Method and apparatus for performing spectral doppler imaging

Abstract

To provide a better method for performing spectral Doppler imaging.SOLUTION: An ultrasound imaging system performs spectral Doppler processing in a manner that a physiological cycle of a subject is considered. In one embodiment, gaps in a spectral Doppler signal are filled taking by a processor that analyzes changes in the spectral Doppler signal caused by a physiological cycle. Spectral Doppler data are scaled to fit with the data occurring before and after a gap. The firing order of an interleaved imaging mode can also be adjusted so that spectral Doppler imaging is not interrupted during pre-defined or user defined portions of a physiological cycle.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed herein relates particularly to ultrasonic imaging and spectral Doppler imaging.

Background Art

[0002] Spectral Doppler is an imaging mode that provides useful information regarding the health of the heart and blood vessels to physicians and healthcare providers. In conventional Doppler processing, an ultrasonic signal is directed at a region of interest, and a Doppler shift caused by reflections from moving tissue or blood flow is detected. Spectral Doppler processing performs an additional step of analyzing the frequency components of the detected Doppler signal. FIG. 1 shows a typical spectral Doppler signal. The horizontal axis represents time, and the vertical axis represents the frequency present in the Doppler signal detected at any given point in time. The Doppler frequency is most often shown as a velocity (e.g., cm per second) taking into account the transmitted carrier frequency, the speed of sound, and the propagation direction.

[0003] During the systolic phase of the cardiac cycle (i.e., when the heart is contracting to eject blood), there are large spikes in the detected velocity of the moving blood. During the diastolic phase of the cardiac cycle (when the heart is being filled with blood), the velocity of the moving blood becomes very slow. How the velocity changes with the cardiac cycle can indicate a disease or other physiological condition.

[0004] To perform spectral Doppler mode inspection, the user operates an ultrasonic probe to direct ultrasonic energy towards a desired region of interest. Then, the user sets controls on the ultrasonic imager to adjust the depth of a range gate that defines a small subset of the region of interest where the Doppler shift of the reflected echo signal is measured. In order to obtain consistent results over multiple cardiac cycles, the range gate should persist at the same location. If the user accidentally moves the probe, the spectral Doppler signal changes. To keep the probe in the desired orientation, many ultrasonic imaging systems interleave one or more other modes into the spectral Doppler processing. For example, B-mode imaging can be interleaved into the spectral Doppler processing by, among other things, transmitting ultrasonic signals on several beam lines to insonify the entire region of interest, then Doppler transmitting on the beam line of the range gate, and then transmitting another set of B-mode imaging signals. The B-mode image of the region of interest is displayed on a video monitor so that the user can verify whether the range gate is in the desired location. Under some conditions, interleaving can cause gaps 10a, 10b, 10c, etc. in the spectral Doppler signal when the Doppler signal is not detected while the imaging system is performing B-mode imaging, as shown in FIG. 2. Gaps in the spectral Doppler signal do not contain useful information and can occur when a physician wants to view the signal.

[0005] As proposed by Robinson in U.S. Patent No. 5,476,097, there is a known technique for filling in the gap portion of a spectral Doppler signal by copying adjacent Doppler data and pasting it into the gap of an interleaved Doppler signal. There are other approaches that perform a moving average (MA) modeling (Christoffersen, U.S. Patent No. 4,559,952) or an autoregressive (AR) modeling (Wong, U.S. Patent No. 5,642,732) of the adjacent Doppler data. These models are used to generate a "clone" of the adjacent Doppler data for filling in the gap. FIG. 3 shows an example of such a gap-filling technique, whereby a portion of the Doppler signal to the left or right of the gap is copied or cloned into the gap. Previous techniques suggest that the left and right copies or clones overlap and blend at the center of the gap in order to smooth the Doppler signal. This approach can make the spectral Doppler signal appear smoother when the signal is not changing rapidly, but such an approach does not work well for gaps that are in the vicinity of a signal where large changes are occurring.

