Keywords:
Artifacts, Aneurysms, Stents, Embolisation, Computer Applications-3D, CT-High Resolution, CT-Angiography, Cone beam CT, Neuroradiology brain, Interventional vascular, Head and neck
Authors:
P. van de Haar, D. Ruijters, J. Timmer; Best/NL
DOI:
10.1594/ecr2013/C-1951
Methods and Materials
VasoCT - High resolution FDCT of intracranial stents
For the purpose of imaging intracranial stents and their surrounding vasculature a dedicated acquisition protocol and reconstruction settings have been developed (VasoCT; Philips Healthcare,
Best,
the Netherlands) [3].
The high resolution protocol consists of 620 projection images acquired over a rotational trajectory of 200°,
while the imaged detector area is set to a diameter of 22 cm and using a pixel size of 0.154 mm.
The X-ray tube voltage is set to 80 kV,
the focal spot to 0.4 mm,
while no additional copper filter is used.
This protocol enables very high spatial resolution 3D reconstructions.
The high resolution protocol can be combined with the injection of iodine contrast medium (either an intravenous injection,
or an on-site intra-cranial injection of diluted contrast),
in order to inspect the interface between stent and vessel lumen.
In this manner it is possible to assess whether the stent has been properly deployed.
Patel et al.
[4] have documented the resulting benefits in spatial resolution,
as can be seen by comparing Fig. 1 (regular soft-tissue FDCT) and Fig. 2 (VasoCT reconstruction).
Metal artifact reduction
In the first step of the Metal Artifact Reduction (MAR) algorithm [5] a regular filtered back-projection reconstruction is produced [6].
From this reconstruction the volumetric regions that display high X-ray absorption (such as metal) are identified.
These regions are then forward projected [7] on the original X-ray images (see Fig. 3 and Fig. 4),
in order to process the high-absorption areas in the images.
These processed images are then used to create an improved reconstruction in a second pass.
The entire process of two passes is performed within about 138 seconds.
Materials
FDCT volumetric reconstructions with endovascularly treated aneurysms were obtained,
while diluted iodine contrast (10% contrast medium and 90% normal saline) was selectively injected in the feeding artery to show the vessel lumen.
The aneurysms had been filled with coils and stents had been placed to close the neck of the aneurysms.
A second pass reconstruction algorithm was used to correct for the streaking artifacts that originate from the coiled volume.