Advances in transcranial Doppler US: imaging ahead

Diagnosis of Delayed Cerebral Ischemia in Patients with Aneurysmal Subarachnoid Hemorrhage and Triggers for Intervention

INTRODUCTION

Delayed cerebral ischemia (DCI) is a major determinant for poor neurological outcome after aneurysmal subarachnoid hemorrhage (aSAH). Detection and treatment of DCI is a key component in the neurocritical care of patients with aSAH after initial aneurysm repair.

METHODS

Narrative review of the literature.

RESULTS

Over the past 2 decades, there has been a paradigm shift away from macrovascular (angiographic) vasospasm as a main diagnostic and therapeutic target. Instead, the pathophysiology of DCI is hypothesized to derive from several proischemic pathomechanisms. Clinical examination remains the most reliable means for monitoring and treatment of DCI, but its value is limited in comatose patients. In such patients, monitoring of DCI is usually based on numerous neurophysiological and/or radiological diagnostic modalities. Catheter angiography remains the gold standard for the detection of macrovascular spasm. Computed tomography (CT) angiography is increasingly used instead of catheter angiography because it is less invasive and may be combined with CT perfusion imaging. CT perfusion permits semiquantitative cerebral blood flow measurements, including the evaluation of the microcirculation. It may be used for prediction, early detection, and diagnosis of DCI, with yet-to-prove benefit on clinical outcome when used as a screening modality. Transcranial Doppler may be considered as an additional noninvasive screening tool for flow velocities in the middle cerebral artery, with limited accuracy in other cerebral arteries. Continuous electroencephalography enables detection of early signs of ischemia at a reversible stage prior to clinical manifestation. However, its widespread use is still limited because of the required infrastructure and expertise in data interpretation. Near-infrared spectroscopy, a noninvasive and continuous modality for evaluation of cerebral blood flow dynamics, has shown conflicting results and needs further validation. Monitoring techniques beyond neurological examinations may help in the detection of DCI, especially in comatose patients. However, these techniques are limited because of their invasive nature and/or restriction of measurements to focal brain areas.

CONCLUSION

The current literature review underscores the need for incorporating existing modalities and developing new methods to evaluate brain perfusion, brain metabolism, and overall brain function more accurately and more globally.

The TCD hyperemia index to detect vasospasm and delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Elevated mean flow velocity (MFV) on transcranial Doppler (TCD) is used to predict vasospasm after aneurysmal subarachnoid hemorrhage (SAH). Hyperemia should be considered when observing elevated MFV. Lindegaard ratio (LR) is commonly used but does not enhance predictive values. We introduce a new marker, the hyperemia index (HI), calculated as bilateral extracranial internal carotid artery MFV divided by initial flow velocity.

METHODS

We evaluated SAH patients hospitalized ≥7 days between December 1, 2016 and June 30, 2022. We excluded patients with nonaneurysmal SAH, inadequate TCD windows, and baseline TCD obtained after 96 hours from onset. Logistic regression was conducted to assess the significant associations of HI, LR, and maximal MFV with vasospasm and delayed cerebral ischemia (DCI). Receiver operating characteristic analyses were employed to find the optimal cutoff value for HI.

RESULTS

Lower HI (odds ratio [OR] 0.10, 95% confidence interval [CI] 0.01-0.68), higher MFV (OR 1.03, 95% CI 1.01-1.05), and LR (OR 2.02, 95% CI 1.44-2.85) were associated with vasospasm and DCI. Area under the curve (AUC) for predicting vasospasm was 0.70 (95% CI 0.58-0.82) for HI, 0.87 (95% CI 0.81-0.94) for maximal MFV, and 0.87 (95% CI 0.79-0.94) for LR. The optimal cutoff value for HI was 1.2. Combining HI <1.2 with MFV improved positive predictive value without altering the AUC value.

CONCLUSIONS

Lower HI was associated with a higher likelihood of vasospasm and DCI. HI <1.2 may serve as a useful TCD parameter to indicate vasospasm and DCI when elevated MFV is observed, or when transtemporal windows are inadequate.

Outcomes following therapeutic intervention of post-traumatic vasospasm: A systematic review and meta-analysis

BACKGROUND

Vasospasm occurrence following traumatic brain injury may impact neurologic and functional recovery of patients, yet treatment of post-traumatic vasospasm (PTV) has not been well documented. This systematic review and meta-analysis aims to assess the current evidence regarding favorable outcome as measured by Glasgow Outcome Scale (GOS) scores following treatment of PTV.

METHODS

A systematic review of PubMed, Ovid MEDLINE, and Ovid EMBASE was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Included manuscripts were methodically scrutinized for quality; occurrence of PTV; rate of favorable outcome following each treatment modality; and follow-up duration. Treatments evaluated were calcium channel blockers (CCBs), endovascular intervention, and dopamine-induced hypertension. Outcomes were compared via the random-effects analysis.

