MR-Guided Focused Ultrasound Thalamotomy in the Setting of Aneurysm Clip.

We report on a 75-year-old woman with a history of right MCA aneurysm clipping and medically refractive right-hand tremor. We successfully performed focused ultrasound thalamotomy of the left ventral intermediate nucleus under MR imaging-guidance at 3T. A thorough pretreatment evaluation of MR thermometry was critical to ensure that adequate precision could be achieved at the intended target.

Non-invasive central nervous system assessment of a porcine model of neuropathic pain demonstrates increased latency of somatosensory-evoked potentials.

Background: The study of chronic pain and its treatments requires a robust animal model with objective and quantifiable metrics. Porcine neuropathic pain models have been assessed with peripheral pain recordings and behavioral responses, but thus far central nervous system electrophysiology has not been investigated. This work aimed to record non-invasive, somatosensory-evoked potentials (SEPs) via electroencephalography in order to quantitatively assess chronic neuropathic pain induced in a porcine model.

Influence of cerebrospinal fluid on power absorption during transcranial magnetic resonance-guided focused ultrasound treatment.

Background: Ultrasound beam aberration correction is vital when focusing ultrasound through the skull bone in transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) applications. Current methods make transducer element phase adjustments to compensate for the variation in skull properties (shape, thickness, and acoustic properties), but do not account for variations in the internal brain anatomy.

Purpose: Our objective is to investigate the effect of cerebrospinal fluid (CSF) and brain anatomy on beam focusing in tcMRgFUS treatments.

The Back Pain Consortium (BACPAC) Research Program: Structure, Research Priorities, and Methods.

In 2019, the National Health Interview survey found that nearly 59% of adults reported pain some, most, or every day in the past 3 months, with 39% reporting back pain, making back pain the most prevalent source of pain, and a significant issue among adults. Often, identifying a direct, treatable cause for back pain is challenging, especially as it is often attributed to complex, multifaceted issues involving biological, psychological, and social components. Due to the difficulty in treating the true cause of chronic low back pain (cLBP), an over-reliance on opioid pain medications among cLBP patients has developed, which is associated with increased prevalence of opioid use disorder and increased risk of death.

Feasibility of non-invasive recording of somatosensory evoked potential in pigs.

Background: Non-invasive measurement of somatosensory-evoked potentials (SEP) in a large animal model is important to translational cognitive research. We sought to develop a methodology for neurophysiological recording via a transcranial electroencephalography (EEG) cap under an effective sedative regimen with dexmedetomidine, midazolam, and butorphanol that will produce sedation instead of anesthesia while not compromising data quality.

Results: Pigs received intramuscular dexmedetomidine, midazolam, and butorphanol for SEP assessment with peroneal nerve stimulation.

Anatomic thermochromic tissue-mimicking phantom of the lumbar spine for pre-clinical evaluation of MR-guided focused ultrasound (MRgFUS) ablation of the facet joint.

Objective: To develop a thermochromic tissue-mimicking phantom (TTMP) with an embedded 3D-printed bone mimic of the lumbar spine to evaluate MRgFUS ablation of the facet joint and medial branch nerve.

Materials And Methods: Multiple 3D-printed materials were selected and characterized by measurements of speed of sound and linear acoustic attenuation coefficient using a through-transmission technique. A 3D model of the lumbar spine was segmented from a de-identified CT scan, and 3D printed.

T2 mapping as a predictor of nonperfused volume in MRgFUS treatment of desmoid tumors.

The objective of this study was to develop an alternative method of non-contrast monitoring of tissue ablation during focused ultrasound treatment. Desmoid tumors are benign but locally aggressive soft tissue tumors that arise from fibroblast cells. Magnetic resonance-guided focused ultrasound (MRgFUS) has emerged as an alternative to conventional therapies, showing promising results in reduction of tumor volume without significant side effects.

The impact of technical parameters on ablation volume during MR-guided focused ultrasound of desmoid tumors.

Purpose: Desmoid tumors are benign, locally aggressive soft tissue tumors derived from fibroblasts. Magnetic resonance-guided focused ultrasound (MRgFUS) is a safe and effective treatment for desmoid tumors. The purpose of this study was to retrospectively review the MRgFUS treatments of desmoid tumors at our institution to determine which technical treatment parameters contributed most significantly to the accumulation of thermal dose.

MR thermometry-guided ultrasound hyperthermia of user-defined regions using the ExAblate prostate ablation array.

