Frank Starr

Preclinical in vivo Evaluation of an Extracorporeal HIFU Device for Ablation of Pancreatic Tumors

Extracorporeal high-intensity focused ultrasound (HIFU) can be used to ablate tissue noninvasively by delivering focused ultrasound energy from an external source. HIFU for clinical treatment of pancreatic cancer has been reported; however, systematic evaluation of the safety and efficacy of pancreatic ablation with HIFU has not been performed. The objectives of this in vivo study are as follows: (1) assess the safety and feasibility of targeting and ablating pancreatic tissue using the FEP-BY02 HIFU system (Yuande Bio-Medical Engineering, Beijing, China); (2) evaluate a method for estimating in situ acoustic treatment energy in an in vivo setting; and (3) identify the optimal treatment parameters that result in safe and effective ablation of the pancreas. The pancreata of 12 common swine were treated in vivo. Prior to therapy, blood was drawn for laboratory analysis. Animals were then treated with extracorporeal HIFU at three different acoustic treatment energies (750, 1000 and 1250 J). Endoscopy was performed prior to and immediately following HIFU therapy to assess for gastric injury. Blood was drawn after completion of the treatment and on days 2 and 7 following treatment to assess for biochemical evidence of pancreatitis. Animals were then euthanized 7 d following treatment and a necropsy was performed to assess for unintended injury and to obtain pancreatic tissue for histology to assess efficacy of HIFU ablation. Histologic scoring of pancreatic tissue changes was performed by a pathologist blinded to the treatment energy delivered. The degree of ablation identified on histology correlated with the treatment energy. No collateral tissue damage was seen at treatment energies of 750 and 1000 J. At 1250 J, thermal injury to the abdominal muscles and gastric ulcers were observed. There were no premature deaths, serious illnesses, skin burns or evidence of pancreatitis on biochemical analysis. HIFU treatment of the pancreas is feasible, safe and can be used to ablate tissue noninvasively. A clinical trial in humans examining the use of extracorporeal HIFU for palliation of pain related to pancreatic cancer is planned.

Ultrasound-guided tissue fractionation by high intensity focused ultrasound in an in vivo porcine liver model

Significance High intensity focused ultrasound (HIFU) therapy is a promising, clinically adopted method of noninvasive tissue ablation used to treat both benign and malignant conditions. This work presents, to our knowledge, the first in vivo validation of a previously developed HIFU-based method that allows for noninvasive fractionation of targeted tissue into subcellular debris—boiling histotripsy—in a large animal model. While fractionating the targeted soft tissue, boiling histotripsy is shown to spare the adjacent connective tissue structures such as blood vessels. The process can be readily targeted and monitored by B-mode ultrasound. The resulting tissue debris are liquid, which provides a potential clinical benefit over thermal ablation in the treatment of tumors that exert uncomfortable pressure on surrounding tissues. 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.

Focused Ultrasound to Expel Calculi from the Kidney: Safety and Efficacy of a Clinical Prototype Device

PURPOSE Focused ultrasound has the potential to expel small stones or residual stone fragments from the kidney, or move obstructing stones to a nonobstructing location. We evaluated the efficacy and safety of ultrasonic propulsion in a live porcine model. MATERIALS AND METHODS Calcium oxalate monohydrate kidney stones and laboratory model stones (2 to 8 mm) were ureteroscopically implanted in the renal pelvicalyceal system of 12 kidneys in a total of 8 domestic swine. Transcutaneous ultrasonic propulsion was performed using an HDI C5-2 imaging transducer (ATL/Philips, Bothell, Washington) and the Verasonics® diagnostic ultrasound platform. Successful stone relocation was defined as stone movement from the calyx to the renal pelvis, ureteropelvic junction or proximal ureter. Efficacy and procedure time was determined. Three blinded experts evaluated histological injury to the kidney in the control, sham treatment and treatment arms. RESULTS All 26 stones were observed to move during treatment and 17 (65%) were relocated successfully to the renal pelvis (3), ureteropelvic junction (2) or ureter (12). Average ± SD successful procedure time was 14 ± 8 minutes and a mean of 23 ± 16 ultrasound bursts, each about 1 second in duration, were required. There was no evidence of gross or histological injury to the renal parenchyma in kidneys exposed to 20 bursts (1 second in duration at 33-second intervals) at the same output (2,400 W/cm(2)) used to push stones. CONCLUSIONS Noninvasive transcutaneous ultrasonic propulsion is a safe, effective and time efficient means to relocate calyceal stones to the renal pelvis, ureteropelvic junction or ureter. This technology holds promise as a useful adjunct to surgical management for renal calculi.

