**4. Characteristics of ICG angiography**

ICG angiography has several advantages. First, it can visualize arterial blood flow by intra‐ venous injection of ICG without catheter manipulation or contrast agent. Second, stenotic portion can be visualized like fluoroscopic angiograms. Third, it takes only ten minutes from preparation to imaging.

However, ICG angiography systems mentioned above have several drawbacks. First, they use laser light source, and the time duration for irradiation is limited to 35 seconds because of the danger of thermal injury. Second, the angiograms are shown in monochrome, making it difficult to recognize the color of tissue. Third, penetration of fluorescence is poor and vessels in the deep layer is hardly visualized.

We have developed a new ICG imaging system, HyperEye Medical System (HEMS, Mizuho Co., Tokyo, Japan) to solve these problems (Figure 3) [9, 12]. It is composed of an imaging unit, a control unit and a monitor. The imaging unit consists of multiple light-emitting diodes (LEDs) which is allocated around an ultra-sensitive color charged-coupled device (CCD) imaging camera with non- Bayer color filter arrays (HyperEye Technology; SANYO Co., Ltd, Tokyo, Japan). This camera detects near infrared rays (380-1200 nm) and visible light at 30 frames per seconds. The control unit is composed of a personal computer and a controller for recording and adjusting the focus, iris and range of imaging.

**Figure 3.** HyperEye Medical System (HEMS) A: Full view of HEMS, composed of imaging unit, control unit, and moni‐ tor. B: The imaging head consists of multiple light-emitting diodes (LED) and an ultrasensitive color charge-coupled

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**Figure 4.** Sentinel node mapping in breast cancer surgery. The ICG stream in lymphatic duct is observed from subareo‐ lar to the axillar lymph nodes after ICG injection to subcutaneous of areolar. A: Fluorescence emitted from ICG inject‐ ed in the breast. The lymphatic duct is identified as fluorescence line (arrow). B: The ICG stream in lymphatic duct. C: ICG in the axillar lymph nodes. The sentinel lymph node is identified as strong fluorescence leading out of lymphatic

device (CCD) camera. C: Control unit consists of controller and analyzing system.

duct.

HEMS can demonstrate the fluorescent images on the background of natural color (Figure 4), which facilitates surgeons to recognize the vessels in the surgical field [12]. Unlimited re‐ cording is another advantage of this system because it uses LEDs as the light source. The imaging head is draped by a sterile cover and is placed at 30 to 50 cm above the targets (Figure 5A). The illumination area is approximately 78.5cm2 (5 × 5 × 3.14cm) on the surgical field. A 5mg of ICG (DiagnogreenTM, DaiichiSankyo Co., Tokyo, Japan ) dissolved in 2 mL of distilled water is injected via a central venous catheter and is flushed by 10 mL of saline per each imaging sequence (Figure 5B) [19]. The right atrium immediately glows white, then right ventricle and pulmonary artery, followed by ascending aorta and the coronary grafts as well as native coronary arteries. Cardiac output affects the time lag of opacification. The images are recorded using a digital image-processing system such as audio video inter‐ weave (AVI) or Smart Draw (SDR) format.

field. These devices visualize the blood flow clearly in monochrome imaging under irradiation of excitation light after ICG injection. The former emits a low-intensity laser (2.7 watts) and demonstrates angiographic image at a frame rate of 30 per second. They allow irradiation and recording time for up to 34 seconds but demonstrate the vessels in monochrome image. These systems have been applied to coronary and graft angiography

ICG angiography has several advantages. First, it can visualize arterial blood flow by intra‐ venous injection of ICG without catheter manipulation or contrast agent. Second, stenotic portion can be visualized like fluoroscopic angiograms. Third, it takes only ten minutes from

However, ICG angiography systems mentioned above have several drawbacks. First, they use laser light source, and the time duration for irradiation is limited to 35 seconds because of the danger of thermal injury. Second, the angiograms are shown in monochrome, making it difficult to recognize the color of tissue. Third, penetration of fluorescence is poor and vessels

