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Neuroradiology |
1 From the Department of Radiology (J. Krejza, E.R.M.), University of Pennsylvania, Science Building, Suite 370, 3600 Market St, Philadelphia, PA 19104; and Departments of Radiology (J. Krejza) and Neurosurgery (J. Kochanowicz, Z.M., J.L.), Bialystok University School of Medicine, Bialystok, Poland. Received October 13, 2003; revision requested January 5, 2004; final revision received August 13; accepted October 1. Supported in part by American Heart Association Established Investigator Award grant 044099N. J. Krejza supported by NATO fellowship program. Address correspondence to J. Krejza (e-mail: Jaroslaw.Krejza{at}uphs.upenn.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: The institutional ethics committee approved the study. Each patient, or members of the patient's family, gave informed consent. One hundred twenty consecutive patients (64 women, 56 men; mean age, 45.5 years ± 13.6 [standard deviation]) were routinely referred for DSA after subarachnoid hemorrhage. Vasospasm was graded as mild (
25% reduction in vessel diameter), moderate (>25% to 50% reduction), or severe (>50% reduction). US was performed 2 hours or less before angiography. The ratio of flow velocity in the middle cerebral artery (VMCA) to flow velocity in the ipsilateral extracranial internal carotid artery (VICA) was calculated. Diagnostic accuracy was evaluated by calculating the area under the receiver operating characteristic curve (Az). The significance of the difference between the two Az values (for US vs DSA) was determined by using the z test with correction for correlated data.
RESULTS: Nine of 120 patients were excluded because of inadequacy of acoustic windows in the squama of temporal bones. Spasm was mild in 17, moderate in 16, and severe in only nine of 222 arteries studied. Arteries with moderate or severe vasospasm were combined in one group. The best-performing parameters were peak systolic velocity and VMCA/VICA ratio. Az values for these two parameters in diagnosis of moderate-to-severe vasospasm were 0.93 and 0.95, and in diagnosis of mild vasospasm, 0.90 and 0.91. Accuracy of the VMCA/VICA ratio calculated on the basis of end-diastolic velocity for diagnosis of mild MCA narrowing was significantly better than that of end-diastolic MCA velocity alone (Az = 0.88 vs 0.84, P < .05). The stepwise approach with use of the VMCA/VICA ratio after flow velocity measurements in the MCA resulted in a decreased number of false-negative findings in both vasospasm subgroups. The thresholds of highest efficiency were at a mean velocity of 94 and 108 cm/sec and a peak systolic VMCA/VICA ratio of 3.6 and 3.9 for diagnosis of mild and moderate-to-severe vasospasm, respectively.
CONCLUSION: Transcranial color-coded duplex US alone or in conjunction with carotid artery US has excellent accuracy for angiographic detection of vasospasm. Use of MCA velocity measurements and VMCA/VICA ratio can increase the accuracy of Doppler US.
© RSNA, 2005
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Cerebral angiography is considered the reference standard for the diagnosis of cerebral vasospasm, but this method is impractical for monitoring of vasospasm because it is invasive and carries the risk of stroke, renal injury, and other complications (4). Other methods, such as computed tomography (CT) and magnetic resonance angiography, have limited sensitivity to vasospasm, cannot be performed at the bedside, and often have limited accessibility (5,6).
The knowledge that blood flow velocity is increased in a constricted vessel has led to the use of transcranial Doppler ultrasonography (US) for detection and bedside monitoring of cerebral vasospasm (7). Nevertheless, the accuracy of conventional transcranial Doppler US for the diagnosis of middle cerebral artery (MCA) spasm differs markedly from one study to another, and these variations have raised concerns about the utility of conventional transcranial Doppler US for the reliable detection of vasospasm (8,9). Investigators in previous studies demonstrated that the diagnostic accuracy of transcranial color-coded duplex US is higher than that of conventional transcranial Doppler US (9–11). With this newer method, up to 80% of angiographically diagnosed cases of mild narrowing and 92% of cases of advanced narrowing of the MCA could be properly classified. Furthermore, standardization of flow velocity with respect to age and sex was found to increase the performance parameters of transcranial color-coded duplex US, especially for the diagnosis of less severe MCA spasms (10).
