If there is one thing worse than having a loved one die in a septic shock it is having to decide whether or not you should pull the plug (an awful but common phrase) on a loved one who is completely unresponsive. If they are in an actual vegetative state -- that is, brain dead, then why keep machines moving the body? That is a travesty of life, not life itself in many people's opinion but what if there is a chance they will recover or a new cure could be found, perhaps the day after you decide to end their present condition? This is probably the most agonizing decision you would ever have to make in life, little else could even compare so isn't it better to have more information? What of those miracles you hear about where someone comes out of a deep comma? Is there no way to improve the chances that you are making the correct decision?.
Fortunately it was recently discovered that a positron emission tomography or a PET scan measuring the use of the body's energy tool, glucose (sugar) will also show which unconscious patients are actually brain dead with no hope of ever waking up, and those with minimal but detectible (only with a PET scan) brain activity and therefore might recover consciousness. This problem of when to stop heroic efforts to keep a patient alive who has had severe head trauma in particular is an ethical dilemma for doctors and a traumatic life decision for the loved ones of the patient since they have to give the go ahead to stop all services which only appear to be keeping the patient alive.
Possibly the most common kind of PET scan is one which follows the uptake and use of glucose through the actual production of positrons, the antimatter twin of electrons, generated artificially in the body and then traced by the gamma radiation they produce as they decay. It turns out that using this simple and common test you can predict with more than 80 percent reliability whether a patient is in what doctors refer to as a vegetative state or have a chance of recovery. This can help doctors decide what advice to give and give comfort to the families who must make the final decision in many hospitals.