Showing papers by "Richard C. Lanza published in 2003"

Large area imaging detector for long-range, passive detection of fissile material

Abstract: Recent events highlight the increased risk of a terrorist attack using either a nuclear or a radiological weapon. One of the key needs to counter such a threat is long-range detection of nuclear material. Theoretically, gamma-ray emissions from such material should allow passive detection to distances greater than 100 m. However, detection at this range has long been thought impractical due to spatially fluctuating levels of natural background radiation. These fluctuations are the major source of uncertainty in detection and mean that sensitivity cannot be increased simply by increasing detector size. Recent work has shown that this problem can be overcome through the use of imaging techniques. In this paper we describe the background problems, the advantages of imaging and the construction of a prototype, large-area (0.57 m/sup 2/) gamma-ray imager to detect nuclear materials at distances of /spl sim/ 100 m.

Small animal imaging by single photon emission using pinhole and coded aperture collimation

Abstract: The aim of this paper is to investigate the basic properties and limits of the small animal imaging systems based on single photon detectors. The detectors for radio imaging of small animals are challenging because of the very high spatial resolution needed, possibly coupled with high efficiency to allow dynamic studies. These performances are hardly attainable with single photon technique because of the collimator that limits both spatial resolution and sensitivity. In this paper we describe a simple desktop detector based on pixellated NaI(Tl) scintillator array coupled with a pinhole collimator and a PSPMT, the Hamamatsu R2486. The limits of such systems as well as the way to overcome them will be shown. In fact better light sampling at the anode level would allow better pixel identification for higher number of pixel that is one of the parameters defining the image quality. Also the spatial resolution would improve. The performances of such layout are compared with others using PSPMTs differing from R2486 for the light sampling at the anode level and different areas. We show how a further step, namely the substitution of the pinhole collimator with a coded aperture, will allow a great improvement in system sensitivity while maintaining very good spatial resolution, possibly submillimetric. Calculations and simulations show that sensitivity would improve by a factor of 50.

High-sensitivity dynamic coded aperture imaging

Abstract: Coded aperture imaging aims at improving the sensitivity of standard imaging optics (pinholes and parallel-hole collimators) by using hundreds of pinholes. Since each pinhole projects a copy of the object onto the detector, copies overlap. The overlap can be undone by computer post-processing with a simple correlation if pinholes are arranged in particular patterns. These are designed so that, when the object is infinitely far from the detector, a perfect image is obtained. In applications such as nuclear medicine and small-animal imaging the object is kept close to the detector to maximize sensitivity and use of the same patterns was shown to result in noticeable artifacts. The existing technique to mitigate near-field artifacts requires taking two images of the object sequentially with two similar masks, but this makes the implicit assumption of a static object. In near-field imaging, however, it is possible to place two detectors on opposite sides of the object and acquire the two images simultaneously. This approach extends the technique to dynamic studies. It also has the benefit of doubling the overall count rate by better utilization of the heads of a clinical gamma camera. Experimental results show that coded aperture optics can follow the movement of a 370-kBq point source at 0.05 s per frame with 3.5-mm resolution over a 12/spl times/12 cm/sup 2/ field of view. Images of a disk source demonstrate that, as in static studies, near-field artifacts can be almost eliminated.