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There is currently little feedback as to whether kidney stones have fractured during shock wave lithotripsy. Resonant scattering of the lithotripter shock wave was used here to differentiate intact and fractured stone models in water. Scattering, including reflection and radiation due to reverberation from within the stone, was calculated numerically with linear elasticity theory and agreed well with measurements made with a focused receiver. Identification of fracture was possible through frequency analysis, where scatter from fractured stones was characterized by higher energy in distinct bands. High-speed photography concurrent with measurement indicated the effect was not due to cavitation.

Vibro‐acoustography (VA) is an ultrasound interrogation and imaging technique with a variety of applications. Here it was used to identify optimal parameters for detecting and imaging kidney stones in phantoms. The parameters varied included the difference frequency and the position in time of the analysis window used for image construction. Experiments in a water tank were conducted using a focused PVDF membrane hydrophone (receiver) placed in a central opening of an annular, dual element transducer (source), itself mounted on a translation stage. Our source consisted of 90‐ms pulses with a center frequency of 2.0 MHz and difference frequencies between 50 and 350 kHz, applied both on and off stone. Variations in the amplitude of the measured ultrasound backscatter and acoustic emissions as a function of difference frequency, between signals from stone and phantom, guided the choice of imaging parameters. The results were detailed images of renal stones measuring 10 dB above the background tissue. These f...

A new method to address the challenging tasks of image‐guidance, targeting, and treatment monitoring during HIFU treatments is presented. The approach, enabled by the use of a novel multi‐layer PZT‐PVDF array with broad receive bandwidth in conjunction with a programmable ultrasound engine, uses the passive‐mode received echoes of the imaging array with a custom pixel‐based beamforming for HIFU focal tracking and targeting, allowing real‐time two‐dimensional (2D) B‐mode visualization of the HIFU beam. Temperature monitoring during treatment is based on acoustic nonlinear propagation theory and the physical relationship of sound speed and attenuation to frequency and temperature. The harmonics‐rich received echoes are processed differentially, encoded into an RGB additive color channel, beamformed, and overlayed in color over regular B‐mode images. Dynamic local temperature changes in the region of interest become visible as the 2D color image changes from frame to frame. Preliminary results on beam visual...

The incidence of kidney stones within the US population is now 10%, and rising. Many patients present with small stones, primary or recurrent, do not indicate interventional stone removal. We previously described a new stone removal method employing selective application of acoustic radiation force, at diagnostic output levels, to reposition stones for passive clearance. In this method, an imaging array transducer transmits pulses for image guidance and focused pulses to reposition the stone. Here we propose a new flash imaging modality to visualize the focused pulse to confirm targeting on the stone. To visualize the focused beam, short pulses were phase‐delayed across the transducer aperture to transmit a focused wave, from which echo data were collected, beamformed, and overlaid on a B‐mode image. The beam profile is visible because echo amplitude is higher within the convergent, focal, and divergent regions. During experiment, a stone was placed within a tissue phantom simulating the kidney lower pole and ureter. Once identified with B‐mode imaging, focal delays were calculated, targeting was confirmed by the beam visualization modality, and the stone was repositioned. Flash imaging visualization of the focused beam could be similarly applied to high‐intensity focused ultrasound therapy. [Work supported by NIH DK43881 NSBRI‐SMST01601.]

Interference in ultrasound imaging when used in connection with high intensity focused ultrasound (HIFU) is avoided by employing a synchronization signal to control the HIFU signal. Unless the timing of the HIFU transducer is controlled, its output will substantially overwhelm the signal produced by ultrasound imaging system and obscure the image it produces. The synchronization signal employed to control the HIFU transducer is obtained without requiring modification of the ultrasound imaging system. Signals corresponding to scattered ultrasound imaging waves are collected using either the HIFU transducer or a dedicated receiver. A synchronization processor manipulates the scattered ultrasound imaging signals to achieve the synchronization signal, which is then used to control the HIFU bursts so as to substantially reduce or eliminate HIFU interference in the ultrasound image. The synchronization processor can alternatively be implemented using a computing device or an application-specific circuit.

