[Nontarget area and threshold selection in 99mTc-DTPA orbital SPECT/CT imaging inthyroid associated ophthalmopathy].

To compare diagnostic value of 4 kinds of target-to-nontarget ratio (T/NT), and to choose a better one to assess thyroid associated ophthalmopathy (TAO) activity.
 Methods: The clinical data were collected for 29 newly-diagnosed patients (58 eyes) with TAO who underwent orbital 99mTc-DTPA single photon emission computed tomography/computed tomography (SPECT/CT) fusion images according to the clinical activity score (CAS). They were divided into an active group (18 cases, 36 eyes), an inactive group (11 cases, 22 eyes), and a control group (9 cases, 18 eyes). Diagnostic value of orbital/occipital lobe radioactive uptake count ratio (T/NT1), orbital/occipital radioactive uptake count ratio (T/NT2), orbital/thalamus radioactive uptake count ratio (T/NT3), and orbital/cerebellar radioactivity uptake count ratio (T/NT4) were calculated, and the CAS of Spearman rank correlation and receiver operating characteristic (ROC) curve were analyzed.
 Results: T/NT1, T/NT2 and CAS were correlated (r1=0.873, r2=0.527; P<0.001), with the better correlation between T/NT1 and CAS and there was no correlation between T/NT3, T/NT4 and CAS (r3=0.039, r4=0.090; P>0.05). Area under the ROC curve of T/NT1 was 0.860, area under the ROC curve of T/NT2 was 0.581, and the accuracy for T/NT1 on TAO activity was good. T/NT1=9.74 could be used as active threshold for judge of TAO in patients.
 Conclusion: There is a good correlation between T/NT1 and CAS. TAO activity assessment possesses high diagnostic value, and SPECT/CT together with imaging anatomical location is more accurate.