Avinash Eranki

Boiling histotripsy lesion characterization on a clinical magnetic resonance imaging-guided high intensity focused ultrasound system.

Purpose High intensity focused ultrasound (HIFU) is a non-invasive therapeutic technique that can thermally ablate tumors. Boiling histotripsy (BH) is a HIFU approach that can emulsify tissue in a few milliseconds. Lesion volume and temperature effects for different BH sonication parameters are currently not well characterized. In this work, lesion volume, temperature distribution, and area of lethal thermal dose were characterized for varying BH sonication parameters in tissue-mimicking phantoms (TMP) and demonstrated in ex vivo tissues. Methods The following BH sonication parameters were varied using a clinical MR-HIFU system (Sonalleve V2, Philips, Vantaa, Finland): acoustic power, number of cycles/pulse, total sonication time, and pulse repetition frequency (PRF). A 3×3×3 pattern was sonicated inside TMP’s and ex vivo tissues. Post sonication, lesion volumes were quantified using 3D ultrasonography and temperature and thermal dose distributions were analyzed offline. Ex vivo tissues were sectioned and stained with H&E post sonication to assess tissue damage. Results Significant increase in lesion volume was observed while increasing the number of cycles/pulse and PRF. Other sonication parameters had no significant effect on lesion volume. Temperature full width at half maximum at the end of sonication increased significantly with all parameters except total sonication time. Positive correlation was also found between lethal thermal dose and lesion volume for all parameters except number of cycles/pulse. Gross pathology of ex vivo tissues post sonication displayed either completely or partially damaged tissue at the focal region. Surrounding tissues presented sharp boundaries, with little or no structural damage to adjacent critical structures such as bile duct and nerves. Conclusion Our characterization of effects of HIFU sonication parameters on the resulting lesion demonstrates the ability to control lesion morphologic and thermal characteristics with a clinical MR-HIFU system in TMP’s and ex vivo tissues. We demonstrate that this system can produce spatially precise lesions in both phantoms and ex vivo tissues. The results provide guidance on a preliminary set of BH sonication parameters for this system, with a potential to facilitate BH translation to the clinic.

Comparison of Noninvasive High-Intensity Focused Ultrasound with Radiofrequency Ablation of Osteoid Osteoma

Objective To evaluate clinical feasibility and safety of magnetic resonance imaging‐guided high‐intensity focused ultrasound (MR‐HIFU) treatment of symptomatic osteoid osteoma and to compare clinical response with standard of care treatment. Study design Nine subjects with radiologically confirmed, symptomatic osteoid osteoma were treated with MR‐HIFU in an institutional review board–approved clinical trial. Treatment feasibility and safety were assessed. Clinical response was evaluated in terms of analgesic requirement, visual analog scale pain score, and sleep quality. Anesthesia, procedure, and recovery times were recorded. This MR‐HIFU group was compared with a historical control group of 9 consecutive patients treated with radiofrequency ablation. Results Nine subjects (7 male, 2 female; 16 ± 6 years) were treated with MR‐HIFU without technical difficulties or any serious adverse events. There was significant decrease in their median pain scores 4 weeks within treatment (6 vs 0, P < .01). Total pain resolution and cessation of analgesics were achieved in 8 of 9 patients after 4 weeks. In the radiofrequency ablation group, 9 patients (8 male, 1 female; 10 ± 6 years) were treated in routine clinical practice. All 9 demonstrated complete pain resolution and cessation of medications by 4 weeks with a significant decrease in median pain scores (9 vs 0, P < .001). One developed a second‐degree skin burn, but there were no other adverse events. Procedure times and treatment charges were comparable between the 2 groups. Conclusion This pilot study shows that MR‐HIFU treatment of osteoid osteoma refractory to medical therapy is feasible and can be performed safely in pediatric patients. Clinical response is comparable with standard of care treatment but without any incisions or exposure to ionizing radiation. Trial registration ClinicalTrials.gov NCT02349971

Technical aspects of osteoid osteoma ablation in children using MR-guided high intensity focussed ultrasound

