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Scatter and detecability in lung SPECT: a Monte Carlo study
Department of Radiation Physics, Göteborg University, Sweden.
Department of Hospital Physics, Section for Nuclear Medicine, Karolinska Hospital, Stockholm, Sweden.
Radiation Physics Department, Lund University, The Jubileum Institute, Lund, Sweden.
Department of Respiratory Medicine and Allergology, Göteborg University, Göteborg, Sweden.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The image quality in SPECT is degraded by scattered photons. The finite energy resolution of the gamma camera makes the detection of scattered photons unavoidable. The effect on the image is impaired contrast and a reduction in the possibilities of detecting small lesions.

The detectability of cold lesions above statistical noise and normal variations in the activity distribution was evaluated using the Monte Carlo technique. A SPECT study of a digital thorax phantom was simulated with cold lesions of different sizes positioned inside the homogeneous activity distribution in the lungs. The contrast-to-noise for a number of energy window settings were assessed, with and without three different scatter correction methods: the dual-window, the triple-energy-window and the Klein-Nishina method.

The contrast was improved by using scatter corrections and the TEW and KN scatter corrections showed the best result. The detectability was not improved by using scatter corrections when normal variations in the lung activity are small compared with the statistical noise level. Lesions of about 2 cm in diameter are detectable. The optimum energy window was found to be 128-154 keV, both with and without scatter corrections.

Keyword [en]
Scatter correction, detectability, SPECT, Monte Carlo, lung
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-89581OAI: diva2:608336
Available from: 2013-02-27 Created: 2013-02-27 Last updated: 2013-02-27
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.
SPECT, attenuation, scatter, detectability, Monte Carlo simulation
National Category
Medical and Health Sciences
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)

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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Gustafsson, Agnetha
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