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Evaluation of attenuation corrections using Monte Carlo simulated lung SPECT
Department of Radiation Physics, University of Göteborg, Sahlgrenska University Hospital, Göteborg, Sweden .
Department of Clinical Physiology, University of Göteborg, Sahlgrenska University Hospital, Göteborg, Sweden .
Department of Radiation Physics, University of Göteborg, Sahlgrenska University Hospital, Göteborg, Sweden .
Department of Clinical Physiology, University of Göteborg, Sahlgrenska University Hospital, Göteborg, Sweden .
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1998 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 43, no 8, 2325-2336 p.Article in journal (Refereed) Published
Abstract [en]

SPECT (single photon emission computed tomography) images are distorted by photon attenuation. The effect is complex in the thoracic region due to different tissue densities. This study compares the effect on the image homogeneity of two different methods of attenuation correction in lung SPECT; one pre-processing and one post-processing method. This study also investigates the impact of attenuation correction parameters such as lung contour, body contour, density of the lung tissue and effective attenuation coefficient. The Monte Carlo technique was used to simulate SPECT studies of a digital thorax phantom containing a homogeneous activity distribution in the lung. Homogeneity in reconstructed images was calculated as the coefficient of variation (CV). The isolated effect of the attenuation correction was assessed by normalizing pixel values from the attenuation corrected lung by pixel values from the lung with no attenuation effects. Results show that the CV decreased from 12.8% with no attenuation correction to 4.4% using the post-processing method and true densities in the thoracic region. The impact of variations in the definition of the body contour was found to be marginal while the corresponding effect of variations in the lung contour was substantial.

Place, publisher, year, edition, pages
1998. Vol. 43, no 8, 2325-2336 p.
National Category
Medical Image Processing
Identifiers
URN: urn:nbn:se:liu:diva-79205DOI: 10.1088/0031-9155/43/8/023PubMedID: 9725607OAI: oai:DiVA.org:liu-79205DiVA: diva2:539121
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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