In vivo imaging for cancer evaluation allows the disease to be diagnosed and monitored within its physiological environment. Many medical disciplines, including immunology, pharmacology, chemistry, and molecular and cell biology, have worked together to create the latest imaging technologies. CT scans, MRIs, optical scans, PET scans, SPECT scans, and ultrasound, are all modalities for in vivo imaging.
X-ray computed tomography, or CT scans, create images of bones and soft tissues. A series of x-rays is directed at the body, from a variety of angles, creating cross-sections of tissue for evaluation. Within the field of cancer, CT scans may be used to both detect and monitor malignancies, as well as to guide radiation therapy, biopsies, and surgeries. Within other fields, CT scans diagnose bone and muscle disorders, find infections and blood clots, and detect internal bleeding and injury.
Another diagnostic tool is the MRI. Magnetic resonance imaging creates detailed pictures of organs and tissues, by using a magnetic field to align water molecules in the body. Then, the machine directs radio waves at the molecules, which cause particles to give off signals. The signals are translated into cross-sectional images, most frequently of the brain and spinal cord. MRI also detects abnormalities of the breasts, bones and joints, and internal organs.
An optical scan forms a picture by directing a light at the body. Photons from the external light source are then wither absorbed or scattered by the tissues, and the patterns are translated by a photon detector. Fluorescence may be detected deep within tissue, so scientists use fluorescent dyes to stain many small molecules. Probes, which stay in the body for an extended period of time, are used to enhance image contrast.
Doctors use PET scans to uncover metabolic changes at the cellular level. PET, which stands for position emission tomography, utilizes small dosages of a radioactive compound. After either swallowing, inhaling, or injection, the compound travels to the organs and tissues. The machine converts the radiant energy from the compound into a 3D image. Diseased cells with increased rates of chemical reaction tend to aggregate the most tracers, and these spots show up as bright areas on the image.
Doctors also use SPECT scans to create images from radioactive compounds. SPECT (single-photon emission computerized tomography) shows the inner workings of different organs, particularly the heart and the brain. Within the realm of cancer, SPECT scans are particularly useful for detecting and tracking bone cancers.
Ultrasound guides biopsy and tumor treatment. Using high-frequency sound waves, to produce images of body structures, ultrasound detects abnormalities in many organs, particularly the prostate. Additional applications outside of cancer include the study of blood flow and the heart, and the evaluation of fetal development.
Imaging in vivo for evaluation of cancer is just one important application of molecular imaging technology. Non-invasive scanning of cancer cells aids doctors at all stages of the disease, from diagnosis, to treatment. Scanning allows doctors to evaluate treatment protocols in the early stages, and allows doctors to closely watch the progression of malignancies throughout the body.