Non-Enhanced MR Imaging of Cerebral Aneurysms: 7 Tesla versus 1.5 Tesla

Purpose

To prospectively evaluate 7 Tesla time-of-flight (TOF) magnetic resonance angiography (MRA) in comparison to 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced magnetization-prepared rapid acquisition gradient-echo (MPRAGE) for delineation of unruptured intracranial aneurysms (UIA).

Material and Methods

Sixteen neurosurgical patients (male n = 5, female n = 11) with single or multiple UIA were enrolled in this trial. All patients were accordingly examined at 7 Tesla and 1.5 Tesla MRI utilizing dedicated head coils. The following sequences were obtained: 7 Tesla TOF MRA, 1.5 Tesla TOF MRA and 7 Tesla non-contrast enhanced MPRAGE. Image analysis was performed by two radiologists with regard to delineation of aneurysm features (dome, neck, parent vessel), presence of artifacts, vessel-tissue-contrast and overall image quality. Interobserver accordance and intermethod comparisons were calculated by kappa coefficient and Lin''s concordance correlation coefficient.

Results

A total of 20 intracranial aneurysms were detected in 16 patients, with two patients showing multiple aneurysms (n = 2, n = 4). Out of 20 intracranial aneurysms, 14 aneurysms were located in the anterior circulation and 6 aneurysms in the posterior circulation. 7 Tesla MPRAGE imaging was superior over 1.5 and 7 Tesla TOF MRA in the assessment of all considered aneurysm and image quality features (e.g. image quality: mean MPRAGE7T: 5.0; mean TOF7T: 4.3; mean TOF1.5T: 4.3). Ratings for 7 Tesla TOF MRA were equal or higher over 1.5 Tesla TOF MRA for all assessed features except for artifact delineation (mean TOF7T: 4.3; mean TOF1.5T 4.4). Interobserver accordance was good to excellent for most ratings.

Conclusion

7 Tesla MPRAGE imaging demonstrated its superiority in the detection and assessment of UIA as well as overall imaging features, offering excellent interobserver accordance and highest scores for all ratings. Hence, it may bear the potential to serve as a high-quality diagnostic tool for pretherapeutic assessment and follow-up of untreated UIA.     

Improved Cerebral Time-of-Flight Magnetic Resonance Angiography at 7 Tesla – Feasibility Study and Preliminary Results Using Optimized Venous Saturation Pulses

Purpose

Conventional saturation pulses cannot be used for 7 Tesla ultra-high-resolution time-of-flight magnetic resonance angiography (TOF MRA) due to specific absorption rate (SAR) limitations. We overcome these limitations by utilizing low flip angle, variable rate selective excitation (VERSE) algorithm saturation pulses.

Material and Methods

Twenty-five neurosurgical patients (male n = 8, female n = 17; average age 49.64 years; range 26–70 years) with different intracranial vascular pathologies were enrolled in this trial. All patients were examined with a 7 Tesla (Magnetom 7 T, Siemens) whole body scanner system utilizing a dedicated 32-channel head coil. For venous saturation pulses a 35° flip angle was applied. Two neuroradiologists evaluated the delineation of arterial vessels in the Circle of Willis, delineation of vascular pathologies, presence of artifacts, vessel-tissue contrast and overall image quality of TOF MRA scans in consensus on a five-point scale. Normalized signal intensities in the confluence of venous sinuses, M1 segment of left middle cerebral artery and adjacent gray matter were measured and vessel-tissue contrasts were calculated.

Results

Ratings for the majority of patients ranged between good and excellent for most of the evaluated features. Venous saturation was sufficient for all cases with minor artifacts in arteriovenous malformations and arteriovenous fistulas. Quantitative signal intensity measurements showed high vessel-tissue contrast for confluence of venous sinuses, M1 segment of left middle cerebral artery and adjacent gray matter.

Conclusion

The use of novel low flip angle VERSE algorithm pulses for saturation of venous vessels can overcome SAR limitations in 7 Tesla ultra-high-resolution TOF MRA. Our protocol is suitable for clinical application with excellent image quality for delineation of various intracranial vascular pathologies.     

Reproducibility of Middle Cerebral Artery Stenosis Measurements by DSA: Comparison of the NASCET and WASID Methods

Purpose

To evaluate the intra- and inter-observer variability of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) criteria for the evaluation of middle cerebral artery (MCA) stenosis using digital subtraction angiography (DSA).

