High-resolution ex vivo magnetic resonance angiography: a feasibility study on biological and medical tissues

The optimal solution for ex vivo MR angiography (MRA) was a compound containing gelatine (0.05 g/mL), the CT contrast agent barium sulphate (0.43 mol/L) and the MR contrast agent gadoteric acid (2.5 mmol/L). It was possible to perform angiography on all specimens. We found that ex vivo MRA could only be performed on fresh tissue because formalin fixation makes the blood vessels permeable to the MR contrast agent.Ex vivo MRA provides high-resolution images of fresh tissue and delineates fine structures that we were unable to visualise by CT. We found that MRA provided detailed information similar to or better than conventional CTA in its ability to visualize vessel configuration while avoiding interfering signals from adjacent bones. Interestingly, we found that vascular tissue becomes leaky when formalin-fixed, leading to increased permeability and extravascular leakage of MR contrast agent.In vivo angiography is frequently employed to produce a structural overview of the intravascular configuration in living tissues [1] whereas angiography of excised organs or post-mortem angiography is rarely performed [2-4]. For example, ex vivo angiography has been used successfully to identify structural components of carotid atherosclerotic plaques [5] and to visualize the renal microvasculature [6]. In addition, post mortem angiography provides information secondary to conventional autopsy in humans and animals [7,8]. Computed tomography angiography (CTA) can be employed with sub-millimetre resolution of vessels in conjunction with an intravascular contrast agent [9]. However, accurate delineation of the entire vessel configuration acquired by CTA is often complicated by the inherent absorption of X-rays in bones and cartilage, characterized as hyperintense areas on CTA images. Magnetic resonance angiography (MRA) is another method, where an intravascular confined paramagnetic compound generates a change in the local magnetization of water, resulting in a hyperintense signal