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Validation of a Novel Noxious Pressure Device for Use in fMRI Pain Studies

Marisa DiMarzio, Michael Spinrad, Maria Hancu, Ellinor Grinde, Jamie Chang, Julia Slyer, Ileana Hancu, Eric Fiveland, Michael Gillogly, Julia Prusik and Julie G. Pilitsis

Background: Most fMRI studies on pain perception utilized thermal stimuli due to the lack of a non-metallic reliable, reproducible mechanical stimulus. We explored 2 potential MR compatible mechanical devices and validated one that induced changes on fMRI.

Purpose: To validate a noxious mechanical stimulus MR compatible device in a healthy cohort and a chronic pain cohort. Further to ensure this device caused changes on fMRI compared to a pressure device.

Methods: Two-healthy controls underwent fMRI scans in the presence/absence of mechanical noxious stimuli using different devices. A paradigm for administering the stimuli with the most robust responses on fMRI was developed. Reproducibility of the device was confirmed in 10 chronic pain patients and age/gender-matched healthy controls. Comparisons of patient demographics including age, sex, and numerical rating scale (NRS) scores between the cohorts were performed using a two-sample t-test. Reproducibility was assessed through repeated-measures ANOVA.

Results: Both devices, when administered at 15 seconds on, 30 seconds off induced primary somatosensory cortex (SI) activation on fMRI. The device affecting the nail bed induced consistent discomfort and was subsequently validated. Specifically, a mean pressure of 15.7 ± 0.05 psi induced discomfort that remained consistent over repeated trials (p=0.74). Further, in healthy controls, there was a significant correlation between pressure applied and NRS scores in controls(p<0.01). In chronic pain patients, a mean pressure of 15.3 ± 0.10 psi provided discomfort during a single trial. This pressure did not differ than that found in healthy controls (p=0.26).

Conclusion: We have developed and validated a novel pressure device which is MRI compatible and provides for improved accuracy. We have demonstrated increased reproducibility compared to existing devices in literature and documented feasibility in pilot fMRI studies. Future work will focus on demonstrating its use in fMRI studies in chronic pain patients.