Iec ts 61895 1999

TECHNICAL SPECIFICATION IEC TS 61895 First edition 1999 10 Ultrasonics – Pulsed Doppler diagnostic systems – Test procedures to determine performance Ultrasons – Systèmes de diagnostic à effet Doppler[.]

General considerations

Types of pulsed Doppler ultrasound systems

Pulsed Doppler ultrasound systems can be categorized into three types: directional, non-directional, and direction-resolving Directional systems indicate whether reflectors or scatterers are moving towards or away from the ultrasonic transducer, while non-directional systems do not provide movement direction information Direction-resolving systems, on the other hand, output Doppler signals on different channels based on the movement direction of reflectors or scatterers These systems utilize techniques such as phase-quadrature demodulation or offset reference frequency demodulation to maintain flow direction information For detailed descriptions and diagrams of these systems, refer to Annex A.

The system can function as an independent instrument or as part of a B-mode and/or flow imaging system It may utilize either a single transducer for both transmission and reception or separate transducers, allowing for operation in continuous wave mode When integrated with a B-mode real-time imaging instrument, it can employ a separate transducer for pulsed Doppler operation or use the same transducer for both pulse echo imaging and pulsed Doppler applications.

LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.

Duplex and triplex scanners incorporate a system that displays the nominal Doppler beam axis direction on the B-mode image This feature enhances Doppler measurements by providing clear indications of both the depth and length of the sample volume.

Operators can align an electronic marker parallel to the axis of a displayed blood vessel, enabling the instrument to calculate the angle between the ultrasound beam and the vessel's direction This setup facilitates the conversion of Doppler frequencies into blood velocities, assuming axial flow Triplex scanners enhance duplex scanner capabilities by displaying images of moving blood, which are color-coded based on blood velocity and superimposed on the B-mode image.

The system can automatically adjust operating parameters based on the sample volume's depth and the tissue characteristics between the transducer and the sample Key parameters that may be adapted include pulse repetition frequency (PRF), focal depth, transducer aperture, and transmission signal spectrum.

The system utilizes spectral analysis of the Doppler signal to present its time-varying frequency spectrum, employing techniques such as the Fast Fourier Transform (FFT) or other spectral analysis methods Additionally, it can display key statistical measures of the Doppler frequency, including maximum, mean, mode, or median values, obtained either from the spectral analyzer or through direct time-domain processing.

The system can utilize interactive or automated measurement and calculation tools to enhance the processing of data obtained from spectrum analysis and Doppler frequency waveforms, enabling the calculation of waveform shape indices and spectral width.

The system may incorporate means for the operator to listen to the Doppler signal using a loudspeaker or headphones.

The system may be a multi-channel instrument having a number of sample volumes and associated Doppler signal channels.

Worst-case conditions

A test method may be applied to determine a particular performance parameter of a system.

Various factors can influence overall performance, each necessitating a specific testing method To achieve optimal performance, certain quantities must be maximized while others should be minimized.

Table 1 outlines the worst-case scenarios for essential parameters in pulsed Doppler ultrasound systems, along with the relevant subclause numbers for appropriate testing methods For instance, minimizing penetration, as detailed in subclause 5.2.4, results in the worst overall performance, while maximizing penetration enhances performance.

Table 1 – Worst case for various quantities, and corresponding subclause numbers

Worst case is minimum value of Worst case is maximum value of

Clutter rejection index 5.4.3.1 High-frequency response error

Beam position and orientation error

Maximum, mean, mode and median frequency estimation errors

Doppler beam axes

To determine the orientation of the ultrasound probe, it is essential to define three orthogonal axes: the nominal Doppler beam direction axis and two lateral Doppler beam axes The first lateral axis is perpendicular to the sound beam axis and lies within the scan plane, while the second lateral axis is also perpendicular to the sound beam axis but is oriented outside the scan plane In a self-contained pulsed Doppler ultrasound system, these axes should be referenced to a specific mark or feature on the probe body For duplex or triplex scanners, the first lateral Doppler beam axis must remain within the scan plane.

Probe/target distance variation and measurement

The Doppler ultrasound system's probe must be mounted on a calibrated positioning mechanism that allows movement in three orthogonal directions, aligned with the nominal Doppler beam direction and the first and second lateral Doppler beam axes Alternatively, the probe can remain stationary while the target is moved along these axes.

Initial conditions

Power supply

To verify that the specified requirements are met across varying power supply voltages, it is essential to conduct tests at different power line voltages, reporting the worst-case test results These tests should utilize the nominal voltage values as well as values that are 10% above and below the nominal In systems powered by the line, the worst-case results should be recorded after a designated warm-up period.

Portable, battery-operated systems weighing under one kilogram must be tested without a warm-up period Testing should only occur for the duration necessary to complete each test, accurately reflecting typical usage conditions.

Heavier battery-powered systems should be tested under the same conditions as the power line operated systems.

