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Imaging

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At some point in your cancer journey, your doctor may order a radiologic study, also known as an imaging study, to get more information about the tumor and its possible spread. However, this is not necessary for small tumors easily assessed on physical exams.

Imaging can help your doctor determine the location and extent of the tumor and how it relates to major structures in the head and neck, as well as to locate evidence of invasion into bone and/or nerves.

There are a few options for imaging, each with its advantages and disadvantages. In some cases, particularly for large and/or advanced tumors, more than one imaging technique might be used.

The two main techniques used in the U.S. to assess the anatomy of the body are computed tomography (CT) scans and magnetic resonance imaging (MRI) scans.

Ultrasounds—an efficient, noninvasive and cost-effective way to get information about disease in the neck—are often used in cases of thyroid cancer. Ultrasound imaging involves the harmless use of sound waves and is often used in combination with performing a fine needle aspiration biopsy.

Positron emission tomography (PET) scans are studies that look at the function of cells in the body. PET scans can be combined with other imaging methods, such as CT scans, to provide functional and anatomic information.

In addition to ultrasounds, functional imaging tests, such as radioactive iodine uptake tests, may also be used for thyroid cancer.

Other imaging tests sometimes used in head and neck cancer include X-rays and esophagrams.

Be sure to tell your doctor if you are or might be pregnant before having any type of imaging study.

CT scan

A CT scan, also called a CAT scan, stands for computer axial tomography scan.

A CT scan is a quick series of X-rays in different orientations that can show very good detail of the anatomy inside your body. It is helpful in determining the extent of the primary tumor and what structures it may have invaded. It can also help pick up evidence of spread into the neck or other parts of the body. While a CT scan can raise the suspicion of cancer, a biopsy is required to confirm a diagnosis.

When your doctor is searching for tumors, a CT scan should be done with contrast injected into your veins, unless you are unable to receive contrast.

Advantages:

  • A quick test that is readily available and gives a great deal of useful anatomic information.
  • Can be done with different sequences to effectively evaluate arteries and veins.
  • Excellent for showing bone anatomy.
  • May be used to guide placement of a needle to perform a biopsy.

Disadvantages:

  • Exposes you to radiation. When used correctly, a CT scan has benefits that far outweigh any risks from radiation exposure, but it is something your doctor keeps in mind and you should be aware of. In select situations, an MRI (which does not expose you to any radiation) could be an alternative to a CT scan.
  • Images can be degraded with movement and dental work.
  • Only shows late changes associated with nerve invasion (such as destruction of the bone as the nerve enters the skull).

What to expect: First, a nurse will insert an intravenous line into a vein to allow for contrast injection if that has been requested by your physician. Then you will have to lie flat on a table with your head in a little holster to help keep it totally still. CT scans are typically open, so you shouldn’t feel enclosed. You will then get an injection of contrast, and soon after, the scanner will start moving and taking pictures; this part should take only one or two minutes. Try not to swallow, speak or move during this quick test.

MRI

MRI stands for magnetic resonance imaging.

The test uses magnets to create a picture of the inside of the body. It is based on magnetic fields around molecules. An MRI is good at showing subtle details of the extent of a tumor. Just like a CT scan (or any anatomic imaging), MRIs can help pick up the spread of cancer to lymph nodes in the neck or to different sites of the body.

An MRI should be done with and without contrast injected into your veins, unless there is some reason you can’t have contrast. Be careful where you go to have an MRI done. Some older MRI machines are weaker and may offer pictures that cannot compare to the latest technology. Also note that normal (or closed) MRIs offer better images than open MRIs. Patients with severe claustrophobia should consult their physician to discuss open vs. closed MRIs.

Advantages:

  • No radiation is involved.
  • Details of the soft tissues are better than that of a CT scan.
  • They show earlier pickup of nerve and skull base involvement.

Disadvantages:

  • They take much longer than a CT scan and are more expensive.
  • Images can be degraded with movement and dental work.
  • Some people feel enclosed inside the MRI machine.
  • There can be loud banging inside the machine, which can be uncomfortable.
  • They are more difficult to schedule.

What to expect: First, a nurse will insert an intravenous line into a vein to allow for contrast injection. Then you will have to lie flat on a table with your head in a holster to help keep it totally still. Due to the strength of the magnets, you will be instructed to remove any metallic objects and to change into a hospital gown before entering the room where the scanner is located. If you have any implanted metal objects in your body, you will likely not be a candidate for an MRI. You will then enter the scanner, and the MRI machine will start moving and taking pictures. This can take 30 to 60 minutes, depending on how the scan is done. Try to stay as still as possible throughout the test. You will be able to communicate with the technician administering the test through a telecommunications system. Be prepared for a loud noise that occurs throughout the MRI scan. Earplugs may be placed to dampen the volume of that sound.

