Objectives:
Guidelines recommend surgical bypass for peripheral chronic total occlusions (CTOs). Endovascular revascularization, however, offers improved morbidity and shorter length of hospitalization. Not all lesions are amenable to this technique but predicting crossability is difficult due to limitations in characterizing CTOs with current imaging techniques. This study demonstrates the ability of MRI to characterize peripheral CTO components with microCT and histologic validation.
Methods:
MRI was performed on 15 excised human peripheral arterial CTO segments from 4 patients. Each sample was imaged at 7 Tesla at high resolution (75μm3 voxels) to produce T2- and T2*-maps using ultrashort echo (UTE) sequences with echo times: {20μs, 500μs, 1ms}. A T2* difference image was produced by subtracting the UTE images and a phase map was constructed. The T2, UTE 20μs and T2* difference images were used together to differentiate CTO components. MicroCT and histology were used to validate regions of interest (ROIs).
Results:
3 independent reviewers identified 47 ROIs. There was excellent agreement between MRI and microCT for calcium (sensitivity 87%, specificity 99%). There was also good agreement between MRI and histology for adipose tissue (100%, 100%), soft tissue (97%, 97%), thrombus (78%, 100%), collagen (83%, 94%) and open lumen (95%, 98%).
Conclusions:
These results demonstrate the potential of high-resolution T2 and T2* imaging using UTE, to characterize lesion components in human peripheral CTOs. Further work is required to better differentiate thrombus from collagen. This study provides the foundation for future studies in determining the lesion crossability in CTOs.
A new correction method for high-resolution energy-dispersive x-ray analyses in the environmental scanning electron microscope