For battery-operated systems, it is essential to evaluate performance based on the worst-case scenario across the entire range of battery voltages, from fully charged to nominal end-of-life levels Additionally, any necessary system tuning or adjustments must adhere to the guidelines provided in the user instructions.

The nominal life-span of a battery should be specified for either continuous or intermittent use, enabling manufacturers to determine the expected battery life for each scenario Additionally, manufacturers can present both optimal performance results, such as those from fully charged batteries, and worst-case outcomes, as long as they clearly indicate the conditions under which these results were achieved.

Target movement direction

In a duplex or triplex scanner, the target movement must align with the scan plane of the pulsed Doppler ultrasound system, unless specified otherwise Conversely, for a stand-alone pulsed Doppler ultrasound system, the target's movement should be confined to the plane defined by the nominal Doppler beam direction and the first lateral Doppler beam axis, unless stated otherwise.

Propagation medium

Many of the tests mentioned can be conducted in a suitable non-attenuative medium with an acoustic velocity of 1,540 m/s, like a 9.0% glycerol solution When utilizing an electronic injection system, it can be connected to the transducer under examination using a solid medium, such as perspex, which has a higher acoustic velocity ranging from 2,700 to 2,800 m/s.

Attenuation using a suitable absorbor is required for the measurement of penetration depth.

This should have an acoustic velocity of 1 540 ms –1 The attenuation may be tissue equivalent

Sensitivity measurements in a flow phantom typically range from 0.45 dB cm$^{-1}$ MHz$^{-1}$ to 0.55 dB cm$^{-1}$ MHz$^{-1}$ However, these values may increase when using an attenuative polyurethane wedge alongside a string test object.

Penetration depth

The maximum depth of penetration along the ultrasound beam (L max) is measured using a

The Doppler test involves using a tissue-mimicking medium to assess the signal power of a moving target compared to noise As the target depth increases, the Doppler signal power reaches a point where it equals the noise power, resulting in a signal-to-noise ratio (SNR) of zero decibels This occurs when the power of the Doppler output with the moving target is twice that of the stationary target.

To achieve a zero decibel signal-to-noise ratio (SNR) in a Doppler test, it may be necessary to reduce the transmitter power if the maximum depth of the test object is inadequate It is important to document the transmitter output setting in this scenario.

The attenuation coefficient of tissue mimicking mediums typically ranges from 0.45 dB cm⁻¹ MHz⁻¹ to 0.55 dB cm⁻¹ MHz⁻¹, which is standard for flow phantoms, although higher values may also be acceptable.

(for example 0,70 dB cm –1 MHz –1 to 0,80 dB cm –1 MHz –1 ) and should be reported along with the results of this test.

It should be noted that penetration depends on the target, and comparisons between systems are valid only if similar targets are used.

Working depth

Measurements should be taken at a distance of L max /2 from the probe face to the target, where L max represents the maximum depth of penetration.

Focusing

When testing duplex or triplex scanners with an operator-set variable focus, it is essential to adjust the nominal focus to align with the depth of the center of the sample volume, or as closely as possible within the limits of the system's focus and sample volume depth settings.

Working Doppler angle

Except where stated otherwise, the angle between the nominal Doppler beam direction axis and the direction of target movement in the Doppler test object should be 0°, 30°, 45°, or 60°.

It should be noted that it may not be possible to achieve all these angles in all test objects (for example 0° in most flow test objects).

In a stand-alone pulsed Doppler ultrasound system, the transducer is positioned so that the beam axis aligns with the probe axis, which should be considered the nominal direction of the Doppler beam In other isolated systems, this nominal direction may vary.

Doppler beam direction axis should be described by the manufacturer.

In duplex and triplex scanners, the working Doppler angle is that measured between the

Doppler beam and the direction of target movement as indicated on the image screen If the

Doppler beam orientation is variable, this angle should be set to 60°.

Wall-thump filter cut-off frequency

In systems with variable wall-thump filter cut-off frequencies, the recommended setting for peripheral vascular applications is 4 × 10⁻⁵ f₀, where f₀ represents the acoustic-working frequency, equating to approximately 3 cm⁻¹ at a Doppler angle of zero For fetal applications, the cut-off frequency should be adjusted to 2 × 10⁻⁵ f₀, while for adult cardiology applications, it should be set to 6 × 10⁻⁵ f₀, or the nearest permissible value by the system.

Transmitter output power

Except where otherwise stated, in systems where the transmitted output power is variable, this power should be set at maximum.

Working pulse repetition frequency (PRF)

Except where otherwise stated, the PRF should be set to 0,4c/L max or the nearest lower frequency allowed by the system.

Doppler (receiver) gain

In systems equipped with a real-time spectrum analyser, the Doppler gain must be adjusted so that, at minimum transmitter power and with a stationary target, the noise remains undetectable on the display Conversely, in systems lacking a spectral analyser, the Doppler gain should be configured to produce a small yet measurable noise signal on the Doppler output.

