With binary data, densitometric information gets lost and makes the method prone to undesirable artifacts. Before receiving the contrast, tell your provider if you take the diabetes medicine metformin (Glucophage). If you have contrast through a vein, you may have a: This is normal and usually goes away within a few seconds. A correct lumen boundary definition with exclusion of calcifications is the other prerequisite. In cerebral angiography, X-ray images show blood vessel abnormalities in the brain. Automated measurements would be desirable in order to obtain reproducible results (,Fig 15). Several image processing techniques for CT angiography are currently being used clinically (or at least advertised by the manufacturers). (The image was created from two digital subtraction angiographic series. The walls of the branches of the intradural cerebral arteries are rarely calcified; therefore, detection of lumen narrowing can be performed with MIP or volume rendering. Figure 18d. A weak area in the wall of a blood vessel that causes the blood vessel to bulge or balloon out (, The most common type of contrast given into a vein contains iodine. 42, No. (a) Axial image shows the right internal carotid artery (ICA) (1), left ICA (2), and left internal jugular vein (3). 4, © 2021 Radiological Society of North America, Clinical Applications of Vascular Imaging, Open in Image 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. 1 – 11 Although it provides 3D anatomic information on vascular structures that is useful for diagnosis and surgical strategy planning, it does not allow visualization of the hemodynamic status of intracranial vessels. (b) On a volume-rendered image from CT angiography, parts of the ICAs are hidden. This is usually done by thresholding. 260, No. 5, European Journal of Vascular and Endovascular Surgery, Vol. 12, No. 36, No. However, if vessels are anatomically not well separated from bone, it is impossible to achieve a clear differentiation. 196, No. If you weigh more than 300 pounds (135 kilograms), talk to your provider about the weight limit before the test. Commercially available vessel analysis tools implement these procedures. (b) Diagram shows the enhancement curves for the right ICA (1), left ICA (2), and left internal jugular vein (3) after injection of 10 mL of contrast material and a saline solution bolus. CTA is typically performed in a radiology department or … 7, No. (a) Two-dimensional histogram based on intensities (x axis) and gradient magnitudes (y axis) obtained from CT angiographic data. List the neurovascular applications of the various image postprocessing tools. In extracranial malformations and hemangiomas, CT can demonstrate both the lesion and the surrounding tissue, information that is critical for therapy planning. Open arrow = air, open arrowhead = soft tissue, solid arrowhead = vessels, solid arrow = osseous tissue. 29, No. Figure 13. Results from a cerebral angiogram are more accurate than those produced by carotid Doppler. MIP images are created by displaying only the highest attenuation value from the data encountered by a ray cast through an object to the viewer’s eye (,5,,6). Voxels lying close to tissue boundaries or inside uniform tissue produce histogram “hits” along the upper or lower regions of the parabolas. 11, Surgery for Cerebral Stroke, Vol. (a) On an image created with one-dimensional transfer functions, vessels and bone cannot be well differentiated because of an overlap in the attenuations of these structures. ), Figure 16b. (d) Volume-rendered image created with the transfer function shifted toward higher Hounsfield unit values results in reduced caliber of the visualized vessels. 64 cases for head and neck CT angiology were randomly divided into Groups A (n = 32) and B (n = 32). (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. Parts of the jaw were manually removed from the image to exempt the left ICA. Clip planes are used to remove parts of the volume. Superimposition of vessels or calcified structures alter lumen visualization (arrow). CT angiography (CTA) combines a CT scan with the injection of dye. 4, Japanese Journal of Radiological Technology, Vol. Different transfer function settings alter the representation of the lumen. (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. 1, 23 March 2012 | Neurosurgical Review, Vol. Opacity values on a spectrum from 0% to 100% (total transparency to total opacity) are assigned along artificial rays that pass through the data (,12). 47, No. (b) Volume-rendered image from bone subtraction CT angiography shows the vessels clearly. 4, American Journal of Ophthalmology, Vol. 39, No. Figure 8b. Moderate stenosis of the left ICA. 10, European Journal of Radiology, Vol. Objective: To investigate the application of low radiation and contrast dose spectral CT angiology using rapid kV-switching technique in the head and neck with subtraction method for bone removal. Describe the various postprocessing tools used in neurovascular images. As only one scan is employed, movement is irrelevant for 2D transfer function volume rendering. 