IEC 61675 1 Edition 2 0 2013 09 INTERNATIONAL STANDARD NORME INTERNATIONALE Radionuclide imaging devices – Characteristics and test conditions – Part 1 Positron emission tomographs Dispositifs d''''image[.]
General
The tomograph must be configured in its standard operational mode for all measurements, without any special adjustments for specific parameters If the tomograph is designed to function in various modes that affect performance parameters, such as differing axial acceptance angles or the presence of septa, these modes should be taken into account during operation.
Two-dimensional and three-dimensional reconstruction results must be reported for each operational mode The configuration of the tomograph, including energy thresholds, axial acceptance angle, and reconstruction algorithm, should be selected based on specific criteria.
It is essential to adhere to the manufacturer's recommendations as outlined If a test cannot be conducted precisely as specified in the standard, the reasons for the deviation and the specific conditions under which the test was performed must be clearly documented.
It is postulated that a POSITRON EMISSION TOMOGRAPH is capable of measuring RANDOM
COINCIDENCES and performing the appropriate correction In addition, a POSITRON EMISSION
TOMOGRAPH shall provide corrections for scatter, ATTENUATION, COUNT LOSS, branching ratio, radioactive decay, and CALIBRATION
The test phantoms shall be centred within the tomograph’s AXIAL FIELD OF VIEW, if not specified otherwise.
S PATIAL RESOLUTION
General
Spatial resolution measurements indicate a tomograph's capability to accurately depict the spatial distribution of a tracer within an object in reconstructed images This assessment is conducted by imaging point sources in air and utilizing a sharp reconstruction filter for image reconstruction While this method does not fully replicate the conditions encountered during patient imaging—where tissue scatter occurs and limited statistics necessitate the use of smoother reconstruction filters or iterative methods—it provides valuable insights into spatial resolution.
RESOLUTION provides an objective comparison between tomographs
The purpose of this measurement is to characterize the ability of the tomograph to recover small objects
The TRANSVERSE RESOLUTION is characterized by the width of the reconstructed TRANSVERSE
POINT SPREAD FUNCTIONS of radioactive POINT SOURCES The width of the spread function is measured by the FULL WIDTH AT HALF MAXIMUM (FWHM) and the EQUIVALENT WIDTH (EW)
Axial resolution in tomographs is determined by the fine axial sampling of volume detectors and can be assessed using a stationary point source These systems, which adhere to the sampling theorem in the axial direction, are distinguished by their axial point characteristics.
SPREAD FUNCTION of a stationary POINT SOURCE would not vary if the position of the source is varied in the axial direction for half the axial sampling distance.
Method
The SPATIAL RESOLUTION of all systems will be assessed in the transverse IMAGE PLANE across two directions: radially and tangentially Furthermore, for systems with adequate axial sampling, the AXIAL RESOLUTION will also be evaluated.
The pixel size in the transverse image plane is determined by the transverse field of view and the image matrix size Accurate measurement of the spread function's width is essential for precise imaging.
FWHM should span at least 5 PIXEL s
For volume imaging systems, the TRIXEL size, in both the transverse and axial dimensions, should be made close to one fifth of the expected FWHM,
The RADIONUCLIDE for the measurement shall be 18 F, with an ACTIVITY such that the percent
COUNT LOSS is less than 5 % or the RANDOM COINCIDENCE rate is less than 5 % of the TOTAL
POINT SOURCES shall be used
Tomographs must utilize point sources suspended in air to reduce scatter for accurate measurements of transverse resolution These resolution measurements should be conducted on two planes that are perpendicular to the long axis of the tomograph, with one measurement taken at the center of the axial field.
OF VIEW and the second on a plane offset from the central plane by 3/8 of the AXIAL FIELD OF
In the VIEW, which represents one-eighth of the AXIAL FIELD OF VIEW from the tomograph's end, sources must be placed at distances of 1 cm, 10 cm, and 20 cm from the SYSTEM AXIS The 20 cm position should be excluded if it falls outside the coverage of the TRANSVERSE FIELD OF VIEW These sources should be aligned along either the horizontal or vertical line that intersects the SYSTEM AXIS, ensuring that both radial and tangential directions are consistent with the image grid.
Data collection will occur for all sources across the six specified positions, either individually or in groups, to reduce acquisition time A minimum of one hundred thousand counts must be obtained for each point source.
Filtered backprojection reconstruction using a ramp filter with the cutoff at the Nyquist frequency of the PROJECTION data or its 3D equivalent shall be employed for all SPATIAL
RESOLUTION data No resolution enhancement methods shall be used
In addition to filtered backprojection results, it is essential to report outcomes from alternate reconstruction algorithms, ensuring that these methods and their parameters are detailed enough for reproducibility of the study findings.
Analysis
The radial and tangential resolutions are established by generating one-dimensional response functions These functions are derived from profiles of the transverse point spread function obtained from the reconstructed 3D image of each point.
The SOURCE is analyzed in both radial and tangential directions at the peak of the distribution Each profile's width is set to twice the expected Full Width at Half Maximum (FWHM) in the directions that are perpendicular to the analysis.
The axial resolution of point source measurements is defined by creating one-dimensional response functions, known as axial point spread functions These functions are derived from profiles taken through the reconstructed 3D image along the axial direction, specifically through the peak of the distribution Each profile's width is set to be twice the expected full width at half maximum (FWHM) in both directions that are perpendicular to the analysis direction.
The Full Width at Half Maximum (FWHM) is calculated through linear interpolation between neighboring pixels at half the peak pixel value, which represents the maximum response function The maximum pixel value, denoted as \(C_m\), is obtained via a parabolic fit that incorporates the peak point and its two closest neighbors To convert these values into millimeter units, they are multiplied by the corresponding pixel width.
