Optimization of somatostatin receptor imaging with In-111 pentetreotide scintigraphy: a phantom study & clinical imaging

Objectives: In order to localize functional neuro endocrine tumor (NET), geometric and radioactive resolution is important for somatostatin receptor scintigraphy (SRS). However, system resolution of single photon emission computed tomography (SPECT) with medium energy collimator is over 10 mm. We evaluated the detection of 10 mm tumor for SRS with In-111 pentetreotide by phantom and clinical study.

Methods: In-111 solution was filled in NEMA IEC body phantom. The radioactivity of background (B.G.) was 3.0 kBq/mL. The radioactivity ratio between tumor mimic sphere and background was from 0.0 to 16.0. The diameter of spheres ranged from 10 to 37 mm. The acquisition time in the phantom study ranged from 5 to 30 min during the planar imaging. In the SPECT imaging, the acquisition time ranged from 5 to 120 min. The SPECT image was corrected by scatter and attenuation. For clinical studies, we followed the guideline of Society of Nuclear Medicine and Molecular Imaging of Technology.

Results: In planar imaging of the phantom, hot sphere of 10 mm was not detected in any study protocol. However, in SPECT imaging of the phantom, hot sphere of 10 mm was detected when radioactivity ratio was 8:1 in 30 min scan duration. In clinical study, 8 mm NET of pancreas was detected only by SPECT imaging.

Conclusion: We concluded that the detection of small NET with 10 mm diameter could be detected by means of SPECT scan.