Materials and Methods

DSA images of 114 cases with 131 stenotic MCAs were retrospectively analyzed. Two radiologists and a researcher measured the degree of MCA stenosis independently using both NASCET and WASID methods. To determine intra-observer agreement, all the observers reevaluated the degree of MCA stenosis 4 weeks later. The linear relation and coefficient of variation (CV) between the measurements made by the two methods were assessed by correlation coefficient and multi-factor analysis of variance (ANOVA), respectively. Intra- and inter-observer variability of the two methods was evaluated by intraclass correlation coefficient (ICC), Spearman’s R value, Pearson correlation coefficient and Bland-Altman plots.

Results

Despite the fact that the degree of MCA stenosis measured by NASCET was lower than measured using the WASID method, there was good linear correlation between the measurements made by the two methods (for the mean measurements of the 3 observers, NASCET% = 0.891 × WASID% - 1.89%; ICC, Spearman’s R value and Pearson correlation were 0.874, 0.855, and 0.874, respectively). The CVs of both intra- and inter-observer measurements of MCA stenosis using WASID were significantly lower than that using NASCET confirmed by the multi-factor ANOVA results, which showed only the measurement methods of MCA stenosis had significant effects on the CVs both in intra- and inter-observer measurements (both P values < 0.001). Intra-observer measurements showed good or excellent agreement with respect to WASID and NASCET evaluation (ICC, 0.656 to 0.817 and 0.635 to 0.761, respectively). Good agreement for the WASID evaluation (ICC, 0.592 to 0.628) and for the NASCET evaluation (ICC, 0.529 to 0.568) was observed for inter-observer measurements. Bland-Altman plots demonstrated that the WASID method had better reproducibility and intra-observer agreement than NASCET method for evaluating MCA stenosis.

Conclusion

Both NASCET and WASID methods have an acceptable level of agreement; however, the WASID method had better reproducibility for the evaluation of MCA stenosis, and thus the WASID method may serve as a standard for measuring the degree of MCA stenosis.     

Diagnostic Accuracy of Computer Tomography Angiography and Magnetic Resonance Angiography in the Stenosis Detection of Autologuous Hemodialysis Access: A Meta-Analysis

Purpose

To compare the diagnostic performances of computer tomography angiography (CTA) and magnetic resonance angiography (MRA) for detection and assessment of stenosis in patients with autologuous hemodialysis access.

Materials and Methods

Search of PubMed, MEDLINE, EMBASE and Cochrane Library database from January 1984 to May 2013 for studies comparing CTA or MRA with DSA or surgery for autologuous hemodialysis access. Eligible studies were in English language, aimed to detect more than 50% stenosis or occlusion of autologuous vascular access in hemodialysis patients with CTA and MRA technology and provided sufficient data about diagnosis performance. Methodological quality was assessed by the Quality Assessment of Diagnostic Studies (QUADAS) instrument. Sensitivities (SEN), specificities (SPE), positive likelihood ratio (PLR), negative likelihood values (NLR), diagnostic odds ratio (DOR) and areas under the receiver operator characteristic curve (AUC) were pooled statistically. Potential threshold effect, heterogeneity and publication bias was evaluated. The clinical utility of CTA and MRA in detection of stenosis was also investigated.

Result

Sixteen eligible studies were included, with a total of 500 patients. Both CTA and MRA were accurate modality (sensitivity, 96.2% and 95.4%, respectively; specificity, 97.1 and 96.1%, respectively; DOR [diagnostic odds ratio], 393.69 and 211.47, respectively) for hemodialysis vascular access. No significant difference was detected between the diagnostic performance of CTA (AUC, 0.988) and MRA (AUC, 0.982). Meta-regression analyses and subgroup analyses revealed no statistical difference. The Deek’s funnel plots suggested a publication bias.

Conclusion

Diagnostic performance of CTA and MRA for detecting stenosis of hemodialysis vascular access had no statistical difference. Both techniques may function as an alternative or an important complement to conventional digital subtraction angiography (DSA) and may be able to help guide medical management.     

Adult Moyamoya Disease: A Burden of Intracranial Stenosis in East Asians?

Background

Both Moyamoya disease (MMD) and intracranial atherosclerotic stenosis (ICAS) are more prevalent in Asians than in Westerners. We hypothesized that a substantial proportion of patients with adult-onset MMD were misclassified as having ICAS, which may in part explain the high prevalence of intracranial atherosclerotic stroke in Asians.

