Radiology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published online before print September 11, 2007, 10.1148/radiol.2451061493
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
2451061493v1
245/2/541    most recent
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Waaijer, A.
Right arrow Articles by Prokop, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Waaijer, A.
Right arrow Articles by Prokop, M.
(Radiology 2007;245:541-548.)
© RSNA, 2007

Neuroradiology

Changes in Cerebral Perfusion after Revascularization of Symptomatic Carotid Artery Stenosis: CT Measurement1

Annet Waaijer, MD, Maarten S. van Leeuwen, MD, PhD, Matthias J.P. van Osch, PhD, Bart H. van der Worp, MD, PhD, Frans L. Moll, MD, PhD, Rob T. H. Lo, MD, Willem P. T. M. Mali, MD, PhD, and Mathias Prokop, MD, PhD

1 From the Departments of Radiology (A.W., M.S.v.L., M.J.P.v.O., R.T.H.L., W.P.T.M.M., M.P.), Neurology (B.H.v.d.W.), and Surgery (F.L.M.), University Medical Center Utrecht, Heidelberglaan 100, Utrecht NL-3508 GA, the Netherlands; and Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands (M.J.P.v.O.). Received August 28, 2006; revision requested November 8; revision received January 16, 2007; final version accepted March 1. Address correspondence to A.W. (e-mail: annetwaaijer{at}gmail.com).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Purpose: To prospectively evaluate changes in brain perfusion computed tomographic (CT) parameters after revascularization of unilateral symptomatic carotid artery stenosis and to determine whether pretreatment perfusion CT parameters can be used to predict changes in cerebral hemodynamics after treatment.

Materials and Methods: This study was medical ethics committee approved, and written informed consent was obtained from all patients. Thirty-six patients (23 men, 13 women; mean age, 67 years) with unilateral symptomatic carotid artery stenosis underwent multi–detector row perfusion CT before and after revascularization. Mean transit time (MTT), cerebral blood volume (CBV), and cerebral blood flow (CBF) were calculated, and relative values based on the comparison between symptomatic and asymptomatic hemispheres—specifically, relative CBV, relative CBF, and difference in MTT—were derived. The absolute and relative perfusion values before treatment were assessed and compared with posttreatment values. These analyses were performed for the group as a whole by using the t test and after subdividing patients into three tertiles according to the difference in MTT by using the Wilcoxon signed rank test.

Results: Among the absolute perfusion values, only the MTT in the symptomatic hemisphere improved significantly after treatment (P < .01). All relative values (difference in MTT, relative CBV, and relative CBF) changed significantly after treatment (P < .05). When the patients were subdivided into three tertiles according to difference in MTT, no significant change in any relative perfusion value could be demonstrated in the lowest tertile, only the difference in MTT improved significantly (P = .004) in the middle tertile, and all relative perfusion values changed significantly (P = .002) in the highest tertile.

Conclusion: Compared with relative CT perfusion values based on interhemispheric comparison, absolute perfusion CT values are less suited for demonstrating changes in cerebral perfusion after revascularization in patients with unilateral symptomatic carotid artery stenosis.

© RSNA, 2007

Clinical trial registration no. ISRCTN 25337470


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
In patients who recently developed symptoms due to internal carotid stenosis of 70% or greater, carotid endarterectomy (CEA) is highly beneficial and leads to a 16% absolute reduction in the 5-year risk of ipsilateral ischemic stroke. Although the effectiveness of CEA in patients with symptomatic internal carotid artery stenosis of 70% or greater is beyond doubt, one stroke is prevented for every six patients who undergo surgery (1). Although surgery may also be considered for patients with 50% or greater stenosis, the number of these patients to treat before one stroke is prevented is more than three times as high (1). To improve the selection of patients for CEA, better understanding of the risk factors for stroke in these patients is required.

