Patent ID: 12212372

Referring now toFIG.1, an ultrasonic diagnostic imaging system constructed in accordance with the principles of the present invention is shown in block diagram form. A transducer array12is provided in an ultrasound probe10for transmitting ultrasonic waves and receiving echo information. The transducer array12may be a one- or two-dimensional array of transducer elements capable of scanning in two or three dimensions, for instance, in both elevation (in 3D) and azimuth. The transducer array12can be coupled to a main beamformer, or as shown an optional microbeamformer14in the probe which controls transmission and reception of signals by the array elements. Microbeamformers are capable of at least partial beamforming of the signals received by groups or “patches” of transducer elements as described in U.S. Pat. No. 5,997,479 (Savord et al.), U.S. Pat. No. 6,013,032 (Savord), and U.S. Pat. No. 6,623,432 (Powers et al.) The main beamformer or the microbeamformer can be coupled by the probe cable to a transmit/receive (T/R) switch16which switches between transmission and reception. A reconstruction filter is also included (in the connector?) between the T/R switch and the beamformer or microbeamformer. This reconstruction filter can convert the ‘digital’ PWM to an analog voltage that the main beamformer or microbeamformer can appropriately sample. The transmission of ultrasonic beams from the transducer array12under control of the main beamformer20or microbeamformer14is directed by a beamformer controller18, which receives input from the user's operation of the user interface or control panel38. Among the transmit characteristics controlled by the transmit controller are the number, spacing, amplitude, phase, frequency, polarity, and diversity of transmit waveforms. Beams formed in the direction of pulse transmission may be steered straight ahead from the transducer array, or at different angles on either side of an unsteered beam for a wider sector field of view. For some applications, unfocused plane waves may be used for transmission, and in this case the receive beams may interrogate the entire field of view simultaneously. Most 1D array probes of relatively small array length, e.g., a 128-element array, do not use a microbeamformer but are driven and respond directly to the main beamformer.

The echoes received by a contiguous group of transducer elements are beamformed by appropriately delaying them and then combining them. The coherent echo signals undergo signal processing by a signal processor26, which includes filtering by a digital filter and noise reduction as by spatial or frequency compounding. The filtered echo signals are coupled to a quadrature bandpass filter (QBP)28. The QBP performs three functions: band limiting the RF echo signal data, producing in-phase and quadrature pairs (I and Q) of echo signal data, and decimating the digital sample rate. The QBP comprises two separate filters, one producing in-phase samples and the other producing quadrature samples, with each filter being formed by a plurality of multiplier-accumulators (MACs) implementing an FIR filter. The quadrature signal samples undergo signal processing by a signal processor16, which includes filtering by a digital filter and speckle reduction as by spatial or frequency compounding. The signal processor can also shift the frequency band to a lower or baseband frequency range, as can the QBP. The digital filter of the signal processor26can be a filter of the type disclosed in U.S. Pat. No. 5,833,613 (Averkiou et al.), for example.

The beamformed and processed coherent echo signals are coupled to a B mode processor30which produces a B mode image of structure in the body such as tissue. The B mode processor performs amplitude (envelope) detection of quadrature demodulated I and Q signal components by calculating the echo signal amplitude in the form of (I2+Q2)1/2. The quadrature echo signal components are also coupled to a Doppler processor34. The Doppler processor34stores ensembles of echo signals from discrete points in an image field which are then used to estimate the Doppler shift at points in the image with a fast Fourier transform (FFT) processor. The rate at which the ensembles are acquired determines the velocity range of motion that the system can accurately measure and depict in an image. The Doppler shift is proportional to motion at points in the image field, e.g., blood flow and tissue motion. For a color Doppler image, the estimated Doppler flow values at each point in a blood vessel are wall filtered and converted to color values using a look-up table. The wall filter has an adjustable cutoff frequency above or below which motion will be rejected such as the low frequency motion of the wall of a blood vessel when imaging flowing blood. The B mode image signals and the Doppler flow values are coupled to a scan converter32which converts the B mode and Doppler samples from their acquired R-θ coordinates to Cartesian (x,y) coordinates for display in a desired display format, e.g., a rectilinear display format or a sector display format. Either the B mode image or the Doppler image may be displayed alone, or the two shown together in anatomical registration in which the color Doppler overlay shows the blood flow in tissue and vessels in the image as shown inFIGS.3a-3c. Another display possibility is to display side-by-side images of the same anatomy which have been processed differently. This display format is useful when comparing images.