Method

We analyzed 352 consecutive patients with ischemic events within the MCA distribution and relevant intracranial arterial stenosis, but no demonstrable carotid or cardiac embolism sources. Conventional angiography was performed in 249 (70.7%) patients, and the remains underwent MRA. The occurrence of the c.14429G>A (p.Arg4810Lys) variant in ring finger protein 213 (RNF213) was analyzed. This gene was recently identified as a susceptibility gene for MMD in East Asians.

Results

The p.Arg4810Lys variant was observed in half of patients with intracranial stenosis (176 of 352, 50.0%), in no healthy control subjects (n = 51), and in 3.2% of stroke control subjects (4 of 124 patients with other etiologies). The presence of basal collaterals, bilateral involvement on angiography, and absence of diabetes were independently associated with the presence of the RNF213 variant. Among 131 patients who met all three diagnostic criteria and were diagnosed with MMD, three-fourths (75.6%) had this variant. However, a significant proportion of patients who met two criteria (57.7%), one criterion (28.6%), or no criteria (20.0%) also had this variant. Some of them developed typical angiographic findings of MMD on follow-up angiography.

Conclusions

Careful consideration of MMD is needed when diagnosing ICAS because differential therapeutic strategies are required for these diseases and due to the limitations of the current diagnostic criteria for MMD.     

High-Resolution Postcontrast Time-of-Flight MR Angiography of Intracranial Perforators at 7.0 Tesla

Background and Purpose

Different studies already demonstrated the benefits of 7T for precontrast TOF-MRA in the visualization of intracranial small vessels. The aim of this study was to assess the performance of high-resolution 7T TOF-MRA after the administration of a gadolinium-based contrast agent in visualizing intracranial perforating arteries.

Materials and Methods

Ten consecutive patients (7 male; mean age, 50.4 ± 9.9 years) who received TOF-MRA at 7T after contrast administration were retrospectively included in this study. Intracranial perforating arteries, branching from the parent arteries of the circle of Willis, were identified on all TOF-MRA images. Provided a TOF-MRA before contrast administration was present, a direct comparison between pre- and postcontrast TOF-MRA was made.

Results

It was possible to visualize intracranial perforating arteries branching off from the entire circle of Willis, and their proximal branches. The posterior cerebral artery (P1 and proximal segment of P2) appeared to have the largest number of visible perforating branches (mean of 5.1 in each patient, with a range of 2–7). The basilar artery and middle cerebral artery (M1 and proximal segment M2) followed with a mean number of 5.0 and 3.5 visible perforating branches (range of 1–9 and 1–8, respectively). Venous contamination in the postcontrast scans sometimes made it difficult to discern the arterial or venous nature of a vessel.

Conclusion

High-resolution postcontrast TOF-MRA at 7T was able to visualize multiple intracranial perforators branching off from various parts of the circle of Willis and proximal intracranial arteries. Although confirmation in a larger study is needed, the administration of a contrast agent for high-resolution TOF-MRA at 7T seems to enable a better visualization of the distal segment of certain intracranial perforators.     

Wingspan Stenting for Severe Symptomatic Intracranial Atherosclerotic Stenosis in 433 Patients Treated at a Single Medical Center

Purpose

To investigate the safety and outcome of intracranial stenting for intracranial atherosclerotic stenosis (IAS).

Materials and Methods

Between July 2007 and April 2013, 433 consecutive patients with IAS >70% underwent intracranial Wingspan stenting, and the data were prospectively analyzed.

Results

Intracranial stenting was successful in 429 patients (99.1%), and the mean stenosis rate was improved from prestenting (82.3± 7.6)% to poststenting (16.6 ± 6.6)%. During the 30-day perioperative period, 29 patients (6.7%) developed stroke. The total perioperative stroke rate was significantly (P <0.01) higher in the basilar artery area than in others, whereas the hemorrhagic stroke rate was significantly (P <0.05) greater in the middle cerebral artery area than in others. The experience accumulation stage (13%) had a significantly (P <0.05) higher stroke rate than the technical maturation stage (4.8%). Clinical follow-up 6–69 months poststenting revealed ipsilateral stroke in 20 patients (5.5%). The one- and two-year cumulative stroke rates were 9.5% and 11.5%, respectively; the two-year cumulative stroke rate was significantly (P <0.05) greater in the experience accumulation stage (18.8%) than in the technical maturation stage (9.1%).

