Abstract
This article highlights the performance measurements of an optical device which aims at upgrading preclinical irradiators. The evaluated device allows acquiring X-ray as well as bioluminescence images with a single sensor. The latter consists of a supercooled camera equipped with a 1024x1024 charge coupling device (each element measuring 13x13µm²). X-ray imaging is feasible, thanks to a conversion phosphor screen. Phantom acquisitions revealed a spatial resolution of 2.5 line pairs per millimetre (0.2mm) for Xray imaging and between 0.4 and 0.7mm for bioluminescence images. Image homogeneity was 0.8 for radiographic images with preclinical imaging parameters and higher than 0.9 for optical images. For functional imaging, contrast to noise ratio (CNR) ranged from 1.3 (for contrast of 2:1 and 0.1s acquisition) up to 253 (for contrast of 32:1 and 5s acquisition). CNR was related to acquisition duration. The device’s overall performance revealed that it is suitable to upgrade existing irradiators and improve laboratory capabilities toward image-guided radiotherapy.
Highlights
Molecular imaging offers many unique opportunities to study biological processes in intact organisms
Bioluminescence imaging (BLI) signal relies on the degradation of luciferin by luciferase enzyme via oxidation/decarboxylation reactions and formation of an intermediate excited state that releases photons to return to stability
To avoid direct X-ray irradiation when using the irradiator without imaging, the camera was deported in a shielded compartment and a mirror guided photons from the imaging chamber to the charge-coupled devices (CCD) (Figure 1)
Summary
Molecular imaging offers many unique opportunities to study biological processes in intact organisms. Bioluminescence can be detected as deep as a few centimeters within the tissue, which allows in situ imaging without any specific observation device (such as glass window), and orthotopic cell implantation can be observed [3]. The CCD is usually supercooled to around -90 ◦C to reduce thermal noise, thereby increasing its ability to detect very low levels of signal. Such technology has been proven to be consistent and reproducible with ±8% standard deviation around mean values of the same acquired object [4]. As cells do not emit any signal if they do not express luciferase enzyme, BLI does not provide any anatomical information to localize tagged cells. That can be used to upgrade an existing preclinical irradiator toward molecular/anatomical imaging, a mandatory step toward image-guided radiotherapy
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