Measurement of cerebral circulation and oxygen metabolism using integrated PET/MRI scanner with oxygen-15 labeled gases: Effects of attenuation correction and real-time motion correction

75 Objectives: Measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) by PET with oxygen-15 labeled gases is useful for diagnosis and treatment planning in cases of chronic occlusive cerebrovascular disease. In the present study, CBF, CBV, OEF and CMRO2 were measured using the integrated design of PET/MRI scanner system with two kinds of attenuation corrections for PET. MR images were also simultaneously measured for real-time head motion correction of PET images. Methods: PET/MRI measurements with the steady-state method of oxygen-15 labeled gases, carbon monoxide (C15O), oxygen (15O2), and carbon dioxide (C15O2) were performed on nine healthy men. Two attenuation corrections for PET were performed using MRI with Dixon sequence (DIXON) and Dixon sequence with model-based bone segmentation (DIXONbone). A real-time motion correction of PET images was also performed using simultaneously measured MR images with BOLD sequence to detect head motion. Image reconstruction of PET was performed using ordered subset expectation maximization method. During each PET scanning, arterial blood sampling were performed to measure the radioactivity concentration in blood. Using these data, the parametric images of CBF, CBV, OEF and CMRO2 were calculated. Results: Mean and SD values of CBF, CBV, OEF, and CMRO2 in the cerebral cortex with attenuation correction by DIXON were 31±4 mL/100mL/min, 2.7±0.2 mL/mL, 0.40±0.07, and 2.5±0.3 mL/100mL/min without real-time motion correction, and 33±4 mL/100mL/min, 2.7±0.2 mL/mL, 0.40±0.07, and 2.6±0.3 mL/100mL/min with real-time motion correction, respectively. Values with of CBF, CBV, OEF, and CMRO2 with attenuation correction by DIXONbone were 35±5 mL/100mL/min, 2.8±0.2 mL/mL, 0.40±0.07, and 2.8±0.3 mL/100mL/min without real-time motion correction, and 38±5 mL/100mL/min, 2.8±0.2 mL/mL, 0.40±0.07, and 3.0±0.4 mL/100mL/min with real-time motion correction, respectively. Conclusion: Using PET/MRI scanner system with the steady-state method of oxygen-15 labeled gases, CBF, CBV, OEF, and CMRO2 could be measured. Values of CBF, CBV, and CMRO2 measured with attenuation correction by DIXON were significantly lower than those measured with attenuation correction by DIXONbone. One of reasons of this is that attenuation correction of DIXON does not take into consideration of photon absorption by bone. OEF values were not affected by attenuation correction methods. Values of CBF and CMRO2 with a real-time motion correction were significantly higher than those without a real-time motion correction. This might be due to an improving tissue mixture between gray and white matter and cerebrospinal fluid by head movement. Using PET/MRI scanner system with adequate corrections, similar values of CBF, CBV, OEF, and CMRO2 with PET alone scanner system reported previously were obtained.