The performance of a fast OSEM reconstruction method with 3D collimator beam modeling and optional attenuation correction ("Flash-3D"), developed by Siemens is investigated using various phantoms, and acquisition parameters. Data Spectrum's Cylinder Phantom with rod and spheres inserts are acquired with varying protocols by systematically changing image quality relevant parameters, such as orbit, or collimator. They are then reconstructed with different methods and varying reconstruction parameters. The rod phantom is acquired with its long axis parallel and perpendicular to the rotation axis. A comparison between the 3D, 2D, 1D iterative methods, with and without attenuation correction, and FBP is done using qualitative and semi-quantitative measures of image quality. The attenuation correction is done using CT-derived mu-maps. Results: The contrast of the hot rods in parallel alignment is for OSEM-3D AC 17% larger than for OSEM-2D AC for the 3 largest rod sections. In this configuration where each slice shows the same structure the difference between 3D and 2D is minor. For the perpendicular alignment the contrast of the OSEM-3D AC reconstruction is 118% larger than from OSEM-2D AC. OSEM-2D AC shows almost identical contrast values as FBP, which is mainly due to the distortions of the rods, due to the 2D beam modeling. OSEM-3D AC comes closest to the expected hot contrast of 3.7 for the Hot-Cold Sphere phantom.Future work will further develop the analysis tools for the phantoms and investigate the affect of varying image quality relevant acquisition and reconstruction parameters.0-7803-8257

The data-driven Pixon noise-reduction method is applied to nuclear studies. By using the local information content, it preserves all statistically justifiable image features without generating artifacts. Statistical measures provide the user a feedback to judge if the processing parameters are optimal. The present work focuses on planar nuclear images with known Poisson noise characteristics. Its ultimate goals are to: (a) increase sensitivity for detection of lesions of small size and/or of small activity-to-background ratio, (b) reduce data acquisition time, and (c) reduce patient dose. Data are acquired using Data Spectrum's cylinder phantom in two configurations: (a) with hot and cold rod inserts at varying total counts and (b) with hot sphere inserts at varying activity-to-background ratios. We show that the method adapts automatically to both hot and cold lesions, concentration ratios, and different noise levels and structure dimensions. In clinical applications, slight adjustment of the parameters may be needed to adapt to the specific clinical protocols and physician preference. Visually, the processed images are comparable to raw images with ~16 times as many counts, and quantitatively the reduced noise equals that obtained with ~50 times as many counts. We also show that the Pixon method allows for identification of spheres at low concentration ratios, where raw planar imaging fails and matched filtering underperforms. Conclusion: The Pixon method significantly improves the image quality of data at either reduced count levels, or low target-to-background ratios. An analysis of clinical studies is now warranted to assess the clinical impact of the method.

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Abstract-Advances in reconstruction techniques and instrumentation improve image quality. Improved image quality could either improve confidence and diagnostic ability, or increase throughput, and lower injected dose. Current imaging guidelines give insuffient consideration to advances in iterative reconstruction methods that include collimator modeling, attenuation, and scatter correction, and best matched acquisitions. Thus advanced reconstruction is often sub-optimally used in a clinical setting. In this work, we first characterize the effects of various acquisition and reconstruction protocols with the explicit aim to reduce scan time without adverse affects as compared to FBP driven protocols. For this we characterize image features, such as nonuniformity and wall thickness of the cardiac insert inside the large anthropomorphic torso phantom (Data Spectrum) and correlate them with human observer ROC results. When reconstructing the data with OSEM with 3D collimator and detector response compensation ("Flash3D") we found that the detection ability is not impacted when using 6∞ angular steps, and thus reducing the acquisition time by 50%, as compared to the current method. A further reduction can be achieved if the rest study is scanned in the continuous instead of the step-and-shoot mode (10%). Dwell time can also be reduced slightly; however the myocardial count density should not be below at least 1 cnt/mm 2 for rest and summed stress. Clinical trials need to confirm the findings.

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