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This, combined with the low spatial resolution and the high amount of scatter intrinsic in SPECT imaging, requires sophisticated correction methods for accurate dosimetry of activity levels. In particular, the low count rate and the continuous spectrum of Bremsstrahlung radiation limit the sensitivity and the quantitative capabilities of Bremsstrahlung SPECT imaging. Although some of these studies have shown the potential of 90Y Bremsstrahlung imaging, for example for accurate dosimetry purposes, even in whole-body imaging, others have highlighted the limitations and challenges of this imaging modality. Several studies have been performed using 90Y, as it emits almost purely β − particles which can not be imaged with PET. Bremsstrahlung imaging typically uses single-photon emission computed tomography (SPECT) equipment (i.e., a gamma camera) to detect the higher energy (compared to Cerenkov radiation) and broad spectrum radiation emitted by decelerating charged particles.
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In fact, apart from these limitations, up to date CLI offers a valid tool to image β − radioisotopes, which can not be imaged with positron emission tomography (PET) and for which Bremsstrahlung imaging has not shown promising results yet.
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Due to the low light level, the detection of Cerenkov luminescence typical requires the same type of imaging system of bioluminescence, that is a high sensitivity charge coupled device (CCD) coupled to a focusing optics and placed in a light-tight environment.Įven if CLI suffers of challenges such as the low light yield and the limited penetration depth, it has been proposed for several applications both in the preclinical and clinical fields. In tissue, the emitted light is then highly scattered and absorbed before reaching the surface, and the tissue optical properties tend to favor the transmission of the red-infrared light, where the Cerenkov emission is minimal. The range and the relatives intensities of the emitted wavelengths are limited by the material properties. The light is emitted on a cone around the particle direction, with a typical continuous spectrum proportional to the inverse wavelength squared. Cerenkov luminescence is emitted when a charged particle traverses a dielectric medium with a velocity greater than the phase velocity of light in the medium. Cerenkov luminescence imaging (CLI) is an optical imaging modality to study charged particles of sufficient energy through the Cerenkov light they produce in biological tissue.