Quantitative MRI of cerebral arterial blood volume.

Baseline cerebral arterial blood volume (CBV(a)) and its change are important for potential diagnosis of vascular dysfunctions, the determination of functional reactivity, and the interpretation of BOLD fMRI. To quantitative measure baseline CBV(a) non-invasively, we developed arterial spin labeling methods with magnetization transfer (MT) or bipolar gradients by utilizing differential MT or diffusion properties of tissue vs. arteries. Cortical CBV(a) of isoflurane-anesthetized rats was 0.6 - 1.4 ml/100 g. During 15-s forepaw stimulation, CBV(a) change was dominant, while venous blood volume change was minimal. This indicates that the venous CBV increase may be ignored for BOLD quantification for a stimulation duration of less than 15 s. By incorporating BOLD fMRI with varied MT effects in a cat visual cortical layer model, the highest ΔCBV(a) was observed at layer 4, while the highest BOLD signal was detected at the surface of the cortex, indicating that CBV(a) change is highly specific to neural activity. The CBV(a) MRI techniques provide quantified maps, thus, may be valuable tools for routine determination of vessel viability and function, as well as the identification of vascular dysfunction.