Clarifying Reconstruction in CTA—2D vs. 3D Rendering

Reconstruction requirements with CTA procedures
In July of 2009, the ACR issued clarification that expressly addresses reconstructions associated with CTA. According to the ACR, post-processing of the CT angiogram to provide multiplanar reformations through 3D renderings is mandatory for the exam to be considered CT angiography. As a result, two dimensional (2D) post-processing no longer constituted a CTA study. When CT scanning is performed using contrast enhanced dynamic-timed imaging and 2D reformatted axial images are obtained or multiplanar reconstructions (MPR) (e.g., coronal, sagittal, or even an off-axis view) are obtained, this should be reported with a standard CT with contrast code that identifies the anatomic area studied. None of these 2D planar reconstructions qualify as “angiographic” reconstruction.

What needs to be documented?
A full documentation and interpretation of the CTA includes not only vessel pathology, but an assessment of the end-organs of the vessels examined for secondary findings and potential alternative causes for the patient’s symptoms. Organs adjacent to the examined vessels should also be viewed for potential pathology.

Acceptable post-processing techniques that constitute a CTA study are the following. Physicians must state in their dictation that one of these 3D techniques was utilized.
• Maximum Intensity Pixel (MIP)
• Volume Rendered Images
• Surface Shaded Rendering
• 3D Reconstructed Images

Document Retention & Archival
Archival of these 3D renderings is also clearly defined by the ACR. It is necessary to have a permanent archive of 3D images acquired on a CTA study. The images from which 3D images are created are insufficient for the reporting of a CTA study. When reformatted images are acquired and interpreted in addition to the CT axial images, the reformatted images are a part of the study and should be permanently archived.

References

• Clinical Examples in Radiology (Fall 2008, p. 11)
• ACR Radiology Coding Source (May-June, 2009)

With best regards,
Jennifer Bash, RHIA, CPC, CIRCC, RCC
Coding Documentation & Education Manager