PET scan

PET stands for positron emission tomography.

A PET scan is a functional test and not an anatomic test. This means the scan measures the activity of different cells in parts of the body.

Basically, a PET scan creates a three-dimensional image of the body with metabolically active areas of the body lighting up like a light bulb. Certain cells, such as infected cells and cancerous cells, are more active than others. Cancer cells at the primary site as well as in lymph nodes or distant sites can be detected with a PET scan. Lower-grade malignancies or very small cancerous deposits may not be identified on a PET scan. Overactive cells use more sugar, the energy source for every cell in the body. Therefore, by injecting your blood with a small dose of glucose with a tracer attached (such as fluorodeoxyglucose, or FDG), the PET scanner can pick up which parts of the body are more metabolically active than others.

PET scans are used by different types of doctors. For head and neck cancer, doctors are still figuring out in which cases a PET scan is appropriate. Currently, the main uses of PET scans are to identify:

  • The spread of cancer cells to lymph nodes in the neck (regional metastases) or other parts of the body (distant metastases).
  • Recurrent cancer in places difficult to see with the naked eye.
  • A primary tumor when all that has been found is a lymph node with cancer, referred to as metastatic cancer with an unknown primary (CUP).

Advantages:

  • The radioactive tracer decays quickly, so there is very little radiation from the PET scan itself.
  • When combined with a CT scan or MRI, doctors can combine functional imaging with anatomic imaging to obtain more precise information.
  • In some cases, PET scans are better able to distinguish actual cancer from abnormalities related to the effects of radiation that might be seen on a MRI or CT scan.

Disadvantages:

  • PET scan image results are less precise than anatomic studies such as CT scans and MRIs.
  • It takes some time, and you must sit totally still.
  • PET scans are expensive.
  • The functional images alone do not differentiate the specific organ or other structures that are hypermetabolic (the images need to be fused or compared with anatomic imaging for this level of detail).
  • PET scans will not pick up a small focus of cancer that is using a significant amount of glucose; the cancer focus has to be more than one centimeter for today’s PET scanners to pick it up.
  • The PET scan lights up areas that are not necessarily cancer, including infected areas, because cells in those areas might also be using a lot of glucose.

Important points:

  • Prepare for the scan the night before by following all the instructions you are given (including exercise, meal and medication requirements).
  • Since the PET scan typically uses a molecule that looks like glucose (the sugar that all cells in your body use for energy), it is important that you do not have anything to eat (including chewing gum) for at least six hours before the scan.
  • PET scans are often combined with a CT scan, and at times combined with an MRI, to help pinpoint the location of metabolically active cells.

What to expect: A nurse will check your blood glucose level. Also, the nurse will insert an intravenous (IV) line into a vein to allow for injection of a radioactive tracer such as FDG. A radioactive tracer contains radioactive particles, which can be tracked as they move through the body using certain types of scans. It takes about 30 to 120 minutes for the radiotracer to get around your body, at which point the scan will begin.

During the scan, you will have to lie flat and completely still on a table as the donut-shaped PET scanner moves up and down. Try not to speak or move. The scan can take another 30 to 90 minutes. This scan is often combined with a CT scan (or sometimes even an MRI scan), either in the same machine or in a separate machine. The PET scanner does not make loud noises like an MRI machine.

The results of the PET scan and the CT scan (or MRI scan) can then be fused to match the functional image from the PET scan with the anatomic image from the CT scan.

The results are then analyzed by a nuclear medicine doctor or radiology specialist (or both) to create a report. The report will identify areas of increased energy use in the body. The results are given in Standard Uptake Value (SUV). This number is calculated based on the radiotracer uptake of a certain part of the body, the total amount of radiotracer injected and your total body weight.

The interpretation of the PET scan will be made by your doctors, who will use prior treatments, the physical exam results and signs of artifact, such as movement (including speaking or coughing during the test), to formulate an impression. Also, your doctor will compare PET scans over time. Following the treatment, the decrease in the SUV of a particular structure may have importance by reflecting the successful treatment of a cancer or cancerous deposit. Alternatively, the successful surgical removal of a cancer will be reflected by the complete absence of metabolic activity on a surveillance scan (follow-up scan) where the surgery was performed. It is important to note that the healing process of the surgery is itself a cause for hypermetabolism on a study performed within the first few months after the procedure. Similarly, the successful resolution of a cancer treated by radiation alone or in combination with chemotherapy may take months to show the complete loss of metabolic activity in the affected tissues. In general, SUVs above three will make your doctor take notice—but this is not an absolute number by any means.

