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Objective: In biomanufacturing there is a need for quantitative methods to map cell viability and density inside 3D bioreactors to assess health and proliferation over time. Recently, noninvasive MRI readouts of cell density have been achieved. However, the ratio of live to dead cells was not varied. Herein we present an approach for measuring the viability of cells embedded in a hydrogel independently from cell density to map cell number and health., Methods: Independent quantification of cell viability and density was achieved by calibrating the 1 H magnetization transfer- (MT) and diffusion-weighted NMR signals to samples of known cell density and viability using a multivariate approach. Maps of cell viability and density were generated by weighting NMR images by these parameters post-calibration., Results: Using this method, the limits of detection (LODs) of total cell density and viable cell density were found to be 3.88 ×10 8 cells · mL -1 · Hz -1/2 and 2.36 ×10 9 viable cells · mL -1 · Hz -1/2 respectively., Conclusion: This mapping technique provides a noninvasive means of visualizing cell viability and number density within optically opaque bioreactors., Significance: We anticipate that such nondestructive readouts will provide valuable feedback for monitoring and controlling cell populations in bioreactors.

This experiment examined the effects of nitric oxide (NO) synthase inhibition on brain intracellular pH, regional cortical blood flow, and NADH fluorescence before and during 3 h of focal cerebral ischemia using in vivo fluorescence imaging. Thirty fasted rabbits under 1% halothane were divided into four treatment groups receiving N omega-nitro-L-arginine methyl ester (L-NAME) intravenously at 20 min prior to ischemia (0.1, 1, and 10 mg/kg and 1 mg/kg + 5 mg/kg L-arginine) and two control groups (nonischemic and ischemic). In ischemic controls, brain pH(i), declined to 6.73 +/- 0.03 at 30 min and remained acidotic through the remainder of the ischemic period. In the 0.1 mg/kg group, brain pH(i) fell after 30 min of ischemia to 6.76 +/- 0.05 (p < 0.05), but then improved progressively despite occlusion. In the 1 mg/kg group, brain pH(i), remained normal despite middle cerebral artery (MCA) occlusion. In the 10 mg/kg group and in the combined L-NAME + L-arginine group, pH(i) fell after 30 min of ischemia to 6.81 +/- 0.03 (p < 0.05) and remained acidotic. During occlusion, regional cortical blood flow dropped in a dose-dependent manner. After 3 h of ischemia, regional cortical blood flow was 33.9 +/- 10.9 and 25.1 +/- 8.9 ml/100 g/min at doses of 0.1 and 10.0 mg/kg, respectively, L-NAME treatment did not significantly alter the increased NADH fluorescence that accompanied occlusion. This study shows that L-NAME can prevent intracellular brain acidosis during focal cerebral ischemia independent from regional cortical blood flow changes. This experiment suggests that NO is involved in pH(i) regulation during focal cerebral ischemia.