Although only 20% of patients who have had a transient ischemic attack or stroke have significant stenosis or occlusion of the extracranial internal carotid artery (2) and the majority of transient ischemic attacks and ischemic strokes result from thrombosis and/or thromboembolism (3), it has been suggested that severe cerebral hemodynamic compromise is also associated with an increased risk of stroke and/or transient ischemic attack (4–6). To distinguish between patients with and those without hemodynamic impairment, a simple widely available tool to measure cerebral perfusion is required. Cerebral perfusion computed tomography (CT) is now used to detect the penumbra and the irreversible ischemic damage in patients with acute stroke (7,8), to assess secondary cerebral ischemia in patients with subarachnoid hemorrhage (9,10), and in combination with acetazolamide to test the vasomotor reactivity in patients with cerebral occlusive disease (11).

We hypothesized that perfusion CT analysis performed before carotid artery revascularization can be used to distinguish groups of patients with different cerebral hemodynamic response to treatment. Thus, the purpose of our study was to prospectively evaluate changes in brain perfusion CT parameters after revascularization of unilateral symptomatic carotid artery stenosis and to determine whether pretreatment perfusion CT parameters can be used to predict changes in cerebral hemodynamics after treatment.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Patients
All patients were participants in the International Carotid Stenting Study, or ICSS, a randomized controlled trial in which CEA and stent placement are being compared (www.cavatas.com). Study inclusion was based on the presence of symptomatic internal carotid artery stenosis of greater than 50% that was equally suitable for CEA or stent placement. Between September 2003 and May 2005, a perfusion CT examination was added to the ICSS imaging protocol for 53 patients at the University Medical Centre Utrecht. The medical ethics committee of our hospital approved our current study, and written informed consent was obtained from all patients.

For this study, we included only those patients with unilateral carotid artery stenosis. Therefore, exclusion criteria were contralateral stenosis of greater than 50% measured with duplex ultrasonography (US), a modified Rankin scale score of 3 or lower, and the presence of contraindications to CT angiography such as renal failure or contrast material allergy. Seventeen patients were excluded from analysis: Two patients developed an occlusion between the time of pretreatment perfusion CT and the intervention, nine had contralateral carotid artery stenosis of greater than 50%, and six were excluded owing to technical problems with contrast material administration or motion artifacts. Consequently, 36 patients were included in the current study (Table 1). Patients were scanned within 2 weeks before treatment and 1 month after stent placement or CEA. Before revascularization and at 1 month follow-up, the degree of stenosis in the treated carotid artery was assessed in all patients by using duplex US.


View this table:
[in this window]
[in a new window]

  		Table 1. Patient Characteristics

 
Perfusion CT Scanning
Imaging protocol.—Dynamic perfusion CT source images were acquired by using a 16–detector row (MX8000 IDT; Philips Medical Systems, Cleveland, Ohio) or 40–detector row (Brilliance-40, Philips Medical Systems) scanner. Scanning was performed at the level of the basal ganglia, 3 cm above the dorsum sellae, with the scanning angle set parallel to the orbitomeatal line to avoid direct exposure of the eye lenses to radiation. With the 16–detector row scanner, 8 x 3-mm collimation was used and images were reconstructed in two 12-mm slabs, facilitating 2.4-cm coverage. With the introduction of 40–detector row scanning, 32 x 1.25-mm collimation was used and images were reconstructed in four adjacent 10-mm slabs, facilitating 4.0-cm coverage. The cycle time of 2 seconds facilitated the acquisition of 30 images within 60 seconds, which has been shown to yield accurate perfusion data (12). For an optimal signal-to-noise ratio, we used a low peak voltage technique (90 kVp with 16–detector row scanner, 80 kVp with 40–detector row scanner) in combination with 150 mAs (13). Images were reconstructed by using a slightly smoothing head filter (UB Filter; Philips Medical Systems) with a field of view of 160 mm. For all perfusion scanning, a bolus injection of 40 mL of iopromide (300 mg of iodine per milliliter, Ultravist 300; Schering, Berlin, Germany) and then a 40-mL saline chaser bolus were administered at 5 mL/sec by using a power injector with a dual-head system (Stellant Dual CT Injector; Medrad Europe, Beek, the Netherlands).

