ObjectiveFluorescence laparoscopy is an important and indispensable instrument in minimally invasive surgery, combining traditional laparoscopy and fluorescence imaging technology, which is inserted into the abdominal cavity through a small incision to provide real-time, high-precision images for surgery, and especially has significant advantages in tumour detection and precise localisation. 5 mm laparoscopes are widely used in a variety of surgical scenarios due to their thin rods and small footprint, however, their small aperture leads to However, its small aperture results in less fluorescence flux received, limiting its ability in deep lesion detection. In recent years, NIR-Ⅱ fluorescence imaging has been widely investigated due to its higher sensitivity and enhanced deep penetration ability, but most of the existing fluorescence laparoscopy systems are only applied in the visible and NIR-Ⅰ bands, and have not yet taken full advantage of the potential of the NIR-Ⅱ band in deep tissue imaging. In order to enhance the capability of 5 mm fluorescence laparoscopy in lesion detection, designs a visible/NIR-Ⅰ/NIR-Ⅱ tri-band composite 5 mm fluorescence laparoscopy system to improve its detection accuracy and sensitivity of lesions by multi-band imaging.
MethodsTo design a complete three-band fluorescence laparoscopy optical system, the system is divided into two parts, the optical observation lens and the camera adapter, and the two parts are optimised and designed independently. The optical viewer consists of an objective lens, a relay lens group and an eyepiece. The objective lens and relay lens group were first optimized separately before undergoing integrated optimization, while the eyepiece was designed independently to achieve confocal imaging across three bands: visible, NIR-Ⅰ and NIR-Ⅱ (
Fig.6). The camera adapter section was divided into two optical paths, which were similarly optimised to ensure that the size of the three bands imaging was the same (
Fig.7). Finally, the optical viewer and camera adapter were combined by pupil docking to complete the overall laparoscopic system design (
Fig.8). The ability of this laparoscope to detect tumour foci in the tissue body in NIR-Ⅰ and NIR-Ⅱ bands was also simulated and analysed using TracePro software.
Results and DiscussionsThe designed laparoscope system has an entrance pupil diameter of 0.3 mm, a field of view of 80°, and a working distance of 300 mm. In the full-field range of all three bands, the system's root mean square radius is smaller than the Airy disk radius, and the energy is completely distributed within the Airy disk radius. Meanwhile, in the field of view of each band, the MTF values are close to the diffraction limit, and the maximum distortion is less than 20.13% (
Fig.9). The optical system designed exhibits excellent image quality, meeting both design and usage requirements. TracePro software was used to simulate the laparoscope's ability to detect tumor lesions in the NIR-Ⅰ and NIR-Ⅱ bands. When 2 W total power, 45° emission half-angle, and 808 nm wavelength incident light were used to excite a tumor with a 0.5 mm radius located 4 mm deep in the tissue, the detection signal-to-noise ratio in the NIR-Ⅰ band was 3.14 dB. In the NIR-Ⅱ band, at a cooling temperature of -20 ℃, the SNR was 5.52 dB, and at -80 ℃, the SNR was 6.95 dB (
Tab.6). Similarly, when the tumor with a 7 mm radius was located 8.8 mm deep in the tissue, the detection SNR in the NIR-Ⅰ band was 1.78 dB. In the NIR-Ⅱ band, at a cooling temperature of -20 ℃, the SNR was 4.94 dB, and at -80 ℃, the SNR was 6.87 dB (
Tab.7).
ConclusionsA 5 mm fluorescence laparoscope with visible/NIR-Ⅰ/NIR-Ⅱ composite imaging was designed. Simulation analysis shows that the NIR-Ⅱ band has a higher signal-to-noise ratio compared with the NIR-Ⅰ band at the same tissue depth, which can effectively detect deeper tumours and improve the sensitivity and accuracy of tumour detection. Multi-band imaging technology enables laparoscopy to show higher flexibility and accuracy in complex tissue environments, which can meet the needs of deeper tumour detection and can enhance the detection performance of 5 mm laparoscopy for tumour lesions.