John C. Kucewicz

Characterizing an Agar/Gelatin Phantom for Image Guided Dosing and Feedback Control of High-Intensity Focused Ultrasound

The temperature dependence of an agar/gelatin phantom was evaluated. The purpose was to predict the material property response to high-intensity focused ultrasound (HIFU) for developing ultrasound guided dosing and targeting feedback. Changes in attenuation, sound speed, shear modulus and thermal properties with temperature were examined from 20°C to 70°C for 3 weeks post-manufacture. The attenuation decreased with temperature by a power factor of 0.15. Thermal conductivity, diffusivity and specific heat all increased linearly with temperature for a total change of approximately 16%, 10% and 6%, respectively. Sound speed had a parabolic dependence on temperature similar to that of water. Initially, the shear modulus irreversibly declined with even a slight increase in temperature. Over time, the gel maintained its room temperature shear modulus with moderate heating. A stable phantom was achieved within 2 weeks post-manufacture that possessed quasi-reversible material properties up to nearly 55°C.

Focused Ultrasound : Concept for Automated Transcutaneous Control of Hemorrhage in Austere Settings

BACKGROUND High intensity focused ultrasound (HIFU) is being developed for a range of clinical applications. Of particular interest to NASA and the military is the use of HIFU for traumatic injuries because HIFU has the unique ability to transcutaneously stop bleeding. Automation of this technology would make possible its use in remote, austere settings by personnel not specialized in medical ultrasound. Here a system to automatically detect and target bleeding is tested and reported. METHODS The system uses Doppler ultrasound images from a clinical ultrasound scanner for bleeding detection and hardware for HIFU therapy. The system was tested using a moving string to simulate blood flow and targeting was visualized by Schlieren imaging to show the focusing of the HIFU acoustic waves. RESULTS When instructed by the operator, a Doppler ultrasound image is acquired and processed to detect and localize the moving string, and the focus of the HIFU array is electronically adjusted to target the string. Precise and accurate targeting was verified in the Schlieren images. CONCLUSIONS An automated system to detect and target simulated bleeding has been built and tested. The system could be combined with existing algorithms to detect, target, and treat clinical bleeding.

Improved detection of kidney stones using an optimized Doppler imaging sequence

Kidney stones have been shown to exhibit a “twinkling artifact” (TA) under Color Doppler ultrasound. Although this technique has better specificity than conventional B-mode imaging, it has lower sensitivity. To improve the overall performance of TA as a diagnostic tool, Doppler output parameters were optimized in vitro. The collected data supports a previous hypothesis that TA is caused by random oscillations of multiple micron-sized bubbles trapped in the cracks and crevices of kidney stones. A set of optimized parameters were implemented such that the acoustic output remained within the FDA approved limits. Several clinical kidney scans were performed with the optimized settings showing improved SNR relative to the default settings.

Accuracy of kidney stone size in conventional ultrasound Bmode imaging

The objective of this study was to determine the accuracy of conventional ultrasound imaging in sizing kidney stones, since this can be a determining factor in the treatment protocol for fragments on the order of 5 mm. Ex-vivo human kidney stones 3 to 12 mm were imaged in a water bath at depths from 6 to 10 cm using a Philips HDI5000 and Versonics software-based ultrasound system with the C4-2 transducer. Stone sizes were estimated offline a) manually by a sonographer and b) through an automated contrast based edge detection algorithm. Stone size was consistently overestimated with both instruments and by both estimation methods. On average, size was overestimated by 1 to 2 mm for stones 6 cm deep, and the overestimation increased with increasing depth and system gain. The overestimation was independent of actual stone size. These results suggest there is an inherent error in conventional ultrasound that leads to overestimation of stone size. These results also validate the software-based instrument for f...

Prototype for expulsion of kidney stones with focused ultrasound.

Residual fragments remain in over 50% of treatments for lower pole kidney stones. A second‐generation device based on a diagnostic ultrasound system and scanhead has been developed with a unique algorithm for stone detection and the capability to focus ultrasound to expel residual fragments. Focused ultrasound was applied to a bead on string in a water tank as well as to human stones (<5 mm) implanted in the lower pole of a live porcine model via retrograde ureteroscopy. Histological samples were collected and scored in a blinded fashion for therapeutic exposures and for super‐therapeutic levels. The in‐vitro bead was visually observed to move under focused ultrasound. Even with progressive manual displacement of the bead, the system continuously tracked and caused bead movement in real time. In the live porcine model, stones were expelled from the lower pole to the ureteropelvic junction in seconds to minutes using pulses at a duty factor of 0.02 and 8 W total acoustic power. Injury was observed no more ...

