Biomedical subjects

Andrew J DiMeo

Publications and source records attributed to Andrew J DiMeo.

2 recordsLinked to original sources

PubMed2002

A Monte Carlo investigation of dual-planar circular-orbit cone-beam SPECT.

We use Monte Carlo simulations to study the imaging properties of a design for a dual-planar cone-beam (DPCB) single-photon emission computed tomography (SPECT) system. A dual-planar system uses a dual-camera SPECT system and two cone-beam collimators with foci in different axial planes to increase the effective axial field of view (FOV). We simulated nearly noise-free projection data from a computerized brain phantom and a phantom consisting of a series of points. Four configurations were simulated: parallel-beam low-energy high-resolution (LEHR) as a standard for comparison and DPCB at three radii of rotation (ROR) corresponding to the smallest, average and largest ROR required to clear patients' shoulders based on ergonomic data. We compared global measures of average resolution and total acquired counts for the four configurations. We also estimated local spatial frequency response for reconstructions of point sources. Finally, we estimated a local noise power spectrum by simulating 1000 noise realizations of the brain phantom and estimating a local noise covariance at selected points. The noise power spectra were used to estimate spectral signal to noise ratio (SNR) for each configuration. The resolution in the reconstructed image space ranges from 7.2 mm full-width at half-maximum (FWHM) at the minimum ROR to 9.4 mm FWHM at the maximum ROR. The efficiency is inversely related, ranging from 1.5 times that of parallel LEHR at minimum ROR to 2.5 times that of LEHR at maximum ROR. Estimates of system frequency response roughly correspond to the global resolution estimates, but the cone-beam techniques exhibit an unusual secondary peak in the axial-direction response. Estimates of spectral SNR show that the cone-beam configurations almost always result in higher SNR at all spatial frequencies regardless of ROR. The very largest ROR may be an exception. A larger ROR results in significantly higher SNR for low spatial frequencies with small reductions in SNR for mid-range frequencies. We conclude that the DPCB design allows significant improvements in both resolution and noise as compared to conventional parallel designs and that optimizing the ROR for the cone-beam system may improve the performance of certain imaging tasks.

Brain↗

PubMed2002

An observer study evaluating dual-plane circular-orbit cone-beam brain SPECT.

UNLABELLED: Dual-plane circular-orbit cone-beam (DPCB) SPECT uses a pair of dissimilar cone-beam collimators to expand the axial field of view for brain SPECT. We applied observer study methodology to evaluate the improvement in detection of small defects in brain perfusion provided by DPCB SPECT, compared with conventional parallel-beam imaging. We also evaluated the effect of changing the radius of rotation on DPCB imaging. METHODS: Images were realistically simulated using a brain phantom. High-count Monte Carlo simulations were performed for 4 imaging configurations: low-energy high-resolution parallel-beam imaging at a radius of rotation of 18 cm and DPCB imaging (52-cm focal length) at radii of rotation of 20, 24, and 28 cm. These distances corresponded to those required for our camera to clear the shoulders of a patient in the 5th, 50th, and 95th percentiles of shoulder width. Perfusion defects of approximately 1.8-cm diameter were simulated at 4 locations in the brain. Poisson noise was simulated, and images were reconstructed to create a set of 200 images for each of the 4 configurations. All reconstructions used ordered-subset expectation maximization with attenuation modeling. Eight observers viewed images on which the possible location of the defect was marked. The observers were trained using 384 images, were tested using 416 images, and rated on a continuous scale their confidence about the presence of a defect. RESULTS: Using a paired t test for the estimated areas under the receiver operating characteristic (ROC) curve for each observer, we found that all 3 DPCB configurations resulted in higher areas under the ROC curve than did the parallel-beam configuration. Further, area under the ROC curve for the DPCB configurations improved with decreasing radius of rotation. All comparisons were significant at P < 0.05, except for DPCB 20 cm to DPCB 24 cm (P = 0.089). CONCLUSION: Use of a dual-plane cone beam is feasible for brain SPECT and better detects small perfusion defects than does a parallel beam, despite the possibility that the radius of rotation will need to be increased significantly to clear the patient's shoulders. A dual-plane cone beam should be used with the shortest radius of rotation possible to maximize the detectability of small perfusion defects.

Brain↗