Deadtime of scintillation camera systems—definitions, measurement and applications
作者:
Ralph Adams,
Carl Jansen,
George M. Grames,
C. Duane Zimmerman,
期刊:
Medical Physics
(WILEY Available online 2003)
卷期:
Volume 1,
issue 4
页码: 198-203
ISSN:0094-2405
年代: 2003
DOI:10.1118/1.1637295
出版商: American Association of Physicists in Medicine
数据来源: WILEY
摘要:
Fast quantitative dynamic studies with scintillation camera systems require deadtime correction. Although such systems are semiparalyzable, they are most conveniently treated either as paralyzable or nonparalyzable. Paralyzing deadtime (τ) is that deadtime during which a system is unable to provide a second output pulse unless there is a time interval of at least τ between two successive events. Paralyzable systems are characterized by Poisson statistics, so that the “true” counting rateN = R eN τ, whereRis the observed counting rate. Nonparalyzing deadtime (T) is that deadtime during which a system is insensitive after eachobservedevent. The period of insensitivity is not affected by any additional “true” events before full recovery occurs. For nonparalyzable systems the corrected counting rateN = R / (1 − RT). A two‐source method protocol is presented for deadtime measurement. The paralyzing deadtime is calculated by a 5‐dimension Newton–Raphson iteration. The nonparalyzing deadtime is calculated by a quadratic equation. Approximation equations are also presented not requiring a computer. Deadtimes are fitted to polynomial equations as dependent variables of measured counting rate. Algorithms incorporating the polynomials are presented for the deadtime correction of histogram curves. Using either the paralyzing or the nonparalyzing approach, precise deadtime corrections are demonstrated.
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