An improved method for rapid objective measurement of gamma camera resolution

An improved method for an easy, rapid measurement of the intrinsic spatial resolution of a gamma camera is presented. A simplified model was previously developed based solely on mean and standard deviation measurements taken from a region of interest in bar pattern images. This led to an estimate of the modulation transfer function and the full width at half maximum (FWHM) of a line spread function (LSF). The improved method involved expanding the simplified model to incorporate input modulation, square wave input versus the assumed sinusoidal input, aperture (pixel) size, and scatter from the plastic in the bar pattern. The input square wave modulation was calculated to be unity for the typical bar patterns used for gamma cameraquality control assessment. For the typical range of bar sizes available, in combination with the typical resolving capabilities of gamma cameras, the sinusoidal approximation of the bar pattern was found to be valid ( contribution to the measured resolution from higher harmonic frequencies present in a square wave input with an effective input modulation greater than unity by a factor of 4/π). The aperture correction factor was calculated for numerous bar and pixel size combinations. Applying the aperture correction factor results in an improvement in the accuracy of the calculated FWHM values, especially for large apertures (pixel sizes). For a camera with a specified FWHM value of 3.5 mm, the simplified model predicts values ranging from 3.2 to 4.1 mm, when the acquisition matrix varies from 128 2 to 512 2 . When the expanded model is used with the aperture correction applied, this range was reduced to 3.6–3.9 mm. The scatter correction further improved the calculated FWHM (from 3.6 to 3.8 mm). It is suggested that the expanded model should be used when more accurate measurements are desired, such as in acceptance testing.