Donna Roberts MD, PRESENTER: Nothing to Disclose

Abstract: HTML Purpose: For Blood Oxygen Level Dependent (BOLD) fMRI to be a clinically useful test, reliable intra-subject activation must be demonstrated. Studies have documented generally good reproducibility of fMRI, however there still remains an unexplained degree of variability in even the most robust of protocols. Several factors contribute to this difference including subject motion, equipment variables, data analysis methods, and physiological variables. Investigators have attempted to control for most of these parameters, but the physiological state of the brain at the time of the exam has remained largely an uncontrolled variable. We have used a novel technique, transcranial magnetic stimulation (TMS), as a marker for cortical excitability. Using TMS, other studies have shown cortical excitability to be variable within the same subject over time. This variability in cortical excitability could partially account for the variability in fMRI activation. This study was designed to investigate this relationship. We hypothesized that the amount of activation seen on fMRI would correlate directly with the level of cortical excitability as measured by TMS. Methods and Materials: Thirteen healthy volunteers (6 males, 7 females, aged 20-35) underwent TMS for determination of the rMT (resting Motor Threshold) and the CSP (Cortical Silent Period) duration of the right abductor pollucis brevis (APB) muscle. These subjects then underwent fMRI while alternating abduction and adduction of the right APB. TMS and fMRI were repeated 24 hours later. Results: The APB rMT and CSP durations were easily obtained for all thirteen subjects. For statistical analysis, a canonical correlation was performed. The predictor variables were rMT and CSP, measured at 2 time points. The outcome variables were the number of pixels activated in motor cortex on each of the 2 scanning days. The first canonical correlation was 0.81 (chi-square = 14.89, p = .06), indicating that the association of the combination of predictor variables with the combination of outcome variables approached statistical significance. Most of this association appeared attributable to rMT. Conclusion: rMT, together with CSP, was a marginally significant predictor of the amount of fMRI activation seen in motor cortex. These pilot results suggest, but do not prove, that measures of cortical excitability may help to improve the accuracy of fMRI for motor cortex mapping.       Questions about this event email: robertdr@musc.edu

Roberts MD, D, BOLD Functional MRI Activation Correlates with Cortical Excitability Measured by Transcranial Magnetic Stimulation.  Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL. http://archive.rsna.org/2003/3101324.html