The image data produced by the B mode processor30and the Doppler processor34are coupled to an image data memory36, where it is stored in memory locations addressable in accordance with the spatial locations from which the image values were acquired. Image data from 3D scanning can be accessed by a volume renderer42, which converts the echo signals of a 3D data set into a projected 3D image as viewed from a given reference point as described in U.S. Pat. No. 6,530,885 (Entrekin et al.) The 3D images produced by the volume renderer42and 2D images produced by the scan converter32are coupled to a display processor48for further enhancement, buffering and temporary storage for display on an image display40.

In accordance with the principles of the present invention, the beamformer20includes a digital transmit beamformer which is capable of actuating elements of a transducer array in probe10with either linear waveforms or transmit pulses.FIG.2illustrates a channel of a digital transmit beamformer of the present invention in block diagram form. Digital samples of linear and pulse waveforms for transmission in both transmit modes are stored in a waveform sample memory52. The digital samples may be acquired for the memory52by digitally sampling a desired analog transmit waveform with an analog to digital converter. The sample rate of the analog to digital converter should satisfy the Nyquist criterion for sampling by sampling at a frequency which is at least twice that of the highest frequency component of the waveform. Higher sampling rates can be desirable in some implementations. A waveform may be produced by a waveform generator and sampled, for instance, or a waveform may be constructed in the frequency domain and then converted to the time domain for sampling by an inverse Fourier transform. Transmit pulse sequences may be constructed directly in digital form without the need for conversion by producing digital words of one, two, or three bits in accordance with the desired number of pulse levels and in consideration of a clock rate which will cause level transitions in a sequence of samples to occur at the desired times. Other techniques for generating transmit waveforms are well known to those skilled in the art.

A sequence of digital samples, which defines either a linear (e.g., shaped sinusoid) waveform or a pulse sequence, is stored in the memory in sequential memory locations. This enables the sequence to be read out in sequential order by addressing the memory with a read address counter50, as shown in the drawing. The clock rate at which the samples are read out is chosen in consideration of the frequency of the desired waveform. For example, a pulse sequence can be read out at a low clock rate to produce a sequence of long, low frequency pulses, or the same sequence can be read out at a higher clock rate to produce a sequence of more narrow, higher frequency pulses. The same is true when reading out a linear sinusoidal waveform.

A sequence of samples which is read out of the memory52is applied to three types of waveform and pulse transmitters in this example, a digital to analog converter60, a two-level pulser64, and a higher multi-level pulser62which can produce a pulse sequence of three, four or five levels. The transmitter comprises an individual set of these output devices for each channel of the transmit beamformer, with the outputs of the devices coupled to a transducer element70. An enable signal, En1, En2, or En3, from the channel address counter50enables the appropriate output device for that channel. The converter60will convert a sequence of digital words into a linear waveform such as the one shown inFIG.3a. In this example each digital word is an eight-bit word and the word value defines the instantaneous amplitude as one of 256 possible levels. Each dot on the linear waveform100represents an eight-bit waveform sample, and the conversion of the digital word sequence to analog levels produces a linear waveform such as the one shown in the drawing. In this example, the analog waveform100is produced by digital to analog conversion of a sequence of N digital samples.

The two-level pulser64operates in the manner of a D-type flip-flop, with the clock Clk producing an output at the level of the digital word applied to the data input of the pulser. While different size digital samples can be employed, a two-level device only requires the digital sample to be a single bit, which will have either a one or zero value. When the sequence of bits changes from a zero to a one, the clock will transition the output to the high state of a pulse, which will remain high until the input bit sequences changes back to a zero. Transitions of the output pulse sequence will occur in phase with the clock signal. A typical two-level output pulse train106produced by the two-level pulser64is shown inFIG.3d. In most instances, lower frequency readout addressing by the channel address counter is also possible. With fewer samples needed to define the pulse train, and those samples being as small as one bit, fewer memory location of memory52are needed to store the digital samples for a two-level pulse. A large number of pulse train sequences can be stored in the same memory space required for one linear waveform of eight-bit words.

