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CT Angiography of Intracranial Aneurysms: A Focus on Postprocessing¹

¹ From the Department of Neurosurgery, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany. Presented as an education exhibit at the 2002 RSNA scientific assembly. Received May 5, 2003; revision requested June 13 and received July 30; accepted July 31. All authors have no financial relationships to disclose. Address correspondence to B.F.T. (e-mail: tomandl@neuroradiologie-erlangen.de).

View larger version (103K): [in a new window]   Figure 1a.  Effect of FOV on image quality of 3D imaging with SSD in a patient with two aneurysms (arrows in b-d) at the bifurcation of the left middle cerebral artery (MCA). (a) CT image shows the areas covered by three different values for FOV: 200, 120, and 60 mm2. (b) SSD image obtained by reconstructing the data with an FOV of 200 mm2. Arteries appear blurred. (c) SSD image obtained by reconstructing the data with an FOV of 120 mm2. Vascular anatomy is shown more clearly than in b. This FOV contains all relevant intracranial arteries from which aneurysms usually originate while providing good in-plane resolution. Thus, we always use this FOV for detection of intracranial aneurysms. (d) SSD image obtained by reconstructing the data with an FOV of 60 mm2. There is even better demonstration of vascular anatomy than in c. It is sometimes useful to perform a second reconstruction with a narrow FOV such as this when CT angiography is used for therapy planning and very detailed information is required.

View larger version (99K): [in a new window]   Figure 1b.  Effect of FOV on image quality of 3D imaging with SSD in a patient with two aneurysms (arrows in b-d) at the bifurcation of the left middle cerebral artery (MCA). (a) CT image shows the areas covered by three different values for FOV: 200, 120, and 60 mm2. (b) SSD image obtained by reconstructing the data with an FOV of 200 mm2. Arteries appear blurred. (c) SSD image obtained by reconstructing the data with an FOV of 120 mm2. Vascular anatomy is shown more clearly than in b. This FOV contains all relevant intracranial arteries from which aneurysms usually originate while providing good in-plane resolution. Thus, we always use this FOV for detection of intracranial aneurysms. (d) SSD image obtained by reconstructing the data with an FOV of 60 mm2. There is even better demonstration of vascular anatomy than in c. It is sometimes useful to perform a second reconstruction with a narrow FOV such as this when CT angiography is used for therapy planning and very detailed information is required.

View larger version (98K): [in a new window]   Figure 1c.  Effect of FOV on image quality of 3D imaging with SSD in a patient with two aneurysms (arrows in b-d) at the bifurcation of the left middle cerebral artery (MCA). (a) CT image shows the areas covered by three different values for FOV: 200, 120, and 60 mm2. (b) SSD image obtained by reconstructing the data with an FOV of 200 mm2. Arteries appear blurred. (c) SSD image obtained by reconstructing the data with an FOV of 120 mm2. Vascular anatomy is shown more clearly than in b. This FOV contains all relevant intracranial arteries from which aneurysms usually originate while providing good in-plane resolution. Thus, we always use this FOV for detection of intracranial aneurysms. (d) SSD image obtained by reconstructing the data with an FOV of 60 mm2. There is even better demonstration of vascular anatomy than in c. It is sometimes useful to perform a second reconstruction with a narrow FOV such as this when CT angiography is used for therapy planning and very detailed information is required.

View larger version (113K): [in a new window]   Figure 1d.  Effect of FOV on image quality of 3D imaging with SSD in a patient with two aneurysms (arrows in b-d) at the bifurcation of the left middle cerebral artery (MCA). (a) CT image shows the areas covered by three different values for FOV: 200, 120, and 60 mm2. (b) SSD image obtained by reconstructing the data with an FOV of 200 mm2. Arteries appear blurred. (c) SSD image obtained by reconstructing the data with an FOV of 120 mm2. Vascular anatomy is shown more clearly than in b. This FOV contains all relevant intracranial arteries from which aneurysms usually originate while providing good in-plane resolution. Thus, we always use this FOV for detection of intracranial aneurysms. (d) SSD image obtained by reconstructing the data with an FOV of 60 mm2. There is even better demonstration of vascular anatomy than in c. It is sometimes useful to perform a second reconstruction with a narrow FOV such as this when CT angiography is used for therapy planning and very detailed information is required.

View larger version (125K): [in a new window]   Figure 2.  Importance of an adequate window setting to demonstrate the intracranial arteries within the skull base. CT image obtained with a window width of 500 HU and a center of 150 HU. Both ICAs can be clearly differentiated within the carotid canals (arrows).

View larger version (159K): [in a new window]   Figure 3a.  Preparation of the volume for analysis. (a) Posterosuperior image shows large veins (arrowheads), which are typically also visible in CT angiography of intracranial vessels and preclude an unobstructed view of the circle of Willis and the basilar artery (arrow). (b) Left lateroposterior image shows easy elimination of the most obscuring venous structures by using a clip plane (dotted white line) parallel to the clivus. (c) Posterosuperior image obtained after application of the clip plane (dotted white line) shows that the basilar artery is demonstrated completely (arrowheads).