Test frequency

The test frequency, essential for conducting tests, refers to the Doppler frequency utilized by the electronic injection test device, which corresponds to the frequency of the injected audio signal For alternative test devices, the mean Doppler frequency is applicable Unless specified otherwise, a standard test frequency of \$5 \times 10^{-4} f_o\$ or a frequency designated by the manufacturer should be employed.

Working sample volume length

In systems with variable sample volume lengths, the nominal sample volume length should be established at \$25 \times 10^6 / f_o\$ mm, where \$f_o\$ represents the acoustic working frequency in hertz If a greater length is permissible by the system, it should be used; otherwise, the nearest available length should be selected.

Doppler signal power measurement

Doppler signal power is measurable at a Doppler output connector using devices with an accuracy exceeding 5% at the relevant signal level The measurement should be expressed in terms of mean square signal volts and root-mean-square values.

(r.m.s.) volts or in decibels relative to 1,0 volts r.m.s A true reading r.m.s meter is suitable.

Note that only relative values are required in all the tests.

Zero signal noise level

To effectively display the Doppler signal on the sonogram, the receiver level and transmitted power output are adjusted to utilize the full grey scale range When the target's motion is halted, or the injected signal from the electronic injection device is turned off, the signal level at the Doppler output is recorded as the zero signal noise level.

Doppler frequency response

Frequency response range

The frequency display baseline must be set to zero, with frequency response measured from 0 Hz to the upper Nyquist limit The shift frequency of the electronic Doppler test object or the speed of the moving target is varied within this range The time-average Doppler output signal level is recorded as a function of Doppler frequency using an r.m.s voltmeter or power meter, along with a mean frequency measurement method To determine the low and high-frequency response frequencies, identify the points where the output voltage is 3 dB below the peak level, although alternative limits may be specified This procedure also applies to multiply peaked response curves, focusing on the lowest value between the peaks.

–3 dB level relative to the largest peak described above.

If the response curve is multiply peaked and the lowest value between the peaks is below the

The minimal detectable signal level is determined by taking the smallest value found between the peaks at a -3 dB level relative to the largest peak A horizontal line graph at this signal will intersect the frequency response curve at this minimum and two additional points.

The results of the test should include the low- and high-frequency response values, accompanied by a statement that qualifies the minimum level in relation to the highest value.

It is essential to compare the minimum and maximum frequency limits with those specified by the system or outlined in the system specifications, and to report any discrepancies found.

Note that the minimum frequency is the wall-thump cut-off frequency.

The procedure should be repeated for the negative frequency range, from 0 Hz to the lower

Deviation from flat response

In the frequency range from zero to the upper Nyquist frequency, the maximum deviation from a flat response should be expressed as half the signal level range (in decibels) between the maximum and minimum frequency limits and the highest measured level.

The procedure should be repeated for the negative frequency range, from 0 Hz to the lower

Large signal performance

Large spurious signals can lead to errors in ultrasound Doppler receivers, akin to the behavior of communication system receivers This section examines the extent of these effects caused by interfering signals, focusing on levels that are typically encountered in practical applications.

5.4.3.1 Fixed target effect on sensitivity (clutter rejection)

The impact of highly reflective fixed targets on the amplitude of Doppler output can be assessed using a small vessel or string Doppler test object This method allows for the evaluation of changes in the Doppler signal.

Doppler output must be reported as the change in decibels when a highly reflective target is positioned within the sample volume, specifically on the far side of the string or small vessel from the transducer To achieve optimal results, the target should be placed as close as possible to the moving string or vessel and oriented for maximum echo reflection It is recommended to use a sufficiently large spherical target to ensure a strong echo without causing overload, thereby minimizing alignment issues The Doppler output should be monitored while the fixed target is moved laterally and axially within the sample volume, with the maximum change in output being documented.

The electronic Doppler test object is utilized to assess the clutter rejection capability of the instrument It generates a test frequency with an amplitude that ensures the Doppler output is at least 20 dB above the noise level, while remaining well below saturation During testing, the object produces a stationary frequency signal with zero Doppler shift, and the signal's amplitude is increased until a 3 dB change in the Doppler output is observed, assuming that the zero Doppler frequency signal does not directly contribute to the output.

Doppler ouput power The ratio of the stationary to test Doppler frequency signal amplitudes generated by the electronic Doppler test object is recorded as the clutter rejection index.

Harmonic distortion can be measured according to IEC 61206, specifically in section 2.3.3.1 An electronic Doppler test object can be utilized for this measurement, where a spectrum analyser is connected to the Doppler output The harmonic distortion is calculated by measuring the sum of the powers of the harmonics at the test frequency and expressing it as a percentage of the signal power at that frequency The distortion is reported at Doppler signal output levels starting at 10 dB above the noise level and increasing in 10 dB increments until the distortion surpasses 10%.

