Single High-intensity Focused Ultrasound Research Articles

Optical method for direct temperature measurement of high intensity focused ultrasound heating

The acoustic pressure field or heat deposition from the passage of an ultrasonic wave can produce a perceptible alteration in the medium’s optical refractive index. With proper placement of the light source and imaging camera, the optical effect can be recorded. This talk describes an optical temperature measurement methodology dubbed laser-ray-bundle (LRB) of the heat deposition from a high intensity focused ultrasound (HIFU) transducer in a transparent tissue phantom. The method does not require calibration, and directly converts the thermo-optic signal to temperature without recourse to any iterative computations. LRB boasts of excellent temporal and spatial resolutions and high temperature sensitivity better than any fine wire thermocouple. Furthermore, it is completely non-invasive. The LRB method is demonstrated with the heat deposition from single millisecond long HIFU pulses in a PDMS tissue phantom or from a train of single pulses with very good performance. The method represents a new capability for quickly assess a HIFU transducer output, and for laboratory and preclinical studies of heating near tissue interfaces including bone, air, or fat. A preliminary experimental setup for measuring the acoustic pressure field is presented.

A theragnostic HIFU transducer and system for inherently registered imaging and therapy.

One big challenge with high intensity focused ultrasound (HIFU) is the difficulty in accurate prediction of focal location due to the complex wave propagation in heterogeneous medium even with imaging guidance. This study aims to overcome this by combining therapy and imaging guidance with one single HIFU transducer using the vibro-acoustography (VA) strategy. Based on the VA imaging method, a HIFU transducer consisting of 8 transmitting elements was proposed for therapy planning, treatment and evaluation. Inherent registration between the therapy and imaging created unique spatial consistence in HIFU transducer's focal region in the above three procedures. Performance of this imaging modality was first evaluated through in-vitro phantoms. In-vitro and ex-vivo experiments were then designed to demonstrate the proposed dual-mode system's ability in conducting accurate thermal ablation. Point spread function of the HIFU-converted imaging system had a full wave half maximum of about 1.2 mm in both directions at a transmitting frequency of 1.2 MHz, which outperformed the conventional ultrasound imaging (3.15 MHz) in in-vitro situation. Image contrast was also tested on the in-vitro phantom. Various geometric patterns could be accurately 'burned out' on the testing objects by the proposed system both in vitro and ex vivo. Implementation of imaging and therapy with one HIFU transducer in this manner is feasible and it has potential as a novel strategy for addressing the long-standing problem in the HIFU therapy, possibly pushing this non-invasive technique forward towards wider clinical applications.

High intensity focused ultrasound for the treatment of solid tumors: a pilot study in canine cancer patients

Purpose To investigate the safety, feasibility, and outcomes of High-Intensity Focused Ultrasound (HIFU) for the treatment of solid tumors in a spontaneous canine cancer model. Methods Dogs diagnosed with subcutaneous solid tumors were recruited, staged and pretreatment biopsies were obtained. A single HIFU treatment was delivered to result in partial tumor ablation using a commercially available HIFU unit. Tumors were resected 3–6 days post HIFU and samples obtained for histopathology and immunohistochemistry. Total RNA was isolated from paired pre and post treated FFPE tumor samples, and quantitative gene expression analysis was performed using the nCounter Canine IO Panel. Results A total of 20 dogs diagnosed with solid tumors were recruited and treated in the study. Tumors treated included Soft Tissue Sarcoma (n = 15), Mast Cell Tumor (n = 3), Osteosarcoma (n = 1), and Thyroid Carcinoma (n = 1). HIFU was well tolerated with only 1 dog experiencing a clinically significant adverse event. Pathology confirmed the presence of complete tissue ablation at the HIFU targeted site and immunohistochemistry indicated immune cell infiltration at the treated/untreated tumor border. Quantitative gene expression analysis indicated that 28 genes associated with T-cell activation were differentially expressed post-HIFU. Conclusions HIFU appears to be safe and feasible for the treatment of subcutaneous canine solid tumors, resulting in ablation of the targeted tissue. HIFU induced immunostimulatory changes, highlighting the canine cancer patient as an attractive model for studying the effects of focal ablation therapies on the tumor microenvironment.

