DOI: 10.1148/radiol.2452061670
(Radiology 2007;245:362-366.)
© RSNA, 2007
CT Angiography versus MR Angiography in the Evaluation of Acute Neurovascular Disease1
Charles L. Truwit, MD
1 From the Department of Radiology, Hennepin County Medical Center, 701 Park Ave, Minneapolis, MN 55415; and Department of Radiology, University of Minnesota, Minneapolis, Minn. Received September 26, 2006; accepted November 1; final version accepted December 15.
Correspondence: Address correspondence to the author (e-mail: truwit{at}umn.edu).
Editor's note: Please see my January 2007 From the Editor communication titled "Radiology 2007: The Year Ahead" for information regarding this new feature—Controversies—in Radiology.
—Anthony V. Proto, MD, Editor
At the 2005 meeting of the Radiological Society of North America, eight topics were included in two separate focus sessions titled Controversies in Neuroradiology. Among these was an exchange of viewpoints concerning the relative merits of magnetic resonance (MR) angiography versus computed tomographic (CT) angiography in neurovascular disease. The proponents of each were Brian Bowen, MD, PhD (for MR angiography) and Charles Truwit, MD (for CT angiography). Although disagreements may persist about which technique to use in different clinical situations, the readers of these two contributions will obtain a sense of the advantages and disadvantages of each technique.
—Robert M. Quencer, MD
 |
INTRODUCTION
|
|---|
With the recent advances in both thrombolytic therapy for acute stroke and endovascular therapy for ruptured aneurysm, the diagnostic evaluation of neurovascular disease has evolved substantially. More important, although arguments can be made about the relative strengths of CT angiography versus those of MR angiography, the fact is that with the arrival of 16–detector row or greater multidetector CT scanners, digital subtraction angiography has lost its primacy both as a screening tool and as a first-line modality in the evaluation of patients with symptoms of acute stroke. Currently, the issue really is whether to perform CT angiography or MR angiography (1–3).
Today, CT angiography is performed with multidetector CT scanners, typically four-section or greater. With that in mind, CT angiography of the carotid arteries and circle of Willis is a very rapid examination; it is easily performed, and images from the examination are straightforward to interpret. In fact, at our institutions (Hennepin County Medical Center and University of Minnesota, Minneapolis, Minn), we use a triple study that includes unenhanced CT, followed by CT angiography of the carotid arteries and circle of Willis and CT perfusion. To avoid venous enhancement, we perform CT angiography prior to CT perfusion.
In general, there is little time to wait for serum creatinine levels. In the emergency department, during the evaluation of vital signs and intravenous cannulation, all patients receive a bolus of sodium bicarbonate for nephroprotection. By the time the patient who has been evaluated has arrived in the CT suite and has undergone unenhanced CT, at least 10 minutes have passed, allowing the bicarbonate time to alkalinize the urine and offer nephroprotection against the creation of free radicals in the renal medulla (4). With the assumption that intracranial hemorrhage is absent, both CT angiographic and CT perfusion studies are performed, and the data are transferred to the workstation (Vitrea; Vital Images, Minnetonka, Minn) for immediate review. On-call residents are required to master these basic three-dimensional workstation functions prior to being on call; hence, the study is performed, images are reviewed by the on-call resident, and images are made available within minutes for the on-call neuroradiologist to evaluate remotely.
Unlike the MR counterpart, CT perfusion is both qualitative and (reproducibly) quantitative (Fig 1). Under the best of circumstances, an MR study that includes the capability to exclude hemorrhage, demonstrate a stroke, demonstrate vascular occlusion (ie, a potentially treatable form of stroke), and demonstrate a reversible component of the ischemic brain will take at least 20–30 minutes. Moreover, whereas for us the MR study requires calling in an MR technologist, which may consume an additional 30 minutes of ischemic brain time, the CT technologist is in house. At our institutions, the CT, CT angiographic, and CT perfusion examination can be performed in less than 15 minutes from the time the patient arrives in the CT suite.
