"ART-FUN": an integrated software for functional analysis of the aorta

A new software platform "ARTerial FUNction" was developed to analyse cine and phase contrast MR acquisitions in the ascending and descending aorta. It provides an exhaustive description and analysis of time velocity waveforms, as well as the accurate estimation of local and regional aortic function and stiffness indices.

The main functions implemented in this platform, running under MATLAB, include : 1) import of DICOM cine and flow data (including the specific headers needed for further analysis of data); 2) segmentation (manual or automatic) of axial sections of the aorta; 3) analysis of flow data and waveforms recorded in the segmented arterial lumens; 4) advanced comparison of flow data between the ascending and descending aorta, including an automatic estimation of the propagation speed of the velocity wave; 5) export of results to Excel data sheets.

Here we describe specifically the automatic contouring of the aortic lumen integrated in this software. The method is based on a 3D snake deformable surface, modelling the evolution of aortic lumen with time; this allows the introduction of smoothness constraints both in the 2D image plan and the time axis. This cylindrical like surface is deformed under the influence of "external forces" including the classical attraction by the image gradient but also specific potentials to avoid the attraction of the contour by vascular structures surrounding the ascending aorta, such as the pulmonary artery and vena cava.

The duration of this segmentation ranges from 5 seconds (descending aorta, True-FISP sequence, breathhold, square pixel size = 0.58 mm, 31 cardiac phases) to 35 seconds (ascending aorta, FISP-2D, free breathing, square pixel size = 0.37 mm, 51 cardiac phases) on a basic laptop. Figure 1 presents the evolution of the normalized area of the section in the ascending and descending aorta using the previously described True-FISP sequence.

Figure 1

Horizontal axis: phases of the cardiac cycle (22.4 ms per sample). Vertical axis: area of the lumen normalised by the proto-diastolic area. Plain line: ascending aorta, dotted line: descending aorta. The propagation delay of the pulse wave in the aortic arch is visible and the larger distensibility of the aortic wall at the level of the descending aorta is visible as well.

The software was successfully tested on various MR sources, including General Electric, Siemens and Philips 1.5 T and 3 T scanners, thus making possible the processing of multi vendor acquisitions in multi centric studies.