The multi-level pulser62produces a multi-level pulse train such as pulse trains102and104shown inFIGS.3band3c. Pulser62can be constructed using a digital decoder driving stacked, oppositely poled switching transistors which are coupled to voltage supplies for the pulse levels. A three-level pulse train104as shown inFIG.3ccan require only two voltage levels (+HV and −HV) as shown inFIG.2, which will produce a pulse train such as104with a high (+HV), low (−HV) and intermediate (reference or ground) pulse level. A three-level pulse can be defined by two bits for the three levels, and the digital decoder can be as simple as a two-bit register into which the two-bit samples are sequentially loaded to drive the switching transistors.

For pulse trains of five, six or seven levels, additional supply voltage levels are required. The five-level pulse train102inFIG.3b, for instance, can be produced using two positive voltage supplies (+HV and ++HV) and two ground or negative supplies (−HV and −−HV), for instance. Three-bit words are necessary to define the five possible pulse levels, which can be decoded into the five signals necessary to drive the switching transistors, for example. Like the two-level pulse train ofFIG.3d, the digital sample sequences for the three- and five-level pulse trains104and102need fewer sample words than are needed for the linear waveform100, and those words are of a lesser number of bits, meaning that they, too, require fewer memory storage locations than does the sample sequence for the linear waveform100. The K, L, and M sample sequence lengths will generally be less than the N sample sequence needed for the linear waveform.

The beamformer transmitter shown inFIG.2can drive a transducer element70with either a linear or a pulse transmit waveform, depending upon which stored pulse or waveform sequence is read from the memory52by the channel address counter50, and which output device60,62or64is enabled by an enable signal.FIG.2shows the components for one channel of a beamformer transmitter, with each element or patch of an array transducer driven by its own transmit channel. Thus, each transmit beamformer channel is characterized by its own set of output devices and its own channel address counter.

In accordance with a preferred implementation of the present invention, a plurality of channels share the same waveform sample memory. That is, the linear and pulse samples for multiple channels and multiple transducer elements are stored and read from a common waveform memory. Furthermore, the selection of a transmit waveform by one channel address counter for one transducer element is independent of the choices of transmit waveforms by the other channel for the other transducer elements. Thus, the active transmit aperture used to produce a transmit beam can, if desired, transmit different waveforms or pulses from different elements during the same transmit event. Moreover, many, and possibly all, of the channel address counters of the channels of the active transmit aperture are reading out their transmit waveform sequences from the waveform sample memory at the same time.

How this is done is shown in further detail in the illustration of the bank of channel address counters50shown inFIG.4. This drawing shows a group of sixteen channel address counters50which are fabricated with a shared waveform sample memory52on one ASIC integrated circuit. An address counter80of each channel address counter is coupled to address lines of the shared waveform sample memory52. A sequence of samples for a desired waveform is addressed by the counter, starting with a starting address and counting through the consecutively addressed samples until all of the samples for the waveform are read out. The starting address for the sequence of samples is initially loaded into the address counter80from a waveform select register82. In order to steer and focus the transmit beam from an active transmit aperture of transducer elements, the times of transmission by each channel must be phased, or delayed, by a delay profile appropriate for the beam steering and focusing. This requires the start of transmission by each element to be uniquely delayed in accordance with the delay profile. In the special case of an unsteered beam, that is, one which is transmitted normal to the face of the array, the beam profile is symmetrical and elements equidistant on either side of the beam center will exhibit the same delay. In other instances, each channel will have its own delay for combined steering and focusing. The delay for a channel is implemented by a delay counter84, which is initially loaded with a delay count appropriate for the delay required in that channel. A transmit synchronization signal, issued by a common controller for all of the channels, actuates the delay counters84, each of which begins to count down the delay for its channel. When a delay counter reaches zero, the appropriate delay for the channel has expired and the delay counter84enables its address counter80to begin to count and issue consecutive addresses for the digital sample words of the waveform. As previously mentioned, the counting begins with the proper starting address for the sequence of samples to be transmitted. The counting of samples is controlled by a sample counter86, which has been previously loaded with the number of samples comprising the sample sequence. When counting is enabled by the delay counter84, the sample counter86begins to count down, with each count incrementing the address counter by another bit. Thus, the address counter produces a sequence of consecutive sample memory addresses, beginning with the starting address of the desired sample sequence for that particular channel, and continues to issue consecutive addressed to the waveform memory until the sample counter has counted the required number of samples of the sequence. When the sample counter reaches zero, counting and incrementing of the address counter stops, as the entire required sample sequence has been read from the memory.

