ABSTRACT
Most of the existing imaging modalities such as radiography, X-ray transmission computed tomography, and ultrasound provide anatomical information. The potential of positron imaging has been known since the 1950s. Subsequently, positron imaging systems have been developed at Washington University in St. Louis, Donner Laboratory at Berkeley, and at the University of Chicago in collaboration with Searle Radiographics. The scintillators used in positron imaging equipment include: sodium iodide, barium fluoride, bismuth germanate, and gadolinium orthosilicate. However, the energy discrimination in positron imaging reduces coincidence sensitivity by a factor of 4 to 25. Positron emission tomography requires a correction for attenuation so that the results can be quantitated. It is of historical importance to mention that the first positron scanner was developed at Massachusetts General Hospital in 1970. There are advantages and disadvantages of time-of-flight positron emission tomography (TOFPET) as compared with the conventional non-TOFPET.
