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This study was performed to investigate the iterative reconstruction of a segment of a long object using cone-beam projections acquired with a practical-sized detector. This reconstruction problem is commonly called the cone-beam long object problem. The cone-beam focal-point trajectories studied were either helical or helical with planar arcs. We assume that the long object is confined in a tall supporting cylinder and that the cone-beam detector is wide enough that the projections are not truncated transversely. If the detector is not wide enough, we use two asymmetric cone-beam detectors, each covering at least one-half of the field of view in the transverse direction. The detector size in the axial direction is not large enough to cover the segment. The detector size is used to determine the maximal helical pitch. A data sufficiency condition is established to design a focal-point trajectory. The trajectory then defines a convex hull. Projection rays that touch the region outside the convex hull and inside the supporting cylinder are discarded in the iterative algorithm. Computer simulations and experimental data verify that the proposed data acquisition and discarding strategy result in accurate segment reconstruction. Index Terms--Cone beam, helical SPECT, iterative reconstruction, long-object CT Problem.

A commercial three-detector single-photon emission computed tomography (SPECT) system that enables simultaneous acquisition of transmission and emission data without increasing patient scanning time has been designed and manufactured. This system produces a reconstructed attenuation coefficient distribution that can be used to correct for photon attenuation in the emission reconstruction. The three detectors with fan-beam collimators are mounted to the gantry in a triangular arrangement. A transmission line source assembly was mounted at the focal line of one of the detectors and controlled to move in synchrony with the opposing fan-beam collimator. Data from transmission and emission sources at different energies were acquired in one detector, while the other two simultaneously acquired emission data. A transmission source of 153Gd was used with 99mTc-labeled radiopharmaceuticals, and 57Co was used with 201Tl. Algorithms were developed to subtract crosstalk between transmission and emission energy windows in all three detectors. A transmission maximum-likelihood iterative algorithm was used to reconstruct the attenuation distribution, which was used in combination with an iterative maximum-likelihood expectation-maximization algorithm to compensate for the attenuation of the projection of the emission distribution. The results in phantom studies displayed greater uniformity of activity with attenuation-corrected reconstruction. This was demonstrated visually and quantitatively by using anterior-to-inferior ratios close to one and low spatial %rms error as a measure of improved uniformity. Index Terms - Anger gamma camera, attenuation correction, brain SPECT, cardiac SPECT, clinical imaging hardware, clinical imaging software, emission computed tomography, fan-beam tomography, iterative reconstruction, simultaneous transmission and emission imaging, single-photon emission computed tomography, SPECT, transmission computed tomography.

In this study, we compare the accuracy of the transmission and emission maps, produced using both a Gd/Tc and a Tc/Tl transmission-emission source combination. In both cases, the transmission and emission data are acquired simultaneously. This results in contamination of the data acquired in the lower energy window by events from the higher energy isotope. We use standard methods to correct for this contamination when using a Gd/Tc combination and propose a new method for use with the Tc/Tl combination. The Tc/Tl combination yields more accurate: transmission images than the Gd/ Tc combination. However, when a single factor is used to scale the attenuation coefficients measured using the transmission source to those appropriate for the emission isotope/energy, the resulting error in the attenuation map used for attenuation correction is larger for the Tc/Tl combination than for the Gd/Tc combination. For this study, neither combination yielded emission maps which were significantly superior (in terms of reconstructed emission ratios) to the other.