Don’t jump to any conclusions based on your reading of a report. Consult your doctors about their interpretation.

Ultrasound

An ultrasound uses sound waves to show vessels, organs and lymph nodes all over the body, particularly in the neck and thyroid gland. Since sound waves do not go through bone, ultrasounds are not used for imaging of structures located more deeply in the face or head.

Advantages:

  • No radiation exposure.
  • No pain and little to no discomfort.
  • It’s dynamic, and the person performing the ultrasound can spend more time on areas of concern.
  • At the same time as performing an ultrasound, the doctor can place a needle into a lymph node or nodule and draw off cells for a biopsy.

Disadvantages: It can’t be used to see areas hidden behind bone because the sound waves are blocked by bone, so its use is fairly limited in primary tumors of the head and neck.

What to expect: A technician or a radiologist will place some cold jelly over the area being examined and will rub a plastic probe over the area and take pictures. Your technician or radiologist can see enlarged lymph nodes and nodules deep in the neck and can even provide details about them, such as if they have fluid inside or have many blood vessels around them. The time to complete the examination will depend on a number of factors, but you can expect it to take 15 to 30 minutes.

X-rays

X-rays are quick, cost-effective and easy to perform. They work by shooting X-rays into a certain part of your body (your chest, for example) as you stand against a film on the other side of your body. Different tissue densities allow different amounts of X-rays through, and this results in a “picture” that distinguishes different structures.

X-rays are not the best type of imaging for finding abnormalities within soft tissue. They are better at picking up findings when soft tissue is located against air (for example, a soft tissue nodule in the air-filled lung) or when soft tissue is against or located in bone (for example, when a tumor invades into the jawbone). For head and neck cancer, especially within the mouth, a panoramic radiograph X-ray (sometime called a Panorex) can be extremely useful to analyze the area around the teeth and the jawbones.

Advantages: Quick, affordable and easy to perform

Disadvantages:

  • A small amount of radiation is administered.
  • Not the best at distinguishing different tissues.
  • Not great at differentiating abnormalities in soft tissue.

Important information: The most common use of X-rays in head and neck cancer is for chest X-rays to check for spread of cancer into the lungs or the possibility of a different cancer in the lungs. Some doctors will recommend a chest X-ray every few months or every year if you have had head and neck cancer, because patients who have had head and neck cancer are also at a higher risk of getting lung cancer.

What to expect: A technician or radiologist may give you a lead apron to shield parts of your body not being X-rayed in order to protect you from excessive exposure to radiation. You will lie on a table or stand against a wall while the images are being created. The technician will probably step out of the room and trigger the X-ray machine from behind a protective wall. You will not feel anything, and the process will take just moments.

Esophagram

An esophagram is a constant X-ray (fluoroscopy) taken while you swallow a special liquid that lights up on the X-ray images. The liquid will be either barium or gastrografin. As you drink the liquid, the technician will take pictures of the liquid moving down your esophagus. Normally, there should be a smooth line of liquid going down your throat. If there is a tumor in the cervical esophagus, there will be a small indentation at the edge of the esophagus or even a complete blockage in the case of a large tumor.

Apart from tumors, an esophagram can also be used to diagnose other problems causing difficulty with swallowing. In head and neck cancer, for example, patients can develop strictures (scar bands and resultant narrowing) of the esophagus. This can be a complication of treatment of a cancer in which the esophagus becomes scarred and narrowed, making it difficult to eat and drink. This complication can develop a few years after treatment. If the scarring completely blocks off the esophagus, it will become impossible to swallow even your own saliva.

Advantages: Esophagrams are quick, affordable and effective for screening for tumors.

Disadvantages: There is very limited anatomic detail. You will probably need a diagnostic procedure to confirm any findings.

What to expect: Pre-procedure instructions might include not eating or drinking anything prior to the test. Then just follow the instructions, which will include drinking the liquid as the X-ray machine takes a continuous run of photos in different positions. You will probably have to do this a few times.

A variation of the standard esophagram is a different test called a modified barium esophagram. This test is done together by a speech pathologist and a radiologist with barium-infused foods and drinks. You will drink and/or eat substances of different consistency as the constant X-rays are taken. The pictures, however, will be of the mouth and throat (rather than the esophagus). This test can identify problems in swallowing in the mouth and throat, as well as drinks or food going down the wrong tube into the lungs (aspiration). A modified barium swallow can be useful to determine when it is safe for a patient to resume or continue swallowing if there is concern about recurrent aspiration of food, liquid or even saliva.

