Magnetic resonance imaging (MRI) provides high-resolution anatomical information. In this study, we investigated the usefulness of an MRI-constrained method for image reconstruction of positron emission tomography (PET) . We started the reconstruction process with a conventional Bayesian reconstruction (BAY) method. Typically after 7 iterations, we calculated the apparent radioactivity ratio between gray matter and other tissues such as white matter and cerebrospinal fluid from both the PET image and tissue classification probability images generated from segmented MR images, and then increased this ratio to enhance the functional boundary gradient. We multiplied the apparent ratio by 2.0. Subsequently, the cross-correlation between anatomical and enhanced functional boundary maps was incorporated into BAY using the weighted line site method. This algorithm was tested with simulated PET projection data generated from an MRI based three-dimensional brain phantom, including the effects of resolution, attenuation, scatter and Poisson noise. The reconstructed images were evaluated in terms of root mean square distance (RMSD) from the true image. This method improved RMSD by 39.6%, 33.5%, and 33.0% on average, compared to (i) the filtered backprojection method, (ii) the maximum-likelihood expectation-maximization method and (iii) BA Y method, respectively. Our preliminary results suggest that incorporation of both anatomical and tissue classification information into the image reconstruction process is useful for improving the qualitative and quantitative accuracy of PET images.
In the present study, we examined the influences of gender and ages on accumulation in the patellae on scintigram. The subjects were 828 patients who underwent bone scintigraphy during the past one and half years at the Department of Radiology, Nagoya University Hospital. Patients younger than 20 years old and those with abnormality of the patellae were excluded. The degree of accumulation in the patellae was evaluated using the A-P whole body scintigraphy in comparison with accumulation at the diaphysis of the femur and classified to two categories, “Positive” (higher accumlation than that of the diaphysis of the femur) and“Negative” (equal or lower than that of the diaphysis of the femur) . In general, the degree of accumulation was higher in females than in males. In both males and females, the degree of accumulation increased with age. A difference between the two sides in the degree of accumulation in the patellae was observed in 32% of subjects. The results of this study may serve as basic data for the interpretation of bone scintigrams.