Bone demineralization, dehydration and stasis put astronauts at increased risk of forming kidney stones in space. The color-Doppler ultrasound "twinkling artifact," which highlights kidney stones with color, can make stones readily detectable with ultrasound; however, our previous results suggest twinkling is caused by microbubbles on the stone surface which could be affected by the elevated levels of carbon dioxide found on space vehicles. Four pigs were implanted with kidney stones and imaged with ultrasound while the anesthetic carrier gas oscillated between oxygen and air containing 0.8% carbon dioxide. On exposure of the pigs to 0.8% carbon dioxide, twinkling was significantly reduced after 9–25 min and recovered when the carrier gas returned to oxygen. These trends repeated when pigs were again exposed to 0.8% carbon dioxide followed by oxygen. The reduction of twinkling caused by exposure to elevated carbon dioxide may make kidney stone detection with twinkling difficult in current space vehicles.

Purpose
To compare the abilities of three pulsed focused ultrasound regimes (that cause tissue liquefaction, permeabilization, or mild heating) to release tumor-derived microRNA into the circulation in vivo and to evaluate release dynamics.

Materials and Methods
All rat experiments were approved by the University of Washington Institutional Animal Care and Use Committee. Reverse-transcription quantitative polymerase chain reaction array profiling was used to identify candidate microRNA biomarkers in a rat solid tumor cell line. Rats subcutaneously grafted with these cells were randomly assigned among three pulsed focused ultrasound treatment groups: (a) local tissue liquefaction via boiling histotripsy, (b) tissue permeabilization via inertial cavitation, and (c) mild (<10°C) heating of tissue, as well as a sham-treated control group. Blood specimens were drawn immediately prior to treatment and serially over 24 hours afterward. Plasma microRNA was quantified with reverse-transcription quantitative polymerase chain reaction, and statistical significance was determined with one-way analysis of variance (Kruskal-Wallis and Friedman tests), followed by the Dunn multiple-comparisons test.

Results
After tissue liquefaction and cavitation treatments (but not mild heating), plasma quantities of candidate biomarkers increased significantly (P value range, <.0001 to .04) relative to sham-treated controls. A threefold to 32-fold increase occurred within 15 minutes after initiation of pulsed focused ultrasound tumor treatment, and these increases persisted for 3 hours. Histologic examination confirmed complete liquefaction of the targeted tumor area with boiling histotripsy, in addition to areas of petechial hemorrhage and tissue disruption by means of cavitation-based treatment.

Conclusion
Mechanical tumor tissue disruption with pulsed focused ultrasound–induced bubble activity significantly increases the plasma abundance of tumor-derived microRNA rapidly after treatment.

The purpose is to compare the abilities of three pulsed focused ultrasound regimes (that cause tissue liquefaction, permeabilization, or mild heating) to release tumor-derived microRNA into the circulation in vivo and to evaluate release dynamics. Mechanical tumor tissue disruption with pulsed focused ultrasound–induced bubble activity significantly increases the plasma abundance of tumor-derived microRNA rapidly after treatment.

Pancreatic cancer is characterized by extensive stromal desmoplasia, which decreases blood perfusion and impedes chemotherapy delivery. Breaking the stromal barrier could both increase perfusion and permeabilize the tumor, enhancing chemotherapy penetration. Mechanical disruption of the stroma can be achieved using ultrasound-induced bubble activity-cavitation. Cavitation is also known to result in microstreaming and could have the added benefit of actively enhancing diffusion into the tumors. Here, we report the ability to enhance chemotherapeutic drug doxorubicin penetration using ultrasound-induced cavitation in a genetically engineered mouse model (KPC mouse) of pancreatic ductal adenocarcinoma. To induce localized inertial cavitation in pancreatic tumors, pulsed high-intensity focused ultrasound (pHIFU) was used either during or before doxorubicin administration to elucidate the mechanisms of enhanced drug delivery (active vs. passive drug diffusion). For both types, the pHIFU exposures that were associated with high cavitation activity resulted in disruption of the highly fibrotic stromal matrix and enhanced the normalized doxorubicin concentration by up to 4.5-fold compared with controls. Furthermore, normalized doxorubicin concentration was associated with the cavitation metrics (P < 0.01), indicating that high and sustained cavitation results in increased chemotherapy penetration. No significant difference between the outcomes of the two types, that is, doxorubicin infusion during or after pHIFU treatment, was observed, suggesting that passive diffusion into previously permeabilized tissue is the major mechanism for the increase in drug concentration. Together, the data indicate that pHIFU treatment of pancreatic tumors when resulting in high and sustained cavitation can efficiently enhance chemotherapy delivery to pancreatic tumors.

