Using a multimodal near-infrared spectroscopy and MRI to quantify gray matter metabolic rate for oxygen: A hypothermia validation study
Mada Hashem,
Qiong Zhang,
Ying Wu,
Thomas W. Johnson,
Jeff F. Dunn
Affiliations
Mada Hashem
Biomedical Engineering Graduate Program, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Department of Radiology, Faculty of Medicine, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Hotchkiss Brain Institute, University of Calgary, Alberta, T2N 4N1, Canada; Experimental Imaging Centre, Cumming School of Medicine, University of Calgary, Alberta, T2N 4N1, Canada
Qiong Zhang
Department of Radiology, Faculty of Medicine, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Hotchkiss Brain Institute, University of Calgary, Alberta, T2N 4N1, Canada; Experimental Imaging Centre, Cumming School of Medicine, University of Calgary, Alberta, T2N 4N1, Canada
Ying Wu
Department of Radiology, Faculty of Medicine, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Hotchkiss Brain Institute, University of Calgary, Alberta, T2N 4N1, Canada; Experimental Imaging Centre, Cumming School of Medicine, University of Calgary, Alberta, T2N 4N1, Canada
Thomas W. Johnson
Biomedical Engineering Graduate Program, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Department of Radiology, Faculty of Medicine, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Hotchkiss Brain Institute, University of Calgary, Alberta, T2N 4N1, Canada; Experimental Imaging Centre, Cumming School of Medicine, University of Calgary, Alberta, T2N 4N1, Canada
Jeff F. Dunn
Department of Radiology, Faculty of Medicine, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Hotchkiss Brain Institute, University of Calgary, Alberta, T2N 4N1, Canada; Experimental Imaging Centre, Cumming School of Medicine, University of Calgary, Alberta, T2N 4N1, Canada; Corresponding author. Department of Radiology, University of Calgary, 3330 Hospital Drive, N.W., Calgary, Alberta, T2N 4N1, Canada.
Non-invasive quantitative imaging of cerebral oxygen metabolism (CMRO2) in small animal models is crucial to understand the role of oxidative metabolism in healthy and diseased brains. In this study, we developed a multimodal method combining near-infrared spectroscopy (NIRS) and MRI to non-invasively study oxygen delivery and consumption in the cortex of mouse and rat models. The term CASNIRS is proposed to the technique that measures CMRO2 with ASL and NIRS. To determine the reliability of this method, CMRO2 values were compared with reported values measured with other techniques. Also, the sensitivity of the CASNIRS technique to detect changes in CMRO2 in the cortex of the animals was assessed by applying a reduction in core temperature, which is known to reduce CMRO2. Cerebral blood flow (CBF) and CMRO2 were measured in five mice and five rats at a core temperature of 37 °C followed by another measurement at 33 °C. CMRO2 was 7.8 ± 1.8 and 3.7 ± 0.9 (ml/100 g/min, mean ± SD) in mice and rats respectively. These values are in good agreement with reported values measured by 15O PET, 17O NMR, and BOLD fMRI. In hypothermia, we detected a significant decrease of 37% and 32% in CMRO2 in the cortex of mice and rats, respectively. Q10 was calculated to be 3.2 in mice and 2.7 in rats.In this study we showed that it is possible to assess absolute values of metabolic correlates such as CMRO2, CBF and oxygen extraction fraction (OEF) noninvasively in living brain of mice and rats by combining NIRS with MRI. This will open new possibilities for studying brain metabolism in patients as well as the many mouse/rat models of brain disorders.
