Seeing biological processes has always been extremely rewarding and has had the greatest impact on my scientific career. As a graduate student, I spent a lot of time at the microscope observing cell division and chromosome segregation, which helped bring about a better understanding of these complex biological processes. In the field of medicine, imaging technologies have brought tremendous benefit for diagnosis and prognosis of human diseases. Technological advances in medical imaging hardware and software have resulted in the acquisition of data with better resolution, sensitivity and quantitation.
I recently attended BioClinica’s oncology symposium focused on the uses of imaging in oncology clinical trials. After hearing a few talks on medical imaging, I immediately gained an appreciation for the most common modalities used in oncology studies and precisely how they inform physicians and help guide treatment. Imaging provides physicians with valuable information regarding the location, size, dynamics, severity, and drug responses of tumors. In this post, I will briefly highlight the imaging modalities of Computed Tomography (CT), Magnetic Resonance Imaging (MRI), and Positron Emission Tomography (PET), all of which are commonly used in clinical oncology to inform decisions regarding patient prognosis and treatment options.
CT is a classic imaging technique developed over 30 years ago. With >50 million CT scans performed annually in the US alone, it is the workhorse of modern day clinical imaging. CT relies on the use of X-rays taken from many different angles which are reconstructed to provide three dimensional images. Although CT provide oncologists with high resolution images and fast acquisition times, this modality can be limiting due to the use of radiation, (restricting the number of scans which can be taken for a given patient) and low quality of tissue contrast (necessitating the use of exogenous contrasting agents). Recent improvements in CT, including helical scanning and the use of multiple detectors, are helping to further increase image resolution and provide more detailed images of tumors. Additionally, there is a growing field of research to develop CT compatible contrasting agents for obtaining tumor biochemical information to supplement anatomical information.
MRI is a versatile imaging modality which uses strong magnets and radiofrequency energy to visualize internal structures and tissues. Images obtained by MRI provide high spatial resolution and soft tissue contrast without the use of ionizing radiation. However, the sensitivity of MRI often necessitates large dosing of contrasting agents. For the oncologist, specialized MRI has become an important tool for providing physiological data to assist with cancer treatment. For example, dynamic contrast-enhanced MRI (DCE-MRI), in which a contrasting agent is used, can provide valuable information regarding tumor microvasculature and perfusion, important parameters for assessing tumor growth and drug response.
Positron Emission Tomography (PET) is another common modality used to evaluate biochemical changes and molecular targets in cancer patients. Unlike other modalities, PET relies on the use of a radionuclide tracer that is specific to the target of interest. In the clinic, PET is mainly used to image cancer through the use of a radiolabeled glucose analog called FDG, which can identify areas in the body showing increased metabolism. Whole body FDG-PET scans are routinely performed to locate, stage, and monitor cancers. Although the use of PET provides excellent sensitivity, quantitative readouts and early detection of biological processes, it still has a requirement for a radioactive tracer and provides images which lack anatomical reference (usually addressed by multimodality imaging with CT or MRI).
Molecular Imaging continues to transform the way in which physicians and oncologists monitor and treat disease. Although I have only touched briefly on three common imaging modalities, I encourage you to learn more about these techniques which impact medicine and patient health on a daily basis. The engineering of improved detection platforms and the addition of novel imaging agents with increased target specificity promises to provide powerful tools to facilitate improved cancer prognosis, diagnosis, and patient outcomes.
