ABSTRACT
For proper attenuation correction of SPECT images, a set of 3D attenuation maps specific to the imaging slices is needed. Among the many different approaches for deriving the attenuation maps, fan beam transmission CT (FBTCT), performed on the same SPECT system as emission imaging, has many promising and clinically practical features. The major problem of FBTCT is that the current SPECT systems do not have a large enough field of view (FOV) to cover the typical cross-sectional size of patients. To address this problem, we have developed a novel asymmetric fan (AsF) sampling scheme to extend the FOV to practical sizes for clinical TCT imaging on existing SPECT systems. This AsF scheme samples only half of the intended FOV in each projection; the other half would be sampled in an opposing projection after detector rotation. We have implemented the AsF sampling on a three-head SPECT system through a specially designed source-collimator assembly. We have modified the conventional convolution backprojection algorithm to facilitate simple and fast image reconstruction. The feasibility of the approach is confirmed by the quality of the derived TCT images of various phantoms and human subjects. The AsF sampling scheme could also have applications in other general transmission CT systems.
Subject(s)
Tomography, Emission-Computed, Single-Photon/methods , Tomography, X-Ray Computed/methods , Biophysical Phenomena , Biophysics , Evaluation Studies as Topic , Humans , Models, Structural , Models, Theoretical , Radiographic Image Interpretation, Computer-Assisted/instrumentation , Radiographic Image Interpretation, Computer-Assisted/methods , Tomography, Emission-Computed, Single-Photon/instrumentation , Tomography, X-Ray Computed/instrumentationABSTRACT
The results of an autopsy study of Opisthorchis viverrini infection in 181 accident subjects in northeast Thailand are presented. The age-prevalence profiles were similar whether determined by faecal examination for parasite eggs or by recovery of worms from the liver. The prevalence increased rapidly with age and reached a plateau at 70-80% in adults. The overall prevalence estimated by faecal examination was 69.2%, while that measured by worm recovery was 79.2%. The average intensity of infection, as indicated by eggs per gram of faeces, rose with age and became relatively stable in groups over 20 years of age. Worm burden also increased rapidly with age, reaching a peak in the 31-40 year groups and slightly declining in the 2 oldest age groups. Fluke distribution between individual subjects was highly dispersed; most people harboured no or low worm burdens (0-200 worms) while a small group of subjects (16.5%) carried 66% of the total worms recovered. The distribution of flukes within the liver appeared to be homogeneous. The results of the present study were similar to those from field studies, and possible mechanisms that generate these observed patterns of infection are discussed.