View larger version (127K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1a: Acute right middle cerebral artery stroke. (a, b) Transverse unenhanced CT scans reveal subtle loss of gray matter intensity of insular cortex (arrows on a and b) and lateral putamen (arrow on b). (c–e) CT perfusion scans show core of infarction as gray area (arrows on c) and otherwise increased cerebral blood volume (arrowhead on c) in penumbral tissue, despite (d) substantially diminished cerebral blood flow and (e) increased mean transit time.
|
|
View larger version (109K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1b: Acute right middle cerebral artery stroke. (a, b) Transverse unenhanced CT scans reveal subtle loss of gray matter intensity of insular cortex (arrows on a and b) and lateral putamen (arrow on b). (c–e) CT perfusion scans show core of infarction as gray area (arrows on c) and otherwise increased cerebral blood volume (arrowhead on c) in penumbral tissue, despite (d) substantially diminished cerebral blood flow and (e) increased mean transit time.
|
|
View larger version (123K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1c: Acute right middle cerebral artery stroke. (a, b) Transverse unenhanced CT scans reveal subtle loss of gray matter intensity of insular cortex (arrows on a and b) and lateral putamen (arrow on b). (c–e) CT perfusion scans show core of infarction as gray area (arrows on c) and otherwise increased cerebral blood volume (arrowhead on c) in penumbral tissue, despite (d) substantially diminished cerebral blood flow and (e) increased mean transit time.
|
|
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1d: Acute right middle cerebral artery stroke. (a, b) Transverse unenhanced CT scans reveal subtle loss of gray matter intensity of insular cortex (arrows on a and b) and lateral putamen (arrow on b). (c–e) CT perfusion scans show core of infarction as gray area (arrows on c) and otherwise increased cerebral blood volume (arrowhead on c) in penumbral tissue, despite (d) substantially diminished cerebral blood flow and (e) increased mean transit time.
|
|
View larger version (118K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1e: Acute right middle cerebral artery stroke. (a, b) Transverse unenhanced CT scans reveal subtle loss of gray matter intensity of insular cortex (arrows on a and b) and lateral putamen (arrow on b). (c–e) CT perfusion scans show core of infarction as gray area (arrows on c) and otherwise increased cerebral blood volume (arrowhead on c) in penumbral tissue, despite (d) substantially diminished cerebral blood flow and (e) increased mean transit time.
|
|
Should the unenhanced CT examination reveal subarachnoid hemorrhage, our protocol is to continue directly to CT angiography. Because vasospasm would be an atypical observation at the time of presentation, the CT perfusion examination is not performed (5,6). In this situation, CT angiography covers only the intracranial circulation. Again, the examination is reviewed by the on-call resident, and results are made available to the on-call neuroradiologists and neurosurgeons.
The evaluation of an intracranial aneurysm by using CT angiography offers numerous primary advantages beyond the simplicity of acquisition (7). Specifically, CT angiography is more likely than MR angiography to be dispositive of the question of whether to use a coil versus a clip. Whereas both CT angiography and MR angiography offer depiction of the aneurysm neck, measurements of the aneurysm size and neck-to-dome ratio, and a complete evaluation of the intracranial circulation to assess multiplicity of aneurysms, the comparative equality of the two ends here, in my opinion.
CT angiography is not affected by flow-related inhomogeneities, so commonly seen at MR angiography of giant and fusiform aneurysms (7–11). CT angiography is performed in seconds, as opposed to minutes, effectively eliminating MR angiography–limiting patient motion. Further, CT angiography offers more complete intracranial coverage in less time than does MR angiography. With CT angiography, neither overestimates nor underestimates of measurements are observed to the extent that they are with MR angiography (7–11). CT angiography offers direct evidence of mural calcification at or near the aneurysm neck that would tend to preclude use of a surgical clip (7–11). CT angiography offers the best evaluation of adjacent dural landmarks in determining the intra- versus extradural location of the aneurysm (7–11). CT angiography is much more accurate than is MR angiography for demonstrating branch vessel incorporation (Fig 2) into the aneurysm, perhaps indicating the need for stent placement prior to endo-occlusive therapy (7–11). Similarly, CT angiography is more reliable for demonstrating the anterior communicating artery and is more helpful than is MR angiography for depicting acute intraaneurysmal thrombus, an important factor in the decision tree of whether to use a clip versus a coil (7,8). Finally, electrocardiographically gated reconstruction of a CT angiogram (as in cardiac CT angiography) may reveal a pulsating bleb, presumably secondary to wall thinning, correlating with the site of aneurysmal rupture (12,13).
