Abstract
This review article explains the methodology of breath-hold cerebrovascular reactivity mapping, both in terms of acquisition and analysis, and reviews applications of this method to presurgical mapping, particularly with respect to blood oxygen level-dependent fMRI. Its main application in clinical fMRI is for the assessment of neurovascular uncoupling potential. Neurovascular uncoupling is potentially a major limitation of clinical fMRI, particularly in the setting of mass lesions in the brain such as brain tumors and intracranial vascular malformations that are associated with alterations in regional hemodynamics on either an acquired or congenital basis. As such, breath-hold cerebrovascular reactivity mapping constitutes an essential component of quality control analysis in clinical fMRI, particularly when performed for presurgical mapping of eloquent cortex. Exogenous carbon dioxide challenges used for cerebrovascular reactivity mapping will also be discussed, and their applications to the evaluation of cerebrovascular reserve and cerebrovascular disease will be described.
Highlights
At Johns Hopkins, we have developed a BH cerebrovascular reactivity (CVR) protocol that has been successfully implemented in approximately 95% of patients who have undergone routine clinical blood oxygen level– dependent (BOLD) fMRI presurgical mapping examinations during the past 4 years
Despite concerns in research studies regarding the lack of absolute quantification of CVR by using BH CVR mapping, variable repeatability/reproducibility, and variable patient compliance, as discussed above in detail, we have found such a technique to be perfectly adequate for regional relative CVR assessment in the setting of structural brain lesions such as brain tumors
Because the levels of CO2 achieved with BH CVR are unknown and because the presence of BOLD signal change in impaired tissue is dependent on CO2 elevations achieved, the final CVR maps would be expected to have lower prediction accuracy for type II fMRI errors than those in which tight control of CO2 is applied
Summary
The Breath-Hold Cerebrovascular Reactivity Mapping Technique hypercapnia challenges have been used in conjunction with BOLD imaging to very effectively evaluate brain CVR, the criterion standard technique for such CVR mapping has been exogenous carbon dioxide (CO2) gas administration during MR imaging.[11,12,13] The breath-hold (BH) technique offers a simpler alternative that is easier to implement in the clinical setting and yet can produce similar increases in arterial CO2 levels and resultant useful BOLD CVR maps as those achieved by using gas-inhalation techniques.[14] This technique involves short-duration BHs, typically in the range of 10 –30 seconds, which alternate with periods of normal breathing.
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