Hyperspectral imaging of vascular anastomosis associated with blood flow and hemoglobin concentration

The feasibility of optical non-invasive evaluation of the graft function of vascular anastomosis was investigated in vitro using hyperspectral imaging (HSI) in the wavelength range from 500 to 600 nm. A Y-shaped vessel was made using porcine carotid arteries having an inner diameter of 3.5 to 4 mm. The graft vessel was anastomosed at a 45° angle with 8-0 polypropylene suture. Fresh porcine blood at an oxygen saturation of 100% was circulated in the specially designed circuit loop and through the graft or main vessel. The vessels were then irradiated with light, and the reflected light was captured with an HSI camera. The attenuation (A) image at each wavelength (λ) was obtained and the spectral A(λ) image was created. The spectral A(λ) image showed graft patency and changes in the hemoglobin concentration. The A(λ) decreased as the flow rate increased due to the orientation of the red blood cells. The experimental results indicated that imaging of the hemoglobin concentration without distortion from blood flow is possible using two wavelengths: 625 and 770 nm. This method is able to distinguish between the blood flow and changes in hemoglobin concentration. The multispectral and hyperspectral imaging method is useful for the non-invasive evaluation of graft function.

I. Introduction

Non-invasive optical methods using visible and near-infrared light for monitoring and imaging blood flow and hemoglobin concentration within blood vessels have been used in various fields, such as neuroscience [1]–[4] and fundoscopy [5]–[6]. There is also motivation to use optical imaging for intraoperative evaluation of vascular anastomosis, such as coronary arterial bypass grafting (CABG). CAGB surgery is the most widely conducted operation in the field of cardiovascular surgery and has been performed more than 15,000 times in Japan in 2009 [7]. However, there is the possibility of early postoperative graft failure. Therefore, a method to evaluate graft function is required [8]. Although graft patency can be visualized using intraoperative fluorescence imaging [9], the fluorescent agent introduces side effects in no small part. We speculate that spectral imaging is capable of label-free visualization and can provide a more detailed evaluation of graft function. However, there is little knowledge about the comprehensive optical characteristics of vascular anastomosis in the visible and near-infrared wavelength ranges. In this study, the optical attenuation (A) in the wavelength range from 500 to 900 nm associated with blood flow and hemoglobin concentration in the vascular anastomosis was investigated using hyperspectral imaging (HSI) [10]. The wavelength dependency of both the optical path length and scattered light component of the attenuation was analyzed. Finally, the feasibility of the quantitative imaging of graft function and the optimal wavelength range are discussed.