Every study in this series answers a different question. Structural MRI asks whether tissue is damaged. Diffusion imaging asks whether the wiring is organized. SPECT asks something else entirely: **which parts of this brain are getting blood, and which parts are working too hard or not hard enough.**
It is also the most contested modality in the protocol, and I would rather give you the argument than the sales pitch.
How Does a SPECT Scan Work?
Single-photon emission computed tomography begins with a small amount of radiotracer injected into a vein. The tracer distributes according to blood flow, and because regional blood flow tracks regional neural activity, where the tracer accumulates is a proxy for where the brain is working.
The scanner then images that distribution and produces a three-dimensional map.
Two acquisitions are typical: one at rest, and one during a concentration task. The second matters more than it sounds. A brain can look adequate at idle and fall apart under demand, which is precisely the complaint people describe — that they are fine until they have to sustain effort, and then they are not.
What Does It Show After a Head Injury?
The findings that recur are patterns of reduced perfusion, most often in the frontal and temporal lobes, alongside regions of overactivity and shifts in cerebellar and brainstem flow.
What draws me to it is that the pattern tends to correspond to how the patient actually describes feeling. Reduced frontal perfusion in someone reporting that planning, sequencing, and holding attention have become effortful is a coherent picture. That correspondence is not proof of causation, but it is a different experience from handing someone a normal structural scan and having nothing to say about why they cannot work a full day.
There is a published body of work here. Researchers have reported that perfusion abnormalities alone distinguish professional football players from a healthy population, and separate work has examined long-term brain function in retired NFL players using this modality (Amen et al., 2011; Amen et al., 2016). A systematic review of SPECT in traumatic brain injury drew on 374 eligible articles and reported that positive predictive value rose from 59% to 95% at one-year follow-up, that the most frequently abnormal regions were frontal (94%) and temporal (77%), and that SPECT outperformed both CT and MRI in the studies reviewed (Raji et al., 2014).
Read that paragraph and you would conclude the case is settled. It is not, and the next section is why.
Why Is SPECT Contested?
I am going to lay this out fully, because you will find it eventually and you should hear it from me first.
**The American College of Radiology rates SPECT "usually not appropriate" for head trauma.** That rating applies across all head-trauma scenarios in its appropriateness criteria updates, including chronic cases with cognitive deficits. It is the body that sets appropriateness standards for imaging in the United States, and it is not a marginal voice (Wortzel, 2022).
**The strongest supportive review is not independent.** Daniel Amen is a listed author on the Raji systematic review, and Amen Clinics produced a substantial share of the primary literature that review evaluates. That does not make the findings false. It does mean the review is not an outside assessment of the work, and "Level IIA evidence" in that paper is the authors' own grading rather than a society's.
**A headline number did not replicate.** A widely cited study reported that functional imaging separated traumatic brain injury from post-traumatic stress disorder with "100% sensitivity, specificity and accuracy" in a focused dataset (Amen et al., 2015). In the same paper, the large community sample — many thousands of scans rather than a few hundred — produced lower sensitivity, specificity, and accuracy. The authors also state plainly that the analysis was retrospective and that higher levels of evidence would come from prospective or randomized designs. Anyone quoting the 100% figure without the second half of that sentence is misleading you.
**There is a named critique in a top-tier journal.** A commentary in the *American Journal of Psychiatry* challenged the diagnostic claims made for resting SPECT in psychiatry, citing the absence of empirical data supporting them and raising the ethical question of administering a radioactive isotope without sound clinical rationale (Adinoff & Devous, 2010).
And there is a real cost side. SPECT involves an injected radiotracer and a radiation dose, which is a meaningfully different proposition from an MRI sequence.
So Why Do We Still Use It?
Because the criticism above is aimed at a claim I am not making.
The ACR rating addresses whether SPECT should be a routine, standalone diagnostic for head trauma. I agree with that rating on those terms. If someone offers you a SPECT scan as the test that will diagnose your concussion, that is not supportable.
What we use it for is narrower. It is one input in an integrated protocol, ordered when structural imaging has come back unremarkable in a symptomatic patient, and read alongside the other studies rather than in place of them. Its value is that it images **function under load** when everything else has imaged anatomy at rest, and it is the only study in our protocol that does. Everything else in the series — [structural imaging of the junction](post-what-an-mri-of-the-craniocervical-junction-shows.html) included — photographs a system that is holding still.