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2: CT angiographic image of the intracranial circulation includes coverage down to foramen magnum. Three-dimensional view reveals 3-mm aneurysm (arrow) of right posterior inferior cerebellar artery origin with incorporation of posterior inferior cerebellar artery (arrowhead) into aneurysm. Although MR angiography could depict aneurysm, intracranial MR angiography often excludes posterior circulation at level of posterior inferior cerebellar artery. (Image courtesy of P. Villablanca, MD, UCLA, Los Angeles, Calif.)
|
|
In addition to the evaluation of intracranial aneurysms, CT angiography offers considerable potential in the evaluation of intracranial arteriovenous malformations (14). Although MR angiography is typically performed with MR imaging and, therefore, offers more potential in the depiction of arteriovenous malformations once the diagnosis is known, CT angiography with 64-section equipment actually offers a thin-section, time-resolved evaluation of the nidus of an arteriovenous malformation. In this manner, small aneurysms on the feeding vessels and within the nidus may be detected. This diagnostic feature is still problematic at MR angiography, largely due to venous contamination that obscures underlying arterial and nidal anatomy (14). For spinal vascular malformations, although it is impractical to use CT angiography for screening examinations, CT angiography does have potential once the diagnosis is known. Segmental CT angiography can be performed in a time-resolved manner, and CT angiographic images can subsequently be reconstructed at a three-dimensional workstation. Finally, in the setting of acute brain and spine trauma, CT angiography of the skull base and neck can be performed at the time of the initial trauma evaluation (Fig 3). With the availability of rapid curved multiplanar reformatting at advanced imaging workstations, it is now routine to assess carotid and/or vertebral artery dissection. Although some would argue that digital subtraction angiography remains the reference standard, it is now accepted that CT angiography is a very viable technique for such assessment in the setting of acute trauma (15).
View larger version (106K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a: (a) Sagittal reconstructed CT image in patient with diffuse idiopathic skeletal hyperostosis and acute fracture at C4-5 (arrow) and bilateral vertebral artery transection. (b–d) CT angiographic images of the cervical vertebral circulation reveal flow in the right vertebral artery at the C2-3 level. (b) Coronal and (c) sagittal multiplanar reformation and (d) three-dimensional views show retrograde contrast enhancement from the anterior circulation down the basilar into the vertebral arteries. Arrows show end of retrograde contrast enhancement due to proximal vertebral artery transections. (Left side not shown.)
|
|
View larger version (63K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b: (a) Sagittal reconstructed CT image in patient with diffuse idiopathic skeletal hyperostosis and acute fracture at C4-5 (arrow) and bilateral vertebral artery transection. (b–d) CT angiographic images of the cervical vertebral circulation reveal flow in the right vertebral artery at the C2-3 level. (b) Coronal and (c) sagittal multiplanar reformation and (d) three-dimensional views show retrograde contrast enhancement from the anterior circulation down the basilar into the vertebral arteries. Arrows show end of retrograde contrast enhancement due to proximal vertebral artery transections. (Left side not shown.)
|
|
View larger version (77K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3c: (a) Sagittal reconstructed CT image in patient with diffuse idiopathic skeletal hyperostosis and acute fracture at C4-5 (arrow) and bilateral vertebral artery transection. (b–d) CT angiographic images of the cervical vertebral circulation reveal flow in the right vertebral artery at the C2-3 level. (b) Coronal and (c) sagittal multiplanar reformation and (d) three-dimensional views show retrograde contrast enhancement from the anterior circulation down the basilar into the vertebral arteries. Arrows show end of retrograde contrast enhancement due to proximal vertebral artery transections. (Left side not shown.)
|
|
View larger version (100K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3d: (a) Sagittal reconstructed CT image in patient with diffuse idiopathic skeletal hyperostosis and acute fracture at C4-5 (arrow) and bilateral vertebral artery transection. (b–d) CT angiographic images of the cervical vertebral circulation reveal flow in the right vertebral artery at the C2-3 level. (b) Coronal and (c) sagittal multiplanar reformation and (d) three-dimensional views show retrograde contrast enhancement from the anterior circulation down the basilar into the vertebral arteries. Arrows show end of retrograde contrast enhancement due to proximal vertebral artery transections. (Left side not shown.)