High-intensity focused US (HIFU) is becoming more widely used for noninvasive and minimally invasive ablation of benign and malignant tumors. Recent studies suggest that HIFU can also enhance targeted drug delivery and stimulate an antitumor immune response in many tumors. However, targeting pancreatic and liver tumors by using an extracorporeal source is challenging due to the lack of an adequate acoustic window. The development of an EUS-guided HIFU transducer has many potential benefits including improved targeting, decreased energy requirements, and decreased potential for injury to intervening structures.

The transducer successfully created lesions in gel phantoms and ex vivo bovine livers. In vivo studies demonstrated that targeting and creating lesions in the porcine pancreas and liver are feasible. An EUS-guided HIFU transducer was successfully designed and developed with dimensions that are appropriate for endoscopic use. The feasibility of performing EUS-guided HIFU ablation in vivo was demonstrated in an in vivo porcine model. Further development of this technology will allow endoscopists to perform precise therapeutic ablation of periluminal lesions without breaching the wall of the gastric tract.

Objective
To provide an update on a research device to ultrasonically reposition kidney stones transcutaneously. This article reports preclinical safety and effectiveness studies, survival data, modifications of the system, and testing in a stone-forming porcine model. These data formed the basis for regulatory approval to test the device in humans.

Materials and Methods
The ultrasound burst was shortened to 50 ms from previous investigations with 1-s bursts. Focused ultrasound was used to expel 2- to 5-mm calcium oxalate monohydrate stones placed ureteroscopically in 5 pigs. Additionally, de novo stones were imaged and repositioned in a stone-forming porcine model. Acute safety studies were performed targeting 2 kidneys (6 sites) and 3 pancreases (8 sites). Survival studies followed 10 animals for 1 week after simulated treatment. Serum and urine analyses were performed, and tissues were evaluated histologically.

Results
All ureteroscopically implanted stones (6/6) were repositioned out of the kidney in 14 ± 8 minutes with 13 ± 6 bursts. On average, 3 bursts moved a stone more than 4 mm and collectively accounted for the majority of relocation. Stones (3 mm) were detected and repositioned in the 200-kg stone-forming model. No injury was detected in the acute or survival studies.

Conclusion
Ultrasonic propulsion is safe and effective in the porcine model. Stones were expelled from the kidney. De novo stones formed in a large porcine model were repositioned. No adverse effects were identified with the acute studies directly targeting kidney or pancreatic tissue or during the survival studies indicating no evidence of delayed tissue injury.

The clinical use of high intensity focused ultrasound (HIFU) therapy for noninvasive tissue ablation has been recently gaining momentum. In HIFU, ultrasound energy from an extracorporeal source is focused within the body to ablate tissue at the focus while leaving the surrounding organs and tissues unaffected. Most HIFU therapies are designed to use heating effects resulting from the absorption of ultrasound by tissue to create a thermally coagulated treatment volume. Although this approach is often successful, it has its limitations, such as the heat sink effect caused by the presence of a large blood vessel near the treatment area or heating of the ribs in the transcostal applications. HIFU-induced bubbles provide an alternative means to destroy the target tissue by mechanical disruption or, at its extreme, local fractionation of tissue within the focal region. Here, we demonstrate the feasibility of a recently developed approach to HIFU-induced ultrasound-guided tissue fractionation in an in vivo pig model. In this approach, termed boiling histotripsy, a millimeter-sized boiling bubble is generated by ultrasound and further interacts with the ultrasound field to fractionate porcine liver tissue into subcellular debris without inducing further thermal effects. Tissue selectivity, demonstrated by boiling histotripsy, allows for the treatment of tissue immediately adjacent to major blood vessels and other connective tissue structures. Furthermore, boiling histotripsy would benefit the clinical applications, in which it is important to accelerate resorption or passage of the ablated tissue volume, diminish pressure on the surrounding organs that causes discomfort, or insert openings between tissues.

