Assessment of cerebral perfusion is essential for the accurate diagnosis and medical treatment of patients with cerebral ischemia. In order to reduce permanent disability, the prevention and early detection of cerebral ischemia are very important. The development of a method for noninvasive and repeated measurement of cerebral perfusion is needed. Conventional methods for the evaluation of cerebral hemodynamics include cerebral catheter angiography,3,4 computed tomography (CT),5,6 magnetic resonance imaging (MRI),7–10 transcranial Doppler (TCD),11,12 single-photon emission computed tomography (SPECT),13,14 and positron emission tomography (PET).15,16 These techniques allow measurement of cerebral perfusion deficits, but they have several limitations. Cerebral catheter angiography is invasive, perfusion CT and MRI require injection of a contrast agent, and SPECT and PET require administration of a radioisotope. Repeated measurement is often difficult because of these limitations. TCD and arterial spin-labeling MRI have been developed as noninvasive in vivo imaging methods. However, with TCD, the measurement area is limited, and the examination is dependent on the skill of the operator. Arterial spin-labeling MRI does not yet have sufficient diagnostic accuracy to be used in clinical practice. All of the aforementioned methods require restraint of the patient. Furthermore, measurements at the bedside cannot be performed, because the equipment required for these examinations (other than TCD) is not portable.