1, Geriatrics & Gerontology International, Vol. CT angiography is usually the first choice for evaluating cerebral aneurysms. 2, Journal of the Korean Society of Radiology, Vol. Profile of the ideal tissue boundary and the corresponding result at CT angiographic reformation. The latter method removes only interfering tissue (bone or densely enhanced veins) from the CT angiography data and retains soft tissue as well as contrast-enhanced vessels for further evaluation. Test bolus method. Automatic vessel boundary definition depends on explicit or implicit parameter settings; it should be kept in mind that changing these settings may considerably influence the grading of stenosis (,Fig 8,,). S1, 8 October 2015 | American Journal of Neuroradiology, Vol. The ICA calcification complicates analysis of the residual lumen with automatic and manual procedures. Philadelphia, PA: Elsevier; 2018:chap 4. These techniques increasingly provide a quality of vessel analysis comparable to that achieved with intraarterial three-dimensional rotational angiography. 08, No. The individual start delay can be optimized by placing the scan between the arterial peak and venous contrast material upslope. 3, The British Journal of Radiology, Vol. Predefined tissue boundary templates can be interactively placed and adjusted over the corresponding 2D histogram with immediate feedback on volume-rendered images. (b) Sagittal MPR image. For evaluation of the basal intracranial arteries, a scan range of approximately 100 mm needs to be covered. 3, Clinical Neurology and Neurosurgery, Vol. Too much weight can damage the scanner. Segmentation can be performed manually or (semi)automatically. 57, No. Nowadays, spiral CT systems with acquisition capabilities of up to 64 sections per gantry rotation are introduced in clinical practice. This technique is employed to display tortuous structures; however, manual definition of curved planes is usually highly error prone and often inappropriate for exact measurements. 92, No. In CT venography, scan speed is not a major issue, so image quality does not degrade if four-row scanners are used instead of 16–64-section scanners. Curved planar reformation provides a 2D image that is created by sampling CT volume data along a predefined curved plane. 8, No. 09, 14 March 2017 | British Journal of Neurosurgery, Vol. 1, 1 September 2011 | Radiology, Vol. Other tests that may be done instead of CT scan of the head include: Barras CD, Bhattacharya JJ. (e, f) Volume-rendered image from bone subtraction CT angiography (e) and image from digital subtraction angiography (f) show that the lesion has no feeding vessels from the ICA (inset). Figure 19b. 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). 2, European Journal of Radiology, Vol. 3, 1 October 2008 | RadioGraphics, Vol. Conventional angiography is the gold standard for identifying intracranial aneurysms (Bose, 2007). Aneurysms of the right ICA and left posterior cerebral artery. Different transfer function settings alter the representation of the lumen. 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. Typical in-plane resolution with application of a CT angiography protocol (64 × 0.6-mm detector configuration, 120 kV, 140 mAs [effective], field of view of 120 mm, medium sharp convolution kernel) is 0.6–0.7 mm and through-plane resolution is 0.5–0.7 mm, thus providing isotropic data. A common location for intracranial atherosclerotic lesions is the carotid siphon. To avoid the complex task of adjusting transfer function thresholds in two dimensions, a predefined transfer function shape that represents the boundary between two tissues was defined (,,Fig 10b). You must be still during the exam, because movement causes blurred images. 7, No. 16, No. To deliver an appropriate amount of iodine, injection rates of 4–5 mL/sec and highly concentrated contrast medium (iodine, 350–370 mmol/mL) are preferable. ,Figure 9 explains the behavior of the gradient magnitude around tissue boundaries for the one-dimensional case. (a, b) Volume-rendered images created without shading at low opacity (a) and high opacity (b) show accentuated vessel boundaries. The ideal kernel would combine low image noise and sharp edge definition, maintaining good low-contrast resolution. Atherosclerosis is the most common arterial disease responsible for ischemic stroke. (b) On a volume-rendered image from CT angiography, parts of the ICAs are hidden. 