Precise real-time correction of anger camera deadtime losses.
An earlier paper dealt with modeling of the camera in terms of the resolving times, tau0 and T, of the paralyzable detector and nonparalyzable computer system, respectively, for the case of a full energy window. A second paper presented a decaying source method for the accurate real-time measurement of these resolving times. The present paper first shows that the detector system can be treated as a single device with a resolving time tau0 dependent on source distribution. It then discusses camera operation with an energy window, window fraction being fw = Rp/Rd < or = 1, where Rd and Rp are the detector and pulse-height-analyzer (PHA) outputs, respectively. The detector resolving time is shown to vary with window fraction according to tau0p = tau0p/f(w), while T is unaffected, so that operation may be paralyzable or nonparalyzable depending on window setting and the ratio kT = T/tau0. Regions of interest are described in terms of the ROI fraction, fr =Rr IR < or = 1, and resolving time, tau0r = tau0p/fr, where R and Rr are the recorded count rates for the field-of-view and the region-of-interest, respectively. As tau0p and tau0r are expected to vary with input rate, it is shown that these can be measured in real-time using the decaying source method. It is then shown that camera operation both with fw < or = 1 and fr < or = 1 can be described by the simple paralyzable equation r = ne(-n), where n=Nwtau0p=Nrtau0r and r=Rptau0p=Rrtau0r, Nw, and Nr being the input rates within the energy window and the region of interest, respectively. An analytical solution to the paralyzable equation is then presented, which enables the input rates Nw = n/tau0p and Nr = n/tau0r to be obtained correct to better than 0.52% all the way up to the peak response point of the camera.
Woldeselassie
Tilahun
T
Faculty of Technology, Addis Ababa University, Ethiopia.
D004867:Equipment Design; D015902:Gamma Cameras; D006801:Humans; D015233:Models, Statistical; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation* / Q000379:methods