小动物SPECT/CT探测甲状腺功能减低大鼠生长抑素受体分布的初步研究

The study of biodistribution of ^(99m)Tc-octreotide in hypothyroid rats induced by ^(131)I internal irradiation

目的观察131I内照射所致甲状腺功能减低(简称甲减)Wistar大鼠99mTc-奥曲肽(99mTc-octreotide)全身显像,以了解甲减大鼠生长抑素受体的异常分布。方法实验组14只Wistar大鼠腹腔注射131I-碘化钠注射液500μCi(1.85×105Bq)剂量/只,另设6只正常Wistar大鼠为对照组。第8周随机抽取实验组7只和对照组2只Wistar大鼠腹腔注射99mTc-奥曲肽,1~1.5 h后进行SPECT/CT显像。结果 99mTc-奥曲肽主要经泌尿和肝胆系统排泄,心脏显像较淡。7只实验大鼠肩背部出现阳性显像,其中2只甲状腺阳性显像,而眼眶未出现显像。2只对照大鼠甲状腺出现阳性显像。结论实验大鼠肩背部奥曲肽浓聚被认为与甲减伴黏液性水肿有关,甲状腺阳性显像被认为是游离99mTc所致,甲状腺未显像的实验大鼠考虑为131I内照射后甲状腺明显缩小和功能减退。本研究采用腹腔注射99mTc-奥曲肽,血本底较低,用于观察大鼠特殊部位显像是可行的,而显像剂吸收较少、靶器官较小可能是眼眶阴性显像的主要原因。

Objective To evaluate 99mTc-octreotide whole-body imaging in hypothyroid Wistar rats induced by 131I internal irradiation,and to investigate the abnormal distribution of somatostatin receptors.Methods 14 Wistar rats in the test group received 131I-NaI of 500 μCi(1.85×105Bq)dose each via intraperitoneal injection.6 Wistar rats were set as controls.At week eight,7 rats in the test group and 2 rats in the control group were randomly selected and imaged by SPECT/CT after 1-1.5 h intraperitoneal injection of 99mTc-octreotide.Results 99mTc-octreotide was mainly shown renal and hepatobiliary excretion,and cardiac imaging was lighter.The shoulder back of 7 rats in the test group appeared positive imaging,of which only 2 rats showed positive imaging of thyroid whereas no positive imaging of orbital.2 control rats appeared positive imaging of thyroid.Conclusion The results indicated that the hypothyroidism accompanied with myxedema is correlated with high concentration of octreotide in the shoulder back of the rats in the test group.The positive thyroid imaging is caused by free 99mTc.The negative thyroid imaging indicates the shrinkage of thyroid and hypothyroidism.Intraperitoneal injection of 99mTc-octreotide,which generates low background,is applied in this study.This method is applicable for detection of the special portion of the body image,but the low absorbance of imaging agent as well as the limited room for observation may be the main reason of negative imaging of thyroid.