Background: Hyperthermia therapy (HT) has shown to be an effective adjuvant to radiation, chemotherapy, and immunotherapy. In order to be safe and effective, delivery of HT requires maintenance of target tissue temperature within a narrow range (40-44 °C) for 30-60 min, which necessitates conformal heat delivery and accurate temperature monitoring. The goal of this project was to develop an MR thermometry-guided hyperthermia delivery platform based upon the ExAblate prostate array that would achieve uniform stable heating over large volumes within the prostate, while allowing the user to precisely control the power deposition patterns and shape of the region of treatment (ROT).

Effect of Sonication Duration and Power on Ablation Depth During MR-Guided Focused Ultrasound of Bone.

Purpose: To evaluate the effect of differences in sonication duration and power on the size of postcontrast ablation zone following magnetic resonance-guided focused ultrasound (MRgFUS) of bone in a swine femoral bone model.

Materials And Methods: Experimental procedures received approval from the Institutional Committee on Animal Research. MRgFUS was used to create two thermal lesions in the left femur of six pigs.

MRgFUS for desmoid tumors within the thigh: early clinical experiences.

Background: Desmoid tumors are benign but locally aggressive non-malignant tumors derived from fibroblasts. Surgery, chemotherapy, and radiation therapy have been the mainstay of treatment, but recurrence is common and side effects can result in significant morbidity. In this case series, we highlight our experiences performing treatments in the thigh, including strategies for optimizing ablation size and safety.

T2-based temperature monitoring in bone marrow for MR-guided focused ultrasound.

Background: Current clinical protocols for MR-guided focused ultrasound (MRgFUS) treatment of osseous lesions, including painful bone metastases and osteoid osteomas, rely on measurement of the temperature change in adjacent muscle to estimate the temperature of the bone. The goal of this study was to determine if T2-based thermometry could be used to monitor the temperature change in bone marrow during focused ultrasound ablation of bone lesions.

Methods: We investigated the dependence of T2 on temperature in ex vivo bovine yellow bone marrow at 3T and studied the influence of acquisition parameters on the T2 measurements.

Evaluation of MRI protocols for the assessment of lumbar facet joints after MR-guided focused ultrasound treatment.

Background: MR-guided focused ultrasound (MRgFUS) might be a very safe and effective minimally invasive technique to treat facet joint pain caused by arthritis and other degenerative changes. However, there are still safety concerns for this treatment and challenges regarding MR imaging and temperature mapping due to susceptibility effects between the bone and soft tissue near the joint, which has resulted in poor MR image quality. The goal of this research was to evaluate multiple magnetic resonance imaging (MRI) pulse sequences for characterizing ablated lumbar facet joint lesions created by high-intensity focused ultrasound (FUS) and compare the findings to histological tissue assessment.

PROMISe trial: a pilot, randomized, placebo-controlled trial of magnetic resonance guided focused ultrasound for uterine fibroids.

Objective: To evaluate the feasibility of a full-scale placebo-controlled trial of magnetic resonance-guided focused ultrasound for fibroids (MRgFUS) and obtain estimates of safety and efficacy.

Design: Pilot, randomized, placebo-controlled trial.

Setting: University medical center.

Quantifying temperature-dependent T1 changes in cortical bone using ultrashort echo-time MRI.

Purpose: To demonstrate the feasibility of using ultrashort echo-time MRI to quantify T1 changes in cortical bone due to heating.

Methods: Variable flip-angle T1 mapping combined with 3D ultrashort echo-time imaging was used to measure T1 in cortical bone. A calibration experiment was performed to detect T1 changes with temperature in ex vivo cortical bone samples from a bovine femur.

T2-based temperature monitoring in abdominal fat during MR-guided focused ultrasound treatment of patients with uterine fibroids.

Background: Near-field heating is a potential problem in focused ultrasound treatments, as it can result in thermal injury to skin, subcutaneous fat, and other tissues. Our goals were to determine if T2-based temperature mapping could be used reliably to measure near-field heating in adipose tissue and whether it is practical to perform such mapping during focused ultrasound treatments.

Methods: We investigated the dependence of T2 on temperature in ex vivo adipose tissue at 3T using a double-echo fast spin echo (FSE) sequence.

International consensus on use of focused ultrasound for painful bone metastases: Current status and future directions.