View larger version (132K): [in a new window]   Figure 3b.  Preparation of the volume for analysis. (a) Posterosuperior image shows large veins (arrowheads), which are typically also visible in CT angiography of intracranial vessels and preclude an unobstructed view of the circle of Willis and the basilar artery (arrow). (b) Left lateroposterior image shows easy elimination of the most obscuring venous structures by using a clip plane (dotted white line) parallel to the clivus. (c) Posterosuperior image obtained after application of the clip plane (dotted white line) shows that the basilar artery is demonstrated completely (arrowheads).

View larger version (160K): [in a new window]   Figure 3c.  Preparation of the volume for analysis. (a) Posterosuperior image shows large veins (arrowheads), which are typically also visible in CT angiography of intracranial vessels and preclude an unobstructed view of the circle of Willis and the basilar artery (arrow). (b) Left lateroposterior image shows easy elimination of the most obscuring venous structures by using a clip plane (dotted white line) parallel to the clivus. (c) Posterosuperior image obtained after application of the clip plane (dotted white line) shows that the basilar artery is demonstrated completely (arrowheads).

View larger version (89K): [in a new window]   Figure 4a.  Influence of 3D visualization techniques on the detection of intracranial aneurysms. (a) MIP image (superior view) shows the bifurcation of the left MCA (arrow). Owing to the lack of depth information, the image does not allow visualization of two aneurysms at this site. (b, c) SSD (b) and dVR (c) images (superior views) of the bifurcation of the left MCA show the two aneurysms (arrows).

View larger version (108K): [in a new window]   Figure 4b.  Influence of 3D visualization techniques on the detection of intracranial aneurysms. (a) MIP image (superior view) shows the bifurcation of the left MCA (arrow). Owing to the lack of depth information, the image does not allow visualization of two aneurysms at this site. (b, c) SSD (b) and dVR (c) images (superior views) of the bifurcation of the left MCA show the two aneurysms (arrows).

View larger version (111K): [in a new window]   Figure 4c.  Influence of 3D visualization techniques on the detection of intracranial aneurysms. (a) MIP image (superior view) shows the bifurcation of the left MCA (arrow). Owing to the lack of depth information, the image does not allow visualization of two aneurysms at this site. (b, c) SSD (b) and dVR (c) images (superior views) of the bifurcation of the left MCA show the two aneurysms (arrows).

View larger version (106K): [in a new window]   Figure 5a.  Analysis of CT angiography data with MPR and thin-section MIP. (a-c) Sagittal (a), coronal (b), and axial (c) MPR images show a small aneurysm at the bifurcation of the right MCA (arrow). Note the large intracerebral hematoma (arrowheads in a), which is usually not demonstrated on threshold-based 3D images. (d-f) Sagittal (d), coronal (e), and axial (f) MIP images obtained with thin sections of 20 mm show the aneurysm more clearly (arrow) and show the intracerebral hematoma as well (arrowheads in d).

View larger version (115K): [in a new window]   Figure 5b.  Analysis of CT angiography data with MPR and thin-section MIP. (a-c) Sagittal (a), coronal (b), and axial (c) MPR images show a small aneurysm at the bifurcation of the right MCA (arrow). Note the large intracerebral hematoma (arrowheads in a), which is usually not demonstrated on threshold-based 3D images. (d-f) Sagittal (d), coronal (e), and axial (f) MIP images obtained with thin sections of 20 mm show the aneurysm more clearly (arrow) and show the intracerebral hematoma as well (arrowheads in d).

View larger version (122K): [in a new window]   Figure 5c.  Analysis of CT angiography data with MPR and thin-section MIP. (a-c) Sagittal (a), coronal (b), and axial (c) MPR images show a small aneurysm at the bifurcation of the right MCA (arrow). Note the large intracerebral hematoma (arrowheads in a), which is usually not demonstrated on threshold-based 3D images. (d-f) Sagittal (d), coronal (e), and axial (f) MIP images obtained with thin sections of 20 mm show the aneurysm more clearly (arrow) and show the intracerebral hematoma as well (arrowheads in d).

View larger version (104K): [in a new window]   Figure 5d.  Analysis of CT angiography data with MPR and thin-section MIP. (a-c) Sagittal (a), coronal (b), and axial (c) MPR images show a small aneurysm at the bifurcation of the right MCA (arrow). Note the large intracerebral hematoma (arrowheads in a), which is usually not demonstrated on threshold-based 3D images. (d-f) Sagittal (d), coronal (e), and axial (f) MIP images obtained with thin sections of 20 mm show the aneurysm more clearly (arrow) and show the intracerebral hematoma as well (arrowheads in d).

