Clinical cerebrovascular applications of arterial ultrasound volume flow rate estimates

In vivo evaluation of quantitative MR angiography in a canine carotid artery stenosis model

BACKGROUND AND PURPOSE

Large-vessel cerebral blood flow quantification has emerged as a potential predictor of stroke risk. QMRA uses phase-contrast techniques to noninvasively measure vessel flows. To evaluate the in vivo accuracy of QMRA for measuring the effects of progressive arterial stenosis, we compared this technique with invasive flow measurements from a sonographic transit-time flow probe in a canine model.

MATERIALS AND METHODS

A sonographic flow probe was implanted around the CCA of hound dogs (n = 4) under general anesthesia. Pulsatile blood flow and arterial pressure were continuously recorded during CCA flow measurements with QMRA. A vascular tourniquet was applied around the CCA to produce progressive stenosis and varying flow rates. Statistical comparisons were made by using the Pearson product moment correlation coefficient.

RESULTS

A total of 60 paired CCA flow measurements were compared. Mean blood flows ranged between 21 and 691 mL/min during QMRA acquisition as measured by the flow probe. The correlation coefficients between flow probe and QMRA measurements for mean, maximum, and minimum volume flow rates were 0.99 (P < .0001), 0.98 (P < .0001), and 0.96 (P < .0001), respectively. The overall proportional difference between the 2 techniques was 7.8 ± 1%. Measurements at higher flow rates and in the absence of arterial stenosis had the lowest PD.

CONCLUSIONS

Noninvasive CCA flow measurements by using QMRA are accurate compared with invasive flow-probe measurements in a canine arterial flow model with stenosis and may be useful for the evaluation of the hemodynamic effects of stenosis caused by cerebrovascular atherosclerosis.

Accuracy of volumetric flow rate measurements: an in vitro study using modern ultrasound scanners

OBJECTIVE

Volumetric flow measurement with Doppler ultrasound is useful in assessing blood flow as part of an evaluation of arteriovenous fistula maturity in patients undergoing hemodialysis. In this study, we assessed both accuracy and variability in volumetric flow measurements obtained using modern and commercially available ultrasound systems and an in vitro experimental setup.

METHODS

Volumetric flow measurements using duplex ultrasound were obtained by 3 users operating 5 different systems for randomized flow in the range of 100 to 1000 mL/min. Users performed 3 consecutive measurements at a given flow rate. Data were analyzed using statistical techniques to assess measurement accuracy and variability.

RESULTS

Over the span of flow rates studied, the root mean square error (RMSE) for the 5 ultrasound systems ranged from 38.8 to 79.7, 36.8 to 52.0, 73.0 to 85.3, 26.7 to 44.6, and 43.9 to 93.5 mL/min. Corresponding average RMSE values were 60.3, 42.7, 81.1, 37.2, and 64.4 mL/min, respectively. A linear regression analysis of mean interobserver measurements revealed an excellent correlation for all ultrasound systems (r(2) > 99.1%). Assessment of intraobserver measurements revealed no statistically significant differences for any ultrasound system evaluated (P > .94). Comparison of interobserver measurements indicates no statistically significant differences between any of the 5 systems (P > .14).

CONCLUSIONS

Modern ultrasound systems are reasonably accurate in blood flow measurement in an experimental setup mimicking clinically relevant blood flow ranges in a hemodialysis fistula. Users need adequate training and experience to perform multiple measurements and use appropriate techniques to minimize errors in flow measurement.

Increased locoregional blood flow in brain tumors after cervical spinal cord stimulation

OBJECT

Patients with high-grade gliomas have poor prognoses following standard treatment. Generally, malignant brain tumors have a decreased blood flow that results in increased resistance to radiation and reduced delivery of chemotherapeutic agents and oxygen. The aim of the present study was to assess the effect of spinal cord stimulation (SCS) on locoregional blood flow in high-grade tumors in the brain.

METHODS

Fifteen patients (11 with Grade III and four with Grade IV brain tumors) had SCS devices inserted prior to scheduled radiotherapy. Both before and after SCS, the patients underwent the following procedures: 1) single-photon emission computerized tomography (SPECT) scanning; 2) middle cerebral artery (MCA) blood flow velocity measurements (centimeters/second) with the aid of transcranial Doppler (TCD) ultrasonography; and 3) common carotid artery (CCA) blood flow volume quantification (milliliters/minute) based on time-domain processing by using color Doppler ultrasonography. The indices demonstrated on SPECT scanning before SCS were significantly lower (p < 0.001) in tumor sites compared with those in peritumoral sites (32%) and healthy contralateral areas (41%). Poststimulation results revealed the following: 1) a mean increase of 15% in tumor blood flow in 75% of patients (p = 0.033), as demonstrated on SPECT scanning: 2) a mean increase of greater than 18% in systolic and diastolic blood flow velocities in both tumorous and healthy MCAs in all but one patient (p < 0.002), as exhibited on TCD ultrasonography; and 3) a mean increase of greater than 60% in blood flow volume in tumorous and healthy CCAs in all patients (p < 0.013), as revealed on color Doppler ultrasonography studies.