NOTE A and B are the points where the interpolation count curve cuts the line of half-maximum value Then
Each EQUIVALENT WIDTH (EW) shall be measured from the corresponding response function
EW is calculated from Equation (1):
∑ 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 widthin millimetres (see Figure 2)
NOTE EW is given by the width of that rectangle having the area of the LINESPREAD FUNCTION and its maximum value C m
The PIXEL width PW is xi+1 – xi
The areas shaded differently are equal
Figure 2 – Evaluation of EQUIVALENT WIDTH ( EW )
Report
RADIAL RESOLUTION, TANGENTIAL RESOLUTION, and AXIAL RESOLUTION (FWHM and EW) for each
POINT SOURCE position shall be calculated and reported Transverse and axial PIXEL dimensions shall be reported
If special reconstruction methods were used, the results of the tests should be reported together with the exact description of the methodology.
Tomographic sensitivity
General
Tomographic sensitivity measures the detection rate of coincidence events from a radioactive source, particularly at low activity levels where count losses and random coincidences are minimal This parameter is crucial for accurately assessing the true measurement rate in tomographic imaging.
The occurrence of coincidences in a radioactive source distribution is influenced by several factors, such as the type of detector material, its size and packing fraction, the diameter of the tomograph ring, the axial acceptance window, and the geometry of the septa Additionally, factors like attenuation, scatter, dead-time, and energy thresholds also play a significant role.
Purpose
The purpose of this measurement is to determine the detected rate of UNSCATTERED TRUE
COINCIDENCES per unit of ACTIVITY concentration for a standard volume source, i.e a cylindrical phantom of given dimensions.
Method
The tomographic sensitivity test places a specified volume of radioactive solution of known
ACTIVITY concentration in the TOTAL FIELD OF VIEW of the POSITRON EMISSION TOMOGRAPH and observes the resulting COUNT RATE The system’s sensitivity is calculated from these values
Accurate assays of activity, measured with a dose calibrator or well counter, are crucial for the test's reliability Maintaining absolute calibration with these devices is challenging, often limited to an accuracy of 10% For applications requiring greater precision, absolute reference standards utilizing positron emitters should be considered.
The last frame of the PET COUNT RATE PERFORMANCE test (4.6) can also be used to determine the SLICE SENSITIVITY and VOLUME SENSITIVITY
The RADIONUCLIDE used for these measurements shall be 18 F The amount of ACTIVITY used shall be such that the percentage of COUNT LOSSES is less than 2 %
The test phantom is a solid right circular cylinder made of polyethylene, featuring a specific density of (0.96 ± 0.01) g/cm³, an outer diameter of (203 ± 3) mm, and an overall length of (700 ± 5) mm It includes a (6.5 ± 0.3) mm hole drilled parallel to its central axis at a radial distance of (45 ± 1) mm For easier fabrication and handling, the cylinder may be constructed from multiple segments that are assembled during testing It is crucial to ensure a tight fit between these segments to prevent any small gaps, which could lead to narrow axial regions of scatter-free radiation.
The test phantom LINE SOURCE insert is a clear polyethylene or polyethylene coated plastic tube (800 ± 5) mm in length, with an inside diameter of (3,2 ± 0,2) mm and an outside diameter of (4,8 ± 0,2) mm
The test phantom LINE SOURCE must be filled with water mixed with the specified amount of ACTIVITY to a length of (700 ± 5) mm and sealed at both ends It should be inserted into the test phantom hole to ensure the ACTIVITY aligns with the polyethylene phantom's length The assembled test phantom with the LINE SOURCE is then placed on the standard patient bed provided by the MANUFACTURER and rotated accordingly.
The LINE SOURCE insert should be placed closest to the patient bed, ensuring the phantom is centered within the TRANSVERSE FIELD OF VIEW to within 5 mm If centering the phantom solely by elevating the patient bed is not feasible, additional mounting methods, such as foam blocks outside the AXIAL FIELD OF VIEW, may be utilized In such instances, it is essential to report both the actual mounting methods used and the elevation of the table.
The 6,5 mm hole is for insertion of the LINE SOURCE
Figure 3 – Scatter phantom configuration and position on the imaging bed
Each coincident event between individual detectors shall be taken into account only once
Data shall be assembled into SINOGRAMs All events shall be assigned to the transverse slice passing the midpoint of the corresponding LINE OF RESPONSE
At least 500 000 true coincident counts shall be acquired
The ACTIVITY concentration in the phantom shall be corrected for decay to determine the average ACTIVITY concentration, a ave , during the data acquisition time, T acq , by the following
= exp ln2 1 exp ln2 ln2
V is the volume of the phantom;
A cal is the ACTIVITY times branching ratio ("positron activity") measured at time T cal ;
T 0 is the acquisition start time;
T 1/2 is the RADIOACTIVE HALF-LIFE of the RADIONUCLIDE
No corrections for detector normalization, COUNT LOSS, SCATTERED TRUE COINCIDENCES, and
ATTENUATION shall be applied The data shall be corrected for RANDOM COINCIDENCES.
Analysis
All PIXELS in the SINOGRAM located further than 25 cm from the SYSTEM AXIS shall be set to zero
The total counts \( C_{i,\text{tot}} \) for each slice \( i \) are calculated by summing all pixels in the corresponding sinogram The slice sensitivity \( S_i \) for unscattered events is determined using Equation (3).
S i = C i − i (3) where SF i is the corresponding SCATTER FRACTION (see 4.5)
The VOLUME SENSITIVITY, S tot , shall be the sum of S i over all slices of the tomograph within the
Report
For each slice i, report the values of S i The VOLUME SENSITIVITY S tot shall also be reported.
Uniformity
No test has been specified to characterize the uniformity of reconstructed images, because all methods known so far will mostly reflect the noise in the image.
Scatter measurement
General
The scattering of primary gamma rays from positron annihilation leads to coincidence events that can misrepresent the location of radiation sources Differences in design and implementation result in varying sensitivities to scattered radiation among positron emission tomographs.
Purpose
The purpose of this procedure is to measure the relative system sensitivity to scattered radiation, expressed by the SCATTER FRACTION (SF), as well as the values of the SCATTER
FRACTION in each slice SF j
Method
The test phantom is a solid right circular cylinder made of polyethylene, featuring a specific density of (0.96 ± 0.01) g/cm³, an outer diameter of (203 ± 3) mm, and an overall length of (700 ± 5) mm It includes a (6.5 ± 0.3) mm hole drilled parallel to its central axis at a radial distance of (45 ± 1) mm To facilitate fabrication and handling, the cylinder may be constructed from multiple segments that are assembled during testing It is crucial to ensure a tight fit between these segments, as even minor gaps can permit narrow axial regions of scatter-free radiation.