View larger version (117K): [in a new window]   Figure 5e.  Analysis of CT angiography data with MPR and thin-section MIP. (a-c) Sagittal (a), coronal (b), and axial (c) MPR images show a small aneurysm at the bifurcation of the right MCA (arrow). Note the large intracerebral hematoma (arrowheads in a), which is usually not demonstrated on threshold-based 3D images. (d-f) Sagittal (d), coronal (e), and axial (f) MIP images obtained with thin sections of 20 mm show the aneurysm more clearly (arrow) and show the intracerebral hematoma as well (arrowheads in d).

View larger version (153K): [in a new window]   Figure 5f.  Analysis of CT angiography data with MPR and thin-section MIP. (a-c) Sagittal (a), coronal (b), and axial (c) MPR images show a small aneurysm at the bifurcation of the right MCA (arrow). Note the large intracerebral hematoma (arrowheads in a), which is usually not demonstrated on threshold-based 3D images. (d-f) Sagittal (d), coronal (e), and axial (f) MIP images obtained with thin sections of 20 mm show the aneurysm more clearly (arrow) and show the intracerebral hematoma as well (arrowheads in d).

View larger version (200K): [in a new window]   Figure 6a.  Threshold-dependent 3D visualization with SSD. (a) Superoposterior view obtained with a lower threshold of 100 HU shows smaller arteries like the left PICA (arrow) and venous structures (arrowheads). (b) Superoposterior view obtained by increasing the lower threshold to 200 HU shows arteries that appear thinner compared with those in a and even demonstrate discontinuities (arrow). The venous structures are nearly eliminated (arrowheads), resulting in a less complex image.

View larger version (182K): [in a new window]   Figure 6b.  Threshold-dependent 3D visualization with SSD. (a) Superoposterior view obtained with a lower threshold of 100 HU shows smaller arteries like the left PICA (arrow) and venous structures (arrowheads). (b) Superoposterior view obtained by increasing the lower threshold to 200 HU shows arteries that appear thinner compared with those in a and even demonstrate discontinuities (arrow). The venous structures are nearly eliminated (arrowheads), resulting in a less complex image.

View larger version (162K): [in a new window]   Figure 7a.  Basic principles of volume rendering. Groups of voxels are selected according to their Hounsfield unit values. Every group has its own color and opacity. A low opacity makes the objects transparent. dVR image (superior view) of a patient with two aneurysm clips (a) and photograph of the workstation screen (b). The voxels representing the metal clips (arrows in a) are colored blue with a high opacity. Bone (voxels between 200 and 2,000 HU) is colored white with an opacity of 49%. Finally, the voxels between 90 and 300 HU that contain the vascular information are colored red with a 50% opacity.

View larger version (90K): [in a new window]   Figure 7b.  Basic principles of volume rendering. Groups of voxels are selected according to their Hounsfield unit values. Every group has its own color and opacity. A low opacity makes the objects transparent. dVR image (superior view) of a patient with two aneurysm clips (a) and photograph of the workstation screen (b). The voxels representing the metal clips (arrows in a) are colored blue with a high opacity. Bone (voxels between 200 and 2,000 HU) is colored white with an opacity of 49%. Finally, the voxels between 90 and 300 HU that contain the vascular information are colored red with a 50% opacity.

View larger version (100K): [in a new window]   Figure 8a.  Different possibilities for examining an aneurysm of the left MCA with dVR. (a) Frontal image obtained without shading. (b) Frontal image obtained with shading (addition of an artificial light source), which gives the objects more depth. (c) Frontal image obtained by selecting only a small group of voxels with a low opacity. The vessels appear transparent, thus allowing visualization of a branch of the MCA running behind the aneurysm (arrow). (d) Left frontolateral transparent image allows the orifice of the feeding artery to be seen through the aneurysm (arrow). (e) Frontal "virtual endoscopic" image, obtained by selecting only a small group of voxels with a high opacity, shows a pseudoconnection between the aneurysm and an adjacent artery (arrow). This "kissing vessel" artifact is a partial volume problem that is often seen on CT angiograms of intracranial aneurysms. (f) Anterocaudal image obtained with high opacity shows the close relationship of the aneurysm to the lower branch of the MCA (arrow).

View larger version (115K): [in a new window]   Figure 8b.  Different possibilities for examining an aneurysm of the left MCA with dVR. (a) Frontal image obtained without shading. (b) Frontal image obtained with shading (addition of an artificial light source), which gives the objects more depth. (c) Frontal image obtained by selecting only a small group of voxels with a low opacity. The vessels appear transparent, thus allowing visualization of a branch of the MCA running behind the aneurysm (arrow). (d) Left frontolateral transparent image allows the orifice of the feeding artery to be seen through the aneurysm (arrow). (e) Frontal "virtual endoscopic" image, obtained by selecting only a small group of voxels with a high opacity, shows a pseudoconnection between the aneurysm and an adjacent artery (arrow). This "kissing vessel" artifact is a partial volume problem that is often seen on CT angiograms of intracranial aneurysms. (f) Anterocaudal image obtained with high opacity shows the close relationship of the aneurysm to the lower branch of the MCA (arrow).

