CIMT and CAC are both scans that look for early artery disease, but they look in different places with different tools. CIMT is an ultrasound of the carotid arteries in your neck. CAC is a CT scan that measures calcified plaque in the arteries of your heart.
They are not equal in what they can tell you. The calcium score has much stronger evidence for predicting heart attacks. CIMT has no radiation and can be repeated freely, but US guidance does not recommend it for routine risk prediction. Here is how the two compare, and why some people have both.
Key takeaways
- CIMT is an ultrasound of the neck arteries, and CAC is a CT scan that measures calcified plaque in the heart arteries.
- Of the two, the calcium score is far better supported as a predictor of heart attacks.
- CIMT involves no radiation, but US guidance does not recommend it for routine risk prediction.
- Carotid ultrasound is more informative when it shows actual plaque, and small changes on repeat CIMT scans should not be over-read.
- If the two scans disagree, the calcium score carries more weight for heart risk, and imaging is optional.
What each scan images
CIMT stands for carotid intima-media thickness. A technician moves an ultrasound probe over the side of your neck and measures the thickness of the two inner layers of the carotid artery wall. A careful scan also notes whether any carotid plaque is present. It is painless and uses the same kind of technology as a pregnancy ultrasound.
CAC stands for coronary artery calcium. A CT scanner takes images of your heart in a visit of under 15 minutes, with no injection and no contrast dye. Software adds up the calcium found in the coronary artery walls and reports a single score. Calcium marks plaque that has been in place for a while.
So one scan looks at wall thickness in the neck, and the other counts calcified plaque in the heart. Each has its own guide: CIMT ultrasound and the coronary calcium score.
CIMT and CAC compared
| Feature | CIMT | CAC score |
|---|---|---|
| Arteries examined | Carotid arteries in the neck | Coronary arteries of the heart |
| Technology | Ultrasound | Low-dose CT |
| What it measures | Artery wall thickness, plus carotid plaque if present | Amount of calcified plaque |
| Radiation | None | About 1 to 1.5 mSv |
| Evidence for predicting heart events | Weak for wall thickness. Better when plaque is seen | Strong and consistent |
| Guideline position | Not recommended for routine risk prediction | Reasonable when a treatment decision is uncertain |
| Main blind spot | Wall thickness alone predicts events poorly | Misses plaque that has not calcified |
How strong is the evidence for each?
This is where the two scans part ways, and it is worth being direct about it.
For the calcium score, the evidence is strong. Large studies that followed people for a decade or more have found that heart attack and stroke rates rise step by step with the score. Our calcium score guide walks through those results.
For CIMT, the evidence is disappointing. A pooled analysis of 14 population studies covering 45,828 people found that adding carotid wall thickness to a standard risk score improved ten-year prediction only slightly, and the authors judged the gain unlikely to be of clinical importance.1 The 2013 ACC/AHA risk assessment guideline did not recommend CIMT for routine assessment of the risk of a first cardiovascular event.2
The two have also been compared directly. In MESA, a US study of about 6,800 adults, the presence of coronary calcium improved prediction of heart disease more than carotid plaque or a high wall thickness did. A wall thickness at or above the 75th percentile, taken alone, did not predict events.3
Where carotid ultrasound does better: plaque and stroke
Carotid ultrasound is more useful when it finds actual plaque. A meta-analysis of 11 population studies with more than 54,000 participants found that carotid plaque predicted future heart attacks more accurately than wall thickness did.4
The carotid arteries also supply the brain. In the MESA comparison, carotid plaque improved prediction of stroke and mini-stroke, while coronary calcium did not add to it.3 That is a real, if modest, point in favor of looking at the neck as well as the heart.
If you have a CIMT, ask whether the report describes plaque, not only a thickness number or a "vascular age". The plaque finding is the part with better evidence behind it.
Radiation, cost and repeat scans
Radiation. CIMT has none. A calcium scan involves a small dose of about 1 to 1.5 mSv, which is one reason it is not repeated often.5
Cost. In Cardio Res-Q, the calcium scan is done at an outside imaging facility as a separate self-pay study, typically $100 to $200. The CIMT is part of the Enhanced Assessment, done in the clinic's Conshohocken office, and is not priced separately here. Prices for either scan elsewhere vary, so ask before you book.
Repeating. Calcium builds slowly, and our program page describes the calcium score as typically done about once every five years. CIMT can be repeated sooner because there is no radiation.
Be cautious about reading too much into small changes on repeat CIMT scans. A pooled analysis of 16 studies with nearly 37,000 people found that the change in carotid wall thickness between two scans did not predict cardiovascular events, and where people were scanned several times, the measured change was not consistent from one interval to the next.6 A repeat CIMT can be a useful prompt to stay on track. It is not proven as a way to tell whether treatment is working.
Why the Cardio Res-Q Enhanced Assessment includes both
The two scans cover different territory. The calcium score is the stronger predictor of heart events, but it sees only calcified plaque in the heart arteries. A carotid ultrasound looks at a different artery, involves no radiation, and can show plaque that has not calcified.
Together they give a baseline of what is physically present in two artery beds, to set beside your blood work. Neither replaces the labs, and neither is a diagnosis. A normal CIMT does not cancel a high calcium score, and if the two disagree, the calcium score carries more weight for heart risk.
Imaging is also optional. For some people the lab results and history are enough to decide on a plan, and a scan would not change it.
The Enhanced Assessment ($999) includes both a CIMT ultrasound and a coronary calcium score, along with Dr. Varano's clinical evaluation, advanced labs and a personalized heart protection plan. The Comprehensive Assessment ($775) covers the evaluation, labs and plan without the imaging.
To decide between them, read Comprehensive vs. Enhanced: which to choose. When you are ready, book through the Cardio Res-Q program page.
Are You a Candidate for Cardio Res-Q?
Three quick questions about the risk factors we screen for. Your answers stay between you and the clinic.
Frequently asked questions
If I can only have one scan, which should it be?
For predicting heart attack risk in an adult without symptoms, the calcium score has the stronger evidence. CIMT may be preferred when avoiding radiation is the priority, but its ability to predict events is weaker. Your clinician can tell you whether either scan would change your plan.
My CIMT was normal. Can I skip the calcium score?
A normal CIMT does not rule out plaque in the heart arteries. The two scans look at different vessels, and wall thickness in the neck is not a reliable stand-in for coronary plaque.
Is CIMT the same as a carotid Doppler?
No. A carotid Doppler or duplex scan is a diagnostic test that looks for significant narrowing and measures blood flow, usually in people with symptoms or a known problem. CIMT measures wall thickness as a marker of early artery change.
Does either scan need preparation?
Neither needs an injection or contrast dye. The imaging center will give you instructions for the calcium scan, and our team will tell you how to prepare for the CIMT.
Related reading
This article is for general education and is not medical advice. Decisions about testing and medication should be made with your clinician. If you have chest pain or other symptoms of a heart attack, call 911.