Calculations.—Perfusion CT data were transferred to a postprocessing workstation (Philips Medical Systems, Best, the Netherlands), at which the cerebral blood volume (CBV), mean transit time (MTT), and cerebral blood flow (CBF) were calculated. Time-enhancement curves based on the passage of contrast material through the anterior cerebral artery and the superior sagittal sinus yielded the arterial input function (AIF) and the venous output function (VOF), respectively. To determine the AIF, an operator with more than 3 years experience in brain CT image reading (A.W.) placed a large region of interest (ROI) that included both anterior cerebral arteries at each slab. Thereafter, the computer selected the optimal curve in 1 pixel on the basis of the height of the peak and the size of the area under the curve. Thus, this curve could be placed in the ipsilateral or contralateral anterior cerebral artery; however, since our deconvolution-based program was delay insensitive, a possible difference in timing would not influence the perfusion measurements. The same ROI placement process was performed to determine the VOF within the superior sagittal sinus. Visual inspection was always performed to ensure that the entire AIF and at least three points of the down slope of the VOF were included.

The CBV was calculated as the ratio of the area under the time-concentration curve for the first contrast material bolus passage through the tissue to the area under the curve for the VOF. The MTT, the average time required for the blood to cross the capillary network, was calculated by using a deconvolution operation (14). According to the central volume principle, the CBF was calculated from the measured CBV and MTT: CBF = CBV/MTT (15). This method has been shown to be the most accurate at lower injection rates (16,17). The same operator (A.W.) always determined the AIF and VOF, visually controlled the curves, and performed the subsequent postprocessing of the ROIs for quantitative measurements.

Postprocessing.—To quantify changes in perfusion parameters before and after CEA or stent placement, the two slabs closest to the level of the basal ganglia on the pretreatment perfusion CT scan were matched to two corresponding slabs at the same level on the posttreatment scan. On each slab, an ROI corresponding to the cortical flow territory of the middle cerebral artery in both hemispheres was manually outlined according to the maps of Damasio (18). We ensured that infarcted tissue was excluded from the ROI. Bone, vessels, and cerebrospinal fluid were automatically removed (Fig 1).


Figure 1
View larger version (45K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1: Manual outlining of middle cerebral artery territory on transverse CT sections. Left image shows the temporal maximum intensity projection. Green overlay on middle image shows the selected region—without bone, vessels, or cerebrospinal fluid—used to calculate perfusion values. Right image shows the colored perfusion MTT map.

 
Statistical Analyses
Perfusion CT analysis yielded absolute perfusion data—CBV, expressed in milliliters per 100 g of tissue; MTT, expressed in seconds; and CBF, expressed in milliliters per 100 g of tissue per minute—for each pixel in the symptomatic and asymptomatic hemispheres. Because brain perfusion measurements are subject to high intersubject variation and are influenced by physiologic parameters (19,20), we chose to include relative perfusion data in our analysis by normalizing the values measured in the symptomatic hemisphere to the values measured in the asymptomatic hemisphere. As a relative measure of MTT, we chose the absolute difference in MTT between the symptomatic and asymptomatic hemispheres (dMTT) because the MTT itself is derived from the difference in width between two curves—those for the AIF and the voxel of interest. To determine the relative CBV (rCBV), we calculated the symptomatic hemisphere–to–asymptomatic hemisphere ratios because these parameters are derived from the ratio of the areas under the attenuation curves (VOF and voxel of interest). Ratios were also calculated to determine the relative CBF (rCBF). For each perfusion CT scan, the mean of measurements in the two evaluated slabs was calculated for both absolute and relative data.

