PMID- 21815394
OWN - NLM
STAT- MEDLINE
DCOM- 20110824
LR  - 20240506
IS  - 0094-2405 (Print)
IS  - 0094-2405 (Electronic)
IS  - 0094-2405 (Linking)
VI  - 38
IP  - 6
DP  - 2011 Jun
TI  - Development and evaluation of a model-based downscatter compensation method for 
      quantitative I-131 SPECT.
PG  - 3193-204
AB  - PURPOSE: The radionuclide 131I has found widespread use in targeted radionuclide 
      therapy (TRT), partly due to the fact that it emits photons that can be imaged to 
      perform treatment planning or posttherapy dose verification as well as beta rays 
      that are suitable for therapy. In both the treatment planning and dose 
      verification applications, it is necessary to estimate the activity distribution 
      in organs or tumors at several time points. In vivo estimates of the 131I 
      activity distribution at each time point can be obtained from quantitative 
      single-photon emission computed tomography (QSPECT) images and organ activity 
      estimates can be obtained either from QSPECT images or quantification of planar 
      projection data. However, in addition to the photon used for imaging, 131I decay 
      results in emission of a number of other higher-energy photons with significant 
      abundances. These higher-energy photons can scatter in the body, collimator, or 
      detector and be counted in the 364 keV photopeak energy window, resulting in 
      reduced image contrast and degraded quantitative accuracy; these photons are 
      referred to as downscatter. The goal of this study was to develop and evaluate a 
      model-based downscatter compensation method specifically designed for the 
      compensation of high-energy photons emitted by 131I and detected in the imaging 
      energy window. METHODS: In the evaluation study, we used a Monte Carlo simulation 
      (MCS) code that had previously been validated for other radionuclides. Thus, in 
      preparation for the evaluation study, we first validated the code for 131I 
      imaging simulation by comparison with experimental data. Next, we assessed the 
      accuracy of the downscatter model by comparing downscatter estimates with MCS 
      results. Finally, we combined the downscatter model with iterative 
      reconstruction-based compensation for attenuation (A) and scatter (S) and the 
      full (D) collimator-detector response of the 364 keV photons to form a 
      comprehensive compensation method. We evaluated this combined method in terms of 
      quantitative accuracy using the realistic 3D NCAT phantom and an activity 
      distribution obtained from patient studies. We compared the accuracy of organ 
      activity estimates in images reconstructed with and without addition of 
      downscatter compensation from projections with and without downscatter 
      contamination. RESULTS: We observed that the proposed method provided substantial 
      improvements in accuracy compared to no downscatter compensation and had 
      accuracies comparable to reconstructions from projections without downscatter 
      contamination. CONCLUSIONS: The results demonstrate that the proposed model-based 
      downscatter compensation method is effective and may have a role in quantitative 
      131I imaging.
FAU - Song, Na
AU  - Song N
AD  - Division of Medical Imaging Physics, Department of Radiology, Johns Hopkins 
      Medical Institutions, Baltimore, Maryland 21287, USA. nsong5@jhu.edu
FAU - Du, Yong
AU  - Du Y
FAU - He, Bin
AU  - He B
FAU - Frey, Eric C
AU  - Frey EC
LA  - eng
GR  - R01 CA109234/CA/NCI NIH HHS/United States
GR  - R01 CA 109234/CA/NCI NIH HHS/United States
PT  - Evaluation Study
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
RN  - 0 (Iodine Radioisotopes)
SB  - IM
MH  - Humans
MH  - Image Processing, Computer-Assisted
MH  - Iodine Radioisotopes
MH  - *Models, Theoretical
MH  - Monte Carlo Method
MH  - Photons
MH  - *Scattering, Radiation
MH  - Tomography, Emission-Computed, Single-Photon/*methods
PMC - PMC3125085
EDAT- 2011/08/06 06:00
MHDA- 2011/08/25 06:00
PMCR- 2012/06/01
CRDT- 2011/08/06 06:00
PHST- 2011/08/06 06:00 [entrez]
PHST- 2011/08/06 06:00 [pubmed]
PHST- 2011/08/25 06:00 [medline]
PHST- 2012/06/01 00:00 [pmc-release]
AID - 028106MPH [pii]
AID - 10.1118/1.3590382 [doi]
PST - ppublish
SO  - Med Phys. 2011 Jun;38(6):3193-204. doi: 10.1118/1.3590382.