Magnetic Resonance Imaging (MRI)
MRI plays a crucial role in the evaluation and management of head and neck cancers (HNC) owing to its superior soft tissue contrast and capacity to offer functional information. MRI can be used for cancer diagnosis, tumor staging, and treatment
planning. The main component of most MRI scanner is a large tube-shaped or
cylindrical magnet. The MRI scanner uses strong magnetic fields, radio waves, and
the inherent magnetic properties of hydrogen protons in the body's tissues to
generate highly detailed anatomical and functional images without using
ionizing radiation. In some cases, contrast dyes are used to illuminate certain
structures in the body. These dyes may be injected directly into the
bloodstream with a needle and syringe or they may be swallowed, depending on
the area of the body being studied. With MRI, it is possible to distinguish
between normal and diseased tissue and precisely pinpoint tumors within the
body. It is also useful in detecting metastases.
Additionally, the MRI provides greater
contrast between the different soft tissues of the body than a CT scan. Thus,
it is especially useful for imaging the brain, connective tissue, spine,
muscles, and the inside of bones. To perform the scan the patient lies down on
a padded table that gently glides or slides into the opening or bore of the MRI
scanner.
MRI tests are painless and there is no radiation involved. It takes much longer than a CT scan and is more expensive. Some patients report feelings of mild to severe anxiety and/or restlessness during the test. A mild sedative before the test can be administered to those who are claustrophobic or find it difficult to lie still for long periods of time. MRI machines produce loud banging, thumping, and humming sounds. Wearing earplugs can reduce the effect of noise.
CT of the head and neck showing a cystic lesion
PET/CT imaging plays a vital role in the comprehensive management of head and neck cancers, from initial diagnosis and staging to treatment planning, response assessment, and post-treatment surveillance. It provides better evaluation of the primary tumor site, cervical lymph node metastases, and distant metastases compared to conventional imaging.
It is also important to realize that these tests are not perfect and can miss a small tumor (less than one inch). A thorough physical examination should also accompany any scanning procedure.
PET and CT scans are often done in the same session and are performed by the same machine. While the PET scan demonstrates the biological function of the body, the CT scan provides information with respect to the location of any increased metabolic activity. By combining these two scanning technologies, a physician can more accurately diagnose and identify existing cancer.
The general recommendation is to perform fewer PET/CT scans the longer the elapsed time from the surgery that removed the cancer. Generally, PET/CT is performed every three to six months during the first year, then every six months during the second and then yearly throughout the fifth year. Some patients are followed yearly throughout life with PET/CT, and others undergo them if recurrence or a new malignancy is suspected. These recommendations, however, are not based on studies and are merely the opinion or consensus among the specialists. More scans are performed if there are concerns or suspicious findings. When scheduling a PET and/or CT scan any potential benefit gained by the information should be weighed against any potential deleterious effects of exposure to ionizing radiation and or X rays.
Sometimes physicians do not need a PET scan and only request a CT dedicated to the area in question. Such a CT is more precise compared to a combined PET/CT; the former can also include the injection of contrast material to assist in the diagnosis of the problem.
On occasion CT is not helpful, especially in those who had extensive dental work, including filings, crowns or implants that can interfere with the interpretation of the data. Not performing a CT spares the patient from receiving a substantial amount of radiation. Instead an MRI of the area can be done.
CT/PET showing left lesion in the left floor of the mouth and a spread to the lymph glands
When viewing the scans, radiologists compare the new scan(s) to the old ones to determine if there have been any changes. This can be useful in determining if there is new pathology.
Plain X-rays
have a limited role in the diagnosis and staging of HNC. More advanced imaging
modalities like CT, MRI, and PET are preferred for comprehensive evaluation of HNC.
Ultrasound is widely used for initial
detection and characterization of head and neck masses, including thyroid
nodules, lymph node metastases, and other soft tissue masses. It is
particularly useful for evaluating cervical lymph node metastasis in HNC,
aiding in tumor staging and post-treatment follow-up.
Ultrasound guidance can be used for
fine-needle aspiration biopsy (FNAB) or core biopsy of suspicious masses,
providing a minimally invasive method for tissue sampling and diagnosis.
In follow-up of treated HNC, ultrasound
is effective for detecting recurrence, especially regional lymph node
recurrence and in early-stage (stage I) primary tumors.
Advantages of ultrasound include being
non-invasive, widely available, cost-effective, and lacking ionizing radiation
exposure.
Ultrasound image of a neck mass
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