A NEW ITERATIVE RECONSTRUCTION TECHNIQUE FOR ATTENUATION CORRECTION IN HIGH-RESOLUTION POSITRON EMISSION TOMOGRAPHY

A new iterative reconstruction technique (NIRT) for positron emission computed tomography (PET), which uses transmission data for nonuniform attenuation correction, is described, Utilizing the general inverse p roblem theory, a cost functional which includes a noise term was deriv ed. The cost functional was minimized using a weighted-least-square ma ximum a posteriori conjugate gradient (CG) method. The procedure invol ves a change in the Hessian of the cost function by adding an addition al term. Two phantoms were used in a real data acquisition. The first was a cylinder phantom filled with uniformly distributed activity of 7 4 MBq of fluorine-18. Two different inserts were placed in the phantom . The second was a Hoffman brain phantom filled with uniformly distrib uted activity of 7.4 MBq of F-18. Resulting reconstructed images were used to test and compare a new iterative reconstruction technique with a standard filtered backprojection (FBP) method, The results confirme d that NIRT, based on the conjugate gradient method, converges rapidly and provides good reconstructed images. In comparison with standard r esults obtained by the FBP method, the images reconstructed by NIRT sh owed better noise properties, The noise was measured as rms% noise and was less, by a factor of 1.75, in images reconstructed by NIRT than i n the same images reconstructed by FBP. The distance between the Hoffm an brain slice reconstructed by FBP and the perfect PET Hoffman brain slice created from the MRI image was 0.526, while the same distance fo r the Hoffman brain slice reconstructed by NIRT was 0.328. The NIRT me thod suppressed the propagation of the noise without visible loss of r esolution in the reconstructed PET images.