Abstract Background: Osteoid osteoma (OO) is a painful bone tumour occurring in children and young adults. Magnetic resonance imaging-guided high intensity focussed ultrasound (MR-HIFU) allows non-invasive treatment without ionising radiation exposure, in contrast to the current standard of care treatment with radiofrequency ablation (RFA). This report describes technical aspects of MR-HIFU ablation in the first 8 paediatric OO patients treated in a safety and feasibility clinical trial (total enrolment of up to 12 patients). Materials and methods: OO lesions and adjacent periosteum were treated with MR-HIFU ablation in 5–20 sonications (sonication duration = 16–48 s, frequency = 1.2 MHz, acoustic power = 20–160 W). Detailed treatment workflow, patient positioning and coupling strategies, as well as temperature and tissue perfusion changes were summarised and correlated. Results: MR-HIFU ablation was feasible in all eight cases. Ultrasound standoff pads were shaped to conform to extremity contours providing acoustic coupling and aided patient positioning. The energy delivered was 10 ± 7 kJ per treatment, raising maximum temperature to 83 ± 3 °C. Post ablation contrast-enhanced MRI showed ablated volumes ranging 0.46–19.4 cm3 extending further into bone (7 ± 4 mm) than into soft tissue (4 ± 6 mm, p = 0.01, Mann–Whitney). Treatment time ranged 30–86 min for sonication and 160 ± 40 min for anaesthesia. No serious treatment-related adverse events were observed. Complete pain relief with no medication occurred in 7/8 patients within 28 days following treatment. Conclusions: MR-HIFU ablation of painful OO appears technically feasible in children and it may become a non-invasive and radiation-free alternative for painful OO. Therapy success, efficiency, and applicability may be improved through specialised equipment designed more specifically for extremity bone ablation.

Treatment planning and patient positioning for MR-guided high intensity focused ultrasound treatment: a systematic approach

Treatment duration as well as time spent on patient positioning imposes limitations on therapeutic use of MR-guided High Intensity Focused Ultrasound (MR-HIFU). Reduction of overall treatment time is especially important in potential pediatric applications and in other cases where general anesthesia must be used, due to the risks associated with prolonged anesthesia. Typically, up to 4 hours are allotted for the procedure, with patient positioning and treatment planning requiring an hour or more. If re-positioning is required during treatment, acquisition of needed images and re-planning of treatment may require 30 minutes or longer before ablation can resume. These delays limit the total time allowed for treatment, limiting the size of tumors that can be treated and increasing the risks as well as the cost of the procedure. The aim of this study is to evaluate the information needed to accurately plan MR-HIFU ablation of solid extremity tumors and to rationally design a practical approach to patient positioning for such treatments.

The optimization of treatment planning and ablation rate improvements on feasibility of pediatric MR-HIFU applications

Magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) ablation provides a precise, non-invasive treatment for lesions in adults. In children, MR-HIFU’s potential remains largely unexplored, though its non-invasive and non-ionizing nature holds promise. Yet, pediatric patients pose challenges affecting treatment: young children require general anesthesia, exhibit wide ranges of anatomy, and have varying lesion sizes and locations. These demonstrate a need for standardized treatment approaches and physical aids to optimize patient position, reduce time-intensive repositioning, and thus reduce overall treatment time. Further improvement of ablation rate and reduction of risk are also possible via improved monitoring of skin temperature during ablation and mild hyperthermia. Improvements in treatment planning and volumetric rate may save time and allow for treatment of larger lesions, increase patient throughput, and possibly increase efficacy and lower cost. This study aims to quantify and examine how such improvements could increase the time allocated for direct ablation and produce better outcomes.

Optical measurement of skin temperature in MR-HIFU

MR-guided high-intensity focused ultrasound (MR-HIFU) treatments may cause skin heating in the vicinity of the treatment site. Current MR thermometry methods do not provide reliable measurements of skin temperature either during the sonication or during the cool-down periods between sonications. These technical challenges require additional pauses to decrease the likelihood of skin burns, thus impacting treatment duration. Therefore, quantitative, accurate, and rapid techniques are needed to measure surface skin temperature during HIFU treatment. This study aims to develop an optical method that detects temperature changes at the skin surface to maintain a safe skin temperature during treatment and to reduce pauses between sonications.