Vasodilatory Responses and Magnetic Resonance Angiography

This study measured the responses of both extracranial (internal carotid arteries) and intracranial (middle cerebral/angular, basilar arteries) intravascular arterial volume flow rates to acetazolamide using phase-contrast magnetic resonance angiography. Twenty-eight newly studied patients were subdivided into four groups: Group I-Nonocclusive, asymptomatic (n = 7, or 14 carotid and middle cerebral/angular artery sides); Group II-unilateral carotid transient ischemic attacks, nonhemodynamic (embolic), varying stenoses (n = 11); Group III-unilateral carotid transient ischemic attacks, hemodynamic, varying stenoses (n = 5); and Group IV-unilateral carotid occlusion, asymptomatic (n = 5). The data were separated into nonischemic and ischemic sides so as to illustrate group differences based on vasodilatory responses to acetazolamide. For example, the percent change in volume flow rates over baseline values for the ischemic-side middle cerebral arteries of Group III was significantly the lowest of all of the vasodilatory responses (?25 ± 11% vs 40 ± 14% for group II ischemic middle cerebral/angular artery sides, p = 0.008). Group III patients also had significantly lower standing blood pressures (p = 0.012), higher number of transient ischemic attacks (p = 0.008), and shorter duration of events (p = 0.013). Determinations of volume flow rate continue to assist in determining the degree of hemodynamic compromise of a particular vascular territory.     

Magnetic Resonance Angiography in the Evaluation of Dural Carotid-Cavernous Fistulas

The diagnosis of dural carotid-cavernous fistula is often elusive. The 2 patients described experienced the insidious onset of ocular signs and symptoms. Evaluation over several months including computed tomography and magnetic resonance imaging revealed only nonspecific abnormalities. In both patients, magnetic resonance angiography showed features characteristic of carotid-cavernous shunting, confirmed by cerebral arteriography. Magnetic resonance angiography is an important tool for the evaluation of patients with suspected dural carotidcavernous fistulas.     

Magnetic Resonance Angiography in Patients with Brain Infarction

This study evaluated the role of magnetic resonance angiography (MRA) in detecting extra- or intracranial vascular disease in 118 patients with brain infarction and the accuracy of MRA diagnosis when compared with conventional angiography in patients who had both investigations. Magnet ic resonance angiography ruled out extra- and intracranial large vessel disease in 36% of the patients. MRA also demonstrated extra- or intracranial disease in 56% (probably symptomatic in 31, possibly symptomatic in 18, and asymptomatic in 17 patients), and provided no information in 8% of the 118 patients. Among the 176 major vessels visualized by both MRA and conventional angiography, conventional angiography confirmed the presence of 9/10 extracranial and 32/40 intracranial large vessel abnormalit ies detected on MRA. There were two false-negative findings on MRA: occlusion of a distal branch of middle cerebral artery, and an asymptomatic posterior cerebral artery stenosis. Magnetic resonance angiography is a clinically useful method for screening extra- and intracranial disease in patients with brain infarction and selecting high-yield patients for conventional angiography.     

Magnetic Resonance Angiography of a Posterior Cerebral Artery Occlusion

A 45-year-old woman suddenly had severe pain in the right eye and blurred vision. Physical findings were normal except for left homonymous hemianopia. Laboratory test results were normal. However, magnetic resonance images showed evidence of cerebral infarctions in the right posterior cerebral artery distribution. In addition, magnetic resonance angiography was consistent with absent flow of that vessel.     

Magnetic Resonance Angiography in Glomus Arteriovenous Malformation of the Cervical Spine

Conventional magnetic resonance imaging (MRI) and spine magnetic resonance angiography (MRA) demonstrated a glomus-type intradural arteriovenous malformation of the upper cervical region of the spine in a 24-year-old woman. Gadolinium-enhanced, three-dimensional, phase-contrast angiography displayed the nidus and feeders of the arteriovenous malformation. The clinical features of the two most common types of spinal arteriovenous malformations (dural arteriovenous fistula and glomus intradural arteriovenous malformation) are reviewed. Conventional MRI and spine MRA may obviate the need for performing total spinal myelography in patients suspected of having spinal arteriovenous malformations.     

