In-111-DTPA-octreotide (OctreoScan) is still pivotal for neuroendocrine tumor imaging, despite the introduction of Ga-68-octreotide tracers. Low-dose computed tomography (LDCT) assists in the localization of SPECT findings but often results in uncertain interpretation. This retrospective study evaluates the impact of coregistration of In-111-DTPA-octreotide SPECT/LDCT with diagnostic CT on interpretation.Methods
Thirty-five consecutive studies, in which coregistration was performed because of uncertain interpretation, were evaluated. Presence of somatostatin receptors was categorized retrospectively as definitely positive, probably positive, probably negative, or definitely negative with and without rigid registration with diagnostic CT, and possible added value of coregistration was evaluated.Results
Coregistration was performed in 35 studies. However, on subsequent reading, 4 SPECT/CTs yielded definite results and were omitted. Coregistration was helpful in 30 of the remaining 31 cases, changing reading to definitely positive (7) or to definitely negative (23). In 13 of the 23 cases, diagnosis changed from probably positive to definitely negative. Coregistration contributed in 42 of 48 sites, with greatest benefit in the liver (13/14), pancreas (10/10), and lymph nodes (6/6).Conclusions
Coregistration is becoming increasingly easier and may be utilized when SPECT/LDCT is inconclusive.