P1B-3 Noninvasive Bleeding Detection and Localization Using Three Dimensional Doppler Ultrasound

Blood loss from extremity wounds is the number one cause of preventable battlefield death today. In civilian casualties, exsanguinations due to internal bleeding are the most significant cause of death in trauma victims. The goal of DARPAs deep bleeder acoustic coagulation (DBAC) program is to stop bleeding quickly enough to prevent the transition from nonprogressive shock to progressive shock, which occurs when the soldier loses 25% of the blood volume. Coagulative therapies such as HIFU and electrocautery can be used to quickly stop internal bleeding to prevent onset of progressive and irreversible hemorrhagic shock, which ultimately leads to death. However, the onset of bleeding must be detected and the site spatially localized in order to treat these trauma wounds effectively. Towards meeting the final goal of the DBAC program, we have performed preliminary studies on in vitro tissue mimicking phantoms to identify unique Doppler based signatures that are indicative of bleeding. In this study, we present the results and validation of a 3D Doppler ultrasound technique to detect and localize the bleeding site by tracking the change in resistance index (RI) at the bleed origin. Significant RI change was obtained at the intersection of the primary vessel (feeding the bleeder) and the bleeding site (jet). Pulsatile flow with near zero diastolic flow was present in the primary vessel and the non-bleeding branches. Within the bleeding jet, continued or elevated forward flow was present during diastole resulting in reduction of RI. The estimated bleed location showed excellent agreement with independent ground truth estimates. The results illustrate potential for the applicability of the technique in battlefield trauma and civilian emergency care applications.

Ultrasound-based cell sorting with microbubbles: A feasibility study

The isolation and sorting of cells is an important process in research and hospital labs. Most large research and commercial labs incorporate fluorescently or magnetically labeled antibodies adherent to cell surface antigens for cell identification and separation. In this paper, a process is described that merges biochemical labeling with ultrasound-based separation. Instead of lasers and fluorophore tags, or magnets and magnetic particle tags, the technique uses ultrasound and microbubble tags. Streptavidin-labeled microbubbles were mixed with a human acute lymphoblastic leukemia cell line, CCL 119, conjugated with biotinylated anti-CD7 antibodies. Tagged cells were forced under ultrasound, and their displacement and velocity quantified. Differential displacement in a flow stream was quantified against erythrocytes, which showed almost no displacement under ultrasound. A model for the acoustic radiation force on the conjugated pairs compares favorably with observations. This technology may improve on current time-consuming and costly purification procedures.

Design and characterization of a research phantom for shock-wave enhanced irradiations in high intensity focused ultrasound therapy

The use of shock waves for enhancing thermal effects and mechanically ablating tissue is gaining increased attention in high intensity focused ultrasound (HIFU) therapies for applications such as tumor treatment, drug delivery, and immunotherapy. For abdominal targets, the presence of ribs and inhomogeneous adipose tissue can affect shock formation through aberration, absorption, and diffraction. The goal of this study was to design and characterize a phantom that simulates an abdominal body wall, ribs, and target tissues for investigating the impact of different structures on shock formation in situ.

A training phantom for ultrasound-guided boiling histotripsy therapy

Boiling histotripsy (BH) uses millisecond-long focused ultrasound pulses with shocks to mechanically disrupt targeted tissue under real-time ultrasound monitoring. However, adipose tissue and ribs can interfere with BH therapy through aberration, absorption, and diffraction. Here we introduce a robust abdominal wall phantom that includes fat, muscle, and rib layers for demonstrating the use of BH and investigating the impact of anatomic structures on treatment success. The skin is a silicone sheet; the fat and muscle layers are poly-vinyl alcohol phantoms with irregular-shaped walls; the ribs are 3D-printed sections from a human model anatomically relevant to liver or kidney treatments. The target is a transparent alginate or polyacrylamide gel that allows visualization of the lesion. The pieces are assembled in a water-filled container providing coupling between layers and allowing components to be shifted in position relative to the transducer. A BH transducer (1.2 MHz, 12.5 cm focal length, f# = 1) con...

Autoregressive ultrasound imaging method to enhance kidney stone twinkling and suppress blood flow.

“Twinkling” is a widely reported ultrasound artifact whereby kidney stones and other similar calcified, strongly reflective objects appear as turbulent, flowing blood in color and power Doppler. The twinkling artifact has been shown to improve kidney stone detection over B‐mode imaging alone, but its use has several limitations. Principally, twinkling can be confused with blood flow, potentially leading to an incorrect diagnosis. Here a new method is reported for explicitly suppressing the display of color from blood flow to enhance and/or isolate the twinkle signal. The method applies an autoregressive model to standard Doppler pulses in order to differentiate tissue, blood flow, and twinkling. The algorithm was implemented on a software‐based, open architecture ultrasound system and tested by a sonographer on phantoms and on stones implanted in a live porcine kidney. Stones of 3–10 mm were detected reproducibly while suppressing blood flow in the image. In conclusion, a new algorithm designed to specifi...