View larger version (133K): [in a new window]   Figure 8c.  Different possibilities for examining an aneurysm of the left MCA with dVR. (a) Frontal image obtained without shading. (b) Frontal image obtained with shading (addition of an artificial light source), which gives the objects more depth. (c) Frontal image obtained by selecting only a small group of voxels with a low opacity. The vessels appear transparent, thus allowing visualization of a branch of the MCA running behind the aneurysm (arrow). (d) Left frontolateral transparent image allows the orifice of the feeding artery to be seen through the aneurysm (arrow). (e) Frontal "virtual endoscopic" image, obtained by selecting only a small group of voxels with a high opacity, shows a pseudoconnection between the aneurysm and an adjacent artery (arrow). This "kissing vessel" artifact is a partial volume problem that is often seen on CT angiograms of intracranial aneurysms. (f) Anterocaudal image obtained with high opacity shows the close relationship of the aneurysm to the lower branch of the MCA (arrow).

View larger version (130K): [in a new window]   Figure 8d.  Different possibilities for examining an aneurysm of the left MCA with dVR. (a) Frontal image obtained without shading. (b) Frontal image obtained with shading (addition of an artificial light source), which gives the objects more depth. (c) Frontal image obtained by selecting only a small group of voxels with a low opacity. The vessels appear transparent, thus allowing visualization of a branch of the MCA running behind the aneurysm (arrow). (d) Left frontolateral transparent image allows the orifice of the feeding artery to be seen through the aneurysm (arrow). (e) Frontal "virtual endoscopic" image, obtained by selecting only a small group of voxels with a high opacity, shows a pseudoconnection between the aneurysm and an adjacent artery (arrow). This "kissing vessel" artifact is a partial volume problem that is often seen on CT angiograms of intracranial aneurysms. (f) Anterocaudal image obtained with high opacity shows the close relationship of the aneurysm to the lower branch of the MCA (arrow).

View larger version (103K): [in a new window]   Figure 8e.  Different possibilities for examining an aneurysm of the left MCA with dVR. (a) Frontal image obtained without shading. (b) Frontal image obtained with shading (addition of an artificial light source), which gives the objects more depth. (c) Frontal image obtained by selecting only a small group of voxels with a low opacity. The vessels appear transparent, thus allowing visualization of a branch of the MCA running behind the aneurysm (arrow). (d) Left frontolateral transparent image allows the orifice of the feeding artery to be seen through the aneurysm (arrow). (e) Frontal "virtual endoscopic" image, obtained by selecting only a small group of voxels with a high opacity, shows a pseudoconnection between the aneurysm and an adjacent artery (arrow). This "kissing vessel" artifact is a partial volume problem that is often seen on CT angiograms of intracranial aneurysms. (f) Anterocaudal image obtained with high opacity shows the close relationship of the aneurysm to the lower branch of the MCA (arrow).

View larger version (128K): [in a new window]   Figure 8f.  Different possibilities for examining an aneurysm of the left MCA with dVR. (a) Frontal image obtained without shading. (b) Frontal image obtained with shading (addition of an artificial light source), which gives the objects more depth. (c) Frontal image obtained by selecting only a small group of voxels with a low opacity. The vessels appear transparent, thus allowing visualization of a branch of the MCA running behind the aneurysm (arrow). (d) Left frontolateral transparent image allows the orifice of the feeding artery to be seen through the aneurysm (arrow). (e) Frontal "virtual endoscopic" image, obtained by selecting only a small group of voxels with a high opacity, shows a pseudoconnection between the aneurysm and an adjacent artery (arrow). This "kissing vessel" artifact is a partial volume problem that is often seen on CT angiograms of intracranial aneurysms. (f) Anterocaudal image obtained with high opacity shows the close relationship of the aneurysm to the lower branch of the MCA (arrow).

View larger version (59K): [in a new window]   Figure 9a.  Standard 3D projections obtained by using dVR interactively on the workstation (left) and diagrams of the corresponding arterial anatomy (right). This systematic analysis is of extreme importance, especially when an aneurysm is detected at first glance, to ensure that additional aneurysms are not missed. ACA = anterior cerebral artery, PCA = posterior cerebral artery, PCom = posterior communicating artery, VA = vertebral artery. (a) Superior view of all of the intracranial arteries. In many cases, larger aneurysms are immediately visible on this overview. (b) Posterior view of the basilar and vertebral arteries. Aneurysms of the PICA and the basilar artery tip can be detected on this view. AICA = anterior inferior cerebellar artery. (c) Lateral view of the intracranial part of the ICA. Note that the ICA is partially obscured by osseous structures, making detection of aneurysms in this area difficult with 3D images alone. (d) Unobstructed view of the MCA bifurcation obtained from a superior angle. (e) Unobstructed view of the anterior communicating artery (ACom) obtained from a superior angle. (f) Unobstructed view of the anterior communicating artery (ACom) and the bifurcation of the left MCA obtained from an inferior angle after elimination of the skull base by using a clip plane (Fig 3).

