Tom Leslie

Spatiotemporal Monitoring of High-Intensity Focused Ultrasound Therapy with Passive Acoustic Mapping

PURPOSE To demonstrate feasibility of monitoring high-intensity focused ultrasound (HIFU) treatment with passive acoustic mapping of broadband and harmonic emissions reconstructed from filtered-channel radiofrequency data in ex vivo bovine tissue. MATERIALS AND METHODS Both passive acoustic emissions and B-mode images were recorded with a diagnostic ultrasound machine during 180 HIFU exposures of five freshly excised, degassed bovine livers. Tissue was exposed to peak rarefactional pressures between 3.6 and 8.0 MPa for 2, 5, or 10 seconds. The B-mode images were analyzed for hyperechoic activity, and threshold levels were determined for the harmonic (1.17 mJ) and broadband (0.0137 mJ) components of the passively reconstructed source energy to predict tissue ablation. Both imaging methods were compared with tissue lesions after exposure to determine their spatial accuracy and their capability to help predict presence of ablated tissue. Performance of both methods as detectors was compared (matched-pair test design). RESULTS Passive mapping successfully aided prediction of the presence of tissue ablation more often than did conventional hyperechoic images (49 of 58 [84%] vs 31 of 58 [53%], P < .001). At 5.4-6.3-MPa exposures, sensitivity, specificity, negative predictive value, and positive predictive value of the two methods, respectively, were 15 of 20 versus five of 21 (P = .006), eight of nine versus eight of nine (P = .72), 15 of 16 versus five of six (P = .53), and eight of 13 versus eight of 24 (P = .011). Across HIFU exposure amplitude ranges, passive acoustic mapping also aided correct prediction of the visually detected location of ablation following tissue sectioning in 42 of 45 exposures for which the harmonic and broadband threshold levels for tissue ablation were exceeded. Early cavitation activity indicated the focal position within the tissue before irreversible tissue damage occurred. CONCLUSION Passive acoustic mapping significantly outperformed the conventional hyperecho technique as an ultrasound-based HIFU monitoring method, as both a detector of lesion occurrence and a method of mapping the position of ablated tissue.

Extracorporeal high intensity focused ultrasound for renal tumours: a 3-year follow-up.

Study Type – Therapy (case series)
Level of Evidence 4

High intensity focused ultrasound in the treatment of abdominal and gynaecological diseases

In recent years high intensity focused ultrasound (HIFU) has received increasing interest as a non-invasive modality for the treatment of tumours of solid organs. Surgeons continue their quest to find the optimal technique whereby a diseased organ can be treated with a minimum of damage to the patient, while providing a comprehensive treatment to produce either cure or resolution of symptoms. Two of the areas in which HIFU is beginning to establish itself as a real therapeutic alternative, are in the treatment of abdominal and gynaecological disease. In this paper, we will review the literature available regarding the use of HIFU in the treatment of various organs: liver, kidney, pancreas, bladder, uterus and vulva.

Visually directed high-intensity focused ultrasound for organ-confined prostate cancer: a proposed standard for the conduct of therapy

To propose a standard for the conduct of visually directed transrectal high‐intensity focused ultrasound (HIFU) and to offer a formal description of the changes observed on B‐mode ultrasonography (US) during this procedure. We describe our early experience of using two different treatment methods; algorithm‐based HIFU and visually directed HIFU for the treatment of organ‐confined prostate cancer.

High-intensity focused ultrasound principles, current uses, and potential for the future.

High-intensity focused ultrasound (HIFU) continues to be a very attractive option for minimally invasive procedures. Using well-established principles, this ablative therapy can be used to treat a number of benign and malignant diseases with few side effects. During the last 15 years, there has been an enormous amount of work, both laboratory based and in the form of clinical trials, aimed at developing devices that can deliver treatments with safe and effective outcomes. In this article, we aim to outline the principles of HIFU, describe the current commercially available machines and their applications, and discuss the role of HIFU in the future.

