Brain Imaging: Functional MRI vs. SPECT Scans—What’s the Difference?

There are many types of brain imaging— a veritable alphabet soup that includes CT, MRI, fMRI, and SPECT—so it can be confusing to know which one is best for your specific concerns. An easy way to demystify this is by understanding that imaging is generally divided into two categories. One looks at structure, kind of like the architecture of the body or its specific parts, and the other is function, which tells your doctor how the parts are working.

The Basics of Structural Brain Imaging

Two of the most common types of structural brain imaging are computed tomography (CT or “CAT” scan) and magnetic resonance imaging (MRI). After a head trauma, stroke, or because of severe headaches, a CT or MRI is often done to assess the integrity of the brain’s anatomy. These procedures can identify if any parts of the brain are abnormal in size, if anything is missing, or if something is there that shouldn’t be, such as a blood clot or tumor.

The Big Difference Between Structural and Functional Brain Imaging

What the structural imaging procedures do not provide is detailed information about how a brain is actually working. This is where functional brain imaging comes in. This type of advanced camera technology is utilized to see how a brain functions by assessing the blood flow and activity in the brain.

There are a few different types of cameras and procedures that are used to do this imaging, and two of them are:

• SPECT—which stands for single-photon emission computed tomography
• fMRI—or functional magnetic resonance imaging

Both modalities provide a lot of detailed information about how well the various areas of the brain work, but there are some big differences in the way they can do this.

How fMRI Works

The technology for fMRI was developed in the early 1990s, and it allows researchers and doctors to see the activity in specific areas of the brain. For the procedure, the patient lies inside a tube that has a powerful magnet that is 10,000 times stronger than the earth’s magnetic field. In a nutshell, fMRI can construct detailed pictures of the brain by combining radiofrequency energy waves and magnetic fields that interact with the magnetic properties in the water molecules of our blood. These real-time images show activity—or blood flow—to certain areas in the brain in response to a particular task.

Depending on what brain functions are being assessed, the patient will be given a specific task to do such as mentally reacting to something with thoughts or feelings. The areas that are activated by the task will “light up” and be captured during the imaging.

However, one of the biggest challenges with using fMRI is that each task looks at only a particular area or circuit in the brain. So for example, if a person had a head injury, each area of the brain that is of concern would have to be assessed with a different task to activate it. Depending on a patient’s symptoms, the doctor might want to analyze the function of these 7 parts of the brain:

• Prefrontal, dorsal lateral frontal, and orbital frontal cortex
• Right and left temporal lobes
• Cerebellum
• Occipital lobe

And although the blood flow information that is obtained can be very helpful, using fMRI to do this can be quite time-consuming and expensive. Brain SPECT, on the other hand, can reveal blood flow and activity of the whole brain with just a single scan. Here’s why.

How Brain SPECT Works

Like fMRI, brain SPECT imaging is used to evaluate blood flow and activity throughout the brain. A SPECT scan provides 3 important pieces of information:

• Areas of the brain that work well
• Areas that are underactive
• Areas that are too active

SPECT is a nuclear medicine procedure that has been used by the doctors at Amen Clinics for more than 30 years to help them more clearly understand the function of their patients’ brains.

The SPECT Scan Process is Easy

To prepare for the imaging, a patient will sit in a quiet room and a little IV will be placed in their arm. An imaging solution with a very small amount of a radioactive tracer is inserted into the IV The solution does not have iodine, so rarely does anyone have an allergic reaction to it. The tracer is taken up into the brain cells within a few minutes of the injection and creates a “snapshot” of the patient’s brain activity.

About 30 minutes after the injection, the patient will be taken into the camera room and lie down on the imaging table for about 20 minutes while the camera’s detectors rotate around their head—patients do not have to go into a tube. The camera gathers data from the “snapshot” of brain activity created from the injection.

Once the images have been processed, they are read by a highly skilled physician who writes a detailed report about the patient’s brain function. At Amen Clinics, this information is then evaluated by the doctor, along with other testing and the patient’s clinical history, to create a comprehensive treatment plan for the patient.

Brain SPECT Scans Provide Important Information

Because SPECT looks at the function of the entire brain, a single SPECT scanning process can provide important details about the biological underpinnings of symptoms. For example, if a patient has depression, without looking at the brain it would be hard to know if it is being caused by:

• An undiagnosed head injury
• Toxic exposure
• Inflammation or infection
• Overactive limbic area
• Underactive prefrontal cortex

SPECT scans are an efficient and relatively simple way to identify any abnormal patterns in the brain that are driving a patient’s symptoms. Recently, the Canadian Association of Nuclear Medicine published their new practice guidelines which endorse the use of brain SPECT imaging for the assessment of:

• Neuropsychiatric disorders, such as ADHD, bipolar disorder, depression, obsessive compulsive disorder (OCD), and posttraumatic stress disorder (PTSD)
• Suspected dementia, such as Alzheimer’s disease, frontal temporal lobe dementia, vascular dementia, and mild cognitive impairment
• Traumatic brain injury
• Substance abuse
• Stroke

Both fMRI and SPECT are fascinating tools of medical imaging technology. And while each assess brain activity, in the clinical setting, fMRI is largely used to look at specific areas of brain function as they relate to surgery planning and risk for the biopsy or removal of brain tumors or for epilepsy surgery.

SPECT, on the other hand, is used to identify abnormal brain function that contributes to a multitude of neurological and psychiatric disorders, thereby providing valuable information that greatly improves patient outcomes.

Mental health issues can’t wait. At Amen Clinics, we’re here for you. We offer in-clinic brain scanning and appointments, as well as mental telehealth, remote clinical evaluations, and video therapy for adults, children, and couples. Find out more by speaking to a specialist today at 888-288-9834 or visit our contact page here.