Different transfer function settings alter the representation of the lumen. Computed tomography angiography (CTA) uses an injection of contrast material into your blood vessels and CT scanning to help diagnose and evaluate blood vessel disease or related conditions, such as aneurysms or blockages. 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. Parts of the jaw were manually removed from the image to exempt the left ICA. Aneurysms of the right ICA and left posterior cerebral artery. If the CT data meet the requirements of isotropy, spatial resolution is similar to the original source images. Large vascular malformation with significant arteriovenous shunting. (b) On a volume-rendered image from CT angiography, parts of the ICAs are hidden. 1, Current Neurology and Neuroscience Reports, Vol. (b) Voxels corresponding to osseous tissue (arrow) and vessels enhanced with contrast medium (arrowhead) are easily identifiable in the 2D transfer function editor. Clinical History: [ ] Technique: CT angio of the neck: Following rapid IV bolus of contrast material, rapid helical imaging with very thin slices from the aortic arch to the lower cranial level was performed. To individualize the timing of contrast material injection, automatic bolus tracking techniques (Smart Prep, CARE Bolus, and Sure Start) can be employed (,2). This is usually done by thresholding. Neurovascular applications for these various image postprocessing methods include steno-occlusive disease, dural sinus thrombosis, vascular malformations, and cerebral aneurysms. (The image was created from two digital subtraction angiographic series.). In-plane spatial resolution is predominantly determined by detector geometry and the convolution kernel; it is not substantially improved in scanners with increasing detector row numbers. Test bolus injection is the alternative to assess the individual circulation time. 2, 23 December 2010 | American Journal of Neuroradiology, Vol. With binary data, densitometric information gets lost and makes the method prone to undesirable artifacts. Usually, cerebral angiography is used after another test has already found an abnormality.Angiography is used to help detect and diagnose acute stroke. Placing one or more seed points initiates the segmentation of the target structure. 88, No. Automated measurements would be desirable in order to obtain reproducible results (,Fig 15). On these cross-sectional images, measurements are performed, and the site of measurement as well as the results can be superimposed on a volume-rendered image of the corresponding vessel to provide anatomic orientation. Figure 4. CT scans use more radiation than regular x-rays. Figure 14a. Conclusion • Despite recent advances in CT angiography and MR angiography, DSA remains the standard imaging technique for evaluation of the cerebral vasculature . Figure 2c. While patient movement between the two scans can be compensated for in cranial CT angiography, movements can result in incomplete bone or calcification removal in carotid CT angiography, unless additional registration steps or preprocessing is performed. 37, No. 28, No. A slab- or section-based rigid registration can compensate for movement in the longitudinal axis. If you absolutely must be given such contrast, your provider may give you antihistamines (such as Benadryl) or steroids before the test. The reconstruction algorithm (convolution kernel) influences the spatial resolution in plane. Postprocessing Strategies for Various Neurovascular Indications. For bone subtraction CT angiography, nonenhanced and contrast-enhanced spiral CT data sets are required. 2, Journal of the American Society of Echocardiography, Vol. A CT scan can reduce or avoid the need for invasive procedures to diagnose problems in the skull. The limited spatial resolution of CT angiography images does not fully delineate this ideal edge profile; edges are always smoothed to a certain extent. The bone mask is tentatively expanded in three dimensions with morphologic dilation. However, plaque calcifications (arrow in b) remain in the bone subtraction image because of misregistration due to arterial pulsation. France accepts BD diagnoses relying on a score based on lack of opacification of 7 intracerebral vessels in CTA images. 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. They may lead to termination of the segmentation process or “algorithmic leakage.”. (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). 1, EMC - Radiologie et imagerie médicale - Cardiovasculaire - Thoracique - Cervicale, Vol. Computed tomography angiography (CTA) is a rapidly developing technology with great potential. 1, Journal of Trauma and Acute Care Surgery, Vol. 1, Neuroimaging Clinics of North America, Vol. (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. 