Quantification of the radionuclide image

The clinical value of radionuclide images can be increased by using quantification. The earliest radionuclide images were digital or quantitative in nature, but they were soon replaced by analog photoscans. Now, with the introduction of computers, quantitative digital scanning is again becoming widely used. Interfacing either rectilinear scanners or Anger-type scintillation cameras to a computer is no longer a difficult problem. Relatively low costs, insignificant dead times, and dependability are easy to achieve. The selection of an appropriate sampling interval is an important problem in quantitative scanning. If the interval is too large, resolution is degraded; it it is too small, costs increase rapidly, and counts recorded during each interval become so small that they lack statistical validity. This is true for both spatial (the static image) and temporal (dynamic function) analysis. Using sampling theory, a basis for interval selection is developed. With an Anger-type scintillation camera, 128×128 recording results in negligible degradation of resolution, a 64×64 array introduces detectable but acceptable loss, and a 32×32 array results in serious loss. The computer/camera system at the Denver VA Hospital has been designed for maximum flexibility and ease of use by the clinician and technician. New developments for this system allow display in different shades of gray with variable contrast, selective intensification of levels or regions of interest, framing rates of 20/sec, input of remote analog signals via telephone, resolution enhancement, and a sophisticated curve-analysis program with functions such as curve fitting, integration, differentiation, Fourier transformation, and deconvolution. Resolution enhancement of static images is carried out in the frequency domain through a new adaptive method of filtering and deconvolution with empirically selected logarithmic functions. Use of the system for dynamic studies is illustrated using radionuclide angiocardiography. Ventricular end systolic and diastolic volume, ejection fractions, and forward and backward (regurgitant) stroke volumes through all four cardiac valves can be determined quantitatively. Computed radioisotopic end diastolic volumes and ejection fractions correlate well with similar measurements determined by left cine ventriculography.