First, we analyzed the data for the total group of patients and compared the absolute pre- and posttreatment values by using a paired t test. Subsequently, we analyzed the relative data and compared the pre- and posttreatment dMTT, rCBF, and rCBV. Finally, we grouped patients into three tertiles according to the baseline dMTT. The MTT was chosen because it is the least affected by gray and white matter differences and has been shown to be the most reproducible (21,22). In each tertile group, the pre- and posttreatment rCBV, dMTT, and rCBF were compared by using the Wilcoxon signed rank test. Statistical analyses were performed by using the SPSS, version 12.0 (SPSS, Chicago, Ill), software package. P < .05 was considered to indicate statistical significance.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
None of the included patients had symptoms due to carotid artery stenosis during the interval between pre- and posttreatment CT, and all but one patient had normalized duplex US carotid artery values after treatment. When we subdivided patients into three tertiles according to dMTT, we found no significant difference in the number of patients randomly assigned to undergo stent placement or surgery between the groups (lowest tertile group: seven stents; middle tertile group: four stents; highest tertile group: nine stents). The mean stenosis degree measured with duplex US ranged from 78% for the lowest tertile to 93% for the highest tertile.

Absolute Perfusion Parameters
When we compared absolute perfusion CT parameters before and after revascularization, we observed only a significant decrease in MTT in the symptomatic hemisphere: from 5.7 seconds ± 1.5 before to 4.8 seconds ± 1.2 after treatment (P < .01). No other absolute perfusion parameter changed significantly (P > .05) (Table 2).


View this table:
[in this window]
[in a new window]

  		Table 2. Comparison of Pre- and Posttreatment CT Perfusion Data for Symptomatic and Asymptomatic Hemispheres

 
Relative Perfusion Parameters
The mean rCBV decreased from 1.09 ± 0.15 before to 0.96 ± 0.12 after revascularization (P < .001), the mean dMTT decreased from 1.30 seconds ± 1.10 before to 0.18 seconds ± 0.40 after treatment (P < .001), and the mean rCBF increased from 0.85 ± 0.18 before to 0.92 ± 0.14 after treatment (P < .005) (Table 2).

When patients were subdivided into tertiles according to the pretreatment dMTT, substantial differences between the three groups were observed (Table 3). In the lowest tertile, no relative perfusion parameter changed significantly; in the middle tertile, only the dMTT changed significantly; and in the highest tertile, all relative perfusion parameters changed significantly after treatment (Figs 2, 3).


View this table:
[in this window]
[in a new window]

  		Table 3. Comparison of Relative Perfusion CT Measurements for Three Tertile Patient Groups according to Pretreatment dMTT

 

Figure 2A
View larger version (10K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2a: (a) rCBV, (b) dMTT, and (c) rCBF values measured separately in three tertiles before and after treatment. Graph data show that in the third tertile, all parameters changed significantly (P = .002) after treatment; in the second tertile, only the dMTT changed significantly (P = .004); and in the first tertile, no parameter changed significantly. Mean values before and after treatment, as well as standard deviations of the means, are shown for each group.

 

Figure 2B
View larger version (11K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2b: (a) rCBV, (b) dMTT, and (c) rCBF values measured separately in three tertiles before and after treatment. Graph data show that in the third tertile, all parameters changed significantly (P = .002) after treatment; in the second tertile, only the dMTT changed significantly (P = .004); and in the first tertile, no parameter changed significantly. Mean values before and after treatment, as well as standard deviations of the means, are shown for each group.

 

Figure 2C
View larger version (11K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2c: (a) rCBV, (b) dMTT, and (c) rCBF values measured separately in three tertiles before and after treatment. Graph data show that in the third tertile, all parameters changed significantly (P = .002) after treatment; in the second tertile, only the dMTT changed significantly (P = .004); and in the first tertile, no parameter changed significantly. Mean values before and after treatment, as well as standard deviations of the means, are shown for each group.

