The Brain Thermal Response as a Potential Neuroimaging Biomarker of Cerebrovascular Impairment

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The authors evaluated the use of noninvasive MR thermometry in patients with cerebrovascular disease, and hypothesized that the presence of a measurable brain thermalresponse would reflect the tissue hemodynamic state. MR imaging and MR thermometry were performed in 10 patients undergoing acetazolamide challenge for chronic, anterior circulation steno-occlusive disease. Cerebrovascular reactivity was calculated with BOLD imaging and arterial spin-labeling methods. Brain temperature was calculated pre- and post-acetazolamide using previously established chemical shift thermometry. They observed significant, voxelwise quadratic relationships between cerebrovascular reactivity from BOLD imaging and the brain thermal response and baseline brain temperatures, concluding that brain thermal response is a potential noninvasive biomarker for cerebrovascular impairment.

Abstract

 

Representative CVR percentage augmentation maps calculated with BOLD and ASL, along with a BTR map overlaid on a T1-weighted image. Images are all from the same subject (a 32-year-old woman) with unilateral left MCA stenosis without infarction. The white grid overlay represents the MR thermometry grid derived from multivoxel spectroscopy analysis using the water-NAA chemical shift difference. Diffusion-weighted imaging demonstrates no evidence for acute infarction. Images are displayed in the radiologic convention. Impaired CVR in the left hemisphere is present in both BOLD and ASL, with a greater severity of impairment in ASL likely related to delay sensitivity and tag decay (see text). The BTR map demonstrates an asymmetric thermal response, with less brain cooling following vasodilatory stimulus in the diseased left hemisphere, indicated by lower and more positive BTR values and corresponding primarily to the areas of greatest impairment in the anterior and posterior MCA borderzone territories.
Representative CVR percentage augmentation maps calculated with BOLD and ASL, along with a BTR map overlaid on a T1-weighted image. Images are all from the same subject (a 32-year-old woman) with unilateral left MCA stenosis without infarction. The white grid overlay represents the MR thermometry grid derived from multivoxel spectroscopy analysis using the water-NAA chemical shift difference. Diffusion-weighted imaging demonstrates no evidence for acute infarction. Images are displayed in the radiologic convention. Impaired CVR in the left hemisphere is present in both BOLD and ASL, with a greater severity of impairment in ASL likely related to delay sensitivity and tag decay (see text). The BTR map demonstrates an asymmetric thermal response, with less brain cooling following vasodilatory stimulus in the diseased left hemisphere, indicated by lower and more positive BTR values and corresponding primarily to the areas of greatest impairment in the anterior and posterior MCA borderzone territories.

BACKGROUND AND PURPOSE

Brain temperature is critical for homeostasis, relating intimately to cerebral perfusion and metabolism. Cerebral thermometry is historically challenged by the cost and invasiveness of clinical and laboratory methodologies. We propose the use of noninvasive MR thermometry in patients with cerebrovascular disease, hypothesizing the presence of a measurable brain thermal response reflecting the tissue hemodynamic state.

MATERIALS AND METHODS

Contemporaneous imaging and MR thermometry were performed in 10 patients (32–68 years of age) undergoing acetazolamide challenge for chronic, anterior circulation steno-occlusive disease. Cerebrovascular reactivity was calculated with blood oxygen level–dependent imaging and arterial spin-labeling methods. Brain temperature was calculated pre- and post-acetazolamide using previously established chemical shift thermometry. Mixed-effects models of the voxelwise relationships between the brain thermal response and cerebrovascular reactivity were computed, and the significance of model coefficients was determined with an F test (P < .05).

RESULTS

We observed significant, voxelwise quadratic relationships between cerebrovascular reactivity from blood oxygen level–dependent imaging and the brain thermal response (x coefficient = 0.052, P < .001; x2coefficient = 0.0068, P < .001) and baseline brain temperatures (x coefficient = 0.59, P = .008; x2 coefficient = −0.13, P < .001). A significant linear relationship was observed for the brain thermal response with cerebrovascular reactivity from arterial spin-labeling (P = .001).

CONCLUSIONS

The findings support the presence of a brain thermal response exhibiting complex but significant interactions with tissue hemodynamics, which we posit to reflect a relative balance of heat-producing versus heat-dissipating tissue states. The brain thermal response is a potential noninvasive biomarker for cerebrovascular impairment.

 

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The Brain Thermal Response as a Potential Neuroimaging Biomarker of Cerebrovascular Impairment
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jross
Jeffrey Ross • Mayo Clinic, Phoenix

Dr. Jeffrey S. Ross is a Professor of Radiology at the Mayo Clinic College of Medicine, and practices neuroradiology at the Mayo Clinic in Phoenix, Arizona. His publications include over 100 peer-reviewed articles, nearly 60 non-refereed articles, 33 book chapters, and 10 books. He was an AJNR Senior Editor from 2006-2015, is a member of the editorial board for 3 other journals, and a manuscript reviewer for 10 journals. He became Editor-in-Chief of the AJNR in July 2015. He received the Gold Medal Award from the ASSR in 2013.

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