The global prevalence and incidence of renal calculi is reported to be increasing. Of the patients that undergo surgical intervention, nearly half experience symptomatic complications associated with stone fragments that are not passed and require follow-up surgical intervention. In a clinical simulation using a clinical prototype, ultrasonic propulsion was proven effective at repositioning kidney stones in pigs. The use of ultrasound to reposition smaller stones or stone fragments to a location that facilitates spontaneous clearance could therefore improve stone-free rates. The goal of this study was to determine an injury threshold under which stones could be safely repositioned.

Kidneys of 28 domestic swine were treated with exposures that ranged in duty cycle from 0%–100% and spatial peak pulse average intensities up to 30 kW/cm² for a total duration of 10 min. The kidneys were processed for morphological analysis and evaluated for injury by experts blinded to the exposure conditions.

At a duty cycle of 3.3%, a spatial peak intensity threshold of 16,620 W/cm² was needed before a statistically significant portion of the samples showed injury. This is nearly seven times the 2,400-W/cm² maximum output of the clinical prototype used to move the stones effectively in pigs.

The data obtained from this study show that exposure of kidneys to ultrasonic propulsion for displacing renal calculi is well below the threshold for tissue injury.

Focused ultrasonic propulsion is a new noninvasive technique designed to move kidney stones and stone fragments out of the urinary collecting system. However, to our knowledge the extent of tissue injury associated with this technique is not known. We quantitated the amount of tissue injury produced by focused ultrasonic propulsion under simulated clinical treatment conditions and under conditions of higher power or continuous duty cycles. We compared those results to extracorporeal shock wave lithotripsy injury.

Therapeutic ultrasound has an increasing number of applications in urology, including shockwave lithotripsy, stone propulsion, tissue ablation, and hemostasis. However, the threshold of renal injury using ultrasound is unknown. The goal of this study was to determine kidney injury thresholds for a range of intensities between diagnostic and ablative therapeutic ultrasound. A 2 MHz annular array generating spatial peak pulse average intensities (ISPPA) up to 28,000 W/cm² in water was placed on the surface of in vivo porcine kidneys and focused on the adjacent parenchyma. Treatments consisted of pulses of 100 μs duration triggered every 3 ms for 10 minutes at various intensities. The perfusion-fixed tissue was scored by 3 blinded independent experts. Above a threshold of 16,620 W/cm², the majority of injury observed included emulsification, necrosis and hemorrhage. Below this threshold, almost all injury presented as focal cell and tubular swelling and/or degeneration. These findings provide evidence for a wide range of potentially therapeutic ultrasound intensities that has a low probability of causing injury. While this study did not examine all combinations of treatment parameters of therapeutic ultrasound, tissue injury appears dose-dependent.

Purpose
Focused ultrasound has the potential to expel small stones or residual stone fragments from the kidney, or move obstructing stones to a non-obstructing location. The purpose of this study was to evaluate the efficacy and safety of ultrasonic propulsion in a live porcine model.

Material and Methods
Calcium oxalate monohydrate kidney stones and laboratory model stones (2–8 mm) were ureteroscopically implanted within the renal pelvicalyceal system of 12 kidneys in eight domestic swine. Transcutaneous ultrasonic propulsion was performed using a Philips HDI C5-2 imaging transducer and Verasonics diagnostic ultrasound platform. Successful stone relocation was defined as stone movement from the calyx to the renal pelvis, ureteropelvic junction (UPJ) or proximal ureter. Efficacy and procedure time were determined. Three blinded experts evaluated for histologic injury to the kidney in control, sham, and treatment arms.

Results
All stones were observed to move during treatment, and 65% (17/26) were relocated successfully to the renal pelvis (3), UPJ (2), or ureter (12). Average successful procedure time was 14±8 min and required 23±16 ultrasound bursts of ~1 sec duration. There was no evidence of gross or histologic injury to the renal parenchyma in kidneys exposed to 20 bursts (1 sec duration, 33 sec intervals) at the same output (2400 W/cm²) used to push stones.

Conclusions
Non-invasive transcutaneous ultrasonic propulsion is a safe, effective, and time-efficient means to relocate calyceal stones to the renal pelvis, UPJ, or ureter. This technology holds promise as a useful adjunct to the surgical management of renal calculi.

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.