Anup Shah

Focused Ultrasound to Expel Calculi From the Kidney

PURPOSE A persistent stone burden after renal stone treatment may result in future patient morbidity and potentially lead to additional surgery. This problem is particularly common after treatment of lower pole stones. We describe a potential noninvasive therapeutic option using ultrasound waves to create a force sufficient to aid in stone fragment expulsion. MATERIALS AND METHODS Human stones were implanted by retrograde ureteroscopy or antegrade percutaneous access in a live porcine model. The calibrated probe of a system containing ultrasound imaging and focused ultrasound was used to target stones and attempt displacement. To assess for injury an additional 6 kidneys were exposed for 2 minutes each directly to the output used for stone movement. Another 6 kidneys were exposed to more than twice the maximum output used to move stones. Renal tissue was analyzed histologically with hematoxylin and eosin, and nicotinamide adenine dinucleotide staining. RESULTS Stones were moved to the renal pelvis or ureteropelvic junction by less than 2 minutes of exposure. Stone velocity was approximately 1 cm per second. There was no tissue injury when tissue was exposed to the power level used to move stones. Localized thermal coagulation less than 1 cm long was observed in 6 of 7 renal units exposed to the level above that used for ultrasonic propulsion. CONCLUSIONS Transcutaneous ultrasonic propulsion was used to expel calculi effectively and safely from the kidney using a live animal model. This study is the first step toward an office based system to clear residual fragments and toward use as a primary treatment modality in conjunction with medical expulsive therapy for small renal stones.

Patient Positioning and Port Placement for Robot-Assisted Surgery

Abstract The introduction of robotic surgical systems and their integration into minimally invasive procedures have changed the landscape of laparoscopic surgery dramatically. Intuitive Surgicals da Vinci Surgical System was first approved by the Food and Drug Administration for cardiothoracic procedures in the late 1990s. This trend quickly spread through other surgical specialties, with urologists as one of the frontrunners in adoption. Subsequently, pediatric urologists have adopted robot-assisted procedures in selected centers, performing procedures such as pyeloplasty for ureteropelvic junction obstruction, partial and complete nephrectomy, and both intravesical and extravesical ureteral reimplantation. In this article, we will discuss technical considerations related to patient positioning and port placement in pediatric robot-assisted surgery.

B-mode Ultrasound Versus Color Doppler Twinkling Artifact in Detecting Kidney Stones

PURPOSE To compare color Doppler twinkling artifact and B-mode ultrasonography in detecting kidney stones. PATIENTS AND METHODS Nine patients with recent CT scans prospectively underwent B-mode and twinkling artifact color Doppler ultrasonography on a commercial ultrasound machine. Video segments of the upper pole, interpolar area, and lower pole were created, randomized, and independently reviewed by three radiologists. Receiver operator characteristics were determined. RESULTS There were 32 stones in 18 kidneys with a mean stone size of 8.9±7.5 mm. B-mode ultrasonography had 71% sensitivity, 48% specificity, 52% positive predictive value, and 68% negative predictive value, while twinkling artifact Doppler ultrasonography had 56% sensitivity, 74% specificity, 62% positive predictive value, and 68% negative predictive value. CONCLUSIONS When used alone, B-mode is more sensitive, but twinkling artifact is more specific in detecting kidney stones. This information may help users employ twinkling and B-mode to identify stones and developers to improve signal processing to harness the fundamental acoustic differences to ultimately improve stone detection.

Quantitative Assessment of Shockwave Lithotripsy Accuracy and the Effect of Respiratory Motion

BACKGROUND AND PURPOSE Effective stone comminution during shockwave lithotripsy (SWL) is dependent on precise three-dimensional targeting of the shockwave. Respiratory motion, imprecise targeting or shockwave alignment, and stone movement may compromise treatment efficacy. The purpose of this study was to evaluate the accuracy of shockwave targeting during SWL treatment and the effect of motion from respiration. PATIENTS AND METHODS Ten patients underwent SWL for the treatment of 13 renal stones. Stones were targeted fluoroscopically using a Healthtronics Lithotron (five cases) or Dornier Compact Delta II (five cases) shockwave lithotripter. Shocks were delivered at a rate of 1 to 2 Hz with ramping shockwave energy settings of 14 to 26 kV or level 1 to 5. After the low energy pretreatment and protective pause, a commercial diagnostic ultrasound (US) imaging system was used to record images of the stone during active SWL treatment. Shockwave accuracy, defined as the proportion of shockwaves that resulted in stone motion with shockwave delivery, and respiratory stone motion were determined by two independent observers who reviewed the ultrasonographic videos. RESULTS Mean age was 51 ± 15 years with 60% men, and mean stone size was 10.5 ± 3.7 mm (range 5-18 mm). A mean of 2675 ± 303 shocks was delivered. Shockwave-induced stone motion was observed with every stone. Accurate targeting of the stone occurred in 60% ± 15% of shockwaves. CONCLUSIONS US imaging during SWL revealed that 40% of shockwaves miss the stone and contribute solely to tissue injury, primarily from movement with respiration. These data support the need for a device to deliver shockwaves only when the stone is in target. US imaging provides real-time assessment of stone targeting and accuracy of shockwave delivery.

