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Monte Carlo (MC) simulation of SPECT imaging using medium-energy (ME) and highenergy (HE) photons involves intense calculations of photon transport within both the phantom modeling the patient and the collimator where the penetration (P) and scatter (S) components of the total response are non-negligible as compared to the geometric (G) component. The purpose of this study is to develop fast MC simulation methods that substantially reduce computation time while maintaining high accuracy. The SIMSET MC code was used to simulate transport of photons from a point source or source distribution from the 3D NCAT phantom. The energy, position, and direction of travel of each photon were stored in a listmode data file. The 2D collimator point source response function (PSRF), including the G, P and S components, was determined at a series of source distances uing the MCNP MC code. Lookup table of the 2D PSRFs as a function of source distance for a specific collimator design and photon energy was generated by interpolating the series of MC simulated PSRFs. The G component at each source distance was normalized to one and the P and S components were scaled accordingly. An algorithm was developed to read the listmode data, select photons within a given energy window, calculate the distances between the photons and the collimator, determine the PSRFs from the appropriate lookup table, and add them to the projection data. The PSRFs at different source distances obtained from using the fast MC method showed excellent agreement with direct MC simulation. We conclude that by using lookup tables obtained from previously defined MC simulated PSRFs of the collimator, accurate simulation of SPECT imaging using ME and HE photons can be obtained at substantially reduced computational time.0-7803-7636-6/03/$17.00

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Bioptigen spectral-domain optical coherence tomography (SDOCT) is leading the development of OCT for applications in clinical and pre-clinical research applications. Bioptigen's exceptional image quality, fully customizable highspeed image acquisition, and versatility of scanning optics combine in the only SDOCT system suitable for use from the clinic to the operating suite, for neonatal patients to adult, and for non-invasive imaging of animal models in the research lab. TechnologySDOCT is a second-generation imaging technology that is rapidly changing the face of ophthalmic disease management. OCT fills a niche between microscopy and ultrasound as an imaging modality that enables the depth-resolved imaging of tissue microstructure with axial and lateral resolution on the micron level. Images acquired on Bioptigen's 840nm ophthalmic SDOCT systems demonstrate an unmatched level of detail, owing to depth-independent axial resolution of 4.5 microns and lateral resolution at the retina of 20 microns. Bioptigen's system is ready for the future, with an upgrade option for ultrahigh-resolution imaging down to three microns.Bioptigen ophthalmic SDOCT systems acquire, process, and display images at 17,000 lines. This image acquisition rate results in a reduction of the number of motion artifacts, eliminating the need to normalize distortions in cross-sectional B-scans caused by patient motion. High-density 1,000-line images are acquired at 17 frames per second, and high-density volumes of 100,000 lateral positions are acquired in just six seconds. System SpecificationsBioptigen SDOCT is designed to provide the researcher, physician, and patient with the most advanced set of imaging tools to diagnose and treat eye disease from the very earliest stages. Resolving power is critical for assessing early symptoms of eye disease, whether it is the formation of drusen in early-stage age-related macular degeneration (AMD), the onset of choroidal neovascularization (CNV), and fractional changes in retinal edema or retinal nerve fibre layer (RNFL) thicknesses. Bioptigen systems provide 4.5-micron resolution for imaging the retina from the inner retina through to the choroid, or for high-resolution imaging of anterior structures such as the cornea, the sclera, and the angle. Superior imaging depth provides dramatic images of the optic nerve head through to the lamina cribosa. A simple change in optics allows for imaging of anterior structures such as the cornea and sclera, enabling the imaging of features such as Bowman's membrane in the cornea and Schlemm's canal at the angle. Further, the Bioptigen system is compatible with every broadband sources, providing resolution better than 3 microns; ultra high-resolution sources are available as an option. Bioptigen high-resolution systems are ideally suited for glaucoma and macular analysis, and for tracking disease change in combination with drug, laser, or surgical therapy.These performance advantages are brought to a broader patient and subject base through unmatched system versatili...

The purpose of this study is to evaluate 4D reconstruction methods for the processing of gated cardiac single photon emission computed tomography (SPECT) images from obese patients.Clinical gated SPECT projection data were reconstructed using the ordered-subsets expectationmaximization (OS-EM) IntroductionMyocardial SPECT imaging is frequently the imaging technique of choice used to visualize perfusion defects of the heart. Cardiac gating adds a vital dimension to myocardial imaging, enabling the diagnostician to visualize cardiac motion and wall thickening, and assess cardiac function quantitatively by means of chamber volumes calculated by clinical software packages. A principal problem with gated SPECT images is the increase in noise due to the division of acquired counts into time frames, and this issue is magnified in the case of obese patients, due to additional attenuation from the larger body size. The images can be noisy enough for clinicians to discount 4D data altogether in this population of patients.Our hypothesis is that 4D reconstruction methods applied to gated studies in this population will result in more usable images with less noise degradation and no loss of temporal resolution as compared to images smoothed with 2D and 3D Fourier filters. The rescaled block-iterative maximum a posteriori (RBI-MAP) algorithm is a modified version of the iterative RBI-EM algorithm, closely related to the ordered-subset, expectation-maximization (OS-EM) algorithm [1]. The former incorporates useful features of the MAP reconstruction method (particularly by the use of Gibbs priors [2], which are designed to retain edge features while smoothing noise, thus contributing to better temporal resolution when applied in the time dimension [3]). It is not known whether 4D reconstruction methods result in improved image quality in reconstructed gated SPECT images from obese patients, as compared to 3D reconstruction methods. Thus, the aim of this study is to evaluate this question by means of computer simulation tools described herein. MethodsAnthropometric data was used to obtain a distribution of body dimensions across different populations. This information was used to determine an appropriate body size to use in building a standard obese male and female non-uniform rational B-spline-based (NURBS) cardiac torso (NCAT) phantom. The NCAT phantom is a computerized phantom which includes models of cardiac and respiratory motion, allows for the modeling of perfusion and motion defects of the myocardium, for the modeling of different organ and body sizes, as well as for the modification of radioactivity uptake ratios and attenuation maps [4], [5]. It is thus a very powerful tool that provides the researcher with a gold standard on which to test the efficacy of different reconstruction