When a parent starts with occasional forgetfulness, you may not worry much. But then the mental lapses get serious when a forgotten pot on the stove starts a fire. Unfortunately, neurologists can't confirm whether a patient has Alzheimer's disease - only an autopsy can do that.

A newly approved test can't definitively diagnose the disease yet, but it gets doctors pretty close. The test uses a mildly radioactive fluorescent dye called Amyvid, which latches onto amyloid plaques in the brain. Identifying amyloid plaques can tell doctors if someone has dementia or could develop dementia. They're protein fragments that normally break down, but cause disease when they accumulate into hard insoluble plaques.

It is unclear whether amyloid plaques cause Alzheimer's, but their presence is indicative of the disease. Once Amyvid, the fluorescent dye, binds to the plaque, a positron emission tomography or PET scan reveals where the protein clusters. While a clear scan is a relief, a positive scan doesn't necessarily mean someone has Alzheimer's disease. Twenty to 30 percent of people over 65 have some plaque but may never develop dementia.

The test is significant to Alzheimer's research since it will allow scientists to identify and track people with dementia, expanding their knowledge about the causes of Alzheimer's and its progression. Scientists can also monitor how the disease develops under experimental therapeutics.

Finding effective treatment for Alzheimer's disease will become more pressing as America's population ages. It is the number one cause of dementia in America, affecting 5.4 million people. By 2050, costs for treating Alzheimer's patients are projected to soar to one trillion dollars.

Eventually, people with early signs of dementia will be able to get the new PET scan. While some will want to be prepared, not everyone wants the crushing news.