The Effect of High-Intensity Focused Ultrasound on Aqueous Humor Dynamics in Patients with Glaucoma

To investigate the effects of high-intensity focused ultrasound (HiFU) on aqueous humor dynamics in patients with glaucoma. Comparative, nonrandomized, interventional study. Adult patients with a diagnosis of open-angle glaucoma or ocular hypertension with suboptimal intraocular pressure (IOP) control despite maximum medical treatment who required further IOP optimization. All patients underwent comprehensive ophthalmic examination before aqueous humor dynamics study measurements, including fluorophotometry and digital Schiøtz tonography. All patients received 6 seconds of HiFU therapy. Aqueous humor dynamics studies were repeated 3 months after the treatment (patients had 4-week washout from their glaucoma medication before their aqueous humor dynamics study measurements at baseline and the 3-month visit). Intraocular pressure, facility of topographic outflow, aqueous flow rate, and uveoscleral outflow. Thirty eyes of 30 patients were included in the study. At the 3-month postoperative visit, the mean postwashout IOP was reduced by 16% (31.7±5.3 vs. 26.6±4.8 mmHg, P= 0.004), and aqueous flow rate was decreased by 15% (2.07±0.73 vs. 1.77±0.55 μl/min, P= 0.05) from baseline. Neither the tonographic outflow facility nor the uveoscleral outflow was significantly different from baseline. There is a 20% risk of treatment failure (those who needed further glaucoma surgical intervention) within 1 month after a single HiFU treatment (n= 6). Only 25 patients (80%) were able to undergo post-treatment washout measurements, and in these eyes, only 26.6% of eyes achieved >20% IOP reduction at 3 months compared with baseline. We investigated the aqueous humor dynamics effects of a cyclodestructive procedure and specifically HiFU in patients with uncontrolled open-angle glaucoma on maximum tolerated medical therapy. High-intensity focused ultrasound reduced IOP 3 months postoperatively by 16% and aqueous flow decreased by 15% without any significant effect on tonographic outflow facility and uveoscleral outflow.

High-Intensity Focused Ultrasound Using a Toroidal Transducer as an Adjuvant Treatment for Placenta Accreta: A Preliminary Ex Vivo Study

BackgroundPlacenta accreta is an abnormal invasion of the placenta within the myometrium, which has increasing rate and could result in maternal mortality or morbidity. The objective of this study was to evaluate the feasibility of treating placenta accreta with high-intensity focused ultrasound (HIFU) using an ex vivo model. Material and methodsA toroidal HIFU transducer working at 2.5 MHz with an integrated ultrasound-imaging probe was used. Ex vivo experiments were performed in eight human placentae (from 39 to 40 weeks) within a configuration that mimicked clinical conditions as closely as possible. The fetal side of the placenta was placed in contact with the sterile envelope that covered the HIFU device to simulate the uterine serosa. HIFU lesions were studied on sonograms and macroscopically. ResultsIn total, 19 single HIFU lesions were created with the same exposure parameters for all of the lesions. The exposure time was 75 s. The acoustic power was 90 W. HIFU lesions were created at different distances (2, 6, 7 and 8 mm) from the uterine serosa by adjusting the thickness of the coupling water and thus, the distance between the HIFU emitters and placental tissues. All of the lesions were homogeneous and approximately spherical in shape. The two diameters of the HIFU lesions were on average 14.6±2.1 mm and 14.1±2.3 mm. Lesions were immediately visible on sonograms after each HIFU exposure as a hyperechoic region. The distance between the surface of the placenta and HIFU lesion as measured on ultrasound images was closely correlated with the same distance that was measured on gross pathology (r=0.89, p<0.05). ConclusionsThis study demonstrates that HIFU may be an interesting option for adjuvant treatment during a cesarean of placenta accreta. These results must be validated under real clinical conditions.

Two-year efficacy of single-session high-intensity focused ultrasound (HIFU) ablation of benign thyroid nodules.