Ureteroscopic Ultrasound Technology to Size Kidney Stone Fragments: Proof of Principle Using a Miniaturized Probe in a Porcine Model

PURPOSE A prototype ultrasound-based probe for use in ureteroscopy was used for in vitro measurements of stone fragments in a porcine kidney. METHODS Fifteen human stones consisting of three different compositions were placed deep in the collecting system of a porcine kidney. A 2 MHz, 1.2 mm (3.6F) needle hydrophone was used to send and receive ultrasound pulses for stone sizing. Calculated stone thicknesses were compared with caliper measurements. RESULTS Correlation between ultrasound-determined thickness and caliper measurements was excellent in all three stone types (r(2) = 0.90, p < 0.0001). All 15 ultrasound measurements were accurate to within 1 mm, and 10 measurements were accurate within 0.5 mm. CONCLUSION A 3.6F ultrasound probe can be used to accurately size stone fragments to within 1 mm in a porcine kidney.

Novel High-Intensity Focused Ultrasound Clamp—Potential Adjunct for Laparoscopic Partial Nephrectomy

BACKGROUND AND PURPOSE Partial nephrectomy (PN) can be technically challenging, especially if performed in a minimally invasive manner. Although ultrasound technology has been shown to have therapeutic capabilities, including tissue ablation and hemostasis, it has not gained clinical use in the PN setting. The purpose of this study is to evaluate the ability of a high-intensity ultrasound clamp to create an ablation plane in the kidney providing hemostasis that could potentially aid in laparoscopic PN. METHODS A new instrument was created using a laparoscopic Padron endoscopic exposing retractor. Ultrasound elements were engineered on both sides of the retractor to administer high-intensity ultrasound energy between the two sides of the clamp. This high-intensity focused ultrasound (HIFU) clamp was placed 2 to 2.5 cm from the upper and lower poles of 10 porcine kidneys to evaluate its effectiveness at different levels and duration of energy delivery. PN transection was performed through the distal portion of the clamped margin. Kidneys postintervention and after PN were evaluated and blood loss estimated by weighing gauze placed at the defect. Histologic analysis was performed with hematoxylin and eosin and nicotinamide adenine dinucleotide staining to evaluate for tissue viability and thermal spread. RESULTS Gross parenchymal changes were seen with obvious demarcation between treated and untreated tissue. Increased ultrasound exposure time (10 vs 5 and 2 min), even at lower power settings, was more effective in causing destruction and necrosis of tissue. Transmural ablation was achieved in three of four renal units after 10 minutes of exposure with significantly less blood loss (<2 g vs 30-100 g). Nonviable tissue was confirmed histologically. There was minimal thermal spread outside the clamped margin (1.2-3.2 mm). CONCLUSION In this preliminary porcine evaluation, a novel HIFU clamp induced hemostasis and created an ablation plane in the kidney. This technology could serve as a useful adjunct to laparoscopic PN in the future and potentially obviate the need for renal hilar clamping.

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 ...

Clinical assessment of shockwave lithotripsy accuracy.

Kidney stone movement primarily due to patient respiration compromises shock wave lithotripsy (SWL) targeting and efficacy. The objective of this study is to describe the use of B‐mode ultrasound to evaluate the accuracy of targeting during SWL. Patients undergoing electrohydraulic SWL were enrolled into this institutionally approved research study. A commercial diagnostic ultrasound imaging system, either Philips HDI 5000 or iU‐22, was used to intermittently visualize and detect any shockwave‐induced motion of the stone during 1–3 min periods. Four patients (mean age 52.7) underwent treatment of seven renal stones with mean individual stone size of 10.41 ± 4.5 mm. A mean of 2937 shocks (range 2750–3000) were delivered at a rate of 1–2 Hz and charging voltage of 14–26 kV. Stone oscillation or jumping at the exact time of individual shock delivery was visualized with ultrasound: no stones completely failed to move. Accurate alignment, as interpreted by positive stone motion, occurred in a mean of 50 ± 20.4...

Visualization of a focused ultrasound beam to guide radiation force‐induced clearance of kidney stones.

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...

Radiation pressure from ultrasound to help kidney stones pass.

Residual kidney stone fragments often remain months after treatment. These fragments may nucleate new stones and contribute to a 50% recurrence within 5 years. Here, a research focused ultrasound device was used to generate fragment motion with the goal of facilitating passage. Natural and artificial stones 1–8 mm in length were surgically placed in the urine space in pig kidneys. The ultrasound source was a 2.75‐MHz, eight‐element annular array with a 6‐cm radius of curvature. At adjustable focal depths of 5–8 cm, the focal pressure beam width in water was about 2 mm, and peak pressure was about 4 MPa. Targeting was done by ultrasound using B‐mode and twinkling artifact that stones produce in Doppler mode. The commercial imaging probe was placed within and oriented down the axis of the therapy probe. Ultrasound and fluoroscopy showed the stones moving in real‐time under the influence of the focused ultrasound. Stones moved on the order of 1 cm/s away from the source and several stones moved several centi...