Assessing MR-compatibility of somatosensory stimulation devices: A systematic review on testing methodologies

Abstract

Functional magnetic resonance imaging (fMRI) has been extensively used as a tool to map the brain processes related to somatosensory stimulation. This mapping includes the localization of task-related brain activation and the characterization of brain activity dynamics and neural circuitries related to the processing of somatosensory information. However, the magnetic resonance (MR) environment presents unique challenges regarding participant and equipment safety and compatibility. This study aims to systematically review and analyze the state-of-the-art methodologies to assess the safety and compatibility of somatosensory stimulation devices in the MR environment. A literature search, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines, was performed in PubMed, Scopus, and Web of Science to find original research on the development and testing of devices for somatosensory stimulation in the MR environment. Nineteen records that complied with the inclusion and eligibility criteria were considered. The findings are discussed in the context of the existing international standards available for the safety and compatibility assessment of devices intended to be used in the MR environment. In sum, the results provided evidence for a lack of uniformity in the applied testing methodologies, as well as an in-depth presentation of the testing methodologies and results. Lastly, we suggest an assessment methodology (safety, compatibility, performance, and user acceptability) that can be applied to devices intended to be used in the MR environment.

Systematic review registration: https://www.crd.york.ac.uk/prospero/, identifier CRD42021257838.

Keywords: MR-compatible; MR-safe; compatibility; functional MRI (fMRI); magnetic resonance imaging (MRI); safety; somatosensory stimulation devices.

FIGURE 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 flow diagram illustrating the magnetic resonance (MR) studies identification, screening, and inclusion (Page et al., 2021).

FIGURE 2

Actuation principles presented in the records included in this review: the majority of the records opted for the piezoelectric principle, followed by the pneumatic and the electromagnetic; the electrical-actuation method was described in a single record.

FIGURE 3

Communication methods between the scanner and the control rooms described in the records included in this review: a similar percentage of records opted for the waveguide and penetration panel and only one paper used both configurations; the remaining records did not specify the communication method (N.A.).

FIGURE 4

Intended applications of the stimulation devices described in the records included in this review: stimulation of the upper limbs was the main application of the devices considered here, followed by the stimulation of the lower limbs, the face and the hands.

FIGURE 5

Safety tests applied to the stimulation devices considered in the records included in this review: the majority of the records included did not need to perform a safety assessment; of those who did it, two evaluated the displacement force (Disp. force), the conductance between leads, and the heating of the device; only one record defined the safety distance for device safe-operation.

FIGURE 6

Compatibility tests performed by the records included in this review. (A) Image quality metrics: signal-to-noise ratio (SNR), temporal signal-to-noise ratio (tSNR), and signal-to-fluctuation-noise (SFNR) were the most utilized metrics to evaluate image quality, followed by visual inspection, radiofrequency (RF) emission, standard deviation of the image intensity time-course (SD), and power spectral density; some records did not specify the metrics assessed (other measures). (B) Device performance evaluation: the majority of the records did not verify the device performance in the magnetic resonance (MR) environment.

FIGURE 7

Additional tests performed by some of the included records: proof of concept imaging studies, additional safety measures, user acceptability tests, and evaluation of the participant’s safe exit from the magnetic resonance (MR) scanner in case of an emergency.

FIGURE 8

Magnetic resonance scanners (A) and sequences (B) utilized by the records included in this review: the majority of the records tested their devices at a 3T scanner (some records did not specify the scanner utilized (N.A.) utilizing both anatomical (Ant.) and functional (Funct.) acquisition sequences; remaining records used functional, anatomical, field-map (FM) or a combination of all these sequences.

FIGURE 9

Comparison of actuation principles in the following categories: frequency, amplitude, duration, locus, MR-friendliness, cost, reliability, and wearability. Actuation principles were ranked based on the subjective opinion of the authors after considering the records included in this review and the general literature. A high ranking means a better position compared to the other actuation principles (frequency: wide range of frequencies; amplitude: high intensity of vibration; duration: better temporal variation in the stimuli presented; locus: small contact area/better spatial resolution; MR-friendliness: less ferromagnetic components; cost: cheaper; reliability: more reliable; wearability: more wearable).

FIGURE 10

Proposed protocol to assess devices intended for research purposes to be used in the magnetic resonance environment according to the information found in our review. The assessment process should start from safety assessment, passing to compatibility (including device performance and image quality assessments), and finally, acceptability assessment. RF, radiofrequency; SNR, signal-to-noise ratio; tSNR, temporal signal-to-noise ratio; SFNR, signal-to-fluctuation-noise; SD, standard deviation.