By Dr Amaresh Hombal MD
Cancer is uncontrolled growth of abnormal cells in the body. Any tissue in the body can be affected by cancer. Cancer growth can invade adjacent parts of the body. Cancer may also spread to more distant parts through the lymphatics or bloodstream. The chances of surviving the disease vary greatly by the type and location of the cancer and the extent of disease at the start of treatment. Hence it is very essential to detect cancer in its early stage and initiate appropriate treatment.
Cancer can be detected in a number of ways, including the presence of certain signs and symptoms, lab tests, or medical imaging. Once a possible cancer is detected it is diagnosed by microscopic examination of a tissue sample. Cancer is usually treated with chemotherapy, radiation therapy and surgery.
An imaging test is a way to see something that's going on inside your body. These tests send forms of energy (x-rays, sound waves, radioactive particles, or magnetic fields) through the body. The changes in energy patterns made by body tissues create an image or picture. These pictures can show normal body structures and function as well as abnormal ones caused by diseases such as cancer.
Imaging tests are used for cancer in many ways. They are sometimes used in screening, to look for cancer in its early stages, even though a person has no symptoms. A mammogram is an example of an imaging test used for cancer screening. They can help find out if the symptoms are caused by a tumor or by some other type of disease. They can also help predict whether a tumor is likely to be cancer. This can help doctors decide if there is a need for biopsy (removal of a small piece of tissue for laboratory examination). They can show exactly where the tumor is, even deep inside the body.
Once cancer is diagnosed, imaging can help find out the stage of the cancer (figuring out how far the cancer has spread). They can be used to plan treatment, such as when pinpointing where the beams should be focused in radiation therapy. They can show if a tumor has become smaller, stayed the same, or grown after treatment. This can give a doctor an idea of how well treatment is working. They can help find out if a cancer has come back (recurred) after treatment.
Radiography employs use of X-rays to produce shadow-like images of certain organs or tissues. X-rays are very good at finding certain bone problems. They can show some organs and soft tissues, but MRI and CT scans often give better pictures of them. Still, X-rays are faster, easy to get, and cost less than other scans. A Mammogram is an X-ray of the breast. A screening mammogram is used to look for signs of breast disease when there are no breast symptoms or problems. This helps detect cancer in its early stages, even before a lump can be felt, when treatment can be most successful. Diagnostic mammograms are performed in order to evaluate a breast complaint or abnormality detected by physical exam.
Ultrasound machine creates images called sonograms by transmitting high-frequency sound waves through the body. As the sound waves bounce off your organs and tissues, they create echoes which are converted into images. Ultrasound is very good at giving pictures of some diseases of soft tissues.
Ultrasound is also a good way to tell fluid-filled cysts from solid tumors because they make very different patterns. We often use ultrasound to guide a needle to do a biopsy. Special ultrasound machines, known as Doppler flow machines, are able to show how blood flows through vessels. This is helpful because blood flow is different in tumors than in normal tissue. Color Doppler has made it easier for doctors to find out if cancer has spread into blood vessels.
CT scans use controlled amounts of X-rays and reconstruct a slice or cross-section of the body. The image shows your organs and soft tissues more clearly than standard x-rays. CT scans have been very useful in helping doctors find cancer. CT scans can show a tumor's shape, size, and location, and even the blood vessels that feed the tumor - all without having to cut into the patient.
We often use CT scans to guide a needle to remove a tissue sample. This is called a CT-guided biopsy. They can also be used to guide needles into tumors for some types of cancer treatments like radioablation. By comparing CT scans done over time, doctors can see how a tumor is responding to treatment or find out if the cancer is recurring after treatment.
MRI uses strong magnets instead of radiation to make the images. An MRI scan can take cross-sectional views from many angles, as if someone were looking at a slice of your body from the front, from the side, or from above your head. MRI creates pictures of soft tissue parts of the body that are sometimes hard to see using other imaging tests. MRI is very good at finding and pinpointing some cancers.
An MRI with contrast dye is the best way to see many tumors. MRI can also be used to look for signs that cancer may have spread (metastasized) from where it started to another part of the body. MRI images can also help doctors plan treatment such as surgery or radiation therapy. MRI has an advantage over others that it does not employ ionizing radiation like x-rays.
Nuclear scans make pictures based on the body's chemistry rather than on physical shapes and forms. These use substances called radionuclides that release low levels of radiation. Body tissues affected by certain diseases, such as cancer, may absorb more or less of the tracer than normal tissues. Special cameras pick up the pattern of radioactivity to create pictures that show where the material travels and where it collects.
If cancer is present, the tumor may show up on the picture as a "hot spot", an area of increased tracer uptake. Depending on the type of scan done, the tumor may instead be a "cold spot", a site of decreased uptake. Nuclear scans have different names, depending on the organ involved. Some of the more commonly are Bone scans, Myocardial perfusion scans, PET scans and Thyroid scans.
So to conclude, medical imaging tests are used in cancer in many ways. They are used to look for cancer (screen), diagnose or exclude cancer. They help in guiding for tissue biopsy. Once cancer is diagnosed, they are used to find out how far it has spread (stage) and help plan the treatment. Imaging tests are then used to follow up cancer to help determine if cancer treatment is working. Finally, they can help find out if a cancer has recurred after treatment.