Fully Integrated Ultra-thin Intraoperative Micro-imager for Cancer Detection Using Upconverting Nanoparticles

Abstract

Purpose: Intraoperative detection and removal of microscopic residual disease (MRD) remain critical to the outcome of cancer surgeries. Today's minimally invasive surgical procedures require miniaturization and surgical integration of highly sensitive imagers to seamlessly integrate into the modern clinical workflow. However, current intraoperative imagers remain cumbersome and still heavily dependent on large lenses and rigid filters, precluding further miniaturization and integration into surgical tools.

Procedures: We have successfully engineered a chip-scale intraoperative micro-imager array-without optical filters or lenses-integrated with lanthanide-based alloyed upconverting nanoparticles (aUCNPs) to achieve tissue imaging using a single micro-chip. This imaging platform is able to leverage the unique optical properties of aUCNPs (long luminescent lifetime, high-efficiency upconversion, no photobleaching) by utilizing a time-resolved imaging method to acquire images using a 36-by-80-pixel, 2.3 mm [Formula: see text] 4.8 mm silicon-based electronic imager micro-chip, that is, less than 100-µm thin. Each pixel incorporates a novel architecture enabling automated background measurement and cancellation. We have validated the performance, spatial resolution, and the background cancellation scheme of the imaging platform, using resolution test targets and mouse prostate tumor sample intratumorally injected with aUCNPs. To demonstrate the ability to image MRD, or tumor margins, we evaluated the imaging platform in visualizing a single-cell thin section of the injected prostate tumor sample.

Results: Tested on USAF resolution targets, the imager is able to achieve a resolution of 71 µm. We have also demonstrated successful background cancellation, achieving a signal-to-background ratio of 8 when performing ex vivo imaging on aUCNP-injected prostate tumor sample, improved from originally 0.4. The performance of the imaging platform on single-cell layer sections was also evaluated and the sensor achieved a signal-to-background ratio of 4.3 in resolving cell clusters with sizes as low as 200 cells.

Conclusion: The imaging system proposed here is a scalable chip-scale ultra-thin alternative for bulky conventional intraoperative imagers. Its novel pixel architecture and background correction scheme enable visualization of microscopic-scale residual disease while remaining completely free of lenses and filters, achieving an ultra-miniaturized form factor-critical for intraoperative settings.

Keywords: Intraoperative microscopy; Silicon imager; Time-resolved imaging; Upconverting nanoparticle.

Fig. 1.

Concept overview of the proposed imaging platform: a Illumination scheme of lanthanide-based upconverting nanoparticles. b Proposed time-resolved optics-free intraoperative imaging platform for optically guided surgeries. c Diagram of time-resolved image acquisition sequence.

Fig. 2.

Impact of carriers generated by emission and excitation on pixel (illuminated with 5-ms long pulses of 18 W/cm² 980 nm light): a Normalized decay profiles of aUCNP emission, baseline (dark current), and NIR-generated background. b Diagram of the dual-photosensor pixel architecture illustrating the main and uncovered photosensor as well as the secondary (covered) photosensor for measuring the local background level.

Fig. 3.

Acquired images and signal intensity cross section of 3 line-pair clearances (distance between line pairs) on the USAF resolution target plate (illuminated with 5-ms-long pulses of 18 W/cm2 980 nm light): a Line-pair clearance of 112 µm. b Line-pair clearance of 89 µm. c Line-pair clearance of 71 µm.

Fig. 4.

Excised prostate tumor imaging results with IVIS spectrum imager: a Image of excised tumor specimen acquired using the 660-nm emission filter (with 20-nm pass band) on the IVIS spectrum imager (excitation provided by custom-modified and external continuous 980-nm laser source). b Measured emission of specimen under continuous 980-nm excitation light (22 W/cm²).

Fig. 5.

Ex vivo experiment images: a High-resolution microscope image of excised intratumorally injected prostate tumor (Tint = 1 s). b Microscope image of excised prostate tumor with matched pixel pitch (to micro-chip sensor). c Main photosensor image of micro-chip sensor. d Secondary photosensor image of micro-chip sensor. e Image of main photosensor after applying the background adjustment and correction scheme.

Fig. 6.

Single-cell thin-layer imaging experiment: a Composite microscope image of a 14-µm-thin section of intratumorally injected prostate tumor specimen, with the green color representing tissue texture obtained using autofluorescence under a 450-nm excitation light and red representing the UCNP emission captured using a continuous 45 W/cm² 980 nm excitation (Tint = 1 s). b Background-adjusted image of the 14-µm-thin section captured on the micro-chip under pulsed 980-nm excitation (45 W/cm²).