Transient ischemic dilation on [13N]NH3 PET/CT in ischemic and non-ischemic patients

Aim/Introduction Transient ischemic dilation (TID) is a functional parameter of the left ventricle, determined by either the ratio between the stress left ventricular (LV) volume and the rest LV volume from static images or by the stress/rest ratio of end-systolic (ESV) or end-diastolic volumes (EDV) from the gated series. TID ratio is a validated marker of both severe and extensive coronary artery disease and a predictor for cardiac outcomes in Single Photon Emission Computed Tomography (SPECT). In Positron Emission Tomography integrated with Computed Tomography (PET/CT) it has been scarcely described and only using 82Rb as the radiotracer. This study aims to evaluate the appearance of TID (TID static, TID gated ESV and TID gated EDV) in [13N]NH3 PET/CT. Materials and Methods One-hundred and one [13N]NH3 PET/CT examinations from 70 normal and 31 ischemic patients were included retrospectively. PET/CT examinations were processed using two different software packages, Corridor 4DM and Cedars-Sinai QPET. Values of TID static, TID gated ESV and TID gated EDV were retrieved from each software package. TID static values were automatically calculated by both software packages. TID ESV and EDV were calculated from ESV and EDV in rest and stress, acquired from each software’s gated series. For statistical analysis independent t-tests were performed to evaluate the differences of TID values between normal and ischemic population, and ANOVA with Bonferroni post-hoc was performed to evaluate the behaviour of TID values in different extents of ischemic burden. Results All TID values obtained from Corridor 4DM were significantly higher in ischemic patients than in normal population, regardless of the quantification method [TID static (p<0.001), TID gated ESV (p<0.001) and TID gated EDV (p=0.004)]. However, with Cedars-Sinai QPET significant differences were detected only for TID static (p=0.017) and TID gated ESV (p= 0.002), but not for TID gated EDV (p=0.37). When comparing among different degrees of ischemia in Cedars-Sinai QPET, it was found that both TID static and TID gated ESV increased in accordance with the ischemia extent, although significant differences were observed only in the comparison between the highest and lowest quartiles of ischemia extent [Q1 vs Q4 (p= 0.004)]. In Corridor 4DM, the values of TID gated EDV and TID gated ESV proved to be significantly higher (p<0.05) in the group with the highest ischemic burden than for all the other quartiles with less ischemia. TID static presented a similar pattern, however it did not reach statistical significance between the third and fourth quartile [Q3 vs Q4 (p= 0.11)]. Conclusion TID ratios assessed with [13N]NH3 PET/CT are higher in ischemic patients than in normal patients and related to the ischemic extent. It should be taken into account that processing software and metric quantification method may influence the TID values in [13N]NH3 PET/CT.