Are there any other ways to further improve the performance of transcranial color-coded duplex US for the diagnosis of MCA spasm? Failures in the proper classification of MCA spasms and consequent less-than-perfect accuracy of transcranial color-coded duplex US in this application are mainly due to false-negative findings caused by increased cerebrovascular impedance and false-positive findings caused mainly by hyperemia and/or hyperperfusion (12,13). Lindegaard et al (14) first proposed the use of the ratio of flow velocity in the MCA to that in the extracranial part of the internal carotid artery (ICA). They used this VMCA/VICA ratio (which was called the Lindegaard index) to help distinguish states of increased flow in the MCA caused by genuine spasm from those caused by hyperemia. To our knowledge, however, no attempt has been made to determine the accuracy of the VMCA/VICA ratio obtained with transcranial color-coded duplex US for the diagnosis of MCA spasm. Furthermore, no publication to date has reported the use of a VMCA/VICA ratio based on blood velocity measurements obtained with transcranial color-coded duplex US used in conjunction with standard carotid artery US.
Thus, the purpose of our study was to prospectively determine the accuracy of transcranial color-coded duplex US used alone and in conjunction with carotid artery US for the diagnosis of MCA spasm, with intraarterial digital subtraction angiography (DSA) used as the reference standard.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Patients were enrolled while at the Bialystok University Hospital, which serves as a primary and tertiary care center. From August 2000 to February 2002, 120 consecutive patients (age range, 14–72 years; mean age, 45.5 years ± 13.6 [standard deviation]) with subarachnoid hemorrhage were prospectively examined with transcranial color-coded duplex US in conjunction with carotid artery duplex US, 2 hours or less before examination with DSA, which was scheduled for clinical purposes. Patients scheduled to undergo emergency angiography on weekends or after normal working hours were not included. US examinations were performed in the angiographic facility to minimize logistical problems, time delays, and any discrepancies between US and angiographic examinations that might have resulted from pharmacologic or therapeutic interventions during the interval between the two tests.
The study group consisted of 64 female patients (age range, 18–71 years; mean age, 46.7 years ± 13.0) and 56 male patients (age range, 14–72 years; mean age, 45.1 years ± 13.9).
Ninety-two patients (76.6%) had intracranial hemorrhage, including 56 with only subarachnoid hemorrhage and 36 with both intracerebral and subarachnoid hemorrhage detected at CT. Twenty-eight patients (24.4%) were admitted because cerebral aneurysm was suspected on the basis of evidence of blood in cerebrospinal fluid obtained with a lumbar puncture. The mean and range of intervals between the occurrence of subarachnoid hemorrhage and the performance of transcranial color-coded duplex US and/or angiography in the study patients were 2.5 days and 0.5–12 days, respectively.
The patients were grouped according to the modified scale of the World Federation of Neurological Surgeons (15), with clinical grades based on Glasgow Coma Scale scores, as follows: 71 patients were in grade 1 (score of 15), 31 patients were in grade 2 (score of 12–14), 13 were in grade 3 (score of 9–11), three were in grade 4 (score of 6–8), and two were in grade 5 (score of 3–5).
