Radioisotopes Research Today is a free monthly online journal that collates and summarizes the latest research about Radioisotopes, including details on radioimmunotherapy, radionuclides, procedures, hazards.

Three-dimensional maximum a posteriori (MAP) imaging with radiopharmaceuticals labeled with three Cu radionuclides.

Ruangma A, Bai B, Lewis JS, Sun X, Welch MJ, Leahy R, Laforest R

Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA. ruangma@wustl.edu

BACKGROUND: One of the limiting factors in achieving the best spatial resolution in positron emission tomography (PET), especially in small-animal PET, is the positron range associated with the decay of nuclides, and usual PET image reconstruction algorithms do not provide a correction for the positron range. This work presents initial results obtained with the maximum a posteriori (MAP) algorithm, which has been developed to include an accurate model of the camera response, the Poisson distribution of coincidence data and the fundamental physics of positron decay including the positron range. METHODS: Phantoms were imaged with three positron emitting isotopes of Cu ((60)Cu, (61)Cu and (64)Cu), and mice and rats were imaged with two radiopharmaceuticals labeled with these isotopes in a microPET-R4 camera. These isotopes decay by positron emission with very different end-point energies resulting in wildly different spatial resolutions. Spatial resolution improvement and image quality offered by the MAP algorithm were studied with the line source phantom and a miniature Derenzo phantom. In addition, three mice and three rats were sequentially injected over a 48-h period with Cu-pyruvaldehyde bis(N(4)-methylthiosemicarbazone) (for blood flow to organs) and Cu-1,4,7,10-tetraazacyclododecane-1,4,7-tri(methanephosphonic acid) (for bone imaging) labeled with the said three isotopes of Cu. RESULTS: The line source experiment showed that comparable spatial resolution is possible with all three isotopes when using the positron range correction in MAP. The in vivo images obtained from (60)Cu and (61)Cu and reconstructed with 2D filtered back projection algorithms provided by the camera manufacturer show reduced clarity due to degraded spatial resolution arising from the extended positron ranges as compared with (64)Cu. MAP reconstructions exhibited a higher resolution with clearer organ delineation. CONCLUSION: Inclusion of a positron range model in the MAP reconstruction algorithm may potentially result in significant resolution recovery for isotopes with larger positron ranges.

Published 20 March 2006 in Nucl Med Biol, 33(2): 217-26.
Full-text of this article is available online (may require subscription).

© 2005-2008 Radioisotopes Research Today. All Rights Reserved.