| 1. |
- Ljungberg, Michael, et al.
(författare)
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Introduction to the Monte Carlo Method
- 1998
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Ingår i: Monte Carlo Calculations in Nuclear Medicine: Applications in Diagnostic Imaging. - 750304790 ; , s. 37-37
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Almquist, Helén, et al.
(författare)
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Quantitative SPECT by attenuation correction of the projection set using transmission data: evaluation of a method
- 1990
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Ingår i: European Journal Of Nuclear Medicine. - 1432-105X. ; 16:8-10, s. 587-594
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Tidskriftsartikel (refereegranskat)abstract
- A method for measuring attenuation coefficients in single-photon emission tomography (SPECT) is described and evaluated, together with a method for attenuation correction using these measured attenuation coefficients. Build-up, caused by scattered photons, is corrected for by a simple substitution in the algorithms. Transmission studies are performed with a 99mTc- or 57Co flood source, and emission phantom studies with 99mTc line sources. The method is evaluated with variable but well-defined phantoms. The result is accurate attenuation coefficients for different densities, dimensions and geometries, and an accuracy of corrected emission activities of better than +/- 10% in most cases. The present limitations of the method for attenuation correction are discussed.
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| 3. |
- de Jong, H W, et al.
(författare)
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The influence of backscatter material on 99mTc and 201Tl line source responses
- 1999
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Ingår i: Physics in Medicine and Biology. - 1361-6560. ; 44:3, s. 665-679
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Tidskriftsartikel (refereegranskat)abstract
- SPECT projections are contaminated by scatter, resulting in reduced image contrast and quantitative errors. When tissue is present behind the source, some of the detected photons backscatter via this tissue. Particularly in dual-isotope SPECT and in combined emission-transmission SPECT, backscatter constitutes a major part of the down-scatter contamination in lower-energy windows. In this paper, the effects of backscatter material were investigated. Planar images of 99mTc and 201Tl line sources between varying numbers of Perspex slabs were analysed using the photopeak windows and various scatter windows. In the 99mTc photopeak window no significant change in total counts due to backscatter material was measured. In the 201Tl photopeak window an increase of about 10% in total counts was observed. In the scatter windows an even more explicit influence of backscatter material was measured. For instance, at a forward depth of 10 cm, total counts of a 99mTc source detected in the 72 keV window eventually doubled with increasing backscatter material, compared with the situation without backscatter material. The backscatter contribution plateaued when more than 5-10 cm of scatter material was placed behind the source. In conclusion, backscatter should be taken into account, particularly in model-based down-scatter correction methods in dual-isotope SPECT and combined emission-transmission SPECT.
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| 4. |
- Floreby, L, et al.
(författare)
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Deformable Fourier surfaces for volume segmentation in SPECT
- 1998
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Ingår i: Proceeedings of the Fourteenth International Conference on Pattern Recognition. - 1051-4651. - 0818685123 ; 1, s. 358-360
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Konferensbidrag (refereegranskat)abstract
- Three-dimensional boundary finding based on Fourier surface optimization is presented as a method for segmentation of SPECT images. Being robust against noise and adjustable with respect to its detail resolution, it forms an interesting alternative in this application area. A three-dimensional approach can also be assumed to increase the possibility of delineating low contrast regions, as compared to a two-dimensional slice-by-slice approach. We apply boundary finding to Monte Carlo simulated SPECT images of the computer-based anthropomorphic Zubal phantom in order to evaluate the influence of object contrast and noise on the segmentation accuracy. Segmentation is also performed in real patient images
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| 5. |
- Gustafsson, Agnetha, et al.
(författare)
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Evaluation of attenuation corrections using Monte Carlo simulated lung SPECT
- 1998
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 43:8, s. 2325-2336
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 6. |
- Hademenos, George J, et al.