 

Figure 3
View larger version (68K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 3: Left-sided carotid artery stenosis in a patient from the third tertile. Top row shows transverse CT perfusion maps (first to third images from left) and sagittal angiogram (far right) obtained before treatment. Bottom row shows corresponding perfusion maps and angiogram obtained after treatment. Note the prolonged MTT, slightly increased CBV, and decreased CBF on the ipsilateral side before treatment in contrast to the symmetry of brain perfusion after treatment.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
The main findings of our study are threefold: First, absolute perfusion CT values, compared with relative values based on interhemispheric ratios (rCBV and rCBF) or differences (dMTT), were less suited for demonstrating changes in cerebral perfusion after carotid artery revascularization in patients with unilateral symptomatic carotid artery stenosis. In our study, the only absolute value that changed significantly after treatment was the MTT in the symptomatic hemisphere. Second, all relative values (rCBV, rCBF, and dMTT) changed significantly after treatment. Third, subdividing patients into three tertiles according to the dMTT enabled us to differentiate the group in which no significant change in cerebral hemodynamics could be detected (lowest tertile), the group in which only dMTT improved significantly (middle tertile), and the group with cerebral hemodynamics for all relative perfusion parameters (highest tertile).

Investigators in early studies of cerebral perfusion after CEA reached conflicting conclusions (23), and improved imaging techniques have not resolved this controversy (21,24–26). A part of the conflicting findings can be explained by the fact that the investigators in most of these studies did not distinguish between patients with and those without a baseline perfusion deficit. Further confusion has been caused by combining data from symptomatic and asymptomatic patients, combining data on carotid occlusions and carotid stenoses, and combining data from patients with unilateral and those with bilateral disease, despite the differences in response to treatment among these various groups (21,27–29).

Thus, although earlier study results represented evidence of the presence of impaired perfusion in some patients with symptomatic carotid artery stenosis, it was not clear which individual patients would see a hemodynamic benefit from treatment, to what extent hemodynamic improvement could be expected, or which technique or parameter provided the most useful information. Our study results indicate that for patients with unilateral symptomatic carotid artery stenosis, the dMTT can be used to differentiate groups of patients in whom cerebral perfusion will improve to varying extents owing to carotid artery intervention.

MTT has been shown to be inversely correlated with cerebral perfusion pressure (30), and according to the formula CBF = CBV/MTT, CBF is inversely related to MTT and proportional to CBV. During the first phase of hemodynamic compromise, reduced cerebral perfusion pressure results in a prolonged MTT owing to vasodilatation (31). This vasodilatation can be identified as an increase in CBV. Consequently, the CBF may remain within the normal range. As the cerebral perfusion pressure further decreases with a concurrent increase in MTT, compensatory vasodilatation reaches a maximum and advanced hemodynamic compromise results in reduced CBF (31). Thus, the MTT may represent an early and sensitive parameter for the detection of perfusion deficits (30,32).

Therefore and because of the relative robustness of MTT measurements (21,22), we chose the MTT as a selection parameter and differentiated three groups according to the interhemispheric difference in dMTT at baseline. However, while the interhemispheric dMTT normalized after treatment, the rCBF remained below 1.0 for all three groups, indicating reduced CBF in the hemisphere ipsilateral to the stenosis. The cause of this lack of normalization is unclear, but it may be related to the presence of irreversible intracranial vasculature changes.

To our knowledge, our study is the first work in which impaired cerebral perfusion was demonstrated in a subgroup of patients with unilateral symptomatic carotid artery stenosis by using a perfusion CT technique. Unlike positron emission tomography (PET) and single photon emission CT techniques, perfusion CT enables direct measurement of the MTT, and in contrast to transcranial Doppler US, perfusion CT enables territorial analysis. Although the patients in the highest tertile had the highest degree of stenosis on average, the severity of stenosis in the patients in the lowest tertile ranged from 55% to 95%. This shows that stenosis degree is not the only factor that indicates the severity of perfusion impairment; this finding is in accordance with previous study findings (33).

Our study had limitations. First, absolute quantitative perfusion CT analysis data are subject to physiologic variations and are influenced by postprocessing steps (22,34). Some of these limitations, which are intrinsic to absolute perfusion values, can be overcome by using relative perfusion parameters—specifically, relating the absolute perfusion data in the symptomatic hemisphere to the perfusion data in the contralateral asymptomatic hemisphere. The advantage of using this approach is the elimination of physiologic variations and interpatient differences in total cerebral perfusion, but the disadvantage is results that will be more difficult to interpret when significant stenoses are present in both carotid arteries. In addition, the presence of carotid artery stenosis has been shown to influence the AIF and to result in overestimation of the absolute MTT and underestimation of the absolute CBF at perfusion magnetic resonance imaging (35). Despite discussions about the optimal location for placement of the AIF (36), investigators in a recent publication reported that there was no significant difference in perfusion CT values based on the ipsilateral or contralateral AIF in patients with severe carotid artery stenosis (37).