Conclusion

Wingspan stenting for intracranial atherosclerotic stenosis is safe and the long-term stroke rate after stenting is low in a Chinese subpopulation.     

Long-Term Risk of Cardiovascular Disease among Type 2 Diabetic Patients with Asymptomatic Intracranial Atherosclerosis: A Prospective Cohort Study

Objective

To investigate whether asymptomatic middle cerebral artery (MCA) stenosis is associated with risk of cardiovascular disease (CVD) in Chinese with type 2 diabetes.

Methods

In this prospective cohort study, 2,144 Hong Kong Chinese with type 2 diabetes and without history of stroke or atrial fibrillation were recruited in 1994–1996 and followed up for a median of 14.51 years. Participants were assessed at baseline for MCA stenosis using transcranial Doppler. We performed survival analysis to assess the association between asymptomatic MCA stenosis and first CVD event, defined as ischemic stroke, acute coronary syndrome (ACS) or cardiovascular death.

Results

Of the 2,144 subjects, MCA stenosis at baseline was detected in 264 (12.3%). Rates of stroke, ACS and cardiovascular death per 100 were, respectively, 2.24, 2.92 and 1.11 among participants with stenosis, higher than among those without stenosis. Ten-year cumulative occurrence of stroke, ACS and cardiovascular death in subjects with MCA stenosis was 20%, 24% and 10%, respectively, higher than the corresponding values for subjects without stenosis(all P<0.001). After adjusting for covariates, MCA stenosis was found to be an independent predictor of stroke [hazard ratio (HR) 1.40, 95%CI 1.05–1.86; P = 0.02], ACS (HR 1.35, 95%CI 1.04–1.75; P = 0.02) and cardiovascular death(HR 1.56, 95%CI 1.04–2.33; P = 0.03).

Conclusions

Asymptomatic MCA stenosis is a risk factor for CVD in Chinese with type 2 diabetes, and detection of asymptomatic MCA stenosis by transcranial Doppler can identify diabetic individuals at high risk of future CVD. This finding is particularly important for diabetic individuals in Asia, where intracranial atherosclerosis is common.     

Quantification of Blood Flow in Internal Cerebral Artery by Optical Flow Method on Digital Subtraction Angiography in Comparison with Time-Of-Flight Magnetic Resonance Angiography

Objective

This study compared data on the blood flow velocity in the internal carotid artery, which was obtained using the optical flow method (OFM) with digital subtraction angiography (DSA) and the time-of-flight (TOF) technique using magnetic resonance angiography (MRA).

Materials and Methods

Images were obtained from 12 cerebrovascular patients who underwent both brain DSA and MRA imaging. The OFM was applied on the DSA images to determine the average blood flow velocity. The calculated results were compared with the values obtained from the TOF-MRA data. A linear fit was performed on the data and Bland-Altman plots were analyzed.

Results

The blood flow velocity was closely associated with vascular diseases. Color-coding of the OFM measurements were superimposed on to the DSA images, which quantitatively illustrated the relative flow in the vessels. The average blood flow velocity was calculated using OFM and DSA, which demonstrated a high correlation with the MRA measurements in the anterior-posterior (AP) view (R = 0.71). In contrast, the average blood flow velocity was low in the lateral view (R = 0.28). The consistency between the high and low blood velocity in the AP view was better compared to the lateral view. The blood flow velocity distribution in the AP view was statistically closer to the MRA measurement compared to the lateral view.

Conclusions

This study evaluated the correlation of blood flow measured using DSA and TOF-MRA in a small heterogeneous group of patients with cerebrovascular lesions. OFM with DSA imaging reveals hemodynamic information and TOF-MRA.     

Evaluation of the Combined Application of Ultrasound Imaging Techniques for Middle Cerebral Artery Stent Surveillance and Follow-Up Study

Objective

In recent years, cerebral artery stenting has become an effective method for the treatment of cerebral artery stenosis. However, methods for assessing efficacy and techniques for follow-up imaging still need to be developed. This study was designed to evaluate the application of transcranial color-coded sonography (TCCS) in assessing stenting of middle cerebral artery (MCA) stenosis. And, two new imaging techniques (vascular enhancement technology (VET) and 3-dimensional (3D) imaging) were tried out and evaluated.

