Number 271 (Story #1), May 16, 1996 by Phillip F. Schewe and Ben Stein SHARPER, CHEAPER PET SCANS. At the recent APS meeting in Indianapolis, Simon Cherry of UCLA (310-825-4334) described MicroPET, a positron-emission tomography (PET) system that can resolve structures as small as 0.006 cubic centimeters (about the volume of a sesame seed), a nearly tenfold improvement in resolution over conventional scanners, at an estimated price of $300,000, less than one-fifth the cost of conventional PET systems. Used to provide images of such things as brain activity, PET detects pairs of gamma rays released when positrons from a radioactive tracer in the bloodstream annihilate electrons in the patient's body. Scheduled to be fully complete in July, MicroPET brings about increased resolution by employing smaller scintillation crystals (made of lutetium oxyorthosilicate) for detecting the gammas. The crystals are small enough that they can be read out using optical fibers, which convey light to a multichannel phototube consisting of 64 individual elements, greatly reducing the need for numerous expensive tubes. (Much of the technology was adapted from high-energy particle physics.) This system is suitable for imaging the smaller-scale anatomies of laboratory animals used in drug trials.