An optional repeat counter88is coupled to the sample counter. The purpose of the repeat counter is to cause the sample counter and address counter to read out the same sequence of samples again. This enables production of a longer waveform by successively reading out a number of shorter waveforms. For example, suppose that a particular sample sequence defines one cycle of a transmit waveform. Further suppose that it is desired to transmit a three-cycle waveform. The repeat counter will cause the address counter and its associated components to address the same one-cycle sample sequence three times in succession, thereby producing a three-cycle waveform for transmission. In this example the repeat counter is initialized with a count of three, and when it reaches zero all three cycles will have been read from the waveform memory and memory addressing by the channel ends.

Each channel address counter50also includes a waveform enable register or decoder90. This device is loaded with a digital word prior to transmission which enables the desired output device60,62, or64for transmission by that channel. The waveform enable word may be a three-bit word of a binary value of either 001, 010, or 100 which, when loaded into a register, will produce a high signal on one of three output lines for enable control. Alternately, the waveform enable device may be a two-bit decoder for the three enabling output lines.

A simple example will illustrate the sequencing and interaction of the components of a channel address counter and the sample waveform memory. Suppose that there are 256 samples in memory for a waveform which is to be transmitted by a particular transducer element, and that this sequence of samples is stored in sequence beginning at memory address 1024. Further suppose that transmission by the transducer element is to be delayed by the time of 100 clock cycles of the clock which increments the delay counter84. This channel address counter is initialized by loading the starting memory address of 1024 into the address counter from the waveform select register82, loading the delay counter84with the delay time of 100, loading the sample counter86with the sample sequence length of 256, and loading the repeat counter with a repeat count of one. When the transmit synchronization signal is received from a central or common controller, the delay counter84begins counting down from 100. When the delay counter reaches zero, the sample counter86is enabled and begins to count down from 256, incrementing the address counter which issues consecutive memory addresses to the waveform sample memory, beginning with the starting address of 1024. When the sample counter reaches zero, at which time the full waveform of 256 samples has been read from memory, the sample counter decrements the repeat counter88from one to zero. The zero value from the repeat counter halts the sample counter, and waveform sample readout is complete. Thus, following a delay time of 100 delay clock cycles, the desired waveform of 256 samples has been read from memory and transmitted by the transducer element. The other channels for the active transmit aperture are functioning in the same way, using the same or different starting addresses for their waveform sample sequences, so that pulse or linear waveforms for a plurality of transducer elements are provided concurrently by the waveform sample memory for the same transmit event. The transmitter can also control the timing of these enabled devices relative to the transmit waveform. The transmit/receive (TR) switch, for example, may not open and close instantaneously, so a control signal can be provided to the TR switch to open before the transmit waveform starts. Likewise, the linear transmitter may also need time to power-up and later power-down before and after the waveform.

Previous efforts toward digital transmit beamformers have tried to use various shortcuts in attempts to reduce memory size requirements. All of these approaches have, in various ways, limited transmitter performance, increased hardware or software complexity, or suffered combinations of these effects. A conventional approach has been to provide each channel with its own waveform memory. If the same waveform is to be used by multiple channels, it must be stored in the memory of each channel with this approach. A common, shared memory makes more efficient use of memory storage space. Another proposal is to store waveform samples for two waveforms as halves of double words in memory, so that half of a readout word is used for one waveform and the other half is used for another waveform. This necessarily requires the two waveforms to be used for the same transmission, preventing each channel from selecting a waveform independently of the other. It also requires different delays for the two waveforms to be applied in subsequent processing. Another proposal has been to read out samples for two waveforms in interleaved fashion, ping-ponging back and forth between the two waveforms. This approach mandates redirecting the samples into two paths for the two waveforms, and also halves the high frequency resolution of the resultant transmit beams since the waveform sample rate is cut in half, a problem which can be overcome by doubling the read speed, which may not be feasible or desirable. Yet another approach has been to store only the envelope of the transmit waveform, and subsequently modulate the envelope with a high frequency carrier. This requires a modulator to be implemented and operate before a waveform can be transmitted. Still another approach is to store only a few waveforms in memory, then perform interpolations of them to generate additional waveforms. This requires a waveform interpolator to be implemented and operate before a waveform can be transmitted. Other approaches have called for storing one or only a few waveforms in memory, then weighting or phasing them or adding successive waveform increments to generate the additional required waveforms. Again, additional hardware or software is needed to perform these operations, and the time required to execute them before transmission must be figured into the waveform production time. And the delays must be implemented in a subsequent operation. A preferred implementation of a transmit beamformer of the present invention avoids all of these deficiencies and complexities by allowing each channel to address a desired waveform in memory independently of the selections by other channels. This independent operation of the transmit channels is made possible by having all channel address counters on an ASIC share a common waveform sample memory, which all of the channels can access simultaneously and independently. Since the channel address counters and their common memory are all on the same integrated circuit, all address bus routing is done on the IC so that no IC pins are needed for waveform sample addressing. The implementation ofFIG.4shows sixteen address counters which, together with their waveform sample memory, are fabricated on the same ASIC. Thus, eight of these ASICs will support a 128-element array requiring 128 transmit channels. Higher integration is also possible and desirable. When 32 or 64 or 128 channel address counters and their shared memory are fabricated on the same ASIC, only four, two or one such transmit ASIC is required to support a 128-element array.

