Use of profile analysis for the measurement of organ dimensions

We have developed a method for measurement of organ dimension based on the use of the full width half maximum (FWHM) of profiles taken through an organ. In vitro studies were performed using a large rectangular lucite box filled with water. Five circular lucite phantoms with internal diameters of 1.4-10.2 cm and 1 elliptical phantom with dimensions 9.6 x 4.0 cm were filled with 99mTc-pertechnetate at various concentrations. Phantoms were imaged on a gamma camera at a depth of 5-25 cm in water and the FWHM calculated from horizontal profiles taken across the cylinders. The FWHM showed no variation with 99mTc concentration in the same cylinder. Phantom profiles were deconvolved with a system line spread function measured under similar conditions of scatter and depth. The correction factor to convert the deconvolved profile FWHM to true diameter was independent of cylinder depth and diameter over a range of FWHM 3-10 cm and depth 5-25 cm. The mean value for the correction factor was 1.23 +/- 0.04 for circular phantoms and 1.14 +/- 0.02 for the elliptical phantom. This technique should allow an objective and reproducible estimate of organ dimensions from planar images that is relatively independent of the depth and size of an organ.