View larger version (64K): [in a new window]   Figure 9b.  Standard 3D projections obtained by using dVR interactively on the workstation (left) and diagrams of the corresponding arterial anatomy (right). This systematic analysis is of extreme importance, especially when an aneurysm is detected at first glance, to ensure that additional aneurysms are not missed. ACA = anterior cerebral artery, PCA = posterior cerebral artery, PCom = posterior communicating artery, VA = vertebral artery. (a) Superior view of all of the intracranial arteries. In many cases, larger aneurysms are immediately visible on this overview. (b) Posterior view of the basilar and vertebral arteries. Aneurysms of the PICA and the basilar artery tip can be detected on this view. AICA = anterior inferior cerebellar artery. (c) Lateral view of the intracranial part of the ICA. Note that the ICA is partially obscured by osseous structures, making detection of aneurysms in this area difficult with 3D images alone. (d) Unobstructed view of the MCA bifurcation obtained from a superior angle. (e) Unobstructed view of the anterior communicating artery (ACom) obtained from a superior angle. (f) Unobstructed view of the anterior communicating artery (ACom) and the bifurcation of the left MCA obtained from an inferior angle after elimination of the skull base by using a clip plane (Fig 3).

View larger version (46K): [in a new window]   Figure 9c.  Standard 3D projections obtained by using dVR interactively on the workstation (left) and diagrams of the corresponding arterial anatomy (right). This systematic analysis is of extreme importance, especially when an aneurysm is detected at first glance, to ensure that additional aneurysms are not missed. ACA = anterior cerebral artery, PCA = posterior cerebral artery, PCom = posterior communicating artery, VA = vertebral artery. (a) Superior view of all of the intracranial arteries. In many cases, larger aneurysms are immediately visible on this overview. (b) Posterior view of the basilar and vertebral arteries. Aneurysms of the PICA and the basilar artery tip can be detected on this view. AICA = anterior inferior cerebellar artery. (c) Lateral view of the intracranial part of the ICA. Note that the ICA is partially obscured by osseous structures, making detection of aneurysms in this area difficult with 3D images alone. (d) Unobstructed view of the MCA bifurcation obtained from a superior angle. (e) Unobstructed view of the anterior communicating artery (ACom) obtained from a superior angle. (f) Unobstructed view of the anterior communicating artery (ACom) and the bifurcation of the left MCA obtained from an inferior angle after elimination of the skull base by using a clip plane (Fig 3).

View larger version (28K): [in a new window]   Figure 9d.  Standard 3D projections obtained by using dVR interactively on the workstation (left) and diagrams of the corresponding arterial anatomy (right). This systematic analysis is of extreme importance, especially when an aneurysm is detected at first glance, to ensure that additional aneurysms are not missed. ACA = anterior cerebral artery, PCA = posterior cerebral artery, PCom = posterior communicating artery, VA = vertebral artery. (a) Superior view of all of the intracranial arteries. In many cases, larger aneurysms are immediately visible on this overview. (b) Posterior view of the basilar and vertebral arteries. Aneurysms of the PICA and the basilar artery tip can be detected on this view. AICA = anterior inferior cerebellar artery. (c) Lateral view of the intracranial part of the ICA. Note that the ICA is partially obscured by osseous structures, making detection of aneurysms in this area difficult with 3D images alone. (d) Unobstructed view of the MCA bifurcation obtained from a superior angle. (e) Unobstructed view of the anterior communicating artery (ACom) obtained from a superior angle. (f) Unobstructed view of the anterior communicating artery (ACom) and the bifurcation of the left MCA obtained from an inferior angle after elimination of the skull base by using a clip plane (Fig 3).

View larger version (41K): [in a new window]   Figure 9e.  Standard 3D projections obtained by using dVR interactively on the workstation (left) and diagrams of the corresponding arterial anatomy (right). This systematic analysis is of extreme importance, especially when an aneurysm is detected at first glance, to ensure that additional aneurysms are not missed. ACA = anterior cerebral artery, PCA = posterior cerebral artery, PCom = posterior communicating artery, VA = vertebral artery. (a) Superior view of all of the intracranial arteries. In many cases, larger aneurysms are immediately visible on this overview. (b) Posterior view of the basilar and vertebral arteries. Aneurysms of the PICA and the basilar artery tip can be detected on this view. AICA = anterior inferior cerebellar artery. (c) Lateral view of the intracranial part of the ICA. Note that the ICA is partially obscured by osseous structures, making detection of aneurysms in this area difficult with 3D images alone. (d) Unobstructed view of the MCA bifurcation obtained from a superior angle. (e) Unobstructed view of the anterior communicating artery (ACom) obtained from a superior angle. (f) Unobstructed view of the anterior communicating artery (ACom) and the bifurcation of the left MCA obtained from an inferior angle after elimination of the skull base by using a clip plane (Fig 3).