[0006] Considering these problems, a better method for performing spectral Doppler imaging is needed. SUMMARY OF THE INVENTION

[0007] To address the above problems, the disclosed technology relates to an ultrasonic imaging system that performs spectral Doppler processing by analyzing a physiological function of interest. In one embodiment, the data used to fill gaps in interleaved spectral Doppler signals is scaled or adjusted based on where the gaps are in the physiological cycle. In one embodiment, the average frequency of segments of spectral Doppler signals that occur before and after a gap is determined and used to modify a copy or clone of adjacent spectral Doppler data to fill the gap. In one embodiment, the average frequency of spectral data before and / or after a gap is used to shift the average frequency of a copy or clone of adjacent Doppler data so as to generate a spectral Doppler signal with an average frequency that fits between the average frequencies of adjacent portions of the spectral Doppler signal.

[0008] In one embodiment, the system performs spectral Doppler processing during one or more predefined times in the physiological cycle of the subject. In one embodiment, the spectral Doppler processing is not interrupted at peak systole or at the end of the diastolic portion of the cardiac cycle. The processor estimates when an event occurs in the cardiac cycle of the subject and modifies the firing order of the spectral Doppler processing with respect to other imaging modes so that the other imaging modes are not used at predefined or user-selected points in the cardiac cycle.

[0009] In one embodiment, the display of the spectral Doppler signal on the video monitor is triggered based on a threshold of the spectral Doppler signal or from a signal received from an external sensor. When a trigger threshold is defined, the displayed spectral Doppler signal appears stationary on the video monitor.

[0010] In another embodiment, the processor of the ultrasonic imaging system records and stores the length of the spectral Doppler data that includes a predefined number of physiological cycles. Investigations performed at different times can always include the same number of cycles and are thus more easily comparable. Further, the derived waveforms (e.g., peak, average waveforms, etc.) are more easily comparable across different investigations.

Brief Description of the Drawings

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[0017] As described above, the described technique relates to improving spectral Doppler (pulse wave (PW) or continuous wave (CW)) imaging modes used in an ultrasonic imaging system. In one embodiment, gaps in the Doppler signal caused by an interleaved imaging mode are filled with actual or replicated Doppler data adjusted according to a physiological function of the subject (e.g., the cardiac cycle). In one embodiment, the Doppler data is copied from a region before or after the gap and mixed (e.g., scaled in frequency) such that the average frequency of the copied or replicated data falls between the average frequencies of the Doppler data before and after the gap.

[0018] FIG. 4A shows a spectral Doppler signal recorded over a single cardiac cycle of a subject. The spectral Doppler signal includes sections of Doppler data separated by several gaps. In this figure, two Doppler data sections 100, 104 are recorded at the end of the diastolic phase of the cardiac cycle. Doppler data section 108 is recorded during the rise to the peak of the systolic phase of the cardiac cycle, and Doppler data section 112 is recorded at the peak of the systolic phase. Gap 106 occurs at the beginning of the systolic phase, and gap 110 occurs just before the peak of the systolic phase.

[0019] To fill gaps (e.g., gaps 106, 110), the processor analyzes one or more sections of Doppler data before and / or after the gap. The Doppler data for filling the gap is scaled based on the analysis and used to fill the gap. In one embodiment, the processor determines the average frequency of the Doppler data of several recorded sections such as sections 100, 104, 108, and 112 and determines how to create the data to be used to fill the gap.

[0020] In one embodiment, the Doppler data adjacent to the gap (or approximately adjacent such as within 1 - 3 gaps) is copied or replicated and mixed / scaled. It can also be determined from the analysis of the recorded Doppler data which side of the gap the data is acquired from. In the example shown, there are gaps 106, 110 occurring in the systolic portion of the cardiac cycle before reaching the peak at 112 and before reaching the peak with one set of the actual Doppler data 108 recorded in the middle of the peak. In one embodiment, the Doppler data 108 is scaled both up and down in frequency such that the average frequency of the scaled data falls between the average frequencies of the adjacent actual Doppler data and is copied to fill gaps 106 and 110.

