Search

Motion of the head during brain positron emission tomography (PET) acquisitions has been identified as a source of artifact in the reconstructed image. A number of techniques have been proposed to correct for this motion artifact, but they are unable to correct for a motion during an acquisition. The aim of this study was to develop a sinogram-based motion correction (SBMC) technique to correct directly the head motion during a PET scan using a motion tracking system and list-mode data acquisition. This method uses a rebinning procedure whereby the lines of response (LOR) are geometrically transformed according to the current values of six-dimensional motion data. A Michelogram was recomposed using the rebinned LOR, and the motion-corrected sinogram was generated. In the motion corrected image, the blurring artifact due to the motion was reduced by the SBMC technique. This technique was applied to actual PET data acquired in the list-mode, and demonstrated the potential for real-time motion correction of head movements during a PET acquisition. Index Terms--Motion correction, optical tracking system, PET, sinogram.

Transmission-dependent convolution subtraction (TDCS) is a promising technique in quantitative SPECT for subtracting the scatter components from emission images. Usually, a 20% photopeak energy window is used in SPECT acquisitions. To date, no investigation has assessed the effects of energy windows in the subtraction of scatter components from emission images with the TDCS technique. To evaluate the energy dependence of the TDCS technique, we analyzed photopeak energy windows of 5%, 10%, 15%, 20%, 25%, 30%, and 35% using [sup.99m]Tc radionuclide. The scatter fractions for a point source placed in a water phantom were estimated using the triple-energy-window (TEW) technique. These estimates were used to establish the parameters of the TDCS equation as a function of transmission. The estimated parameters were applied to the TDCS technique to subtract the scatter components from data of corresponding energy windows using nonuniform and uniform phantoms. All data were reconstructed with the OSEM algorithm. The energy window dependence of the TDCS technique was verified by comparing the coefficients of variance (COV) of the data from the uniform phantom of each energy window. Ten Poisson deviates were generated from each projection's data from the uniform phantom. The nonuniform phantom results showed that the estimated parameters effectively estimated the scatter component from the projection image for each energy window. The COV for the 5%, 10%, 15%, 20%, 25%, 30%, and 35% windows were 2.10%, 1.76%, 1.44%, 1.39%, 1.34%, 1.37%, and 1.61%, respectively. In the TDCS technique, any photopeak energy window from 15% to 30% may work almost as well as judged by the COV measured for a uniform phantom in this study. The best window by that measure was the 25% window. Index Terms--Energy dependency, scatter correction, SPECT, TDCS.

A new input function monitoring system has been developed and evaluated using a GSO detector assembly for both PET and SPECT quantitative studies. Energy resolutions were 11% for 511 kev photons, 20% for 140 keV([sup.99m]Tc) photons and 28% for 70 keV([sup.201]Tl) photons, enabling the use of this system in SPECT studies. The paired assembly of crystals provided an absolute sensitivity of approximately 7% for PET tracers and 70% for [sup.99m]Tc and [sup.201]Tl (SPECT tracers). Multiple arrangement of paired detectors would make it possible to correct for the transit time of radioactivity through the catheter tube. This study demonstrates that the present system can be of use in both clinical and small animal studies using SPECT and PET tracers. Index Terms--Arterial input function monitor, positron emission tomography (PET), single photon emission tomography.

Attenuation and scatter of photons are the main causes that hinder the quantification of regional cerebral blood flow (rCBF) value by single photon emission computed tomography (SPECT), using [sup.99m]Tc-Ethyl cysteinate dimer (ECD). We investigated the effects of attenuation correction and scatter correction on rCBF values with [sup.99m]Tc-ECD SPECT. In particular, the applicability of uniform attenuation maps ([mu] maps) was evaluated in terms of errors on the estimated CBF values and the optimal threshold levels for extracting brain contours. SPECT scans were performed on seven subjects, in the presence of [sup.99m]Tc-ECD. Quantitative [K.sub.1] images were computed using the reconstructed images and the input function obtained with the frequent arterial blood sampling method. The images were reconstructed by the ordered subset expectation maximization (OSEM) reconstruction in which uniform and segmented [mu] maps were used for attenuation correction with and without scatter correction. The transmission-dependent convolution subtraction technique was utilized for scatter correction. Segmented and uniform [mu] maps were generated from magnetic resonance (MR) images. We also produced uniform [mu] maps using ECD images obtained at various threshold levels and [mu] values (0.11, 0.15, and 0.172 [cm.sup.-1]). Scatter correction improved the image contrast dramatically. There were no significant differences between [K.sub.1] images with attenuation and scatter corrections assuming a uniform [mu] map (not 0.15 but 0.172 [cm.sup.-1]) and those corrected with segmented [mu] maps for most regions. However, in the former images, values were overestimated for deep structures (e.g., overestimation of 9.5% in the striatum and 7.3% in the central semi oval). This small but significant error was also observed in phantom studies and Monte Carlo simulations. We show that the overestimation using uniform [mu] maps is due to the weight of the path length in the bone. Absolute [K.sub.1] values were sensitive to the threshold level when the edge of the brain was determined from the ECD images, but the variation of the estimated [K.sub.1] was [+ or -] 9.0% when the optimal threshold level was selected. This study suggests that the use of uniform attenuation [mu] maps provides reasonable accuracy, despite a small but significant error in deep structure regions, and that uniform [mu] maps may be provided from the emission data alone in this patient population. Index Terms--Attenuation correction, scatter correction.