Assessing the efficacy of single high-intensity focused ultrasound (HIFU) ablation in benign thyroid nodules beyond 12 months. One hundred and eight patients underwent single HIFU treatment. Extent of nodule shrinkage [by volume reduction ratio (VRR)] and obstructive symptom score [by 0-10 visual analogue scale (VAS)] were evaluated for 24 months after treatment. VRR (%) was calculated based on the formula: [baseline volume - volume at visit] / [baseline volume] × 100. Binary logistic regression was performed to evaluate factors associated with 24-month treatment success (VRR ≥ 50%). After treatment, the mean (± SD) VRR at 3, 6, 12 ,18 and 24 months were 51.32 ± 20.71%, 62.99 ± 22.05%, 68.66 ± 18.48%, 69.76 ± 17.88% and 70.41 ± 17.39%, respectively, while the median (IQR) VAS at baseline, 6, 12 and 24 months was gradually lowered from 4.0 (2.0), 2.0 (1.0), 2.0 (1.0) to 1.0 (2.0), respectively. Sixty-three (58.3%) nodules had a further volume reduction (i.e. > 4.5%) from 12 to 24 months, while 22 (20.4%) nodules had a volume increase of > 4.5% from 12 to 24 months. Small pre-ablation nodule volume was a significant determinant for treatment success at 24 months (OR=1.045, 95% CI=1.021-1.092, p = 0.038). A majority of nodules had further volume reduction beyond 12 months after single HIFU ablation, but since one-fifth of nodules had a notable volume increase beyond 12 months, a longer period of surveillance would be necessary. Small pre-ablation nodule volume was a significant factor determining 24-month treatment success. • Small but significant nodule shrinkage continues beyond 12 months after single treatment. • Obstructive symptom continues to improve beyond 12 months after single treatment • Smaller-sized nodules have a greater chance of treatment success at 24 months.

Sequential high intensity focused ultrasound (HIFU) ablation in the treatment of benign multinodular goitre: an observational retrospective study.

Assessing the efficacy and safety of sequential high-intensity focused ultrasound (HIFU) ablation in a multinodular goitre (MNG) by comparing them with single HIFU ablation. One hundred and four (84.6%) patients underwent single ablation of a single nodule (group I), while 19 (15.4%) underwent sequential ablation of two relatively-dominant nodules in a MNG (group II). Extent of shrinkage per nodule [by volume reduction ratio (VRR)], pain scores (by 0-10 visual analogue scale) during and after ablation, and rate of vocal cord palsy (VCP), skin burn and nausea/vomiting were compared between the two groups. All 19 (100%) sequential ablations completed successfully. The 3- and 6-month VRR of each nodule were comparable between the two groups (p > 0.05) and in group II, the 3- and 6-month VRR between the first and second nodules were comparable (p = 0.710 and p = 0.548, respectively). Pain score was significantly higher in group II in the morning after ablation (2.29 vs 1.15, p = 0.047) and nausea/vomiting occurred significantly more frequently in group II (15.8% vs 0.0%, p = 0.012). However, VCP and skin burn were comparable (p > 0.05). Sequential ablation had comparable efficacy and safety as single ablation. However, patients undergoing sequential ablation are at higher likelihood of pain in the following morning and nausea/vomiting after ablation. • Sequential HIFU ablation is well-tolerated in patients with two dominant thyroid nodules • More pain is experienced in the morning following sequential HIFU ablation • More nausea/vomiting is experienced following sequential HIFU ablation.

Combination therapeutic effects of high intensity focused ultrasound and Metformin for the treatment of adenomyosis.

Adenomyosis is a pathological gynaecological condition characterized by benign invasion of the endometrium into the myometrium. High intensity focused ultrasound (HIFU) is one of the most common therapeutic strategies for the treatment of adenomyosis. However, the efficacy of single HIFU therapy is insufficient for the treatment of patients with adenomyosis. In the present study, the efficacy of HIFU and metformin for the treatment of adenomyosis was analyzed in 274 patients with adenomyosis who were admitted to Jinan Maternity and Child Care Hospital. The results demonstrated that there was a significant reduction in menstrual flow and pain between patients who received HIFU and metformin, and those who received single HIFU treatment (P<0.01). Furthermore, the outcomes demonstrated that inflammatory cytokines levels were significantly lower compared with the baseline values (P<0.01). In conclusion, the outcomes of the current study indicate that combined HIFU and metformin treatment is more efficacious in patients with enlarged adenomyosis compared with single HIFU treatment.