That is my clinical position, and I present it as a position rather than as a settled matter. The honest summary is that SPECT shows something real, that what it shows correlates with symptoms more often than anatomy does, and that the field has not established it as a diagnostic at the individual-patient level.
Does This Help Separate a Brain Problem From a Neck Problem?
This is where it earns its place for me, and it cuts against my own bias rather than for it.
Most of my clinical work concerns the craniocervical junction. A protocol that could only ever return "it's the neck" would be worthless, and I would have no way of knowing when I am the wrong person for a case.
Perfusion imaging is a brain study. It says nothing about ligaments. When a symptomatic patient shows a marked frontal and temporal perfusion pattern alongside a craniocervical examination that is genuinely unremarkable, that is information pointing away from my territory, and the appropriate response is to say so and refer.
The converse is equally useful. A perfusion pattern that concentrates in cerebellar and brainstem flow, in a patient with a measurably displaced junction, [restricted cerebrospinal fluid movement at the foramen magnum](post-watching-spinal-fluid-move-with-cine-mri.html), and position-dependent neurological findings, reads as a coherent story about supply and drainage rather than about damaged tissue.
Sometimes there really is a brain problem. Saying that out loud, and acting on it, is part of what makes the rest of the assessment trustworthy.
What Should You Ask Before Getting One?
Three questions, and they apply to any facility offering this study.
**What specific question is this scan being ordered to answer?** If the answer is "to see what's going on," that is not a clinical indication.
**What will change depending on the result?** A study that cannot alter the plan is a study you do not need.
**How does this fit with what the other imaging showed?** SPECT read in isolation is where the overreach lives. Read as one of several convergent findings, it contributes something the others cannot.
You are also entitled to ask what the radiation dose is and whether a non-radiation alternative would answer the same question. Arterial spin labeling MRI measures perfusion by magnetically labeling your own blood, with no tracer and no radiation. It is less established for this application at present, but it is where this part of the field is heading, and it is a reasonable thing to ask about.
Has Your Imaging Only Shown Anatomy?
If every scan you have had imaged structure at rest and came back normal while you continued to struggle under any real cognitive demand, a study that measures function under load is asking a different question.
Ordering it deliberately, reading it against everything else, and telling you honestly what it does and does not establish is the work we do at Cerebral. If you'd like a real evaluation, we're here.
References
- Amen DG, Raji CA, Willeumier K, et al. Functional neuroimaging distinguishes posttraumatic stress disorder from traumatic brain injury in focused and large community datasets. *PLoS One*. 2015;10(7):e0129659. https://pubmed.ncbi.nlm.nih.gov/26132293/
- Amen DG, Newberg A, Thatcher R, et al. Impact of playing American professional football on long-term brain function. *Journal of Neuropsychiatry and Clinical Neurosciences*. 2011;23(1):98–106. https://pubmed.ncbi.nlm.nih.gov/21304145/
- Amen DG, Willeumier K, Omalu B, et al. Perfusion neuroimaging abnormalities alone distinguish National Football League players from a healthy population. *Journal of Alzheimer's Disease*. 2016;53(1):237–241. https://pubmed.ncbi.nlm.nih.gov/27128374/
- Raji CA, Tarzwell R, Pavel D, et al. Clinical utility of SPECT neuroimaging in the diagnosis and treatment of traumatic brain injury: a systematic review. *PLoS One*. 2014;9(3):e91088. https://pubmed.ncbi.nlm.nih.gov/24646878/
- Wortzel HS. Advanced neuroimaging and mild traumatic brain injury litigation, revisited. *Journal of the American Academy of Psychiatry and the Law*. 2022;50(3):336–341. https://jaapl.org/content/50/3/336
- Wortzel HS, Filley CM, Anderson CA, et al. Forensic applications of cerebral single photon emission computed tomography in mild traumatic brain injury. *Journal of the American Academy of Psychiatry and the Law*. 2008;36(3):310–322. https://pubmed.ncbi.nlm.nih.gov/18802178/
- Adinoff B, Devous M. Scientifically unfounded claims in diagnosing and treating patients. *American Journal of Psychiatry*. 2010;167(5):598. https://pubmed.ncbi.nlm.nih.gov/20439400/