Focused Ultrasonic Propulsion of Kidney Stones: Review and Update of Preclinical Technology

INTRODUCTION A noninvasive tool to reposition kidney stones could have significant impact in the management of stone disease. Our research group has developed a noninvasive transcutaneous ultrasound device. A review and update of the current status of this technology is provided. DISCUSSION OF TECHNOLOGY: Stone propulsion is achieved through short bursts of focused, ultrasonic pulses. The initial system consisted of an eight-element annular array transducer, computer, and separate ultrasound imager. In the current generation, imaging and therapy are completed with one ultrasound system and a commercial probe. This generation allows real-time ultrasound imaging, targeting, and propulsion. Safety and effectiveness for the relocation of calyceal stones have been demonstrated in the porcine model. ROLE IN ENDOUROLOGY: This technology may have applications in repositioning stones as an adjunct to lithotripsy, facilitating clearance of residual fragments after lithotripsy, expelling de novo stones, and potentially repositioning obstructing stones. Human trials are in preparation.

Pulsed high-intensity focused ultrasound enhances delivery of doxorubicin in a preclinical model of pancreatic cancer

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. .

Endoscopic high-intensity focused US: technical aspects and studies in an in vivo porcine model (with video)

BACKGROUND 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. OBJECTIVE To design, develop, and test an EUS-guided HIFU transducer for endoscopic applications. DESIGN A preclinical, pilot characterization and feasibility study. SETTING Academic research center. PATIENTS Studies were performed in an in vivo porcine model. INTERVENTION Thermal ablation of in vivo porcine pancreas and liver was performed with EUS-guided focused US through the gastric tract. RESULTS 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. LIMITATIONS This was a preclinical, single-center feasibility study with a limited number of subjects. CONCLUSION 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.

Selective reduction of multifetal pregnancy using high-intensity focused ultrasound in the rabbit model

High‐order multifetal pregnancies carry a significant risk of obstetric complications and poor pregnancy outcome. Selective reduction has traditionally been performed using transabdominal and transvaginal ultrasound‐guided intracardiac injection of potassium chloride. We have previously shown that high‐intensity focused ultrasound (HIFU) can create a coagulative tissue necrosis in the sheep fetus. The objective of this study was to investigate the feasibility of non‐invasive selective fetal reduction using HIFU in a rabbit model.

Magnetic resonance imaging of the hepatobiliary system: Intestinal absorption studies of manganese mesoporphyrin

RATIONALE AND OBJECTIVES We studied the intestinal absorption of manganese mesoporphyrin (Mn-mesoporphyrin), a potential oral hepatobiliary contrast agent. METHODS Mn-mesoporphyrin was complexed with monoolein and taurocholate (mixed micelles). Portal venous delivery and biliary excretion were measured after intestinal administration in rats and rabbits, and the mechanism of intestinal transport was studied in a combined lymph-bile fistula model in rats. T1-weighted magnetic resonance (MR) images of the liver were obtained in rats and domestic pigs before and after gastric administration of Mn-mesoporphyrin in mixed micelles. RESULTS A 2.2-fold increase of portal venous Mn concentration was found 90 min after intestinal administration of the complex. None was found in the lymph collected from the thoracic duct, indicating a transcellular transport mechanism through the intestinal mucosa with portal venous delivery. Mn-mesoporphyrin levels in bile peaked between 240 and 270 min after administration (200-fold increase). The greatest liver enhancement (20-90%) was measured 360 min after administration. CONCLUSION The feasibility of intestinal delivery of Mn-mesoporphyrin, a lipophilic hepatobiliary contrast agent was demonstrated.

Release of Cell-free MicroRNA Tumor Biomarkers into the Blood Circulation with Pulsed Focused Ultrasound: A Noninvasive, Anatomically Localized, Molecular Liquid Biopsy

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.

Gallstone susceptibility to in vitro fragmentation by a 480-nm pulsed dye laser. Correlation with computed tomography characteristics

The object of this investigation was to determine gallstone susceptibility to laser lithotripsy and to discover whether this susceptibility is related to the computed tomography (CT) appearance of gallstones. Gallstones collected from surgery were scanned by CT and classified as homogeneously dense (greater than 90 Hounsfield units [HU]), homogeneously faint (30-60 HU), or rimmed. Sixty stones were subjected to laser energy at 20, 40, 60, 80, or 100 mJ. Fracture and fragmentation (all particles less than 2 mm) were assessed in relation to the energy level setting and number of laser pulses delivered. The authors found that a 480-nm, flashlamp-pumped pulsed dye laser can fragment completely all the types of human gallstones that were tested, although there is significant variability in gallstone susceptibility to laser lithotripsy. This susceptibility varies with CT appearance: dense stones require fewer pulses and lower energies for fracture and fragmentation, compared to faint or rimmed stones. The authors anticipate that CT characterization of gallstones may be a clinically useful screening tool before laser lithotripsy.