Physical Factors Affecting Quantitative Measurements Using Camera-Based Single Photon Emission Computed Tomography (Spect)

Abstract
The qualitative imaging capability of single photon emission computed tomography (SPECT) using complete angular sampling has previously been demonstrated by several investigators. In order to obtain quantitative information such as absolute volumes and regional radionuclide concentrations using SPECT systems it is necessary to determine the system characteristics which contribute to the intrinsic measurement process and limit its precision. This manuscript describes some of the more important physical factors which can affect the measurement process of scintillation camera based SPECT systems and provides information concerning the type of quantitative measurements that can currently be obtained with these devices. Using our rotating camera based SPECT system the root mean square (rms) noise level in attenuation corrected images of a uniform cylindrical source was measured and found to agree with theoretically predicted vaiues obtained with the following equation: %rms = 100 (1.8)3/2 π Reff Rs1/2 Abody Cavg / 21/2Ntotal1/2(FF)1/2 where Reff is the "effective" radius of the source, RS is the actual source radius, Abody is the attenuation factor for surrounding non-source body material, Cavg is the average attenuation correction factor for the center of the source, Ntotal is the total number of events, and FF is the algorithm filter factor and equals the integral of the square of the spatial frequency filter function. Using a semi-automatic region of interest (ROI) program and the multi-slice capability of our SPECT system, the volumes of plastic spherical sources placed inside a larger cylindrical source were measured.