[0021] In one embodiment, the copied Doppler data is scaled in the time domain by mixing the data (e.g., by multiplying the data by sine waves having different average frequencies). For example, if the average frequency of Doppler data 108 is 1500 Hz and the average frequency of Doppler data 112 at peak systole is 2000 Hz, a copy of Doppler data 108 is mixed upward so that the data has an average frequency that varies up to 1750 Hz and can be used to fill gap 110. Similarly, if the average frequency of Doppler data 104 is 1000 Hz, a copy of Doppler data 108 is mixed downward to have an average frequency of 1250 Hz and is used to fill gap 106. The mixing frequency need not be constant. In some embodiments, the mixing frequency is not constant and can be determined by the frequency of the actual Doppler data adjacent to the edge of the gap. In this way, the copied data smoothly fits the actual data and avoids frequency discontinuities.

[0022] In one embodiment, received Doppler data having an average frequency between the average frequencies of adjacent ones is selected and scaled to fill the gap (e.g., Doppler data 108 has an average frequency between the average frequencies of Doppler data sections 104 and 112 and is used to fill gaps 106 and 110). In another embodiment, Doppler data occurring before the gap can be used, or Doppler data after the gap can be used.

[0023] The disclosed technique is not limited to using only one average frequency. In some embodiments, multiple average frequencies can be calculated from subsections of adjacent Doppler data, such as average frequencies every 5 microseconds. Calculating multiple average frequencies from subsections of adjacent Doppler data can be utilized to predict the trend of the Doppler data and thereby scale the Doppler data more accurately. In some embodiments, additional average frequencies from Doppler data other than two adjacent sections of Doppler data (sections 100, 112 in FIG. 4A) can be used to fill gap 106. In some embodiments, the utilization of additional average frequencies from additional sections can be used to predict where in the cardiac cycle the gap is occurring, such as whether the gap is at the systolic peak or diastolic trough.

[0024] In some embodiments, the gap is not filled with copied or replicated Doppler data. Instead, pre-fast Fourier transformed echo data is generated such that the FFT of the generated echo data has the signal characteristics necessary to smoothly fill the gap. For example, when the data is scaled based on the average frequency of the Doppler data adjacent to the gap, the pre-FFT echo data is generated such that the average frequency of the FFT of the generated echo data becomes the desired average frequency.

[0025] In some embodiments, an inverse FFT such as x(t)=IFFT(X(f)), where X(f) is the desired Doppler data in the frequency domain, can be used to generate the pre-FFT echo data.

[0026] When synthetic pre-FFT echo data are generated, they are added to the actually recorded echo data and analyzed in the frequency domain to generate a continuous spectral Doppler signal. In one embodiment, the spectral Doppler data are copied and mixed to a desired frequency. The inverse FFT of the spectral Doppler signal is calculated by a processor, and the synthesized pre-FFT data are combined with the pre-FFT data received during gaps and processed together to generate a spectral Doppler signal without gaps.

[0027] The disclosed embodiments scale the Doppler data copied to the gaps based on the detected average frequency of the Doppler data adjacent to the gaps, but it will be understood that other measurements of the spectral Doppler signal, such as central frequency, peak frequency, minimum frequency, frequency spread, etc., may be used. Also, the scaling need not be linear (e.g., midway between adjacent ones) to fill the gaps. The scaling can be performed such that the plots of the frequency measurements or other parameters used for scaling follow smoothly with the cardiac cycle or other physiological cycles. Such scaling is by splines or the like to achieve a smooth curve.

[0028] In another embodiment of the disclosed technique, the transmit order of the ultrasound system is changed so that spectral Doppler imaging is not interrupted during one or more desired periods of the physiological cycle. Many clinicians are interested in the characteristics of the spectral Doppler signal at the end of diastole and at the peak of the systolic portion of the cardiac cycle. In some embodiments, to ensure that actual spectral Doppler signal data rather than synthetic are obtained during these times, the processor of the ultrasound imaging system can change the transmit order of the transmit signals of an ultrasound imaging system operating in an interleaved transmit mode so that spectral Doppler imaging is not interrupted during these times.