(författare)
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A Monte Carlo Investigation of the Dual Photopeak Window Scatter Correction Method
- 1993
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 40:2, s. 179-185
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Tidskriftsartikel (refereegranskat)abstract
- Results from a Monte Carlo investigation of the dual photopeak window (DPW) scatter correction method are presented for point and extended sources of Tc-99m in both homogeneous and nonhomogeneous attenuating media. The DPW method uses the ratio of counts in two nonoverlapping energy windows within the photopeak region as input to a regression relation. A pixel-by-pixel estimate of the scatter in the summed windows is obtained and subtracted to yield an estimate of the primary. An approximate tenfold decrease in the scatter fraction and an excellent agreement with the shape of the true scatter distribution were observed.
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| 7. |
- Hademenos, George J, et al.
(författare)
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A Scatter Correction Method for 201-Tl images: A Monte Carlo Investigation
- 1993
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 40:4, s. 1179-1186
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Tidskriftsartikel (refereegranskat)abstract
- Results from the application of a modified dual photopeak window scatter correction method to Monte Carlo simulated Tl-201 emission images are presented. In the Monte Carlo investigation, individual simulations are performed for six radiation emissions of Tl-201. For each emission, point sources of Tl-201 are imaged at various locations in a water-filled elliptical tub phantom using three energy windows. The DPW method is applied to each point source image to estimate the scatter distribution. For point source images in both homogeneous and nonhomogeneous attenuating media, the application of this modified version of DPW results in an approximately sixfold reduction in the scatter fraction and an excellent agreement of the shape of the tails between the estimated scatter distribution and the Monte Carlo-simulated truth. This method is also applied to two views of an extended cardiac distribution within an anthropomorphic phantom, again resulting in at least a sixfold improvement between the scatter estimate and the Monte Carlo-simulated true scatter.
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| 8. |
- Hademenos, George J, et al.
(författare)
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The Influence of Phantom Size, Shape, and Density, and Collimator Selection on the Dual Photopeak Scatter Correction Method
- 1994
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 41:1-2, s. 364-368
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Tidskriftsartikel (refereegranskat)abstract
- Results from a Monte Carlo investigation are presented for the application of the dual photopeak window (DPW) scatter correction method to phantom geometries of varying shapes, sizes, and densities as well as to several collimators. A Monte Carlo program was used to simulate a Tc-99m point source at locations of 0.5 cm from the phantom surface, at the center, 0.5 cm from the bottom, and 4/5 the distance lateral from the center for each case of variation. DPW was then used to correct for scatter using a regression relation determined for a 30.5 cm×23.0 cm water-filled elliptical tub phantom using an ultrahigh resolution collimator. The application of DPW in all cases accounted for an approximate twelve-fold reduction in scatter fraction with an excellent agreement between the true scatter and scatter estimate distributions both at the tails and under the peak of the point spread functions.
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| 9. |
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| 10. |
- Kimiaei, Shahrok, et al.
(författare)
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Evaluation of optimally designed planar-concave collimators in single-photon emission tomography
- 1997
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Ingår i: European Journal Of Nuclear Medicine. - : Springer Science and Business Media LLC. - 1432-105X .- 1619-7070 .- 1619-7089. ; 24:11, s. 1398-1404
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Tidskriftsartikel (refereegranskat)abstract
- The imaging properties of optimally designed planar-concave (PC) collimators were evaluated by means of Monte Carlo simulations. The evaluation was done with respect to total system spatial resolution and the overall image noise distribution in single-photon emission tomography. The results showed that the non-isotropy with PC collimators, assessed by the ratio of the full-width at half-maximum in the radial and tangential directions, was reduced by about 60% as compared with a conventional parallel-hole collimator for sources located 200 mm away from the centre of rotation. Furthermore, the image noise distribution along the object radius became more uniform when the curved collimator was used. The maximum increase in noise due to use of the curved collimator was about 45% close to the edge of the phantom, where the hole length was about 3 times longer. We also showed with Monte Carlo simulations that the spatial resolution of the lateral cortex when using the curved collimator was significantly improved due to improved radial resolution.
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