Magnetic resonance assessment of microvascular patency in reimplanted rabbit ears

Magnetic resonance angiography (MRA) provides a means of noninvasive vascular imaging of microvascular vessels. Before conducting comparative studies and value assessments of a new method, it is necessary to evaluate the reproducibility and reliability of the technique. In an experimental study with five rabbits, we investigated the feasibility of MRA imaging of microsurgical vessels. We also attempted to demonstrate the reproducibility of the method.

We performed MRA imaging of the vascular tree of five New Zealand white rabbit ears, including normal ears, after microvascular reimplantation of the ear and in occlusion experiments on the ear. Scans of four reimplanted ears were performed after the microvascular procedure. In four occlusion experiments, the central vessels were totally occluded by a ligature, and scans were carried out prior to and immediately after occlusion. We used a fast imaging with steady-state precession (FISP) three-dimensional (3-D) rephased-dephased sequence (28-msec repetition time [TR], 18-msec echo time [TE], and a 20 degrees flip angle).

In normal rabbit ears and in the reimplantation cases, MRA imaging was able to show the flow within the vascular tree. In the reimplanted ears, MRA images confirmed patency in all anastomosed vessels. The diagnosis of occlusion appeared to be secure in the fully completed experiments (two of four) when it was based on the absence of a signal in the occluded vessels. Because of poor image quality during preligation scanning, we prematurely canceled two experiments.

This study demonstrates that MRA imaging could correctly identify 1-mm vascular channels. Because of the long acquisition time, motion could compromise the reliability of the technique in human subjects.