For pediatric patients, adequate attenuation correction can be obtained with very-low-dose CT (80 kVp, 5 mAs, 1.5:1 pitch), and such correction leads to a 100-fold dose reduction relative to diagnostic CT. For adults undergoing CT with 5 mAs and 1.5:1 pitch, the tube voltage needs to be increased to 120 kVp to prevent undercorrection.

Measures of structure activity concentration and volume carry independent information; both reveal group differences in prodromal AD.

The geometric component of the point spread function (PSF) of a gamma camera collimator can be determined analytically, and the penetration component can be calculated readily by numerical ray-tracing. A Monte Carlo simulation of photon transport which includes collimator scatter is developed. The simulation was implemented with an array processor which propagates up to 1024 photons in parallel, allowing accurate estimates of the total radial PSF in less than a day. The simulation was tested by imaging monoenergetic point sources of Tc-99m, Cr-51, and Sr-85 (140, 320, and 514 keV, respectively) on a General Electric Star Cam with low-energy, general-purpose, and medium-energy collimators. Comparisons of measured and simulated PSFs demonstrate the validity of the model and the significance of collimator scatter in the degradation of image quality.

(99m)Tc-MDP SPECT provides a quantitative method for assessing mandibular condylar uptake as a reflection of the activity of mandibular growth. The maximum pixel value of a 2-D ROI using external standardization and the right to left ratio of the condylar uptake provide the potential for quantitative evaluation of patients with mandibular asymmetry. These parameters will be further evaluated in an upcoming clinical investigation.