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Restoration of single photon emission computed tomography (SPECT) images is usually performed either on two-dimensional (2-D) projection images (pre-reconstruction restoration) or on SPECT slices (post-reconstruction restoration). This study presents the application of a three-dimensional (3-D) filter in restoring SPECT images. The 3-D filter is shown to perform better tha the 2-D methods because it takes into consideration the interslice information in the filtering process and has a relatively space-invariant blur function. To reduce the space-variance of the 3-D point spread function (PSF), conjugate projections were combined by geometric averaging before reconstruction. We investigated the potential of 3-D Wiener and power spectrum equalization (PSE) filters. These filters were applied to SPECT images of a resolution phantom and a large, truncated cone phantom containing two types of cold spots: a sphere, and a triangular prism. The filters were also applied to clinical images of the liver and spleen. The images were acquired on an ADAC GENESYS camera. A comparison was performed between results obtained in this study and those obtained by 2-D pre-reconstruction restoration and 2-D post-reconstruction restoration filters. Quantitative analysis of the 3-D restored images performed through measurement of root mean squared (RMS) errors and contrast ratios showe a considerable reduction in error and increase in contrast over images restored using the two other methods.

The discrete filtered backprojection (DFBP) algorithm used for the reconstruction of single photon emission computed tomography (SPECT) images affects image quality because of the operations of filtering and discretization. The discretization of the filtered backprojection process can cause the modulation transfer function (MTF) of the SPECT imaging system to be anisotropic and nonstationary, especially near the edges of the camera's field of view. The use of shift-invariant restoration techniques fails to restore large images because these techniques do not account for such variations in the MTF. This study presents the application of a two-dimensional (2-D) shift-variant Kalman filter for post-reconstruction restoration of SPECT slices. This filter was applied to SPECT images of a hollow cylinder phantom; a resolution phantom; and a large, truncated cone phantom containing two types of cold spots, a sphere, and a triangular prism. The images were acquired on an ADAC GENESYS camera. A comparison was performed between results obtained by the Kalman filter and those obtained by shift-invariant filters. Quantitative analysis of the restored images performed through measurement of root mean squared errors shows a considerable reduction in error of Kalman-filtered images over images restored using shift-invariant methods.

This paper presents a restoration scheme for single photon emission computed tomography (SPECT) images that performs restoration before reconstruction (prereconstruction restoration) from planar (projection) images. A comparison is performed between results obtained in this study and those obtained by a method reported previously where the restoration is performed after reconstruction (postreconstruction restoration). The filters investigated are the Wiener and power spectrum equalization filters. These filters are applied to SPECT images of a hollow cylinder phantom and a cardiac phantom acquired on a Siemens Rota camera. Quantitative analysis of the results are performed through measurements of contrast ratios and root mean squared errors. The prereconstruction restored images show a significant decrease in the root mean squared error and an increase in contrast over the postreconstruction restored images.

1 Hydroxychavicol (HC; 10-50 μM), a betel leaf component, was found to suppress the 2% H[sub 2]O[sub 2]induced lucigenin chemiluminescence for 53-75%. HC (0.02-2 μM) was also able to trap superoxide radicals generated by a xanthine/xanthine oxidase system with 38-94% of inhibition. Hydroxyl radicals-induced PUC18 plasmid DNA breaks was prevented by HC (1.6-16 μM). 2 A 24-h exposure of KB cells to HC (0.5, 1 mM) resulted in 54-74% cell death as analysed by a 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. HC (10, 50 μM) further suppressed the growth of KB cells (15 and 76%, respectively). Long-term colony formation of KB cells was inhibited by 51% with l0 μM HC. 3 Pretreatment of KB cells with 100 μg HC inhibited the attachment of KB cells to type I collagen and fibronectin by 59 and 29%, respectively. 4 Exposure of KB cells to 0.1 mM HC for 24 h resulted in cell cycle arrest at late S and G2/M phase. Increasing the HC concentration to 0.25 and 0.5 mM led to apoptosis as revealed by detection of sub-G[sub 0]/G[sub 1] peaks with a concomitant decrease in the number of cells residing in late S and G[sub 2]/M phase. 5 Inducing the apoptosis of KB cells by HC was accompanied by marked depletion in reduced form of GSH (> 0.2 mM) and the increasing of reactive oxygen species production (>0.1 mM) as analysed by CMF- and DCF-single cell fluorescence flow cytometry. 6 These results indicate that HC exerts antioxidant property at low concentration. HC also inhibits the growth, adhesion and cell cycle progression of KB cells, whereas its induction of KB cell apoptosis (HC > 0.1 mM) was accompanied by cellular redox changes. [ABSTRACT FROM AUTHOR]