Second, we did not compare perfusion CT values with values obtained with a reference standard such as PET or xenon CT. However, previous studies have revealed that the CBF measured with perfusion CT correlates well with values measured by using these established techniques (16,37).

Third, we included patients who were treated with carotid endarterectomy as well as stent placement. In our opinion, this was acceptable because the patients were randomly assigned to either treatment strategy and no major differences in terms of the success of carotid artery revascularization were expected. We confirmed a minimal difference in revascularization results with duplex US measurements, which demonstrated normalization of peak systolic velocities in all but one patient, who was treated with stent placement. The fact that the highest tertile group included more patients who were treated with stents was not significant.

Fourth, although all of the included patients had a Rankin scale score of 3 or lower, some of them still could have had a cerebral infarction. We included these patients because they represented a relevant part of the population of all patients who may benefit from treatment. However, to obtain representative perfusion values in cases of cerebral infarction, we always avoid including infarcted brain tissue in ROIs.

In conclusion, we found that absolute perfusion CT values were less suited for demonstrating changes in cerebral perfusion after carotid artery revascularization than were relative values based on interhemispheric comparison in patients with unilateral symptomatic carotid artery stenosis. Relative pretreatment perfusion CT values can help to identify patients in whom carotid artery revascularization will most likely lead to improved cerebral hemodynamics.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
IMPLICATIONS FOR PATIENT CARE
 References
 


   IMPLICATIONS FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
References
 


   FOOTNOTES
 

Abbreviations: AIF = arterial input function • CBF = cerebral blood flow • CBV = cerebral blood volume • CEA = carotid endarterectomy • dMTT = absolute difference in MTT between symptomatic and asymptomatic hemispheres • MTT = mean transit time • rCBF = relative CBF • rCBV = relative CBV • ROI = region of interest • VOF = venous output function

Clinical trial registration no. ISRCTN 25337470

Author contributions: Guarantors of integrity of entire study, A.W., M.P.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all au-thors; literature research, A.W., M.J.P.v.O., B.H.v.d.W., W.P.T.M.M., M.P.; clinical studies, A.W., M.S.v.L., M.P.; statistical analysis, A.W., M.J.P.v.O., W.P.T.M.M., M.P.; and manuscript editing, all authors

