A computerized tablet system for evaluating treatment of essential tremor by magnetic resonance guided focused ultrasound

Abstract

Background: Transcranial magnetic resonance guided focused ultrasound is an emerging technology under evaluation for treatment of essential tremor, a prevalent movement disorder. A qualitative evaluation is performed by a clinician periodically during the procedure to maximize treatment effects and minimize adverse effects. The present work demonstrates a magnetic resonance-compatible method to enable more precise, quantitative measurement of tremor severity.

Methods: Tremor severity was measured in 12 patients pre-, post-, and intra-operatively, using a magnetic resonance-compatible tablet and a computerized adaptation of drawing tasks from the widely-used Fahn-Tolosa-Marin Tremor Rating Scale. Tremor metrics based on spectral analysis were calculated for each drawing and compared using Wilcoxon signed rank tests.

Results: Tremor metrics in the dominant (treated) hand were significantly and consistently lower post-operatively compared to pre-operatively, but there was no significant difference in the non-dominant (untreated) hand, as expected. Intra-operative metrics were intermediate between pre- and post-operative metrics.

Conclusions: Use of the tablet for quantitative tremor measurement was demonstrated pre-, post-, and intra-operatively during treatment of essential tremor, complementing standard qualitative assessment. With additional work, the system has potential to add objectivity to clinical trials and to aid treatment decision-making by providing a metric for optimization during the procedure, which may eventually lead to more optimal treatment. Enhancements and further studies are suggested, and extensions to fMRI studies of essential tremor and Parkinson's disease are also likely.

Keywords: Drawing; Essential tremor; Magnetic resonance guided focused ultrasound; Magnetic resonance imaging; Movement disorders; Tablet.

Fig. 1

Testing computer and MRI-compatible tablet. The tablet was placed on the participant’s lap when seated for pre- and post-operative tests, and was supported by cushions on the participant’s abdomen for intra-operative testing during MRgFUS

Fig. 2

Prototype interface used for data selection and quality inspection. The upper left plot shows the raw cursor data (blue) and the selected, resampled cursor data (green overlay), which can be compared with the drawing screenshot (not shown). The upper right plot shows the speed over time (blue) and the selected data points (green dots). The lower plot shows the fast Fourier transform of the selected speed data, from which peaks were chosen for tremor metric calculation

Fig. 3

Example pre-operative drawings from a single participant. The three drawings (a–c) were made using the dominant hand (to be treated). The preprocessed, fast Fourier transformed speed data are plotted (d–f) below each drawing, with the tremor metric (TM) annotated above the largest peak

Fig. 4

Example post-operative drawings from a single participant. Data are displayed in the same format as in Fig. 3, for the same participant immediately after MRgFUS treatment. In this example, all the post-operative tremor metrics were lower than the pre-operative values

Fig. 5

Plots of tremor metrics. Tremor metrics plotted on a logarithmic scale (mm/s²), measured at each time point (Pre: pre-operative; Intra: intra-operative; Post: post-operative) with Dominant (a–c) and Non-Dominant (d–f) hands, for each of the 3 drawing types (columns). Each participant’s data points are distinguished by different symbols and joined by lines to help visualize changes. The intra-operative metrics are the mean of one to three separate tests conducted on the MRI scanner table, generally between ablative sonications later in the procedure