Abstract
CT perfusion (CTP) is a powerful tool for the assessment of cerebrovascular disease. However, CTP maps are significantly different depending on CTP software and algorithm, even when using identical image data. We developed a phase-ratio image map (PI map), which was a novel perfusion map, without using CTP software. The purpose of this study was to investigate the usefulness of the PI map by comparing it with a positron emission tomography (PET) image. Twenty patients (16 men, 4 women; mean age: 61.6 years) with unilateral cervical and intracranial steno-occlusive disease underwent CTP. CTP source images were obtained at 1-s intervals of 23 times and 5 intervals using dynamic multiphase imaging. An early-phase image was generated by computing the average of CT images for 5 s in the vicinity of the peak enhancement curve of a normal hemisphere. A delayed-phase image was generated by computing the average of CT images for 5 s immediately after the early phase. The PI map was created by dividing the delayed-phase image by the early-phase image. We investigated the validity of the PI map compared with PET-cerebral blood flow (CBF). Lesion-to-normal ratios between a PET-CBF and the PI map or two conventional CTP-CBFs were observed and compared, and the relative errors were also compared. There was a strong correlation between the PET-CBF and the PI map (R=0.82). Correlations between the PET-CBF and two CTP-CBFs were weak (R=0.30) and middle (R=0.62), respectively. The relative error between the PI map and the PET-CBF was within 10% in most cases. The PI map was more similar to the PET-CBF on perfusion evaluation, and did not depend on CTP software. The robustness and simplicity of the PI mapping method would be advantageous compared with conventional CTP mapping methods.
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