9, No. (c) Thin-slab MIP image shows the clip and beam-hardening artifacts. It is mainly performed on the outpatient basis, and … Individual timing of contrast material injection (bolus tracking or test bolus injection) is mandatory to take advantage of phase-resolved image acquisition. Figure 7. (a) Axial source image. 21, No. If you weigh more than 300 pounds (135 kilograms), talk to your provider about the weight limit before the test. Three-dimensional rendering of vascular malformations in the head and neck provides an excellent anatomic overview of the lesion and may enhance spatial perception for the surgeon or interventional radiologist. 9, Magnetic Resonance in Medical Sciences, Vol. In the presence of calcifications, the residual lumen cannot be assessed with MIP, thin-slab MIP, or surface-rendering techniques without prior bone elimination. Although cerebral catheter angiography or digital subtraction angiography are both performed in the interventional radiology department and are still generally regarded as the gold standard for the imaging of cerebrovascular disorders, those techniques are time consuming and are associated with a small, but significant, rate of permanent neurologic complications. 76, No. 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. 6, Japanese Journal of Radiological Technology, Vol. If bone subtraction CT angiography is applied, a 3D model of the venous cerebral vasculature without interfering bone can be created by using MIP or volume rendering (,Fig 17). Image created with segmentation shows punched-out defects (arrows) at vessel-bone contact areas. Open arrow = air, open arrowhead = soft tissue, solid arrowhead = vessels, solid arrow = osseous tissue. A variety of techniques have been proposed for postprocessing of the resulting images. 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 2D transfer functions shows similar results. The definition of the trapezoid strongly affects vascular lumen measurements (,Fig 5,,,). Bilateral stenoses of the distal ICA. Follow-up with CT angiography after interventional or surgical treatment faces considerable challenges: Clips or coils usually cause beam-hardening artifacts, altering the Hounsfield unit values in surrounding soft tissue and vessels. The kidneys help remove iodine out of the body. (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. Applying the algorithm on calcified plaque can result in excessive reduction of the residual lumen, which is impossible to check on the final image. In extracranial malformations and hemangiomas, CT can demonstrate both the lesion and the surrounding tissue, information that is critical for therapy planning. 35, No. Commercially available vessel analysis tools implement these procedures. In the emergency situation (stroke or subarachnoid hemorrhage), a robust and fast imaging technique capable of answering all vital clinical questions and allowing clear therapeutic decisions is mandatory. 30, No. 3, Interventional Cardiology Clinics, Vol. 92, No. 4, 28 December 2013 | Abdominal Imaging, Vol. allergy) and time constraints. Conventional angiography remains the standard imaging method, but CT angiography (CTA) is emerging as an alternative. 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). The newest scanners can image your entire body, head to toe, in less than 30 seconds. (b) On a volume-rendered image from CT angiography, parts of the ICAs are hidden. CT angiography (CTA) combines a CT scan with the injection of dye. Several image processing techniques for CT angiography are currently being used clinically (or at least advertised by the manufacturers). At CT venography, a thrombosed dural sinus is revealed as an irregular filling defect in the sinus or absence of contrast medium in the sinus (empty delta sign). 35, No. 4, IEEE Transactions on Biomedical Engineering, Vol. A particular problem in threshold-based segmentation algorithms are areas with close contact of two tissue types with comparable attenuation, such as bone and contrast-enhanced vessels (course of the ICA through the skull base; intraforaminal sections of the vertebral artery) (,Fig 6) (,15,,16). 199, No. Individually adapted image planes exactly perpendicular to the vessel lumen should be created interactively to allow precise quantitative analysis of both lumen and vessel wall. Otherwise—as for threshold-based techniques—exaggeration of stenosis may result. Segmentation can be performed manually or (semi)automatically. (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. 