[0029] FIG. 5 shows a simplified block diagram of an ultrasonic imaging system including a processor or programmed logic configured to change the transmission order of transmitted ultrasonic signals so that spectral Doppler imaging is not interrupted during one or more target periods. The ultrasonic imaging system 200 includes an imaging transducer 210 and a receive (RX) electronics 214 (such as an amplifier, filter, A / D converter, digital signal processor, and graphics processor, etc.) that processes received analog echo signals and generates digital echo data for display on one or more video monitors 216. The RX electronics 214 is coupled to the transducer 210 via a transmit / receive switch 212 that opens when the transducer is directing ultrasonic signals towards the target region and closes when the RX electronics 214 is receiving the corresponding echo signals.

[0030] On the transmit side, a transmit logic circuit 220, such as a dedicated logic circuit, processor, or FPGA, is configured to generate drive signals for individual piezoelectric elements within the transducer 210. The drive signals generated depend on the type of imaging mode being used. For example, in B-mode imaging, drive signals are generated that direct the transmitted ultrasonic waves to every corner of the target region so as to apply sound waves to the entire region. In spectral Doppler imaging, drive signals are generated that produce ultrasonic pulses along the same beam line so that frequency shifts of the return echoes in the range gate region can be detected. The transmit circuit 224 includes circuitry for boosting the voltage of the drive signals generated by the transmit logic circuit 220 to a level sufficient to vibrate the piezoelectric elements within the transducer 210 to generate corresponding acoustic signals.

[0031] In one embodiment of the present invention, the firing order of the drive signal generated by the transmission logic circuit 220 is controlled by a programmed processor 250 or other logic circuit to ensure that spectral Doppler imaging is not interrupted during one or more specified times in the target physiological cycle. In one embodiment, the processor 250 monitors the physiological cycle of the target and receives signals from one or more sensors 260 coupled to the target. In one embodiment, the physiological cycle is the cardiac cycle, and the sensor 260 is an EKG sensor, an SPO2 sensor, a pacemaker, or any other sensor capable of detecting the heartbeat or pulse of the target, including the Doppler ultrasound signal itself. The processor 250 is configured to execute instructions stored on a non-transitory computer-readable medium or hard-coded to receive signals from the sensor 260. From the signals, the processor 250 is programmed to analyze past physiological cycles and predict the timing at which events will occur in the next physiological cycle. For example, when the heart rate is relatively stable, the time of the next systolic phase can be determined by extrapolation from the time of the previous systolic phase. In other cases, the body's electrical signals (e.g., EKG signals) precede the actual physical response by a sufficient amount of time to allow the processor 250 to adjust the order of the drive signals generated by the transmission logic circuit 220 prior to special points in the physiological cycle where the spectral Doppler imaging mode should not be interrupted. In some embodiments, the logic for predicting the systolic and diastolic phases is based on the predicted times measured from previous cycles or detected biological signals. In other embodiments, machine learning, artificial intelligence, or neural networks are trained on historical data (e.g., sequences of EKG or respiratory signals, pacemaker signals, etc.) and can be utilized to predict the systolic and diastolic phases of the cardiac cycle. Based on the predicted phases, the firing order of the ultrasound imaging system is adjusted to ensure spectral Doppler imaging between these portions of the physiological cycle.

[0032] Modification of the drive signal generated by the transmission logic circuit 220 can be controlled by slowing the B-mode frame rate, changing the number of lines transmitted or received within a frame for B-mode imaging, or changing the time during which spectral Doppler mode and B-mode imaging are performed. In one embodiment, the processor 250 modifies the firing order of the generated drive signal so that the spectral Doppler imaging mode is not interrupted at the peak of systole or the end of diastole. In other embodiments, the user can select one or more periods using an input user control 270 (such as a keyboard, touch screen, trackball, trackpad, voice command, button, knob, etc.) that can specify one or more portions of a physiological cycle during which spectral Doppler imaging is not interrupted.

[0033] The physiological cycle described above is the cardiac cycle, but it will be understood that other physiological cycles such as the respiratory cycle can also be used. The respiratory cycle can be monitored or detected by a respiratory sensor that provides a signal indicative of the cycle to the processor 250. The order / timing of the drive signal from the transmission logic 220 is adjusted so that spectral Doppler imaging is not interrupted during predefined or user-selected portions of the respiratory cycle.

