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

Ruangma, Ananya; Bai, Bing; Lewis, Jason S.; Sun, Xiankai; Welch, Michael J.; Leahy, Richard; Laforest, Richard

doi:10.1016/j.nucmedbio.2005.11.001

« Previous Next »Nuclear Medicine and Biology
Volume 33, Issue 2 , Pages 217-226, February 2006

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

Ananya Ruangma
- Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
- Washington University School of Medicine, Campus Box 8225, 510 South Kingshighway Boulevard, St. Louis, MO 63110, USA. Tel.: +1 314 362 8423; fax: +1 314 362 5428.
Bing Bai
- Signal and Image Processing Institute, University of Southern California, Los Angeles, CA 90089, USA
Jason S. Lewis
- Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
Xiankai Sun
- Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
Michael J. Welch
- Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
Richard Leahy
- Signal and Image Processing Institute, University of Southern California, Los Angeles, CA 90089, USA
Richard Laforest
- Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
- Corresponding author. Tel.: +1 314 362 8423; fax: +1 314 362 5428.

Received 16 August 2005; received in revised form 17 October 2005; accepted 8 November 2005.

Abstract

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 (⁶⁰Cu, ⁶¹Cu and ⁶⁴Cu), 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(N⁴-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 ⁶⁰Cu and ⁶¹Cu 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 ⁶⁴Cu. 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.

Keywords: MAP, PET, Positron range, Cu radionuclides