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Biotech / Medical : IMAT - ultrafast tomography for coronary artery disease -- Ignore unavailable to you. Want to Upgrade?

To: art slott who wrote (2439)	5/6/1998 12:49:00 AM
From: Steven Durrington	Read Replies (2) \| Respond to of 3725

Art, What is PET scanning in 1000 words or less ? I'll try to keep down the volume here.... Positron Emission Tomography is a kind of very specialized Nuclear Medicine Procedure, but is far more sensitive for the applications it is used for (more on that in a moment). The PET scanner looks like a conventional CT scanner from the outside - a big box with a donut in the middle into which the scan table is moved. It is a multimillion dollar piece of equipment in itself, but also needs an on-site Cyclotron machine to produce the radioactive isotopes used for the scans (which have relatively short half lives and can't be transported quickly enough over medium to large distances without decaying significantly). Cyclotrons don't come cheap. A PET scanner works on this principle - the patient is injected with a radioactive isotope which is "attached" to a pharmaceutical agent which in turn has an affinity with a certain part of the body. The combined isotope/drug is called a "radiopharmaceutical". Radioactive decay can be by several means - alpha or beta particle emission, gamma ray emission, neutron emission or other particles such as a positron. The type of isotope used in PET is one that decays by emitting a positron - "Antimatter" for you science fiction types (a positive electron). Antimatter doesn't last too long in our galaxy, and very soon after the positron is emitted, it encounters an electron and when the two meet, KABOOM ! The two annihilate each other. But, as Mr Einstein pointed out, energy and matter are interchangeable, and you can't really destroy matter or energy - just change it's form. The annihilated positron and electron create 2 high energy gamma ray photons with an energy of about 512 KeV which move away from each other at 180 degrees at the speed of light. The PET scanner has a ring of very sensitive detectors around the patient which detects the incoming gamma rays, and records when the photons arrived at opposing detector panels and from which line of sight within the patient. If the gamma rays arrive in opposing detectors almost instantaneously, then they are from the same annihilation and are recorded. The random striking of gamma rays is filtered out by the computer. The image is made up of millions of detections of opposing 512 KeV photons. The isotopes most commonly used in PET scanning are Fluorine, Ammonia and Carbon. They are attached to the pharmaceuticals, and according to how the body is functioning, the radiopharmaceuticals are attracted to various normal and abnormal parts of the body. PET scanning is a functional test - it doesn't give great anatomical detail, but is very sensitive in detecting differences in metabolic processes. The 3 big applications for PET at the moment are :- 1. Brain Scanning, to assess tumours, epilepsy centres, loss of brain function, etc. (For brain scans, you have to keep the patient sensorily deprived before the scan, as isotopes can be attracted to areas of the brain in disproportionate amounts if the patient's visual cortex is overstimulated, or if they're singing songs in their head, etc. 2. Whole body scanning, to assess spread of metastastes, foci of infections, etc. and, yes, you probably guessed it... 3. CARDIAC SCANNING !!! The Radiopharmaceutical used for heart scans is FDG - Fluorodeoxyglucose. Basically radioactive sugar, which is metabolized by the heart muscle, and is used to scan the heart to assess viability of cardiac muscle (myocardium) in patients with ischaemic heart disease (a familiar theme is being heard here...). The PET heart scan is much more sensitive than a Thallium scan done in conventional nuclear medicine, and in many instances, the PET scan shows viable myocardium in cases where other tests have given bad results. Hence, doctors can choose those patients who are worthwhile to pursue coronary artery bypass grafts (CABG = "Cabbage"), as their myocardium is hanging tough, despite the blockages in the coronary arteries. It seems to me that IMAT is merging with the PET scanning producer to provide an A to Z cardiac diagnostic service - the CT screening to help prevent disease onset, and the PET scanning for those for whom it is almost too late, but clinical decisions ride heavily on viability of remaining cardiac tissue. Sounds interesting, and I'll continue to monitor the company and this thread. It's 0730 hrs here, and time to start work. Good night Nth America. Regards, Durro