Immediate effect and safety of HIFU single treatment for male subcutaneous fat reduction.

The increasing search for procedures for fat reduction is related to dissatisfaction with body shape. High-intensity focused ultrasound (HIFU) has been proven effective in body sculpting when used noninvasively to reduce subcutaneous fat and improve body contour. This study aimed to evaluate the immediate effect and safety of HIFU single treatment for male localized fat and body remodeling. Twenty-four male subjects (18 to 59years old) with BMI≤30kg/cm² and at least 2cm of abdominal fat received a single HIFU treatment session. Individuals were subjected to abdominal measurements before and after procedure. In addition, biochemical analyses of blood samples were performed to assess possible inflammatory effects or oxidative stress induction by the treatment. High-intensity focused ultrasound was found to be an effective treatment in reducing localized adiposities in the abdominal region. A significant decrease (0.6%) was observed in infraumbilical circumference of subjects submitted to HIFU single treatment when compared with control subjects. The laboratory parameters did not present any appreciable changes. This study further strengthens the current view that HIFU is an effective and safe tool for localized fat reduction.

High-intensity focused ablation (HIFU) of single benign thyroid nodule rarely alters underlying thyroid function

Background: High intensity focused ultrasound (HIFU) is a promising ablation technique for benign thyroid nodules. However, its effect on underlying thyroid function remains unknown. We aimed to evaluate the 6 months changes in serum thyroid stimulating hormone (TSH) and free thyroxine (FT4) after HIFU treatment.Methods: Eighty-three consecutive patients who underwent single HIFU ablation for symptomatic benign thyroid nodule were analysed. Eligible patients had serum TSH and FT4 checked before treatment (baseline), 1 week, 3 and 6 months following HIFU treatment. Primary endpoints were hypothyroidism (FT4 < 12 pmol/L) and hyperthyroidism (FT4 > 23 pmol/L) in the 6 months following treatment. To express extent of nodule ablation relative to the total gland volume, an ablation volume ratio was calculated by [(Ablated nodule volume/total thyroid volume)/(total thyroid volume)] × 100.Results: Relative to baseline, 1-week serum TSH significantly dropped (from 1.16 to 0.76 mIU/L, p < 0.001) while 1-week serum FT4 significantly rose (from 16.0 to 17.8 pmol/L, p < 0.001). However, 3- and 6-months TSH and FT4 did not changed significantly from baseline (p > 0.05). No patients developed hyperthyroidism while one (1.4%) developed hypothyroidism (FT4 = 11 pmol/L) at 3 months and 6 months. Interestingly, this patient had a previous lobectomy and an ablation volume ratio of 64.00%.Conclusions: Hypothyroidism following single HIFU ablation occurred rarely (1.4%) and resulted in little clinical relevance. Given that only one patient developed hypothyroidism following single HIFU ablation, it remains unclear how patients with different amount of parenchyma and relative extent of ablation may affect subsequent thyroid function.

Thermal Ablation of the Pancreas With Intraoperative High-Intensity Focused Ultrasound: Safety and Efficacy in a Porcine Model.

New focal destruction technologies such as high-intensity focused ultrasound (HIFU) may improve the prognosis of pancreatic ductal adenocarcinoma. Our objectives were to demonstrate the safety and efficacy of intraoperative pancreatic HIFU ablation in a porcine model. In a porcine model (N = 12), a single HIFU ablation was performed in either the body or tail of the pancreas, distant to superior mesenteric vessels. All animals were sacrificed on the eighth day. The primary objective was to obtain an HIFU ablation measuring at least 1 cm without premature death. In total, 12 HIFU ablations were carried out. These ablations were performed within 160 seconds and on average measured 20 (15-27) × 16 (8-26) mm. The primary objective was fulfilled in all but 1 pig. There were no premature deaths or severe complications. High-intensity focused ultrasound treatment was associated with a transitory increase in amylase and lipase levels, and pseudocysts were observed in half of the pigs without being clinically apparent. All ablations were well delimited at both gross and histological examinations. Intraoperative thermal destruction of porcine pancreas with HIFU is feasible. Reproducibility and safety have to be confirmed when applied close to mesenteric vessels and in long-term preclinical studies.

