Abstract: A Clinical Trial for Three-Dimensional Vascular Mapping of Anterolateral Thigh Flap Distally-Branching Perforator Vessels Based on Photoacoustic Tomography: The Protocol and Preliminary Results

Abstract

BACKGROUND: Thin free flaps are challenging procedures. In particular, the failure of thin anterolateral thigh (ALT) flaps is reported to be associated with the distal branching pattern of the perforator vessels. In a previous study, we demonstrated the feasibility of using photoacoustic tomography (PAT) to identify ALT perforators and their branching patterns in the subcutaneous layer, especially those in oblique or horizontal orientations.1 In this paper, we present the protocol and preliminary results of a clinical trial for three-dimensional vascular mapping of the distal ALT perforators using PAT imaging. METHODS: Patients for whom reconstructive surgery using an ALT flap was planned were recruited. Four days before the operation, the bilateral anterolateral aspects of the mid-thigh were examined by PAT. The perforator orientation, as determined by ultrasound, was marked with red ink. The body surface was marked every 4 cm with purple ink. The acquired data were processed three-dimensionally using a laboratory-made imaging software program. The depth of the visualized perforator vessels and the distal networks were distinguished based on the color gradation. The body surface markings were preserved until the operation day using a film sheet. Two days before the operation, the three-dimensional vascular data were converted into a two-dimensional vascular map using a projective image reconstruction technique. A semi-automated normal vector detection method and curvature approximation were applied to maintain accuracy. The depth was indicated by color gradation on a sterilized transparent sheet. The mapping sheet was attached to the patient’s thigh before the operation. The skin incision was performed with cutting the transparent mapping sheet. The stem portion of the perforator vessels was evaluated at the level of fascia lata. RESULTS: The first clinical trial involved a 32-year-old male patient with a malignant chest-wall tumor. Each PAT scan took approximately 5 minutes per thigh. The perforator vessels were visualized at the expected points by ultrasonography. A two-dimensional vascular mapping sheet was prepared by drawing the courses of the subcutaneous micro-vessels using projection mapping. Our computing technique projected the trajectories of the vessels in the subcutaneous layer onto a two-dimensional transparent sheet and showed the depth by color gradation. The stem portion of the perforator vessels, as estimated by PAT, was correlated with the operative findings at the points that penetrated the fascia. CONCLUSION: The first clinical trial protocol revealed the efficacy of PAT in creating a three-dimensional vascular map of the anterolateral thigh in the clinical setting.