Focused ultrasound surgery (FUS), in particular magnetic resonance guided FUS (MRgFUS), is an emerging non-invasive thermal treatment modality in oncology that has recently proven to be effective for the palliation of metastatic bone pain. A consensus panel of internationally recognised experts in focused ultrasound critically reviewed all available data and developed consensus statements to increase awareness, accelerate the development, acceptance and adoption of FUS as a treatment for painful bone metastases and provide guidance towards broader application in oncology. In this review, evidence-based consensus statements are provided for (1) current treatment goals, (2) current indications, (3) technical considerations, (4) future directions including research priorities, and (5) economic and logistical considerations.

Bone remodeling after MR imaging-guided high-intensity focused ultrasound ablation: evaluation with MR imaging, CT, Na(18)F-PET, and histopathologic examination in a swine model.

Purpose: To serially monitor bone remodeling in the swine femur after magnetic resonance (MR) imaging-guided high-intensity focused ultrasound (HIFU) ablation with MR imaging, computed tomography (CT), sodium fluorine 18 (Na(18)F)-positron emission tomography (PET), and histopathologic examination, as a function of sonication energy.

Materials And Methods: Experimental procedures received approval from the local institutional animal care and use committee. MR imaging-guided HIFU was used to create distal and proximal ablations in the right femurs of eight pigs.

MRI-guided high-intensity focused ultrasound ablation of bone: evaluation of acute findings with MR and CT imaging in a swine model.

Purpose: To evaluate hyperacute (<1 hour) changes on magnetic resonance (MR) and computed tomography (CT) imaging following MR-guided high-intensity focused ultrasound (MRgHIFU) in a swine bone model as a function of sonication number and energy.

Materials And Methods: Experimental procedures received approval from the local Institutional Animal Care and Use Committee. MRgHIFU was used to create distal and proximal ablations in the right femur of eight pigs.

Model-based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR-guided endorectal HIFU ablation array.

Purpose: Feasibility of targeted and volumetric hyperthermia (40-45 °C) delivery to the prostate with a commercial MR-guided endorectal ultrasound phased array system, designed specifically for thermal ablation and approved for ablation trials (ExAblate 2100, Insightec Ltd.), was assessed through computer simulations and tissue-equivalent phantom experiments with the intention of fast clinical translation for targeted hyperthermia in conjunction with radiotherapy and chemotherapy.

Methods: The simulations included a 3D finite element method based biothermal model, and acoustic field calculations for the ExAblate ERUS phased array (2.

Approaches for modelling interstitial ultrasound ablation of tumours within or adjacent to bone: theoretical and experimental evaluations.

Purpose: The objectives of this study were to develop numerical models of interstitial ultrasound ablation of tumours within or adjacent to bone, to evaluate model performance through theoretical analysis, and to validate the models and approximations used through comparison to experiments.

Methods: 3D transient biothermal and acoustic finite element models were developed, employing four approximations of 7-MHz ultrasound propagation at bone/soft tissue interfaces. The various approximations considered or excluded reflection, refraction, angle-dependence of transmission coefficients, shear mode conversion, and volumetric heat deposition.

Clinical applications for magnetic resonance guided high intensity focused ultrasound (MRgHIFU): present and future.

It has been well known for decades that high intensity focused ultrasound (HIFU) generates heat in tissues resulting in coagulative necrosis. Implementation, however, has been slow, due to difficulties with finding an appropriate imaging modality that could not only guide treatment, but also provide real-time thermal feedback. These problems have been overcome with the newest magnetic resonance-guided high intensity focused ultrasound systems (MRgHIFU).

Comparison of temperature processing methods for monitoring focused ultrasound ablation in the brain.

Purpose: To investigate the performance of different reconstruction methods for monitoring temperature changes during transcranial magnetic resonance imaging (MRI)-guided focused ultrasound (MRgFUS).

Materials And Methods: Four different temperature reconstruction methods were compared in volunteers (without heating) and patients undergoing transcranial MRgFUS: single baseline subtraction, multibaseline subtraction, hybrid single baseline/referenceless reconstruction, and hybrid multibaseline/referenceless reconstruction. Absolute temperature error and temporal temperature uncertainty of the different reconstruction methods were analyzed and compared.

Hybrid referenceless and multibaseline subtraction MR thermometry for monitoring thermal therapies in moving organs.

Purpose: Magnetic resonance thermometry using the proton resonance frequency (PRF) shift is a promising technique for guiding thermal ablation. For temperature monitoring in moving organs, such as the liver and the heart, problems with motion must be addressed. Multi-baseline subtraction techniques have been proposed, which use a library of baseline images covering the respiratory and cardiac cycle.