Photoacoustic computed tomography (PACT) has been extensively explored in animal brains but never in the human brain due to its limited field of view (FOV), imaging speed, penetration depth, and sensitivity. Here, we present the first application of PACT in functional human brain imaging. Motor and language functional tasks were employed and performed by post-hemicraniectomy patients. The brain activities were recorded at a 10-cm–diameter FOV, 350-μm/2-s spatiotemporal resolution, and ~2-cm penetration depth using a newly developed massively parallel three-dimensional PACT system. Quantitative validation of the PACT results against 7 Tesla MRI revealed comparable angiographic structures and functional activation in the same FOV. The obtained results represent a critical step toward broader-scope human brain imaging applications using PACT technology.
The variation in quantitative measures extracted from computed tomography (CT) perfusion parametric maps due to changes in dose was evaluated. A CT perfusion phantom was scanned on a Philips CT scanner using AAPM recommendations at 2 different speeds and varying x-ray exposure. The acquired images were post-processed using the TeraRecon software. The software outputted Cerebral Blood Flow (CBF), Cerebral Blood Volume (CBV), Mean Transit Time (MTT) maps and Time Attenuation Curves (TAC) of the artery and the vein rods of the phantom. Measurements were made in regions of interest (ROIs) in the two tissue rods (foreground) and 5 regions in the background, across the different parametric maps, respectively. Mixed effect model with AR (1) covariance structure was used to compare measurements across different dose levels as repeated measured random effect. Dunnet adjustment was used for posthoc pairwise comparisons. For the foreground ROI, no significant changes in the measured mean CBF, CBV, and MTT values were observed with changes in dose. As expected, the standard deviation (SD) of CBF and CBV decreased as dose increased. At each dose, higher speed settings were consistently associated with higher SD of CBF and lower MTT. For the background ROI, the measured mean CBF and CBV were significantly higher at lower dose levels, and the SD of CBF decreased as the dose increased. The MTT of the background did not vary with dose. We conclude that radiation dose affects perfusion metrics especially for low or no flow conditions.
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