This paper investigates the performance of 1 mm resolution Cadmium Zinc Telluride (CZT) detectors for positron emission tomography (PET) capable of positioning the 3-D coordinates of individual 511 keV photon interactions. The detectors comprise 40 mm × 40 mm × 5 mm monolithic CZT crystals that employ a novel cross-strip readout with interspersed steering electrodes to obtain high spatial and energy resolution. The study found a single anode FWHM energy resolution of 3.06±0.39% at 511 keV throughout most the detector volume. Improved resolution is expected with properly shielded front-end electronics. Measurements made using a collimated beam established the efficacy of the steering electrodes in facilitating enhanced charge collection across anodes, as well as a spatial resolution of 0.44±0.07 mm in the direction orthogonal to the electrode planes. Finally, measurements based on coincidence electronic collimation yielded a point spread function with 0.78±0.10 mm FWHM, demonstrating 1 mm spatial resolution capability transverse to the anodes – as expected from the 1 mm anode pitch. These findings indicate that the CZT-based detector concept has excellent performance and shows great promise for a high-resolution PET system.

The erythrocyte membrane skeleton deforms constantly in circulation, but the mechanics of a junctional complex (JC) in the network is poorly understood. We previously proposed a 3-D mechanical model for a JC (Sung, L. A., and C. Vera. Protofilament and hexagon: A three-dimensional mechanical model for the junctional complex in the erythrocyte membrane skeleton. Ann Biomed Eng 31:1314-1326, 2003) and now developed a mathematical model to compute its equilibrium by dynamic relaxation. We simulated deformations of a single unit in the network to predict the tension of 6 alphabeta spectrin (Sp) (top, middle, and bottom pairs), and the attitude of the actin protofilament [pitch (theta), yaw (phi) and roll (psi) angles]. In equibiaxial deformation, 6 Sp would not begin their first round of "single domain unfolding in cluster" until the extension ratio (lambda) reach approximately 3.6, beyond the maximal sustainable lambda of approximately 2.67. Before Sp unfolds, the protofilament would gradually raise its pointed end away from the membrane, while phi and psi remain almost unchanged. In anisotropic deformation, protofilaments would remain tangent but swing and roll drastically at least once between lambda(i) = 1.0 and approximately 2.8, in a deformation angle- and lambda(i)-dependent fashion. This newly predicted nanomechanics in response to deformations may reveal functional roles previous unseen for a JC, and molecules associated with it, during erythrocyte circulation.

We analyze time-averaged spectra from 86 bright gamma-ray bursts from the Ðrst 5 years of the Burst And Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory to determine whether the lowest energy data are consistent with a standard spectra form Ðt to the data at all energies. The BATSE Spectroscopy Detectors have the capability to observe photons as low at 5 keV. Using the gamma-ray burst locations obtained with the BATSE Large Area Detectors, the Spectroscopy DetectorsÏ low-energy response can be modeled accurately. This, together with a postlaunch calibration of the lowest energy Spectroscopy Detector discriminator channel, which can lie in the range 5È20 keV, allows spectral deconvolution over a broad energy range, D5 keV to 2 MeV. The additional coverage allows us to search for evidence of excess emission, or for a deÐcit, below 20 keV. While no burst has a signiÐcant (º3 p) deÐcit relative to a standard spectra model, we Ðnd that 12 bursts have excess lowenergy emission, ranging between 1.2 and 5.8 times the model Ñux, that exceeds 5 p in signiÐcance. This is evidence for an additional low-energy spectral component in at least some bursts, or for deviations from the power-law spectral form typically used to model gamma-ray bursts at energies below 100 keV.

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