Cherenkov Excited Luminescence Metabolic Sensing (CELMS)

PROJECT ABSTRACT A fundamentally new approach to molecular imaging is developed here, using high energy x-rays from a widely available linear accelerator (Linac) for precise, multi-angle, multi-shaped, excitation of optical molecular probes deep within tissue via the Cherenkov light. Cherenkov Excited Luminescence Metabolic Sensing (CELMS) was developed to probe small molecule molecular tracers of pertinent tissue function in vivo, to take advantage of the highly developed Linac x-ray sources for high-resolution molecular sensing in small animals. CELMS can be used to image through 3 cm of tissue, preserving the exquisite molecular sensitivity of optical luminescence at M-nM concentrations in vivo, while achieving millimeter level spatial sampling. This combination of ultra-high molecular sensitivity, combined with deep penetrance and spatial sampling is far better than any comparable small animal modality possible today. The thin sheets of x-rays used are shaped by multi-leaf collimators and are swept over the tissue to localize the excitation volumes of Cherenkov in vivo, allowing precise knowledge of where the detected light came from. Time-resolved emission can be captured with time-gated intensified sensors for luminescence lifetime data, that we are advancing. We also advance probes for lifetime sensing of oxygen partial pressure (pO2) and tissue acidity (pH). CELMS achieves similar benefits to light-sheet fluorescence microscopy but can image through the whole body of a rat. While the diffuse optical luminescence still has to exit the body, reconstruction-based recovery can improve the localization through iterative image reconstruction, achieved with full knowledge of where the excitation beam was within the body. Most importantly, high energy x-rays are less absorbed than lower kVp x-rays, and so this can be achieved with a radiation dose as low as a CT scan. The design can implicitly allow longitudinal temporal sampling or spatial heterogeneity histogram sampling. Advanced non-toxic biocompatible probes have been uniquely developed for this application, that do not require toxicity associated with heavy metals or nanoparticles. To advance the technology for translation to other medical centers, we identify low-cost approaches that can work with any Linac, through innovations in hardware, open-source software, and suitable metabolic probes. In the hardware advancement we invent a new sensor approach to maximize capture of every possible photon per Linac pulse, thereby minimizing dose required. The techniques can be distributed with a Linac treatment plan that is completed with a delivered dose less than a diagnostic CT scan, <10 mGy. In the probes, a new version of bright-emitting, biocompatible, implanted oxygen sensors will be advanced with high potential for daily measurement in the same locations. Taken together this project will provide the tool for a fundamentally new low-cost way to image metabolic signatures of tissue that could be widely available in any academic medical center, with superior image resolution, deeper tissue penetration, and better linearity of response than is possible today.