Photon-Counting CT: A Sharper Window Into The Heart

21 Sep 2026 | Murmurs Newsletter

By Asst Prof Natalie Koh, Senior Consultant, Cardiology

Computed tomography, or CT, has become an important part of modern heart care. For many patients with chest pain or suspected coronary artery disease, CT coronary angiography allows doctors to look directly at the heart arteries without inserting a catheter into the body. Over the years, cardiac CT has become faster, safer and more accurate. Photon-counting CT is the next major step in this evolution.

What is photon-counting CT?

A conventional CT scanner uses X-rays that pass through the body to create detailed cross-sectional images. In most current scanners, the detector first converts X-rays into light, and then into an electrical signal. Photon-counting CT works differently. It detects individual X-ray photons more directly and converts them into digital information.

This sounds technical, but the practical difference is easier to understand: photon-counting CT can produce sharper images with less image noise. It can also separate different X-ray energy levels, giving doctors more information from the same scan. For patients, this may mean clearer images, improved diagnostic confidence and, in selected cases, lower radiation exposure.

Why does this matter for the heart?

The heart is one of the most challenging organs to scan. It moves constantly. Its arteries are small, often only a few millimetres wide. Disease may appear as cholesterol-rich plaque, calcium, narrowing of the artery, or changes around previous stents or bypass grafts.

Conventional CT coronary angiography is already a powerful test, especially for ruling out significant coronary artery disease. However, it can be limited in some situations. Heavy calcium can create a "blooming" artefact, where calcium appears larger than it really is and obscures the artery channel. Small vessels and stents can also be difficult to assess. In some patients, this can lead to uncertainty: is the artery truly severely narrowed, or is the scan limited by image artefact?

Figure 1: A comparison of scans produced by the photon-counting CT (left) and conventional CT (right).

Figure 2: Non-calcified coronary artery plaque as identified by the Photon-counting CT.

Photon-counting CT helps because of its higher spatial resolution, improved spectral imaging and reduced noise. In cardiovascular imaging, these features may improve assessment of small vessels, dense calcification and coronary stents. This does not mean every patient needs photon-counting CT. The right test still depends on the clinical question, the patient's symptoms, kidney function, heart rhythm, contrast suitability and overall risk. But when the question is anatomically complex, better image quality can change the clinical encounter.

A simple patient example

Consider a patient in his 60s with diabetes and exertional chest discomfort. A conventional CT scan might show coronary calcium, but the calcium could make it difficult to tell whether there is a truly severe narrowing. In the past, this uncertainty might have led to further testing, repeat imaging or invasive coronary angiography.

With photon-counting CT, the artery may be seen more clearly. If the scan shows that the narrowing is not severe, the patient may avoid an unnecessary invasive test. If the scan shows significant disease, the cardiology team can plan the next step more confidently. Just as importantly, the scan may reveal the overall burden and pattern of coronary plaque, allowing the consultation to move beyond "blocked or not blocked" toward prevention: cholesterol lowering, blood pressure control, diabetes optimisation, lifestyle change and, where appropriate, more intensive preventive medications.

This is where cardiac imaging is moving. The goal is not simply to take sharper pictures. The goal is to use better images to make better decisions.

Patient benefits

For patients, the potential benefits of photon-counting CT include sharper images of the heart arteries, especially where small structures, calcium or stents need careful assessment. This greater diagnostic precision may reduce uncertainty after the scan. In selected protocols, radiation exposure may also be lower. Where improved image quality allows the care team to answer the clinical question more confidently, patients may also need fewer repeat or additional tests.

Another important benefit is more personalised prevention. CT can show not only whether an artery is narrowed, but also the presence and extent of coronary plaque. This can help doctors and patients have a more informed discussion about long-term cardiovascular risk and preventive treatment.

At the same time, patients should not request a scan simply because the technology is available. A scan is useful only when it is clinically appropriate. The best first step is to speak with a doctor, who can decide whether cardiac imaging is needed and, if so, which test is most suitable.

Which patients may benefit most?

Photon-counting CT may be especially useful for selected patients undergoing cardiac CT, including those with:

Suspected coronary artery disease where a clear anatomical answer is needed;
Heavy calcium deposits in the arteries, which can make conventional CT images harder to interpret;
Previous coronary stents or bypass surgery, where detailed assessment of the treated vessels is needed;
Complex cardiovascular risk factors, such as diabetes, a strong family history of premature heart disease, chronic kidney disease or inherited conditions that cause very high cholesterol or elevated levels of a cholesterol particle called lipoprotein(a), where imaging may help refine prevention decisions.

Photon-counting CT is not intended as a blanket screening test for the general population. Not every patient with risk factors needs a scan, and not every patient with chest discomfort is best served by CT. The decision to perform cardiac CT should be made by the treating clinician after assessing the patient's overall clinical context. The scan is most useful when it can answer a specific question and guide a next step, for example, whether symptoms are due to coronary artery disease, whether further testing is needed, or whether preventive treatment should be intensified.

Access through NHCS and SKH

Through NHCS Cardiology @ SKH, a collaboration between NHCS and Sengkang General Hospital (SKH), residents in the northeast have had access to cardiac services and expertise since 2018. The recent launch of the Siemens Healthineers NAEOTOM Alpha photon-counting CT scanner at SKH in April 2025 further strengthens these capabilities, allowing patients to benefit from advanced imaging closer to home.

For Physicians: When and how to refer

There is no need to request photon-counting CT directly. Instead, referrals should focus on the clinical problem: symptoms, risk profile, previous test results, and the question that needs to be answered. The cardiology team will then determine whether cardiac CT is appropriate, and whether photon-counting CT adds value for that particular patient.

This distinction is important. Advanced imaging should support clinical decision-making; it should not replace it. The aim is not to increase scanning, but to ensure that the right patient receives the right test at the right time.

Referral to cardiology may be appropriate for patients with stable chest pain suggestive of angina, unexplained exertional breathlessness where cardiac disease is suspected, abnormal or equivocal stress testing, known coronary disease with recurrent symptoms, or complex cardiovascular risk where specialist risk assessment and prevention may change management.

Patients with acute chest pain, ongoing symptoms at rest, syncope, haemodynamic instability or suspected acute coronary syndrome should be sent urgently to the Emergency Department.

Photon-counting CT represents a meaningful advance in cardiac imaging. Used appropriately, it gives clinicians a sharper and safer way to see the heart arteries while giving patients a clearer path from diagnosis to prevention and treatment. The key phrase is "used appropriately": not everyone needs a scan, and the decision should always begin with clinical assessment.