IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium最新文献

We use receiver operating characteristic (ROC) analysis of a location-known-exactly (LKE) lesion detection task to compare the image quality of SPECT reconstruction with and without various combinations of attenuation correction (AC), scatter correction (SC) and resolution compensation (RC). Hybrid images were generated from Tc-99m labelled NeoTect clinical backgrounds into which Monte Carlo simulated solitary pulmonary nodule (SPN) lung lesions were added, then reconstructed using several strategies. Results from a human-observer study show that attenuation correction degrades SPN detection, while resolution correction improves SPN detection, even when the lesion location is known. This agrees with the results of a previous localization-response operating characteristic (LROC) study using the same images, indicating that location uncertainty is not the sole source of the changes in detection accuracy.

An earlier localization ROC (LROC) study that found attenuation correction (AC) degraded the detection of solitary pulmonary nodules (SPN) in hybrid SPECT lung images had several potential shortcomings related to the simulation methods. We sought to address these issues with a revised LROC study. Clinical Tc-99m NeoTect scans acquired with a simultaneous transmission-emission protocol defined the normal cases in a single-slice LROC study. Abnormal cases contained a simulated 1-cm lung lesion. Four rescaled-block-iterative EM (RBI) reconstruction strategies applied: 1) AC, scatter correction (SC), and resolution compensation (RC); 2) AC only; 3) RC only; and 4) no corrections (NC). Images from these strategies underwent 3D Gaussian post-smoothing. Performances were defined by the average area under the LROC curve obtained from three human observers. The strategy ranking in order of decreasing performance was: 1) RBI with RC; 2) RBI with all corrections; 3) RBI with AC; and 4) RBI with no corrections. A multireader-multicase (MRMC) analysis only found significant patient and patient-strategy effects. The conflicting results concerning AC from this study and the previous one may revolve around lesion masking effects, which, by design, were not a factor in the current study.

A human-model observer for tumor detection-localization studies featuring multislice-multiview (or volumetric) image displays has been introduced. This volumetric observer, an extension of multiclass linear observers previously tested with single-slice and multislice displays, produces rating and localization data by integrating perception measurements from the different image views. A channelized NPW (CNPW) version of the observer was evaluated against humans for a background-known-exactly (BKE) detection task involving localization of Tc-99m Neotect lesions in simulated SPECT lung images. An LROC study evaluated two RBI reconstruction strategies that used different combinations of corrections for attenuation, scatter, and distance-dependent system resolution, and coronal, sagittal, and transverse slices were presented to the observers. Model-observer ranking of these strategies did not match that of the humans. Follow-up studies exploring several possible remedies for the model observer, including strategy-specific search regions and an internal-noise mechanism, showed little change. Future work will examine variations from the BKE assumption as a means of reconciling the rankings.

We compare the image quality of SPECT reconstruction with and without an anatomical prior. Area under the localization-response operating characteristic (LROC) curve is our figure of merit. Simulated Ga-67 citrate images, a SPECT lymph-nodule imaging agent, were generated using the MCAT digital phantom. Reconstructed images were read by human observers.Several reconstruction strategies are compared, including rescaled block iterative (RBI) and maximum-a-posteriori (MAP) with various priors. We find that MAP reconstruction using prior knowledge of organ and lesion boundaries significantly improves lesion-detection performance (p < 0.05). Pseudo-lesion boundaries, regions without increased uptake which are incorrectly treated as prior knowledge of lesion boundaries, do not decrease performance.

We investigated the use of partial collimation on a clinical PET scanner by removing septa from conventional 2D collimators. The goal is to improve noise equivalent count-rates (NEC) compared to 2D and 3D scans for clinically relevant activity concentrations. We evaluated two cases: removing half of the septa (2.5D); and removing two-thirds of the septa (2.7D). System performance was first modeled using the SimSET simulation package, and then measured with the NEMA NU2-2001 count-rate cylinder (20 cm dia., 70 cm long), and 27 cm and 35 cm diameter cylinders of the same length. An image quality phantom was also imaged with the 2.7D collimator. SimSET predicted the relative NEC curves very well, as confirmed by measurements, with 2.5D and 2.7D NEC greater than 2D and 3D NEC in the range of ~5-20 mCi in the phantom. We successfully reconstructed images of the image quality phantom from measured 2.7D data using custom 2.7D normalization. Partial collimation shows promise for optimized clinical imaging in a fixed-collimator system.

We present a simulation study of the effect of different degrees of collimation on countrate performance of a hypothetical PET scanner with LSO crystals. The simulated scanner is loosely based on the geometry of the Siemens Biograph Hi-Rez scanner.System behavior is studied with a photon tracking simulation package (SimSET).We investigate the NEMA NU2-2001 count rate and scatter fraction behavior for systems with different amounts of collimation, which is achieved by adding septa to the fully-3D system as in clinical use. We study systems with 2, 5, 11, and 40 septa. The effect of collimation is studied for three patient thicknesses.The resulting count rate curves for true, scattered, and random coincidences as well as noise equivalent count rates are compared for the different collimation cases. Improved countrate performance with partial collimation is seen. However, except for the largest diameter phantom, the NEC rate increase is seen at higher activities than those used clinically.The NEC countrate versus activity curves for the LSO systems are also compared to those from a BGO system where partial collimation increases NEC countrate over a clinically relevant activity range.

SimSET (a Simulation System for Emission Tomography) is being modified to more accurately simulate typical PET block detector tomographs. A new detector module that models the detector system as a collection of rectangular boxes is being added to the software. The new model is sufficiently general to allow many more imaginative or speculative detector systems to be simulated.

We outline the design of a new small-animal PET system. This system employs modular scintillation cameras composed of nine PMTs coupled by a light guide to a monolithic NaI(Tl) scintillation crystal. The basic principles of the PET system are presented along with an overview of the electronics and position-estimation scheme. The potential advantages of this design are discussed and preliminary reconstructed images are presented.