2, Journal of Clinical Neuroscience, Vol. S1, 8 October 2015 | American Journal of Neuroradiology, Vol. Short scan times require short contrast material injection. (b) Sagittal MPR image. CT angiography technique (scan protocol, con-trast material injection protocol, image recon-struction methods) and data visualization tech-nique (image postprocessing). (The image was created from two digital subtraction angiographic series. An angiogram of the brain is performed by a radiologist who will first place an intravenous injection into the patients arm to supply the body any required fluids or medication. (c) Image from selective catheter angiography shows the same findings as CT angiography. 10, No. Analysis on the basis of a centerline determined with segmentation and skeletonization. The utility of the contrast material bolus can be increased if a saline bolus is appended. Pulsation of the arteries and soft-tissue shifts at the level of the carotid bifurcation can lead to insufficient removal of calcified plaque when bone mask–based subtraction techniques are used (,Fig 14,) (,16). Interactive manipulation of the volume rendering presets is necessary to differentiate between infundibular dilatation of the vessel origin and true aneurysm (,46). (The image was created from two digital subtraction angiographic series. Figure 12. CT angiography is a type of medical test that combines a CT scan with an injection of a special dye to produce pictures of blood vessels and tissues in a part of your body. (c) MPR image aligned perpendicular to the vessel optimally depicts the residual lumen (solid arrow) and plaque calcification (dotted arrow). The aim of this review is to present optimized data acquisition techniques for multidetector spiral CT and meth-ods of image postprocessing and to discuss their Large vascular malformation with significant arteriovenous shunting. Three-dimensional models of the head and neck area can be created by stacking the slices together. Voxels lying close to tissue boundaries or inside uniform tissue produce histogram “hits” along the upper or lower regions of the parabolas. (b) On a volume-rendered image from CT angiography, parts of the ICAs are hidden. (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. Shaded surface display image shows bone and contrast-enhanced vessels as well as calcified plaque. (b) Image created from the original CT angiographic data shows the location of the aneurysm clip, which was completely removed from the image. Thin-slab MIP image (slab thickness = 15 mm) shows the cervical part of the carotid artery. Aneurysms of the right ICA and left posterior cerebral artery. 3, European Journal of Radiology, Vol. 1, 24 January 2013 | Surgical and Radiologic Anatomy, Vol. 3, 8 July 2011 | RadioGraphics, Vol. (b) Image created from the original CT angiographic data shows the location of the aneurysm clip, which was completely removed from the image. Aneurysms of the right ICA and left posterior cerebral artery. CT angiography is not suited to exclusion of small intracranial arteriovenous malformations; delineation of the nidus is another domain of digital subtraction angiography, which provides the highest spatial and temporal resolution as well as dynamic information (,42). 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). 7, No. An exact definition of the centerline is crucial for reliable measurements, because slight deviations from the center can generate artificial stenosis. CT angiography (CTA) is performed by scanning the patient during a rapid IV contrast bolus infusion while the contrast is in the arterial phase. Use of a high-opacity setting improves the 3D representation; however, the enhanced cavernous sinus hides small portions of the ICA. (c) On a volume-rendered image created with shading, the 3D impression is improved but edge definition is reduced. MIP image from bone subtraction CT venography shows the large cerebral veins and sinuses. (c) Image from selective catheter angiography shows the same findings as CT angiography. Top left: On a 3D display image, the segmented part of the left carotid artery is colored red. The most widely used techniques are multiplanar reformation (MPR), thin-slab maximum intensity projection, and volume rendering. If bone or calcifications are within the projection ray, these structures are represented on the MIP image instead of the contrast-enhanced vessel because of higher attenuation values. 5, 9 January 2018 | Computer Methods in Biomechanics and Biomedical Engineering, 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. Although the process of segmentation is semiautomatic, user interaction is necessary to set additional seeding points or to intervene in cases of inclusion of neighboring structures due to leakage of the region-growing algorithm. Figure 18e. 4, Radiologic Clinics of North America, Vol. You must be still during the exam, because movement causes blurred images. CT angiography of the chest (CTA chest) is a cross-sectional diagnostic examination that can be performed ECG-gated or non-ECG gated. 