View larger version (36K): [in a new window]   Figure 9f.  Standard 3D projections obtained by using dVR interactively on the workstation (left) and diagrams of the corresponding arterial anatomy (right). This systematic analysis is of extreme importance, especially when an aneurysm is detected at first glance, to ensure that additional aneurysms are not missed. ACA = anterior cerebral artery, PCA = posterior cerebral artery, PCom = posterior communicating artery, VA = vertebral artery. (a) Superior view of all of the intracranial arteries. In many cases, larger aneurysms are immediately visible on this overview. (b) Posterior view of the basilar and vertebral arteries. Aneurysms of the PICA and the basilar artery tip can be detected on this view. AICA = anterior inferior cerebellar artery. (c) Lateral view of the intracranial part of the ICA. Note that the ICA is partially obscured by osseous structures, making detection of aneurysms in this area difficult with 3D images alone. (d) Unobstructed view of the MCA bifurcation obtained from a superior angle. (e) Unobstructed view of the anterior communicating artery (ACom) obtained from a superior angle. (f) Unobstructed view of the anterior communicating artery (ACom) and the bifurcation of the left MCA obtained from an inferior angle after elimination of the skull base by using a clip plane (Fig 3).

View larger version (180K): [in a new window]   Figure 10a.  Visualization of the intracranial arteries with 3D dVR performed by using different colors. Superior views show the arteries colored red (a) and blue (b). It is not known whether the colors affect the detection rate of intracranial aneurysms with CT angiography.

View larger version (179K): [in a new window]   Figure 10b.  Visualization of the intracranial arteries with 3D dVR performed by using different colors. Superior views show the arteries colored red (a) and blue (b). It is not known whether the colors affect the detection rate of intracranial aneurysms with CT angiography.

View larger version (105K): [in a new window]   Figure 11a.  Use of CT angiography for planning endovascular therapy. (a) Anterior 3D dVR image obtained with a high opacity shows an irregular aneurysm of the left intracranial carotid bifurcation (arrow). (b) Anterior transparent dVR image obtained with a low opacity shows the measured diameters of the dome and neck of the aneurysm (arrow). The maximal diameter of the dome was almost 7 mm. (c) Posteroanterior DSA image of the left ICA obtained after placement of the first coil. Because the exact measurements of the aneurysm (arrow) were determined with CT angiography, a 7-mm-diameter platinum coil was used first.

View larger version (109K): [in a new window]   Figure 11b.  Use of CT angiography for planning endovascular therapy. (a) Anterior 3D dVR image obtained with a high opacity shows an irregular aneurysm of the left intracranial carotid bifurcation (arrow). (b) Anterior transparent dVR image obtained with a low opacity shows the measured diameters of the dome and neck of the aneurysm (arrow). The maximal diameter of the dome was almost 7 mm. (c) Posteroanterior DSA image of the left ICA obtained after placement of the first coil. Because the exact measurements of the aneurysm (arrow) were determined with CT angiography, a 7-mm-diameter platinum coil was used first.

View larger version (59K): [in a new window]   Figure 11c.  Use of CT angiography for planning endovascular therapy. (a) Anterior 3D dVR image obtained with a high opacity shows an irregular aneurysm of the left intracranial carotid bifurcation (arrow). (b) Anterior transparent dVR image obtained with a low opacity shows the measured diameters of the dome and neck of the aneurysm (arrow). The maximal diameter of the dome was almost 7 mm. (c) Posteroanterior DSA image of the left ICA obtained after placement of the first coil. Because the exact measurements of the aneurysm (arrow) were determined with CT angiography, a 7-mm-diameter platinum coil was used first.

View larger version (123K): [in a new window]   Figure 12a.  Use of CT angiography for planning surgical therapy in a patient with two small aneurysms at the bifurcation of the right MCA. Arrows = aneurysms. (a) Three-dimensional dVR image obtained with a high opacity shows anatomic information nearly identical to the intraoperative findings (c). (b) Transparent dVR image obtained with a low opacity shows the orifice of the main stem of the MCA (arrowhead). Such images are often helpful in demonstrating the anatomy behind the vascular structures. (c) Photograph shows the intraoperative findings.

View larger version (128K): [in a new window]   Figure 12b.  Use of CT angiography for planning surgical therapy in a patient with two small aneurysms at the bifurcation of the right MCA. Arrows = aneurysms. (a) Three-dimensional dVR image obtained with a high opacity shows anatomic information nearly identical to the intraoperative findings (c). (b) Transparent dVR image obtained with a low opacity shows the orifice of the main stem of the MCA (arrowhead). Such images are often helpful in demonstrating the anatomy behind the vascular structures. (c) Photograph shows the intraoperative findings.

View larger version (113K): [in a new window]   Figure 12c.  Use of CT angiography for planning surgical therapy in a patient with two small aneurysms at the bifurcation of the right MCA. Arrows = aneurysms. (a) Three-dimensional dVR image obtained with a high opacity shows anatomic information nearly identical to the intraoperative findings (c). (b) Transparent dVR image obtained with a low opacity shows the orifice of the main stem of the MCA (arrowhead). Such images are often helpful in demonstrating the anatomy behind the vascular structures. (c) Photograph shows the intraoperative findings.

