The assessment of cerebral perfusion and metabolism is crucial in evaluating the indications for bypass surgery and other revascularization procedures in patients with chronic hemodynamic cerebral ischemia. In particular, it is necessary to detect misery perfusion(Powers' stage II), which is defined as an increased oxygen extraction fraction and increased cerebral blood volume or impaired cerebrovascular reactivity, with a constant cerebral metabolic rate of oxygen. Among the imaging techniques available for this purpose, 15O-positron emission tomography(PET)and acetazolamide-challenge single-photon emission computed tomography(SPECT)remain the de facto standards; however, these have substantial limitations such as invasiveness and the risk of severe adverse effects. Recently, several less invasive, easy-to-use techniques, such as perfusion computed tomography and magnetic resonance(MR)imaging, arterial spin labeling, quantitative susceptibility mapping, intravoxel incoherent motion, MR spectroscopy, and single-slab MR angiography, have also been introduced. These techniques may serve as alternatives to PET or SPECT if validation studies are successful and standardization among vendors is achieved.