(The transfer functions in b and c are identical.) (The transfer functions in b and c are identical.) Segments with a relevant stenosis always need to be reevaluated with adapted cross-sectional images in order to exclude exaggeration of stenosis by local misregistration or an inadequate bone mask. 29, No. Profile of the ideal tissue boundary and the corresponding result at CT angiographic reformation. Figure 3. 35, No. People with kidney disease or diabetes may need to receive extra fluids after the test to help flush the iodine out of the body. Calcified plaque can be rendered transparent with meticulous parameter setting (,Fig 5a,,,). (d) Volume-rendered image created with 2D transfer functions shows similar results. A CT scan can reduce or avoid the need for invasive procedures to diagnose problems in the skull. 7th ed. 80, No. 32, No. These procedures can be time-consuming and may exceed practical limits in routine clinical work flow. From these seed points, more and more neighboring voxels that fulfill predefined criteria are included in the segmentation (,14). Lighting effects enhance the appreciation of spatial relationships between structures. BACKGROUND AND PURPOSE: Lack of cerebral circulation is an important confirmatory test for brain death (BD). Tell the scanner operator right away if you have any trouble breathing during the test. If bone mask subtraction is applied to calcified plaque, it is important that only voxels representing bone or calcification are removed from the data without additional mask dilations. (a, b) Volume-rendered images created without shading at low opacity (a) and high opacity (b) show accentuated vessel boundaries. (c) On a volume-rendered image created with shading, the 3D impression is improved but edge definition is reduced. Contrast can be given through a vein (IV) in your hand or forearm. Segmentation algorithms are often based on the principle of region growing (,13). 12, No. The major advantage of more detector rows is higher through-plane resolution by reducing the width of a single detector row from 1–1.25 mm (four–detector row CT) to 0.5–0.6 mm (64–detector row CT) (,1). 08, No. Bone subtraction CT angiography is a robust method of bone elimination, not requiring user interaction. The vertebral arteries are clearly demonstrated without artificial lumen reduction at the vertebral foramen. Figure 15. 38, No. CT angiography (CTA) combines a CT scan with the injection of dye. 10, European Journal of Radiology, Vol. Commercially available vessel analysis tools implement these procedures. A real boundary corresponds to a function that abruptly jumps between intensity values of neighboring tissues. Generating “boneless” 3D images became possible with modern postprocessing techniques, but one should keep in mind the potential pitfalls of these techniques and always double-check the final results with source or MPR images. The right carotid artery is partly visualized; an occlusion of the right ICA is evident. Computed tomographic (CT) angiography has been improved significantly with the introduction of four- to 64-section spiral CT scanners, which offer rapid acquisition of isotropic data sets. Computed tomography angiography - brain; CTA - skull; CTA - cranial; TIA-CTA head; Stroke-CTA head; Computed tomography angiography - neck; CTA - neck; Vertebral artery - CTA; Carotid artery stenosis - CTA; Vertebrobasilar - CTA; Posterior circulation ischemia - CTA; TIA - CTA neck; Stroke - CTA neck. (a, b) Coronal MPR (a) and thin-slab MIP (b) images show the internal structure of the lesion and thinning of the skull in detail. Atherosclerotic lesions are usually located at the carotid bifurcation, the carotid siphon, and—with smaller hemodynamic relevance—the origin from the aortic arch. Aneurysms of the right ICA and left posterior cerebral artery. Volume rendering has supplanted shaded surface display in virtually all CT angiography indications. Aneurysms of the right ICA and left posterior cerebral artery. Use of a high-opacity setting improves the 3D representation; however, the enhanced cavernous sinus hides small portions of the ICA. Figure 19a. 2, Journal of the Korean Society of Radiology, Vol. (c, d) Volume-rendered images created with the one-dimensional transfer function technique (c) and from segmented data with a high-opacity setting (d) provide the best 3D representation but do not show the thrombosed parts of the lesion. This region is difficult to evaluate with CT angiography, as the vessel is partly embedded in the skull base, with a tortuous course and often circular calcifications of the vessel wall. The injection protocols need to be simple and standardized to guarantee excellent and reproducible results on a 24-hour basis. Figure 1a. The delay between injection of contrast material and data acquisition is targeted to the cerebral veins. If volume rendering techniques are applied, the affected vessel segment may not be represented by the transfer function, generating the impression of vascular stenosis or occlusion. CT stands for computed tomography. This technique does not require any kind of preprocessing such as segmentation or filtering and produces high-quality results just by adjustment of the applied 2D transfer function. 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