Cherenkov-excited luminescence scanned imaging

Abstract

Ionizing radiation is commonly delivered by medical linear accelerators (LINAC) in the form of shaped beams, and it is able to induce Cherenkov emission in tissue. In fluorescence-based microscopy excitation from scanned spots, lines, or sheets can be used for fast high-resolution imaging. Here we introduce Cherenkov-excited luminescence scanned imaging (CELSI) as a new imaging methodology utilizing 2-dimensional (∼5-mm-thick) sheets of LINAC radiation to produce Cherenkov photons, which in turn excite luminescence of probes distributed in biological tissues. Imaging experiments were performed by scanning these excitation sheets in three orthogonal directions while recording Cherenkov-excited luminescence. Tissue phantom studies have shown that single luminescent inclusions ∼1 mm in diameter can be imaged within 20-mm-thick tissue-like media with minimal loss of spatial resolution. Using a phosphorescent probe for oxygen, PtG4 with the CELSI methodology, an image of partial pressure of oxygen (pO₂) was imaged in a rat lymph node, quantitatively restoring pO₂ values in differently oxygenated tissues.

Figure 1.

The relative radiation dose planned for use in CELSI is shown (a) with respect to many other diagnostic and therapeutic applications. The setup of the ICCD and rat is shown (b), and the geometry of the LINAC sheet-scans in 3 orthogonal directions (c).

Figure 2.

The ICCD camera and phantom geometry is shown in the photo (a) and the schematic (b). The diffuse emission images (c) are shown, if a single broad excitation beam was set to cover the whole scanned region, the diffuse emission surface profiles appear as shown in (d), whereas when a sheet-scan is used they were as shown in (e). When deconvolution of the sheet beam shape was included the line profiles were as shown in (f).

Figure 3.

The line-scan emission data from the LINAC sheet moving in each of the 3 orthogonal directions is shown in (a) for 226 locations across with 1 cGy dose per sheet, and the data reduced to (b) just 10 sheet locations across. The delivered energy was reduced to 0.02 cGy/sheet and scans repeated in (c) and again downsampled to 10 sheet locations in (d). Backprojected reconstructions are shown overlaid on the CT scans in (e) and (f) for the two conditions with the luminescence intensity in red. The pO2 emission lifetime data is shown in (g) from the lymph node.