Subjects will participate in three study visits over the course of the study period. The screening visit will include an assessment of eligibility as well as the collection of the MDS diagnosis. The second visit, during which all subjects receive a single intravenous injection of 123I-ALTROPANE® followed by SPECT imaging, will include appropriate safety assessments before and after dosing. The third visit will include follow-up safety. The subjects' participation in the study will range between 30 and 40 days.