The last frame of the COUNT RATE CHARACTERISTIC test (4.6) may be used to determine the
SCATTER FRACTION if the test is performed with 18 F
The RADIONUCLIDE for the measurement shall be 18 F with an ACTIVITY such that the percentage of COUNT LOSSesis less than 5 %
The LINE SOURCE insert for the test phantom is a clear polyethylene or polyethylene-coated plastic tube measuring 800 ± 5 mm in length, with an inside diameter of 3.2 ± 0.2 mm and an outside diameter of 4.8 ± 0.2 mm This tube is designed to be filled with a specific quantity of ACTIVITY and is threaded through a 6.5 mm hole in the test phantom.
The LINE SOURCE insert of the test phantom must be filled with water mixed with the specified amount of ACTIVITY to a length of (700 ± 5) mm and sealed at both ends It should be positioned in the test phantom's hole to ensure the ACTIVITY aligns with the polyethylene phantom's length The assembled test phantom with the LINE SOURCE is then placed on the standard patient bed provided by the MANUFACTURER and rotated accordingly.
The LINE SOURCE insert should be placed closest to the patient bed, ensuring that the phantom is centered within both the TRANSVERSE and AXIAL FIELD OF VIEW to an accuracy of 5 mm If centering the phantom in the TRANSVERSE FIELD OF VIEW is not achievable solely by elevating the patient bed, additional mounting methods, such as foam blocks outside the AXIAL FIELD OF VIEW, may be utilized It is essential to document the actual mounting methods and the elevation of the table used.
Each coincident event between individual detectors shall be taken into account only once
Data shall be assembled into SINOGRAMS All events will be assigned to the slice at the midpoint of the corresponding LINE OF RESPONSE The acquisition should contain a minimum of
No corrections for variations in detector sensitivity, SCATTERED TRUE COINCIDENCES, COUNT
LOSS, or ATTENUATION shall be applied to the measurements
The data shall be corrected for RANDOM COINCIDENCES.
Analysis
For tomographs with an AXIAL FIELD OF VIEW of 65 cm or less, SINOGRAMs of TRUE
COINCIDENCES shall be generated for each acquisition i of slice j For tomographs with an AXIAL
FIELD OF VIEW greater than 65 cm, SINOGRAMs of TRUE COINCIDENCES shall be generated for each acquisition for slices within the central 65 cm
Oblique SINOGRAMs are collapsed into a single SINOGRAM for each respective slice (by single- slice rebinning) while conserving the number of counts in the SINOGRAM
The SINOGRAM j of TRUE COINCIDENCES will be processed by setting all PIXELS beyond 25 cm from the SYSTEM AXIS to zero Additionally, for each PROJECTION ANGLE φ within the SINOGRAM, the center location of the LINE will be determined.
SOURCE response shall be determined by finding the PIXEL having the greatest value Each
The PROJECTION will be adjusted to align the PIXEL with the highest value to the central PIXEL of the SINOGRAM Following this alignment, a sum projection will be generated, where each PIXEL in the sum projection represents the total of the PIXELs from each angular PROJECTION that share the same radial offset Additionally, the left and right PIXEL intensities, denoted as C L,j and C R,j, will be calculated at the edges of a strip with a width of ± 20 mm from the center of the profile established in the previous step.
Figure 4) Linear interpolation shall be employed to find C L,j and C R,j
NOTE In the summed projection the scatter is estimated by the counts outside the 40 mm wide strip plus the area of the LSF below the line CL,j – CR,j
Figure 4 – Evaluation of SCATTER FRACTION e) The average of the two PIXEL intensities C L,j and C R,j shall be multiplied by the number of
The number of scatter counts \( C_{s,j} \) for slice \( j \) is determined by the PIXELs, including fractional values, that correspond to the width of the strip, along with the total counts from PIXELs outside the strip Additionally, the TRUE COINCIDENCES \( C_{TOT,j} \) for slice \( j \) are calculated as the total of all counts in the sum projection, which encompasses both SCATTERED TRUE COINCIDENCES and other counts.
The SCATTER FRACTION SF j for each slice shall be calculated as shown in equation (4): j j j C s
The SCATTER FRACTION SF shall be computed by equation (5):
Report
For each slice j that was processed, SF j shall be reported (Equation (4)) The SCATTER
FRACTION SF shall also be reported (Equation (5)).
PET COUNT RATE PERFORMANCE
General
PET COUNT RATE PERFORMANCE depends in a complex manner on the spatial distribution of
ACTIVITY and scattering materials, on the trues-to-singles ratio, on the COUNT RATE
CHARACTERISTIC of the SINGLES RATE, and on the setup of the measurement conditions In addition, COUNT RATE performance is strongly influenced by the amount of RANDOM
COINCIDENCEs and by the accuracy of the subtraction of these events.
Purpose
This procedure aims to assess the deviations from the linear relationship between the count rate of true coincidences and activity, which are influenced by count losses Given that modern PET tomographs utilize count loss correction schemes, it is essential to evaluate the accuracy of these correction algorithms.
Method
The test phantom is a solid right circular cylinder made of polyethylene, featuring a specific density of (0.96 ± 0.01) g/cm³, an outer diameter of (203 ± 3) mm, and an overall length of (700 ± 5) mm It includes a (6.5 ± 0.3) mm hole drilled parallel to its central axis at a radial distance of (45 ± 1) mm For easier fabrication and handling, the cylinder may be constructed from multiple segments that are assembled during testing It is crucial to ensure a tight fit between these segments to prevent any small gaps, which could lead to narrow axial regions of scatter-free radiation.
The measurement will utilize the radionuclide 11 C, with activity variation determined by radioactive decay over approximately 10 half-lives The final frame must be captured with a count loss of less than 1% The initial activity level should be sufficiently high to enable the measurement of two key rates: a) R t,max, which represents the maximum count rate of true coincidences, and b) R NEC,max, indicating the maximum noise equivalent count rate.
