One of the most useful tests in the evaluation of FTD is magnetic resonance imaging (MRI). MRI uses magnetic fields and radio waves, without any X-rays, to produce images of the inside of your body. It is non-invasive and considered very safe, but some people with metal implants and cardiac pacemakers are unable to have MRI. Talk to your doctor or the imaging technician if you have any concerns about entering the magnet. Some people find lying in the scanner produces anxiety or claustrophobia because of the tube-like shape or the loud sounds during the scan. Sedation may be available to you if needed, but relaxation techniques like deep breathing, visualization and meditation can also help. Some MRI scanners allow you to listen to music or watch a movie. To get the best pictures, you need to be as still as possible while in the scanner.
FTD leads to loss of brain tissue that is visible on MRI scans of patients while patients are still alive. Different areas of the brain are affected (early on) by different types of FTD:
- FTD (frontal lobes): responsible for personality, judgment and planning/organization
- SD (anterior temporal lobes): store general information about the world, very important for language and face recognition, critical for understanding the emotions of others
- PNFA (left frontal lobe): produces spoken language
A computed tomography (CT) scan is similar to the MRI but does not image brain structure with the fine precision of MR. A CT scan is an X-ray technique that produces cross-sectional images of the inside of your body or head. Typically scans last only a few minutes, during which time you should lie still. You may hear some whirring and clicking noises during this test, which is normal. In order to make the CT image, you will be briefly exposed to X-ray radiation, so be sure to discuss any concerns you have with your doctor.
Functional scans, by single-photon emission computed tomography (SPECT), functional MRI (fMRI) or positron emission tomography (PET), typically demonstrate decreased activity in the frontal and temporal lobes. Amyloid imaging with PET can tell whether the patient is suffering from Alzheimer's disease, versus frontotemporal dementia. This is still experimental but can be obtained in some centers.
A SPECT scan shows how blood flows through arteries in the brain. A radioactive material (tracer) is injected into a vein in the arm, and then the scanner detects the movement of the tracer through the brain and computes the brain activity. Brain areas affected by FTD show diminished activity. As with any neuroimaging procedure, you will need to lie as still as possible so that the machine can obtain accurate pictures. After the scan, be sure to drink plenty of fluids. Most of the radioactive tracer leaves your body through your urine within a few hours after your SPECT scan. Talk to your doctor if you're concerned about your exposure to radiation during a SPECT scan.
Functional MRI is a special type of scan done in the MRI scanner. It shows changes in blood flow in the brain, which represent active areas of the brain using more or less blood to perform certain tasks. The experience and equipment is similar to that of a structural MRI scan.
PET scans show the activity of tissues by measuring the energy usage (metabolic activity) of your brain. Like a SPECT scan, PET combines a brain camera and a radioactive material (tracer). The tracer is what allows doctors to see how your body tissues absorb and use different chemicals in real time. 30-45 minutes prior to the scan, a tracer is injected into your bloodstream. Once the tracer has had time to reach your brain, you'll lie on a table that moves slowly through the scanner. By detecting metabolic changes in the brain, your doctor can see which areas are healthy versus dysfunctional. Be sure to remain as still as possible so that the machine can get accurate pictures. Depending on the information your doctor needs, you may be asked to perform certain tasks like read or speak to activate specific areas of your brain. Once the scan is complete, be sure to drink plenty of fluids to flush out any tracer left in your body.