In Vivo Differentiation of Two Vessel Wall Layers in Lower Extremity Peripheral Vein Bypass Grafts: Application of High Resolution Inner-Volume Black Blood 3D FSE

摘要

Lower extremity peripheral vein bypass grafts (LE-PVBG) imaged with high-resolution black blood 3D inner-volume (IV) FSE MRI at 1.5T possess a two layer appearance in T1W images while only the inner layer appears visible in the corresponding T2W images. This study quantifies this difference in six patients imaged six months post-implantation, and attributes the difference to the T2 relaxation rates of vessel wall tissues measured ex vivo in two specimens with histologic correlation. The visual observation of two LEPVBG vessel wall components imaged in vivo is confirmed to be significant (p<0.0001), with a mean vessel wall area difference of 6.8±2.7 mm² between contrasts, and a ratio of T1W to T2W vessel wall area of 1.67±0.28. The difference is attributed to a significantly (p<0.0001) shorter T2 relaxation in the adventitia (T2=52.6±3.5ms) compared to the neointima/media (T2=174.7±12.1ms). Notably, adventitial tissue exhibits bi-exponential T2 signal decay (p<0.0001 vs mono-exponential). Our results suggest that high-resoultion black blood 3D IV-FSE can be useful for studying the biology of bypass graft wall maturation and pathophysiology in vivo, by enabling independent visualization of the relative remodeling of the neo-intima/media and adventitia.