Single application of high-intensity focused ultrasound as primary therapy of localized prostate cancer: Treatment-related predictors of biochemical outcomes

ObjectiveRecent reports on high-intensity focused ultrasound (HIFU) treatment of localized prostate cancer suggest that preoperative risk groups of tumor recurrence are strong predictors of oncological outcomes. The purpose of this study is to determine the prognostic significance of treatment-related factors in relation to patient characteristics for biochemical outcomes after HIFU. MethodsThis retrospective single-center study included patients treated from December 2002 to December 2010 for localized prostate cancer with two generations of Ablatherm® HIFU devices (A1 and A2). All the patients underwent single HIFU treatment session under the concept of whole-gland therapy. Prostate surgery was performed before HIFU to downsize enlarged glands. Androgen deprivation therapy (ADT) was discontinued before HIFU. Biochemical failure (BCF) was defined as prostate specific antigen (PSA) nadir + 1.2 ng/mL (Stuttgart definition). Predictors of BCF were determined using Cox regression models. As covariates, patient-related factors (age, tumor characteristics, ADT) were compared with treatment-related factors (prostate volume, HIFU device generation, conduct of therapy, prostate edema, patient movement, anesthetic modalities). ResultsThree hundred and twenty-three (98.8%) out of 327 consecutive patients were evaluable for BCF. Median (interquartile range) follow-up was 51.2 (36.6–80.4) months. The overall BCF-rate was 23.8%. In multivariate analyses, higher initial PSA-values (Hazard ratio [HR]: 1.03; p < 0.001) and higher D'Amico risk stages (HR: 3.45; p < 0.001) were patient-related predictors of BCF. Regarding treatment-related factors, the A2 HIFU device was associated with a decreased risk of BCF (HR: 0.51; p = 0.007), while prostate edema had an adverse effect (HR: 1.8; p = 0.027). Short follow-up and retrospective study design are the primary limitations. ConclusionSuccess in a single HIFU session depends not merely on tumor characteristics, but also on treatment-related factors. Ablation is more efficacious with the technically advanced A2 HIFU device. Heat-induced prostate edema might adversely affect the outcome.

Rapid method for assessing relative tissue stiffness using MR acoustic radiation force imaging

ABSTRACTAcoustic radiation force imaging (ARFI) has been suggested as a tool for remote palpation. In this study an MR‐ARFI sequence, based on echo‐planar‐imaging, is introduced, for remote semi‐quantitative assessment of local tissue stiffness. The focal zone of a high intensity focused ultrasound (HIFU) is positioned at the region of interest and a single HIFU burst is transmitted. The method then measures the entire time integral of the resulting displacement at the focal zone. Combining this measurement with the Kelvin–Voigt viscoelastic tissue model, a local stiffness index is obtained. The method was implemented on gel phantoms, ex‐vivo bovine brain and chicken liver specimens. The results have demonstrated the ability to evaluate the relative local stiffness within 600 ms and to distinguish between different tissues on the basis of their stiffness index. The method may potentially be used for remote palpation of suspicious regions for diagnostic purposes, or for providing a mechanical feedback during therapeutic procedures, such as thermal ablation.

Single high intensity focused ultrasound session as a whole gland primary treatment for clinically localized prostate cancer: 10-year outcomes.