4, Japanese Journal of Radiological Technology, Vol. ROI = region of interest. 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. The depth information along the projection ray is lost; to visualize the spatial relationship of various structures, the volume has to be rotated and viewed from different angles. 3, The British Journal of Radiology, Vol. Threshold values of 150 HU (a), 200 HU (b), and 250 HU (c) result in calculated stenosis values of 35%, 55%, and 65%, respectively. 1, American Journal of Veterinary Research, Vol. If contrast is used, you may also be asked not to eat or drink anything for 4 to 6 hours before the test. 35, No. 3, No. Because bone and calcifications are seen as a particular problem in CT angiography, a variety of different approaches have been advocated to cope with this problem. In: Adam A, Dixon AK, Gillard JH, Schaefer-Prokop CM, eds. (a) Two-dimensional histogram based on intensities (x axis) and gradient magnitudes (y axis) obtained from CT angiographic data. (c) MPR image aligned perpendicular to the vessel optimally depicts the residual lumen (solid arrow) and plaque calcification (dotted arrow). Segmentation algorithms are often based on the principle of region growing (,13). Tumor invasion of the right transverse sinus. A more difficult problem is multidimensional movement of the jaw or the vertebral bones. Atherosclerosis is the most common arterial disease responsible for ischemic stroke. The short scan times of 64–detector row scanners allow arterial phase imaging with clearly different attenuation values of arteries and veins, while marked venous enhancement is likely to occur with four– to 16–detector row CT. Venous enhancement is not a crucial factor in the detection of cerebral aneurysms, except for extensive enhancement of the cavernous sinus. 1, Journal of the Korean Society of Radiology, Vol. The algorithm selectively eliminates bone from the CT angiography data set, retaining both soft tissue and contrast-enhanced vessels. Moderate stenosis of the left ICA. Lumen measurement is dependent on a correct window level setting (,3). (a) Axial image shows the right internal carotid artery (ICA) (1), left ICA (2), and left internal jugular vein (3). Let your provider know if you have ever had an allergic reaction to injected contrast dye. These are good conditions for image registration, and complete bone removal as well as removal of calcified plaque can be expected. 32, No. After reading this article and taking the test, the reader will be able to: Discuss the principles of data acquisition for CT angiography. MRI of the brain and/or cervical spine occasionally identifies a source of angiogram-negative acute SAH such as a thrombosed aneurysm, cavernous malformation, cerebral amyloid angiopathy, or spinal vascular malformation, but the overall diagnostic yield is low. Shaded surface display, or surface rendering, is an algorithm that provides a good 3D impression of the surface of an object. Catheter brain angiogram is a minimally invasive diagnostic procedure where especially detailed images of brain vessels are obtained. (c) On an image created with a low-opacity setting, the sinus is transparent, thus allowing visualization of the vessel boundary. Figure 20c. After loading both data sets, processing is performed automatically without any user interaction. Figure 5b. Figure 13. However, one should keep in mind the potential pitfalls of these techniques and always double-check the final results with source or MPR imaging. (a) Axial image shows the right internal carotid artery (ICA) (1), left ICA (2), and left internal jugular vein (3). Mortality is high among patients with aneurysm rupture, and prompt localization of the aneurysm is critical to determine the appropriate neurosurgical or endovascular intervention. Profile of the ideal tissue boundary and the corresponding result at CT angiographic reformation. 1023, American Journal of Roentgenology, Vol. CT stands for computed tomography. (a, b) Volume-rendered images created without shading at low opacity (a) and high opacity (b) show accentuated vessel boundaries. Bone subtraction algorithms work well at the skull base because the skull is a rigid compartment and the vessels are sufficiently fixed. Many vessel analysis tools offer automatic lumen measurement procedures. The ICA calcification complicates analysis of the residual lumen with automatic and manual procedures. Orthogonal views of the vessel are required to evaluate the lumen (,33), which is most comfortably done by creating a centerline first and reformatting cross-sectional views along this line subsequently with the aid of vessel analysis suites. CT angiography (CTA) combines a CT scan with the injection of dye. 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