[0034] According to another embodiment of the disclosed technique, the spectral Doppler signal is displayed on a video monitor starting from the point where the signal has a detected characteristic such as a specific frequency or velocity threshold. Modern ultrasound systems display the spectral Doppler signal at any point, which makes it difficult to change the tracking of the spectral Doppler due to the lack of synchronization between waveforms (e.g., a new waveform overwriting a previously displayed waveform). Instead of starting the display of the signal at any point in time, the processor 250 of the imaging system analyzes the signal and starts the display of the signal when the characteristics of the spectral Doppler signal (such as average frequency / velocity or peak frequency / velocity, power or other attributes) have a predefined or user-selected value. This has the effect of always aligning the signal at a relatively same location on the horizontal axis of the display at the start of the sweep, regardless of the current physiological function of the subject. In another embodiment, an external sensor such as an EKG sensor provides a measurement of the detected physiological signal, and the trigger is defined by an event of the received signal. For example, the QRS complex of the EKG signal defines a repeating point of the cardiac cycle that can be used to start the display of the spectral Doppler signal. In some embodiments, the display of the spectral Doppler signal can be started after a variable delay that is timed by the processor after the detection of a trigger event in the sensor signal. The delay can be pre-programmed, set by the user, or variable based on the analysis of the signal from the sensor.

[0035] FIG. 6 shows a typical display of a spectral Doppler signal 320 that begins to sweep across the display when the Doppler signal meets a defined criterion such as a specific peak frequency value trigger point 330. The effect is achieved in a manner similar to an electrical oscilloscope, whereby the processor analyzes the signal to identify the point at which the signal meets the defined trigger criterion and begins displaying the signal after that point. The signal can be a spectral Doppler signal recorded in real time or a spectral Doppler signal previously recorded and stored in the memory 280. In some embodiments, the spectral Doppler is buffered so that a portion of the signal prior to the trigger can be displayed. For example, the initial systolic portion of the signal preceding the trigger point 330, as shown in FIG. 6B, can be stored in memory and displayed to the operator as needed. Further, the "triggered" and thus time-aligned signals can be combined with previously triggered Doppler signals to improve the signal-to-noise ratio (SNR). For example, the aligned signals can be averaged or envelope detected to improve the quality of the signal. The heart beat period can vary by approximately 10% from cycle to cycle, and their lengths can be adjusted by making them longer or shorter so that they are the same length before averaging or combining them in order to average or cross-process them.

[0036] According to another embodiment of the disclosed technology, the processor 250 is operative to store a consistent number of physiological events in the recorded ultrasonic signals rather than a predetermined time in seconds as is done in most current ultrasonic imaging systems. In one embodiment, the processor is programmed to store Doppler signals that cover a defined number of cycles, such as 4, 8 heartbeats, etc. The processor analyzes the signals generated for the indication of defined points (e.g., peak velocity points) in the physiological cycle and records the signals until a defined number of points are detected. For example, in spectral Doppler imaging, the processor can record and store a Doppler signal that includes 4 heartbeat events regardless of the patient's heart rate. Further, as shown in FIG. 6, this signal reflecting a predetermined heart rate can be shown starting from a desired trigger point. The processor 250 is programmed to analyze the Doppler signal and determine whether the length of the Doppler signal is more or less than a predefined number of physiological events. If there are fewer physiological events in the signal than the determined number, additional signals are recorded. If there are more physiological events in the signal, the recorded signal is trimmed to include only the determined number of physiological events. Thus, studies performed on subjects at different times always include the same number of physiological events and are easy to compare. The number of physiological events to be stored may be defined by the user or may be defined by an expert committee, an insurance company, or based on general business practices.

[0037] The embodiments of the subject matter and the operations described in this specification can be implemented by digital electronic circuitry, or by computer software, firmware, hardware, or combinations of them, including the structures disclosed in this specification and their structural equivalents. Embodiments of the subject matter described in this specification can be implemented as one or more computer programs, i.e., as one or more modules of computer program instructions encoded on a computer storage medium for execution by, or to control the operation of, a data processing apparatus.

