RECONSTRUCTIVE Detection of Perforators Using Thermal Imaging Yezen Sheena, M.R.C.S.(Eng.) Toby Jennison, M.R.C.S.(Eng.) Joseph T. Hardwicke, F.R.C.S.(Plast.) O. Garth Titley, F.R.C.S.(Plast.) Birmingham, United Kingdom

Background: Perforator flaps are commonly used in reconstructive surgery and require accurate vascular anatomy navigation. Several imaging methods help surgeons, including hand-held Doppler, color Doppler ultrasound, computed tomography, and magnetic resonance angiography. A growing literature supports the efficacy of thermal imaging in identifying perforators. This study assessed the efficacy of thermal imaging and perforator anatomy in four body regions. Methods: Twenty volunteers had their abdomen, sacrum, and both anterolateral thighs assessed for cutaneous perforators using thermal imaging. Key surface landmarks were marked with black crosshairs centered on the umbilicus, superior natal cleft, and traditional anterolateral thigh flap markings. All thermal imaging–identified perforators were marked by red crosses, immediately checked with a hand-held Doppler device, and marked with blue circles if not confirmed. A color digital photograph taken of each region was analyzed. Results: Thermal imaging identified a total of 757 “hotspots,” of which 732 (97.0 percent) were confirmed by hand-held Doppler. In 40 anterolateral thighs, the mean number of perforators identified was 1.3 within 2.5 cm and 4.6 within 5 cm of traditional landmarks. In the abdomen, the mean number of perforators was 0.7 and 3.7 within 2.5 cm and 5 cm of the umbilicus, respectively. In the sacral region, there was a mean number of 0.3 and 2.3 perforators within 2.5 cm and 5 cm, respectively, of the superior natal cleft. Conclusions: Thermal imaging is a quick, easy method of assessing cutaneous perforators. It should be considered a useful adjunct, and further investigated, to determine its best role among the established perforator imaging methods.  (Plast. Reconstr. Surg. 132: 1603, 2013.) CLINICAL QUESTION/LEVEL OF EVIDENCE: Diagnostic, II.

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erforator flaps are commonly used as local pedicled flaps and for free tissue transfer. Successful surgery depends on identifying viable vessels, and this requires a detailed knowledge of the underlying vascular anatomy. Unfortunately, perforators often have a variable location and course, making dissection challenging. At first, anatomical landmarks, defined by cadaveric imaging and intraoperative studies, were used to help locate suitable perforators.1,2 Taylor and Palmer performed cadaveric studies using a lead oxide injection technique to demonstrate human perforator anatomy and introduced the concept of angiosomes: composite blocks of tissue supplied by a single source artery.1 From the Department of Plastic Surgery, University Hospitals of Birmingham NHS Foundation Trust, New Queen Elizabeth Hospital. Received for publication February 27, 2013; accepted June 26, 2013. Copyright © 2013 by the American Society of Plastic Surgeons DOI: 10.1097/PRS.0b013e3182a80740

More recently, imaging methods have been successfully used preoperatively to assess perforator anatomy. These methods include hand-held Doppler ultrasound, color Doppler ultrasound, computed tomography angiography, and magnetic resonance angiography.3 Each method has significant disadvantages: hand-held Doppler ultrasound Disclosure: None of the authors has a financial interest in any of the products or devices mentioned in this article. No funding was received toward this study.

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Plastic and Reconstructive Surgery • December 2013 takes time and may miss perforators or identify false positives.4,5 Color Doppler ultrasound, computed tomography angiography, and magnetic resonance angiography require a radiologist or specialist with expertise and are therefore less accessible and more expensive.3 Magnetic resonance angiography and computed tomography angiography expose the patient to the risks of intravenous contrast, and the latter to ionizing radiation.3,6,7 Thermography, or thermal imaging, detects infrared radiation from an object to produce an image based on the local temperature. Clinically, this demonstrates areas of relatively increased skin temperature corresponding to local blood supply.8–10 Arai and Fukuda first described this process more than 40 years ago, demonstrating what we now refer to as the “hotspots” corresponding to perforators.11 As technology has advanced, thermal imaging’s potential has increased. New-generation cameras are smaller (more portable), pick up smaller temperature differences (more sensitive), and have improved software and real-time higher-resolution visual displays (more accurate and user-friendly). All increase the potential for “surgical thermography” (preoperative perforator detection and planning, intraoperative surgical dissection, and postoperative monitoring) in a quick, easy, portable, and accurate high-resolution video capture. In this study, we aimed to assess whether thermal imaging is effective at locating cutaneous perforators by comparing it with traditional hand-held Doppler ultrasound and then assessed three commonly used sites for perforator-based tissue transfer: the anterolateral thighs, the deep inferior epigastric artery perforator (DIEP), and the sacral areas.