Three-Dimensional Contrast-Enhanced Magnetic Resonance Angiography of Carotid Artery after Stenting

PURPOSE: This study presents 3-dimensional, contrast-enhanced, magnetic resonance (MR) angiographic appearances of the carotid artery after stenting. METHODS: The authors reviewed contrast-enhanced MR angiograms of 18 carotid arteries in 13 patients. These arteries were not stenotic or occluded in the stented segment, as shown on carotid angio-grams (11 patients) or carotid Doppler images (2 patients) obtained later. RESULTS: Five patients had 1 stent in each of their bilateral carotid arteries. One patient with 1 stent in 1 artery underwent the examination twice with different MR coils. Different artifact patterns were found in 19 carotid-stent examinations. Type 1a involved short segments of false narrowing or false focal occlusion at both ends of the stent (n = 12); the carotid artery in the stented segment between the ends was normal. Types 2a and 2b occurred along the stented segment of the artery between the 2 ends of the stent. Type 2a was milder, with segmental faint signal intensity or luminal stenosis in the entire length of the stented segment (n = 5). Type 2b was total loss of luminal signal intensity over the whole length of the stented segment (n = 2). Last, type 1b was a band of hyperintensity at the ends of type 2a or 2b artifacts. Types 1a and 1b were due to susceptibility effect, and types 2a and 2b were from radio-frequency shielding effect. Both of these effects were identified in MR angiogram of nitinol stents and stainless steel stents. CONCLUSION: Awareness of these artifacts is essential to prevent misdiagnosis.     

Transcranial Doppler Sonography Guided by Magnetic Resonance Angiography for Improved Monitoring of Intracranial Arteries

Transcranial Doppler (TCD) sonography combines the advantages of real–time hemodynamic information, cost–effectiveness, and bedside application. However, measurements can be difficult to reproduce because the spatial resolution and the determination of insonation angles are limited. The purpose of this study was to use the high anatomic resolution of threedimensional (3D) magnetic resonance angiography (MRA) images for the stereotactic guidance of TCD in order to improve the accuracy and reproducibility of TCD examinations. The MRA examinations were performed on a 1.5 T scanner using a 3D flow compensated gradient–echo sequence. A noninvasive stereotactic mask was used for image registration. The MRA data were then transferred to a personal computer. An infrared tracking system registered the position of the head and the ultrasound probe during TCD. This enabled the authors to superimpose a virtual ultrasound beam onto the MRA projections of the intracranial arteries displayed on the monitor of the personal computer. This allows the examiner to easily identify the insonated intracranial artery and displays the insonation angle. In volunteer examinations (n=1 0), the accuracy and reproducibility     

脑血管储备的影像学评估

脑血管储备(cerebrovascular reserve,CVR,又称脑血流储备、脑血液动力学储备、脑灌注储备、脑自身调节储备)是指在生理或病理刺激作用下,脑血管通过小动脉和毛细血管平滑肌的代偿性扩张或收缩(Bayliss效应)维持脑血流正常稳定的能力。脑血管储备功能的检     

Collateral Flow in Magnetic Resonance Angiography: Prognostic Value for Vertebrobasilar Stenosis With Stroke Recurrence