Method

We enrolled 43 patients with cerebral artery stenosis for vascular stent implantation. All patients were examined by ultrasonography and confirmed through digital subtraction angiography. The stenosis was imaged and blood flow parameters were analyzed before and after the procedure using TCCS. VET and 3D imaging model were used in part of the patients. Important postoperative hemodynamic changes were noted.

Results

1) Adequate stent image was present in 41 out of 43 patients as detected by postoperative 2-dimensional imaging. Images lacking clarity were obtained in 2 patients. 2) The perioperative and postoperative (one week follow-up) instantaneous blood flow velocity at the site of stenosis was significantly decreased (P<0.05) when compared with preoperative levels. Differences between postoperative (one week follow-up) and preoperative blood flow velocity were significant (P<0.05). Differences in blood flow velocity at long-term follow-up (six months and two years) compared to one-week values were not statistically significant (P>0.05). 3) VET imaging visualizes the MCA lumen and stent morphology clearly. 3D ultrasound can be used for imaging of the stent shape as well as its inner surface.

Conclusion

TCCD can be considered a quick and effective clinical detection method to evaluate the intracranial arterial hemodynamics changes before and after stenting treatment for MCA stenosis. New imaging technologies 3D and VET can achieve additional image information.     

Assessment of Dynamic Cerebral Autoregulation in Patients with Basilar Artery Stenosis

Background and Aims

Previous studies have shown impaired cerebral autoregulation (CA) in carotid and middle cerebral artery (MCA) stenosis/occlusion. Little is known about CA in patients with basilar artery (BA) stenosis. We therefore investigated dynamic CA patterns in BA stenosis using transfer function analysis (TFA).

Methods

We measured spontaneous oscillations of blood flow velocity (CBFV) in the right posterior cerebral artery (PCA), and left MCA and mean arterial pressure (ABP) continuously in 25 patients with BA stenosis (moderate n=16 with 50-69% occlusion and severe n=9 with ≥70% occlusion) and 22 healthy volunteers in supine position during 6 circles per minute deep breath. Analysis was based on the ‘black-box’ model of transfer function deriving phase and gain in both PCA and MCA.

Results

Though changes of phase shift and gain between the patients and healthy controls were observed in MCA, the differences are however not significant. Phase shift in PCA was significantly decreased in severe stenosis when comparing with healthy controls and moderate stenosis (4.2±34.2° VS 41.1±40.4°, 4.2±34.2° VS 34.2±27.2°, both p<0.05), whilst the gain in PCA is increased for moderate BA stenosis and decreased for severe BA stenosis. Furthermore, we found that phase shift were almost abolished in patients with ischemic stroke who developed unfavorable clinical outcome (mRs>2) on the 90 days after stroke onset.

Conclusion

Dynamic CA in PCA reduces in patients with severe BA stenosis and those with ischemic stroke who present poor outcome in 90 days after stroke onset. Phase shift might be a sensitive index prompting impaired CA in posterior circulation.     

Elevated Intracranial Pressure and Cerebral Edema following Permanent MCA Occlusion in an Ovine Model

Introduction

Malignant middle cerebral artery (MCA) stroke has a disproportionately high mortality due to the rapid development of refractory space-occupying cerebral edema. Animal models are essential in developing successful anti-edema therapies; however to date poor clinical translation has been associated with the predominately used rodent models. As such, large animal gyrencephalic models of stroke are urgently needed. The aim of the study was to characterize the intracranial pressure (ICP) response to MCA occlusion in our recently developed ovine stroke model.

Materials and Methods

30 adult female Merino sheep (n = 8–12/gp) were randomized to sham surgery, temporary or permanent proximal MCA occlusion. ICP and brain tissue oxygen were monitored for 24 hours under general anesthesia. MRI, infarct volume with triphenyltetrazolium chloride (TTC) staining and histology were performed.

Results

No increase in ICP, radiological evidence of ischemia within the MCA territory but without space-occupying edema, and TTC infarct volumes of 7.9+/-5.1% were seen with temporary MCAO. Permanent MCAO resulted in significantly elevated ICP, accompanied by 30% mortality, radiological evidence of space-occupying cerebral edema and TTC infarct volumes of 27.4+/-6.4%.

