Imaging-guided High-intensity Focused Ultrasound Research Articles

High-intensity focused ultrasound tumor ablation: Review of ten years of clinical experience

High-intensity focused ultrasound (HIFU) is a technique to destroy tissue at depth within the body, selectively and without harming overlying and adjacent structures within the path of the beam because the ultrasonic intensity at the beam focus is much higher than that outside of the focus. Diagnostic ultrasound is the first imaging modality used for guiding HIFU ablation. In 1997, a patient with osteosarcoma was first successfully treated with ultrasound imaging-guided HIFU in Chongqing, China. Over the last decade, thousands of patients with uterine fibroids, liver cancer, breast cancer, pancreatic cancer, bone tumors, and renal cancer have been treated with ultrasound imaging-guided HIFU. Based on several research groups' reports, as well as our ten-year clinical experience, we conclude that this technique is safe and effective in treating human solid tumors. HIFU is a promising technique. Most importantly, HIFU offers patients another alternative when those patients have no other treatment available.

High intensity focused ultrasound ablation: A new therapeutic option for solid tumors

Surgery has been the standard of care in selected cases with solid tumors. However, a majority of patients are unable to undergo surgical resection because of the tumor sites, advanced stages, or poor general condition. High intensity focused ultrasound (HIFU) is a novel non-invasive technique that is capable of producing coagulative necrosis at a precise focal point within the body, without harming overlying and adjacent structures even within the path of the beam. Diagnostic ultrasound was the first imaging modality used for guiding HIFU ablation in the 1990 s. Over the last decade, thousands of patients with uterine fibroids, liver cancer, breast cancer, pancreatic cancer, bone tumors, renal cancer have been treated with ultrasound imaging-guided HIFU (USgHIFU) worldwide. This USgHIFU system [Chongqing Haifu (HIFU) Tech Co., Ltd., Chongqing, China] was first equipped in Asia, now in Europe. Several research groups have demonstrated that HIFU is safe and effective in treating human solid tumors. In 2004, the magnetic resonance guided focused ultrasound surgery (MRgFUS) was approved by the United States Food and Drug Administration (FDA) for clinical treatments of uterine fibroids. We conclude that HIFU offers patients another choice when no other treatment available or when patients refused surgical operation. This technique may play a key role in future clinical practice.

Pulsatile Flow Phantom for Ultrasound Image-Guided HIFU Treatment of Vascular Injuries

A pulsatile flow phantom was developed for studies of ultrasound image-guided high intensity focused ultrasound (HIFU) application in transcutaneous hemostasis of injured blood vessels. The flow phantom consisted of a pulsatile pump system with instrumented excised porcine carotid artery, which was imbedded in a transparent agarose gel to model structural configuration of in vivo tissues. Heparinized porcine blood was circulated through the phantom. The artery was injured using an 18-gauge needle to model a penetrating injury in human peripheral vasculature. A HIFU transducer with the diameter of 7 cm, focal length of 6.3 cm and frequency of 3.4 MHz was used to seal the puncture. Ultrasound imaging was used to localize and target the puncture site and to monitor the HIFU treatment. Triphasic blood flows present in the human arteries were reproduced, with flow rates of 50 to 500 mL/min, pulse rates of 62 to 138 beats/min and peak pressures of 100 to 250 mm Hg. The penetrating injury of an artery was mimicked successfully in the flow phantom setting and was easily visualized both optically through the transparent gel and with power Doppler ultrasound imaging. Hemostasis was achieved in 55 ± 31 s ( n = 9) of HIFU application. Histologic observations showed that a HIFU-sealed puncture was filled with clotted blood and covered with a fibrin cap. The pulsatile flow phantom provides a controlled and repeatable environment for studies of transcutaneous image-guided HIFU application in hemostasis of a variety of blood vessel injuries. (E-mail: adasi@u.washington.edu)

Blood Flow Occlusion Via Ultrasound Image-Guided High-Intensity Focused Ultrasound and Its Effect on Tissue Perfusion