Recommendations for the initial ACTIVITY required to meet these objectives should be supplied by the MANUFACTURER
The LINE SOURCE insert for the test phantom is a clear polyethylene or polyethylene-coated plastic tube measuring 800 ± 5 mm in length, with an inside diameter of 3.2 ± 0.2 mm and an outside diameter of 4.8 ± 0.2 mm This tube is designed to be filled with a specific quantity of ACTIVITY and is threaded through a 6.5 mm hole in the test phantom.
The LINE SOURCE insert of the test phantom must be filled with water mixed with the specified amount of ACTIVITY to a length of (700 ± 5) mm and sealed at both ends It should be positioned in the test phantom's hole to ensure the ACTIVITY aligns with the polyethylene phantom's length The assembled test phantom with the LINE SOURCE is then placed on the standard patient bed provided by the MANUFACTURER and rotated accordingly.
The LINE SOURCE insert should be placed closest to the patient bed, as illustrated in Figure 3 The phantom must be centered within 5 mm in both the TRANSVERSE FIELD OF VIEW and the AXIAL FIELD OF VIEW If centering the phantom in the TRANSVERSE FIELD OF VIEW is not achievable by simply elevating the patient bed, additional support, such as foam blocks, should be used outside the AXIAL FIELD OF VIEW.
VIEW can be used In this case the actual mounting means and the actual table elevation shall be reported
To begin the test, a source of relatively high ACTIVITY is placed in the field of view of the
POSITRON EMISSION TOMOGRAPH Regular measurements are then taken while the ACTIVITY in the phantom decays over several HALF LIVES A decrease in the event rate accompanies the
As the ACTIVITY decays, the system's efficiency in processing coincident events improves, leading to a point where COUNT LOSSES can be considered negligible By allowing sufficient time for decay, one can achieve a measurement of the COUNT RATE of TRUE COINCIDENCES that is largely unaffected by processing losses This COUNT RATE can then be extrapolated for further analysis.
COINCIDENCES back to higher ACTIVITY levels and comparing it to the COUNT RATE of TRUE
At elevated activity levels, coincidences can be measured to estimate count losses experienced by the system The effectiveness of this method is heavily reliant on collecting sufficient statistics at lower activity levels, which may necessitate multiple measurements at reduced count rates.
Each coincident event between individual detectors shall be taken into account only once.
Analysis
4.6.4.1 Test of the PET COUNT RATE PERFORMANCE
Data shall be assembled into SINOGRAMS All events will be assigned to the slice at the midpoint of the corresponding LINE OF RESPONSE
No corrections for variations in detector sensitivity, scatter, COUNT LOSS, or ATTENUATION shall be applied to the measurements
For tomographs with an AXIAL FIELD OF VIEW of 65 cm or less, SINOGRAMs of TRUE
COINCIDENCES shall be generated for each acquisition i of slice j For tomographs with an AXIAL
FIELD OF VIEW greater than 65 cm, SINOGRAMs of TRUE COINCIDENCES shall be generated for each acquisition for slices within the central 65 cm
The relationship between COUNT RATE and ACTIVITY in the TOTAL FIELD OF VIEW of the tomograph will be assessed, ensuring that the time per frame is under one-half of the specified limit.
The radioactive half-life is defined by the time it takes for half of a radioactive substance to decay In the context of data acquisition, the last three frames may require a longer duration, with a minimum of 500,000 true coincident counts needed for each of these frames.
The initial ACTIVITY in the phantom shall be determined from the ACTIVITY injected into the phantom as measured in a calibrated dose calibrator
The SINOGRAMS shall be analyzed without COUNT LOSS correction All PIXELS in the SINOGRAM located further than 25 cm from the SYSTEM AXIS shall be set to zero
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 (6):
= exp ln2 1 exp ln2 ln2
A cal is the ACTIVITY times branching ratio ("positron 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 18 F or 11 C, respectively
For each time frame \(i\), calculate the total event rate \(R_{\text{TOT},i,j}\) for each slice \(j\) by dividing the total coincidences in slice \(j\) by the acquisition time for frame \(i\) Next, determine the random event rate \(R_{r,i,j}\) for each slice \(j\) by dividing the random coincidences in slice \(j\) by the acquisition time for frame \(i\) Additionally, compute the true event rate \(R_{t,i,j}\) for each slice \(j\) by dividing the true coincidences in slice \(j\) by the acquisition time for frame \(i\) Finally, assess the noise equivalent count rate \(R_{\text{NEC},i,j}\) for each slice \(j\) using the specified equation.
NOTE For this evaluation the NEC formula (Equation (7)) accounts for randoms and scatter corrections, and does not account for other effects like time of flight
Total system COUNT RATES R TOT,i , R t,i , R r,i , and R NEC,i are computed as the sum of the corresponding slice COUNT RATES over all slices j
4.6.4.2 Test of COUNT LOSS correction scheme
For tomographs with an AXIAL FIELD OF VIEW of 65 cm or less, all slices shall be reconstructed
For tomographs with an AXIAL FIELD OF VIEW greater than 65 cm, only slices in the central
65 cm shall be reconstructed COUNT LOSS and randoms correction shall be applied to the data Images shall be reconstructed using standard methods without decay correction
All analyses will be conducted on each reconstructed image \(i,j\) The average activity \(A_{\text{ave},i}\) for each acquisition \(i\) will be calculated The average effective activity concentration \(A_{\text{eff},i}\) for each acquisition \(i\) will be determined by dividing \(A_{\text{ave},i}\) by 22000 cm\(^3\), the volume of the test phantom.
A circular Region of Interest (ROI) with an 18 cm diameter, centered on the transverse field of view rather than the line source, will be drawn on each reconstructed image slice j For each acquisition i, the number of true coincidences, denoted as \(C_{ROI,i,j}\), will be measured within this ROI for each slice The count rate of true coincidences, represented as \(R_{ROI,i,j}\), will be calculated by taking the ratio of \(C_{ROI,i,j}\) to \(T_{acq,i}\).
