**1. Introduction**

Defect reconstruction still remains one of the main fields of interest in plastic surgery. Assessment of flap viability has been shown to be effective using the correct length-to-width ratio in the case of random pattern flaps for clinical evaluation [1,2].

When multimorbid oncological patients who might have undergone irradiation preoperatively or should undergo irradiation postoperatively, further reliable assessment of flap perfusion is necessary to avoid complications such as wound healing disorders and partial or complete flap loss [1]. Therefore, the correct intraoperative detection of malperfused areas is one of the points of interest [1,3]. Skin is especially one of the common areas for collateral injury caused by radiotherapy and increasingly in diagnostic radiology by the use of fast multislice CT scanners and fluoroscopically guided interventions [4]. Skin

**Citation:** Müller-Seubert, W.; Ostermaier, P.; Horch, R.E.; Distel, L.; Frey, B.; Cai, A.; Arkudas, A. Intra- and Early Postoperative Evaluation of Malperfused Areas in an Irradiated Random Pattern Skin Flap Model Using Indocyanine Green Angiography and Near-Infrared Reflectance-Based Imaging and Infrared Thermography. *J. Pers. Med.* **2022**, *12*, 237. https://doi.org/ 10.3390/jpm12020237

Academic Editor: Moon-Soo Lee

Received: 17 November 2021 Accepted: 27 January 2022 Published: 8 February 2022

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tolerance has often been the limiting factor in radiotherapy [5]. Currently, skin injuries lead to long-lasting burdens for the patients being treated.

Irradiation of tissue leads to ischemia and finally results in tissue fibrosis [6]. Briefly, irradiation induces DNA damage and the generation of reactive oxygen species leading to activation of the immune system and the recruitment of inflammatory cells. These neutrophils release additional inflammatory mediators. Furthermore, lymphocytes and monocytes migrate to the irradiated tissue. Monocytes differentiate into macrophages, which—together with other cells such as fibroblasts—release the transforming growth factor-beta (TGF-β), which stimulates fibroblasts to differentiate into myofibroblasts. In the end, myofibroblasts secrete extracellular matrix proteins and lead to increased tissue stiffness [7]. Besides these factors, vascular injury and changes in microvascular function are a primary pathogenetic signal for the procedure of fibrosis [8]. Early inflammatory vascular changes such as an increase in leukocyte adhesion due to irradiation can be seen within one hour after irradiation [9]. The developed tissue fibrosis itself reduces the perfusion of the irradiated tissue [7,10]. Furthermore, irradiation seems to have a negative impact on flap dimension [11].

To determine tissue perfusion, different imaging modalities have been tested, such as laser Doppler flowmetry for cutaneous circulation [12], infrared thermography [13], indocyanine green angiography [1,14] and near-infrared reflectance-based imaging [15]. While these devices may eventually predict the malperfusion accurately, there might be differences in their features such as application handling and invasivity.

This study evaluates the different imaging modalities—infrared thermography, indocyanine green angiography and near-infrared reflectance-based imaging [16,17]—to predict malperfused areas in an irradiated random pattern fasciocutaneous flap model.

#### **2. Materials and Methods**

Twenty-five male Lewis rats (age 14 ± 2.5 weeks (range 10–19 weeks)) weighing 336 ± 22.4 g (range 283–390 g) were operated in 5 different treatment groups. The study was approved by the ethic committee of the government of Middle Franconia (RUF-55.2.2- 2532-2-1275-15).

#### *2.1. Surgical Procedure*

Anesthesia was performed using isofluran. For analgesia, the animals received butorphanol (0.5–2 mg per kg) and meloxicam (1 mg per kg). Two modified caudally based McFarlane flaps were harvested at the rat's back with a length of 6 cm and a width of 1 cm. The flaps were located parallel and 1 cm lateral to the spine (Figure 1). The flaps were harvested by incision along their medial, lateral and cranial side so that their caudal base was 1 cm cranial of the spina iliaca posterior superior. The dissection was deep to the panniculus carnosus and superficial to the deep fascia. After raising the flap, it was reinserted to its bed and sutured using monofilament sutures. Postoperative analgesia was performed using meloxicam. The rats received an antibiotic treatment with enrofloxacin (7.5 mg per kg) for 5 days.