The measurement of harmonic distortion can be conducted as outlined in section 2.3.3.3 of IEC 61206, or by utilizing an electronic Doppler test object This device generates a low-frequency signal at 10% of the test frequency, while maintaining the low-frequency signal level at 30 dB above the test frequency signal A spectrum analyser is then used to measure the combined power of the signals at the test frequency, both above and below the low frequency, which is expressed as a percentage of the test frequency signal power This value represents the percentage intermodulation distortion The distortion is recorded at Doppler signal output levels that are 10 dB above the noise level, with additional measurements taken in 10 dB increments until the distortion surpasses 10%.

Spatial response

Sample volume response

To assess sensitivity variations within the sample volume, as well as its lateral widths and axial length, specific tests can be employed These measurements are determined by the distances between points where the instrument's response to a moving target decreases to a defined fraction of the maximum response.

The test should be carried out at the working sample volume length setting at depths of

0,2 kL max where k = 1, 2, 3, 4, or as specified by the manufacturer.

Measurements taken with various targets can yield different dimensional values for the sample volume due to variations in sensitivity based on the target's acoustic response However, measurements from a single target type can still be utilized for comparative analysis.

The Doppler signal power from an ideal string test object is directly proportional to the line integral of sensitivity variation along the string path, reflecting the signal power from a moving monopole scatterer at different positions However, real-string behavior may deviate from this ideal model.

Doppler test objects resulting from finite scatterer dimensions, string thickness and periodicity in string structure, for example, has yet to be fully investigated [2].

Due to the intricate scattering behavior of small-sphere targets and its frequency-dependent variations, the small-ball Doppler test object is not advisable for use in pulsed Doppler ultrasound systems or those with narrow beam widths until its performance limits are thoroughly assessed.

When measuring low Doppler signal power in the presence of significant background noise, such as near L MAX, it is essential to subtract the measured noise power from the total signal-plus-noise power.

Doppler signal connector in order to estimate the Doppler signal power.

To optimize the Doppler signal measurement, the probe is adjusted both axially and laterally until the signal power reaches its maximum Following this, the probe is aligned parallel to the nominal Doppler beam direction The distances at which the Doppler signal power decreases to –6 dB and –20 dB from the maximum are recorded, providing the 6 dB and 20 dB axial sample volume lengths at an angle of 60°.

Measurements are conducted at Doppler angles of 45° and 75°, and these results are extrapolated to determine the sample volume length at 90° This extrapolated length is then compared to the nominal sample volume length provided by the pulsed Doppler ultrasound system.

To optimize the sample volume at the working depth, adjust the length from its minimum to maximum value in five equal increments or as permitted by the system.

6 dB and 20 dB sample volume lengths at 90° reported together with the nominal sample volume lengths indicated by the pulsed Doppler ultrasound system.

The measurements carried out in 5.5.1.1 are repeated, with the difference that the probe is moved laterally perpendicular to the string This gives the first lateral sample volume width.

The measurements are repeated with the probe rotated by 90 ° about the nominal Doppler beam direction axis, giving the second lateral sample volume width.

Sample volume position registration error

Using a string Doppler test object, the sample volume is moved along the beam until the

The maximum Doppler signal power is recorded, after which the sample volume is shifted to two positions where the Doppler signal power decreases by 3 dB from the maximum level.

A duplex or triplex scanner measures the registration error by calculating the distance along the Doppler beam from the midpoint between the centers of the sample volumes, as displayed on the screen, to the image of the string.

Beam position and orientation

The tests aim to assess the deviation of the beam axis position and orientation from the nominal Doppler beam direction They are ideally conducted alongside the sample volume lateral response tests During the process, the coordinates where the Doppler power drops to –6 dB from the maximum are determined, and the mid-point coordinates along the two lateral beam axes are recorded These mid-point coordinates represent the measured beam axis The deviations in beam position at a specific depth are calculated by comparing these coordinates to the nominal beam direction axis coordinates at that depth.

The test rig must be designed to ensure that the coordinates of the string and the nominal Doppler beam direction are accurately defined within the coordinate system established by the calibrated probe positioning system.

Dashed line – nominal Doppler beam axis direction

Dotted line – true Doppler beam axis direction

This figure illustrates the views along the line that is perpendicular to the plane containing the string and the nominal Doppler beam direction axis, as well as along the direction of the string It presents beam deviation measurements (e2, e1) at a depth d along the second (a) and first (b) lateral beam axes.

Figure 1 – Probe/string geometry for beam position and orientation test

Intrinsic broadening

In this test, a spectrum analyser is utilized to analyze the Doppler signal, enabling the display of spectra for signals lasting several seconds and facilitating the measurement of the 6 dB spectral width The measurement accuracy relies on the frequency and amplitude resolution of the spectrum analyser, the width of the spectrum being assessed, and the product of signal duration and frequency resolution It is crucial to configure the spectrum analyser, its settings, and the signal duration appropriately to achieve accurate measurements of the 6 dB spectral width.

The test should be carried out at the working sample volume length setting at depths of

0,2kL max where k = 1, 2, 3, 4, or as specified by the manufacturer.