For each slice j, the extrapolated COUNT RATE of the TRUE COINCIDENCES R Extr,i,j , shall be calculated This rate would have been obtained for acquisition i if there were no COUNT
LOSSES To minimize the effects of statistics, R Extr,i,j shall be obtained by the following equation (8):
R (8) where k = 1 is the acquisition with the lowest ACTIVITY, and the sum is computed over the three lowest-ACTIVITY acquisitions
For each slice j of each acquisition i, the relative COUNT RATE error ∆r i,j in percentage units shall be calculated by the following equation (9):
Report
4.6.5.1 PET COUNT RATE PERFORMANCE (see 4.6.4.1)
The article discusses the plotting of four key quantities as a function of the average effective activity concentration, \( A_{\text{ave},i \) in the system These quantities include: a) \( R_{t,i} \) – the count rate of true coincidences; b) \( R_{r,i} \) – the count rate of random coincidences; c) \( R_{\text{NEC},i} \) – the noise equivalent count rate; and d) \( R_{\text{TOT},i} \) – the count rate of total coincidences.
The key values to report from the plot include: a) \( R_{t,\text{max}} \) – the maximum count rate of true coincidences; b) \( R_{\text{NEC,max}} \) – the maximum noise equivalent count rate; c) \( A_{t,\text{max}} \) – the activity concentration at which \( R_{t,\text{max}} \) is achieved; and d) \( A_{\text{NEC,max}} \) – the activity concentration at which \( R_{\text{NEC,max}} \) is attained.
The method used for estimating RANDOM COINCIDENCES shall be reported
4.6.5.2 Accuracy of COUNT LOSS correction (see 4.6.4.2)
A graph of the highest and lowest values among the slices of ∆ r i,j versus a eff,i shall be created using a linear scale The data points may be joined to form a continuous curve
The maximum value of the bias |∆ r i,j | in the ACTIVITY range up to the A NEC,max shall be reported.
Image quality and quantification accuracy of source ACTIVITY
General
Contrast and noise are factors that affect image quality; their combination determines lesion detectability Contrast depends on the lesion-to-background ACTIVITY concentration ratio
Image contrast is further compromised by finite SPATIAL RESOLUTION, scatter and randoms
The contrast resolution is affected by the noise present in the background surrounding a lesion.
Purpose
This section aims to evaluate the image quality factors and quantification accuracy of the PET scanner under standard imaging conditions To simulate these conditions, a torso-shaped phantom will be utilized, featuring multiple 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 To ensure quantification accuracy, the measured concentrations in the spheres, background, and lung cylinder insert are compared to their actual activity concentrations Furthermore, the scanner's capability to quantify activity concentration is assessed based on varying sphere sizes.
Method
The whole-body phantom is to be used for all measurements (see Figure 5) into which hollow spheres and lung insert are placed (see Figure 6) r = 1 47 r = 77
Dimensions are in millimetres and are given within ± 1 mm Material: Polymethylmethacrylate
The phantom length shall be at least 180 mm ± 5 mm
Figure 5 – Cross-section of body phantom φ 13 ± 0,5 φ 10 ± 0,5 φ 37 ± 1 φ 28 ± 1 φ 22 ± 1 φ 17 ± 0,5 d = 1 14, 4 φ 17 φ 37
All specified diameters refer to the internal measurements The spheres must have a wall thickness of no more than 1 mm, and their centers should be equidistant from the mounting plate's surface Additionally, the spheres may be constructed from glass The lung insert cylinder is positioned centrally within the image quality phantom, extending the full length of the chamber with a diameter of 50 ± 2 mm.
Figure 6 – Phantom insert with hollow spheres
The hollow spheres, decreasing in diameter, are circularly arranged and centered 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, extends throughout 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, and is devoid of activity, effectively simulating the desired conditions.
The scatter phantom, positioned at the head end of the whole-body phantom, features a LINE SOURCE to simulate external field of view source activity Known activity concentrations are incorporated into all fillable spheres, the image quality phantom background, and the scatter phantom The average activity concentration in the LINE SOURCE is designed to match the background activity concentration of the image quality phantom.
Mid-point of scan 2 position
Figure 7 – Image quality phantom and scatter phantom position for whole body scan acquisition
A whole-body acquisition covering the length of the whole-body phantom shall be obtained
The algorithms for image reconstruction, scatter, and attenuation correction will align with the standard whole-body clinical imaging protocol, producing pixel values in kBq/ml Before this process, scanner calibration is essential Additionally, results from enhanced image reconstructions may be reported 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 average activity concentrations within these ROIs are then utilized for analysis.
The RADIONUCLIDE for the measurement shall be 18 F
The ACTIVITY concentration in the whole-body phantom background shall be (5 ± 0,3) kBq/ml
The spheres must contain an ACTIVITY concentration ranging from 3.8 to 4.2 times that of the background The LINE SOURCE within the scatter phantom should have an ACTIVITY of (110 ± 5) MBq All ACTIVITY concentrations are defined at the beginning of the acquisition, and the RADIONUCLIDE in all phantoms must be thoroughly mixed.
NOTE These concentrations correspond to a typical clinical dosage of 350 MBq in a 70 kg PATIENT for whole body imaging
The accuracy of the test relies heavily on the precise assays of activity utilized Maintaining absolute calibration in the dose calibrator poses challenges, particularly when aiming for accuracies finer than required.
10 %, may be used to assay starting ACTIVITY levels Absolute reference standards using positron emitters should be considered if higher degrees of accuracy are required
If the MANUFACTURER recommends a lower dosage for this test, the ACTIVITY concentration in all phantoms may be lowered proportionately The report shall include the MANUFACTURER recommended dosage
The whole-body phantom is positioned on the tomograph's patient bed, ensuring it is centered within the transverse field of view The plane that intersects the center of the spheres in the phantom must align with the axial field of view's center Additionally, the line-source scatter phantom is placed directly on the patient bed, adjacent to the head-end of the image quality phantom.
A whole-body acquisition must be conducted using a whole-body phantom, consisting of multiple stationary scans with standard overlap between positions The "step size," which is the axial distance the bed moves between scans, may be less than the axial field of view (AFOV) At least three scan positions are essential, with the first position determined by the second, ensuring it is axially centered over the transverse plane of the spheres Position 1 is set towards the scatter phantom at a distance equal to the clinical step size The final scan at position 3 involves moving the scanner a step size distance toward the opposite end of the phantom, ensuring the center of the AFOV extends beyond the phantom's end If the scanner's AFOV is inadequate to cover the necessary length in three steps, additional scan positions in either direction will be required.
