Described herein is a method for detecting changes in blood flow in a tissue portion and/or body portion of an individual. The method can be used to detect any sort of pathology, trauma or insult which results in blood flow change. Specifically, this method uses hyperpolarized 129Xe MRI to detect xenon perfusion changes in tissues such as brain tissue that corresponds to changes in blood flow, for example, changes caused by functional activities of the brain or regions of the body where blood flow may be compromised.