CONCLUSIONS

Preliminary data show that SCS can modify locoregional blood flow in high-grade malignant tumors in the brain, thus indicating that SCS could be used to improve blood flow, oxygenation, and drug delivery to such tumors and could be a useful adjuvant in chemoradiotherapy.

Color velocity imaging quantification in the detection of intracranial collateral flow

BACKGROUND AND PURPOSE

The development of intracranial collateral circulation is associated with a lower risk of stroke. A noninvasive technique that can reliably detect the presence of intracranial collaterals would be a valuable factor in the assessment of risk in patients with occlusive cerebrovascular disease.

METHODS

Color velocity imaging quantification was used to measure the blood flow volume of the common carotid and vertebral arteries in 40 patients with carotid occlusive disease. The blood flow volumes in these arteries were correlated with angiographic evidence of collaterals to establish the best cutoffs for detecting intracranial collateral circulation.

RESULTS

A blood flow volume of either > or =370 mL/min in the common carotid artery or > or =120 mL/min in the vertebral artery was indicative of the presence of intracranial collaterals. The sensitivity and specificity for the common carotid artery were 92.3% [95% confidence interval (CI), 62.1 to 99.6] and 92.1% (95% CI, 77.5 to 97.9), respectively. The sensitivity and specificity for the vertebral artery were 75.0% (95% CI, 35.6 to 95.5) and 87.5% (95% CI, 66.5 to 96.7), respectively.

CONCLUSIONS

Color velocity imaging quantification offers a noninvasive, accurate method for detecting the presence of intracranial collateral circulation and quantifying its magnitude. This technique would be a useful adjunct in screening or continuous monitoring of patients with severe carotid occlusive disease.

Blood flow volume quantification of cerebral ischemia: comparison of three noninvasive imaging techniques of carotid and vertebral arteries

OBJECTIVE

Determination of blood flow volume is useful in assessing ischemic cerebrovascular disease. We compared the blood flow volume measurement of three noninvasive imaging techniques, namely color velocity imaging quantification, spectral Doppler imaging quantification, and MR phase-contrast flow quantification, to see how well the flow values determined by each technique agreed with one another.

SUBJECTS AND METHODS

Flow volume quantification was tested experimentally using a flow simulator and by the three techniques in the vertebral and internal carotid arteries of 40 patients with histories of cerebral ischemia. In the flow simulation study, the flow values in each technique were compared with the phantom flow by the Wilcoxon's signed rank test. In the patient study, the flow values between each paired technique were compared by paired t test. The significance level was taken at p less than 0.05.

RESULTS

Flow volumes were measured by color velocity imaging quantification. MR phase-contrast flow quantification agreed with the phantom flow simulation within the tested range, and spectral Doppler imaging quantification values were significantly overestimated. In patients, a large variation of the blood flow volume was obtained between each technique (p < 0.05). Among them, spectral Doppler imaging quantification showed the highest flow values in the vessels (internal carotid arteries, 312.6 mL/min; vertebral arteries, 112.0 mL/min), followed by color velocity imaging quantification (internal carotid arteries, 216.8 mL/min; vertebral arteries, 58.1 mL/min) and MR phase-contrast flow quantification (internal carotid arteries, 169.1 mL/min; vertebral arteries, 66.5 mL/min).

CONCLUSION

Blood flow volume measurements determined by the three noninvasive imaging techniques on the same vessel can differ widely, and spectral Doppler imaging quantification consistently overestimated the flow volume. It is, therefore, essential that the same technique, preferably color velocity imaging quantification or MR phase-contrast flow quantification, be used for clinical follow-up investigations in the future.

Preferred technique for blood flow volume measurement in cerebrovascular disease

BACKGROUND AND PURPOSE

A noninvasive reliable technique that can reveal cerebral blood flow volume could be a valuable tool in screening programs for stroke prevention. In diagnostic ultrasonography, spectral Doppler imaging (SDI) is popular among sonologists and vascular technologists to estimate blood flow volume despite its documented inaccuracy and the availability of the more accurate technique of color velocity imaging (CVI). The aim of the present study was to demonstrate the discrepancy of blood flow volume estimation with CVI and SDI with use of an "internal" standard.

METHODS

The common, internal, and external carotid arteries of 50 healthy subjects (22 men, 28 women, age range 19 to 54 years) were examined with CVI and SDI. The total blood flow volume of the internal and external carotid arteries was then compared with the ipsilateral common carotid artery flow. An accurate technique would demonstrate no difference. The difference (expressed as a percent inconsistency) was therefore a measure of the accuracy of the method.

RESULTS

The mean+/-SD inconsistency was found to be 10.6+/-8.3% for CVI and 27.9+/-14.3% for SDI. The difference in inconsistency between CVI and SDI in measurement of carotid blood flow volume was statistically significant (P<0.01).

CONCLUSIONS

CVI is more accurate than SDI in the determination of blood flow volume in the carotid arteries. For noninvasive clinical estimation of cerebrovascular blood flow volume, CVI quantification should be the preferred technique.