View larger version (112K): [in a new window]   Figure 13a.  Infundibular dilatation at the origin of the right PICA. (a) Superoposterior dVR image shows an aneurysmal structure along the right vertebral artery (arrow). (b) Superoposterior dVR image obtained by lowering the threshold for the group of voxels that contain the vascular information shows that the structure is an infundibular dilatation at the origin of the right PICA (large arrow). Note that some small arteries like the left PICA (large arrowhead) and the right anterior inferior cerebellar artery (small arrow, small arrowhead) have also become visible.

View larger version (119K): [in a new window]   Figure 13b.  Infundibular dilatation at the origin of the right PICA. (a) Superoposterior dVR image shows an aneurysmal structure along the right vertebral artery (arrow). (b) Superoposterior dVR image obtained by lowering the threshold for the group of voxels that contain the vascular information shows that the structure is an infundibular dilatation at the origin of the right PICA (large arrow). Note that some small arteries like the left PICA (large arrowhead) and the right anterior inferior cerebellar artery (small arrow, small arrowhead) have also become visible.

View larger version (173K): [in a new window]   Figure 14a.  Kissing vessel artifact. (a) CT angiogram (superior view) shows an aneurysm of the left anterior communicating artery (arrowhead) adjacent to the right ICA (arrow). An aneurysm at the bifurcation of the left MCA is also seen. (b) Right frontal dVR image shows a large connection (arrow) between the right ICA and the aneurysm (arrowhead). (c) Transparent dVR image clearly shows the connection (arrow). Arrowhead = aneurysm. (d, e) Transparent (d) and virtual endoscopic (e) dVR images show a hole (arrow) between the right ICA and the aneurysm. (f) DSA image shows no connection between the right ICA and the aneurysm (arrow). A separate angiogram was obtained for each carotid artery, and the images were combined manually. To demonstrate the lack of a connection, the space between the right ICA and the aneurysm is shown as larger than it actually was.

View larger version (92K): [in a new window]   Figure 14b.  Kissing vessel artifact. (a) CT angiogram (superior view) shows an aneurysm of the left anterior communicating artery (arrowhead) adjacent to the right ICA (arrow). An aneurysm at the bifurcation of the left MCA is also seen. (b) Right frontal dVR image shows a large connection (arrow) between the right ICA and the aneurysm (arrowhead). (c) Transparent dVR image clearly shows the connection (arrow). Arrowhead = aneurysm. (d, e) Transparent (d) and virtual endoscopic (e) dVR images show a hole (arrow) between the right ICA and the aneurysm. (f) DSA image shows no connection between the right ICA and the aneurysm (arrow). A separate angiogram was obtained for each carotid artery, and the images were combined manually. To demonstrate the lack of a connection, the space between the right ICA and the aneurysm is shown as larger than it actually was.

View larger version (81K): [in a new window]   Figure 14c.  Kissing vessel artifact. (a) CT angiogram (superior view) shows an aneurysm of the left anterior communicating artery (arrowhead) adjacent to the right ICA (arrow). An aneurysm at the bifurcation of the left MCA is also seen. (b) Right frontal dVR image shows a large connection (arrow) between the right ICA and the aneurysm (arrowhead). (c) Transparent dVR image clearly shows the connection (arrow). Arrowhead = aneurysm. (d, e) Transparent (d) and virtual endoscopic (e) dVR images show a hole (arrow) between the right ICA and the aneurysm. (f) DSA image shows no connection between the right ICA and the aneurysm (arrow). A separate angiogram was obtained for each carotid artery, and the images were combined manually. To demonstrate the lack of a connection, the space between the right ICA and the aneurysm is shown as larger than it actually was.

View larger version (111K): [in a new window]   Figure 14d.  Kissing vessel artifact. (a) CT angiogram (superior view) shows an aneurysm of the left anterior communicating artery (arrowhead) adjacent to the right ICA (arrow). An aneurysm at the bifurcation of the left MCA is also seen. (b) Right frontal dVR image shows a large connection (arrow) between the right ICA and the aneurysm (arrowhead). (c) Transparent dVR image clearly shows the connection (arrow). Arrowhead = aneurysm. (d, e) Transparent (d) and virtual endoscopic (e) dVR images show a hole (arrow) between the right ICA and the aneurysm. (f) DSA image shows no connection between the right ICA and the aneurysm (arrow). A separate angiogram was obtained for each carotid artery, and the images were combined manually. To demonstrate the lack of a connection, the space between the right ICA and the aneurysm is shown as larger than it actually was.