The acquisition time T p for a single position shall be computed as follows:
T p = (d ax /100 cm) × 30 min (10) where d ax is the axial distance in centimeters the bed translates between positions (step size)
Additional measurements can be taken for different values of scan time and axial coverage If additional measurements are taken, those values shall be included in the final report
Before beginning the emission acquisition, a comprehensive whole-body CT scan is performed using X-ray techniques in accordance with the established clinical protocol.
If the scanner is does not have a CT component, then the prescribed method of transmission imaging must be applied and reported
For emission scans, it is essential to utilize an acquisition matrix, determine the appropriate field of view size, and set the slice thickness Additionally, choose between 2D or 3D acquisition modes and apply multiple scan overlaps as recommended for standard clinical whole-body scans.
Corrections for random coincidences must be clearly reported, along with the methods used for enhancements like time-of-flight information and depth-of-interaction The start time of the emission scans serves as the reference for calculating and reporting phantom activity concentrations.
Transverse slices will be reconstructed throughout the length of the image quality phantom using the standard whole-body imaging protocol It is essential to report the reconstruction algorithm, methods for attenuation, scatter, and count loss corrections, as well as the post-reconstruction image filter and all related parameters Additionally, if the PET system includes advanced reconstruction software features like time-of-flight and resolution recovery, these results should be documented separately.
Data analysis
For image quality and quantitative accuracy analyses 2D circular ROIs are drawn over the spheres and whole-body phantom background on selected slices
The transverse slice coinciding with the central plane of the hot spheres shall be identified
In the S-slice, circular regions-of-interest (ROIs) will be created over the six spheres The diameter of each ROI must closely match the inner diameter of the spheres without exceeding it The average pixel value will be calculated for these ROIs.
P j for each sphere shall be computed
Transverse slices within ± 1 cm and ± 2 cm from the S-slice will be identified Twelve 37 mm diameter regions of interest (ROIs) will be drawn on these four slices and the S-slice, ensuring they are positioned at least 15 mm away from the edge of the phantom.
In Figure 8, the placement of background Regions of Interest (ROIs) on the S-slice is illustrated For each of the five smaller diameter spheres, concentric ROIs will be created 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, as outlined in the NEMA Standards Publication NU 2-2007, which details performance measurements of positron emission tomographs.
Figure 8 – 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
4.7.4.1.4 Whole-body scan lung and background ROIs
Draw a 37 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 37 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.
PIXEL values for all regions and label as WBBkg k and WBLung k , respectively for slice k = 1,n where n is the last slice
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 4.7.4.1.2
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
S j is the standard deviation of the background ROI values for sphere j, as computed in section 4.7.4.1.3
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 section 4.7.4.1.2
B j is the average of the background ROI values for sphere j, as computed in section
CN j is the noise coefficient of variation for sphere j, as computed in equation (12)
Compute the percent deviation from true ACTIVITY concentration in the phantom background as follows (Equation (14)):
∆ Q B is the percent deviation from true ACTIVITY concentration in the background;
B 37 is the average PIXEL value for 37 mm ROI in the background (see 4.7.4.1.3) in units of kBq/ml;
A B is the ACTIVITY concentration in the phantom background
4.7.4.4 Accuracy of scatter and ATTENUATION corrections
The accuracy of scatter and attenuation corrections is evaluated throughout the background and lung insert across the entire length of the phantom For each slice, a residual error in the lung insert is determined, while quantification accuracy is assessed for the background region of interest (ROI) in every slice.
The residual error in the lung insert is calculated as follows (Equation (15)):
∆ 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 in units of kBq/ml;
A B is the ACTIVITY concentration in the phantom background
The quantification accuracy in the background is calculated as follows (equation (16)):
∆ QWB k is the percent residual error in slice k;
WBBkg k is the average PIXEL value in the background in slice k in units of kBq/ml;
A B is the ACTIVITY concentration in the phantom background
4.7.4.5 Accuracy of PET and CT image registration
Proper alignment of PET and CT image volumes is essential for accurate diagnosis and attenuation correction The X, Y, and Z centroids of each sphere in the PET 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 whole-body scan and the corresponding CT scan will serve as a basis for comparing the two image volumes.
In the PET scan, encircle the spheres entirely and designate all pixels in the region of interest (ROI) that exceed 1.25 times the average background (Bj for sphere j as defined in section 4.7.4.1.3).
ROI to one, otherwise set them to zero The X, Y, and Z-centroids are then calculated as follows (equations (17), (18), and (19)):
C X,j = Σ x * ROI PET , j (x,y,z)/Σ ROI PET,j (x,y,z); for all x,y,z of ROI (17)
C Y,j = Σ y * ROI PET,j (x,y,z)/Σ ROI PET,j (x,y,z); for all x,y,z of ROI (18)
C Z,j = Σ z * ROI PET,j (x,y,z)/Σ ROI PET,j (x,y,z); for all x,y,z of ROI (19) Then identify C PET , j = (C X,j , C Y,j, C Z,j )as the centroid coordinate for sphere j for PET
To perform a CT scan, it is essential to fully encircle the spheres Assign a value of one to all PIXELs in the region of interest (ROI) that correspond to the sphere wall, while setting all other PIXELs to zero The X, Y, and Z centroids are subsequently calculated using specific equations.
C X,j = Σ x * ROI CT , j (x,y,z)/Σ ROI CT,j (x,y,z); for all x,y,z of ROI (20)
C Y,j = Σ y * ROI CT,j (x,y,z)/Σ ROI CT,j (x,y,z); for all x,y,z of ROI (21)
C Z,j = Σ z * ROI CT,j (x,y,z)/Σ ROI CT,j (x,y,z); for all x,y,z of ROI (22) Then identify C CT , j = (C X,j , C Y,j, C Z,j )as the centroid coordinate for sphere j for CT
Calculate the distance between the PET and CT centroids for each sphere.
