Cardiothoracic Ratio


Measure cardiothoracic ratio on posterioranterior and anteroposterior radiographs


 #Cardiac Size on Chest Radiograph






 Jay Nance

Panel Chair

 Carlo De Cecco

Panel Reviewers

Cardiac Panel 


 Creative Commons 4.0

Status  Public Commenting

Clinical Implementation

Value Proposition

The chest radiograph is often the first imaging study that is available. It can be used as a quick initial screening tool for cardiomegaly, which in and of itself can be used as a marker for heart disease. A quick visual assessment by a radiologist is sometimes inaccurate. An AI algorithm can be trained to make an accurate assessment of cardiomegaly based on single-view chest radiograph (anteroposterior [AP] or posterioranterior [PA]). Additionally, the algorithm can indicate which specific chambers contribute most to the enlarged cardiac silhouette.


A 60-year-old male with no prior imaging is admitted to the ED for shortness of breath. A chest radiograph is obtained as part of the initial workup. The algorithm evaluates the image and determines whether the patient’s heart is enlarged. The radiologist is informed of this categorization at the time of interpretation. Additionally, the algorithm is able to evaluate for enlargement of the left atrium (or other specific chambers).

Workflow Description

The image obtained from the modality is sent to PACS and the AI engine. The image is analyzed by the engine. If the image is a PA view, a simple cardiothoracic ratio (width of heart/width of thorax) is computed. If the image is an AP view, a “modified” cardiothoracic ratio is computed. The system categorizes the heart as enlarged or normal in size based on whether the cardiothoracic ratio is greater than 0.5. If the heart is enlarged, the angle of the carina is measured by the system. If the angle is greater than 100 degrees, the presence of left atrial enlargement is suggested. A message is sent to PACS from the engine with the information.

Considerations for Dataset Development

Procedures(s): X-ray, Chest

View(s): {AP, PA}


Sex at Birth: {Male, Female}

Technical Specifications




XRAY, Chest



Data Type




Body Region


Anatomic Focus



Primary Outputs

Cardiothoracic Ratio

RadElement ID



Cardiac size expressed as cardiothoracic ratio

Data Type


Value Set




Future Development Ideas

If the cardiothoracic ratio is greater than 0.5, then suggest cardiomegaly. If the cardiothoracic ratio is greater than 0.5 and the carina angle is greater than 100 degrees, then suggest atrial enlargement.

Public Commenting

Use cases are meant to be a primary vehicle for distributing clinical information to the developer community. They pinpoint precise scenarios within radiology workflows where potential automation could add noticeable value and establish standards for interpreting and passing corresponding common data elements. Implementing effective standards requires the perspective from all stakeholders. So to that end, we encourage your feedback on use cases.

To submit comments, please email with the use case title(s) and relevant comments by January 1, 2019. If more convenient, you may also download this use case and comment directly on the PDF. Just attach the PDF copy on the email.