Cavitation-based third ventriculostomy using MRI-guided focused ultrasound.

OBJECT: Transcranial focused ultrasound is increasingly being investigated as a minimally invasive treatment for a range of intracranial pathologies. At higher peak rarefaction pressures than those used for thermal ablation, focused ultrasound can initiate inertial cavitation and create holes in the brain by fractionation of the tissue elements. The authors investigated the technical feasibility of using MRI-guided focused ultrasound to perform a third ventriculostomy as a possible noninvasive alternative to endoscopic third ventriculostomy for hydrocephalus. METHODS: A craniectomy was performed in male pigs weighing 13-19 kg to expose the supratentorial brain, leaving the dura mater intact. Seven pigs were treated through the craniectomy, while 2 pigs were treated through ex vivo human skulls placed in the beam path. Registration and targeting was done using T2-weighted MRI sequences. For transcranial treatments a CT scan was used to correct the beam from aberrations due to the skull and maintain a small, high-intensity focus. Sonications were performed at both 650 kHz and 230 kHz at a range of intensities, and the in situ pressures were estimated both from simulations and experimental data to establish a threshold for tissue fractionation in the brain. RESULTS: In craniectomized animals at 650 kHz, a peak pressure ≥ 22.7 MPa for 1 second was needed to reliably create a ventriculostomy. Transcranially at this frequency the ExAblate 4000 was unable to generate the required intensity to fractionate tissue, although cavitation was initiated. At 230 kHz, ventriculostomy was successful through the skull with a peak pressure of 8.8 MPa. CONCLUSIONS: This is the first study to suggest that it is possible to perform a completely noninvasive third ventriculostomy using ultrasound. This may pave the way for future studies and eventually provide an alternative means for the creation of CSF communications in the brain, including perforation of the septum pellucidum or intraventricular membranes.

MR-guided focused ultrasound surgery, present and future.

MR-guided focused ultrasound surgery (MRgFUS) is a quickly developing technology with potential applications across a spectrum of indications traditionally within the domain of radiation oncology. Especially for applications where focal treatment is the preferred technique (for example, radiosurgery), MRgFUS has the potential to be a disruptive technology that could shift traditional patterns of care. While currently cleared in the United States for the noninvasive treatment of uterine fibroids and bone metastases, a wide range of clinical trials are currently underway, and the number of publications describing advances in MRgFUS is increasing. However, for MRgFUS to make the transition from a research curiosity to a clinical standard of care, a variety of challenges, technical, financial, clinical, and practical, must be overcome. This installment of the Vision 20∕20 series examines the current status of MRgFUS, focusing on the hurdles the technology faces before it can cross over from a research technique to a standard fixture in the clinic. It then reviews current and near-term technical developments which may overcome these hurdles and allow MRgFUS to break through into clinical practice.

Comparison of ultrasonically activated scalpel and traditional technique in radial artery harvesting; an electron microscopic evaluation.

OBJECTIVE: Use of the radial artery (RA) as a conduit in coronary artery bypass grafting (CABG) has become increasingly popular in recent years. The aim of this prospective randomized study is to determine how the endothelial wall and blood flow of RA are differently affected with the usages of ultrasonic scalpel and conventional electrocautery in addition to effects of hypothermia and storage solutions. Histopathologic study was achieved by electron microscope to evaluate endothelium of the grafts. METHODS: Between 2008 and 2009, 182 patients with coronary artery diseases were operated for coronary artery revascularization. The radial arteries were harvested for 40 of these patients and divided into two groups depending on the use of the ultrasonic cautery (UC) (n=20) and the high-frequency electrocautery (EC) (n=20). Patients were divided into two subgroups according to the storage media of the graft. RA was preserved in situ at room temperature (Group 1) and normothermic organ bath (NOB) (Group 2). Harvesting time, use of hemostatic clips, frequency of spasm, in situ free flow, temperature and endothelial damage were compared between the two groups. Statistical analysis was performed using one-way ANOVA, Friedman and unpaired t tests. RESULTS: In all groups, blood flows were significantly decreased as parallel to the local temperatures. Second and third phase flows were similar in group EC1 and UC1 (p>0.05). Free flow was increased in group UC+NOB when comparing with only EC group (60.4±9.83 ml/min and 40.8±7.50 ml/min, p<0.001), whereas the graft preparing time "t2" was shorter in group EC than UC (10.9±2.42 min and 15.2±1.31 min, p<0.01). Nonetheless scoring of the groups in terms of endothelial cell structure and mitochondrial morphological changes did not show any significant difference. CONCLUSION: If endothelial integrity of the RA can be preserved along with the application of systemic temperature (NOB), regardless of harvesting technique, it provides better flow rates.