The test involves using a string test object, where the Doppler beam direction is aligned with the working Doppler angle relative to the string The string speed is adjusted to ensure that the mean frequency of the Doppler signal spectrum matches the Doppler test frequency The probe is then moved both axially and laterally while monitoring the Doppler signal power until it reaches its maximum The 6 dB spectral width of the measured Doppler signal spectrum is calculated as a percentage of the test frequency, which is reported as the percentage intrinsic spectral broadening.

Dead zone

In a string Doppler test, the target depth is gradually reduced until the Doppler signal power falls to –20 dB of the maximum power recorded in section 5.4.1 This depth is subsequently reported as the dead zone thickness.

Acoustic working frequency

This should be measured by the zero-crossing frequency or spectrum analysis methods as detailed in 3.4 of IEC 61102.

Flow direction separation

This should be measured as detailed in 2.6 of IEC 61206.

Velocity estimation accuracy

These tests are to be carried out on a system having a velocity estimation facility.

In a string Doppler test, the velocity measured by the Doppler ultrasound system is compared to the actual string speed under standard working conditions The analysis focuses on string speeds ranging from –2 m/s to +2 m/s, with increments of 0.04 m/s, or speeds that correspond to ±0.8 of the frequency at which aliasing occurs, whichever results in the smallest Doppler frequency magnitude The error in these measurements is reported accordingly.

The velocity measurement error is assessed using a fixed string speed that produces a mean Doppler shift matching the test frequency at a Doppler angle of 60° This analysis includes extreme Doppler angles specific to the system under evaluation, as well as several intermediate angles.

Volume flow estimation accuracy

The test must be conducted on systems equipped with a flow estimation capability, following the guidelines outlined in section 2.7 of IEC 61206 A suitable object for the flow test is detailed in reference [10].

Maximum, mean, mode and median frequency estimation accuracy

The Doppler system's ability to accurately estimate spectral parameters, including maximum Doppler frequency and mean frequency, is influenced by machine-dependent factors like detection algorithms and the characteristics of the Doppler spectrum The estimation accuracy of these parameters is also affected by their rate of change The following tests evaluate the accuracy of spectral parameter estimation and its dependence on the rate of change, focusing solely on the impact of machine processing rather than physical effects like geometric spectral broadening.

To conduct these tests, it is essential to generate a Doppler signal characterized by a time-varying spectrum with controllable and known frequency content The only suitable test object that fulfills these requirements is an electronic device.

The test object must utilize a simulated Doppler signal characterized by a consistent spectral shape and mean frequency It is essential to incorporate at least three distinct spectra: a narrow symmetrical spectrum with a 20 dB spectral width ranging from 0.1 to 0.2 times the mean frequency, a wide symmetrical spectrum with a 20 dB spectral width between 0.4 and 0.6 times the mean frequency, and a wide asymmetrical spectrum that also has a 20 dB spectral width in the range of 0.4 to 0.6 times the mean frequency, with a mode frequency exceeding the mean frequency by at least 0.2 times the mean frequency.

For each spectrum, tests should be carried out using three positive and three negative mean frequencies In each case, the three frequencies should be such that

− the minimum frequency in the spectrum is equal to the wall-thump filter 3 dB cut-off frequency;

− the maximum frequency in the spectrum is equal to the upper 3 dB cut-off of the system frequency response (see 5.4.1);

− they are mid-way between these two frequencies.

The system must undergo testing with simulated Doppler signals that exhibit sinusoidal mean-frequency variation It is essential that the amplitude of this variation is calibrated so that the resulting peak frequency aligns with the upper 3 dB cut-off of the system's frequency response.

The sinusoidal mean-frequency variation, denoted as \$f_{vm}\$, should be adjusted from 1.0 Hz to 50 Hz in at least six increments, while recording the errors in the calculated maximum, mean, mode, and median frequencies Figures 2 and 3 illustrate typical spectra along with the variations in minimum, mean, and maximum frequencies For each \$f_{vm}\$ and spectrum combination, the average bias and standard deviation of the error must be reported, ensuring that the estimation error for these metrics remains below 10% over a sufficiently large number of cycles These tests are to be conducted at signal-to-noise ratios of 0 dB, 10 dB, 20 dB, and 40 dB.

Figure 2 – Sinusoidal variation of minimum, mean and maximum simulated Doppler signal frequencies

This figure illustrates four types of frequency spectra: a narrow positive symmetrical spectrum (a), a wide positive symmetrical spectrum (b), a wide positive asymmetrical spectrum (c), and a wide negative asymmetrical spectrum (d) The frequencies represented include minimum (1), mean (2), maximum (3), and mode (4), with the mode and mean frequencies being equal in the symmetrical spectra.