[0038] A computer storage medium can be, or can include, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Further, a computer storage medium is not a propagated signal, but a computer storage medium can be the source or destination of computer program instructions encoded in an artificially generated propagated signal. Also, a computer storage medium can be, or can include, one or more separate physical components or media (such as multiple CDs, disks, or other storage devices). The operations described in this specification can be implemented as operations performed by a data processing apparatus on data stored on one or more computer-readable storage devices or received from other sources.

[0039] The terms "processor" and "logic circuit" include all kinds of devices, apparatuses, and machines for processing data, including, for example, programmable processors, computers, system-on-chips, or multiple ones or combinations of them. The apparatus can include special purpose logic circuitry, such as an FPGA (field programmable gate array), an ASIC (application specific integrated circuit), or hard-wired logic circuitry.

[0040] A computer program (also known as a program, software, software application, script, or code) can be described in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system.

[0041] The processes and logical flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform actions by operating input data and generating output. The processes and logical flows can be performed by special purpose logic circuitry, such as an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and the apparatus can also be implemented as special purpose logic circuitry, such as an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit).

[0042] Processors suitable for the execution of a computer program include, by way of example, any one or more processors of both general and special purpose microprocessors, and any kind of digital computer. In general, a processor receives instructions and data from a read-only memory or a random access memory or both. Essential elements of a computer are a processor for performing actions in accordance with instructions, and one or more memory devices for storing the instructions and data. Also, in general, a computer includes or is operatively coupled to one or more mass storage devices for storing data, such as magnetic disks, magneto-optical disks, or optical disks, or receives data therefrom, or transfers data thereto, or both. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and storage devices, including by way of example semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0043] To provide interaction with a user, embodiments of the subject matter described in this specification may be implemented on an imaging system having a display device for displaying information to the user, such as an LCD (liquid crystal display), LED (light emitting diode), or OLED (organic light emitting diode) monitor, and a keyboard and a pointing device, such as a mouse or trackball, by which the user can provide input to the computer. In some implementations, a touch screen can be used to display information and receive input from the user. Other types of devices can be used to provide interaction with the user; for example, feedback provided to the user can be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback, and input received from the user can be in any form including acoustic, voice, or tactile input.

[0044] From the foregoing, it will be understood that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims

1. An ultrasonic imaging system for performing spectral Doppler imaging, comprising: a transducer configured to transmit an ultrasonic signal to a region of interest of a subject and receive a corresponding echo signal, wherein the transmitted ultrasonic signal is a signal for spectral Doppler imaging interleaved with signals for other imaging modes; a processor configured to execute instructions to copy a received spectral Doppler signal and adjust one or more signal characteristics of the copied spectral Doppler signal to fill a gap in a spectral Doppler signal caused by the other imaging mode, wherein the signal characteristics vary according to a physiological cycle of the subject; The ultrasonic imaging system comprising the above.

2. The processor is configured to execute instructions to analyze an average frequency of one or more received spectral Doppler signals before, after, or before and after the gap, and scale the average frequency of the copied spectral Doppler signal to fill the gap based on the average frequency of the received spectral Doppler signals. The ultrasonic imaging system according to Claim 1.

3. The processor is configured to execute instructions to determine a plurality of average frequencies for a portion of the received spectral Doppler signal and adjust the average frequency of the copied spectral Doppler signal based on the determined plurality of average frequencies. The ultrasonic imaging system according to Claim 1.

4. The processor is configured to execute instructions to analyze one or more parameters selected from a peak frequency, a low frequency, an average frequency, a center frequency, a variance, and a power of the received spectral Doppler signal, and adjust a corresponding parameter of the copied spectral Doppler signal based on the analyzed one or more parameters. The ultrasonic imaging system according to Claim 1.

5. The processor is configured to execute instructions to analyze one or more parameters selected from peak frequency, low frequency, average frequency, center frequency, variance, and power of the spectral Doppler signals received before and after the gap, and adjust the corresponding parameters of the copied spectral Doppler signal such that the adjusted parameters are between the values of the parameters of the spectral Doppler signals before and after the gap. The ultrasonic imaging system according to claim 1.

