Los Angeles Times: Arterial spin labeling uses MRI to track magnetically tagged water molecules in blood as it flows through the brain. Combined with neuropsychological testing, the technique revealed low blood flow to patients' posterior cingulate cortex some 18 months before any notable decline in their cognitive capabilities. The researchers used the technique on 148 test subjects who displayed no symptoms of cognitive decline. When the same subjects were tested 18 months later, 73 were diagnosed with "deteriorating cognitive function." A comparison of the brain scans of the test subjects with those of patients known to have mild cognitive decline revealed that even before all the people with cognitive decline were diagnosed, they were  showing signs of low blood flow. Although there is no known treatment for neurodegenerative diseases such as Alzheimer's, arterial spin labeling could provide an early detection method.