Functional MRJ (IMRI) is capable of mapping functional regions of the human cortex in response to any hemodynamic stress. IMRI can map brain response to a vascular stress. The vascular challenge is the standard protocol of breathing 5% carbon dioxide for periods of up to 40 seconds. Carbon dioxide can quickly increase CBF to those areas sensitive to the challenge and can determine regions in jeopardy of stroke. Clinical IMRI potential exists in mapping vascular stress. Methods and Results Using our IMRI method to detect brain response to a vascular challenge, increases in local brain function or activity will induce local increases in blood flow and thus increases in tissue image intensity. The response over the brain is then mapped as an image of """"""""vascular response"""""""". The IMRI protocol consists of a series of images acquired over a 7-10 minute protocol. By switching the C02 on and off every 40 seconds, we can track those pixels in each image which respond to the challenge. We can distinguish between gray and white matter, or between stroked and normal brain. Typical results of this protocol are shown in Figure 19 for the repeated challenge of carbogen-aircarbogen-air inhalation. Inhalation of carbogen for 40 second periods produced small changes (2-6%) in observed image intensity, robust enough for image subtractions and for correlation analyses. Gray matter (GM) was seen to respond more vigorously than white matter. Deep gray matter response was also noted. No effect was seen within the ventricles that could be due to changes in CSF inflow. Discussion Our approach lends itself well to a large family of global hemodynamic paradigms such as Diamox. Application of a reversible and mild vasoactive stress (or perturbation) can be """"""""tracked"""""""" non-invasively with MRI, including features of quantitation.
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