One of the first steps in diagnosing mesothelioma is to conduct imaging tests using X-ray, MRI, CT, or PET scans.
Imaging scans are the least invasive diagnostic method available.
Imaging tests alone are never enough to confirm a mesothelioma diagnosis.
Imaging tests provide an important look at any tumors, spreading and possible staging.
These tests may work best in combination, as they have their own advantages and limits.
A critical step in arriving at a mesothelioma diagnosis is to get a view of what is happening inside the body. Physicians have a number of imaging tests at their disposal to investigate the various symptoms and physical conditions caused by the disease. These tests may be as simple as a chest X-ray or as sophisticated as a PET scan.
While imaging tests cannot definitively provide a mesothelioma diagnosis on their own, the information provided by imaging technology is essential for aiding in diagnosis, staging the disease, and making treatment decisions.
Often the first imaging study used to investigate symptoms of mesothelioma—or almost any condition that affects the heart or lungs—is a chest X-ray. A chest X-ray or “plain film” is created by shining a small amount of X-ray radiation through person’s chest and collecting the resulting impression on a radiosensitive plate. Tissues within the body reflect the X-rays to varying degrees:
- Bone reflects almost all x-rays
- Lung tissue allows most X-rays to pass straight through
The result is a two-dimensional image of the contents of the chest.
Chest X-rays can be useful for mesothelioma surveillance. People at risk for developing mesothelioma, such as smokers with significant asbestos exposure, may receive periodic chest X-rays to detect any abnormalities. However, even under ideal circumstances, a chest X-ray can only provide limited information about mesothelioma. X-ray images may show a pleural effusion (excess fluid around the lungs) that can be a symptom of mesothelioma, but could also indicate other abnormalities in the lung or the pleura. Therefore, X-rays are often only the first step in diagnosis, and additional tests may be needed to confirm the presence of mesothelioma.
Computerized Tomography (CT) Scans
A CT scan requires the patient to lie on a small bench, which is moved through a doughnut-shaped imaging device. This device takes a series of X-ray images called “slices.” Each slice is a horizontal X-ray image of the entire body. The computer connected to the CT scanner will then stack the image slices to provide a three-dimensional (3D), reconstructed image of the patient’s body.
Sometimes, patients will be given a certain type of dye, called a radiopaque dye, such as barium or iodine to help enhance the resulting images. These radiopaque dyes may be ingested or injected into a vein, depending on the area that is being focused on by the scan.
The 3D image obtained from a CT scan provides a far more detailed view of a person’s internal anatomy than a simple, two-dimensional X-ray image. Indeed, a CT scan is more than 90% sensitive for detecting malignant pleural (lung) mesothelioma. Although it is less effective at detecting peritoneal (abdomen) mesothelioma, CT scans are still the most useful imaging study for diagnosing peritoneal mesothelioma.
Physicians can learn several important things about mesothelioma from a CT scan. While a tissue biopsy is necessary for a definitive diagnosis, a CT scan can strongly suggest the diagnosis or even rule out a mesothelioma diagnosis altogether. A CT scan can also be used to help estimate the stage of the mesothelioma. Finally, information obtained from the CT image can help physicians determine whether the tumor can or should be removed with surgery.
Magnetic Resonance Imaging (MRI)
An MRI is similar to a CT scan in that a person is enclosed within a large, circular device while lying down. However, instead of using X-rays, an MRI uses a powerful magnet to create cross-section images of a person’s body. These images can be stacked to form a 3D model of the patient’s internal anatomy. With newer, more powerful magnets, MRI devices can produce anatomical images with incredibly high resolution. Thus, MRIs can provide images of the chest and abdomen that are far more detailed than even a CT scan. Also, because MRIs use magnets instead of X-rays, patients are not exposed to potentially dangerous radiation.
Because of its higher resolution, an MRI may be a bit better at detecting mesothelioma than a CT scan. In particular, MRIs can help detect cases in which mesothelioma has metastasized (spread to other parts of the body), whereas CT scans may not. An MRI may also be preferred for patients who cannot tolerate certain dyes used during CT scans.
The major disadvantage of an MRI is that it takes much longer than a CT scan, which can be uncomfortable and cause anxiety. MRIs are also considerably more expensive than CT scans.
Positron Emission Tomography (PET) Scan
A PET scan works differently than other imaging techniques. Instead of exposing a patient to X-rays or a strong magnetic field, the energy detected during a PET scan comes an intravenous injection of a radioactive isotope, which is detected by the PET scanner.
Typically, the radioactive isotope is embedded within a molecule of glucose (i.e., sugar). Since tumor cells, including mesothelioma cells, are more metabolically active than normal cells, they require more glucose for energy. Tumor cells in the body will take up more of the radioactive glucose and create a stronger signal on the PET scanner. Nuclear medicine specialists can detect the presence of tumors and see if the cancer has invaded or spread to other regions of the body.
PET scans can be useful in diagnosing malignant pleural mesothelioma and distinguishing between benign and malignant lung diseases in general. Moreover, PET scans may be useful in determining the prognosis of patients with malignant pleural mesothelioma. PET scanners are sensitive enough to detect small increases in metabolic activity, which means they can detect even extremely small collections of cancer cells in remote locations in the body.
The major limitation of a PET scan is that the resolution of the images it produces is relatively low. Consequently, most modern cancer centers use a dual-imaging approach that combines a PET scan with a CT scan. A dual PET-CT scan provides physicians. With a high-resolution 3D image of the patient, along with detailed information about the location of cancer cells throughout the body. Numerous studies have shown that combined PET-CT scans are the most reliable imaging technique for diagnosing and staging pleural mesothelioma. This imaging technology is less valuable in the diagnosis and staging of peritoneal mesothelioma, but may be helpful in certain cases.