Radioactive iodine uptake test

Radioactive iodine uptake tests (also called thyroid scans) are nuclear scans used to diagnose thyroid disease. For thyroid cancer, a thyroid scan can be used after surgical removal of thyroid cancer to find hidden thyroid cancer cells. Also, in some cases it can be used after removal of your thyroid gland for cancer, to kill off any remaining thyroid cancer cells by giving higher doses of the radioactive iodine.

In this test, radioactively labeled iodine is taken by mouth. A special camera will then measure different parts of your body to look for emission of radioactive material anywhere in your body (which would indicate thyroid-type cells).

As with any test, there are some risks, including damage of certain cells from radiation.

Also, this test cannot be administered to pregnant women, breast-feeding women or young children except in special circumstances.

A number of factors can influence the test results, including certain medications, diseases and diets. Also, if you recently had a CT scan with iodine-containing contrast, the results might be altered. Talk to your doctor about these issues before taking the test.

What to expect: Prepare for the test with the instructions provided to you. This might include not eating anything a couple of hours before the test and holding off on thyroid medications for some time before the test. There are two strategies your doctors could use to prepare you for this test and treatment1, Schlumberger M, Catargi B, Borget I, et al for the Tumeurs de la Thyroïde Refractaires Network for the Essai Stimulation Ablation Equivalence Trial. Strategies of radioiodine ablation in patients with low-risk thyroid cancer. N Engl J Med. 2012;366:1663-1673.2 Mallick U, Harmer C, Yap B, et al. Ablation with low-dose radioiodine and thyrotropin alfa in thyroid cancer. N Engl J Med. 2012;366:1674-1685.:

  1. You could be asked to stop any thyroid replacement medications for approximately two to six weeks before the RAI test/treatment. This is called thyroid hormone withdrawal.
  2. You could continue your thyroid replacement medication but be administered recombinant human thyrotropin two days prior to the RAI test/treatment.

Thyroid hormone withdrawal is done to starve your body of thyroid hormone. When you take radioactive iodine, the remaining thyroid and thyroid cancer cells are eager to take up the iodine to try to make thyroid hormone. However, because the iodine is radioactive, it actually ends up destroying the cell instead of making thyroid hormone. Basically, thyroid hormone withdrawal makes RAI work better. Side effects of thyroid hormone withdrawal will begin after a few weeks, and towards the end of the withdrawal period you might begin to feel exceptionally tired. There is a special form of thyroid hormone called liothyronine (brand name Cytomel), which needs to be stopped about two weeks before RAI treatment.

Recombinant thyrotropin (brand name Thyrogen) is a way to avoid the side effects of thyroid hormone withdrawal. This injection is another way to make thyroid cells hungry for iodine.

When you are ready to do the test, you will be given a capsule or a liquid that you should take four to 24 hours before the test. This capsule contains a radioactive form of iodine that is taken up by thyroid cells in the body. After the pre-established time period, you will lie in a machine, and a gamma probe will measure areas of radioactivity in the thyroid region as well as the rest of the body if you are getting a whole body radioactive iodine uptake test. The amount of radioactivity in different parts of the body will be reported. If you are doing this test after a thyroidectomy, any sites of uptake of radioactive iodine may indicate thyroid cells remain. If this is found in the neck or the lungs, it raises the suspicion of thyroid cancer. If this is found in the thyroid bed, where the thyroid used to be, this could be either thyroid cancer or normal thyroid tissue left behind after removal of the thyroid gland.

Special radioactive precautions must be taken to prevent exposure of other individuals to harmful radioactivity.

After the test, you might be asked to make sure you flush the toilet and wash your hands thoroughly after you urinate, because the radioactive substance leaves your body through your urine. Any special precautions will typically be required for only 24 to 48 hours.

The exact type of radioactive iodine will depend on the reason for the test:

  • I-123 is used to diagnose sites of thyroid tissue.
  • I-131 is used to either identify or destroy sites of thyroid tissue.

After you have been treated with RAI, your doctors will probably schedule you for a post-treatment RAI scan. This is a way to see how effective the treatment was in getting rid of any residual thyroid tissue anywhere in your body.

For more information about thyroid cancer, visit the Thyroid Cancer Care Collaborative.


References

1 Schlumberger M, Catargi B, Borget I, et al for the Tumeurs de la Thyroïde Refractaires Network for the Essai Stimulation Ablation Equivalence Trial. Strategies of radioiodine ablation in patients with low-risk thyroid cancer. N Engl J Med. 2012;366:1663-1673.

2 Mallick U, Harmer C, Yap B, et al. Ablation with low-dose radioiodine and thyrotropin alfa in thyroid cancer. N Engl J Med. 2012;366:1674-1685.