Objective: To describe a novel system developed for real-time noninvasive monitoring of treatment efficacy in patients undergoing MR-guided Focused Ultrasound (MRgFUS) treatment for refractory tremor.

Background: MRgFUS is a non-invasive approach, for treating parkinson and essential tremor disorders, recently approved by the Food and Drug Administration (FDA) in the United States[1-4]. However, objective, quantitative, and real time measure[5-9] of the tremor characteristics is required to improve the procedure and evaluate its efficacy. Here, we develop an inexpensive ($<300) MRI-compatible motion tracking system (Hardware and software) to objectively assess and quantify tremors during MRgFUS treatments.

Method: A low-cost computer interfaced via I2C with a BNO-055 sensor providing acceleration values at 40Hz sampling rate was used to adequately capture tremor motion. A graphics user interface was programmed using the PyQtGraph library rendering real-time data for visualization. An RF detector synchronizes the sensors with the MR scanner making the system vendor independent. Tremor tracking has been tested successfully on a parkinsonian patient [figure1 & figure2] and another with essential tremor [figure3].

Results: Change in amplitude and frequency of the tremor with successive sonication treatments achieving higher target temperatures is presented in figure 1. There is a reduction(~30%) in amplitude of the 5Hz frequency tremor after the 3^rd Sonication and a significant reduction (~95%) with lower frequency shift after the 5^th sonication and mostly suppressed (~98%) after the final sonication. Figure 2 provides an analysis of parkinsonian tremor mean absolute value of accelerations over the course of the procedure, which reduce significantly after 4^th and 5^th sonications with an almost complete cessation by the 8^th sonication. Figure 3 demonstrates spirals drawn by the patient with action tremor and its characteristic graphs (amplitude and frequency) throughout the sonications. The tremor abates after each sonication and patient can draw the spirals more coherently as validated by the characteristic graphs.

Conclusion: This open-source system is an objective tool for clinicians to track tremor changes effectively in real-time over the course of MRgFUS procedure. Patient data demonstrates adequate quantization of the frequency and amplitude of the tremor with treatment progression.

References: [1] Rossi, P.J., et al., Proceedings of the third annual deep brain stimulation think tank: a review of emerging issues and technologies. 2016. 10: p. 119. [2] Wang, T.R., R. Dallapiazza, and W.J.J.I.J.o.H. Elias, Neurological applications of transcranial high intensity focused ultrasound. 2015. 31(3): p. 285-291. [3] Bruno, F., et al., An experience-based review of HIFU in functional interventional neuroradiology: transcranial MRgFUS thalamotomy for treatment of tremor. 2020: p. 1-10. [4] Dobrakowski, P.P., et al., MR-guided focused ultrasound: a new generation treatment of Parkinson’s disease, essential tremor and neuropathic pain. 2014. 20(3): p. 275-282. [5] Lourenço, J., et al. Low Cost Inertial Measurement Unit for Motion Capture in Biomedical Applications. in Doctoral Conference on Computing, Electrical and Industrial Systems. 2016. Springer. [6] Galinski, D. and B. Dehez. Evaluation of initialization procedures for estimating upper limb kinematics with MARG sensors. in 2012 4th IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob). 2012. IEEE. [7] Chen, B., et al., Design and validation of a novel mr-compatible sensor for respiratory motion modeling and correction. 2016. 64(1): p. 123-133. [8] Rijkhorst, E.-J., et al. Simulating dynamic ultrasound using MR-derived motion models to assess respiratory synchronisation for image-guided liver interventions. in International Conference on Information Processing in Computer-Assisted Interventions. 2010. Springer. [9] Franceschiello, B., et al., 3-Dimensional magnetic resonance imaging of the freely moving human eye. 2020. 194: p. 101885.

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