1. Department of Radiology; Division of Nuclear Medicine; University of Maryland School of Medicine; Baltimore MD 21201 USA
2. Department of Radiology; Division of Nuclear Medicine; University of Massachusetts Medical School; Worcester MA 01655 USA
3. Department of Radiology; Carl E. Ravin Advanced Imaging Laboratory; Duke University Medical Center; Durham NC 27705 USA
4. Department of Biomedical Engineering; Worcester Polytechnic Institute; Worcester MA 01609 USA