Abstract Background Model-independent analysis with B-spline regularization has been used to quantify myocardial blood flow (perfusion) in dynamic contrast-enhanced cardiovascular magnetic resonance (CMR) studies. However, the model-independent approach has not been extensively evaluated to determine how the contrast-to-noise ratio between blood and tissue enhancement affects estimates of myocardial perfusion and the degree to which the regularization is dependent on the noise in the measured enhancement data. We investigated these questions with a model-independent analysis method that uses iterative minimization and a temporal smoothness regularizer. Perfusion estimates using this method were compared to results from dynamic 13N-ammonia PET. Results An iterative model-independent analysis method was developed and tested to estimate regional and pixelwise myocardial perfusion in five normal subjects imaged with a saturation recovery turboFLASH sequence at 3 T CMR. Estimates of myocardial perfusion using model-independent analysis are dependent on the choice of the regularization weight parameter, which increases nonlinearly to handle large decreases in the contrast-to-noise ratio of the measured tissue enhancement data. Quantitative perfusion estimates in five subjects imaged with 3 T CMR were 1.1 ± 0.8 ml/min/g at rest and 3.1 ± 1.7 ml/min/g at adenosine stress. The perfusion estimates correlated with dynamic 13N-ammonia PET (y = 0.90x + 0.24, r = 0.85) and were similar to results from other validated CMR studies. Conclusion This work shows that a model-independent analysis method that uses iterative minimization and temporal regularization can be used to quantify myocardial perfusion with dynamic contrast-enhanced perfusion CMR. Results from this method are robust to choices in the regularization weight parameter over relatively large ranges in the contrast-to-noise ratio of the tissue enhancement data.

Our objective was to harmonize multicenter 89Zr PET imaging for oncology trials and to evaluate lesion detection. Methods: Seven PET scanners were evaluated using a custom chest oncology phantom with 9 spheric lesions 7-20 mm in diameter. A 4:1 signal-to-background ratio simulated a patient dose of 92.5 MBq. Various image reconstructions were evaluated. Images were assessed for lesion detection, and recovery coefficients and background signal variance were measured. Results: Two scanners failed to provide acceptable images and data. Optimal reconstruction algorithms enabling adequate lesion detection and reliable quantification across the other 5 scanners were determined without compromising the data quality. On average, 95% of the 10-mm lesions were detected, and the 7-mm lesion was visualized by only 1 scanner. Background variance was 8.6%-16%. Conclusion: We established multicenter harmonization procedures for 89Zr PET imaging in oncology, optimizing small-lesion (≥10 mm) detectability and accurate quantification. [ABSTRACT FROM AUTHOR]

Cardiac SPECT is typically performed clinically with static imaging protocols and visually assessed for perfusion defects based upon the relative intensity of myocardial regions. Dynamic imaging, however, has the potential to provide quantitative measures of flow, possibly improving diagnosis. The objective of this study was to compare the information content of dynamic and static thallium SPECT imaging as measures of myocardial perfusion. Studies were performed in four canines, each with an occlusion placed on the left anterior descending coronary artery. Dynamic SPECT imaging was performed at rest and under adenosine stress, and subsets of the data were summed to provide corresponding static datasets for identical physiologic conditions. Microsphere-derived flow measurements were used as the gold standard. The dynamic data were fit to a two-compartment model to provide regional estimates of wash-in rate parameters. Occluded-to-normal ratios were also calculated for each canine study. The results show comparable correlations with microspheres for both wash-in and static scaled image intensities. The dynamic data provided higher defect contrasts, which were more accurate than the static occluded to normal ratios. Preliminary studies were also performed in two patients and the static and dynamic data compared. These results show that dynamic thallium imaging may provide improved diagnostic information compared to static imaging for myocardial perfusion SPECT studies. Index Terms--Blood flow, dynamic imaging, single photon emission computed tomography, thallium.

Transmission scans are an important part of the process of obtaining patient attenuation maps for accurate SPECT (single photon emission computed tomography) imaging. In order to avoid truncation of the projection data, asymmetric cone-beam imaging geometries were investigated. By using the Beacon[TM] SPECT system, it was shown that in the acquisition process transmission and emission imaging geometries can be different. Utilizing this new system, cone-beam transmission scans can be performed while the parallel collimators are attached for emission data acquisition. Patient and phantom studies were performed and compared with x-ray CT. A whole-body helical scan to obtain a whole-body attenuation map is also proposed. For helical asymmetric cone-beam geometries, at least two detectors are required in order to provide sufficient cone-beam data. If two detectors are used, they must have opposite geometries. Computer simulations were performed to demonstrate the feasibility of the proposed asymmetric helical cone-beam scanning geometry.