High-intensity focused ultrasound treatment of liver tumours: post-treatment MRI correlates well with intra-operative estimates of treatment volume

OBJECTIVES To assess the safety and feasibility of high-intensity focused ultrasound (HIFU) ablation of liver tumours and to determine whether post-operative MRI correlates with intra-operative imaging. METHODS 31 patients were recruited into two ethically approved clinical trials (median age 64; mean BMI 26 kg m(-2)). Patients with liver tumours (primary or metastatic) underwent a single HIFU treatment monitored using intra-operative B-mode ultrasound. Follow-up consisted of radiology and histology (surgical trial) or radiology alone (radiology trial). Radiological follow-up was digital subtraction contrast-enhanced MRI. RESULTS Treatment according to protocol was possible in 30 of 31 patients. One treatment was abandoned because of equipment failure. Transient pain and superficial skin burns were seen in 81% (25/31) and 39% (12/31) of patients, respectively. One moderate skin burn occurred. One patient died prior to radiological follow-up. Radiological evidence of ablation was seen in 93% (27/29) of patients. Ablation accuracy was good in 89% (24/27) of patients. In three patients the zone of ablation lay ≤2 mm outside the tumour. The median cross-sectional area (CSA) of the zone of ablation was 5.0 and 5.1 cm(2) using intra-operative and post-operative imaging, respectively. The mean MRI:B-mode CSA ratio was 1.57 [95% confidence interval (CI)=0.57-2.71]. There was positive correlation between MRI and B-mode CSA (Spearmans r=0.48; 95% CI 0.11-0.73; p=0.011) and the slope of linear regression was significantly non-zero (1.23; 95% CI=0.68-1.77; p<0.0001). CONCLUSIONS HIFU ablation of liver tumours is safe and feasible. HIFU treatment is accurate, and intra-operative assessment of treatment provides an accurate measure of the zone of ablation and correlates well with MRI follow-up.

HIGH-INTENSITY FOCUSED ULTRASOUND FOR LOCALIZED PROSTATE CANCER: INITIAL EXPERIENCE WITH A 2-YEAR FOLLOW-UP

To report on the short‐term functional and oncological results, from one institution, of high‐intensity focused ultrasound (HIFU) for treating localized prostate cancer.

High-intensity focused ultrasound ablation of liver tumours: can radiological assessment predict the histological response?

Cancer therapies usually depend on cross-sectional imaging for the assessment of treatment response. This study was designed to evaluate the ability of MRI to predict zones of necrosis following the use of high-intensity focused ultrasound (HIFU) to treat liver metastases. Patients with liver metastases, who had been scheduled for elective surgical resection of their tumours, were recruited to this non-randomized Phase II study. In each case, a proportion of an index liver tumour target was ablated. The response to HIFU was assessed after 12 days using contrast-enhanced MRI and compared directly with histological analysis at the time of surgery. Eight patients were treated, of whom six were subsequently assessed with both MRI and histology. There were no major complications. MRI predicted complete ablation in three cases. In each case, histological analysis confirmed complete ablation. In one case, the region of ablation observed on MRI appeared smaller than predicted at the time of HIFU, but histology revealed complete ablation of the target region. The predominant characteristic of HIFU-ablated tissue was coagulative necrosis but heat fixation was evident in some areas. Heat-fixed cells appeared normal under haematoxylin and eosin staining, indicating that this is unreliable as an indicator of HIFU-induced cell death. This study demonstrates that HIFU is capable of achieving selective ablation of pre-defined regions of liver tumour targets, and that MRI evidence of complete ablation of the target region can be taken to infer histological success.

The incidence of chronic scrotal pain after vasectomy : a prospective audit

To assess the extent of scrotal pain in men before and after vasectomy, to produce accurate data for the benefit of men considering this procedure, and hence improved informed consent about the outcomes, as chronic scrotal pain after vasectomy is a poorly quantified clinical problem.

Laparoscopic high‐intensity focused ultrasound for renal tumours: a proof of concept study

Study Type – Therapy (case series)
Level of Evidence