Transcranial Color-coded Duplex US
Two investigators performed transcranial color-coded duplex US and carotid artery duplex US examinations: one neuroradiologist (J. Krejza) with 8 years of experience in performing and reading transcranial color-coded duplex US examinations and 12 years of experience in carotid artery US, and one neurologist (J. Kochanowicz) with 2 years of experience in transcranial color-coded duplex US and 6 years in carotid artery US. Intracranial cerebral arteries were examined bilaterally through the acoustic windows in the squama of temporal bone by using a US scanner (Toshiba, Toshiba Medical System, Tokyo, Japan) equipped with a 2.5-MHz 90° phased-array probe for both B-mode imaging and color Doppler imaging. Gray-scale imaging allowed easy determination of the suitability of the acoustic windows (16). The M1 segment of the MCA was identified with gray-scale and color imaging, and a 3-mm-wide sample volume was placed on the color image of the artery at the site of the highest flow acceleration. To determine the angle of insonation, a linear marker provided with the scanner was placed, with visual guidance, on the color Doppler image of the arterial segment that was insonated, and its direction was fitted to be oriented along the long axis of the segment (Fig 1). In older subjects, the horizontal segment of the MCA sometimes is not included in the imaging plane because of the more ventral or tortuous course of the artery. In such situations, our solution was to build up a mental map of the M1 course from several oblique sections of the vessel, obtained by smoothly tilting the probe. The sample volume was then placed within the initial segment of the artery, and angle correction was accomplished by aiming at this dummy vessel (16). The angle between the linear marker and the ultrasound beam, which was displayed automatically on the screen of the scanner, was considered a two-dimensional approximation of the angle of insonation. This allowed the angle-corrected blood flow velocity to be measured. The time-averaged mean maximum flow velocity, peak systolic velocity, and end-diastolic velocity were calculated with automatic tracing or, in cases of weak Doppler signal, manual tracing of the maximum frequency envelope of the Doppler waveform. The tracing was performed by the investigators during the examination. Manual tracing was necessary in approximately 15% of cases.
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The VMCA/VICA (Lindegaard index) ratio was calculated by referencing the velocity in the MCA to the velocity in the ipsilateral extracranial ICA. The ratios were calculated by using statistical software separately for each velocity measurement (mean time-averaged maximum flow velocity, peak systolic velocity, and end-diastolic velocity) after the completion of all US examinations.
Angiographic Studies
Selective intraarterial DSA was performed via the femoral artery by using the Seldinger approach in both ICAs and in at least one vertebral artery in every patient. Standard images included anteroposterior and lateral views and one oblique view, which were obtained routinely at injection rates of 6 mL/sec and imaging rates of 3 frames per second (Argos 2 M, Mecall, Milan, Italy). The field of view was 30 cm for all views. Two neuroradiologists who were unaware of the US findings, one of whom was an author (Z.M.) with 3 years of experience in angiography and the other of whom had 14 years of experience in angiography, independently reviewed all angiograms to detect and quantify cerebral vasospasm. Discordant readings by the two neuroradiologists in 27 arteries were resolved by consensus, with the help of a third neuroradiologist (E.M., with 8 years of experience). The results of repeated (follow-up) angiographic examinations were excluded from our analysis.
The view that showed the most severe MCA narrowing was used for comparison with transcranial color-coded duplex US findings. All measurements were performed by using electronic calipers on the digital display station. The resolution of this technique in distance measurement is 0.1 mm. To quantify the degree of narrowing, we compared the site of maximal reduction in the horizontal segment of the MCA with a normal segment in the artery adjacent to the narrowed segment. The choice of a normal vessel diameter was made according to a standard algorithm for selecting an unaffected segment and was based on the diameter of (a) a prestenotic segment, (b) a poststenotic segment, or (c) the terminal portion of the ICA (18). The diameter of the vessel in question was also compared with that of the contralateral artery to facilitate classification. Vasospasm was graded as mild (reduction of 25% in vessel caliber), moderate (reduction of >25% to 50%), or severe (reduction of >50%), as previously reported (10,14). Moderate (>25% to 50%) or severe (>50%) narrowing of the terminal portion of the ICA also was registered.
