Functional Imaging: What Is It?
Functional imaging is a way of using new technology to see changes in blood flow and other activity in a specific part of the body. While more well-known methods, such as the CT and MRI, look at physical things such as bones and organs, functional imaging looks at activity in a certain part of the body. What exactly does “activity” mean? It can mean several things – blood flowing through a blood vessel; or the movement of water or chemicals inside of a tumor. Activity refers to something that is moving, which normal imaging methods cannot capture.
A big challenge in planning cancer treatment is that the edges of tumors are often not easily seen. As a tumor grows, it affects nearby cells and tissues, making it hard to know where the tumor begins and where it ends. As a result, doctors often treat a large area around a tumor. While this treats the cancer, it also may hurt normal cells around the tumor.
Functional imaging is a tool made by teams of researchers that is used by physicists, chemists, mathematicians, computer scientists, and doctors. It allows doctors to see a tumor, as well as the activity in and around it. It captures what the cancer is doing – not just its location. This type of imaging can be used for many types of disease, including cancer (which includes mesothelioma), high cholesterol, Alzheimer’s disease, heart disease, and others.
The Use of “Tracers” in Functional Imaging
Functional imaging uses tracers to detect what is happening in a certain part of the body. Tracers are similar to chemicals in the body, such as glucose or other fluids in the blood. These tracers act differently in tumors than they do in normal cells. They light up on functional images as they flow through certain organs or body parts. What this affords the doctor, is the ability to then see what is actually happening in a certain part of the body, rather than just looking at a picture of it.
Types of Functional Imaging
There are many different machines that can be used for functional imaging, such as those seen in the list below:
Types of Functional Imaging
- Positron emission tomography (PET)
- Single photon emission computed tomography (SPECT)
- Computed tomography (CT) perfusion imaging
- Functional magnetic resonance imaging (fMRI)
- Diffusion-weighted MRI (DWI)
- Dynamic contrast-enhanced MRI (DCE-MRI)
- Magnetic particle imaging (MPI)
- Optical imaging
- Functional photoacoustic microscopy (fPAM)
In many cases, functional imaging will combine MRI or CT with a PET scan. The MRI/CT shows the shape and place of a tumor. The PET scan shows its activity. Together, doctors can see a clear picture of the tumor itself as well as what it is doing. They can then more easily treat the cancer without affecting nearby parts of the body. Doctors use information from these studies to plan the best treatment for each patient.
Using Functional Imaging in Mesothelioma
In mesothelioma, the functional imaging methods described above may be more useful than more common imaging methods such as a CT or an MRI. By using tracers, doctors can use PET scans with other imaging techniques to not only see the size, shape, and location of a tumor, but also to understand many other processes. For example, functional imaging can determine the activity level (metabolism) of a certain mesothelioma tumor. Metabolism is usually higher in mesothelioma cells than nearby cells.
Pleural mesothelioma, a disease caused by exposure to asbestos, occurs when tumors form on the thin sheet of lining surrounding the chest cavity. A problem with this type of mesothelioma is that the tumors are often shaped differently from other tumors. There are often many small tumors with different sizes and shapes. This makes them very hard to see and makes it very hard to know what they’re doing.
In pleural mesothelioma, the cancer spreads out in a flat pattern in the chest. Most other cancers appear as ball-shaped tumors. As a result, it is difficult to put this type of mesothelioma into a staging category and then give the right kind of treatment. Also, as thin, flat sheets, this type of cancer can enclose organs and be easily hidden. This is why using functional imaging to look at processes within the cancer, rather than just shape and size, is very useful.
New Research in Mesothelioma
Dr. Lin Cheng and several others located at the Institute of Cancer Research and other hospitals in the United Kingdom published an article in August of 2015. This article looked specifically at functional imaging in mesothelioma. The authors looked at common imaging tests such as CT and MRI. But they also looked at newer functional imaging tests such as PET, DWI, and DCE-MRI. They wanted to see how such imagining tests might be used for pleural mesothelioma.
“By quantifying how these measurements change with treatment, it is possible to observe treatment effects.”
Lin Cheng, MD; Institute of Cancer Research, United Kingdom
More importantly, they talked about how these images would change when a treatment was given. This is important, as it could show how a treatment is working. For example, PET imaging uses tracers, which are absorbed by mesothelioma cells. When the test is given before and after treatment, the amount of absorption on the scan can give doctors an idea of how well the treatment is working. Similarly, DWI looks at the movement of water molecules in mesothelioma tumors. By looking at this movement, it is easier for doctors to see whether a treatment is working or not.
Treatment plans for mesothelioma must be developed for each individual patient. No two patients are exactly the same. Doctors need to know sizes, shapes, locations, and activity levels of tumors in mesothelioma in order to give the best treatment for each individual patient. It is important for doctors to have as much information as possible so that they can alter a treatment regimen if it isn’t working.
Future Directions in Mesothelioma Imaging
Since pleural mesothelioma tumors may affect nearby cells and tissue, functional imaging is an important area of future study for this disease. In the past, CT scans alone have been widely used as the main imaging test for mesothelioma. However, CT may underestimate how tumors affect the chest wall. While a normal MRI can provide more information, it doesn’t provide information on the activity of a tumor. Given this, functional imaging techniques are important for getting a better idea of not only the size and shape of a tumor or series of tumors, but activity levels as well.
These methods will hopefully help doctors accurately stage the cancer. From there they can develop a treatment plan with the patient that has the highest potential for success. The authors from the UK study above state that for patients with pleural mesothelioma, newer functional imaging tests can lead to better evaluation and better treatment plans for patients.
By using tracers, functional imaging tests can provide much more information that can be used to look at whether a tumor has grown, shrunk, or returned. With functional imaging, the many types of healthcare workers that treat pleural mesothelioma – such as cancer doctors, surgeons, and radiation therapists – are better able to offer effective treatments to patients. This is because they are able to learn much more about the cancer itself.