Establishment of spleen scan in mice

Objectives There is no proper imaging tool for evaluation of spleen in mice. The authors aimed to establish spleen scan in mice using 99mTc-labeled denatured red blood cell (99mTc-dRBC).

Methods C57BL6 mice were used. Modified in vivo labeling and heat denaturation method was employed. Briefly, stannous chloride (0.02 μg/g weight; PYP, Fujifilm) was injected via tail vein; 20 min later, 80 μL of blood was obtained through cardiac puncture; the blood was mixed with 20 μL of ACD; 99mTc-pertechnetate (11.1-14.8 MBq) was applied to the blood for 25 min at 37oC and then for 30 min at 49oC after centrifugation (2000 RPM, 5 min), cell pellet containing 99mTc-dRBC was obtained and re-suspended in 200 μL normal saline for injection. SPECT/CT scan was performed 30 min p.i. using a SPECT/CT system (NanoSPECT/CT, Bioscan). Hemorrhage model (n=3) was generated by retro-orbital bleeding (250 μL), and SPECT/CT images were obtained 1 hr later. Spleen sizes were measured using a software (InVivoScope, Bioscan). Spleen-to-liver and spleen-to-bowel ratios (n=3-4) were compared among spleen scan, none-contrast CT, human contrast-enhanced CT (Ultravist, Bayer) and animal contrast-enhanced CT (eXIATM160, Binitio Biomedical).

Results The labeling efficiency of 99mTc-dRBC was 97±3.0% (mean±S.D.). Spleen volume of mice was 83.81±20.46 mm3 before hemorrhage and 87.62±32.80 mm3 after hemorrhage (p>0.05). The spleen-to-bowel ratios were significantly greater (p<0.05) for spleen scan (52.0±17.4) than for none-contrast CT (1.1±0.4), human-contrast CT (2.3±0.9), and animal-contrast CT (5.1±4.5). The spleen-to-liver ratios were also significantly greater (p<0.05) for spleen scan (5.8±1.3) than for none-contrast CT (1.1±0.5), human-contrast CT (1.1±0.3), and animal-contrast CT (2.6±0.5).

Conclusions We successfully established mouse spleen scan using 99mTc-dRBC. The spleen was most clearly delineated using the 99mTc-dRBC scan compared to enhanced or none-enhanced CT. Mouse spleen volume did not change by simple hemorrhage, which means other biological processes are related to the volume change of spleen