Faculty Bibliography

Describes a multicounter unit with buffers for storage and transmission of collected counts to the host computer. The system is highly flexible, inexpensive, and able to communicate with computers without direct memory access capability. A prototype has been built at New York University Medical Center for use with a 200-element detector array for measuring the 3-D distribution of cerebral blood flow. The multicounter will free the computer from continuous scanning of the detectors to perform on-line display and storage of collected data. An important feature of the unit is that its proper operation can be quickly verified with the aid of the host computer and detailed diagnosis obtained in case of malfunction

A new stationary 200-element ultrapure germanium (HPGe) array has been tested for accuracy and sensitivity in quantitating the distributed concentration of single-gamma-emitting radionuclides in phantoms approximating the size of the human brain. The phantoms consisted of 42 blocks of 39.1 cm3 average volume. Fourteen different permutations were studied. The concentrations in the blocks varied from 0i to 4.64 muCi/cm3. This first-generation instrument makes it possible to reconstruct the distributed concentration with a mean relative error of 8.3% at 200,000 counts per sample (1,000 counts/detector), and has sensitivities of 6,200 and 12,000 cps, respectively, for 1 muCi/cm3 of Xe-133 and Tc-99. The reconstruction algorithm is based on the conjugate gradient method of solving the set of linear equations that account for geometric, attenuation, and scatter factors. The results have implications for measuring the distribution of the partition coefficients, blood flow, blood volume, and concentration of tracers emitting single gamma photons in 42 anatomic subvolumes (30 cm3 average) of the entire brain simultaneously