Conclusions

Permanent proximal MCAO in the sheep results in space-occupying cerebral edema, raised ICP and mortality similar to human malignant MCA stroke. This animal model may prove useful for pre-clinical testing of anti-edema therapies that have shown promise in rodent studies.     

Scan-Rescan Reproducibility of High Resolution Magnetic Resonance Imaging of Atherosclerotic Plaque in the Middle Cerebral Artery

Purpose

To evaluate the scan-rescan reproducibility of high-resolution magnetic resonance imaging (MRI) of middle cerebral artery (MCA) plaque, and calculate the number of subjects needed for future longitudinal clinical studies.

Material and Methods

Twenty two patients with MCA plaque were scanned twice by a T₂-weighted fast-spin-echo sequence at 3T. Areas and volumes of MCA lumen, total vessel and plaque were quantified and compared between two repeated scans. Agreement and measurement error was quantified by intraclass correlation coefficient (ICC) and coefficient of variance (CV) as defined by standard deviation (SD) of pair wise difference / mean. Sample size needed to detect 5% to 20% changes in area/volume was calculated using 80% power and 5% significance level.

Results

There was no significant different between the area and volume measurements of two repeated scans (p>0.05) with good agreement (ICC range 0.97–0.98 for area and 0.99 for volume). Relatively small measurement errors were observed with CVs range 6.1%-11.8% for area quantification and 4.9%-8.0% for volume quantification. Volume measurements tended to have 19.7% to 32.2% smaller CVs compared with area measurements. Sample size calculation showed a group of 47 patients was sufficient to detect 5% to 10% changes in MCA area/volume.

Conclusion

High resolution MRI is feasible for quantifying intracranial plaque area and volume in longitudinal clinical studies with low scan-rescan variability. Volume measurement tends to be more reproducible compared with area measurements.     

Non-Contrast Enhanced MR Angiography (NCE-MRA) of the Calf: A Direct Comparison between Flow-Sensitive Dephasing (FSD) Prepared Steady-State Free Precession (SSFP) and Quiescent-Interval Single-Shot (QISS) in Patients with Diabetes

Objectives

To compare the image quality and diagnostic performance of two non-contrast enhanced MR angiography (NCE-MRA) techniques using flow-sensitive dephasing (FSD) prepared steady-state free precession (SSFP) and quiescent-interval single-shot (QISS) for the calf arteries in patients with diabetes.

Materials and Methods

Twenty six patients underwent the two NCE-MRA techniques followed by contrast-enhanced MRA (CE-MRA) of lower extremity on a 1.5T MR system. Image quality scores, arterial stenosis scores, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), vessel sharpness, and diagnostic accuracy for detecting more than 50% arterial stenosis were evaluated and statistically compared using CE-MRA as the reference standard.

Results

All examinations were performed successfully. Of the total 153 calf arterial segments obtained in the 26 patients, FSD and QISS showed no significant difference in the number of diagnostic arterial segments (151 [98%] vs. 147 [96%], respectively, P>0.05). The image quality of FSD was higher than that of QISS in the peroneal artery and posterior tibial artery (P<0.05), but no significant difference in the anterior tibial artery (P>0.05). SNR and CNR of FSD were higher than those of QISS (P<0.01), while FSD showed comparable vessel sharpness compared with QISS (P>0.05). The time efficiency of SNR and CNR between FSD and QISS showed no significant difference when taking into account the times for FSD-related scout scans. There was no difference in sensitivity (95% vs. 93%, P>0.05) and negative predictive value (98% vs. 97%, P>0.05) between FSD and QISS for detecting stenosis greater than 50%. However, FSD showed higher specificities (99% vs. 92%, P<0.05) and diagnostic accuracy (98% vs. 92%, P<0.05) compared to QISS.

Conclusion

Both FSD and QISS had similar high sensitivity and negative predictive value for detecting calf arteries with over 50% stenosis, but FSD showed slightly higher diagnostic specificity and better depiction of arterial lesions due to its isotropic submillimeter spatial resolution. QISS, being an easier to use and less time-consuming technique, could be a method of choice for rapid screening of arterial disease of the lower extremity.     

Quantitative Analysis of Respiration-Related Movement for Abdominal Artery in Multiphase Hepatic CT

Objectives

Respiration-induced motion in the liver causes potential errors on the measurement of contrast medium in abdominal artery from multiphase hepatic CT scans. In this study, we investigated the use of hepatic CT images to quantitatively estimate the abdominal artery motion due to respiration by optical flow method.

