ROI Propagation - Aortic Distension

In order to illustrate use of the tool, we will use a single slice axial TrueFISP cine sequence (40 cardiac phases) through the ascending and descending aorta. This image is shown as a movie below.

A cine sequence of the aorta

We will outline the ascending and descending aorta on a few cine frames, propagate the ROIs to all time points and then go on to calculate the distension.

Having loaded the image into Jim's main display, we launched the ROI Propagation toolkit and, using Spline ROIs, outlined the ascending and descending aorta at 4 time points: at the beginning and end of the cardiac cycle, and two points around systole. These are illustrated below:

TrueFISP cine sequence with ROIs outlining the ascending and descending aorta on four cardiac phases

Initially, we used the settings:

Number of shape coefficients = 4. The vessels have a simple outline shape, and 4 shape coefficients is enough to capture the variations in shape.
Changes are periodic with time. This is an E.C.G. triggered cine sequence, where the last image frame joins back to the first at the end/start of the cardiac cycle.
The number of time coefficients was not set manually.

However, these settings resulted in a 'bleb' forming on the ascending aorta in some of the image frames, as illustrated below.

Propagated ROIs with a bleb on some cardiac phases
'Bleb' seen in some cine frames

During the propagation, the ROI has erroneously been attracted to the epicardial wall, rather than the aorta. This was corrected by manually setting the number of time coefficients to 20. Running the propagation again the resulted in a smoother transition from frame-to-frame, and the outline of the aorta was then followed accurately across all frames:

ROIs propagated accurately across all cardiac phases.

Notice that even with only 4 shape coefficients, the outline can be accurately represented.

Calculating the areas and distensions

We will now go on to calculate the distension of the aorta. Select the 'Area and Distension' tab in the 'Propagated ROI Calculations' panel: Tab to calculate areas and distensions

Click the Button to perform the calculation on the propagated ROIs button to start the area and distension calculation.

The areas of the ROIs over time will be calculated, together the distension (maximum change in area / minimum area) for each ROI, and the results presented in a dialog:

Report dialog for distension

You can save these data to a report, either in plain text format, or in PDF format by clicking the appropriate button.

Also, for each ROI, you will see a pop-up graph, like the one below, showing the area enclosed by the ROI through the cardiac cycle:

Graph dialog showing the area through the cardiac cycle for one ROI

Finally, for each ROI, you will see a pop-up graph, showing the percentage change in area (distension) through the cardiac cycle for all the ROIs:

Graph dialog showing the change in area through the cardiac cycle for
all the ROIs

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