 6, 7, and 14 Lastly, the axial resolution (FWHM and EW) will be assessed in the axial direction for each position outlined in section 4.4.4.6, with supporting visuals in Figures 6 and 7.
The PIXEL size and the number of PROJECTIONS shall be stated
The reported data from the measured point spread functions includes the radial resolution (FWHM and EW) for each position in the radial direction, as detailed in section 4.4.4.6 and illustrated in Figures 6, 7, and 14 Additionally, the tangential resolution (FWHM and EW) is provided for each position in the tangential direction, also based on the measurements from section 4.4.4.6 Lastly, the axial resolution (FWHM and EW) is reported for each position in the axial direction, as described in section 4.4.4.6 and shown in Figures 6 and 7.
Tomographic image quality
Contrast and noise significantly influence image quality, with their interplay determining the detectability of lesions The contrast is primarily influenced by the ratio of lesion-to-background activity concentration Additionally, finite spatial resolution and scatter further diminish image contrast At low contrast levels, the presence of background noise can hinder the visibility of lesions.
Subclause 4.4.5 aims to assess the image quality factors of SPECT and SPECT/CT scanners under standard imaging conditions To replicate these conditions, a torso-shaped phantom will be utilized, featuring several hot spheres of varying diameters and a cold cylinder insert within a warm background.
The detectability of lesions is evaluated by measuring the contrast of hot spheres against background noise Furthermore, the scanner's capability to recover contrast is assessed based on varying sphere sizes.
The wholebody phantom is to be used for all measurements (see Figure 15) into which hollow spheres and lung insert are placed (see Figure 16)
Dimensions are in millimetres and are given within ± 1 mm
NOTE The phantom length shall be at least 180 mm ± 5 mm
Figure 15 – Cross-section of body phantom
The wall thickness of the spheres shall be ≤ 1 mm
The centres of the spheres shall be at the same distance from the surface of the mounting plate
The spheres can also be made from glass
The lung insert cylinder is centred within the image quality phantom and has length that extends through the entire chamber and diameter of 50 ± 2 mm
NOTE All diameters given are inside diameters
Figure 16 – Phantom insert with hollow spheres
Hollow spheres of decreasing diameter are circularly arranged on a single plane, featuring hollow stems that allow for the filling of the spheres with a radioactive liquid The lung cylinder insert, measuring (50 ± 2) mm in diameter, spans the length of the phantom chamber It is filled with a low atomic number material, having a density of (0.30 ± 0.10) g/cm³, which is free of activity and effectively simulates lung attenuation.
A SPECT acquisition covering the length of the wholebody phantom shall be obtained
The algorithms employed for image reconstruction, as well as scatter and attenuation correction, will align with the standard SPECT clinical image protocol for bone or cardiac imaging Additionally, results from enhanced image reconstructions may be presented separately.
After the acquisitions and image reconstruction, regions of interest (ROIs) are delineated on specific image slices, focusing on the hot spheres, cold cylinder insert, and the background of the image quality phantom The analysis is conducted using the average pixel values from these ROIs.
The RADIONUCLIDE for the measurement shall be 99m Tc
The total ACTIVITY in the wholebody phantom background should be 500 MBq This corresponds to a concentration of approximately 80 kBq/ml The spheres shall be filled with an
ACTIVITY concentration that is between 7,6 and 8,4 times the ACTIVITY concentration in the background All ACTIVITY concentrations are specified for the time at the start of acquisition
The relative ACTIVITY concentrations in the phantom background and spheres shall be determined independently by planar imaging of 5 cm 3 aliquots of the two solutions using the same DETECTOR HEAD
The whole-body phantom is positioned on the tomograph's patient bed, ensuring it is centered within the transverse field of view Additionally, a line drawn through the center of the whole-body phantom must remain parallel to the system axis.
A SPECT acquisition must be conducted over the entire length of the whole-body phantom If the axial field of view is adequate to encompass the phantom's length, the acquisition can be completed in a single scan position However, if the axial field of view is insufficient, additional scan positions in either direction will be required.
OF VIEW of the scanner is insufficient to cover the required length
– a circular orbit with a RADIUS OF ROTATION of 25 cm or more;
– a low-energy high resolution PARALLEL HOLE COLLIMATOR appropriate for clinical imaging of
In a 360° acquisition, the number of PROJECTIONS is typically 120 or 128, corresponding to a rotation of 3° or 2.8° between steps If the SPECT system has a limited angular range of less than 360°, the maximum permitted range will be utilized, maintaining the same step rotation of 3° or 2.8° For multiple detector SPECT systems, each detector contributes to the total number of PROJECTIONS.
