Multimodal laparoscopic coincidence gamma imaging system for near-infrared fluorescence guided surgery: a preclinical study

Abstract

Purpose: Minimally invasive surgery has advantages in terms of quality of life and patient outcomes. Recently, near-infrared (NIR) fluorescence guided surgery has widely used for preclinical and clinical trials. However, NIR fluorescence has a maximum penetration capability of 10 mm. Radiographic imaging can be a solution to overcome the depth issue of NIR fluorescence. For this reason, the performance of the multimodal imaging system, which integrates annihilation gamma (511 keV) rays, NIR fluorescence, and color images, was evaluated.

Approach: The multimodal imaging system consisted of a laparoscopic module, containing an internal detector for annihilation gamma events and cameras for optical imaging, and a flat module for coincidence detection with the internal detector. The acquired images were integrated by an algorithm with post image processing and registration. To evaluate the performance of the proposed multimodal imaging system, the images of a resolution target, a square bar target filled with a fluorescence dye, and a sodium-22 point source were analyzed. A preclinical test for axillary sentinel lymph node (SLN) biopsy with a rat model was conducted.

Results: The spatial resolution of color images was equivalent to 4 lp/mm. The modulation transfer function of NIR fluorescence at 1 lp/mm was 0.83. The 511 keV gamma sensitivity and spatial resolution of the point source were 0.54 cps/kBq and 2.1 mm, respectively. The image of 511 keV gamma rays showed almost the same intensity regardless of the thickness of the tissue phantom. In the preclinical test, an integrated image of the SLN sample of the rat model was obtained with the proposed multimodal imaging system.

Conclusions: With the proposed laparoscopic system, a merged image of the sample was obtained with the rat model. The annihilation gamma rays showed penetration capability with the tissue-mimicking phantom superior to that of NIR fluorescence.

Keywords: annihilation gamma ray; fluorescence guided surgery; image reconstruction; minimally invasive surgery; multimodal imaging system; near-infrared fluorescence.

Fig. 1

The structure of the multimodal imaging device with the coincidence detector.

Fig. 2

The coincidence detector: (a) the small detector in the laparoscopic module and (b) one block of the flat detector.

Fig. 3

The optical system of the laparoscopic module: (a) the optical parts in the laparoscopic moduel and (b) the optical parts in the image acquisition box.

Fig. 4

Schematic diagram of the image reconstruction, post-processing, and integration processes.

Fig. 5

The performance evaluation of the proposed multimodal imaging system: (a) the intensity of the NIR fluorescence image, (b) the spatial resolution of the NIR fluorescence image, (c) the performance of the color (visible) image, (d) the performance of the 511 keV gamma image, and (e) the penetration depth with a tissue mimicking phantom.

Fig. 6

Setup of the preclincal test: (a) the laparoscopic module and the flat detector, (b) injection site of the rat model, and (c) acquired images of the hybrid tracer labeled with NIR fluorescence (top) and 511 keV gamma rays (bottom).

Fig. 7

The performance of color (visible) image: (a) the color (left), individual RGB channels, and grayscale (right) images of the USAF 1951 resolution target, (b) 1-D line profile in the ROI, and (c) MTF curves of the acquired image.

Fig. 8

The spatial resolution of NIR fluorescence image: (a) the image of the bar target, (b) the MTF curve of the image, and (c) the 1-D intensity curve of the image.

Fig. 9

The intensity measurement of NIR fluorescence image: (a) the acquired image of ICG-DMSO solution, (b) 3-D surface plot of the image, and (c) the bar graph of intensity in the ROI.

Fig. 10

The image and the line profile of (a) the Na-22 point source and (b) the existence of the tissue phantom.

Fig. 11

Comparison of penetration depth with the tissue phantom: (a) a snapshot (8-bit) of the acquired phantom image, (b) the acquired grayscale image of NIR fluorescence (top) and 511 keV gamma rays (bottom), and (c) the total pixel value in the ROI (white line).

Fig. 12

The images of the preclinical study with the rat model: (a) right after injection, (b) 2 h later, (c)–(e) a dissected sample of SLN (color, NIR fluorescence, and gamma) 3 h later, and (f) a merged image of the SLN sample.