Figure 3 – Simulated Doppler spectra with a constant mean frequency or at an instant when using a sinusoidal mean-frequency variation

Minimum frequency waveform Mean frequency waveform Maximum frequency waveform

Velocity waveform indices estimation accuracy

Doppler ultrasound systems utilize algorithms to calculate velocity waveform shape indices, including the pulsatility index, resistance index, and A/B ratio These indices can be derived either automatically from the maximum frequency envelope of the displayed spectrum or manually from an operator's trace The accuracy of these results is influenced by the algorithms, sample volume, and spectral analysis methods, which can lead to discrepancies between maximum frequency waveform shapes and actual velocity waveforms To ensure precise estimation of velocity waveform indices, it is essential to use a pulsatile flow test object with a known time-varying velocity field that minimally distorts the system's sample volume In the absence of such a test object, algorithms can be evaluated using an electronic test object that simulates Doppler signals with known time-varying spectra.

Doppler ultrasound systems exhibit significant variability, and there is no universal agreement on the necessary accuracy levels It is essential to conduct tests to verify the estimation accuracy claimed by the manufacturer.

When conducting tests with a pulsatile flow-test object, it is essential to utilize waveforms with known index values that span the declared range of the system being evaluated The test object vessel must be positioned at the working depth, ensuring that the angle between the vessel axis and the nominal Doppler beam direction aligns with the working Doppler angle Additionally, the discrepancy between the measured index and the known index of the pulsatile flow should be reported for each tested waveform Tests should be performed at signal-to-noise ratios of 0 dB and 10 dB.

The system's transmitted output power control allows for adjustments between 20 dB and 40 dB Testing should be conducted using two different vessel diameters: a narrow spectrum with a diameter greater than five times the larger dimension of the 6 dB width or length of the sample volume, and a wide spectrum with a diameter smaller than the smaller dimension of the 6 dB width or length of the sample volume.

When utilizing an electronic test object, it is essential to generate Doppler signals with known maximum frequency waveforms and to evaluate the system using both narrow and wide spectra The spectra employed for frequency estimation tests, as outlined in section 5.14, are appropriate for this purpose Due to the lack of consensus on the definition of "maximum" frequency—where a typical Doppler spectrum diminishes to zero because of intrinsic spectral broadening—the maximum frequency of the simulated Doppler signal spectrum should be clearly defined This definition could include the frequency below which 95% of the total Doppler signal power is contained Additionally, the range of velocity indices and signal-to-noise ratios should align with those used in tests involving the pulsatile flow test object.

To evaluate the system's response to varying amplitude velocity waveforms caused by breathing or involuntary patient movements, the electronic test object must generate simulated Doppler signals These signals should exhibit a smooth and random reduction in velocity waveform amplitude, decreasing from a maximum to a minimum value of half the maximum amplitude This transition should occur over a duration of at least two and no more than ten cardiac cycles.

The deviation of each index calculated by the system from the index of the maximum amplitude waveform should be declared.

The above tests should be carried out with cardiac periods of 400 ms, 800 ms and 1 600 ms or at three periods spanning the declared range of the system.

Test objects

Test objects suitable for pulsed Doppler ultrasound systems are described briefly in

Section 3 of IEC 61206 and in [10] In addition, an electronic Doppler test object is described briefly here.

Flow, string, belt and electronic test objects together with their strengths and limitations are described in [2].

The moving belt test object, which features a distributed target made of a motor-driven belt with scattering material in a fluid bath, is effective for specific applications.

Doppler frequency response (5.4.1, 5.4.2, 5.4.3.2) tests, the intrinsic broadening test (5.8) and the velocity estimation accuracy test (5.12).

Reporting the characteristics of the test object that are known or likely to influence the test results is crucial for accurate interpretation of the findings.

Electronic test object

Partially reflecting interface or mem brane

Figure 4b – Alternative coupling arrangement between probe and test object transducers

In an electronic, acoustically coupled test-object, transmitted pulses from the probe of the system under test received by one transducer of the test object are mixed with a simulated

Doppler signal to generate Doppler shifted pulses which are retransmitted back to the probe.

The system under test simulates Doppler shifts by receiving pulses from targets, resulting in a received radio frequency (r.f.) signal that contains two sidebands, effectively mimicking simultaneous forward and receding flow A single sideband system, which enables operators to switch between sidebands, has been previously described by Wallace and Whittingham The system illustrated in figure 4a offers the capability to generate a Doppler signal without the limitations of sideband selection, accommodating any time-varying frequency content within the Nyquist bounds of ±0.5.

The pulse received on transducer 1 undergoes a 90° phase shift, with both the original and phase-shifted signals being fed into the real and imaginary connections of a complex multiplier Xc The other input consists of the in-phase and quadrature components from a simulated Doppler signal The output from the complex multiplier yields either the real or imaginary part, which is essential for further processing.

The Doppler shifted signal is transmitted from transducer 2 back to the probe of the system under test, with coupling achieved through a perspex block or an angled partial reflector The simulated Doppler signal can range from a single-frequency sine wave to a time-varying spectrum typical of arterial signals This signal may be generated in analogue form using a noise source and a filter with a time-varying frequency response, or in digital form followed by a digital-to-analogue converter To evaluate the system's response to clutter signals, higher amplitude Doppler signals can be superimposed on those simulating blood flow.

