What Imaging Tests Are Used in Cancer?
We use imaging tests to scan the body, detect problems, and figure out what they are. Imaging tests are our most important tool for looking for cancer, finding out how far it has spread, and see if cancer treatment is working.
What are Imaging Tests?
An imaging test is a method used to allow doctors to see what's going on in your body. These tests send forms of energy (such as x-rays, sound waves, radioactive particles, or magnetic fields) into your body. Different tissues respond differently to these energy types; thus, anatomical images are formed where we can select the borders of the tissues, or an abnormal formation (e.g. a tumor) in a tissue becomes noticeable.
What are Imaging Tests Used for in Oncology?
Imaging tests are used in cancer for many reasons:
- To look for cancer in its early stages, when it has not yet shown any symptoms. These may be called early detection or cancer screening tests.
- To look for a tumor in a person who has complaints or shows signs of cancer. We call this the primary tumor search. They can also help decide whether the complaints are due to cancer or another disease.
- Sometimes they can help predict whether a tumor is likely to become cancer. This can help healthcare professionals decide whether a biopsy is necessary (in a biopsy, a small sample of the suspicious tissue is taken and examined under a microscope). A biopsy is almost always needed to be sure a change is a cancer.
- They can show where the tumor is, even deep inside the body. This helps to see if a biopsy needs to be done.
- They can help find the stage of cancer (whether cancer has spread and/or how far it has spread).
- In radiotherapy, to show where the beam should be focused, for radiotherapy planning.
- They can show that a tumor shrinks with treatment, stays the same, or grows after treatment. This gives the oncology team an idea of how well the treatment is working.
- They can help find out if cancer has recurred after treatment.
Imaging tests are only one part of cancer diagnosis and treatment. A complete cancer examination also includes your medical history (complaints and risk factors), physical exam, blood tests, and other laboratory tests.
Detailed imaging is requested before cancer treatment, that is, at the time of diagnosis, to be used later. These images are then used to monitor changes during treatment.
Imaging Tests May Not Always Be Perfect
Imaging tests are one of our most important guides in cancer treatment, but they have limits. For example, often these tests alone cannot definitively show whether a change is due to cancer.
Imaging tests can show cancer only after the tumor has reached a certain size. Tumors need to reach a size of about 5 millimeters to be noticed by radiological methods, and there are almost a million cancer cells in a 5-millimeter tumor. There is no imaging method that shows a single cancer cell yet; this issue is one of the most important research areas of cancer medicine (nuclear scans such as PSMA-PET and liquid biopsies are being tried for this purpose). It is these undetectable cancer cells that are the reason why cancer treatment is continued even though no tumor is seen in imaging tests.
Who Conducts and Interprets Imaging Tests?
A doctor, a radiology technician, or other certified healthcare professional may perform an imaging test. The test can be done in a hospital, a private clinic, an imaging center, or a doctor's office. In large medical centers, imaging tests are usually done in the radiology or nuclear medicine department.
Radiologists and nuclear medicine specialists are doctors who specialize in imaging techniques; They are the people who both manage the shooting process and interpret the images made during the test. The radiologist or nuclear medicine specialist writes a report on the findings and sends the report to your doctor. A copy of the report will become part of your health records. Your other doctors (oncologists, surgeons, etc.) may also view the images.
Types of Imaging Tests
Different imaging tests show different organs well. In which organ the doctors suspect a tumor, they prefer the appropriate radiological method.
- Computed tomography (CT): X-rays are used. It shows the lungs and intra-abdominal organs well.
- Magnetic resonance imaging (MRI): Electromagnetic field and radiofrequency waves are used. It is preferred in tumors of the brain, liver, breast, bones, head and neck, and lower abdomen.
- Mammography: X-rays are used. Breast cancer screening.
- Nuclear medicine scans (eg PET-CT, PET-MRI): Radioactive particles are used and the resulting nuclear scan image can be combined with computed tomography or magnetic resonance imaging. It is used for imaging organ tumors all over the body (PET-CT is weak in the brain and liver).
- Ultrasound (USG): Sound waves are used. In superficial tumors of the breast, liver, abdominal organs, head and neck region. In addition, biopsies are often performed under USG guidance.
Anatomical, Functional, or Combined Imaging?
Patient management in oncology increasingly relies upon imaging for diagnosis, response assessment, and follow-up. The clinical availability of combined functional-anatomic imaging modalities, which integrate the benefits of visualizing tumor biology with those of high-resolution structural imaging, revolutionized the clinical management of oncologic patients. Conventional high-resolution anatomic imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI) excel at providing details regarding lesion location, size, morphology, and structural changes to adjacent tissues; however, these modalities provide little insight into tumor physiology. With the increasing focus on molecularly targeted therapies, imaging radiolabeled compounds with positron emission tomography (PET) and single-photon emission tomography (SPECT) are often used to provide insight into a tumor's biologic functions and its surrounding microenvironment. Despite their high sensitivity and specificity, PET and SPECT alone are substantially limited by low spatial resolution and the inability to provide anatomic detail. Integrating SPECT or PET with a modality capable of providing these (i.e. CT or MR) maximizes their separate strengths and provides anatomic localization of physiologic processes with detailed visualization of a tumor's structure. The availability of multi-modality (hybrid) imaging with PET/CT, SPECT/CT and PET/MR improves our ability to characterize lesions and affect treatment decisions and patient management.
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