Brain perfusion imaging predicts survival in Alzheimer's disease

BACKGROUND

The variability of disease course in patients diagnosed with AD makes prediction of survival difficult, despite the identification of numerous predictors to date. This study evaluated the predictive utility of measurements of regional cerebral blood flow (rCBF) obtained with SPECT in a group of AD patients.

METHODS

Fifty AD patients were studied with SPECT and followed longitudinally. SPECT measures of relative rCBF were calculated by measuring radioactivity densities in dorsolateral frontal, orbitofrontal, temporal, and parietal cortex normalized to occipital cortical radioactivity density. Subjects were classified into three tertiles of rCBF ratios for each region. These rCBF ratios were used as predictors of survival in life-table and proportional hazard models to predict survival.

RESULTS

Right parietal rCBF was a significant predictor of survival in the life-table analysis, with subjects in the lowest tertile having shortest survivals. No other brain region was a significant predictor of survival. In a proportional hazards model when a variety of other potential predictors were accounted for, right parietal rCBF ratio remained a significant predictor.

CONCLUSIONS

These results demonstrate that brain perfusion in the right parietal lobe is a significant predictor of survival in patients with AD even when other predictors are taken into consideration. This suggests that SPECT perfusion imaging may provide additional useful information on disease prognosis in AD.

Mucolipidosis type IV: characteristic MRI findings

OBJECTIVE

The objective of this study is to characterize the brain abnormalities on head MRI of patients with mucolipidosis type IV.

BACKGROUND

Mucolipidosis type IV is an autosomal recessive lysosomal storage disease of unknown etiology. Patients develop corneal clouding, retinal degeneration, spastic quadriparesis, and mental retardation. Patients with this disorder have not been studied systematically.

METHODS

We studied prospectively 15 consecutive patients with mucolipidosis type IV using cranial MRI.

RESULTS

Fourteen patients with these typical clinical findings had a hypoplastic corpus callosum with absent rostrum and a dysplastic or absent splenium, signal abnormalities on T1-weighted head MRI images in the white matter, and increased ferritin deposition in the thalamus and basal ganglia. Atrophy of the cerebellum and cerebrum was observed in older patients, which may reflect disease progression. One patient with a mild clinical variant had a normal corpus callosum.

CONCLUSION

Patients with mucolipidosis type IV have characteristic cranial MRI findings that suggest that this disorder causes both developmental and neurodegenerative abnormalities.

Mass effect and death from severe acute stroke

BACKGROUND

In severe acute stroke, the degree of midline cerebral displacement is related to level of consciousness but not to survival. Early identification of patients at high risk of death from mass effect would assist patient management decisions.

METHODS

We measured lesion volume, horizontal pineal displacement (PD), and horizontal septum pellucidum displacement (SD) on axial CT of consecutive patients with severe (Canadian Neurological Scale score < or = 5) acute hemispheric stroke. We correlated CT measurements with the probability of 14-day survival.

RESULTS

Forty-six (39%) of 118 patients died within 14 days and 72 (61%) died within 1 year following stroke. Crude risk factors for 14-day mortality were as follows: lesion volume > or = 400 ml, SD > or = 9 mm, PD > or = 4 mm, intraventricular hemorrhage, and coma on admission. Only SD (p = 0.001) and coma on admission (p = 0.019) remained significant in multivariate analysis, but PD was highly correlated with SD (r = 0.82). PD of > or = 4 mm on a scan performed within 48 hours of stroke onset identified patients with a low probability of 14-day survival (0.16; CI 0 to 0.32) with a specificity of 89% and a sensitivity of 46%.

CONCLUSIONS

The degree of horizontal midline cerebral displacement correlates with the likelihood of death following stroke. Patients with > or = 4 mm PD on CT performed within 48 hours of stroke onset are at high risk for early death.

Anterior translocation of language in patients with left cerebral arteriovenous malformation

We studied seven patients with left cerebral atriovenous malformation (AVM) with superselective arterial injection of anesthetics during angiography to determine whether there was translocation of some language functions to other regions in the ispilateral hemisphere. All patients were right handed. With a catheter inserted into each target vessel, patients underwent aphasia examination in an A-B-A design: (A) baseline, no anesthetic; (B) 1 minute after anesthetic injection; and (A) 12 minutes after injection (when its effects had dissipated). The results showed that six of seven patients had no significant aphasia at baseline or 12 minutes after anesthetic injection. One patient had a mild conduction aphasia at baseline and after anesthetic effects had dissipated. In the six patients with temporoparietal AVM, anesthetic injections into vessels in the lower division of the middle cerebral artery (MCA) not feeding the AVM (e.g., the left angular artery) produced a wide range of language function--from conduction aphasia to dense Wernicke's syndromes. When upper division MCA vessels were injected (e.g., the prefrontal branch), all developed a major aphasic disorder with significant comprehension defects. A seventh patient with a frontal opercular AVM had a mild anomia, semantic paraphasias, and decreased word-list generation when the prefrontal branch was injected. Her comprehension, however, was intact. These data show that patients with posterior cerebral AVM can show language abnormalities where such deficits are not typically seen after acute brain injury. These findings support a posterior-to-anterior extension of some language skills under conditions of brain disease.