METHODS A study using male volunteers was carried out in the Clinical Photography Department of University Hospitals Birmingham NHS Foundation Trust. The room used was kept at a temperature of 23°C throughout the 6-hour study period. Participants gave informed consent, completed a health questionnaire, and had vital observations recorded on the study day. On advice from our Local Research Ethics Committee, as a service evaluation study, formal ethical approval was not required. On each of the 20 volunteers, surface anatomical landmarks for the anterolateral thigh perforators were marked bilaterally using a black marker pen at the midpoint of a line between the anterior superior iliac spine and the superolateral aspect of the patella. Circles with radii of 2.5 cm and 5 cm from the midpoint were marked. For the abdomen, we marked 2.5 cm and 5 cm radii centered on the umbilicus, and for the sacral region, 2.5 cm and 5 cm radii were marked centered on the superior natal cleft. See Video, Supplemental Digital Content 1, for more details, http://links.lww.com/PRS/A903. During the same afternoon, the anterolateral thigh, DIEP, and sacral areas were imaged (in that order) on each individual using a thermal camera (FLIR SC660; FLIR Systems, Inc., Wilsonville, Ore.). In testing the camera to determine our protocol, we verified that patient position did not alter hotspot identification or location. The optimal camera temperature range focus was set to 28 to 32°C. The volunteer laid supine on an examination couch, and the thermal camera was mounted 60 cm above. The volunteer was then positioned in lateral positions to mark and image each thigh, the supine position for the abdomen, and finally prone for the sacral area. The thermal imaging

Video. Supplemental Digital Content 1 demonstrates the materials and methods used to generate the results of this study, http://links.lww.com/ PRS/A903.

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Volume 132, Number 6 • Thermal Imaging to Detect Perforators camera feed was relayed to a laptop for visualization of each anatomical area. Software settings were adjusted to obtain best definition of perforator hotspots seen on the screen compared with the cooler surrounding skin. These were marked with a red marker pen. A hand-held Doppler device was used to look for an audible pulsation at each of the marked hotspots. If an audible pulsation was not located at a thermal imaging–identified hotspot, then the red cross was circled in blue. Finally, the markings were photographed with a color digital camera (Nikon D300; Nikon Corporation, Tokyo, Japan). (See Figure, Supplemental Digital Content 2, which demonstrates the hardware and participant set-up, http://links.lww.com/PRS/A904; Figure, Supplemental Digital Content 3, which shows the marked right anterolateral thigh, http://links.lww. com/PRS/A905; Figure, Supplemental Digital Content 4, which shows the marked left anterolateral thigh, http://links.lww.com/PRS/A906; ­ Figure, Supplemental Digital Content 5, which shows the marked abdomen, http://links.lww.com/PRS/A907; and Figure, Supplemental Digital Content 6, which shows the marked sacrolumbar region, http:// links.lww.com/PRS/A908.) The number of perforators identified by thermal imaging and whether they were confirmed by hand-held Doppler were documented. The photographs were analyzed for anatomical location of perforators and diagnostic accuracy of thermal imaging.