|
|
|
ADVANTAGES OF CT ANGIOGRAPHY
|
|---|
1. Clearer definition of the aneurysm neck, more likely to be dispositive of the question of using a clip versus a coil
2. Direct evidence of mural calcification
3. Better definition of adjacent bone anatomy
4. Improved intravascular contrast definition: overcomes flow-related inhomogeneities seen at MR angiography of giant and fusiform aneurysms
5. More complete intracranial coverage
6. Improved depiction of branch vessel incorporation into an aneurysm
7. Improved depiction of parent vessel for possible stent placement prior to endo-occlusive therapy
8. More consistent demonstration of anterior communicating artery
9. Better definition of intra- versus extradural location of aneurysm
10. Easily performed with accompanying unenhanced CT and dynamic contrast material–enhanced CT perfusion at time of acute stroke
11. Electrocardiographically gated time-resolved CT angiography may reveal bleb at site of aneurysmal rupture
12. Sixty-four–section CT offers thin-section time-resolved CT angiography through arteriovenous malformation nidus
13. CT angiography of the neck in the setting of a cervical spine and/or skull base fracture can be performed at the time of the initial trauma evaluation (Fig 3)
|
DISADVANTAGES OF CT ANGIOGRAPHY
|
|---|
1. Ionizing radiation and thus less well suited than MR angiography for screening examinations of carotid artery, circle of Willis, and spine
2. CT angiography is helpful in evaluation of spinal vascular disease only when location of disease is known, allowing segmental evaluation
3. CT angiography is affected by bone artifact at the base of the skull, compromising the search for a paraophthalmic carotid artery aneurysm
4. Risk of contrast agent–induced nephropathy, although largely offset by sodium bicarbonate nephroprotection
5. Technical errors require rescheduling, whereas unenhanced MR angiography can simply be repeated
|
SUMMARY
|
|---|
Although MR angiography offers many valuable advantages, they are, in my opinion, more related to the screening population and to the nonemergent evaluation of neurovascular disease. In the emergent situation, CT angiography allows faster imaging that can be offered at any time of the day or night.
|
FOOTNOTES
|
|---|
Author stated no financial relationship to disclose.
|
References
|
|---|
- Karamessini MT, Kagadis GC, Petsas T, et al. CT angiography with three-dimensional techniques for the early diagnosis of intracranial aneurysms: comparison with intraarterial DSA and the surgical findings. Eur J Radiol 2004;49(3):212–223.[CrossRef][Medline]
- Hoh BL, Cheung AC, Rabinov JD, Pryor JC, Carter BS, Ogilvy CS. Results of a prospective protocol of computed tomographic angiography in place of catheter angiography as the only diagnostic and pretreatment planning study for cerebral aneurysms by a combined neurovascular team. Neurosurgery 2004;54(6):1329–1342.[CrossRef][Medline]
- Tipper G, U-King-Im JM, Price SJ, et al. Detection and evaluation of intracranial aneurysms with 16-row multislice CT angiography. Clin Radiol 2005;60(5):565–572.[CrossRef][Medline]
- Merten GJ, Burgess WP, Gray LV, et al. Prevention of contrast-induced nephropathy with sodium bicarbonate: a randomized controlled trial. JAMA 2004;291(19):2328–2334.[Abstract/Free Full Text]
- Sviri GE, Britz GW, Lewis DH, Newell DW, Zaaroor M, Cohen W. Dynamic perfusion computed tomography in the diagnosis of cerebral vasospasm. Neurosurgery 2006;59(2):319–325.[CrossRef][Medline]
- Sanelli PC, Ougorets I, Johnson E, Riina HA, Biondi A. Using CT in the diagnosis and management of patients with cerebral vasospasm. Semin Ultrasound CT MR 2006;27(3):194–206.[CrossRef][Medline]
- Kouskouras C, Charitanti A, Giavroglou C, et al. Intracranial aneurysms: evaluation using CTA and MRA: correlation with DSA and intraoperative findings. Neuroradiology 2004;46(10):842–850.[CrossRef][Medline]
- Villablanca JP, Martin N, Jahan R, et al. Volume-rendered helical computerized tomography in the detection and characterization of intracranial aneurysms. J Neurosurg 2000;93(2):254–264.[Medline]
- Villablanca JP, Hooshi P, Martin N, et al. Three-dimensional helical computerized tomography angiography in the diagnosis, characterization, and management of middle cerebral artery aneurysms: comparison with conventional angiography and intraoperative findings. J Neurosurg 2002;97(6):1322–1332.[Medline]
- Villablanca JP, Achiriolaie A, Hooshi P, et al. Aneurysms of the posterior circulation: detection and treatment planning using volume-rendered three-dimensional helical computerized tomography angiography. J Neurosurg 2005;103(6):1018–1029.[Medline]
- Jayaraman MV, Mayo-Smith WW, Tung GA, et al. Detection of intracranial aneurysms: multi-detector row CT angiography compared with DSA. Radiology 2004;230(2):510–518.[Abstract/Free Full Text]