The capability of each channel of a digital transmit beamformer to select one of a plurality of waveform or pulse train sample sequences in memory, independently of the other channels, enables the beamformer to transmit a beam from an active aperture in which different elements transmit different waveforms. Conventional beamformers transmit the same pulse train or waveform, with appropriate delays, from each element of the transmit aperture. The constructive and destructive interference of wavefronts in an image field scanned with a single transmit waveform are well understood and accepted. But the ability to transmit different signals from different elements of the aperture enables additional imaging features to be obtained. One such application of the use of different transmit waveforms to produce a beam with a line focus, whereby different frequencies are focused at different depths. Examples of this application are described in a concurrently filed patent application by the present inventors. Another application is to use different waveforms to drive different elements in a transmit aperture for transmit apodization. As mentioned above, apodization is conventionally performed by multiplying the transmit pulse or waveform by an apodization weighting factor, with the signals for central elements of the aperture being weighted most strongly. This calls for a weighting circuit for the signal of each element which weights the transmit signals before they are applied to the array elements. But the present inventors have recognized that different waveforms can apply different levels of energy to different transducers, and that this phenomenon can be used to produce an apodization effect. Accordingly, the waveforms stored in memory for different elements for an apodized transmission are of different transmit energies. For linear waveforms this is readily accomplished by storing waveform samples of different sample word values. With an 8-bit word providing 256 increments of amplitude resolution, scaling the waveform samples to scale the amplitude of the transmitted linear waveform is a straightforward process. Pulse waveforms, however, are constrained by the system transmit voltage levels. A three-level pulse, for instance, can only have three possible levels: +HV, zero, and −HV determined by the power supply voltage levels. In accordance with the principles of the present invention, the inventors tailor the energy of pulse waveforms by pulse width variation. Pulse width modulation is known in the literature for its use in replicating modulated analog waveforms as described, for instance, in “Width-Modulated Square-Wave Pulses for Ultrasound Applications” by Smith et al., IEEE Trans. on Ultrason., Ferroelec., and Freq. Control, vol. 60, no. 11, (November 2013).FIG.5provides an example of two such three-level pulse waveforms. Pulse waveform PW1inFIG.5ais seen to have four pulses of positive and negative excursions which vary between zero, +HV in the positive direction, and −HV in the negative direction. The areas under the pulses between the positive and negative excursions and the reference level is seen to provide a certain amount of pulse energy. The pulse waveform PW2inFIG.5bis seen to also exhibit four pulses and of the same fundamental frequency. But the pulses of pulse waveform PW2are seen to be narrower than the corresponding pulse excursions of PW1, as is evident from the dashed lines between the two pulse waveforms. Thus, less energy is provided by the PW2pulses, as evident from the smaller area under the pulses between the pulse excursions and the reference level. This transmit energy difference allows the two pulse waveforms to be used in an apodized transmission of these three-level pulses.

