Transcranial Magnetic Resonance-guided Focused Ultrasound Surgery (tcMRgFUS) at 1.5T: this is how we do it

Purpose: Magnetic Resonance-guided Focused Ultrasound (MRgFUS) is an emerging minimally invasive treatment for many neurological conditions. We present the imaging protocol and the technological methods used in the first 1.5T magnetic resonance scanner. Background: Current experiences of tcMRgFUS applications using 3T MRI units include for the treatment of movement disorders such as essential tremor, tremor dominant unilateral idiopathic Parkinson disease as well as for the treatment of neuropathic pain. This technology is constantly expanding the range of clinical indication and application even in 1.5T MR scanner. Findings and procedure details: In our experiences the Focused Ultrasound equipment was integrated with an MRI unit operating at 1.5T. It consists of a hemispheric 1024-element phased-array transducer operating at 650 kHz as those used with 3.0T MRI units. A dedicated 2 channel flexible head coil was developed to maintain an adequate signal to noise ratio (SNR). This coil consists of two silicon-coated rings that are embedded into the elastic membrane used with 3T systems. In our preliminary experience we preferred to use T2-weighted (T2-w) and/or inversion recovery for white matter T2-w sequences for planning and monitoring the procedures. With the two Head coil, thermal imaging resulted reliable and T2-w sequences provided the expected SNR for planning and monitoring the procedure resulting in precise treatment planning and a good localization of the lesion during the ongoing treatment. Conclusion: TcMRgFUS is taking place as a revolutionary treating modality for several neurological disorders. The results obtained with a 1.5T unit lead us to imagine a greater spread of this promising, emerging technology.