Transcranial Magnetic Resonance Imaging– Guided Focused Ultrasound Surgery of Brain Tumors

Abstract

Objective This work evaluated the clinical feasibility of transcranial MRI-guided focused ultrasound surgery (TcMRgFUS). Methods In initial trials in three glioblastoma patients, multiple focused ultrasound exposures were applied up to maximum acoustic power available. Offline analysis of the MR temperature images evaluated the temperature changes at the focus and brain surface. Instrumentation The method combines a hemispherical phased array transducer and patient-specific treatment planning based on acoustic models with feedback control based on MR temperature imaging to overcome the effects of the skull and allow for controlled and precise thermal ablation in the brain. Technical Development TcMRgFUS offers a potential noninvasive alternative to surgical resection. Results We found that it was possible to focus an ultrasound beam transcranially into the brain and to visualize the heating with MR temperature imaging. While we were limited by the device power available at the time and thus appeared to not achieve thermal coagulation, extrapolation of the temperature measurements at the focus and on the brain surface suggests that thermal ablation will be possible with this device without overheating the brain surface, with some possible limitation on the treatment envelope. Conclusion While significant hurdles remain, these findings are a major step forward in producing a completely noninvasive alternative to surgical resection for brain disorders.

Imaging Findings in MR Imaging-Guided Focused Ultrasound Treatment for Patients with Essential Tremor

“…[1][2][3][4][5][6][7] MR imaging-guided focused sonography is now accepted in the treatment of soft-tissue disorders, including prostate cancer and uterine fibroids. Intracranial applications for brain tumors 8,9 and neuropathic pain syndromes 10,11 are currently under investigation. More recently, MR imaging-guided focused sonography was tested in a clinical trial as a treatment for essential tremor.…”

First Non-invasive Thermal Ablation of a Brain Tumor with MR Guided Focused Ultrasound

“…Various solutions to widen the treatment envelope are currently being intensively evaluated, such as using lower ultrasound frequencies, adding ultrasound enhancing microbubbles, or rearranging transducer position and geometry [21]-which presumably will extend the therapeutic potential of HIFU for various CNS diseases in the near future. Another issue is the attenuation of ultrasonic beam in bone (30-60 times higher than in soft tissue) [10,22] which heats the skull and overlying skin. Following sonication of 10-15 s, a 3-5-min break must be taken to allow the bone and skin to cool down.…”

“…Accordingly, the InSightec Neuro system used in these trials received CE marking for functional neurosurgery by the end of 2012. While the noninvasive treatment of brain tumors has been the driving vision for the advancement of HIFU technology for decades [7,8], earlier clinical studies in this field lacked proper image guidance [5], required a craniotomy to create an acoustic window through the skull bone [9], or had limited success due to the technical limitations of the FUS systems available [10]. Here, we report the successful application of noninvasive tcMRgFUS for partial brain tumor ablation in a patient suffering from a centrally located malignant glioma.…”

Non-Invasive in vivo Loss Tangent Imaging: Thermal Sensitivity Estimation at the Larmor Frequency

“…The electrical properties were estimated by analyzing the complex B 1 + map using the Helmholtz equations, [2] and [3] (12): [3] where μ is the permeability. In reality, conductivity can be calculated to a reasonable accuracy using only the phase of B 1 + , while permittivity can be determined from the magnitude of B 1 + alone (12).…”

“…It provides high resolution anatomical information of the human with excellent soft tissue contrast, obtained in a non-invasive manner, and can be used to guide treatments and surgeries through monitoring of temperature and visualization of tumors (1)(2)(3)(4)(5). More recent applications related to hyperthermic therapy include magnetic resonance-guided laser-induced thermal therapy (3) and MR-guided focused ultrasound surgery (2), which demonstrated the possibility for application of MRI as a valuable tool in managing the ablation region.…”