CT Image Orientation: The Radiological Convention
On CT scans, the patient's right side appears on the left side of your viewing screen, and the patient's left side appears on the right side of your viewing screen—you are viewing the patient "from below" as if standing at their feet looking up toward their head. 1
Standard Display Convention for Axial/Transaxial CT Images
The standardized orientation follows the radiological convention established by the American College of Cardiology and American Heart Association:
- The viewer observes the patient from below, with the anterior chest wall at the top of the image 1
- The patient's right side appears on the viewer's left, and the patient's left side appears on the viewer's right 1
- This creates a "mirror image" effect where anatomical structures are flipped horizontally compared to how you would see them if facing the patient 1
Practical Application
- The heart appears on the viewer's right side of the screen because it is predominantly on the patient's left side 1
- The right lung appears on the viewer's left side of the screen 1
- The left ventricle appears to the right of the right ventricle on axial images 1
Other CT Viewing Planes
Sagittal Images
- Display begins with the patient's right side and progresses to the left side 1
Coronal Images
- Display begins with the anterior chest wall and progresses to the posterior chest wall 1
Critical Clinical Pitfall
Always verify image orientation markers (typically "R" or "L" labels) on every CT scan before making clinical decisions, as incorrect labeling or non-standard display settings can lead to catastrophic errors such as operating on the wrong side 2. This is particularly important when reviewing images from outside facilities or on different PACS systems where display conventions may vary.