Materials and Methods

A total of 132 consecutive patients were included in our patient cohort. We apply the optical flow method to compute the motion of the abdominal artery due to respiration.

Results

The minimum and maximum displacements of the abdominal artery motion were 0.02 and 30.87 mm by manual delineation, 0.03 and 40.75 mm calculated by optical flow method, respectively. Both high consistency and correlation between the present method and the physicians’ manual delineations were acquired with the regression equation of movement, y = 0.81x+0.25, r = 0.95, p<0.001.

Conclusion

We estimated the motion of abdominal artery due to respiration using the optical flow method in multiphase hepatic CT scans and the motion estimations were validated with the visualization of physicians. The quantitative analysis of respiration-related movement of abdominal artery could be used for motion correction in the measurement of contrast medium passing though abdominal artery in multiphase CT liver scans.     

A Non-Invasive Method to Assess Cerebral Perfusion Pressure in Geriatric Patients with Suspected Cerebrovascular Disease

Background

Cerebral perfusion pressure (CPP) can adversely impact cerebrovascular hemodynamics but cannot be practically measured in most clinical settings. Here, we aimed to establish a representative mathematical model for CPP in geriatric patients with suspected cerebrovascular disease.

Methods

A total of 100 patients (54 males and 46 females between 60–80 years of age) with suspected cerebrovascular disease and no obvious cerebrovascular stenosis were selected for invasive CPP monitoring via catheterization of the middle segment of the common carotid arteries and openings of the vertebral arteries bilaterally. Curves were function-fitted using MATLAB 7.0, and data was statistically processed by SPSS 20.0.

Results

MATLAB 7.0 constructed eighth-order Fourier functions that fit all recorded CPP curves. Since the coefficients of the 100 functions were significantly different, all functions were standardized to derive one representative function. By manipulating the heart rate and maximum/minimum CPP of the representative function, estimated CPP curves can be constructed for patients with differing heart rates, intracranial pressures (ICPs) and blood pressures.

Conclusions

CPP can be well-modeled through an eighth-order Fourier function that can be constructed from a patient’s brachial artery blood pressure (BABP), ICP and heart rate. This function is representative of geriatric patients with cerebrovascular disease and can be used in the future study of cerebral hemodynamics.     

No Relation between Body Temperature and Arterial Recanalization at Three Days in Patients with Acute Ischaemic Stroke

Background

Recanalization of an occluded intracranial artery is influenced by temperature-dependent enzymes, including alteplase. We assessed the relation between body temperature on admission and recanalization.

Methods

We included 278 patients with acute ischaemic stroke within nine hours after symptom onset, who had an intracranial arterial occlusion on admission CT angiography, in 13 participating centres. We calculated the relation per every 0.1°Celsius increase in admission body temperature and recanalization at three days.

Results

Recanalization occurred in 80% of occluded arteries. There was no relation between body temperature and recanalization at three days after adjustments for age, NIHSS score on admission and treatment with alteplase (adjusted odds ratio per 0.1°Celsius, 0.99; 95% confidence interval, 0.94–1.05; p = 0.70). Results for patients treated or not treated with alteplase were essentially the same.

Conclusions

Our findings suggest that in patients with acute ischaemic stroke there is no relation between body temperature on admission and recanalization of an occluded intracranial artery three days later, irrespective of treatment with alteplase.     

Magnetic Resonance Angiography Signal Intensity as a Marker of Hemodynamic Impairment in Intracranial Arterial Stenosis

Background

Intracranial arterial stenosis (ICAS) is the predominant cause of ischemic stroke and transient ischemic attack in Asia. Change of signal intensities (SI) across an ICAS on magnetic resonance angiography (MRA) may reflect its hemodynamic severity.

Methods

In-patients with a symptomatic single ICAS detected on 3D time-of-flight MRA were recruited from 2 hospitals. Baseline and 1-year follow-up data were collected. Signal intensity ratio (SIR) [ =  (mean post-stenotic SI -mean background SI)/(mean pre-stenotic SI - mean background SI)] was evaluated on baseline MRA to represent change of SIs across an ICAS. Acute infarct volume was measured on baseline diffusion-weighted images (DWI). Relationships between SIR and baseline characteristics as well as 1y outcomes were evaluated.

