Abstract
ObjectiveA new method of delay time estimation was proposed to measure precise cerebral blood flow (CBF) and arterial-to-capillary blood volume (V0) using 15O-water PET.MethodsNineteen patients with unilateral arterial stenoocclusive lesions were studied to evaluate hemodynamic status before treatment. The delay time of each pixel was calculated using least squares fitting with an arterial blood input curve adjusted to the internal carotid artery counts at the skull base. Pixel-by-pixel delay estimation provided a delay map image that could be used for precise calculation of CBF and V0 using a one-tissue compartment model, and the values from this method were compared with those from the slice-by-slice correction method.ResultsThe affected side showed a longer delay time than the contralateral cerebral hemisphere. Although the mean cortical CBF values were not different between the two methods, the slice-by-slice delay correction overestimated CBF in the hypo perfused area. The scatter plot of V0 pixel values showed significant difference between the two correction methods where the slice-by-slice delay correction significantly overestimated V0 in the whole brain (P < 0.05).ConclusionPixel-by-pixel delay correction provides delay images as well as better estimation of CBF and V0, thus offering useful and beneficial information for the treatment of cerebrovascular disease.
Highlights
Precise measurements of cerebral blood flow (CBF) and other hemodynamic parameters are important in the diagnosis of impaired status in cerebrovascular diseases (CVD)
All parametric data showed significant differences between the two hemispheres; CBF, V0 and CMRO2 were significantly lower and cerebral blood volume (CBV) and oxygen extraction fraction (OEF) were significantly higher in the affected side compared with the contralateral hemisphere (P < 0.05)
In the comparison between pixel-by-pixel and slice-by-slice delay correction methods, V0 values were significantly greater with the slice-by-slice than with the pixel-by-pixel correction method both before and after ACZ administration; CBF from the different correction methods did not show significant differences in both conditions
Summary
Precise measurements of cerebral blood flow (CBF) and other hemodynamic parameters are important in the diagnosis of impaired status in cerebrovascular diseases (CVD). For the quantitative measurement of these parameters using positron emission tomography (PET) and 15O-labeled tracers, the steady-state and autoradiographic (ARG) methods based on a single compartment model were proposed to evaluate cerebral hemodynamics [1,2,3,4]. Quantitative values of hemodynamic parameters in the 15O-PET with arterial blood sampling are affected by the accuracy of an input function corrected for parameters such as tracer delay time and dispersion constants [4, 8]. To simplify the model parameter estimation and calculate efficiently using the 1-TCM, programs employed a fixed dispersion constant and a single delay time for the whole brain, or slice-by-slice delay correction was applied [6, 7, 9]. Correction parameters for the whole brain or for each brain slice may cause errors in calculation of hemodynamic parameters because the values could
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