Cancer diagnosis frequently requires imaging studies that in many cases use small amounts of radiation. Procedures such as X-rays; computed tomography (CT); magnetic resonance imaging (MRI); positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are important in clinical decision-making, including therapy and follow-up.
Imaging tests – taking pictures of the inside of the body – are of pivotal importance in the diagnosis and management of cancer patients. The use of diagnostic imaging is one of the first steps in the clinical management of cancer. Diagnostic radiology and nuclear medicine studies play an important role in the screening, staging (finding out the extent of the cancer, such as how large the tumour is, and if it has spread beyond the primary site), follow-up, therapy planning, evaluation of therapy response and the long-term surveillance of patients.
Imaging tests are used for cancer in many ways:
- They are sometimes used to look for cancer in its early stages (when it’s small and has not spread), and a person has no symptoms. This may be called early detection or cancer screening tests.
- They can be used to look for a mass or lump (tumor) if a person has symptoms. They can also help find out if the symptoms are caused by cancer or by some other type of disease.
- They can sometimes help predict whether a tumor is likely to be cancer. This can help health care providers decide if a biopsy is needed. (In a biopsy, a small piece of tissue is taken out and looked at under the microscope.) A biopsy is almost always needed to know for sure that a change is cancer.
- They can show where the tumor is, even deep inside the body. This helps if a biopsy is needed.
- They can help find out the stage of the cancer (figure out if and/or how far the cancer has spread).
- They can be used to plan treatment, such as showing where radiation therapy beams need to be focused.
- They can show if a tumor has shrunk, stayed the same, or grown after treatment. This can give the cancer care team an idea of how well treatment is working.
- They can help find out if a cancer has come back (recurred) after treatment.
Imaging tests are only part of cancer diagnosis and treatment. A complete cancer work-up also includes talking about your medical history (asking questions about your symptoms and risk factors), a physical exam, and blood work or other lab tests.
Many health care providers plan x-rays or other imaging tests before treatment starts. These pictures are then used to track changes during treatment. These are called baseline studies because they show how things looked at the start. They can be compared with later images to see the results of treatment over time.
A reliable diagnosis is necessary to identify the site of the primary tumour, and to assess its size and dissemination to surrounding tissues and to other organs and structures in the body. An appropriate diagnosis is of paramount importance in deciding the therapeutic approach to take and establishing the prognosis.
A mammogram is an X-ray exam of the breast. It’s used to find and diagnose breast disease in women who have breast problems such as a lump, pain, or nipple discharge. It’s also used to check for breast diseases in women who don’t have breast problems. (This is called a screening mammogram.) A mammogram can’t prove that a breast change is cancer. But if it shows something that might be cancer, more testing can be done.
The chance of cure for a cancer patient strongly depends on the stage of the disease at the time of diagnosis. When it is diagnosed at an early stage – before it is too large or has spread – a tumour is more likely to be successfully treated. The early detection of cancer hinges on many factors: the screening of at-risk population; the ability of patients and health professionals to recognise warning signs; and the use of diagnostic methods to differentiate between cancer and other processes, as well as to precisely determine the location and the extension of the tumour. Modern diagnostic imaging technologies provide the ability to discriminate tissues down to a millimetre, using magnetic resonance imaging (MRI) and X-ray computed tomography (CT), while the range of positron emission tomography (PET) and single photon emission tomography (SPECT) are a few millimetres.
Ultrasound uses high-energy sound waves and a computer to make images of blood vessels, tissues, and organs. It can be used to look at how well organs are working and to look at blood flow through vessels. Tumors in the belly (abdomen), liver, and kidneys can often be seen with an ultrasound. (It’s not useful in the chest because the ribs block the sound waves.)
Ultrasound can also be used through a probe that can be put into body openings, like the anus, vagina, or esophagus. This puts it closer to the certain internal organs, which can give a clearer picture.
These scanners take pictures after a radioactive tracer (called a radionuclide) is put into your blood. This type of scan may also be called a radionuclide scan.
The scanner creates pictures that show where the tracer travels and collects. These spots might be tumors or other tissue damage. Some common nuclear scans are bone scans, PET scans, thyroid scans, MUGA scans, and gallium scans. The type of scan done depends on which part of the body your doctor wants to look at.
MRI uses a strong magnet, radio waves, and a computer to make detailed images of organs and other structures inside your body. An MRI is often used to look at the heart, brain, liver, pancreas, male and female reproductive organs, and other soft tissues. MRI can show even small changes in tissues. It can assess blood flow, detect tumors, and diagnose many forms of cancer, evaluate infections, and assess injuries to bones and joints.
Diagnostic imaging can be divided into two broad categories: those methods that define very precisely anatomical details and those that produce functional or molecular images.
The first method (using CT and MRI) can provide exquisite details on lesion location, size, morphology and structural changes to surrounding tissues, but only delivers limited information as to the tumour’s functioning.
The second method (using PET and SPECT) can give insight into the tumour physiology down to the molecular level, but cannot provide anatomical details.
Combining these two methods enables the integration of anatomy and function in a single approach. The introduction of such “hybrid” imaging has allowed for the characterization of tumours in all stages.
The use of different diagnostic imaging techniques that employ various forms of radiation such as X-rays (CT and radiography) and gamma rays (PET and SPECT) has revolutionized the management of cancer patients. Technologies such as positron emission tomography (PET) that rely on the use of radiopharmaceuticals represent a breakthrough in the medical practice due to their capability to decipher, without opening the human body, what is happening at molecular level in a certain cell or tissue. The information obtained from these techniques has enabled significant improvements in patient management and the proper distribution of healthcare resources.