Purpose

The course and morphology of facial artery are important for preoperation evaluation of submental vascularized lymph node flap transfer for patients with lymphedema¹. Facial artery is a main branch of external carotid artery and it is seldom evaluated by MRA. CE-MRA has been proven to be useful for visualizing major arteries in the head and neck such as carotid artery and basilar artery in clinical setting². However, it is difficult to apply the same measurement and to find the optimal acquistion timing in assessing facial artery due to variable travel time of contrast media (CM) in the neck. Furthermore, recent reports³ linking the use of gadolinium-based MR CM with nephrogenic systemic fibrosis have hampered their widespread application in patients with renal insufficiency. A novel non-contrast MRA technique using phase contrast-based (PC) 3D velocity MRA⁴ (Inhance 3D MRA) was recently proposed. Unlike traditional PC-MRA, Inhance 3D MRA is compatible with parallel imaging and utilizes time-efficient elliptical k-space filling technique. The purpose of this study is to determine the performance of Inhance 3D MRA in the depiction of the facial arteries for preoperative planning and compared the result with that in CE-MRA.

Method and Material

Twenty patients with lymphedema were imaged in a 3T clinical scanner (Discovery MR750, GE Healthcare, Milwaukee, USA ) using an 8-channel brain coil as the signal detection and whole body coil for RF transmission. Images from Inhance 3D MRA and CE-MRA were acquired with the matched slice coverage and resolution (FOV=300 mm; matrix=352×224) and other scanning parameters were as follows: TR/TE= 8.9/3.9 msec and 3.9/1.4 msec for Inhance 3D MRA and CE-MRA, respectively. For better depicting the course of facial artery, the facial anatomical reference and neighboring position of lymph node were acquired by sagittal Cube T1-weighted images (T1WI) (TR/TE= 600/13 msec) and fat-saturated Cube T2-weighted images (T2WI) (TR/TE= 2500/76 msec), respectively. The 18 mm-thick slabs were generated by maximum intensity projection (MIP) of Inhance 3D MRA or CE-MRA fused with Cube T1WI or fat-saturated Cube T2WI (Figure 1). The visualibilty of facial artery at two MRA techniques was assessed by two radiologists and rated on four-point score: poor (0), questionable (1), adequate (2) and good (3). To determine the diagnostic ability for clinical application, the results were dichotomized into diagnostic (score 3 and 2) and non-diagnostic (score 1 and 0). The significance differences between the diagnostic and non-diagnostic in MRA results generated by Inhance 3D MRA and CE-MRA were evaluated with the Fisher Exact test.

Result and Discussion

Depending on the results of image score dichotomized into diagnostic and non-diagnostic in two MRA techniques (Table 1), there was no significant difference in the diagnostic ability between Inhance 3D MRA and CE-MRA (p =0.447 and 1 for left and right side facial artery, respectively). A representative morphology of left facial artery was visualized in both Inhance 3D MRA (Figure 1a) and CE-MRA (Figure 1b). Fused MRA with fat-saturated 3D Cube T2WI (Figure 1c and 1d), the lymph node position can be located. This would be helpful for platic surgeon to do preoperative planning. The acquisition timing for CE-MRA has been optimized by finding maximal of CM travel time in evaluating facial artery. Apparently, CE-MRA showed high vessel signal due to the presence of CM compared to that in Inhance 3D MRA. However, the enhanced signal in background tissue caused by venous contamination was also found in CE-MRA (Figure 1b). Unlike CE-MRA, Inhance 3D MRA provides the excellent contrast between background tissue and facial artery.

Conclusion

Our study demonstrated that Inhance 3D MRA is a reliable method for evaluating preoperative facial artery course without concerning the travel time of CM and it could be an alternative to CE-MRA in patient with renal insufficiency. Non-contrast Inhance 3D MRA is expected to have wide clinical application and diagnostic value in the visualization of small artery.

Acknowledgements

No acknowledgement found.