Background and PurposeIntracranial vertebrobasilar atherosclerotic stenosis (IVBAS) is a major cause of posterior circulation stroke. Some patients suffer from stroke recurrence despite receiving medical treatment. This study aimed to determine the prognostic value of a new score for the posterior communicating artery and the P1 segment of the posterior cerebral artery (PCoA-P1) for predicting stroke recurrence in IVBAS.MethodsWe retrospectively enrolled patients with severe IVBAS (70%–99%). According to the number of stroke recurrences, patients were divided into no-recurrence, single-recurrence, and multiple-recurrences groups. We developed a new 5-point grading scale, with the PCoA-P1 score ranging from 0 to 4 based on magnetic resonance angiography, in which primary collaterals were dichotomized into good (2–4 points) and poor (0 or 1 point). Stroke recurrences after the index stroke were recorded. Patients who did not experience stroke recurrence were compared with those who experienced single or multiple stroke recurrences.ResultsFrom January 2012 to December 2019, 176 patients were enrolled, of which 116 (65.9%) had no stroke recurrence, 35 (19.9%) had a single stroke recurrence, and 25 (14.2%) had multiple stroke recurrences. Patients with single stroke recurrence (odds ratio [OR]=4.134, 95% confidence interval [CI]=1.822–9.380, p=0.001) and multiple stroke recurrences (OR=6.894, 95% CI=2.489–19.092, p<0.001) were more likely to have poor primary collaterals than those with no stroke recurrence.ConclusionsThe new PCoA-P1 score appears to provide improve predictions of stroke recurrence in patients with IVBAS.     

Comparison of Transcranial Color-Coded Sonography and Magnetic Resonance Angiography in Acute Ischemic Stroke

BACKGROUND AND PURPOSE: This study was designed to assess the accuracy of transcranial color-coded sonography (TCCS) as compared to magnetic resonance angiography (MRA) for detecting intracranial arterial stenosis in patients with acute cerebral ischemia. METHODS: The authors prospectively identified 120 consecutive patients admitted with acute ischemic stroke and performed both TCCS and MRA with a mean interval of 1 day. TCCS data (sampling depth, peak systolic and end diastolic angle-corrected velocity, mean angle-corrected velocity, and pulsatility index) for middle cerebral arteries (MCAs) were compared to MRA data and classified into 4 grades: normal (grade 1): normal caliber and signal; mild stenosis (grade 2): irregular lumen with reduced signal; severe stenosis (grade 3): absent signal in the stenotic segment (flow gap) and reconstituted distal signal; and possible occlusion (grade 4): absent signal. The cutoffs were chosen to maximize diagnostic accuracy. RESULTS: Interobserver agreement for MRA grading resulted in a weighted-kappa value of 0.776. The rate of poor temporal window was 37% (89/240). Doppler signals were obtained in 135 vessels, and the angle-corrected velocities (peak systolic, end diastolic, mean) were significantly different (P = .001, P = .006, and P < .001) among the MRA grades: grade 1 (100, 47, 68 cm/s), grade 2 (171, 72, 110 cm/s), grade 3 (226, 79, 134 cm/s), grade 4 (61, 26, 39 cm/s). Additionally, an angle-corrected MCA peak systolic velocity > or = 120 cm/s correlates with intracranial stenosis on MRA (grade 2 or worse) with high specificity (90.5%; 95% confidence interval = 78.5%-96.8%) and positive predictive value (93.9%) but relatively low sensitivity (66.7%; 95% confidence interval = 61.2%-69.5%) and negative predictive value (55.1%). CONCLUSION: Elevated MCA velocities on TCCS correlate with intracranial stenosis detected on MRA. An angle-corrected peak systolic velocity > or = 120 cm/s is highly specific for detecting intracranial stenosis as defined by significant MRA abnormality.     

False Evidence of Carotid Stenosis on Magnetic Resonance Angiography Caused by Surgical Clips

Patients with transient ischemic attacks are increasingly studied with magnetic resonance angiography, allowing noninvasive evaluation of both the intracranial and the extracranial vessels. Described here are 3 patients who after endarterectomies presented with transient ischemic attacks and in whom magnetic resonance ang1ography with a two-dimensional time-of-flight pulse sequence showed a false-positive artenal stenosis, as documented by transfemoral carotid angiography. The pseudostenosis was believed to be artifactually caused by operative clips. Results of magnetic resonance angiography should be interpreted with caution in patients with previous neck surgery.