- Hayakawa M, Katada K, Anno H, et al. CT angiography with electrocardiographically gated reconstruction for visualizing pulsation of intracranial aneurysms: identification of aneurysmal protuberance presumably associated with wall thinning. AJNR Am J Neuroradiol 2005;26(6):1366–1369.[Abstract/Free Full Text]
- Ishida F, Ogawa H, Simizu T, Kojima T, Taki W. Visualizing the dynamics of cerebral aneurysms with four-dimensional computed tomographic angiography. Neurosurgery 2005;57(3):460–471.[CrossRef][Medline]
- Coenen VA, Dammert S, Reinges MH, Mull M, Gilsbach JM, Rohde V. Image-guided microneurosurgical management of small cerebral arteriovenous malformations: the value of navigated computed tomographic angiography. Neuroradiology 2005;47(1):66–72.[CrossRef][Medline]
- Chen CJ, Tseng YC, Lee TH, Hsu HL, See LC. Multisection CT angiography compared with catheter angiography in diagnosing vertebral artery dissection. AJNR Am J Neuroradiol 2004;25(5):769–774.[Abstract/Free Full Text]
Rebuttal to Dr Truwit's Comments Advocating CT Angiography
Brian C. Bowen, MD, PhD
In the evaluation of steno-occlusive disease of the carotid, vertebral, and major cerebral arteries by using CT angiography versus MR angiography, Dr Truwit has focused on the setting of acute ischemic stroke. This is an area in which the CT, CT angiographic, and CT perfusion combined examination has a time advantage over combined MR imaging, MR angiography, and MR perfusion, and Dr Truwit has emphasized this point. The argument, however, is misleading because two key factors that are essential in the decision-to-treat algorithm are best determined by using results of MR imaging that accompanies MR angiography: (a) the volume of irreversibly injured brain (infarct core, estimated from diffusion MR imaging) and (b) the presence of an operational "ischemic penumbra" (estimated from diffusion-perfusion MR mismatch). The use of these factors to guide expeditious stroke therapy leads to a different approach—one in which the traditional narrow time windows for treatment are not strictly applied but are modulated depending on the extent of the ischemic penumbra. In terms of rescuing brain at risk for infarction, this approach has been referred to as "physiology is brain," rather than as "time is brain" (1).
Dr Truwit does make a strong case in favor of CT angiography that is based on the greater accessibility and comfort level for detecting subarachnoid hemorrhage afforded by CT currently; however, in the future, greater access to MR imagers in the emergency setting and for nonemergent follow-up will likely lead to an increase in the use of MR imaging for acute stroke. Furthermore, there is a more extensive body of literature that establishes the effectiveness of MR angiographic techniques in the nonacute setting, as alluded to before, than there is for CT angiography. Finally, Dr Truwit has not addressed the success rate for MR angiography versus CT angiography in obtaining clinically useful angiographic information for suspected steno-occlusive disease. In my experience, the radiologist is commonly confronted by practical shortcomings associated with CT angiographic acquisitions: source data in which both arteries and veins are opacified and difficult to distinguish by using targeted region-of-interest processing; inappropriate window width and window level settings, which preclude the differentiation of calcification or bone from opacified vessels or vascular lesions; and finally reliance on CT technologists to do the bulk of the data postprocessing, which includes routine and targeted views. The balance between the radiologists' and the technologists' time that must be spent on data postprocessing to generate diagnostic information is difficult to predict or assign; however, this balance needs to be optimized. In contrast, MR angiographic and MR perfusion postprocessing algorithms are performed online and are performed according to simple rules that are easy for competent technologists to follow, resulting in reproducible vascular images.
|
References
|
|---|
- Gonzalez RG. Imaging-guided acute ischemic stroke therapy: from "time is brain" to "physiology is brain." AJNR Am J Neuroradiol 2006;27:728–735.[Abstract/Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
C. Lum, S. Chakraborty, M. Schlossmacher, M. Santos, R. Mohan, J. Sinclair, and M. Sharma
Vertebral Artery Dissection with a Normal-Appearing Lumen at Multisection CT Angiography: The Importance of Identifying Wall Hematoma
AJNR Am. J. Neuroradiol.,
April 1, 2009;
30(4):
787 - 792.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. H. Rodallec, V. Marteau, S. Gerber, L. Desmottes, and M. Zins
Craniocervical Arterial Dissection: Spectrum of Imaging Findings and Differential Diagnosis
RadioGraphics,
October 1, 2008;
28(6):
1711 - 1728.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. J. Kaufmann and D. F. Kallmes
Diagnostic Cerebral Angiography: Archaic and Complication-Prone or Here to Stay for Another 80 Years?
Am. J. Roentgenol.,
June 1, 2008;
190(6):
1435 - 1437.
[Full Text]
[PDF]
|
|
|
TOP
INTRODUCTION
ADVANTAGES OF CT ANGIOGRAPHY
