About SPECT Imaging
What is SPECT imaging?
SPECT stands for single photon emission computed tomography. It is a nuclear medicine procedure that is widely used to study heart, liver, thyroid, bone, and brain problems. Brain SPECT imaging gives you and your doctor information on the blood flow and activity patterns of your brain.
What is the purpose of the brain SPECT imaging procedure?
Brain SPECT imaging is a proven and reliable measure of brain blood flow and activity; therefore, it is used as a tool in the evaluation and treatment process at Amen Clinics. SPECT imaging effectively shows us the patterns of activity in your brain. It allows our physicians to observe three things: areas of the brain that work well; areas of the brain that work too hard; and areas of the brain that don’t work hard enough.
Why are SPECT studies ordered?
Some of the common reasons include:
- Evaluating the effects of mild, moderate and severe head trauma.
- Evaluating atypical, unresponsive or mixed psychiatric conditions.
- Evaluating the presence of an underlying organic brain condition that contributes to behavioral or emotional disturbances.
- Evaluating aggressive or suicidal behavior.
- Evaluating the extent of brain impairment caused by drug or alcohol abuse or other toxic exposure.
- Subtyping the physiology of underlying mood disorders, anxiety disorders, or attention deficit disorders.
- Brain Optimization/Brain Health Checkup.
- Evaluating suspected seizure activity.
- Evaluating suspected cerebral vascular disease (such as stroke).
- Following-up to evaluate the physiological effectiveness of treatment.
Is the use of brain SPECT imaging accepted in the medical community?
Science has repeatedly recognized the value of brain SPECT imaging for assessing brain function. There is a robust amount of scientific data that support the utility of SPECT for revealing the blood flow patterns underlying many different types of brain problems. Dr. Daniel Amen has authored or co-authored more than 70 peer-reviewed published research studies on brain SPECT imaging.
Are there alternatives to having a SPECT study?
In our opinion, SPECT is the most clinically useful study of brain function for the conditions listed above. There are other studies, such as positron emission tomography (PET) and functional MRI (fMRI); however, they are considerably more costly and are performed mostly in research settings.
Where else can I get a brain SPECT scan?
Brain SPECT imaging for neuropsychiatric indications is only offered in a few centers around the country. We believe our clinics are the best places in the world to have this study done because of our 30-plus years of experience and extensive research on this subject, in addition to the comprehensive individualized treatment plans we give to our patients.
What is it like to get a SPECT scan?
Each scan takes approximately 20 minutes, and you will have two scans on separate days: one while your brain is at rest, and one while focused on a concentration task. For each scan, you will sit in a quiet room and a small IV line will be placed in your arm. During the “concentration” scan, you will take a 15-20-minute computerized test that measures your attention and focus. For the “baseline” scan, you will be instructed to sit quietly and relax. During this period of time (whether you are taking the computer test or relaxing), the imaging solution will be injected through the IV. Once the imaging solution has been absorbed, you will lie down in the scan machine, which has three cameras that will rotate around your head.
Why do you recommend two scans?
Two scans will allow us to evaluate the changes in brain blood flow patterns from a resting state to a concentration state.
Are there any side effects or risks to the study?
Since a SPECT scan is a nuclear medicine procedure, it requires the injection of a very small amount of a radioisotope through a small needle into a vein in the arm. The IV is only inserted for about 10 minutes, and numbing cream is available. The medicine we inject is not an iodine-based dye; therefore, people typically do not have allergic responses to it. The average radiation exposure for one SPECT scan is 0.7 rem. This exposure is similar to the amount from a nuclear bone scan or CT scan—both of which are routinely ordered for many common medical conditions (i.e. bone fractures or head trauma).
Will the SPECT study give a diagnosis?
No. A SPECT study by itself will not give a diagnosis. In fact, no imaging study by itself is a “doctor in a box” that can give accurate diagnoses on individual patients. SPECT imaging helps the physician understand more about the specific function of the brain. Each person’s brain is unique which may lead to varied responses to treatment. At Amen Clinics, diagnoses about specific conditions are made through a combination of clinical history and personal interview, information from family members (if available), questionnaires and checklists, SPECT studies and neuropsychological tests.
How is radiation used in SPECT?
The radiotracer that we use for SPECT is called Technetium 99m. Its signal is detected by the scanner. Combining Tc99m with other molecules (like HMPAO – “Ceretec”) allows Tc99m to enter specific/desired tissues. This allows us to understand the functioning of that tissue.
SPECT requires an injection of 20 to 25mCi (millicuries, the measure of radioactivity inherent to a radiopharmaceutical – in our case, Technetium 99m). The biological effect a dose of radioactivity has on tissues (effective dose), cannot be linearly extrapolated from the radioactivity of a dose of administered radioisotope, and it varies with tissues, so a total radioactivity exposure (effective dose) for the whole body is calculated. This is measured in rem (Roentgen equivalents to man) or Sieverts (one Sievert = 100 rem).
The average radiation exposure for one SPECT scan is 0.7 rem. Two of our SPECT scans are roughly equivalent to, or a bit less than, one CT scan of the abdomen or pelvis (about 0.7, depending on protocol).
This amount of exposure is well below the cut-off level (10.0 rem) for any known potential or observable health risks.
About 5% of the total dose goes to the brain. About 40% of the tracer is excreted within minutes by the kidneys and the remainder by the gallbladder over about 24 hours. Tc99m has a half-life of just over 6 hours. We always encourage patients to drink plenty of water.
I have heard SPECT has low resolution. Some have referred to it as a “poor man’s PET study.”
There’s an advantage of using SPECT (as opposed to PET) in the way we do things: When our clinicians sit down to read a SPECT scan, they use unsmoothed tomographic data acquired at a resolution of 6.6 millimeters. Compare this to cases where PET is used in a clinical setting: the resolution is at best between six and eight millimeters. Clinical SPECT is, in fact, of better resolution. Now, while it’s true that the university PET scanners get marginally better resolution than we do (of about 4.5 millimeters), nobody reads these PET scans clinically like we do. Instead, they use them in statistical comparisons against groups of other scans, in which case their resolution smoothed to7mm, and in many cases, they’re smoothed to a resolution as low as 10mm. At any rate, clinical SPECT wins again.
Some physicians say, “I don’t need a scan for diagnosis, I can tell clinically.” Is this true?
Often, well-trained physicians can tell clinically. But that is not when you order a SPECT scan. You order scans when you are confused, the patient hasn’t responded to your best treatment or the patient’s situation is complicated.
How consistent are the results from day-to-day?
There is less than 3% variability in SPECT scans over time for the same activity. Our own clinical experience, scanning people sequentially, and sometimes 12 years apart, is that SPECT patterns are the same unless you do something to change the brain. SPECT is a reproducible and reliable method for sequential evaluation.