Statistical Analyses
To evaluate the performance of a particular Doppler US parameter for discrimination of a state of spasm from no spasm in the vessel, a set of sensitivity and specificity pairs was calculated for all flow velocity values and VMCA/VICA ratios regrouped for optimal class width from health-related data (19). This set of sensitivity and specificity pairs was plotted as a set of points in a unit square, in terms of true-positive fraction (ie, sensitivity) versus false-positive fraction (ie, 1 – specificity). A receiver operating characteristic (ROC) curve was then constructed on the basis of this set of points in the unit square, and the area under the ROC curve (Az) was estimated by using the clusterbi.for algorithm (20). Clusterbi.for is a software program, written in FORTRAN, that gives parametric estimates of the Az values for each of two ROC curves and that provides the variance and covariance needed for a Z test of H0 (ie, Az1 = Az2) vs Ha (ie, Az1 
Az2) in a situation in which data are both clustered and correlated. Such was the situation in our study because the same sample of patients was used to generate estimated Az values for flow velocities and VMCA/VICA ratios and because there were two observations (one observation in each of two arteries) in each patient. In this study, we had to account for correlation between the two Az value estimates (because they were based on the same sample of patients), as well as for intracluster correlation between the observations in a single patient.
Evaluation of the significance of the difference between the two estimated Az values was performed by using a parametric Z test and the method of Hanley and McNeil (21). The unpaired t test was used to evaluate the age difference between women and men. A P value of less than .05 was considered to indicate a statistically significant difference.
Thresholds of flow velocity and VMCA/VICA ratio that can help to distinguish between states of spasm and nonspasm with the greatest efficiency also were identified, with efficiency defined as the fraction of correct (true) classifications among all classifications, as follows: E = (TP + TN)/N, where E is efficiency, TP is the number of positive test results among diseased patients, TN is the number of negative test results among nondiseased patients, and N is the number of all patients in the study. Efficiency varies between 0 and 1.00 as a function of discriminator position and disease prevalence. When sensitivity is greater than specificity, efficiency increases with increasing prevalence; when sensitivity is less than specificity, the relationship between efficiency and prevalence is the inverse. When sensitivity equals specificity, efficiency becomes independent of the prevalence of disease. When the prevalence of disease is 1.00, efficiency equals sensitivity; at a prevalence of 0, efficiency equals specificity. For a discriminator position at zero, efficiency equals the prevalence of disease; at the highest discriminator position, efficiency equals the complementary value (1 – disease prevalence). At maximal efficiency, the fraction of correct classifications is maximal. Thus, in selecting flow velocity or VMCA/VICA thresholds, we opted for maximal efficiency. In a specific clinical situation, however, a clinician may want to choose thresholds for either maximal sensitivity or maximal specificity, neither of which usually corresponds to maximal efficiency.
The identification of thresholds associated with maximal efficiency, as well as the calculation of sensitivity, specificity, negative and positive predictive values, and the associated confidence interval (CI), were performed by using software developed by Kairisto and Poola (22).
Interobserver agreement in the independent readings of angiographic images by the two neuroradiologists, with regard to the detection of any degree of vasospasm and of moderate-to-severe vasospasm, was assessed by calculating 
coefficients.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Angiographic Data
Vessel narrowing diagnosed at angiography was mild in 17 MCA segments, moderate in 16, and severe in nine. Moderate and severe vasospasms were combined to form one group (moderate-to-severe vasospasm) because the number of occurrences of severe vasospasm was too small to allow a valid statistical analysis. Thus, separate ROC analyses were performed for the subgroup of vessels with moderate-to-severe vasospasm and for those with any grade of vasospasm (that is, both the mild and the moderate-to-severe subgroups). In the former situation, arteries with mild spasm were included in the comparative group. The coefficient for agreement between the two neuroradiologists in angiographic detection of moderate-to-severe MCA spasm was 0.80 (95% CI: 0.67, 0.93). The level of interobserver agreement in the detection of mild MCA spasm was lower, with a value of 0.63 (95% CI: 0.56, 0.70).
Moderate narrowing of the terminal portion of the ICA was found in three patients, and severe narrowing of this segment was found in two patients. One mild and one severe concomitant narrowing of the ipsilateral MCA were found in the subgroups of patients with moderate and severe ICA narrowing, respectively.
Detection of Vasospasm: Comparison of MCA Flow Velocity Measurements and VMCA/VICA Ratios
To enable easy comparison of the accuracy of various Doppler US parameters for the detection of any degree of vasospasm, the ROC curves constructed for flow velocities in the MCA are shown in the same figures as the ROC curves constructed for corresponding VMCA/VICA ratios (Fig 2). The Az values and 95% CIs are given in Table 1.