Miniature dual‐mode transducers can be used for minimally invasive treatment of deep‐seated tumors. While in contact with the tissue, the transducer guides and monitors localized necrosis. Here, an oscillating 5‐element piezo‐composite transducer was characterized, and then evaluated in vitro using porcine liver. Each element was 3.0 x 3.8 mm2 with a geometric cylindrical focus of 14 mm. The transmit frequency was determined by the maximal electro‐acoustic efficiency, 65%, which was found at 5.6 MHz. The transmit‐receive impulse response was 400 ns long at ‐6 dB, and the ‐6 dB fractional bandwidth, centered at 5.6 MHz, was 30%. Axial and lateral resolution measured with a 0.1 mm diameter wire was 0.5 mm and 2.0 mm, respectively. For therapy, all elements radiated simultaneously, and for imaging, independently. Treatment was performed at increments of 20° to form a composite volume of necrosis. At each angle, ultrasound was applied for 60 s at a transducer surface intensity of 15 W/cm2. Pulse‐echo data wer...

We present a summary of Inserm's experience with high power sources, which are necessary for ultrasound thermal therapy and lithotripsy. Moreover, generating high intensity pseudo‐continuous waveforms or high pressure pulses imposes different constraints on the transducer materials, specifically heat and mechanical stress. For thermal therapy, miniature piezoceramic transducers were used for interstitial, intratumoral, and endoluminal applicators. These probes operated at surface intensities up to 50 W/cm2 and generated elementary lesions in vivo within tens of seconds. Piezocomposite transducers were developed for large‐aperture, highly‐focused beams used in extracorporeal or intraoperative treatments. Focal intensities were 1000 W/cm2 or higher and up to 256 elements were utilized. Miniaturized piezocomposite transducers are currently being developed for dual‐mode imaging and therapy. For lithotripsy, piezoelectric shock wave generators were developed as alternatives to electrohydraulic or electromagnet...

Aggressive treatment of localized hepatic metastases, by surgery or other means, was proven to be a viable strategy for improving the prognoses of many patients. In that context, thermal ablation by high intensity ultrasound was proposed and used in clinics. However, for treating deep‐seated tumors and in most cases, radiofrequency and cryotherapy probes are applied interstitially. Interstitial ultrasound applicators were proposed as an intermediate solution. The treatment can be focused, deeper than with other physical agents, and the transducer can eventually both treat and image tissues. In our experience, two approaches were investigated: percutaneous and intratissular, or endo vascular. The active element was a miniature flat transducer operating at a frequency of 5 MHz, for a satisfactory tradeoff between beam penetration and energy absorption. In vivo trials on a porcine model demonstrated that both procedures are minimally invasive and that large thermal lesions, up to 20 mm deep, can be obtained....

Detection of kidney stones and estimation of their sizes is an important part of the lithotripsy treatment. Fluoroscopy is often used to target stones, but not every stone is radio‐opaque and, in addition, fluoroscopy produces ionizing radiation. Acoustic waves offer an alternative way to visualize stones. The acoustic impedance of kidney stones typically differs significantly from that of surrounding tissue. A useful consequence of the impedance mismatch is the possibility to target stones with diagnostic mode ultrasound. Another consequence is that radiation force pushes the stone. Stone displacement may be responsible for the twinkling artifact that has been observed by several authors in color Doppler mode of ultrasound imaging. This effect can be used to detect not only renal and ureteral stones, but also calcifications in other organs (e.g., breast). In this paper we model the radiation force associated with the Doppler diagnostic pulse. The problem is divided into three parts: (1) acoustic scattering; it is solved in finite differences; (2) radiation force calculation; (3) stone velocity estimation supposing the stone sits in soft tissue. [Work supported by NIH DK43881, DK55674, NSBRI SMS00402, and RFBR.]

Shock wave lithotripsy (SWL) is currently conducted with little feedback on whether kidney stones are breaking. To determine if fragmentation could be assessed, acoustic scatter from intact and fractured stone models was calculated numerically and measured in vitro. Acoustic scatter from the stones, which were modeled with glass spheres, was calculated numerically using a linear elastic model, initialized with known elastic constants, and propagated from the stone model surface using the Helmholtz‐Kirchhoff integral. Experimentally, shock waves were generated with a research lithotripter and scatter was measured with a broadband, spherically focused receiver. Calculated and measured results agreed well in the time domain. In frequency, power spectra were integrated to find energy and showed that scatter from the fractured stone model had higher energy in specific frequency bands that were related to the reverberation period. High‐speed photography indicated that cavitation did not adversely affect the analysis of scatter. In this work it was possible to distinguish between the intact and fractured stone models. This method could be applied to stones that fragment gradually under the application of shock waves and potentially be used to estimate fragment size, and therefore the endpoint of therapy. [Work supported by NSBRI SMS00402 and NIH DK43881.]

