Positron emission tomography (PET) and computed tomography (CT) offer several advantages in both the clinic and medical research. The use of PET, a nuclear medicine functional imaging technique, is commonplace for assisting in the diagnosis of disease across areas of oncology, neurology, cardiology, and infectious disease.
Likewise, CT scanning produces cross-sectional images of the head, neck, lungs, and heart to assist in screening for disease. Both devices are used in research to understand disease, its pathogenesis, and its predictors of progression.
Image Credit: Bruker Biospin Gallery.
Traditional PET and CT scanners carry potentially serious health risks
Despite the value and utility of these platforms in medicine and research, both PET and CT carry health risks to animal models and patients, as well as operators and investigators who use these techniques.1 The two imaging methods involve ionizing radiation that can produce damaging effects on study animals and post serious health treats for clinical trial investigators.
In a pre-clinical setting, dose reduction efforts are an important aspect of ensuring animal care and retaining study integrity, particularly during long-term trials that require multiple scans. These efforts also help to reduce radiation exposure to human operators.
Acute radiation dose exposure is associated with skin redness, hair loss, and radiation burns. Comparatively, low and chronic exposure to PET and CT radiation may increase the risk of cancer, making these two imaging modalities an important area of concern.
Total-body PET systems may be an approach for limiting exposure by providing full sample coverage without increasing total scan time, compared with traditional whole-body PET procedures.
Experts agree that strategies are needed to design optimized workflows that can minimize PET and CT dose exposures in both the clinic and the lab. Tracer activity reduction may be the most reliable strategy for reducing radiation exposure to operators.
Low-dose PET/CT could be the solution
In preclinical studies that use animal models, low-dose PET imaging may be helpful for imaging greater numbers of animals while reducing dose exposure.
Low-dose, high-sensitivity PET imaging has been demonstrated to provide suitable resolution and quantitative measurements in a preclinical tumor model in animals. Additionally, low-dose CT imaging techniques have been shown to help achieve suitable tissue contrast and resolution in mice.
Low-dose PET imaging, in particular, can be performed with doses that are close to four-times lower than other standard imaging techniques, thereby reducing the accumulative annual dose exposures to operators as well as minimizing animal dose exposures throughout a trial. Ultimately, this benefit could be crucial in core facilities, considering many employ dedicated personnel to perform the majority of scanning and tracer handling.
A low-dose PET/CT system was recently tested in phantom and in vivo experiments to assess the quality and levels of exposure dose in preclinical animal models.1 The initial phantom experiments in this study were performed to examine data integrity.
The low-dose imaging experiments were conducted using the Si78, an integrated total-body PET/CT system with low-dose capabilities from Bruker Biospin.2 This system features detector architecture that is based on continuous crystals and is coupled to silicon photomultiplier arrays.
In addition to this study, the Si78 PET subsystem – detectors and DAQ – has been used in different PET/magnetic resonance platforms as well as a PET/single-photon emission computed tomography/CT platform.
Using the instrument, the investigators were able to perform total-body mouse PET/CT imaging with doses of less than 10 mGy for each procedure, with imaging procedures lasting only seven seconds, successfully reducing dose exposures to the animal models. These findings may suggest that a low-dose, human total-body PET strategy could improve dose reductions and subsequently reduce scan times.
For imaging skeletal structure, the dose reduction settings of the system offered sufficiently good contrast. When combined with low-dose CT, the investigators of this study wrote that the dose and throughput benefits of low-dose PET can be enhanced even further.
In a preclinical mice breast tumor model, the low-dose PET imaging system was applied, the researchers suggested that the whole-body dose due to the procedure could be lowered to at least 7 mGy, compared to the estimated 14 mGy with standard imaging.
Implications and future directions
In medical practice and clinical research, efforts to reduce radiation and dose exposures are critical for protecting human health and the quality of experimental models. Total-body, low-dose PET imaging techniques provide hope that dose exposures can be effectively reduced in these settings, especially for both patients and operators, without compromising the quality of imaging.
The researchers suggest that low-dose PET and CT platforms can provide cost-saving benefits because this imaging relies on testing of only very low-volume and low-activity tracers. Also, if dose exposures are reduced, so is the risk of cancer, a disease that confers a heavy cost burden on the healthcare system.
Despite their findings, the investigators of the study suggest that a greater number of animals need to be imaged with this low-dose technique to validate their findings. Additionally, it has yet to be determined whether these preliminary findings could translate to human carcinomas.
References:
- Molinos C, et al. (2019) Low-dose imaging in a new preclinical total-body PET/CT scanner. Front Med (Lausanne). DOI: 10.3389/fmed.2019.00088
- PET/CT Si78. Bruker Biospin. Accessed February 11, 2020.
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