CHAPTER 11

Cancer Imaging

PART 1 How Imaging Is Used

Medical imaging technology has revolutionized the screening, study and treatment of cancer. Imaging is used before, during, and after cancer treatment:

Screening. Generally used for people at increased risk of certain types of cancer, screening can help determine if there are abnormal areas present that may be cancerous.

Diagnosis and staging. Imaging can be used to find out how much cancer is in the body, where it’s located, and if it’s metastasized. Imaging can also be used as an aid in biopsy, to guide the doctors to the tumor.

Treatment. Imaging can help to guide cancer treatments by exactly determining tumor location, so that treatment can focus on the tumor alone to minimize damage to nearby tissue. Imaging can also show if a treatment is working by showing if a tumor is shrinking, has changed, or is using less of the body’s resources.

Monitoring for recurrence. After treatment, imaging can be used to see if a cancer has recurred or if it has metastasized elsewhere.

PART 2 Types of Imaging Technology

A number of different types of imaging are used in detecting and treating cancer:

X-ray imaging is used in cancer screening and diagnosis. Mammograms are a form of X-ray used for screening, and they are also used (along with chest radiographs) to determine if cancer has metastasized to other areas of the chest.

Ultrasound uses high-frequency sound waves and their echoes to produce a picture of internal organs or masses on a computer screen. The test is painless and does not expose the patient to radiation.

Magnetic resonance imaging (MRI) scans provide images of soft tissues in the body using radio waves and strong magnets. A computer translates the pattern into a very detailed image of parts of the body. A contrast material is often injected into a vein before the scan to provide clearer images.

Computerized tomography (CT) scans use multiple X-ray images to produce detailed cross-sectional images of the body. As the patient lies on a table, the CT scanner takes numerous X-rays as it rotates around him or her. Sometimes the patient is injected with a contrast dye the help outline structures of the body. A computer program then combines the images to form detailed cross sections, or slices, of the part of the body being studied. Unlike regular X-rays, CT scans can create detailed images of the body’s soft tissues.

Spiral CT is a recent advance in CT imaging. It uses a faster machine that rotates around the body continuously, collecting images more quickly and thus lessening the chance that the images will blurred as a result of breathing motion. In addition, the patient receives less radiation with spiral CT, and the cross sections are thinner, producing more detailed pictures.

Positron emission tomography (PET) scans involve injecting a form of slightly radioactive glucose (known as fluorodeoxyglucose or FDG) into the blood. Cancer cells in the body grow rapidly and absorb large amounts of glucose. The body is then photographed by a special camera to show areas of high glucose concentration.

PET/CT scans are a recent development. PET/CT scanning machines can perform both a PET and a CT scan at the same time, producing images that reflect both the body’s organ function and its structural appearance. The radiologist can compare areas of higher radioactivity on the PET with the appearance of those areas on the CT, improving the ability to detect abnormal areas.

Single photon emission computerized tomography (SPECT) scans are similar to PET scans. In a SPECT scan, radioactive tracers linked to antibodies (proteins that recognize and stick to tumors) are injected into the patient. If a tumor is present, the antibodies will adhere to it, and the SPECT scan will reveal its presence.

LESS

Photo attribution of radiologist and doctors
Copyright 1989 Bill Branson

Photo attribution of chest x-ray with abnormal growth in left lung
Copyright 1988 National Cancer Institute