Performance Evaluation of a Position-Sensitive SiPM-based Gamma Camera for Intraoperative Imaging

TL;DR

This work presents POSiCS, a lightweight, wireless, position-sensitive gamma camera for intraoperative imaging with sentinel lymph node biopsy as a benchmark. By employing dual LEHS/LEHR collimators, LYSO:Ce scintillation, and LG-SiPMs with center-of-gravity reconstruction, the device achieves millimeter-scale spatial resolution and competitive sensitivity suitable for real-time surgical guidance. The study reports ~1.4–1.9 mm intrinsic spatial resolution at 0 cm, energy resolution near 20%, and substantial outside-FOV shielding, with successful Lu-177 imaging up to 113 keV and demonstration of theranostic potential. These results indicate POSiCS can enrich radio-guided surgery workflows by enabling rapid 2D imaging in the operating room, while offering pathways to extend to higher-energy imaging and broader radiotracer compatibility."

Abstract

The POSiCS camera is a handheld, small field-of-view gamma camera developed for multipurpose use in radio-guided surgery (RGS), with sentinel lymph node biopsy (SLNB) as its benchmark application. This compact and lightweight detector (weighing approximately 350 g) can map tissues labeled with Tc-99m nanocolloids and guide surgeons to the location of target lesions. By enabling intraoperative visualization in close proximity to the surgical field, its primary objective is to minimize surgical interventional invasiveness and operative time, thereby enhancing localization accuracy and reducing the incidence of post-operative complications. The design and components of the POSiCS camera emphasize ergonomic handling and compactness, providing, at the same time, rapid image formation and a spatial resolution of a few millimeters. These features are compatible with routine operating-room workflow, including wireless communication with the computer and a real-time display to support surgeon decision-making. The spatial resolution measured at a source-detector distance of 0 cm was 1.9 +/- 0.1 mm for the high-sensitivity mode and 1.4 +/- 0.1 mm for the high-resolution mode. The system sensitivity at 2 cm was evaluated as 481 +/- 14 cps/MBq (high sensitivity) and 134 +/- 8 cps/MBq (high resolution). For both working modes, we report an energy resolution of approximately 20 percent, even though the high-resolution collimator exhibits an increased scattered component due to the larger amount of tungsten.

Figures (11)

• Figure 1: Prototype wireless module of the POSiCS gamma camera.
• Figure 2: Scheme of the full operation and calibration pipeline of the POSiCS camera, from the gamma-ray emission by radio-labelled tissues, to the final image treatment and enhancement, with the possibility of live displaying the reconstructed image.
• Figure 3: Left: Scheme of the Flood map setup used in this work. The estimated distance from the collimator entrance to the center of the cavity is 2 cm. Right: LYSO:Ce scintillator intrinsic radioactivity spectrum registered with POSiCS. The structure of the spectrum depends on the crystal volume and shape, which in turn determines the probability of absorbing the emitted $\gamma$-rays (in coincidence). The long tails are due to the absorption of the initial $\beta$ particle and are therefore shaped after the $\beta$-emission spectrum LYSO-Lutetium176.
• Figure 4: Positions of the Co-57 during the evaluation of the shielding leakage. The scheme is symmetric for the third measurement (at -$45^\circ$).
• Figure 5: Top Left: Example of the reconstructed point source at 3 cm from the camera (free air) with LEHS collimator. Top Right: Resolution of the POSiCS camera in HS mode for different distances. Bottom Left: Example of the reconstructed point source at 3 cm from the camera (free air) with LEHR collimator. Bottom Right: Resolution of the POSiCS camera in HR mode.