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 

  1. Rothwell PM, Eliasziw M, Gutnikov SA, et al. Analysis of pooled data from the randomised controlled trials of endarterectomy for symptomatic carotid stenosis. Lancet 2003;361:107–116.[CrossRef][Medline]
  2. Hankey GJ, Slattery JM, Warlow CP. The prognosis of hospital-referred transient ischaemic attacks. J Neurol Neurosurg Psychiatry 1991;54:793–802.[Abstract/Free Full Text]
  3. Barnett HJ. Hemodynamic cerebral ischemia: an appeal for systematic data gathering prior to a new EC/IC trial. Stroke 1997;28:1857–1860.[Medline]
  4. Blaser T, Hofmann K, Buerger T, Effenberger O, Wallesch CW, Goertler M. Risk of stroke, transient ischemic attack, and vessel occlusion before endarterectomy in patients with symptomatic severe carotid stenosis. Stroke 2002;33:1057–1062.[Abstract/Free Full Text]
  5. Caplan LR, Hennerici M. Impaired clearance of emboli (washout) is an important link between hypoperfusion, embolism, and ischemic stroke. Arch Neurol 1998;55:1475–1482.[Abstract/Free Full Text]
  6. Markus H, Cullinane M. Severely impaired cerebrovascular reactivity predicts stroke and TIA risk in patients with carotid artery stenosis and occlusion. Brain 2001;124:457–467.[Abstract/Free Full Text]
  7. Wintermark M, Reichhart M, Cuisenaire O, et al. Comparison of admission perfusion computed tomography and qualitative diffusion- and perfusion-weighted magnetic resonance imaging in acute stroke patients. Stroke 2002;33:2025–2031.[Abstract/Free Full Text]
  8. Klotz E, Konig M. Perfusion measurements of the brain: using dynamic CT for the quantitative assessment of cerebral ischemia in acute stroke. Eur J Radiol 1999;30:170–184.[CrossRef][Medline]
  9. Nabavi DG, LeBlanc LM, Baxter B, et al. Monitoring cerebral perfusion after subarachnoid hemorrhage using CT. Neuroradiology 2001;43:7–16.[CrossRef][Medline]
  10. van der Schaaf I, Wermer MJ, van der Graaf Y, Velthuis BK, van de Kraats CI, Rinkel GJ. Prognostic value of cerebral perfusion-computed tomography in the acute stage after subarachnoid hemorrhage for the development of delayed cerebral ischemia. Stroke 2006;37:409–413.[Abstract/Free Full Text]
  11. Jain R, Hoeffner EG, Deveikis JP, Harrigan MR, Thompson BG, Mukherji SK. Carotid perfusion CT with balloon occlusion and acetazolamide challenge test: feasibility. Radiology 2004;231:906–913.[Abstract/Free Full Text]
  12. Wintermark M, Smith WS, Ko NU, Quist M, Schnyder P, Dillon WP. Dynamic perfusion CT: optimizing the temporal resolution and contrast volume for calculation of perfusion CT parameters in stroke patients. AJNR Am J Neuroradiol 2004;25:720–729.[Abstract/Free Full Text]
  13. Wintermark M. Using 80 kVp versus 120 kVp in perfusion CT measurement of regional cerebral blood flow. AJNR Am J Neuroradiol 2000;21:1881–1884.[Abstract/Free Full Text]
  14. Axel L. Cerebral blood flow determination by rapid-sequence computed tomography: theoretical analysis. Radiology 1980;137:679–686.[Abstract/Free Full Text]
  15. Meier P, Zierler KL. On the theory of the indicator-dilution method for measurement of cerebral blood flow and volume. J Appl Physiol 1954;6:731–744.[Medline]
  16. Wintermark M, Thiran JP, Maeder P, Schnyder P, Meuli R. Simultaneous measurement of regional cerebral blood flow by perfusion CT and stable xenon CT: a validation study. AJNR Am J Neuroradiol 2001;22:905–914.[Abstract/Free Full Text]
  17. Wintermark M, Maeder P, Thiran JP, Schnyder P, Meuli R. Quantitative assessment of regional cerebral blood flows by perfusion CT studies at low injection rates: a critical review of the underlying theoretical models. Eur Radiol 2001;11:1220–1230.[CrossRef][Medline]
  18. Damasio H. A computed tomographic guide to the identification of cerebral vascular territories. Arch Neurol 1983;40:138–142.[Abstract/Free Full Text]
  19. Parkes LM, Rashid W, Chard DT, Tofts PS. Normal cerebral perfusion measurements using arterial spin labeling: reproducibility, stability, and age and gender effects. Magn Reson Med 2004;51:736–743.[CrossRef][Medline]