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In addition to the accuracy of Doppler US for detection of MCA spasm with ROC analysis, one can determine the diagnostic efficiency of the test for any threshold of blood flow velocity in the MCA or for any VMCA/VICA ratio. The highest efficiency for detection of any degree of vasospasm corresponded to a mean velocity threshold of 94 cm/sec (efficiency, 93%) and a VMCA/VICA ratio of 3.6 (efficiency, 92%), calculated on the basis of peak systolic velocity (Table 2).
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Detection of More Advanced Vasospasm: Comparison of MCA Flow Velocity Measurements and VMCA/VICA Ratios
The accuracy of flow velocity measurements in the MCA and of VMCA/VICA ratios for diagnosis of moderate-to-severe vasospasm were on average 4% higher than those for diagnosis of less advanced vasospasm (Figs 2, 3; Tables 1, 3). The accuracy of flow velocity measurements in the MCA was slightly lower than that of the corresponding VMCA/VICA ratios and ranged from 89% for end-diastolic velocity to 93% for peak systolic velocity, versus 91% and 95% for the corresponding VMCA/VICA ratios (Table 3). The difference between the total Az value for peak systolic velocity and the total Az value for end-diastolic velocity trended toward significance (P = .062). The accuracy of the VMCA/VICA ratio calculated on the basis of peak systolic velocity was substantially better than the accuracy of the ratio calculated on the basis of end-diastolic velocity (P < .05).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The accuracy of transcranial color-coded duplex US used in conjunction with carotid artery US for the detection of advanced MCA spasm appeared similar to the accuracy of transcranial color-coded duplex US alone. This result could have been anticipated, because significant narrowing leads to a substantial increase in flow velocity in the MCA that is well above the normal range and to a substantial decrease in velocity in the ICA (17,24). When mild MCA spasm is included in the diseased group, the accuracy of the VMCA/VICA ratio is somewhat better than that of flow velocity measurements in the MCA, in particular when compared with the accuracy of end-diastolic velocity. The ratios calculated on the basis of mean and end-diastolic velocity, however, seem to be more sensitive than the respective velocities for diagnosis of MCA spasm.
A likely explanation for the higher sensitivity of the VMCA/VICA ratio calculated on the basis of mean and end-diastolic velocity is our relatively high incidence of patients with potentially increased intracranial pressure due to massive intracranial hemorrhage (25). Spasm of the cerebral microvasculature, which is known to occur shortly after subarachnoid hemorrhage (26), should also be taken into account, because the majority of patients underwent DSA within 3 days after ictus. As a result, flow velocity in the ICA decreases, while that in a mildly narrowed MCA might not reach a velocity threshold indicating vasospasm. In such situations, a flow velocity criterion will indicate no spasm, while a VMCA/VICA ratio criterion may (correctly) indicate spasm, thus contributing to the increased sensitivity of the method. The use of transcranial color-coded duplex US in conjunction with carotid artery US reduced the number of false-negative results at the expense of an increase in the number of false-positive results.
Our results suggest that a stepwise approach with the use of flow velocity measurements and the VMCA/VICA ratio for the diagnosis of MCA spasm could further increase the diagnostic accuracy of color-coded duplex US. This approach allowed the detection of all occurrences of moderate-to-severe MCA spasm and a decreased number of erroneous classifications of mild narrowing associated with the use of velocity measurements in the affected MCA. One may conclude that the analysis of several Doppler parameters could further increase the diagnostic accuracy of color-coded duplex US; however, the number of patients in whom velocity measurements in the MCA disagreed with the VMCA/VICA ratio was too small to substantiate such improvement. The improvement in the performance of transcranial color-coded duplex US for diagnosis of mild and moderate-to-severe MCA spasm is of clinical importance, because it allows early diagnosis of the initial phase of the spasm. Hence, transcranial color-coded duplex US may allow us to include patients with mild MCA spasm in the "increased risk" group during early phases of spasm. This capability could influence neurosurgical planning and help to more accurately assess and treat disease in patients at risk for complications from vasospasm at an earlier stage of the disease process (27).
