MR Imaging by Using Very Short Echo Time Sequences after Syngeneic Lung Transplantation in Mice

Abstract

Purpose:To test the in vivo feasibility of magnetic resonance (MR) imaging of ischemia reperfusion injury after syngeneic lung transplantation in mice and to characterize tissue relaxation properties by using very short echo-time (TE) sequences at 4.7 T.Materials and Methods:The experimental protocol was approved by the institutional animal committee. MR imaging was performed in six C57BL/6 mice 24 hours after the animals underwent syngeneic orthotopic left lung transplantation. A small-animal MR imager was equipped with a linear polarized hydrogen birdcage mouse coil. In addition to conventional T1-weighted spoiled gradient-echo and T2-weighted fast spin-echo sequences, three-dimensional very short TE sequences (50-5000 μsec) were performed. Color-encoded parametric maps of T2* transverse relaxation times were calculated on a pixel-by-pixel basis. Quantitative T2* values of the parenchyma of the transplanted lungs and relative spin density were compared by using region-of-interest analysis with the two-sided paired Student t test. After MR imaging, transplanted lungs were processed for histologic examination.Results:Transplanted ventilated lungs in all the mice showed similar low signal intensity with the conventional T1- and T2-weighted sequences. The very short TE sequence exhibited signal yield in the lungs that was higher than that of the noise level. Increased spin density (50.8% ± 26.9 [standard deviation], P = .006) and longer T2* relaxation time (1041 μsec ± 424, P = .016) were found in the transplanted lungs. Best visualization was possible using color-encoded log-transformed parametric T2* maps. Conventional T2-weighted sequences revealed small pleural effusions. Histologic examination demonstrated ischemia reperfusion injury with a predominance of either cell influx or edema.Conclusion:Ischemia reperfusion injury after syngeneic lung transplantation can be visualized and characterized using very short TE sequences showing different MR imaging relaxation properties when compared with normal lung parenchyma.© RSNA, 2012.