Evaluation of Free Flap Perfusion with Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Abstract

Sir: Postoperative monitoring of transplanted free flaps is necessary for the early detection of failure.1 A suitable monitoring method should evaluate not only the patency of microvascular anastomoses but also the perfusion and microcirculation of the whole flap in all tissue layers.2,3 For this reason, we evaluated for the first time the potential use of dynamic contrast-enhanced magnetic resonance imaging. For the dynamic contrast-enhanced measurement, we established an optimized technique using the T1 effects of a paramagnetic gadolinium contrast agent by T1-weighted transverse three-dimensional volumetric interpolated breathhold examination with fat saturation. The increase of signal intensity over time was assessed in the free flap in different representative regions and in the surrounding tissue as reference (Fig. 1, above). For the normally perfused flaps, the mean signal increase was very similar to that of the reference tissue (Fig. 1, below). In compromised flaps, the signal increase was significantly lower.Fig. 1.: (Above) Anatomical regions (slice positions) and regions of interest for evaluation of mean signal intensity versus time of the free parascapular flap and the reference tissue. Region of interest 1 includes the reference tissue, region of interest 2 includes the free flap. (Below) Normally perfused free parascapular flap in a 50-year-old woman. Signal intensity versus time within the free flap (yellow curve) and within the reference tissue (red curve) showing a clear increase of signal intensity of the flap and of the reference tissue.Our magnetic resonance perfusion method enables noninvasive assessment of perfusion with high spatial resolution and a comprehensive and complete high-quality image acquisition of the transplanted tissue. An additional important advantage of magnetic resonance is the excellent imaging for edema, hematoma, and inflammatory tissue reactions at the same time. Even the monitoring of buried flaps is feasible. The main strength of magnetic resonance imaging is its ability to delineate soft tissues throughout the body. Other benefits are the lack of ionizing radiation and the multiplanar capabilities of magnetic resonance imaging. Limitations of magnetic resonance imaging are artifacts caused by metal clips or special osteosynthesis material in osteocutaneous flaps. In addition, it can be difficult to detect a significant capillary perfusion in tissue layers with an extremely high fat content. In patients with severely impaired renal function, the application of gadolinium contrast medium should be avoided. The role of magnetic resonance imaging in modern medicine continues to expand. Magnetic resonance perfusion methods enable noninvasive evaluation of microcirculation not only for free flaps but in any setting in which tissue perfusion needs to be assessed exactly. Possibly with our optimized magnetic resonance imaging technique we have established a useful diagnostic tool for the early recognition of an imminent compartment syndrome, and for detection of muscular diseases such as myositis and many other chronic diseases in which tissue perfusion is altered.4 DISCLOSURE The authors have no financial interest to declare in relation to the content of this article. Lukas Prantl, M.D., Ph.D. Department of Trauma and Plastic Surgery Claudia Fellner, Ph.D. Michael E. Jung, M.D., Ph.D. Institute of Radiology University Medical Center Regensburg Regensburg, Germany