  20. Field AS, Laurienti PJ, Yen YF, Burdette JH, Moody DM. Dietary caffeine consumption and withdrawal: confounding variables in quantitative cerebral perfusion studies? Radiology 2003;227:129–135.[Abstract/Free Full Text]
  21. Kluytmans M, van der Grond J, Viergever MA. Gray matter and white matter perfusion imaging in patients with severe carotid artery lesions. Radiology 1998;209:675–682.[Abstract/Free Full Text]
  22. Fiorella D, Heiserman J, Prenger E, Partovi S. Assessment of the reproducibility of postprocessing dynamic CT perfusion data. AJNR Am J Neuroradiol 2004;25:97–107.[Abstract/Free Full Text]
  23. Schroeder T. Hemodynamic significance of internal carotid artery disease. Acta Neurol Scand 1988;77:353–372.[Medline]
  24. Wilkinson ID, Griffiths PD, Hoggard N, et al. Short-term changes in cerebral microhemodynamics after carotid stenting. AJNR Am J Neuroradiol 2003;24:1501–1507.[Abstract/Free Full Text]
  25. Gauvrit JY, Delmaire C, Henon H, et al. Diffusion/perfusion-weighted magnetic resonance imaging after carotid angioplasty and stenting. J Neurol 2004;251:1060–1067.[Medline]
  26. Ances BM, McGarvey ML, Abrahams JM, et al. Continuous arterial spin labeled perfusion magnetic resonance imaging in patients before and after carotid endarterectomy. J Neuroimaging 2004;14:133–138.[CrossRef][Medline]
  27. Sacca A, Pedrini L, Vitacchiano G, et al. Cerebral SPECT with 99mTc-HMPAO in extracranial carotid pathology: evaluation of changes in the ischemic area after carotid endarterectomy. Int Angiol 1992;11:117–121.[Medline]
  28. Cikrit DF, Dalsing MC, Harting PS, et al. Cerebral vascular reactivity assessed with acetazolamide single photon emission computer tomography scans before and after carotid endarterectomy. Am J Surg 1997;174:193–197.[CrossRef][Medline]
  29. Soinne L, Helenius J, Tatlisumak T, et al. Cerebral hemodynamics in asymptomatic and symptomatic patients with high-grade carotid stenosis undergoing carotid endarterectomy. Stroke 2003;34:1655–1661.[Abstract/Free Full Text]
  30. Derdeyn CP, Grubb RL Jr, Powers WJ. Cerebral hemodynamic impairment: methods of measurement and association with stroke risk. Neurology 1999;53:251–259.[Abstract/Free Full Text]
  31. Schumann P, Touzani O, Young AR, Morello R, Baron JC, MacKenzie ET. Evaluation of the ratio of cerebral blood flow to cerebral blood volume as an index of local cerebral perfusion pressure. Brain 1998;121:1369–1379.[Abstract/Free Full Text]
  32. Wintermark M, Flanders AE, Velthuis B, et al. Perfusion-CT assessment of infarct core and penumbra: receiver operating characteristic curve analysis in 130 patients suspected of acute hemispheric stroke. Stroke 2006;37:979–985.[Abstract/Free Full Text]
  33. Powers WJ, Press GA, Grubb RL Jr, et al. The effect of hemodynamically significant carotid artery disease on the hemodynamic status of the cerebral circulation. Ann Intern Med 1987;106:27–34.[Abstract/Free Full Text]
  34. Sanelli PC, Lev MH, Eastwood JD, Gonzalez RG, Lee TY. The effect of varying user-selected input parameters on quantitative values in CT perfusion maps. Acad Radiol 2004;11:1085–1092.[CrossRef][Medline]
  35. Yamada K, Wu O, Gonzalez RG, Bakker D, et al. Magnetic resonance perfusion-weighted imaging of acute cerebral infarction: effect of the calculation methods and underlying vasculopathy. Stroke 2002;33:87–94.[Abstract/Free Full Text]
  36. Calamante F, Gadian DG, Connelly A. Quantification of perfusion using bolus tracking magnetic resonance imaging in stroke: assumptions, limitations, and potential implications for clinical use. Stroke 2002;33:1146–1151.[Abstract/Free Full Text]
  37. Bisdas S, Nemitz O, Berding G, et al. Correlative assessment of cerebral blood flow obtained with perfusion CT and positron emission tomography in symptomatic stenotic carotid disease. Eur Radiol 2006;16:2220–2228.[CrossRef][Medline]




This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
2451061493v1
245/2/541    most recent
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Waaijer, A.
Right arrow Articles by Prokop, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Waaijer, A.
Right arrow Articles by Prokop, M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
RADIOLOGY RADIOGRAPHICS RSNA JOURNALS ONLINE