FIG.6illustrates use of the two pulse waveforms ofFIG.5to provide an apodized transmission from a transmit aperture of a linear array. The linear array110is comprised of twenty transducer elements112in this example, and are used as the transmit aperture for pulse transmission. The eight central transducer elements are driven by applying pulse waveform PW1to the elements, with appropriate delays for beam steering and focusing. This is indicated by the PW1bracket. The four elements on either side of these central element are driven by applying pulse waveform PW2to those elements, as indicated by the PW2bracket. The two elements on the two ends of the aperture are not actuated. This causes the central elements to be driven with high energy, the four elements to either side of the central elements to be driven with lower energy, and the elements on either end to be driven with even lower (i.e., zero) energy. The apodization function thereby applied to the transmit aperture is shown as the characteristic120, which steps from a higher central level to a lesser level on either lateral side, and finally to a base level. Apodization is thus accomplished without the need for circuitry or software to weight the twenty element signals prior to beam transmission.

An even simpler example of pulse transmit waveforms of different pulse widths and hence different transmit energies is illustrated by the pulse transmit waveforms ofFIGS.3dand3e. Pulse transmit waveform106is a sequence of pulses of a wider pulse width and thus higher transmitted energy, and pulse transmit waveform108is a sequence of pulses of a narrower width and thus lower transmitted energy, and the pulses of both recur at the same fundamental frequency. Since the pulse sequences only have two levels, their digital word size only needs to be a single bit of zero or one for the two levels of the pulse. These pulse sequences can be transmitted by a two-level pulse transmitter having only a unipolar power supply, i.e., +HV and reference or ground level. A sequence of single-bit words can be stored efficiently in the waveform sample memory.

A simple example illustrates the efficiency of using the digital transmitter ofFIG.2to transmit pulse width modulated waveforms rather than pulse width modulation circuitry for each transmit channel. Not only is there no need for additional circuitry, but the pre-stored digital samples use very little memory storage. For example, with the digital data sequences used to transmit the two waveforms ofFIGS.3dand3e, the sequences can be:00000111110000011111000001111100000 and00000011100000001110000000111000000
Thus, each waveform is a sequence of thirty-five 1-bit words, with a total of only 35 bits required for each sequence, a very small memory allocation. Multiple sequences of different pulse widths can be stored with a very small memory requirement. This is a much more economical alternative than pulse width modulation circuitry for each channel as used in the prior art, and more efficient than using an A/D converter and linear amplifier which, for eight-bit words, would require a memory allocation of 280 bits. Three-level pulses such as those ofFIG.5can use 3-bit words, a total of 105 bits for each pulse sequence of the same word length.

FIG.7illustrates in block diagram form an ultrasound probe having a digital transmit beamformer, using circuit embodiments and methods as described above. This preferred embodiment is suitable for implementation within the digital ultrasound transducer probe as shown in the ultrasound system ofFIG.1.

The inventors have recognized and discovered that the previously described inventions, if some of the circuit elements are separated from the ultrasound probe by a known probe cable or other communications path, may suffer from distortion problems. For example, signal distortion may arise in harmonics or reflected signals due to transmission line effects in the probe cable. Interleaving of different transmit modes may introduce jitter. The interaction of the transducer with various relays, cables, and multiplexers may introduce distortion. The inventors have further realized that many or all of these negative effects may be minimized by locating the circuit elements within the ultrasound probe itself.

Therefore in the preferred embodiment shown inFIG.7, the afore-described digital beamformer controller18may be disposed within the ultrasound probe10. The digital beamformer controller18further includes the waveform sample memory52, the channel address counters50a/50b/50c, the transmitter output devices, the associated control circuitry, and the power circuitry.

TheFIG.7ultrasound probe10includes the elements and circuit connections as follows. The digital beamformer controller18may include the waveform sample memory52, which stores transmit waveform data. The transmit waveform data may be downloaded from an ultrasound system console (not shown) prior to a transmit operation via one or more cables or wireless means.

An exemplary waveform sample memory52may have a 256 sample RAM (8-bit waveform and 8-bit apodization) that is available for each channel and can be loaded with identical or separate waveforms for each channel. The RAM may also have bank selection enabling up to 16 different waveforms in each of separate memory allocations, for mixed modes (e.g. simultaneous echo, color, and/or pulse width modulated) or as an alternative way to get different waveforms each channel. Bank selection may be separate for each channel. Example and non-limiting sample clock rate could be 40 Mhz, 60 MHz, 80 MHz, 120 MHz or 160 MHz for input/output of the waveform data.

