Comparing SPECT CT imaging of spleen with Heat-damaged 99mTc-RBC and 99mTc- Sulfur Colloid.

Background: Heterotaxia is a rare disease with high morbidity and mortality, which partially is attributed to asplenia. Two methods for Nuclear visualization of spleen exist. We compare diagnostic value of Heat Damaged (HD) 99mTc-RBC and 99mTc-sulfur colloid (SC) imaging based on case reports. We implemented HD 99mTc-RBCs in attempt to reduce children’s radiation exposure with reducing need for CT and for improving specificity of the splenic study. Patients and Methods: Between July and December 2020, 9 patients were evaluated for spleen including 5 patients with the suspected heterotaxia. 4 infants less than 8 weeks old. 3 children were referred for Sickle cell disease. 1 of the 9 patients was an adult with history of recent peritoneal lesions of unclear etiology and splenectomy secondary to trauma as a child. HD 99mTc-RBC and 99mTc-SC scans were performed following SNMMI guidelines on Siemens Symbia T scanners.

Results: 3 infants required a CT scan for conclusion of diagnosis following 99mTc-SC planar and SPECT imaging. One 99mTc-SC scan for 7 weeks old child demonstrated dextro position of liver and normal splenic activity in the right upper abdominal quadrant while ultrasound scan diagnosed as absent spleen. An ultrasound in 10-day-old male demonstrated spleen with normal echogenicity measuring 1.2 cm in right upper abdominal quadrant, however, there was no evidence of splenic uptake of 99mTc-RBCs also confirmed with SPECT CT. In two cases where spleen was detected close to normal size (about 4cm) both 99mTc-SC and 99mTc-RBC scan confirmed presence of functional activity in the spleen. In case of childhood traumatic asplenia with liver lesions of unclear etiology and negative 99mTc-SC scan, use of HD 99mTc-RBC SPECT CT for localization of lesions helped to avoid unnecessary invasive procedure. In all patients with HD 99mTc-RBC and functional spleen, the uptake in the spleen exceeded hepatic background, however, not to the level that could exclude the need for SPECT CT completion for definitive diagnosis of the presence of the liver. Only in 3 patients with sickle cell disease SPECT alone was conclusive for presence of spleen.

Conclusions: From our experience of 9 patients for evaluation of spleen in the last 6 months suggest HD 99mTc-RBC scan is complementary to the Tc 99m-SC scan and ultrasound scan. Use of HD 99mTc-RBC improves sensitivity of Spleen scan, but does not change specificity. SPECT CT is required in all cases when the differential diagnosis between the uptake in hepatic parenchyma and spleen is needed. Legend: Left - planar AP and lateral images of spleen more prominent than liver with HD 99mTc-RBC; middle - CT; right - SPECT-CT fusion demonstrating functional spleen in dextraposition.

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