Objectives. To assess the treatment outcomes of a single session of whole gland high intensity focused ultrasound (HIFU) for patients with localized prostate cancer (PCa). Methods. Response rates were defined using the Stuttgart and Phoenix criteria. Complications were graded according to the Clavien score. Results. At a median follow-up of 94months, 48 (44.4%) and 50 (46.3%) patients experienced biochemical recurrence for Phoenix and Stuttgart definition, respectively. The 5- and 10-year actuarial biochemical recurrence free survival rates were 57% and 40%, respectively. The 10-year overall survival rate, cancer specific survival rate, and metastasis free survival rate were 72%, 90%, and 70%, respectively. Preoperative high risk category, Gleason score, preoperative PSA, and postoperative nadir PSA were independent predictors of oncological failure. 24.5% of patients had self-resolving LUTS, 18.2% had urinary tract infection, and 18.2% had acute urinary retention. A grade 3b complication occurred in 27 patients. Pad-free continence rate was 87.9% and the erectile dysfunction rate was 30.8%. Conclusion. Single session HIFU can be alternative therapy for patients with low risk PCa. Patients with intermediate risk should be informed about the need of multiple sessions of HIFU and/or adjuvant treatments and HIFU performed very poorly in high risk patients.

Large Volume Coagulation Utilizing Multiple Cavitation Clouds Generated by Array Transducer Driven by 32 Channel Drive Circuits

High-intensity focused ultrasound (HIFU) treatment is a noninvasive treatment, in which focused ultrasound is generated outside the body and coagulates a diseased tissue. The advantage of this method is minimal physical and mental stress to the patient, and the disadvantage is the long treatment time caused by the smallness of the therapeutic volume by a single exposure. To improve the efficiency and shorten the treatment time, we are focusing attention on utilizing cavitation bubbles. The generated microbubbles can convert the acoustic energy into heat with a high efficiency. In this study, using the class D amplifiers, which we have developed, to drive the array transducer, we demonstrate a new method to coagulate a large volume by a single HIFU exposure through generating cavitation bubbles distributing in a large volume and vibrating all of them. As a result, the coagulated volume by the proposed method was 1.71 times as large as that of the conventional method.

Single application of high‐intensity focused ultrasound as a first‐line therapy for clinically localized prostate cancer: 5‐year outcomes

Study Type--Therapy (case series) Level of Evidence 4. What's known on the subject? and What does the study add? High-intensity focused ultrasound (HIFU) therapy has been proposed for the treatment of localized prostate cancer (PCa) for all risk levels of tumour recurrence. The study adds data on the efficacy of a single HIFU application in the treatment of PCa with different risks of recurrence. Durable cancer control was achieved in 81.7% of patients with low-risk disease, with rates of efficacy declining in intermediate- and high-risk tumours. The data suggest that the principal domain for minimal invasive HIFU should be low-risk disease. • To report cancer control results after a single application of high-intensity focused ultrasonography (HIFU) in patients with localized prostate cancer (PCa), stratified by tumour recurrence risk according to D'Amico risk classification. • In a retrospective single-centre study, we analysed the outcomes of patients with localized PCa who were treated with curative intent between December 2002 and October 2006 using an Ablatherm HIFU device (EDAP-TMS, France). • Transurethral resection of the prostate or adenomectomy were performed before HIFU to downsize large prostate glands. • Oncological failure was determined by the occurrence of biochemical relapse, positive biopsy and/or metastasis. Biochemical relapse was defined as a PSA nadir +1.2 ng/mL (Stuttgart definition), or as a rise in PSA level to ≥ 0.5 ng/mL if PSA doubling time was ≤ 6 months. Kaplan-Meier analysis was performed for survival estimates. • A total of 191 consecutive patients were included in the study. The median (range) patient age was 69.7 (51-82) years, and 38, 34 and 28% of these patients were in the low-, intermediate- and high-risk groups, respectively. • The median (range) follow-up was 52.8 (0.2-79.8) months. • At 5 years, overall and cancer-specific survival rates were 86.3% and 98.4%, respectively. • Stratified by risk group, negative biopsy rates were 84.2%, 63.6%, and 67.5% (P = 0.032), 5-year biochemical-free survival rates were 84.8%, 64.9% and 54.9% (P< 0.01), and 5-year disease-free survival rates were 81.7%, 53.2% and 51.2% (P < 0.01), respectively. • Single-session HIFU is recommended as a curative approach in elderly patients with low-risk PCa. Patients at higher risk of tumour progression should be counselled regarding the likely need for salvage therapy, including repeat HIFU.

