A Correction Method for High-Count-Rate Quantitative Radionuclide Angiography

Freedman, Gerald S.; Kinsella, Timothy J.; Dwyer, Andrew J.

doi:10.1148/104.3.713

Cited by 19 publications

(7 citation statements)

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“…Moreover, European Union regulations would probably forbid the use of such an apparatus on patients. Freedman et al (1972), Sorenson (1976) and Inoue et al (1997) assumed that these losses were uniform over the entire scintillation camera detector and therefore used the sensitivity variation obtained for a standard source of known activity.…”

Section: Introductionmentioning

confidence: 99%

Correction of count losses due to deadtime on a DST-XLi (SMVi-GE) camera during dosimetric studies in patients injected with iodine-131

et al. 2002

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In dosimetric studies performed after therapeutic injection, it is essential to correct count losses due to deadtime on the gamma camera. This note describes four deadtime correction methods, one based on the use of a standard source without preliminary calibration, and three requiring specific calibration and based on the count rate observed in different spectrometric windows (20%, 20% plus a lower energy window and the full spectrum of 50-750 keV). Experiments were conducted on a phantom at increasingly higher count rates to check correction accuracy with the different methods. The error was less than +7% with a standard source, whereas count-rate-based methods gave more accurate results. On the assumption that the model was paralysable, preliminary calibration allowed an observed count rate curve to be plotted as a function of the real count rate. The use of the full spectrum led to a 3.0% underestimation for the highest activity imaged. As count losses depend on photon flux independent of energy, the use of the full spectrum during measurement allowed scatter conditions to be taken into account. A protocol was developed to apply this correction method to whole-body acquisitions.

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Section: Introductionmentioning

confidence: 99%

Correction of count losses due to deadtime on a DST-XLi (SMVi-GE) camera during dosimetric studies in patients injected with iodine-131

et al. 2002

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“…Traditionally, this correction factor is applied to the observed object acount rate M 2 , and the corrected count rate ′ N 2 is then calculated as (Freedman et al 1972, Sorenson 1976, Zasadny et al 1993, Woldeselassie 2002):…”

Section: Count Loss Compensation Methods For Images In Photopeak Ener...mentioning

confidence: 99%

“…Another approach for deadtime correction is the monitor source method (Freedman et al 1972, Sorenson 1976, Madsen and Nickles 1986, Woldeselassie 2002. This method is based on the assumption that deadtime losses for the monitor source are the same as those for the imaged object.…”

Section: Introductionmentioning

confidence: 99%

A revised monitor source method for practical deadtime count loss compensation in clinical planar and SPECT studies

2015

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The aim of the study is to verify the fundamental assumption in the monitor source method, i.e. uniform fractional count loss across the field of view (FOV), and to introduce a revised monitor source method for SPECT deadtime correction that minimally interferes with the clinical protocol. SPECT images of non-uniform phantoms (4GBq (99m)Tc) with and without monitor sources (2 × 20MBq (99m)Tc) attached to each detector were acquired nine times over 48 h in the photopeak energy window and the scatter energy window. Fractional count loss uniformity across the FOV was evaluated by correlating count rates in different regions of interest on projection images at different deadtime loss levels. The correction factors were calculated as the ratios of monitor source count rates with and without the phantom. Such factors were applied to the phantom images acquired without the monitor sources. The counting efficiency (count rate per unit activity) of the camera was calculated as a function of activity in the FOV both prior to and after the deadtime count-loss correction. The deadtime correction effectiveness was assessed by the independence of the efficiency on the activity in the FOV. Methods to interpolate the projection deadtime loss, based on limited projections, were also investigated. The fractional deadtime count loss was uniform across the FOV (r > 0.99). After the deadtime correction, the efficiency was largely independent of the activity in the FOV. The median and maximum absolute errors after the deadtime count loss correction were ≤1% and ~2%, respectively. Measured deadtime loss from five views per detector can be used to estimate deadtime count loss with errors ≤1% for all SPECT projections. The revised monitor source method can effectively correct planar and SPECT deadtime loss. Sparse sampling of the projection deadtime loss allows the acquisition of high monitor source counts with minimal time added while preserving the entire useful FOV.

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“…The second approach is that based on the reference or ''monitor source'' method of Freeman et al 7 or the electronic pulser method of Nickles et al 8 These involve placing the source or pulser at the edge of the detector and monitoring its count rate variations to determine a correction factor. This is taken as the ratio cϭR 0r /R r of the monitor-source rate R 0r when measured alone and its rate R r when an activity distribution is being imaged.…”

Section: B Real-time Correction Of Deadtime Lossesmentioning

confidence: 99%

Precise real‐time correction of Anger camera deadtime losses

Woldeselassie¹

2002

Medical Physics

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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.

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A Correction Method for High-Count-Rate Quantitative Radionuclide Angiography

Cited by 19 publications

References 0 publications

Correction of count losses due to deadtime on a DST-XLi (SMVi-GE) camera during dosimetric studies in patients injected with iodine-131

Correction of count losses due to deadtime on a DST-XLi (SMVi-GE) camera during dosimetric studies in patients injected with iodine-131

A revised monitor source method for practical deadtime count loss compensation in clinical planar and SPECT studies

Precise real‐time correction of Anger camera deadtime losses

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