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

If you have neurological or neuropsychiatric issues, brain imaging may be helpful. However, there are many types of brain imaging—a veritable alphabet soup that includes CT, MRI, fMRI, and SPECT. This can make it 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:

• Structural brain imaging: These brain scans look at the structure, or architecture, of the brain.
• Functional brain imaging: These scans evaluate how your brain is working.

Which type is best for your needs? It depends. This blog will cover the basics about structural and functional brain imaging, as well as the differences between two types of functional brain imaging techniques—functional MRI and SPECT. Because SPECT looks at the function of the entire brain, a single SPECT scanning process can provide important details about the biological underpinnings of a patient’s symptoms.

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WHAT IS 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. CT scans and MRI scans 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. What structural imaging procedures do not provide is detailed information about how a brain is actually working.

WHAT IS FUNCTIONAL BRAIN IMAGING?

Functional brain imaging looks at how your brain works. 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, including:

• SPECT (single photon emission computed tomography)
• fMRI (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 which has a powerful magnet that is 10,000 times stronger that 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 fMRI scans 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 IMAGING WORKS

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

• Areas of the brain that work well
• Areas that are underactive
• Area that are overactive

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 SPECT imaging, a patient will sit in a quiet room and a small 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, a doctor evaluates this information along with the results of neuropsychological testing as well as the patient’s clinical history. Based on all of this information, the mental health professional creates a personalized 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 clinical 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
• Overactivity in the deep limbic system
• Underactivity in the 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

Can functional MRI (fMRI) be used instead of a SPECT scan? In cases where brain imaging is needed to evaluate brain function as it relates to surgery planning or risk for the biopsy or removal of brain tumors or for epilepsy surgery, fMRI may be most beneficial. SPECT, on the other hand, is used to identify abnormal brain function that contributes to a multitude of neurological and psychiatric disorders. Anyone struggling with memory loss or mental health disorders may benefit more from SPECT, which provides valuable information and can greatly improve 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.