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Precise real‐time correction of Anger camera deadtime losses
Author(s) -
Woldeselassie Tilahun
Publication year - 2002
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1485996
Subject(s) - detector , energy (signal processing) , window (computing) , fraction (chemistry) , region of interest , spectrum analyzer , field of view , point source , field (mathematics) , physics , computer science , optics , algorithm , mathematics , computer vision , chemistry , organic chemistry , quantum mechanics , pure mathematics , operating system
An earlier paper dealt with modeling of the camera in terms of the resolving times, τ 0and 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 τ 0dependent on source distribution. It then discusses camera operation with an energy window, window fraction being f w= R p/ R d ⩽ 1 , where R dand R pare the detector and pulse‐height‐analyzer (PHA) outputs, respectively. The detector resolving time is shown to vary with window fraction according to τ 0 p= τ0 p/ f w , while T is unaffected, so that operation may be paralyzable or nonparalyzable depending on window setting and the ratio k T= T / τ 0 . Regions of interest are described in terms of the ROI fraction, f r= R r / R ⩽ 1 , and resolving time, τ 0 r= τ0 p/ f r , where R and R rare the recorded count rates for the field‐of‐view and the region‐of‐interest, respectively. As τ 0 pand τ 0 rare 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 f w⩽ 1 and f r⩽ 1 can be described by the simple paralyzable equationr = ne− n, wheren = N wτ 0 p= N rτ 0 randr = R pτ 0 p= R rτ 0 r,N w , and N rbeing 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 N w= n / τ0 pand N r= n / τ0 rto be obtained correct to better than 0.52% all the way up to the peak response point of the camera.