Quantification of Cerebral Blood Flow and Oxygen Metabolism with 3-Dimensional PET and ¹⁵O: Validation by Comparison with 2-Dimensional PET

Abstract

Quantitative PET with 15 O provides absolute values for cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral metabolic rate of oxygen (CMRO 2 ), and oxygen extraction fraction (OEF), which are used for assessment of brain pathophysiology. Absolute quantification relies on physically accurate measurement, which, thus far, has been achieved by 2-dimensional PET (2D PET), the current gold standard for measurement of CBF and oxygen metabolism. We investigated whether quantitative 15 O study with 3-dimensional PET (3D PET) shows the same degree of accuracy as 2D PET. Methods: 2D PET and 3D PET measurements were obtained on the same day on 8 healthy men (age, 21-24 y). 2D PET was performed using a PET scanner with bismuth germanate (BGO) detectors and a 150-mm axial field of view (FOV). For 3D PET, a 3D-only tomograph with gadolinium oxyorthosilicate (GSO) detectors and a 156-mm axial FOV was used. A hybrid scatter-correction method based on acquisition in the dual-energy window (hybrid dual-energy window [HDE] method) was applied in the 3D PET study. Each PET study included 3 sequential PET scans for C 15 O, 15 O 2 , and H 2 15 O (3-step method). The inhaled (or injected) dose for 3D PET was approximately one fourth of that for 2D PET. Results: In the 2D PET study, average gray matter values (mean 6 SD) of CBF, CBV, CMRO 2 , and OEF were 53 6 12 (mL/100 mL/min), 3.6 6 0.3 (mL/100 mL), 3.5 6 0.5 (mL/100 mL/min), and 0.35 6 0.06, respectively. In the 3D PET study, scatter correction strongly affected the results. Without scatter correction, average values were 44 6 6 (mL/100 mL/min), 5.2 6 0.6 (mL/100 mL), 3.3 6 0.4 (mL/100 mL/min), and 0.39 6 0.05, respectively. With the exception of OEF, values differed between 2D PET and 3D PET. However, average gray matter values of scatter-corrected 3D PET were comparable to those of 2D PET: 55 6 11 (mL/100 mL/min), 3.7 6 0.5 (mL/100 mL), 3.8 6 0.7 (mL/100 mL/min), and 0.36 6 0.06, respectively. Even though the 2 PET scanners with different crystal materials, data acquisition systems, spatial resolution, and attenuation-correction methods were used, the agreement of the results between 2D PET and scatter-corrected 3D PET was excellent. Conclusion: Scatter coincidence is a problem in 3D PET for quantitative 15 O study. The combination of both the present PET/CT device and the HDE scatter correction permits quantitative 3D PET with the same degree of accuracy as 2D PET and with a lower radiation dose. The present scanner is also applicable to conventional steady-state 15 O gas inhalation if inhaled doses are adjusted appropriately.

Paradoxical reduction of cerebral blood flow after acetazolamide loading: a hemodynamic and metabolic study with 15O PET

“…The PET images were reconstructed by a filtered-back projection method after 3D Gaussian smoothing with a 6-mm FWHM. Scattered [14,15] .…”

“…The baseline CBV, the baseline cerebral metabolic rate of oxygen (CMRO 2 ), the OEF at baseline, the CBF b , and the CBF after ACZ loading (CBF acz ) were measured following C 15 O and 15 O 2 gas inhalation, and H 2 15 O injection [15] . A cannula was inserted into the radial artery for arterial input.…”

“…Quantitation of reconstructed PET images by the 3-D mode PET scanner has been validated in a previous report [15] .…”

“…The ACZ effect is reported to reach a maximum at 10 to 20 min after administration [4] . According to Kuwabara et al, who reported the time-dependency of the effect of ACZ on the cerebral circulation, the paradoxical CBF reduction is most prominent 5 min after injection Tadashi Watabe, et al Paradoxical reduction of CBF after acetazolamide loading: a study with 15 O PET 855 compared to 20 min after injection [7] . The paradoxical CBF reduction might be detectable more frequently in the early phase (at 5 to 10 min).…”

“…In the present study, we tested the hypothesis that the paradoxical CBF reduction after ACZ loading is associated with a reduction of regional CPP by evaluating the CBF/ CBV ratio in patients with internal carotid artery (ICA)/MCA steno-occlusive disease by means of 15 O positron emission tomography (PET).…”