RESULTS We studied 20 healthy male subjects with an average age of 20 years, no known comorbidities, and normal body mass index, heart rate, blood pressure, and core temperature. In 40 thighs, thermal imaging detected a total of 50 hotspots within 2.5 cm of the traditional anterolateral thigh landmark (mean, 1.3 per thigh; range, zero to four per thigh), and 47 (94 percent) of these hotspots had an audible signal on hand-held Doppler. A total of 184 hotspots were found within 5 cm of the traditional landmark (mean, 4.6 per thigh; range, zero to nine per thigh), and 173 (94 percent) were confirmed by hand-held Doppler. Composite thigh “perforagrams” for all 20 individuals are shown in Figures 1 and 2. Outside the circle’s 5-cm radius, a further 156 thigh perforators were detected; of these, 147 (94 percent) were confirmed by Doppler. Figure 3 shows a typical individual thigh thermogram. Thermal imaging of 20 abdomens revealed 14 hotspots within 2.5 cm of the umbilicus (mean, 0.7 per individual; range, zero to three per individual), and all were confirmed by hand-held Dopper. Of

Fig. 1. All right anterolateral thigh perforators (red dots) identified from the 20 study participants superimposed on one representative right thigh. Black crosshairs were centered on the traditional anterolateral thigh surface landmark with a 2.5-cm radius and 5-cm radius.

Fig. 2. All left anterolateral thigh perforators (red dots) identified from the 20 study participants superimposed on one representative left thigh. Black crosshairs were centered on the traditional anterolateral thigh surface landmark with a 2.5-cm radius and 5-cm radius.

Fig. 3. A representative left anterolateral thigh thermogram (posteromedial right thigh is at the top of image).

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Fig. 4. All paraumbilical perforators identified (red dots) from the 20 study participants superimposed on one representative abdomen. Black crosshairs were centered on the umbilicus with a 2.5-cm radius and 5-cm radius.

73 hotspots within 5 cm of the umbilicus (mean, 3.7 per individual; range, one to eight per individual), 72 (98.6 percent) were confirmed by Doppler. ­Figure 4 demonstrates 73 hotspot locations on a paraumbilical perforagram. More than 5 cm from the umbilicus, a further 149 hotspots were detected by thermal imaging, and 148 (99.3 percent) were confirmed by hand-held Doppler. Figure 5 demonstrates a typical abdominal thermogram. Thermal imaging of 20 sacral regions detected six hotspots within 2.5 cm of the superior natal cleft (mean, 0.3 per individual; range, zero to two per individual), and all were confirmed by handheld Doppler. Forty-five hotspots were detected within 5 cm of the superior natal cleft (mean, 2.3

Fig. 6. All identified sacral perforators (red dots) from the 20 study participants superimposed on one representative sacral region. Black crosshairs were centered on the superior natal cleft with a 2.5-cm radius and 5-cm radius.

per individual; range, zero to six per individual), and all were confirmed by Doppler. Figure 6 demonstrates these on a sacral perforagram. A further 150 perforators were identified within 15 cm of the superior natal cleft, and of these, 147 (98 percent) were confirmed. Figure 7 demonstrates a typical sacral thermogram. In our cohort of 20 individuals, we identified 757 hotspots using thermal imaging, and of these, 732 (97.0 percent) were confirmed as perforators by hand-held Doppler. Table 1 summarizes our findings.

DISCUSSION Hand-held Doppler ultrasound is commonly used to locate perforators, as it is easy, cheap, and

Fig. 5. A representative abdominal thermogram.

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Fig. 7. A representative sacral thermogram.

732 (97%) 757 Study total perforators

192 (98%) 195 147 (98%) 150 39 (100%)

*Total represents all identified perforators in all 20 individuals.

6 (100%) 6

39

220 (99%) 222 148 (99%) 149 58 (98%) 14 (100%) 14

59

320 (94%) 340 147 (94%) 156 126 (94%) 134 47 (94%) 50

Each Mean 1.3 Mean 4.6 thigh range 0–4 range 0–9 Abdomen Mean 0.7 Mean 3.7 range 0–3 range 1–8 Sacrum Mean 0.3 Mean 2.3 range 0–2 range 0–6

Region

Total* Total* Total* Total* Total* Total* TI-Detected TI-detected TI-Detected HHD-Confirmed TI-Detected HHD-Confirmed TI-Detected HHD-Confirmed Total* Total* HHDPerforators Perforators Perforators  5 cm (% TI TI-Detected Confirmed (% TI

Detection of perforators using thermal imaging.

Perforator flaps are commonly used in reconstructive surgery and require accurate vascular anatomy navigation. Several imaging methods help surgeons, ...
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