Standardized Medical Terminology for Cardiac CT: What's in a Name?

See also article by Koweek et al in this issue.

James Roberts, MD, MSc, is a radiologist at St Paul's Hospital in Vancouver, BC, Canada, and a clinical instructor in the department of radiology at the University of British Columbia (UBC). He completed both medical school and a residency in diagnostic radiology at UBC and a fellowship in cardiothoracic imaging at the University of Toronto. He is a member of the Radiology: Cardiothoracic Imaging trainee editorial board.

Kate Hanneman, MD, MPH, is an associate professor at the University of Toronto and a clinician scientist at the Toronto General Hospital Research Institute. She is the director of cardiac imaging research at the Joint Department of Medical Imaging and is an associate editor of Radiology and Radiology: Cardiothoracic Imaging and chair of the Radiology: Cardiothoracic Imaging trainee editorial board. She has received grant funding from the Canadian Institute of Health Research and leads an active research program focused on sustainability and improving health outcomes for patients using cardiac imaging.

A rose by any other name would smell as sweet.

–William Shakespeare, Romeo and Juliet

As cardiac CT continues to become further incorporated into routine clinical practice and as research in the field expands, there is a clear and ongoing need for consensus-based standardized and accurate medical terminology. Clinicians and scientists from various backgrounds have contributed to the exponential growth of cardiac CT research and clinical applications, including cardiology, radiology, physics, and engineering. However, medical terminology related to cardiac CT is currently not unified in clinical reports or research publications (1).

Standardized medical terminology and nomenclature is important as it facilitates communication between imagers and other health care providers. In the era of online patient portals, where increasing numbers of patients can access their imaging reports, clear and consistent use of standardized terminology is also critical for patient-centered communication and understanding (2). Key advantages of standardized medical terminology include facilitating quality improvement, outcomes research, and data analysis; simplifying data extraction for registries; optimizing workflows and billing management; promoting interoperability of imaging studies; and improving patient outcomes (3).

Cardiac imaging has a strong rooting in standardized medical nomenclature, including early multimodality work defining myocardial segmentation (4), standardized terminology and definitions for transthoracic echocardiography (5), as well as more recent efforts to standardize nomenclature for bicuspid valve morphology (6).

In this issue of Radiology: Cardiothoracic Imaging, Koweek et al outline updated standardized medical terminology for cardiac CT in 2023 (1). The purpose of this document is to consolidate multiple terms and to provide clear definitions for terminology applicable to cardiac CT. The authors and committee members are to be commended for gathering multisociety input and bringing this terminology into the modern era of cardiac CT.

In an update from the initial predecessor guideline published in 2011 (7), the new cardiac CT standardized terminology guidelines now include input from multiple representatives and endorsement of major North American cardiac imaging societies including the Society of Cardiovascular Computed Tomography (SCCT), American Association of Physicists in Medicine (AAPM), American College of Radiology (ACR), North American Society for Cardiovascular Imaging (NASCI), and the Radiological Society of North America (RSNA).

The document is organized into tables with recommended terms and abbreviations, definitions, and previous terms (which are not recommended). While some of the terms are specific to cardiac CT (such as Agatston score), others relate to CT more broadly but are applicable to cardiac CT reporting and research (such as motion artifact and virtual noncontrast image).

The updated 2023 terminology guideline also newly includes Radlex^® (radiology lexicon) names and identifiers in each table. Radlex is maintained by RSNA and includes a comprehensive set of radiology terms for use in radiology reporting, decision support, data mining, data registries, education, and research. While Radlex is a radiologic ontology system—a set of concepts and their interrelations now with over 46 000 terms—the standardized terminology refined by Koweek et al is focused on cardiac CT applications.

The recommended terminology in the updated document aligns with other societal guidelines, notably the 2022 Coronary Artery Disease–Reporting and Data System (CAD-RADS 2.0) (8). The authors highlight and justify key changes to recommended terminology, avoiding the previous term mixed plaque in favor of the term partially calcified plaque, which is a more accurate description of the plaque morphology. Classification of partially calcified plaque can be further described by the degree of calcification, including predominantly calcified (75% or greater component of plaque calcified), partially calcified, and predominantly noncalcified (75% or greater of plaque noncalcified).

The recommended term high risk plaque (HRP) features is new, rather than previous but not recommended terms vulnerable plaque features or adverse plaque features. This change aligns with the standardized terminology recommendations in the CAD-RADS 2.0 document. While CAD-RADS 2.0 specifies that at least two of four high-risk plaque features (low attenuation plaque, positive remodeling, napkin-ring sign, and spotty calcification) are required to label a particular plaque as an HRP, the current terminology guidelines demur on the clinical application of this term. Finally, despite frequent use of previous (not recommended) terms calcium score and CAC score, Agatston score is the recommended term, reflecting the technique used to quantify calcium identified from CT images based on the maximum attenuation and area of image pixels with CT numbers greater than 130 HU.

The updated guideline includes a few other recommended terms that might lead to continued search engine use among recipients of cardiac CT imaging reports despite being more accurate. For example, the term CT number (expressed in Hounsfield units) is recommended rather than the previous term CT attenuation, although the latter term is still used frequently in clinical reports. In reference to the dark bands or streaks originating from a highly attenuating structure at CT due to changes in the spectral distribution of polychromatic x-rays during transmission through matter, beam-hardening artifact is the recommended term rather than streak artifact, which is a less accurate but still frequently used term. Similarly, the term partial volume averaging is recommended, rather than the previous term calcium blooming, to describe the phenomenon that arises when different materials are present in a voxel and are averaged and represented by a single CT number. This term is particularly relevant to cardiac CT as it can result in an overestimation of coronary artery atherosclerotic arterial narrowing. Although important for standardization and accurate reporting, it may take time to achieve broad uptake in use of the recommended terms in clinical and research applications.

The most significant update to the new terminology consensus guidelines brings cardiac CT terminology into the modern era, incorporating and defining terminologies related to newer technologies that have evolved since 2011. Recent work in multienergy CT has expanded the scope of cardiac CT to allow for improved assessment of late iodine enhancement and extracellular volume using multienergy CT. The term multienergy CT is recommended rather than the more limited term dual-energy CT. Although dual energy is still used frequently in clinical practice, more recent publications have adopted the term multienergy (9). Photon-counting detector CT is a new generation of CT technology with many applications in cardiac imaging and has shown promise for improving coronary artery evaluation due to its improved spatial resolution and ability to reduce artifacts from calcium or coronary stents (10). The term photon counting detector CT is recommended in favor of the less precise term photon counting CT to emphasize the detector technology. As these cardiac CT–related technologies evolve and others are developed, future updates will be required to keep pace with new developments.

The updated cardiac CT medical terminology document provides clear guidance for cardiologists, radiologists, scientists, and other clinicians involved in cardiac CT on the use of appropriate and recommended terminology and will facilitate clinical communication and research dissemination in the field.