When doctors need to confirm an Alzheimer's diagnosis, they often turn to a combination of brain imaging and cell analysis. Both have their downsides. The latter involves a lumbar puncture, an invasive and painful procedure that’s more commonly known as a spinal tap. A doctor will insert a needle into the lower back to extract a sample of the patient’s cerebrospinal fluid. A lab technician then tests the sample for signs of progressive nerve cell loss and excessive amyloid and tau...