Chest X-Rays Offer Second Look for Heart Disease Risk
Dual-energy lateral images help radiologists spot coronary calcium and could support earlier prevention
Dual-energy (DE) chest X-ray can reliably reveal coronary artery calcium (CAC), a key marker of cardiovascular risk and is a strong predictor of coronary artery disease in asymptomatic individuals. However, radiologists rarely report it, according to a study published in Radiology: Cardiothoracic Imaging.
In the study, Gilbert Boswell, MD, radiologist at UC-San Diego Health, and colleagues found that dual-energy lateral chest radiographs detect CAC with relatively high accuracy compared with a CT calcium scoring reference. “This capability offers a potential opportunity for earlier cardiovascular risk identification in patients already receiving routine chest imaging,” Dr. Boswell said.
According to Dr. Boswell, DE chest radiographic technique allows the creation of images that can emphasize elements of low atomic numbers (hydrogen, carbon, oxygen, nitrogen) and higher atomic numbers (calcium).
“In creating high atomic number images, calcium in the coronary arteries becomes readily apparent if the trained observer knows where to look,” Dr. Boswell said. “We have found that when the detected coronary calcium is as dense or denser than the nearby reference vertebral body endplate accuracy is high, allowing confident reporting.”
Conventional chest X-rays do not allow for creation of images that emphasize separation of calcium from other elements. This limitation is what makes DE imaging so valuable.
“A key finding from our study was that CAC was best detected on the dual-energy lateral view in 86.4% of interpretations compared with only 5% on the dual energy frontal view” Dr. Boswell said. “That advantage is rooted in anatomy and overlap.”
“On the frontal exam the coronary arteries are obscured by the sternum, vertebrae, and can be confused with calcified anterior chest costal cartilage,” he continued. “On the lateral view those limitations are not present. Overlapping structures shift out of the way, making it easier to localize coronary calcium.”
With the diagnostic benefits of the lateral view established, the researchers assessed how well readers with varying levels of experience could learn to identify CAC on DE chest radiographs and which imaging clues were most helpful.
Mild coronary artery calcium (CAC) best illustrated on the frontal image: 66-year-old female. PA and lateral DE high Z images. This was confidently detected by a staff radiologist and a 2nd and 4th year resident and suspected by the other readers. (A) PA image shows a single focus of left anterior descending (LAD) calcium (arrow). This is confirmed on the lateral view. (B) Lateral image demonstrating LAD calcium projecting through two ribs (arrow). Right coronary artery (RCA) calcium detected only in retrospect when correlated with CT (arrowhead). (C) Sagittal oblique CT correlative image.
https://doi.org/10.1148/ryct.240255 ©RSNA 2025
Training Insights and Diagnostic Clues
The study retrospectively reviewed imaging from adults ages 45 to 70 who underwent DE posteroanterior (PA) and lateral chest radiography and had a noncontrast chest CT within three years. The final dataset included 99 individuals (mean age 58.6 years). CT calcium scoring identified CAC in 62 individuals, with a median score of 92.
Seven readers participated, including radiology residents and chest radiologists with varying experience. Before interpreting cases, all readers completed a 30-minute training presentation illustrating CAC appearance on DE chest radiographs, relevant coronary locations and useful imaging artifacts.
Across all readers, sensitivity for detecting CAC as “definitely present” or “possibly present” ranged from 71% to 84%, with specificity ranging from 54% to 92%. Inter-reader agreement ranged from moderate to substantial, demonstrating that readers interpreted DE images consistently even across different experience levels.
Their evaluations showed that readers overwhelmingly recognized the lateral projection as the most reliable vantage point for detecting CAC. To further quantify these advantages, the researchers analyzed how reader performance aligned with the anatomical clarity offered by the DE lateral view.
“The key is understanding what CAC looks like on the DE lateral CXR. Once the interpreter learns that, detection becomes simple.”
— GILBERT BOSWELL, MD
Dr. Boswell described a visual benchmark he finds helpful for building confidence. “As an imaging tool, if we noted density in the expected location of the coronary artery on the lateral view, and it was as dense or denser than the nearby vertebral body endplate, it was a specific sign for CAC,” he said.
He noted that one of the study’s aims was not only to show detectability compared to CAC CT but also to provide many illustrative examples in the supplemental images of the appearance. “We demonstrated that with a short period of training, least experienced readers, such as junior residents, were able to achieve success in detecting CAC,” he said.
He emphasized the familiar radiology principle behind that learning curve. “The key is understanding what CAC looks like on the DE lateral CXR. Once the interpreter learns that detection becomes simple,” Dr. Boswell said. “Like many things in radiology…you only see what you know to look for. That is basic radiology dogma.”
Dr. Boswell and his team identified specific imaging characteristics that helped readers recognize CAC. The most sensitive clues were classic coronary location, a coarse “dot-dash” pattern, and motion-related “ghosting” between DE exposures. The most specific signs were identification of a “tram-track” pattern and confirmation of calcium on both PA and lateral projections, though those tended to occur with higher CAC burden.
Opportunistic Detection and Early Prevention
Dr. Boswell said this imaging technique can fill a gap in the population he serves.
“Our practice is focused on younger healthier members of the U.S. military. Most would not routinely meet criteria for CT calcium score measurement due to their younger age or low clinical suspicion,” he said. “Nevertheless, coronary artery disease has a long pre-clinical asymptomatic course that is not routinely screened for. Early intervention with diet, exercise and increasingly with lipid lowering medical therapy can alter the course of the disease.”
With roughly 100 million chest radiographs performed annually in the U.S., Dr. Boswell sees DE lateral imaging as a practical tool for opportunistic detection in adults who already need a PA and lateral exam for other reasons.
“Many practices already own DE capable equipment. Without additional cost, this equipment can be used to obtain a DE lateral examination,” he said. “This can be part of the routine workflow whenever a PA and lateral CXR is requested in adults for routine indications. The goal is opportunistic detection.”
“As AI tools are developed and iterated, this is a specific strong use case to aid in detection and quantification of CAC to aid the radiologist in reporting,” he said. “This can happen in the background as the radiologist searches for other entities on the CXR and present as an adjunct to the report.”
Dr. Boswell said broader experience will be needed to advance the approach.
“We encourage other practices to gain experience in performing and interpreting dual energy lateral chest radiographs and report their results,” he said. “The next step will be multicenter trials along with developing datasets for AI training.”
For More Information
Access the Radiology: Cardiothoracic Imaging study, “Coronary Artery Calcium Detection with Dual-Energy Posteroanterior and Lateral Chest Radiography: Imaging Clues and Added Value of the Lateral View.”
Read previous RSNA News stories on chest imaging: