What question did this study set out to answer?

This study aims to evaluate the feasibility of combining LiDAR-registered freehand SPECT with NIR-fluorescence imaging for better localisation of tracer-avid lymph nodes.

July 22, 2026Open Access

LiDAR-registered freehand SPECT combined with NIR-fluorescence enables spatial localisation of tracer-avid inguinal lymph nodes: A clinical feasibility study

RVRick W. A. VerdijkAmsterdam University Medical Centers GPGiusi PisanoLeiden University Medical Center MOMatthias N. van OosteromLeiden University Medical Center

Key Points

This study aims to evaluate the feasibility of combining LiDAR-registered freehand SPECT with NIR-fluorescence imaging for better localisation of tracer-avid lymph nodes.
Conducted in 14 patients with penile cancer who underwent lymph node surgery.
Utilized preoperative lymphoscintigraphy and SPECT/CT for imaging.
Compared findings from LiDAR-registered SPECT with conventional assessments on excised lymph node specimens.
LiDAR/fh SPECT successfully localised radioactive hotspots in 38 out of 40 solitary lymph nodes.
Conventional gamma probe and NIR-fluorescence detected 4 and 5 hotspots respectively in ILND specimens, whereas LiDAR/fh SPECT identified all 6 hotspots.
Histopathology confirmed 6 tumour-positive lymph nodes were effectively localised by LiDAR/fh SPECT.

Abstract

Abstract Purpose Conventional ex vivo molecular assessment of nodal specimens lacks three-dimensional (3D) spatial context, making localisation of tracer-avid sentinel nodes (SNs) within large en bloc inguinal lymph node dissection (ILND) specimens challenging. We evaluated the technical feasibility of combining light detection and ranging (LiDAR)-registered freehand SPECT ( fh SPECT) with near-infrared (NIR) fluorescence imaging for spatially augmented localisation of hybrid tracer uptake in solitary SNs and SNs residing within ILND specimens. Methods Fourteen patients with penile cancer (25 cN0 groins; 3 cN1 groins) underwent radio- and fluorescence-guided lymph node (LN) surgery following preoperative lymphoscintigraphy and SPECT/CT. Resected specimens underwent conventional ex vivo assessment, followed by LiDAR-registered fh SPECT with co-registered NIR-fluorescence imaging. These 3D models were compared with conventional ex vivo assessments, preoperative imaging, and histopathological outcomes. Results In total, 40 solitary tracer-avid LNs and 3 ILND specimens underwent ex vivo assessment. LiDAR/ fh SPECT localised radioactive hotspots in 38/40 solitary LNs, consistent with conventional gamma probe assessment, while both conventional and LiDAR-registered NIR-fluorescence imaging detected fluorescent signal in all 40 LNs. Among the 3 ILND procedures, preoperative SPECT/CT identified 6 tracer-avid hotspots within the anatomical resection template. Conventional gamma probe and NIR-fluorescence detected only 4 and 5 hotspots, respectively, whereas LiDAR/ fh SPECT localised all 6 hotspots in the corresponding resected specimens. Histopathology identified 6 tumour-positive LNs, all of which were hybrid tracer-avid and effectively localised by LiDAR/ fh SPECT. Conclusion LiDAR-registered 3D surface mapping provided anatomical context to radioactive and fluorescent molecular imaging signals, enabling localisation of tracer-avid LNs in complex ex vivo ILND specimens. These findings support the feasibility of spatially augmented localisation of hybrid tracer uptake and warrant validation in larger studies.

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