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Examining the effects of the rate of temperature change on healthy spinal cord fMRI responses 2011

General Spine

Christopher, A, Kidd, B. Eng
Rachael, L, Bosma, B. Sc, Non ASSR Member
Patrick, W, Stroman, Ph.D, Non ASSR Member

Poster

Purpose

Spinal cord functional magnetic resonance imaging (spinal fMRI) is the only non-invasive, in vivo means available to assess neuronal changes that occur as a result of injury. However, in order to achieve its clinical potential, characterization of the fMRI response in healthy subjects is needed to demonstrate the sensitivity and reliability of this technique. Previous studies have shown spinal fMRI capable of detecting a signal response corresponding to peripheral heating stimuli.1,2 More importantly, recent studies have indicated that the signal is correlated with the change in temperature, as opposed to the constant heat. Here we demonstrate the effects of changing the heating stimuli parameters on the functional responses in the spinal cord to determine the sensitivity of our method. We hypothesized that there would be a neuronal response corresponding to rising/falling of temperature with significantly stronger responses occurring in response to faster ramping stimuli, than slower heating stimuli.

Methods & Materials

Functional MRI studies of the spinal cord were acquired in healthy subjects using a signal enhancement by extravascular water protons (SEEP) fMRI protocol.1,2 To examine the neuronal activity thermal stimulation was applied in a block paradigm by means of a custom-made device to the anterior side of the right thumb targeting the C6 dermatome at a constant temperature of 44°C. Studies were conducted by applying stimuli with varying ramp speeds (2 or 9 sec), and durations (45 or 72 sec).

Results

Group analysis from all the participants was completed for each of the different stimulus protocols, with results showing areas of consistent neuronal activity appearing in the target activation region. As expected, stronger positive signal responses occurred when the shorter ramps were a part of the stimulus protocol. This effect is even greater when examining protocols that incorporate shorter ramps for heating compared to having brief cooling ramps. In contrast, when longer ramp speeds are applied for the heating there is a notable increase in negative responses.

Conclusion

The results demonstrate that with this method it is possible to detect differences in activity in the spinal cord in response to various varying stimuli. This has implications for the development of a practical clinical method for assessing spinal cord function by means of spinal fMRI.

References/Financial Disclosures

References 1. C.R. Figley and P.W. Stroman, Neuroimage, 44(2), 421(2009) 2. P. W. Stroman, et al., Magn Reson. Imaging 20(1), 1 (2002)