24 January 2020 | RadioGraphics, Vol. This technique is able to create pictures of the blood vessels in the head and neck. (b) Sagittal MPR image. High-grade stenosis with circular calcification of the right ICA. 89, No. Once again, interactive thin-slab MIP or MPR is preferred. Review provided by VeriMed Healthcare Network. (e, f) Volume-rendered image from bone subtraction CT angiography (e) and image from digital subtraction angiography (f) show that the lesion has no feeding vessels from the ICA (inset). Contrast phase-resolved CT of vascular lesions in the head and neck can be performed in a couple of seconds, providing angiographic information as well as information on the surrounding soft tissue. Use of a high-opacity setting improves the 3D representation; however, the enhanced cavernous sinus hides small portions of the ICA. 3, Interventional Cardiology Clinics, Vol. (a) On an image created with one-dimensional transfer functions, vessels and bone cannot be well differentiated because of an overlap in the attenuations of these structures. The exam is highly accurate, but cerebral aneurysms can be overlooked on the initial assessment due to their small size and the complexity of the blood vessels in the brain. The reconstruction increment can be arbitrarily chosen, independent of the detector collimation, but one should keep in mind the amount of resulting data: a reconstruction increment of 50%–75% of the section width may serve as a reasonable rule of thumb. Figure 18f. Different transfer function settings alter the representation of the lumen. Color can be applied to enhance the discrimination between structures, but color is assigned arbitrarily and does not correlate with the linear progression of gray-scale values on conventional CT images. An essential prerequisite for successful postprocessing is good quality of the acquired imaging data. Contrast helps certain areas show up better on x-rays. Figure 19d. CT angiography of the cerebral arteries (also known as a CTA carotids or an arch to vertex angiogram) is a noninvasive technique allows visualization of the internal and external carotid arteries and vertebral arteries and can include just the intracranial compartment or also extend down to the arch of the aorta. To refine the boundary of the segmented structures, morphologic dilation operations may be applied. 21, No. 35, No. With the above-mentioned scan parameters, the scan time would be 21 seconds for four–detector row CT, 7 seconds for 16–detector row CT, and 4 seconds for 64–detector row CT (64 × 0.6 mm, pitch of 1.3, 0.33-second rotation time). 5, Seminars in Roentgenology, Vol. Transfer functions are defined according to the intensities of the structures to be examined. Atherosclerotic plaques can be grouped into calcified and noncalcified ones. 4, Radiologic Clinics of North America, Vol. (b) Sagittal MPR image. 7, Journal of Stroke and Cerebrovascular Diseases, Vol. Interactive MPR and thin-slab MIP are suited to analysis of feeding and draining vessels, but the 3D presentation is limited. MIP image created after bone subtraction CT angiography shows complete elimination of bone; only small calcifications of the hyoid and laryngeal cartilage remain because of swallowing between the non-enhanced and contrast-enhanced acquisitions. A computer creates many separate images of the body area, called slices. As the parameters of the transfer function significantly affect the displayed lumen diameters, this method is difficult to standardize for accurate and reproducible measurements in different patients and different imaging centers (,4). (a) Two-dimensional histogram based on intensities (x axis) and gradient magnitudes (y axis) obtained from CT angiographic data. Wippold FJ, Orlowski HLP. Unlike conventional CTA, where only one, or perhaps two scans are done in coordination with the injection, dynamic CTA acquires a series of scans (between 2-20), at about 1 scan/second, to capture all phases of contrast flow, from arterial to venous. (b) Voxels corresponding to osseous tissue (arrow) and vessels enhanced with contrast medium (arrowhead) are easily identifiable in the 2D transfer function editor. 111, No. The disadvantage is the necessity for an additional injection of about 10 mL of contrast agent (10%–20% increase of total amount). (d) Volume-rendered image created with the transfer function shifted toward higher Hounsfield unit values results in reduced caliber of the visualized vessels. Bone suppression (2D transfer function volume rendering) or bone subtraction techniques improve the delineation of infraclinoid aneurysms, providing free access to the vessel in question (,Fig 19,,,) (,16,,45,,48). (The image was created from two digital subtraction angiographic series.). NB: This article is intended to outline some general principles of protocol design. Shaded surface display, or surface rendering, is an algorithm that provides a good 3D impression of the surface of an object. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. To enhance the detection of maximal lumen narrowing and the point of restitution of normal vessel diameter, the vessel can be displayed in a curved planar reformatted image along the centerline (stretched vessel image) and an additional cross-sectional measurement diagram (,Fig 7). Manual adjustment of both the centerline and lumen boundary is prone to individual errors and may be laborious and time-consuming. Threshold values of 150 HU (a), 200 HU (b), and 250 HU (c) result in calculated stenosis values of 35%, 55%, and 65%, respectively. Interfering factors leading to an inappropriate centerline are calcifications, plaque ulcers, and branching or adjacent vessels (,15). 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