An injection of magnetic nanoparticles into your bloodstream could reveal precisely where harmful viruses are lurking. The particles are coated with antibodies to a particular virus, so they will form clumps that should be visible on conventional body scans if that virus is present. The Harvard team working on the project has already managed to detect viruses in body fluids and tissue samples.
Much of the technology has been tested in humans, but you won't have access to this neat trick for several years.
While this will be a terrific advance in medical diagnostics that far exceeds current PCR technology, knowing you have an infection really is not the solution as it doesn't address the cause. You can review my Gulf War and Killer Pneumonia article for more details.
New Scientist August 22, 2003
Journal of the American Chemical Society August 27, 2003;125(34):10192-10193