Z. H. Cho

Maximum Likelihood PET with Real Data

We compare the maximum likelihood and convolution-backprojection reconstructions of a particular real phantom with count data obtained from the Columbia University Positron Emission Tomographic Scanner, Dichotom II. We find the maximum likelihood reconstruction reduces noise and streak artifacts confirming earlier work with simulated count data.

Phase Delay and Attenuation Corrections in Fourier Transform Nmr Tomographic Imaging

Applications of Fourier transform Nuclear Magnetic Resonance(NMR) to the field of tomographic imaging have become one of the important areas in biomedical imaging. NMR tomography, however, is low sensitivity imaging technique and the sensitivity is closely related to the static magnetic field strength applied to the object. Since the SNR (signal to noise ratio) of NMR imaging is proportional to Ho3/2, a higher magnetic field is a most desirable feature in NMR imaging. For a higher magnetic field, however, the frequency of r.f. signals for both excitation and detection is higher, which results in several undesirable effects such as phase delay and attenuation in the object. In this paper, we have proposed phase and attenuation dependent artifact correction based on the solution of the wave equation for a simple cylindrical model. Results of computer simulations and experiments are demonstrated.

Improvement of light coupling in BGO detector module by optimization of the crystal shape

A detector shape optimization study was carried out for the high-resolution 4*4 array BGO-PMT (bismuth-germanate-photomultiplier-tube) coupling scheme to be used in the spherical positron emission tomograph. To improve the light collection efficiency in the BGO detector array, the authors used bullet-nose-shaped BGO crystal at both the front- and the back-side of the detector, the latter being coupled to the PMTs photocathode. It was hypothesized that the smooth, round front-side bullet-nose shape, by eliminating the sharp corners of the crystal, would improve the light collection efficiency and that the bullet-nose shape at the back-side of crystal, coupled to the PMT, would provide optimal coupling between the crystal and the PMT by the focusing property of the bullet-nose shape. Computer simulations and experimental studies were carried out, confirming these suppositions. >