This study investigated the induction of tissue necrosis by arterial blood flow occlusion using ultrasound image-guided high-intensity focused ultrasound (HIFU). We constructed a prototype HIFU transducer in combination with an imaging probe that provided color Doppler imaging and ultrasound contrast imaging. The HIFU beam was aimed into a branch of the renal artery in vivo. The renal artery branches of eight rabbits were occluded by HIFU at an intensity of 4 kW/cm 2 (from 2 to 10 times of each sonication for 5 s). When the HIFU exposure was successful, complete cessation of blood flow was observed by color Doppler imaging with success rate of 100% (8/8). Furthermore, lack of perfusion was observed in the renal cortex with a contrast-enhanced image. Postmortem histologic evaluation showed a wedge-shaped area of infarction in six of seven cases, corresponding to the lack of the contrast medium in the ultrasound image. These results demonstrated that ultrasound image-guided HIFU can be used to induce arterial occlusion, thus producing infarction and necrosis of the perfused tissue. (E-mail: m_itihara@hotmail.com)

Image-guided acoustic hemostasis for hemorrhage in the posterior liver

We investigated the use of ultrasound image-guided high intensity focused ultrasound (HIFU) to stop bleeding from injuries in the posterior liver. A HIFU transducer with focal length of 3.5 cm and frequency of 3.2 MHz was integrated with an intraoperative high-resolution ultrasound-imaging probe. Wedge tissue extractions, 30-mm long, 5-mm wide and 8-mm deep, were made in the posterior liver surface of five pigs to induce bleeding. The device was positioned on the anterior surface of the liver and HIFU was applied using ultrasound image-guidance. Hemostasis was achieved in 66 ± 18 s (mean ± standard deviation) for 17 HIFU treatments. During 7 min of sham HIFU treatment, none of the control incisions ( n = 7) became hemostatic. Ultrasound image-guided HIFU offers a promising method for hemostasis in surgical settings in which the hemorrhage site is hidden and/or not accessible. (E-mail: adasi@u.washington.edu)

Image-guided HIFU neurolysis of peripheral nerves to treat spasticity and pain

Spasticity, a major complication of central nervous system disorders, signified by uncontrollable muscle contractions, is very difficult to treat effectively. We report on the use of ultrasound (US) image-guided high-intensity focused US (HIFU) to target and suppress the function of the sciatic nerve complex of rabbits in vivo, as a possible treatment of spasticity. The image-guided HIFU device included a 3.2-MHz spherically curved transducer and an intraoperative imaging probe. A focal acoustic intensity of 1480 to 1850 W/cm 2, applied using a scanning method, was effective in achieving complete conduction block in 100% of 22 nerve complexes with HIFU treatment times of 36 ± 14 s (mean ± SD). Gross examination showed blanching of the nerve at the HIFU treatment site and lesion volumes of 2.8 ± 1.4 cm 3 encompassing the nerve complex. Histologic examination indicated axonal demyelination and necrosis of Schwann cells as probable mechanisms of nerve block. With accurate localization and targeting of peripheral nerves using US imaging, HIFU could become a promising tool for the suppression of spasticity. (E-mail: jlf2@u.washington.edu)

Monitoring formation of high intensity focused ultrasound (HIFU) induced lesions using backscattered ultrasound

Backscattered radio frequency (RF) data collected in a series of in vitro experiments, in which HIFU lesions were created in bovine liver tissue, were analyzed using two signal processing approaches to visualize temporal evolution of lesion formation. Change in round-trip travel time provides information related to temperature change during and after therapy. Changes in the RF spectrum related to changes in scattering properties of the heated region were observed before visible changes appeared on B-mode images. Effect of increased attenuation in the necrosed tissue region was also observed. Results demonstrate potential for these two techniques in image-guided HIFU therapy.

Real-time visualization of high-intensity focused ultrasound treatment using ultrasound imaging

High-intensity focused ultrasound (HIFU) and conventional B-mode ultrasound (US) imaging were synchronized to develop a system for real-time visualization of HIFU treatment. The system was tested in vivo in pig liver. The HIFU application resulted in the appearance of a hyperechoic spot at the focus that faded gradually after cessation of HIFU exposure. The duration of HIFU exposure needed for a hyperechoic spot to appear, was inversely related to the HIFU intensity. The threshold intensity required to produce a hyperechoic spot in liver in < 1 s was 970 W/cm 2, in situ. At this HIFU dose, no immediate cellular damage was observed, providing a potential for pretreatment targeting. The real-time visualization method was used in hemostasis of actively bleeding internal pelvic vessels, allowing targeting and monitoring of successful treatment. Real-time US imaging may provide a useful tool for image-guided HIFU therapy. (E-mail: adasi@u.washington.edu)