Report
4.7.5.1 Scan set up and phantom ACTIVITY concentrations
Report scan set up parameters:
– bed “step size” between multiple acquisitions;
– acquisition time per bed position;
– total whole-body scan length;
– CT acquisition parameters: kVp, mAs, slice-thickness;
– PET acquisition parameters: reconstructed field of view diameter, slice thickness, acquisition mode as 2D or 3D, and method of randoms correction;
– reconstruction algorithm, methods used for ATTENUATION, scatter, and dead-time count loss corrections, post reconstruction image filter and all associated parameters
Report the sphere and phantom background ACTIVITY concentrations
Report the noise coefficient of variation for all spheres
Report the contrast recovery coefficients for all spheres Identify the smallest sphere that has a recovery coefficient greater than 0,90
Report the contrast-noise-ratio for all spheres Identify the smallest sphere for which the contrast-noise-ratio exceeds four
Report the percent deviation from true ACTIVITY concentration for the background for the average PIXEL values in the region
4.7.5.4 Accuracy of scatter and ATTENUATION corrections
Plot the residual error in the lung insert and background for every slice
Report the length of any portion of the phantom where the magnitude of the residual error exceeds 10 %
4.7.5.5 Accuracy of PET and CT image registration
Report the deviation distance in mm between the PET and CT centroids for each sphere
General
A document shall accompany each POSITRON EMISSION TOMOGRAPH and shall include the information contained in 5.2 to 5.9.
Design parameters
– Detector element dimensions and number of elements
– Number and configuration of detector elements per block, if applicable
– Number of detector blocks per ring, if applicable
– SINOGRAM sampling (linear and angular)
– Type of transmission source and source ACTIVITY (nominal and recommended range)
– Detector movement (e.g rotational speed, angular range), if any
Configuration of the tomograph
– Axial acceptance angle (2D-mode, 3D-mode)
– Method of RANDOM COINCIDENCE estimation
– Any additional information being considered essential by the MANUFACTURER to characterize normal operation
S PATIAL RESOLUTION
– TRANSVERSE RESOLUTION (radial and tangential) according to 4.2.5
– Axial PIXEL dimension according to 4.2.5
– Transverse PIXEL dimensions according to 4.2.5
Sensitivity
S CATTER FRACTION
– SCATTER FRACTIONs SFi and SF according to 4.5.5
C OUNT RATE performance
– COUNT RATE CHARACTERISTIC and derived quantities according to 4.6.5.1
– Method of correction for RANDOM COINCIDENCES according to 4.6.5.1
– Accuracy of COUNT LOSS correction and associated plots according to 4.6.5.2
5.8 Image quality and quantification accuracy of source ACTIVITY concentrations
– Scan set up and phantom ACTIVITY concentrations according to 4.7.5.1
– Accuracy of scatter and ATTENUATION corrections according to 4.7.5.4
– Accuracy of PET and CT image registration according to 4.7.5.5
[1] IEC/TR 61948-3:2005, Nuclear medicine instrumentation – Routine tests – Part 3:
[2] NEMA NU 2-2010, Performance measurements of positron emission tomographs
COMPUTED TOMOGRAPHY (CT) IEC 60788,rm-41-20
COUNT RATE CHARACTERISTIC IEC 60788, rm-34-21
FULL WIDTH AT HALF MAXIMUM (FWHM) 3.4.4
RADIOACTIVE HALF-LIFE IEC 60788, rm-13-20
REGION OF INTEREST (ROI) IEC 60788, rm-32-63
4.6 PERFORMANCE DU TAUX DE COMPTAGE EN TEP 61
4.7 Qualité d'image et précision de quantification des concentrations d'activité de la source 65
5.7 Performance du taux de comptage 75
5.8 Qualité d'image et précision de quantification des concentrations d'activité de la source 75
Figure 1 – Evaluation de la LMH 54
Figure 2 – Evaluation de la largeur équivalente (LE) 55
Figure 3 – Configuration du fantôme de diffusion et position sur le lit d'examen 57
Figure 4 – Evaluation de la FRACTION DE DIFFUSION 60
Figure 5 – Section transversale du fantôme de corps 66
Figure 6 – Elément de fantôme à sphères creuses 67
Figure 7 – Position du fantôme de qualité d'image et du fantôme de diffusion pour l'acquisition d'images du corps entier 68
Figure 8 – Positionnement des ROI dans le fond du fantôme Douze localisations sont spécifiées 71
DISPOSITIFS D'IMAGERIE PAR RADIONUCLÉIDES – CARACTÉRISTIQUES ET CONDITIONS D'ESSAI – Partie 1: Tomographes à émission de positrons
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The international standard IEC 61675-1 was established by Subcommittee 62C, which focuses on radiotherapy devices, nuclear medicine, and radiation dosimetry, under the IEC Study Committee 62 that addresses electrical equipment in medical practice.
Cette deuxième édition remplace la première édition de la CEI 61675-1, parue en 1998 Elle constitue une révision technique Les exigences concernant les aspects techniques ci- dessous ont été modifiées:
– performance du TAUX DE COMPTAGE;
Le texte de cette norme est issu des documents suivants:
Le rapport de vote indiqué dans le tableau ci-dessus donne toute information sur le vote ayant abouti à l'approbation de cette norme
Cette publication a été rédigée selon les Directives ISO/CEI, Partie 2
Dans la présente norme, les caractères d'imprimerie suivants sont employés:
– Exigences et définitions: caractères romains
– Indications de nature informative apparaissant hors des tableaux, comme les notes, les exemples et les références: petits caractères Le texte normatif à l'intérieur des tableaux est également en petits caractères.
– TERMES DEFINIS A L'ARTICLE 3 DE LA CEI 60601-1, DE LA PRESENTE NORME OU COMME NOTES:
References to articles in this standard are preceded by the term "Article" followed by the relevant article number References to paragraphs in this standard use only the number of the concerned paragraph.
In this standard, the conjunction "or" is used in the sense of an "inclusive or"; therefore, a statement is considered true if any combination of the conditions is true.
