Leszek J. Hahn

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UNLABELLED Coregistration of images from a single subject, acquired by different modalities, is important in clinical diagnosis, surgery and therapy planning. The purpose of this study was to evaluate, using a physical torso phantom, a novel, fully automated method for three-dimensional image registration of CT and SPECT, using radionuclide transmission(More)
Comparisons are made between different analytic attenuation compensation methods used in SPECT imaging. The methods include a multiplicative technique and a single-iterative technique, both applied after filtered backprojection, and two different implementations of an attenuation-weighted filtered backprojection technique (A-W FBP). The methods are compared(More)
The fate of mercury (Hg) released from dental "silver" amalgam tooth fillings into human mouth air is uncertain. A previous report about sheep revealed uptake routes and distribution of amalgam Hg among body tissues. The present investigation demonstrates the bodily distribution of amalgam Hg in a monkey whose dentition, diet, feeding regimen, and chewing(More)
A quantitative study of nonisotropic attenuation in SPECT imaging is presented. The study includes a case where the spatial distribution of the attenuation coefficient is nonuniform, as well as a case where the photon path length in the attenuating medium is variable as a function of direction. The effects are studied using phantoms with known source(More)
Mercury (Hg) vapor is released from dental "silver" tooth fillings into human mouth air after chewing, but its possible uptake routes and distribution among body tissues are unknown. This investigation demonstrates that when radioactive 203Hg is mixed with dental Hg/silver fillings (amalgam) and placed in teeth of adult sheep, the isotope will appear in(More)
X-ray CT is able to image the internal architecture of frozen tissue. Phantoms of distilled water, a saline-gelatin mixture, lard and a calf liver-gelatin suspension cooled by a plastic tube acting as a long liquid nitrogen cryoprobe were used to study the relationship between Hounsfield unit (HU) values and temperature. There is a signature change in HU(More)
The discrete filtered backprojection (DFBP) algorithm used for the reconstruction of single photon emission computed tomography (SPECT) images affects image quality because of the operations of filtering and discretization. The discretization of the filtered backprojection process can cause the modulation transfer function (MTF) of the SPECT imaging system(More)
Photon attenuation is one of the primary causes of artifacts in cardiac single photon emission tomography (SPET). Several attenuation correction algorithms have been proposed. The aim of this study was to compare the effect of using the ordered subsets expectation maximization (OSEM) reconstruction algorithm and Chang's non-uniform attenuation correction(More)
The optimal cooling parameters to maximize cell necrosis in different types of tissue have yet to be determined. However, a critical isotherm is commonly adopted by cryosurgeons as a boundary of lethality for tissue. Locating this isotherm within an iceball is problematic due to the limitations of MRI, ultrasound and CT imaging modalities. This paper(More)
Experiments were conducted using a Siemens Rota camera to study the applicability of two linear shift-invariant (LSI) filters, namely, the Wiener and power spectrum equalization filters, for restoration of planar projections and single-photon-emission computed tomography (SPECT) images. In the restoration scheme, the system transfer function, computed from(More)