PROJECTIONS obtained For example each detector in a dual-detector system will contribute half the images to the total acquisition
The acquisition is designed to collect approximately 50 million counts The time per angular stop T p shall be determined from the measured COUNT RATE and calculated as follows:
T p = 50 × 10 6 counts / (CR × number of PROJECTIONS) (19) where CR is the measured COUNT RATE in counts/s T p should then be rounded up to the nearest whole number of seconds
The IMAGE MATRIX and acquisition zoom applied should be chosen to store PROJECTIONS with
PIXEL size of 3,0 mm to 3,5 mm
Any data necessary for creating the attenuation map and for scatter correction should be acquired or calculated using the standard clinical protocol
Tomographic reconstruction shall be performed over the axial length of the image quality phantom The standard reconstruction method for the clinical imaging protocol used shall be applied
For image quality analysis 2D circular ROIs drawn on selected transverse slices are used
The central plane of the hot spheres will be identified as the "S-slice," where circular Regions of Interest (ROIs) will be drawn over the six spheres The diameter of each ROI should closely match the inner diameter of the spheres without exceeding it The average pixel value \( P_i \) for each ROI will then be calculated.
Transverse slices should be identified at distances of approximately ± 1 cm and ± 2 cm from the S-slice On these four slices, along with the S-slice, twelve 37 mm diameter regions of interest (ROIs) will be established throughout the background, ensuring they are at least 15 mm from the edge of the phantom Each of the five smaller diameter spheres will have concentric ROIs drawn within the 37 mm diameter ROIs, resulting in a total of 60 background ROIs for each sphere diameter, with 12 ROIs on each of the five slices.
The study involves twelve designated locations, each featuring six concentric regions of interest (ROIs) that are identical in size to the sphere ROIs This methodology is adapted from the NEMA Standards Publication NU 2-2007, which outlines performance measurements for positron emission tomographs, and is used with permission.
Figure 17 – Placement of ROIs in the phantom background
For each sphere diameter, compute the average PIXEL value for each of the 60 ROIs, then compute the mean and standard deviation of those 60 ROI values
Draw a 25 mm diameter region of interest (ROI) within the lung insert on each transverse slice throughout the entire length of the image quality phantom Additionally, place a 25 mm diameter ROI in the phantom background, ensuring it is positioned 15 mm from the left edge of the phantom Record the average values obtained from these measurements.
The PIXEL values for all regions are labeled as WBBkg k and WBLung k for each slice k, where k ranges from 1 to n, with n being the final slice in the phantom The average of all WBBkg k values is then calculated and recorded.
The contrast recovery coefficient CR j for each sphere j with a diameter of 10 mm, 13 mm,
17 mm, 22 mm, 28 mm, and 37 mm, respectively, shall be computed The index j is either 10,
13, 17, 22, 28, or 37 and matched to the diameter of the corresponding sphere
P j is the ROI value for sphere j, as computed in 4.4.5.8.1.1;
B j is the average of the background ROI values for sphere j, as computed in section
A S is the ACTIVITY concentration in the spheres;
A B is the ACTIVITY concentration in the background
The noise coefficient of variation CN j for each sphere diameter shall be computed as:
B j is the average of the background ROI values for sphere j, as computed in section 4.4.5.8.1.2;
S j is the standard deviation of the background ROI values for sphere j, as computed in section 4.4.5.8.1.2
The contrast-to-noise ratio CNR j for each sphere diameter shall be computed as:
P j is the ROI value for sphere j, as computed in 4.4.5.8.1.1;
B j is the average of the background ROI values for sphere j, as computed in 4.4.5.8.1.2;
CN j is the noise coefficient of variation for sphere j, as computed in Equation (12)
4.4.5.8.3 Accuracy of ATTENUATION correction and scatter correction
Accuracy of corrections for ATTENUATION and scatter is assessed using the ROIs from the background and the lung insert according to 4.4.5.8.1.3
The residual error in the lung insert is calculated as follows:
∆ LR k = 100 % × WBLung k / WBBkg avg (23) where
∆ LR k is the percent residual error in slice k;
WBLung k is the average PIXEL value in the lung insert ROI in slice k;
WBBkg avg is the average PIXEL value in the phantom background
4.4.5.8.4 Accuracy of the SPECT and CT image registration for SPECT/CT
Proper alignment of SPECT and CT image volumes is essential for accurate diagnosis and attenuation correction To achieve this, the X, Y, and Z centroids of each sphere in the SPECT and CT scans must be calculated using a 3D ROI tool In the absence of a 3D ROI tool, 2D ROIs should be drawn on all slices containing the sphere The quality of the SPECT scan will be compared with the corresponding CT scan to evaluate the alignment of the two image volumes.