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For the quantitation of cerebral blood flow (CBF) using H215O PET, the measurement of arterial input function (AIF) is essential. In this study, for the simplified quantitation, we present a method for the blind and noninvasive extraction of carotid input function (CIF) from dynamic PET images. On 8 healthy volunteers, the PET scans of C15O and H215O were sequentially performed with arterial blood sampling using detector. With the inhalation of C15O gas, dynamic PET data was acquired. And then after the injection of H215O, dynamic PET scans of H215O was perform. For 4 subjects, PET data for both rest and Acetazolamide (ACZ)-induced stress states were acquired, respectively. In the transverse dynamic images of C15O and H215O, the regions of dynamic images including carotid artery were selected by masking. Non-negative matrix factorization (NMF) algorithm was used to extract the CIF from the selected dynamic images. The partial volume correction estimated from dynamic C15O image, was applied to the extracted CIF. Whole brain CBF was estimated by kinetic analysis based on single compartment model. The error was analyzed using the area under the curve (AUC) and estimated CBF. NMF provided the good separation of the component of CIF from others in both images of C15O and H215O. The shape of estimated CIF by NMF was similar with AIF measured by blood sampling. The AUC between the measured AIF and the estimated CIF was not so different at both rest and ACZ states. The difference of CBF before and after the injection of ACZ was also same between the measured AIF and the estimated CIF. These results show that NMF technique may be a tool for the noninvasive extraction of carotid input function, and this carotid input function might be used in the noninvasive quantitation of CBF using H215O PET.