Les formes verbales utilisées dans la présente norme sont conformes à l'usage donné à l'Annexe H des Directives ISO/CEI, Partie 2 Pour les besoins de la présente norme:
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The committee has determined that the content of this publication will remain unchanged until the stability date specified on the IEC website At that time, the publication will be updated accordingly.
• remplacée par une édition révisée, ou
Suite aux progrès réalisés dans le domaine des TOMOGRAPHES A EMISSION DE POSITRONS, la plupart des tomographes peuvent maintenant être utilisés en mode d'acquisition totalement
3D Pour respecter cette tendance, la présente norme décrit les conditions d'essai en tenant compte de cette caractéristique d'acquisition En outre, les TOMOGRAPHES A EMISSION DE
POSITRONS modernes intègrent souvent des EQUIPEMENTS A RAYONNEMENT X POUR
Hybrid PET-CT devices are regarded as the state of the art in the current standard, while specialized positron emission tomography scanners that do not incorporate X-ray technology are considered only as specific cases.
Les méthodes d'essai spécifiées dans la présente partie de la CEI 61675 ont été sélectionnées afin de refléter, autant que possible, l'utilisation clinique des TOMOGRAPHES A
EMISSION DE POSITRONS L'objectif est de faire en sorte que les essais soient réalisés par les
FABRICANTS et de permettre à ces derniers de décrire les caractéristiques des TOMOGRAPHES A
EMISSION DE POSITRONS dans les DOCUMENTS D'ACCOMPAGNEMENT La présente norme n'indique pas quels essais seront effectués par le FABRICANT sur un tomographe particulier
DISPOSITIFS D'IMAGERIE PAR RADIONUCLÉIDES – CARACTÉRISTIQUES ET CONDITIONS D'ESSAI – Partie 1: Tomographes à émission de positrons
La présente partie de la CEI 61675 spécifie la terminologie et les méthodes d'essai relatives à la description des caractéristiques des TOMOGRAPHES A EMISSION DE POSITRONS Les
TOMOGRAPHES A EMISSION DE POSITRONS détectent le RAYONNEMENT D'ANNIHILATION des
RADIONUCLEIDEs émettant des positrons par la DETECTION EN CỌNCIDENCE
Aucun essai n'a été spécifié afin de caractériser l'uniformité des images reconstituées, puisque toutes les méthodes connues jusqu'à présent reflètent principalement le bruit de l'image
The following documents are referenced normatively, either in whole or in part, within this document and are essential for its application For dated references, only the cited edition is applicable For undated references, the latest edition of the referenced document applies, including any amendments.
IEC 60788:2004, Medical electrical equipment – Glossary of defined terms (disponible en anglais seulement)
Pour les besoins du présent document, les termes et définitions donnés dans la
CEI 60788:2004, ainsi que les suivants s'appliquent
3.1 tomographie radiographie d'une ou de plusieurs tranches d'un objet
TOMOGRAPHIE dans laquelle un objet tridimensionnel est coupé en un ensemble de COUPES
D'OBJETS considérées comme étant bidimensionnelles et indépendantes les unes des autres, les PLANS D'IMAGES étant perpendiculaires à l'AXE DU SYSTEME
TPE méthode d'imagerie permettant la représentation de la distribution spatiale des
RADIONUCLEIDES incorporés dans des coupes bidimensionnelles sélectionnées à travers l'objet
Projection transformation involves converting a three-dimensional object into its two-dimensional image or a two-dimensional object into its one-dimensional representation This process integrates the physical properties that define the image along the direction of the projection beam.
Note 1 à l'article: Ce processus est décrit mathématiquement par des intégrales de lignes dans la direction de
PROJECTION (le long de la LIGNE DE REPONSE ); il est appelé "transformée de Radon"
3.1.2.2 faisceau de projection faisceau qui détermine le plus petit volume possible dans lequel la propriété physique qui détermine l'image est intégrée au cours du processus de mesure
Note 1 à l'article: Sa forme est limitée par la RESOLUTION SPATIALE dans chacune des trois dimensions
Note 2 à l'article: Le FAISCEAU DE PROJECTION a généralement la forme d'un cylindre ou d'un cône long et fin En
TOMOGRAPHIE PAR EMISSION DE POSITRONS , il s'agit du volume utile entre deux éléments de détecteurs utilisés en cọncidence
3.1.2.3 angle de projection angle auquel la PROJECTION est mesurée ou acquise
3.1.2.4 sinogramme affichage bidimensionnel de toutes les PROJECTIONs unidimensionnelles d'une COUPE D'OBJET en fonction de l'ANGLE DE PROJECTION
Note 1 à l'article: L' ANGLE DE PROJECTION est affiché sur l'ordonnée, et la coordonnée de la projection linéaire sur l'abscisse
3.1.2.5 coupe d'objet propriété physique correspondant à une coupe dans l'objet qui détermine les informations mesurées et qui est affichée dans l'image tomographique
3.1.2.6 plan d'image plan attribué à un plan dans la COUPE D'OBJET
Note 1 à l'article: Le PLAN D ' IMAGE est généralement le plan médian de la COUPE D ' OBJET correspondante
3.1.2.7 axe du système axe de symétrie caractérisé par les propriétés géométriques et physiques de la disposition du système
In a circular positron emission tomography (PET) scanner, the system axis is defined as the line that passes through the center of the detector ring For rotating detector tomographs, this axis corresponds to the rotation axis.
3.1.2.8 volume tomographique juxtaposition de tous les éléments volumiques qui contribuent aux PROJECTIONs mesurées pour tous les ANGLES DE PROJECTION
3.1.2.8.1 champ de visualisation transversal dimensions d'une coupe à travers le VOLUME TOMOGRAPHIQUE, perpendiculaire à l'AXE DU
Note 1 à l'article: Un CHAMP DE VISUALISATION TRANSVERSAL circulaire est décrit par son diamètre
Note 2 to entry: Dans le cas des VOLUMES TOMOGRAPHIQUES non cylindriques, le CHAMP DE VISUALISATION
TRANSVERSAL peut dépendre de la position axiale de la coupe
AFOV champ caractérisé par les dimensions d'une coupe à travers le VOLUME TOMOGRAPHIQUE, parallèle à et incluant l'AXE DU SYSTEME