View larger version (111K): [in a new window]   Figure 14e.  Kissing vessel artifact. (a) CT angiogram (superior view) shows an aneurysm of the left anterior communicating artery (arrowhead) adjacent to the right ICA (arrow). An aneurysm at the bifurcation of the left MCA is also seen. (b) Right frontal dVR image shows a large connection (arrow) between the right ICA and the aneurysm (arrowhead). (c) Transparent dVR image clearly shows the connection (arrow). Arrowhead = aneurysm. (d, e) Transparent (d) and virtual endoscopic (e) dVR images show a hole (arrow) between the right ICA and the aneurysm. (f) DSA image shows no connection between the right ICA and the aneurysm (arrow). A separate angiogram was obtained for each carotid artery, and the images were combined manually. To demonstrate the lack of a connection, the space between the right ICA and the aneurysm is shown as larger than it actually was.

View larger version (143K): [in a new window]   Figure 14f.  Kissing vessel artifact. (a) CT angiogram (superior view) shows an aneurysm of the left anterior communicating artery (arrowhead) adjacent to the right ICA (arrow). An aneurysm at the bifurcation of the left MCA is also seen. (b) Right frontal dVR image shows a large connection (arrow) between the right ICA and the aneurysm (arrowhead). (c) Transparent dVR image clearly shows the connection (arrow). Arrowhead = aneurysm. (d, e) Transparent (d) and virtual endoscopic (e) dVR images show a hole (arrow) between the right ICA and the aneurysm. (f) DSA image shows no connection between the right ICA and the aneurysm (arrow). A separate angiogram was obtained for each carotid artery, and the images were combined manually. To demonstrate the lack of a connection, the space between the right ICA and the aneurysm is shown as larger than it actually was.

View larger version (136K): [in a new window]   Figure 15a.  Obscuring venous structure in a patient with SAH. Superior (a) and posterior (b) CT angiograms show only part of the right MCA owing to an adjacent vascular structure (arrow). DSA was performed to exclude an aneurysm and showed normal findings.

View larger version (112K): [in a new window]   Figure 15b.  Obscuring venous structure in a patient with SAH. Superior (a) and posterior (b) CT angiograms show only part of the right MCA owing to an adjacent vascular structure (arrow). DSA was performed to exclude an aneurysm and showed normal findings.

View larger version (154K): [in a new window]   Figure 16a.  Partially thrombosed and calcified aneurysm of the right ICA. (a) dVR image (superoposterior view) shows parts of the aneurysm (arrow) but does not allow identification of its origin. (b) Source CT image shows the relationships between the perfused part of the aneurysm (*), the thrombosed part (small arrow), the calcified wall (arrowheads), and the ICA (large arrow).

View larger version (115K): [in a new window]   Figure 16b.  Partially thrombosed and calcified aneurysm of the right ICA. (a) dVR image (superoposterior view) shows parts of the aneurysm (arrow) but does not allow identification of its origin. (b) Source CT image shows the relationships between the perfused part of the aneurysm (*), the thrombosed part (small arrow), the calcified wall (arrowheads), and the ICA (large arrow).

View larger version (156K): [in a new window]   Figure 17a.  CT angiography of a patient with two intracranial aneurysm clips. (a) Three-dimensional dVR image (posterior view) shows an apparent occlusion of the distal basilar artery (arrow). Arrowheads = aneurysm clips. (b, c) Sagittal (b) and axial (c) MPR images show that the apparent occlusion is due to a beam hardening artifact (arrows) caused by the aneurysm clips (arrowheads in c).

View larger version (94K): [in a new window]   Figure 17b.  CT angiography of a patient with two intracranial aneurysm clips. (a) Three-dimensional dVR image (posterior view) shows an apparent occlusion of the distal basilar artery (arrow). Arrowheads = aneurysm clips. (b, c) Sagittal (b) and axial (c) MPR images show that the apparent occlusion is due to a beam hardening artifact (arrows) caused by the aneurysm clips (arrowheads in c).

View larger version (76K): [in a new window]   Figure 17c.  CT angiography of a patient with two intracranial aneurysm clips. (a) Three-dimensional dVR image (posterior view) shows an apparent occlusion of the distal basilar artery (arrow). Arrowheads = aneurysm clips. (b, c) Sagittal (b) and axial (c) MPR images show that the apparent occlusion is due to a beam hardening artifact (arrows) caused by the aneurysm clips (arrowheads in c).

View larger version (169K): [in a new window]   Figure 18a.  Aneurysm of the basilar artery. (a) Superoposterior dVR image shows a 2-mm-diameter aneurysm of the basilar artery at the origin of the right superior cerebellar artery (arrow). (b) On frontal (left) and lateral (right) DSA images, the aneurysm is barely visible (arrow in left image). It was recognized only after the CT angiography results were known.

View larger version (97K): [in a new window]   Figure 18b.  Aneurysm of the basilar artery. (a) Superoposterior dVR image shows a 2-mm-diameter aneurysm of the basilar artery at the origin of the right superior cerebellar artery (arrow). (b) On frontal (left) and lateral (right) DSA images, the aneurysm is barely visible (arrow in left image). It was recognized only after the CT angiography results were known.

View larger version (30K): [in a new window]   Figure 19.  Algorithm for use of CT angiography in patients with SAH.