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Attenuation correction in quantitative SPECT of cerebral blood flow: a Monte Carlo study
Department of Radiation Physics, Göteborg University, Sahlgrenska University Hospital, Göteborg, Sweden .
Department of Radiation Physics, Göteborg University, Sahlgrenska University Hospital, Göteborg, Sweden .
Department of Radiation Physics, Göteborg University, Sahlgrenska University Hospital, Göteborg, Sweden .
Radiation Physics Department, Lund University, The Jubileum Institute, Lund, Sweden .
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2000 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 45, no 12, 3847-3859 p.Article in journal (Refereed) Published
Abstract [en]

Monte Carlo simulation has been used to produce projections from a voxel-based brain phantom, simulating a 99mTc-HMPAO single photon emission computed tomography (SPECT) brain investigation. For comparison, projections free from the effects of attenuation and scattering were also simulated, giving ideal transaxial images after reconstruction. Three methods of attenuation correction were studied: (a) a pre-processing method, (b) a post-processing uniform method and (c) a post-processing non-uniform method using a density map. The accuracy of these methods was estimated by comparison of the reconstructed images with the ideal images using the normalized mean square error, NMSE, and quantitative values of the regional cerebral blood flow, rCBF. A minimum NMSE was achieved for the effective linear attenuation coefficient µeff = 0.07 (0.09) cm-1 for the uniformpre method, the effective mass attenuation coefficient µeff/ρ = 0.08 (0.10) cm2 g-1 for the uniformpost method and µeff/ρ = 0.12 (0.13) cm2 g-1 for the non-uniformpost method. Values in parentheses represent the case of dual-window scatter correction. The non-uniformpost method performed better, as measured by the NMSE, both with and without scatter correction. Furthermore, the non-uniformpost method gave, on average, more accurate rCBF values. Although the difference in rCBF accuracy was small between the various methods, the same method should be used for patient studies as for the reference material.

Place, publisher, year, edition, pages
Institute of Physics Publishing , 2000. Vol. 45, no 12, 3847-3859 p.
National Category
Medical Image Processing
Identifiers
URN: urn:nbn:se:liu:diva-79208DOI: 10.1088/0031-9155/45/12/324PubMedID: 11131204OAI: oai:DiVA.org:liu-79208DiVA: diva2:539131
Available from: 2012-07-03 Created: 2012-07-03 Last updated: 2017-12-07
In thesis
1. Evaluation of attenuation and scatter corrections in lung and brain SPECT
Open this publication in new window or tab >>Evaluation of attenuation and scatter corrections in lung and brain SPECT
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Single Photon Emission Computed Tomography (SPECT) is used to image functional processes in the human body. The image process is affected by physical effects such as attenuation, scatter, spatial resolution and statistical noise. The aim of this work was to investigate how attenuation and scatter effects and their associated correction methods affect the image quality in lung and brain SPECT.

The effects of attenuation and scattering on the image of a uniform activity distribution in the lungs was investigated using Monte Carlo simulated data and the attenuation effect was evaluated in healthy volunteers. The homogeneity was measured as the CV inside a well-defined lung contour. The attenuation effect in lung SPECT was estimated to be about 13-14% expressed as the CV. The homogeneity improved with increasing accuracy of the attenuation correction method. After attenuation correction the remaining inhomogeneity in healthy subjects was considerable and could not be explained by statistical noise and camera non-uniformity. A non-uniform attenuation correction was thus required and a TCT-based density map was found to be adequate in most instances.

The accuracy of the attenuation correction methods was studied in Monte Carlo simulated brain SPECT using the normalised mean square error, NMSE. The different degrees of accuracy in the methods were also reflected in the absolute deviation of the relative regional cerebral blood flow (rCBF) according to the min-max method. The NMSE value improved with the accuracy of the attenuationcorrection method. The difference in relative rCBF value was generally less than 5%. Therefore, it is unlikely that the choice of attenuation correction method will affect the diagnostic accuracy.

The detectability, expressed as the contrast-to-noise-ratio dependence on the choice of energy window, was evaluated using SPECT studies of a thorax phantom containing cold lesions inside the lungs and a realistic brain phantom. The effects of subtractive scatter correction methods such as the dual-window method (DW), the triple-energy-window method (TEW) and the Klein-Nishina method (KN) were also evaluated. An optimal photopeak window setting was found to be 128-154 keV in lung SPECT for a gamma camera with 10% energy resolution, and 130-154 keV in rCBF SPECT for a gamma camera with 9% energy resolution. The detection limit for lung SPECT for spherical lesions is about 2 cm in diameter when normal variations in the lungs are relatively small compared with the statistical noise level. Under these conditions the detectability is degraded by using scatter correction, except when the TEW scatter correction is used for small lesions (<3 cm in diameter), when about the same detectability is achieved.

Place, publisher, year, edition, pages
Göteborg: Göteborgs universitet, 2001. 64 p.
Keyword
SPECT, attenuation, scatter, detectability, Monte Carlo simulation
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-28146 (URN)12959 (Local ID)91-638-4850-X (ISBN)12959 (Archive number)12959 (OAI)
Public defence
2001-06-01, Sal F3 Odontologen, Medicinaregatan 12 D, Göteborg, 09:15 (Swedish)
Opponent
Note

Doktorsavhandling framlagd vid Göteborgs universitet 2001-06-01

Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2013-02-27

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