Acoustic properties of a vibro‐acoustography system designed to detect kidney stones were measured. Our system was formed with two spherical transducers (10 cm diameter, 20 cm curvature) in degassed water that were confocal and separated by an angle of 30 degrees. They were driven at 1.1 MHz and 1.125 MHz to generate a difference frequency of 25 kHz. The acoustic field was characterized by scattering from a known target, the curved surface of a steel cylinder with 6.4 mm diameter. Waveforms of both the low and high frequency scattered signals were measured for different target locations, different hydrophone locations encircling the target, and different acoustic pressures. Focal dimensions of the −6 db pressure profile measured at 25 kHz and the fundamental were both 3×10 mm, in an elliptical shape, which is highly localized. Scatter amplitude was rather insensitive to hydrophone position when the target was in the focus, quite sensitive to hydrophone position when the target was out of the focus, and in...

Vibro‐acoustography can be used to measure material properties and detect calcifications within the body. Two transducers (diameter 10 cm, curvature 20 cm, frequency 1.1 MHz) are placed with overlapping foci in degassed water and driven at different frequencies to produce a dynamic radiation force in the range of 5–50 kHz. A LabVIEW program instructs the transducers to sweep through this frequency range at 500‐Hz increments while a synthetic cylindrical kidney stone is held in the focus in one of three ways: with a rubber band, within an acrylamide gel, or within a finger cot. A low‐frequency hydrophone, 10 cm from the focus and 90 deg from the direction of propagation, detects the radiated acoustic emission from the stone. The average amplitude of five signals is recorded to measure the frequency response of the stone. Unbroken stones exhibited higher amplitude response at frequencies near 10, 25, and 35 kHz. Stones are moved to simulate patient breathing and different in‐focus and out‐of‐focus acoustic ...

Synchronization for image guided therapy using high intensity focused ultrasound (HIFU) and imaging ultrasound is achieved with a new technique that uses the focused transducer as a receiver that can detect the acoustic pulses created by the imaging probe. Without synchronization, interference from the high intensity source occludes the imager’s display unpredictably, degrading the quality of the system. An imaging probe (Sonosite 180) is registered with a HIFU transducer (d=33 mm, roc=55 mm, f=3.5 MHz) such that the scan line bisects the single element focus. When acoustically coupled through a scattering medium, imaging pulses are passively detected with the HIFU transducer and electronically conditioned into a TTL level trigger. A LabVIEW program uses the trigger to create a pulse width modulated signal that controls the timing of HIFU excitation during treatment. Detection takes less than 1% of the time between displayed images when the imager is running at 20 frames per second. HIFU excitations are programmed to occur such that the single element focus is free of interference when viewed with the imager during treatment. With no electrical connections for this new, simple technique, an arbitrary imager can be selected for synchronized image guided therapy. [Work supported by NSBRI.]

High intensity focused ultrasound (HIFU) can necrose tumors or cauterize tissue bleeds at intensities on the order of 1000 w/cm2. A synchronized HIFU and B‐mode ultrasound system reveals a hyperechoic region at the treatment site, which grows with treatment duration and intensity. Our goal was to segment the hyperechoic region representing the lesion via image analysis and measure the ratio of its major and minor axes. Our algorithm uses the RF data as input, processes it, and outputs a binary image that represents the lesions cross‐sectional profile. With depth settings from the clinical ultrasound imager, it is possible to calculate lesion dimensions from the binary image. The algorithm was tested with lesions made in a transparent polyacrylamide tissue phantom that became opaque in response to focal heating during HIFU exposure. Lesion size was recorded simultaneously with ultrasound and a CCD camera, and both measurements agreed well. Additionally, computer segmentation agreed well with segmentation by HIFU users blinded to the experimental conditions. The average difference of the determined ratio was 13% for lesions less than 0.5 cm in length. Thus, it is possible to localize precisely the treated tissue region. [Work supported by NSBRI, NSF, and NIH‐SBIR.]