Results

Thirty-six subjects (86.1% males, mean age 55.0) were recruited. Overall, mean SIR was 0.84±0.23. Mean SIRs were not significantly different between the 23 (63.9%) anatomically severe stenoses and the 13 (36.1%) anatomically moderate stenoses (0.80±0.23 versus 0.92±0.21, p = 0.126). SIR was significantly, linearly and negatively correlated to acute infarct volume on DWI (Spearman correlation coefficient −0.471, p = 0.011). Two patients (5.6%) had recurrent ischemic strokes at 1y, not related to SIR values.

Conclusions

Change of signal intensities across an ICAS on MRA may reflect its hemodynamic and functional severity. Future studies are warranted to further verify the relationships between this index and prognosis of patients with symptomatic ICAS.     

Reversal of Ophthalmic Artery Flow and Stroke Outcomes in Asian Patients with Acute Ischemic Stroke and Unilateral Severe Cervical Carotid Stenosis

Background

The aim of this study was to assess the clinical implications of reversed ophthalmic artery flow (ROAF) for stroke risk and outcomes in subjects with unilateral severe cervical carotid stenosis/occlusion.

Methods

We investigated 128 subjects (101 with acute stroke and 27 without), selected from a large hospital patients base (n  =  14,701), identified with unilateral high-grade cervical carotid stenosis/occlusion by using duplex ultrasonography and brain magnetic resonance imaging. All clinical characteristics were compared for stroke risk between acute stroke and nonstroke groups. Patients with acute stroke were divided into 4 subgroups according to ophthalmic artery flow direction and intracranial stenosis severity, and stroke outcomes were evaluated.

Results

The acute stroke group had significantly higher percentages of ROAF (52.5%, p  =  0.003), carotid occlusion (33.7%, p  =  0.046), and severe intracranial stenosis (74.3%, p<0.001). However, multivariate analysis demonstrated that intracranial stenosis was the only significant risk factor (odds ratio  =  10.38; 95% confidence interval  =  3.64–29.65; p<0.001). Analysis of functional outcomes among the 4 subgroups of patients with stroke showed significant trends (p  =  0.018 to 0.001) for better stroke outcomes from ROAF and mild or no intracranial stenosis. ROAF improved 10–20% stroke outcomes, as compared to forward ophthalmic artery flow, among the patients with stroke and the same degree of severities of intracranial stenosis.

Conclusions

Patients with acute stroke and severe unilateral cervical carotid stenosis/occlusion significantly have high incidence of intracranial stenosis and ROAF. Intracranial stenosis is a major stroke risk indicator as well as a predictor for worse stroke outcomes, and ROAF may provide partial compensation for improving stroke outcomes.     

Low WSS Induces Intimal Thickening,while Large WSS Variation and Inflammation Induce Medial Thinning,in an Animal Model of Atherosclerosis

Objective

Atherosclerotic plaque development in the arterial wall is the result of complex interaction between the wall’s endothelial layer and blood hemodynamics. However, the interaction between hemodynamic parameters and inflammation in plaque evolution is not yet fully understood. The aim of the present study was to investigate the relation between wall shear stress (WSS) and vessel wall inflammation during atherosclerotic plaque development in a minipig model of carotid stenosis.

Methods

A surgical procedure was performed to create left common carotid artery stenosis by placement of a perivascular cuff in minipigs under atherogenic diet. Animals were followed up on 3T MRI, 1 week after surgery and 3, 6, and 8 months after initiation of the diet. Computational fluid dynamics simulation estimated WSS distribution for the first imaging point. Vascular geometries were co-registered for direct comparison of plaque development and features (Gadolinium- and USPIO-Contrast Enhanced MRI, for permeability and inflammation respectively) with the initial WSS. Histological analysis was performed and sections were matched to MR images, based on spatial landmarks.

Results

Vessel wall thickening, permeability and inflammation were observed distally from the stenosis. They were eccentric and facing regions of normal wall thickness. Histological analysis confirmed eccentric plaque formation with lipid infiltration, intimal thickening and medial degradation. High phagocytic activity in the stenosis region was co-localized with high WSS, corresponding to intense medial degradation observed on histology samples.

Conclusion

Lower WSS promotes atherosclerotic plaque development distal to an induced stenosis. Vascular and perivascular inflammation locations were predominant in the high WSS stenosis segment, where medial thinning was the major consequence.