Acad Radiol 2006; 13:1165-1167.
Rist C, Nikolaou K, Flohr T, Wintersperger BJ, Johnson TR, Reiser MF, Becker CR.
Today, coronary artery stenting is the predominant method of nonsurgical myocardial revascularization (1). However, the detailed assessment of the stent lumen remains a major limitation of cardiac multislice computed tomography (MSCT) (2). We report on a novel CT technology called ultra-high-resolution mode (UHR), a special acquisition mode providing considerably enhanced spatial resolution in 64SCT, primarily usable for trauma CT and bone imaging of the inner ear. However, this acquisition mode could also be advantageous for the delineation of coronary artery stents, which was tested in an ex vivo setting as described previously (3). A 2.5-mm diameter stent (Bx-Velocity, Cordis, Langenfeld, Germany; stainless steel 316L length 33 mm, strut dimensions 0.14 mm) was implanted in the proximal left anterior descending artery of a porcine heart shortly after explantation, and was expanded to a diameter of 2.5 mm by inflation of the balloon catheter to nominal pressure (10 atmospheres). Subsequently, the left anterior descending artery was cannu-lated and a mixture of an iodine-containing contrast agent (Iomeron 300, Bracco Imaging SpA, Milan, Italy) and ultrasound gel was injected into the ostium of the artery. In this way, an intraluminal contrast enhancement similar to in vivo CT angiography of the coronary arteries was achieved, with a target attenuation of 250-300 Hounsfield units within the lumen. Finally, the porcine heart was positioned in a plastic container and placed in the scanner gantry similar to the physiologic position of the heart and the path of the coronary arteries in vivo. The specimen was examined using a new-generation 64SCT system with an increased gantry rotation time of 330 ms (64SCT, Somatom Sensation 64, Siemens Medical Solutions, Forchheim, Germany) applying a z-axis flying focal spot technology combined with the UHR functionality (4). The entire volume of the specimen was covered in about 10 seconds. A moveable tantalum comb (grid) is positioned in front of the detector elements, reducing their z-aperture from 0.6 mm to 0.35 mm at isocenter. Two subsequent readings are interleaved and result in projection data with 0.3 mm z-sampling distance and 0.35 mm detector z-aperture. In this way, an isotropic resolution of 0.24 mm is achieved, both in the scan plane and along the z-axis. The specimen were scanned using UHR mode with a nominal spatial resolution of 0.24 X 0.24 mm and with U40 and a special U75 kernel, respectively. For comparison purposes, the intact ex vivo heart was also scanned with 0.6-mm collimation, reconstructed with a slice thickness 0.75 mm and a dedicated stent kernel (B46f). The inner and outer diameters of the stent were measured for both, datasets reconstructed with 0.75-mm slice thickness with B46f kernel, and the images acquired in UHR mode, respectively. Measurements were taken manually in the center of the stent, and at both ends of the stent, on an offline workstation (Siemens Leonardo, Siemens Medical Solutions, Erlangen, Germany), using curved multiplanar reformats.