The use of the VMCA/VICA ratio is associated with several limitations. The flow velocity in the proximal part of the ICA may be diminished because of narrowing of the distal part of the ICA. Also, the normal MCA flow may be reduced because of a distal ICA narrowing that leads to decreased velocity, while in the narrowed MCA the flow velocity will be unpredictable: normal, decreased, or increased. It is apparent that the resultant VMCA/VICA ratio also may vary considerably and thus lead to errors in the detection of MCA spasm. In cases of a lesser degree of ICA narrowing and of normal or decreased distal impedance, an intensive jet flow produced in the narrowed segment can reach the MCA, causing an increase in the VMCA/VICA ratio (28). If distal impedance is increased and/or the MCA itself is narrowed, then the jet flow will be hampered, leading to a decrease in the VMCA/VICA ratio. The former situation will lead to a false-positive result, and the latter, to a false-negative one.
Narrowing of the proximal part of the ICA, which is frequently affected by atherosclerosis, can introduce additional errors into measurements of the VMCA/VICA ratio. In our patient population, we did not find any substantial narrowing of the proximal part of the ICA, probably because our patients with subarachnoid hemorrhage were relatively young. Also, it is to be expected that the flow velocity in the proximal part of the ICA, even in the narrowed artery, may not reach the threshold that indicates substantial narrowing, because distal impedance is usually increased in patients with subarachnoid hemorrhage (26). It might be worthwhile, therefore, to measure velocity in the distal part of the CCA and proximal part of the ICA to determine the ratio of the ICA flow velocity to the CCA flow velocity, a more reliable measurement for determining narrowing of the proximal part of the ICA (17). Significant narrowing of the proximal part of the ICA can affect flow velocity in the MCA and the performance of the VMCA/VICA ratio. It is worth noting that the problem with ICA flow velocity also has a methodologic aspect: Insonations of the proximal part of the ICA performed with a relatively wide linear probe are not error free because of the frequent kinking, spiral course, and/or high bifurcation of the CCA (17). Likewise, measurement of flow velocity with transcranial color-coded duplex US in the intracranial segment of the ICA is less reliable because of the awkward course of the ICA in relation to the ultrasound beam (16).
All US studies were performed close to the angiographic facility, just before the angiographic procedure, to avoid paradoxical discrepancy between the two tests. First, if the reference examination is performed after the US examination, therapeutic intervention during that period might affect the status of the cerebral vasculature as well as hemodynamic parameters. Second, the performance of the US examination in a crowded intensive care unit is more challenging and time-consuming, especially when the patient cannot lie motionless. It also may lead to disparate results because stressful transportation to the angiographic facility may affect the patient's cerebrovascular hemodynamics. Further, the method used to help the patient maintain breathing in the intensive care unit may be different from that in the angiographic facility, which is usually less well equipped than the intensive care unit.
The low prevalence of severe MCA spasm in our population is obviously a result of random sampling of patients after subarachnoid hemorrhage—an approach suggested by Ransohoff and Feinstein (29). Our patients usually were referred for angiography shortly after their admission to the hospital, when vasospasm was less likely to be advanced, whereas severe vasospasm usually develops between the 1st and 3rd week after subarachnoid hemorrhage (1,2). It may be expected that this higher prevalence of severe MCA spasm would not decrease the diagnostic accuracy of either the velocity measurement or the velocity ratio, because significant narrowing of the artery causes a flow velocity increase well above the normal range (17,24). This hypothesis needs to be tested in future studies.
