| 1. |
- Arlig, A, et al.
(author)
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Attenuation correction in quantitative SPECT of cerebral blood flow: a Monte Carlo study
- 2000
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In: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 45:12, s. 3847-3859
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Journal article (peer-reviewed)abstract
- 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 mu(eff) = 0.07 (0.09) cm(-1) for the uniform(pre) method, the effective mass attenuation coefficient mu(eff)/rho = 0.08 (0.10) cm2 g(-1) for the uniform(post) method and mu(eff)/rho = 0.12 (0.13) cm2 g(-1) for the non-uniform(post) method. Values in parentheses represent the case of dual-window scatter correction. The non-uniform(post) method performed better, as measured by the NMSE, both with and without scatter correction. Furthermore, the non-uniform(post) 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.
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| 2. |
- Gustafsson, Agnetha, 1960-, et al.
(author)
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Dual-window scatter correction and energy window setting in cerebral blood flow SPECT: a Monte Carlo study
- 2000
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In: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 45:11, s. 3431-3440
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Journal article (peer-reviewed)abstract
- The image quality in SPECT studies of the regional cerebral blood flow (rCBF) performed with 99mTc-HMPAO is degraded by scattered photons. The finite energy resolution of the gamma camera makes the detection of scattered photons unavoidable, and this is observed in the image as an impaired contrast between grey and white matter structures. In this work, a Monte Carlo simulated SPECT study of a realistic voxel-based brain phantom was used to evaluate the resulting contrast-to-noise ratio for a number of energy window settings, with and without the dual-window scatter correction. Values of the scaling factor k, used to obtain the fraction of scattered photons in the photopeak window, were estimated for each energy window. The use of a narrower, asymmetric, energy discrimination window improved the contrast, with a subsequent increase in statistical noise due to the lower number of counts. The photopeak-window setting giving the best contrast-to-noise ratio was found to be the same whether or not scatter correction was applied. Its value was 17% centred at 142 keV. At the optimum photopeak-window setting, the contrast was improved by using scatter correction, but the contrast-to-noise ratio was made worse.
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| 3. |
- Lundin, Fredrik, et al.
(author)
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Reduced thalamic N-acetylaspartate in idiopathic normal pressure hydrocephalus: a controlled (1)H-magnetic resonance spectroscopy study of frontal deep white matter and the thalamus using absolute quantification
- 2011
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In: Journal of Neurology, Neurosurgery and Psychiatry. - : BMJ Publishing Group. - 0022-3050 .- 1468-330X. ; 82:7, s. 772-778
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Journal article (peer-reviewed)abstract
- Introduction Patients with idiopathic normal pressure hydrocephalus (INPH) frequently have a reduction in cerebral blood flow in the subcortical frontal lobe/basal ganglia/thalamic areas. With magnetic resonance spectroscopy, the metabolism in the brain can be examined. The aim of this study was to investigate if there was a compromised metabolism in the thalamus and in the subcortical frontal areas in INPH patients. This was done by measuring total creatine, myo-inositol, total choline, N-acetylaspartate (NAA), total N-acetylaspartate (tNA), glutamate and lactate levels. A comparison was made with healthy individuals (HI). Subjects and methods 16 patients (nine males, seven females, mean age 74 years, range 49-83) diagnosed as INPH and 15 HI (nine males, six females, mean age 74 years, range 62-89) were examined. 1 H magnetic resonance spectroscopy (1.5 T, point-resolved spectroscopy, echo time/relaxation time 30/3000 ms, volume of interest 2.5-3 ml) was performed in frontal deep white matter and in the thalamus. Absolute quantification with internal water as a reference was used. Results INPH patients had lower NAA (p = 0.02) and lower tNA (p = 0.05) concentrations in the thalamus compared with HI. NAA and tNA in the frontal deep white matter did not differ between patients and HI. The absolute metabolic concentrations of total creatine, myoinositol total choline, tNA, lactate and Cr ratios in frontal deep white matter and in the thalamus were similar in INPH patients and HI. Conclusion Reduced thalamic NAA and tNA in INPH patients suggest a compromised metabolic neuronal function in these regions. Thus, the thalamus might have an important role in the pathogenesis of INPH.
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| 6. |
- Ärlig, A, et al.
(author)
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Selection of collimator for rCBF studies and evaluation of triple-headed SPET using noise-resolution plots
- 1997
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In: Nuclear Medicine Communications. - 1473-5628. ; 18:7, s. 655-661
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Journal article (peer-reviewed)abstract
- We investigated the effect of collimator selection on image quality in regional cerebral blood flow (rCBF) studies of the brain performed with 99Tc(m)-HMPAO. A triple-headed SPET system (GE/CGR Neurocam) was used, together with three sets of parallel-hole collimators - general-purpose (GP), high-resolution (HR) and ultra-high-resolution (UHR). Two image quality parameters were used to describe the image quality, namely, noise and resolution. Noise was measured in experimental and Monte-Carlo simulated SPET studies of a cylinder phantom of uniform activity as the pixel root mean square error (RMS) and as the coefficient of variation (CV) of quantitative rCBF values. Resolution was measured as full-width at half-maximum in experimental SPET studies of a line-source. Plots of noise versus resolution for the different collimators were obtained by varying the cut-off frequency of the Hanning filter applied in the reconstruction of transaxial slices. From these noise-resolution plots, we were able to determine which collimator gave the best resolution for a specific noise level. A lowest reasonable noise level may be established by comparison with the inter-observer CV of the quantification method.
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