Feasibility of a portable PET system for interactive point-of-care (PoC) PET and ultrasound imaging

Positron emission tomography (PET) is a molecular imaging technology that has been used for detection and staging of diseases, and patient stratification to identify candidates for molecularly targeted drugs. Clinical PET/CT scanners are optimized for whole-body diagnostic imaging instead of real-time guidance of interventional procedures or point-of-care (PoC) imaging applications. With rapid advances in novel radio-theranostics, there is growing interest in versatile, accessible molecular imaging tools.

This study evaluates the feasibility of a compact PET device integrated with a clinical ultrasound (US) system to enhance the utility of molecular imaging in PoC settings. Key features being evaluated include: (1) image quality from a compact system with limited angle tomography; (2) interactive scanning to provide visual feedback; and (3) near real-time PET image reconstruction as data is being acquired.

The prototype PoC-PET system features a robotic arm (Kuka KR 10 R1100 sixx), a rotation stage, and eight time-of-flight (TOF) PET detector modules mounted on a trolley. The detectors comprise Lutetium Oxy-orthosilicate (LSO) arrays, silicon photomultiplier (SiPM) arrays, and front-end electronics. An optional US transducer is integrated between two PET detectors, forming a hybrid PET/US probe. The system acquires data in list-mode and reconstructs PET images using a GPU-accelerated list-mode maximum-likelihood expectation-maximization (MLEM) algorithm incorporating time-of-flight (TOF) information. Detector characterization and calibration were performed using a planar source containing ⁶⁴Cu solution. A tumor phantom containing spherical lesions of different diameters (ranging from 3.3 mm to 11.4 mm) was filled with ¹⁸FDG solution with a tumor-to-background activity concentration ratio of 20:1. Images from the PoC-PET prototype are compared to reference images from a clinical PET/CT scanner (Siemens Biograph Vision). Additionally, an ultrasound-compatible silicone phantom containing ⁶⁴Cu solution was imaged by the PoC-PET device and a clinical ultrasound scanner to compare the hybrid PET/US images and conventional PET/CT images. Lastly, Monte Carlo (MC) simulations were conducted to evaluate the feasibility of a scaled-up portable PET device for imaging organs in humans.

The TOF-PET detectors in the system have an energy resolution of 10.4 ± 0.4% full-width-at-half-maximum (FWHM) for 511 keV gamma-rays and a coincidence resolving time (CRT) of ∼267 ± 12 ps FWHM. Initial imaging results indicate that the compact PoC-PET prototype can produce PET images with a resolution that closely approximates clinical PET/CT resolution after data were acquired from 3 to 4 angles. The integrated PET/US images provide both molecular and structural visualization, matching the fidelity of conventional PET/CT systems. MC simulations show reconstructed PET images with insignificant artifacts for head-and-neck and torso imaging of humans using the scaled-up PoC-PET scanner.

A hybrid PET/US device for molecular imaging at PoC settings is feasible. Robotic-assisted scanning combined with TOF-PET detectors and list-mode image reconstruction enables high-quality imaging comparable to traditional PET/CT systems for any organ-of-interest. Real-time image reconstruction and automated fusion will support multi-modal interactive molecular imaging with visual feedback in the future.