The highest efficiency of flow velocity measurements in the MCA appeared at somewhat lower thresholds in our study than in previous studies (9–11), and this difference is probably related to the lower prevalence of moderate and severe vasospasm in our patient sample. However, the VMCA/VICA ratio thresholds that we determined are somewhat higher than those originally recommended by Lindegaard et al (14) as generally diagnostic at conventional transcranial Doppler US for angiographically visible vasospasm. In their group, three patients with MCA narrowing of less than 25% had a VMCA/VICA ratio of less than 3.1, while the ratios in a further five patients with mild vasospasm and 12 patients with moderate vasospasm ranged from 3.1 to 5.9. All patients with severe vasospasm had ratios of more than 5.9. For color-coded duplex US, we suggest that the VMCA/VICA ratio be calculated on the basis of peak systolic velocity and that a value of 3.6 be used for detection of angiographically visible vasospasm (mild narrowing), while the threshold of 3.9 can be recommended for more advanced vasospasm (moderate-to-severe narrowing). All these values are outside the span of normal reference values established by Aaslid et al (7) and Lindegaard et al (14) in a small group of subjects by using conventional transcranial Doppler US. Normal reference values for VMCA/VICA ratio studied with transcranial color-coded duplex US and carotid artery duplex US in a larger subject population need to be established because virtually nothing has been published to date on the putative variability of VMCA/VICA ratio with age, sex, and individual hormonal status (24,30).
DSA has been used in this study as a reference standard, but it is far from perfect, as is illustrated by the moderate level of interobserver agreement for detection of mild vasospasm. The limitations of angiography and other imaging techniques have been discussed in greater detail elsewhere (31). The main drawback seems to be that when angiography is relied on to define the true state of the vessel, it is difficult for the performance of color-coded duplex US to appear better, even if the latter modality allows the detection of occurrences of vasospasm that were missed at angiography.
The explorative nature of our study may limit the direct applicability of our results to general clinical practice because data-dependent analysis may lead to overoptimistic conclusions (32). The proposed diagnostic criteria should be validated to demonstrate the satisfactory performance of color-coded duplex US also in patients from a different population. Furthermore, new data collected in an appropriate patient population at a different center may help to update the proposed criteria through a comparison of predictions with actual observations. The point is that we need evidence that the proposed criteria indeed do what they are intended to do. Further studies are needed to demonstrate the generalizability, clinical credibility, and effectiveness of the proposed diagnostic approach.
In light of our results, one can conclude that moderate-to-severe and mild MCA spasms can be detected with excellent accuracy by using transcranial color-coded duplex US either alone or in conjunction with carotid artery duplex US. The stepwise approach of using MCA velocity measurements and VMCA/VICA ratio may help to further increase the diagnostic accuracy of Doppler US.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Abbreviations: Az = area under the ROC curve • CCA = common carotid artery • CI = confidence interval • DSA = digital subtraction angiography • ICA = internal carotid artery • MCA = middle cerebral artery • ROC = receiver operating characteristic
Author contributions: Guarantor of integrity of entire study, J. Krejza; study concepts and design, J. Krejza, Z.M., J. Kochanowicz; literature research, J. Krejza, J. Kochanowicz; clinical studies, J. Krejza, J. Kochanowicz; data acquisition, J. Kochanowicz, J. Krejza; data analysis/interpretation, J. Krejza, Z.M., E.R.M.; statistical analysis, J. Krejza, Z.M., J. Kochanowicz; manuscript preparation, J. Krejza, Z.M., J. Kochanowicz; manuscript definition of intellectual content and revision/review, all authors; manuscript editing, J. Krejza, J. Kochanowicz; manuscript final version approval, J. Krejza
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References |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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This article has been cited by other articles:
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  A. Rigamonti, A. Ackery, and A. J. Baker Transcranial Doppler monitoring in subarachnoid hemorrhage: a critical tool in critical care: [Monitorage par Doppler transcranien lors d'une hemorragie sous-arachnoidienne : un outil indispensable aux soins intensifs] Can J Anesth, February 1, 2008; 55(2): 112 - 123. [Abstract] [Full Text] [PDF]
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 D. Pelz, T. Andersson, M. Soderman, P. Lylyk, and M. Negoro Advances in Interventional Neuroradiology 2005 Stroke, February 1, 2006; 37(2): 309 - 311. [Full Text] [PDF]
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