6. The processor is configured to execute instructions to generate pre-FFT ultrasonic data from the copied spectral Doppler signal using the adjusted signal characteristics and associate the pre-FFT ultrasonic data with the received pre-FFT data. The ultrasonic imaging system according to claim 1.

7. An ultrasonic imaging system for performing spectral Doppler imaging, a transducer configured to transmit an ultrasonic signal to a region of interest of a subject and receive a corresponding echo signal, wherein the transmitted ultrasonic signal is a signal for spectral Doppler imaging mode interleaved with signals for other imaging modes, a processor configured to execute instructions to adjust drive signals used for the spectral Doppler imaging mode and the other imaging modes such that spectral Doppler imaging is not interrupted during one or more portions of the physiological cycle of the subject. An ultrasonic imaging system comprising the above.

8. The processor is configured to receive a signal from a sensor that senses the physiological signal of the subject and adjust the drive signal such that the spectral Doppler imaging mode is not interrupted during one or more portions of the physiological cycle sensed by the sensor. The ultrasonic imaging system according to claim 7.

9. The processor is configured to execute instructions to predict a time during which spectral Doppler processing is not interrupted from the sensor signal. The ultrasonic imaging system according to claim 8.

10. The processor is configured to execute instructions that analyze signals from the sensor of the physiological cycle and predict, from the analyzed signals, when portions of the physiological signals occur for which the spectral Doppler processing should not be interrupted. The ultrasonic imaging system according to claim 8.

11. The processor is configured to execute instructions that adjust the timing of the signals used for the other imaging mode so that the other imaging mode is not used during the time when the spectral Doppler imaging mode is not interrupted. The ultrasonic imaging system according to claim 7.

12. The other imaging mode is B-mode processing in which ultrasonic signals are transmitted along several beam lines, and the processor is configured to execute instructions that adjust several beam lines used during the B-mode so that the spectral Doppler mode is not interrupted during one or more portions of the physiological cycle. The ultrasonic imaging system according to claim 7.

13. The physiological signal is a cardiac cycle. The ultrasonic imaging system according to claim 7.

14. The physiological signal is a respiratory cycle. The ultrasonic imaging system according to claim 1.

15. The processor is configured to execute instructions that receive input from a user regarding one or more portions of the physiological signal for which spectral Doppler processing should not be interrupted. The ultrasonic imaging system according to claim 7.

16. An ultrasonic imaging system for performing spectral Doppler imaging, a transducer configured to transmit an ultrasonic signal to a region of interest of a subject and generate a corresponding echo signal, the transmitted ultrasonic signal being a signal for spectral Doppler imaging, a display for displaying a spectral Doppler imaging signal, a processor configured to execute instructions that analyze the spectral Doppler signal and start the display of the spectral Doppler signal at the occurrence of a trigger, comprising an ultrasonic imaging system.

17. The trigger is a frequency threshold in the spectral Doppler signal. The ultrasonic imaging system according to claim 16.

18. The trigger is a signal from a sensor of a physiological signal. The ultrasonic imaging system according to claim 16.

19. The sensor is an EKG sensor. The ultrasonic imaging system according to claim 18.

20. The sensor is a respiration sensor. The ultrasonic imaging system according to claim 18.

21. An ultrasonic imaging system for performing spectral Doppler imaging, comprising: A transducer for transmitting an ultrasonic signal to a region of interest of a subject and obtaining a corresponding echo signal, wherein the transmitted ultrasonic signal is a signal for spectral Doppler imaging interleaved with signals for other imaging modes; A memory for storing the recorded spectral Doppler signal; A processor configured to analyze the spectral Doppler signal for a predetermined number of physiological cycles and store the spectral Doppler signal including the predetermined number of physiological cycles in the memory; An ultrasonic imaging system comprising the above.

22. The physiological cycle is a cardiac cycle. The ultrasonic imaging system according to claim 21.

23. The physiological cycle is a respiratory cycle. The ultrasonic imaging system according to claim 21.

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