Imaging brain vasculature with BOLD microscopy: MR detection limits determined by in vivo two-photon microscopy.
Rat brain vasculature was imaged at 9.4T with blood oxygenation level-dependent (BOLD) microscopy. Data were acquired without exogenous contrast agent in <35 min using 3D gradient-echo imaging with 78-microm isotropic resolution. Detailed vascular patterns including intracortical veins and some branches were observed in simple magnitude-contrast data acquired at an experimentally optimized echo time. The venous origin of the dark patterns was confirmed by oxygenation-dependent studies, and when the systemic arterial oxygen saturation level was <80% BOLD microscopy revealed additional intracortical vessels presumed to be of arterial origin. Quantification shows a decrease of intracortical venous density with depth. The full width at half-minimum intensity was 90-190 microm for most intracortical venous vessels identifiable by BOLD venography. Since actual diameters are not directly quantifiable by BOLD, we also measured diameter-dependent intracortical venous density in vivo by two-photon excitation fluorescent microscopy. Density comparisons between the two modalities, along with computer simulations, show that venous vessels as small as approximately 16-30 microm diameter are detectable with 9.4T BOLD microscopy under our experimental conditions.
Park
Sung-Hong
SH
Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15203, USA.
Masamoto
Kazuto
K
Hendrich
Kristy
K
Kanno
Iwao
I
Kim
Seong-Gi
SG
D000818:Animals; D002536:Cerebral Arteries / Q000166:cytology*; D002550:Cerebral Veins / Q000166:cytology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity