Vascular plaque removal / detection

Dual energy plaque detection is a promising, evolving technique which yields very interesting possible applications. Specific modules enable the automated decomposition of calcium and iodine as well as the removal of calcified hard plaques from the images.

Plaque detection with multi-slice systems

Imaging arteriosclerosis and its major complication, arterial occlusive disease, is subject to various challenges. They include:

• an accurate quantification of stenosis
• preoperative planning
• monitoring disease progression or remission
• plaque characterization

The introduction of Multi-Slice CT (MS-CT) systems has further opened the field of CT angiography (CTA) in the recent years. MS-CTA facilitates fast and robust data collection relating to the arterial vascular system within a single spiral acquisition. Furthermore, there are several post processing techniques available to facilitate the evaluation of the images, like shadow surface display (SSD) reconstructions or maximum intensity projections (MIP).

However, these techniques are limited by osseous structures and calcified plaques. An accurate quantification of stenosis often has to be performed manually which is time-consuming and also user-dependent. DSCT`s automated plaque detection has the potential to further improve the accuracy and the acceptance of CTA.

New ways of plaque detection / removal

DSCT uses attenuation information from a dual energy scan. With the help of dedicated algorithms, calcium and iodine can be discriminated from each other. There are two automation modules to support the postprocessing workflow.

• “Hardplaque”
• “Bone Removal”

The “Hardplaque” module in the Dual Energy Software package creates a virtual image stack which contains only calcium and iodine information, assigning positive numbers to all pixels containing iodine, while pixels containing calcium are labelled with negative numbers. All other image information is deleted. For visualization this calcium/ iodine map is fused with the original image. Depending on the choice of the colormap for the overlay, the presence of calcium and iodine can be indicated by different colours.

At the same time, plaque removal is possible using the “Bone removal” module, which sets all voxels containing calcium to zero. As a consequence, bones and calcified plaques are removed from the images. The resulting image stack can be used to create 3D-images unimpaired by calcifications.

Dual Energy is, however, only possible within the in the centre of the gantry, therefore the patient has to be positioned carefully. In obese patients or in anatomical regions with irregular attenuation profiles like the shoulders images quality might be degraded.

Altogether, we think that Dual Energy plaque detection is a promising technique. Especially an automatic and precise quantification of calcium burden and the grading of aterial stenosis may improve vascular evaluations and image reading for routine applications.

Authors: Christoph Thomas, Harald Brodoefel, Martin Heuschmidt, Andreas Kopp

Department of Diagnostic Radiology, University Hospital Tuebingen, Hoppe-Seyler-Str. 3, 72076 Tuebingen, Germany.

See corresponding cases: Calcification of the renal artery, Calcification of the carotid artery
See corresponding protocol: Vacular plaque removal / detection