Clearly, the Doppler signal simulator should generate spurious signals at a much lower level than those anticipated from the system under test.

Description of pulsed Doppler ultrasound systems

Single-channel system

Annex A of IEC 61206 outlines a continuous-wave Doppler ultrasound system, highlighting its distinctions from a pulsed Doppler ultrasound system For further insights into instrumentation design, refer to Reference [4].

The pulsed Doppler ultrasound system offers range resolution, distinguishing it from continuous-wave systems It accomplishes this by periodically sending ultrasound pulses composed of several cycles, rather than a continuous stream This method allows the system to focus on flow within a small sample volume (sv) at a specific distance from the transducer, ensuring that the transit time of the ultrasound pulse to the sample volume and back matches the delay between transmission and receiver sampling.

The block diagram of the system, illustrated in figure A.1, demonstrates that, in contrast to continuous wave systems, the transmission and reception functions are temporally separated, allowing for the use of a single transducer The transmitter gate operates periodically at the system's pulse repetition frequency, and the duration of the gate's opening, along with the transducer's filtering action, defines the length of the transmitted pulse After a specified delay, the output is generated.

The Doppler demodulator samples and holds data until the next sampling occurs In certain systems, the output from the Doppler demodulator is averaged while the range gate is active.

The sample volume length is mainly influenced by the duration of the transmitted pulse and the range gate duration Additionally, in certain cases, the range gate remains open for a brief period relative to the time constant of the low-pass filter that follows the multiplier.

The Doppler demodulator's performance is influenced by the transmitted pulse length and the filter time constant, which together define the sample volume length Additionally, the width of the ultrasound beam determines the sample volume width, while the sample volume depth can be adjusted by changing the delay between transmission and the range-gate.

The signal from the sample-and-hold circuit is amplified and filtered to give the signal at the

The Doppler output connector features filters that include a wall-thump filter similar to those used in continuous wave systems The low-pass filtration of the signal from the Doppler demodulator is influenced by the system's pulse repetition frequency, as the system effectively samples the signal.

The Doppler signal from a sample volume includes a spectrum that contains the desired signal along with replicas at multiples of the pulse repetition frequency To effectively filter this signal, the low-pass filter's cut-off frequency must be set to attenuate components above half the pulse repetition frequency Consequently, the maximum Doppler frequency is restricted to this threshold Additionally, similar to continuous wave instruments, flow direction discrimination can be accomplished by employing an offset frequency reference or utilizing two reference signals.

90° phase shift The system may incorporate a means of listening to the Doppler signal, such as a loudspeaker or headphones, and a means of frequency analysis such as a spectrum analyser.

Multi-channel system

The single-channel pulsed Doppler system can be expanded into a multi-channel system that utilizes multiple sample volumes to simultaneously monitor flow at various positions along the beam This is achieved by incorporating several Doppler demodulator sampling gates, each equipped with its own amplifiers and filters, which are activated at different times after transmission.

Aliasing

Aliasing is a significant issue in pulsed Doppler systems, requiring signals to be sampled at least twice per cycle of their highest frequency component for accurate resolution Insufficient sampling frequency leads to errors in the indicated Doppler frequency In non-directional systems, the indicated frequency is a mirror image of the true Doppler frequency at the Nyquist limit, while in directional systems, it is both mirrored and sign-inverted To optimize frequency range utilization, many systems apply a baseline frequency shift, allowing zero target velocity to align with this shift instead of zero frequency This adjustment enables operators to effectively manage targets with varying positive and negative velocity excursions, maximizing the available frequency range.

Duplex and triplex scanners

A duplex scanner combines a pulsed Doppler ultrasound system with a real-time ultrasonic B-mode imager, enabling the visualization of the Doppler ultrasound beam and sample volume on the B-mode image This feature allows operators to accurately position the sample volume within blood vessels Duplex scanners typically include an electronically generated marker line to measure the Doppler angle, which can be adjusted to align with the blood vessel axis This alignment enables the system to calculate the angle between the ultrasound beam and vessel axes, converting measured Doppler frequency into blood velocity for display Additionally, blood flow can be assessed by measuring the cross-sectional area of the blood vessel using electronic callipers, with diameter measurements taken under the assumption of a circular cross-section.

The combination of a duplex scanner and a colour flow imager is known as a triplex scanner.

Figure A.1 – Single-channel, non-directional pulsed Doppler ultrasound system

Key a 1 First lateral axis a 2 Second lateral axis a 3 Third lateral axis

Figure A.2 – Beam axes for Doppler beam from linear array probe

[1] AIUM Standards Committee, Performance criteria and measurements for Doppler ultrasound devices, American Institute for Ultrasound in Medicine, USA, 1993.

[2] Hoskins, P R., Sherriff, S B and Evans, J A., Testing of Doppler ultrasound equipment,

Institute of Physical Sciences in Medicine, York, UK, 1994.