A noninvasive blood radioactivity monitor system for Positron Emission Tomography (PET) study has been developed. This system has dual plastic scintillators to detect positrons from the wrist artery. One is for monitoring the blood radioactivity in artery and tissue, and another is for monitoring only in tissue, in order to subtract background radiation from tissue. We carried out phantom experiments for evaluating basic characteristics of this monitor system. Clinical experiments using 15O-labeled water were also done to compare this system with a conventional invasive monitor.

Scatter correction is important for absolute quantification in SPECT. Among the approaches taken to achieve scatter correction, some methods using transmission information for scatter estimation require the scatter models based on the physical characteristics of the scattered photons. The influence of the SPECT collimator on the characteristics of the scattered photon, however, has not been well studied yet. In this paper, we investigate the relationship between scatter and collimator design for the use of the transmission-dependent convolution subtraction (TDCS) method. Monte Carlo simulations with various collimator acceptance angles and experiments with four collimators of two SPECT cameras were performed to obtain the scatter fraction (SF) and the line-spread function (LSF) of Tc-99m. The experiments with I-123 also used six collimators of three SPECT systems to obtain the SF and the LSF. In the simulations, the SF of Tc-99m did not change with the collimator acceptance angles. The LSFs measured for Tc-99m showed an excellent agreement between collimators. In the experiments for I-123, the SF was practically the same for the six collimators, although a small difference could be observed due to the septal penetration. Also, the shape of the LSF was very similar between the collimators, and the counts in the background region of reconstructed images did not differ when using different sets of TDCS parameters. These results reveal that scatter is independent of SPECT collimator design for Tc-99m even I-123, and that the TDCS could be applicable to scatter correction of I-123 using a unique collimator-independent set of parameters. Index Terms--Scatter correction, SPECT collimator.

Transmission-dependent convolution subtraction (TDCS) is a promising technique in quantitative SPECT for subtracting the scatter components from emission images. Usually, a 20% photopeak energy window is used in SPECT acquisitions. To date, no investigation has assessed the effects of energy windows in the subtraction of scatter components from emission images with the TDCS technique. To evaluate the energy dependence of the TDCS technique, we analyzed photopeak energy windows of 5%, 10%, 15%, 20%, 25%, 30%, and 35% using 99mTc radionuclide. The scatter fractions for a point source placed in a water phantom were estimated using the triple-energy-window (TEW) technique. These estimates were used to establish the parameters of the TDCS equation as a function of transmission. The estimated parameters were applied to the TDCS technique to subtract the scatter components from data of corresponding energy windows using nonuniform and uniform phantoms. All data were reconstructed with the OSEM algorithm. The energy window dependence of the TDCS technique was verified by comparing the coefficients of variance (COV) of the data from the uniform phantom of each energy window. Ten Poisson deviates were generated from each projection's data from the uniform phantom. The nonuniform phantom results showed that the estimated parameters effectively estimated the scatter component from the projection image for each energy window. The COV for the 5%, 10%, 15%, 20%, 25%, 30%, and 35% windows were 2.10%, 1.76%, 1.44 %, 1.39%, 1.34%, 1.37%, and 1.61%, respectively. In the TDCS technique, any photopeak energy window from 15% to 30% may work almost as well as judged by the COV measured for a uniform phantom in this study. The best window by that measure was the 25% window. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the relationship between scatter and collimator design for the use of the transmission-dependent convolution subtraction method. Methodology; Results and discussion; Conclusions.