Intra-Operative Beta (Positron or Electron) Detectors and Cameras

We have been studying the concept of miniature camera that can perform real-time imaging of molecular signatures of disease in situ, that is, when placed directly on top of the diseased tissue.  The molecular signatures come from existing, clinically approved cancer-avid molecular contrast agents. One example agent is 18F-fluorodeoxyglucose (FDG), a common analog marker for over-expression of certain glucose transporters on cancer cells as well as up-regulation of activity of the enzyme hexokinase inside cancer cells. 18F is a radionuclide label that emits positrons. This radioactive FDG marker has been very successful in cancer imaging using positron emission tomography (PET). Clinical PET imaging of 511 keV photons transported out of the body into distant detectors is relatively insensitive; only 1 out of 100 photon pairs are collected in the standard PET scanner.  Standard clinical PET also has relatively low spatial resolution of ~7-13 millimeters, and has limited contrast resolution due to significant background annihilation photon contamination from other parts of the body. As a result, of its relatively poor photon sensitivity, spatial resolution, and contrast resolution, PET has very low sensitivity for detecting a small population of cancer cells, as is the case, for example, for evaluating tumor margins during surgery.

However, the approach we are proposing to solve these problems and enable resolution of a small population of diseased cells is not PET imaging. In contrast, in the proposed innovative camera the imaging signal comes directly from the 18F positron emissions that are absorbed in a sensor they annihilate; that is, they annihilate in the sensor instead of in the tissue, and we want to directly detect the positrons, the resulting annihilation photons.  In order for this to occur, the imaging sensor is located in situ, for example, in a surgical cavity, in contact with the tumor margins during surgical resection of a primary tumor. This proposed direct contact of the imaging sensor with the tumor margins means that the positron detection probability is extremely high.  Also, the positron distance traveled before it stops (a.k.a. “range”) is <250 microns on average in tissue, and <100 micron on average in the sensor material.  Thus, in this direct contact scenario the positron imaging sensor only detects a signal when the diseased (e.g. tumor) cells are at or very near the margin surface and the intrinsic spatial resolution is on the order of 100 microns or better, which is adequate to visualize a small population of cells that accumulated the radio-labeled biochemical marker.  One challenge is to design the sensor to be very thin so that there is very little annihilation photon background detected, since the chance that a highly-penetrating 511 keV photon will interact with the very thin sensor is extremely small.

People Involved