[3] IEC 61266:1994, Ultrasonics – Hand-held probe Doppler foetal heartbeat detectors –

Performance requirements and methods of measurement and reporting

[4] Evans, D H., McDicken, W N., Skidmore, R and Woodcock J P., Doppler ultrasound: physics, instrumentation and clinical applications, Wiley, Chichester, UK, 1989.

[5] Rickey, D W., Rankin, R., and Fenster, A "A velocity evaluation phantom for colour flow and pulsed Doppler instruments", Ultrasound Med Biol., vol 18, pp 479-494, 1992.

[6] Evans, J A., Price, R and Luhana, F "A novel testing device for Doppler ultrasound equipment", Phys Med Biol., vol 34, pp 1701-1702, 1989.

[7] Wallace, J J A., Martin, K and Whittingham, T A "An experimental single-sideband acoustical re-injection test method for Doppler systems", Physiol Meas., vol 14, pp 479-

[8] Bastos, C A C and Fish, P J "A Doppler signal simulator", Clin Phys Physiol Meas. vol 12, pp 177-183, 1991.

[9] Wang, Y-Y and Fish, P J "Simulating nonstationary in-phase and quadrature Doppler signals using a time-varying impulse response filter", Ultrasound Med Biol., vol 22, pp.

[10] IEC 61685, Ultrasonics – Flow measurement systems – Flow test object (under consideration).

The IEC is committed to providing the highest quality standards and values your feedback to ensure we meet your needs Please take a moment to complete the questions on the following page and send them to us via fax at +41 22 919 03 00 or by mail to the address provided below Thank you for your participation!

Fax to: IEC/CSC at +41 22 919 03 00

Thank you for your contribution to the standards-making process.

Q2 Please tell us in what capacity(ies) you bought the standard (tick all that apply).

I am the/a: purchasing agent R librarian R researcher R design engineer R safety engineer R testing engineer R marketing specialist R other

(tick all that apply) manufacturing R consultant R government R test/certification facility R public utility R education R military R other

Q4 This standard will be used for:

(tick all that apply) general reference R product research R product design/development R specifications R tenders R quality assessment R certification R technical documentation R thesis R manufacturing R other

Q5 This standard meets my needs:

(tick one) not at all R nearly R fairly well R exactly R standard is out of date R standard is incomplete R standard is too academic R standard is too superficial R title is misleading R

I made the wrong choice R other

Q7 Please assess the standard in the following categories, using the numbers:

(6) not applicable timeliness quality of writing technical contents logic of arrangement of contents tables, charts, graphs, figures other

Q8 I read/use the: (tick one)

English text only R both English and French texts R

Q9 Please share any comment on any aspect of the IEC that you would like us to know:

The CEI aims to provide you with the highest possible standards To ensure we continue to meet your expectations, we kindly request some information from you Please take a moment to complete the questionnaire below and return it to us by fax.

+41 22 919 03 00 ou par courrier à l’adresse ci-dessous Merci !

Centre du Service Clientèle (CSC)

Nous vous remercions de la contribution que vous voudrez bien apporter ainsi à la Normalisation Internationale.

Centre du Service Clientèle (CSC)

Q2 En tant qu’acheteur de cette norme, quelle est votre fonction?

(cochez tout ce qui convient)

Je suis le/un: agent d’un service d’achat R bibliothécaire R chercheur R ingénieur concepteur R ingénieur sécurité R ingénieur d’essais R spécialiste en marketing R autre(s)

(cochez tout ce qui convient) dans l’industrie R comme consultant R pour un gouvernement R pour un organisme d’essais/ certification R dans un service public R dans l’enseignement R comme militaire R autre(s)

Q4 Cette norme sera utilisée pour/comme

This article serves as a reference work, focusing on product research, product development studies, specifications, submissions, quality assessments, certifications, technical documentation, theses, and manufacturing The content is evaluated on a scale ranging from not at all to perfectly, ensuring a comprehensive understanding of the various aspects involved.

Q6 Si vous avez répondu PAS DU TOUT à

Q5, c’est pour la/les raison(s) suivantes:

The standard requires revision as it is incomplete, overly theoretical, and too superficial Additionally, the title is ambiguous, and I may not have made the right choice.

Q7 Veuillez évaluer chacun des critères ci- dessous en utilisant les chiffres

(2) au-dessous de la moyenne,

(4) au-dessus de la moyenne,

(6) sans objet publication en temps opportun qualité de la rédaction contenu technique disposition logique du contenu tableaux, diagrammes, graphiques, figures autre(s)

Q8 Je lis/utilise: (une seule réponse) uniquement le texte franỗais R uniquement le texte anglais R les textes anglais et franỗais R

Q9 Veuillez nous faire part de vos observations éventuelles sur la CEI:

Tiêu đề	Ultrasonics – Pulsed Doppler Diagnostic Systems – Test Procedures to Determine Performance
Trường học	International Electrotechnical Commission
Chuyên ngành	Electrical Engineering
Thể loại	Technical Specification
Năm xuất bản	1999
Thành phố	Geneva

Định dạng
Số trang	40
Dung lượng	345,95 KB