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

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. 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. 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 (Spearman's 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). 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.

Measurement of Angle of Ultrasound Propagation from Phase

Acoustic field calibrations often use Fast Fourier Transforms (FFT) to quantify the spectral amplitude components of detected acoustic waveforms. The ability of FFTs to provide phase information is often overlooked. This phase data may be useful in determining the angle of propagation of the ultrasound beam. The angle of propagation at the focal peak (and any other point in the field) can be calculated easily and quickly without additional measurement, and may be the quickest and most accurate method of aligning the sound axis with respect to the beamplotting system's co-ordinates.Acoustic fields have been measured experimentally using a system capable of waveform acquisition. Measurements were made using a fibre-optic hydrophone (Precision Acoustics, UK) which provided spatial resolution of <100 μm. Two operating configurations of a 10 strip array HIFU (high intensity focused ultrasound) transducer were tested, as was a single element HIFU device. Theoretical pressure and phase distributions for these transducers were predicted using a linear acoustic field model. Results show that for the single element, radially symmetric device, beam alignment measurements using phase data at the focal peak are in agreement with the more conventional method based on finding the on-axis peak positions. In the case of a transducer with a number of elements de-activated to produce an asymmetric ultrasound source, the angle of propagation at the focal peak was altered, indicating a change in performance of the transducer which otherwise might not have been detected using the "on-axis peaks" method. Simulations agreed with the experimental data.

Real-Time Monitoring of High-Intensity Focused Ultrasound Lesion Formation Using Acousto-Optic Sensing

High-intensity focused ultrasound (HIFU) is a promising modality that is used to noninvasively ablate soft tissue tumors. Nevertheless, real-time treatment monitoring with diagnostic ultrasound still poses a significant challenge since tissue necrosis, in the absence of cavitation or boiling, provides little acoustic contrast with normal tissue. In comparison, the optical properties of tissue are significantly altered accompanying lesion formation. A photorefractive crystal-based acousto-optic (AO) sensing system that uses a single HIFU transducer to simultaneously generate tissue necrosis and pump the AO interaction is used to monitor the real-time optical changes associated with thermal lesions induced in chicken breast ex vivo. It is found that the normalized change in AO response increases proportionally with the volume of necrosis. This study demonstrates AO sensing can identify the onset and growth of lesion formation in real time and, when used as feedback to guide exposures, results in more predictable lesion formation. (E-mails: laipuxiang@gmail.com or ronroy@bu.edu)

Development of Bladder Outlet Obstruction After a Single Treatment of Prostate Cancer with High-Intensity Focused Ultrasound: Experience with 226 Patients

To investigate the occurrence of bladder outlet obstruction (BOO) after high-intensity focused ultrasound (HIFU) therapy of prostate cancer, the need for secondary transurethral interventions for BOO, and the benefit of transurethral resection of the prostate (TURP) before HIFU. After a single HIFU treatment between 2002 and 2007, 226 consecutive patients were examined and followed at least 2 years. The Ablatherm Maxis and the Integrated Imaging devices were used. The sites of BOO were recorded. Median follow-up after HIFU was 52 months (range 24-80 mos). BOO developed in 58 (25.66%) patients. Repeated BOO episodes were observed in 27 (11.94%), three to seven episodes in 13 (5.75%) patients. Patients with repeated BOO were older than patients with singular BOO (71.75 ± 4.97 vs 68.18 ± 5.03; P = 0.024). In primary BOO, multiple sites of obstruction were more often involved than in repeated BOO (25/58 vs 8/27). Conversely, isolated bladder neck stenosis was predominantly found in patients with ≥two episodes of BOO. The rate of primary BOO was significantly different between patients who had undergone TURP the same day as HIFU or within 2 days of HIFU (33/96; 34.38%) and patients with TURP more than 1 month (16/89; 17.98%) before HIFU (P = 0.032). BOO occurred in 21.95% (9/41) of the patients who were treated with HIFU only. BOO after HIFU is common, particularly affecting the bladder neck. The risk of repeated BOO is associated with age. A longer interval between TURP and HIFU (>1 month) might reduce the risk for the development of BOO.