Channel address counters50a,50b, and50coperate as described previously. Each channel address counter may control one transmitter output device in two ways. Control of the waveform type via waveform sample memory52and energy levels for linear waveforms, +HV, and +HV/−HV, via output signals EN1, EN2, EN3(seeFIG.2). Initiation of a transmit operation by the channel address counters may be enabled by a transmit control signal provided by the ultrasound system console via a wired cable or wireless means such as WiFi, Bluetooth, and the like.

Transmitter output devices are shown as a plurality of groupings of 3 different types of transmitters60,62,64. In one embodiment, each transmit channel has its own respective transmitter output device. Power may be up to 140 Vpp. As previously described, each channel address counter may thus control and correspond to, via the waveform sample memory52, one transmitter output device.

Transmitter output device outputs may be directed through a transmit/receive (TR) switch16in order to properly direct transmit energy and receive energy to the proper circuits. Each transmitter output device may connect transmit energy/voltage to a respective transducer element70in transducer array12, as previously described.

The transmit beamforming circuit, by enabling the interleaving of different waveforms into each channel, benefits several modes of operation. For example, the invention provides an alternative method of performing amplitude-modulation for a contrast mode. The invention provides an alternative method for the push-pulse and tracking transmit for shear-wave imaging. And the invention provides an alternative method of providing spatial apodization in both azimuth and elevation directions with a 1.5D array without requiring a high-channel-count ultrasound system.

Improvements enabled by the invention are several as well. By interleaving several waveforms in the waveform sample memory52, and by locating that waveform sample memory in the ultrasound probe, console system transmitters are not needed, and so jitter introduced by those remote components is minimized. For contrast mode, the transmission in most prior art systems is not fully linear because of distortion introduced into the transmit path (because subtraction of full-amplitude-waveform transmit and half-full-amplitude waveform transmit are not completely cancelled out). The invention's shorter transmit path reduces this distortion.

Conventional transmit beamforming is not practical for aperture apodization in AZ and EL directions due to the large number of system channels required. For example, an implementation of aperture apodization in the EL18-4 1.5D transducer, manufactured by Philips Healthcare would require 640 channels and corresponding 640 separate transmit wires in the probe cable. The current invention, by integrating this transmit beamforming entirely within the ultrasound probe, eliminates this requirement.

Power for the inventive beamformer system may be provided by a separate ultrasound system console via one or more power cables. The power supplied may be either of the several voltages needed for operation, or may be a single source voltage suitable for generating those several voltages within the ultrasound probe. The power is then provided to the plurality of transmitter output devices for the operations as previously described.

Other examples of using an implementation of the present invention to independently control the transmit signals of the elements of a transmit aperture will readily occur to those skilled in the art. It may be desirable to reduce the occurrence of grating lobe artifacts in an image by transmitting higher frequency signals from one side of the transmit aperture and lower frequency signals from the other side when a beam is steered off-axis, for instance.

It should be noted that an ultrasound system suitable for use in an implementation of the present invention, and in particular the component structure of the ultrasound system ofFIGS.1,2, and4, may be implemented in hardware, software or a combination thereof. The various embodiments and/or components of an ultrasound system, for example, the channel address counter and its controller, or components and controllers therein, also may be implemented as part of one or more computers or microprocessors. The computer or processor may include a computing device, an input device, a display unit and an interface, for example, for accessing the internet. The computer or processor may include a microprocessor. The microprocessor may be connected to a communication bus, for example, to access a PACS system or the data network for importing training images. The computer or processor may also include a memory. The memory devices such as the waveform sample memory52may include Random Access Memory (RAM) and Read Only Memory (ROM). The computer or processor further may include a storage device, which may be a hard disk drive or a removable storage drive such as a floppy disk drive, optical disk drive, solid-state thumb drive, and the like. The storage device may also be other similar means for loading computer programs or other instructions into the computer or processor.

As used herein, the term “computer” or “module” or “processor” or “workstation” may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), ASICs, logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of these terms.

The computer or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within a processing machine.

The set of instructions of an ultrasound system including those controlling the acquisition, processing, and display of ultrasound images as described above may include various commands that instruct a computer or processor as a processing machine to perform specific operations such as the methods and processes of the various embodiments of the invention. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software and which may be embodied as a tangible and non-transitory computer readable medium. Further, the software may be in the form of a collection of separate programs or modules such as a transmit control module, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to operator commands, or in response to results of previous processing, or in response to a request made by another processing machine.

Furthermore, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. 112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function devoid of further structure.