Aortic Distension Calculation

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 (Animated: View cine on-line version)

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
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
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:

  • Write to a text file report. A File chooser will appear, for you to choose a log file name. The default file extension for log files is ".log". If the chosen file already exists, an entry will be appended to the log file.
  • Write to a PDF file report. A File chooser will appear, for you to choose a PDF file name. If the chosen file already exists, an entry will be appended to the PDF file.
  • Send a PDF report to a DICOM server. The DICOM server to which it will be sent must already have been set up, and is the current server selected in the DICOM Query/Retrieve tool. See these instructions for how to set up the connection to remote DICOM servers.
  • Save PDF and Send to DICOM. Both save to disk and send to a DICOM server.

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