We have developed a new ICG imaging system, HyperEye Medical System (HEMS, Mizuho Co., Tokyo, Japan) to solve these problems (Figure 3) [9, 12]. It is composed of an imaging unit, a control unit and a monitor. The imaging unit consists of multiple light-emitting diodes (LEDs) which is allocated around an ultra-sensitive color charged-coupled device (CCD) imaging camera with non- Bayer color filter arrays (HyperEye Technology; SANYO Co., Ltd, Tokyo, Japan). This camera detects near infrared rays (380-1200 nm) and visible light at 30 frames per seconds. The control unit is composed of a personal computer and a controller for recording

HEMS can demonstrate the fluorescent images on the background of natural color (Figure 4), which facilitates surgeons to recognize the vessels in the surgical field [12]. Unlimited re‐ cording is another advantage of this system because it uses LEDs as the light source. The imaging head is draped by a sterile cover and is placed at 30 to 50 cm above the targets

field. A 5mg of ICG (DiagnogreenTM, DaiichiSankyo Co., Tokyo, Japan ) dissolved in 2 mL of distilled water is injected via a central venous catheter and is flushed by 10 mL of saline per each imaging sequence (Figure 5B) [19]. The right atrium immediately glows white, then right ventricle and pulmonary artery, followed by ascending aorta and the coronary grafts as well as native coronary arteries. Cardiac output affects the time lag of opacification. The images are recorded using a digital image-processing system such as audio video inter‐

(5 × 5 × 3.14cm) on the surgical

[17] and peripheral arterial surgery [18].

preparation to imaging.

84 Artery Bypass

in the deep layer is hardly visualized.

and adjusting the focus, iris and range of imaging.

weave (AVI) or Smart Draw (SDR) format.

(Figure 5A). The illumination area is approximately 78.5cm2

**4. Characteristics of ICG angiography**

**Figure 3.** HyperEye Medical System (HEMS) A: Full view of HEMS, composed of imaging unit, control unit, and moni‐ tor. B: The imaging head consists of multiple light-emitting diodes (LED) and an ultrasensitive color charge-coupled device (CCD) camera. C: Control unit consists of controller and analyzing system.

**Figure 4.** Sentinel node mapping in breast cancer surgery. The ICG stream in lymphatic duct is observed from subareo‐ lar to the axillar lymph nodes after ICG injection to subcutaneous of areolar. A: Fluorescence emitted from ICG inject‐ ed in the breast. The lymphatic duct is identified as fluorescence line (arrow). B: The ICG stream in lymphatic duct. C: ICG in the axillar lymph nodes. The sentinel lymph node is identified as strong fluorescence leading out of lymphatic duct.

**Figure 5.** HEMS in use during cardiac surgery. A: The imaging head is draped by a sterile cover and placed at 30 to 50 cm above the targets. B: ICG solution is injected via a central venous catheter.

We have assessed coronary grafts by means of HEMS since 2007 and have classified the flow

Reprinted from Surgery Today, 2011; 41:1467-1474, Yamamoto M et. al. Assessing Intraoperative Blood Flow in

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The results of HEMS assessment were compared with fluoroscopic CAG one year after CABG and have found that the former accurately predicted the outcomes of grafts (Figure.6D-F). [12]. Thus, visualization of graft flow is helpful for surgeons to make decisions of revision in the

Visualization of myocardial perfusion is another feature of HEMS. Figure 6C shows an obstructed anastomosis in the left internal thoracic arterial graft, causing perfusion defect in the anterior wall around the anastomosis, whereas myocardium in the diagonal region is well opacified. Detter et. al. reported that myocardial perfusion can be quantitatively assessed by

**1.** Normal flow: smooth opacification of the graft and then coronary artery (Fig 6A).

**Table 1.** Reported clinical studies on the indocyanine green imaging system in coronary artery bypass grafting

Delay: delayed graft enhancement compared to other grafts (Fig 6B)


ICG angiography with digital image processing system [25].

Occlusion: no enhancement of the graft (Fig 6C)

pattern as follows [12].

Cardiovascular Surgery., copyright (2011)

**2.** Abnormal flow:

operating room.