RESULTS

Fourteen studies with 1885 PTV patients were quantitatively analyzed: 982 patients who received tailored therapeutic intervention and 903 patients who did not receive tailored therapy. For patients undergoing treatment, the rate of favorable outcome was 57.3 % (500/872 patients; 95 % CI 54.1 - 60.6 %) following administration of CCBs, 94.1 % (16/17 patients; 95 % CI 82.9 - 100.0 %) following endovascular intervention, and 54.8 % (51/93 patients; 95 % CI 44.7 - 65.0 %) following dopamine-induced hypertension. Of note, the endovascular group had the highest rate of favorable outcome but was also the smallest sample size (n = 17). Patients who received tailored therapeutic intervention for PTV had a higher rate of favorable outcome than patients who did not receive tailored therapy: 57.7 % (567/982 patients; 95 % CI 54.1 - 60.8 %) versus 52.0 % (470/903 patients; 95 % CI 48.8 - 55.3 %), respectively.

CONCLUSIONS

The available data suggests that tailored therapeutic intervention of PTV results in a favorable outcome. While endovascular intervention of PTV had the highest rate of favorable outcome, both CCB administration and dopamine-induced hypertension had similar lower rates of favorable outcome.

Velocity field estimation in transcranial small vessel using super-resolution ultrasound imaging velocimetry

Based on the diameter and position information of small vessels obtained by transcranial super-resolution imaging using 3 MHz low-frequency chirp plane waves, a Gaussian-like non-linear compression was adopted to compress the blood flow signals in spatiotemporal filtering (STF) data to a precise region, and then estimate the blood flow velocity field inside the region over the adjacent time intervals using ultrasound imaging velocimetry (UIV). Imaging parameters, such as the mechanical index (MI), frame rate, and microbubble (MB) concentration, are critical during the estimation of velocity fields over a short time at high MB contrast agent concentrations. These were optimized through experiments and algorithms, in which dividing the connected domain was proposed to calculate MB cluster spot centroid spacing (SCS) and the spot-to-flow area ratio (SFAR) to determine the suitable MB concentration. The results of the in vitro experiments showed that the estimation of the small vessel flow velocity field was consistent with the theoretical results; the velocity field resolution for vessels with diameters of 0.5 mm and 0.3 mm was 36 μm and 21 μm, and the error between the mean velocity and the theoretical value was 0.7 % and 0.67 %, respectively.

The effects of aneurysmal subarachnoid hemorrhage on cerebral vessel diameter and flow velocity

BACKGROUND

Transcranial Doppler flow velocity is used to monitor for cerebral vasospasm following aneurysmal subarachnoid hemorrhage. Generally, blood flow velocities appear inversely related to the square of vessel diameter representing local fluid dynamics. However, studies of flow velocity-diameter relationships are few, and may identify vessels for which diameter changes are better correlated with Doppler velocity. We therefore studied a large retrospective cohort with concurrent transcranial Doppler velocities and angiographic vessel diameters.

METHODS

This is a single-site, retrospective, cohort study of adult patients with aneurysmal subarachnoid hemorrhage, approved by the UT Southwestern Medical Center Institutional Review Board. Study inclusion required transcranial Doppler measurements within </= 24 hours of vessel imaging. Vessels assessed were: bilateral anterior, middle, posterior cerebral arteries; internal carotid siphons; vertebral arteries; and basilar artery. Flow velocity-diameter relationships were constructed and fitted with a simple inverse power function. A greater influence of local fluid dynamics is suggested as power factors approach two.

RESULTS

98 patients were included. Velocity-diameter relationships are curvilinear, and well fit by a simple inverse power function. Middle cerebral arteries showed the highest power factors (>1.1, R²>0.9). Furthermore, velocity and diameter changed (P<0.033) consistent with the signature time course of cerebral vasospasm.

CONCLUSIONS

These results suggest that middle cerebral artery velocity-diameter relationships are most influenced by local fluid dynamics, which supports these vessels as preferred endpoints in Doppler detection of cerebral vasospasm. Other vessels showed less influence of local fluid dynamics, pointing to greater role of factors outside the local vessel segment in determining flow velocity.

Neuromonitoring in Children with Cerebrovascular Disorders

BACKGROUND

Cerebrovascular disorders are an important cause of morbidity and mortality in children. The acute care of a child with an ischemic or hemorrhagic stroke or cerebral sinus venous thrombosis focuses on stabilizing the patient, determining the cause of the insult, and preventing secondary injury. Here, we review the use of both invasive and noninvasive neuromonitoring modalities in the care of pediatric patients with arterial ischemic stroke, nontraumatic intracranial hemorrhage, and cerebral sinus venous thrombosis.

METHODS

Narrative review of the literature on neuromonitoring in children with cerebrovascular disorders.

RESULTS

Neuroimaging, near-infrared spectroscopy, transcranial Doppler ultrasonography, continuous and quantitative electroencephalography, invasive intracranial pressure monitoring, and multimodal neuromonitoring may augment the acute care of children with cerebrovascular disorders. Neuromonitoring can play an essential role in the early identification of evolving injury in the aftermath of arterial ischemic stroke, intracranial hemorrhage, or sinus venous thrombosis, including recurrent infarction or infarct expansion, new or recurrent hemorrhage, vasospasm and delayed cerebral ischemia, status epilepticus, and intracranial hypertension, among others, and this, is turn, can facilitate real-time adjustments to treatment plans.

CONCLUSIONS

Our understanding of pediatric cerebrovascular disorders has increased dramatically over the past several years, in part due to advances in the neuromonitoring modalities that allow us to better understand these conditions. We are now poised, as a field, to take advantage of advances in neuromonitoring capabilities to determine how best to manage and treat acute cerebrovascular disorders in children.

Intracranial and Extracranial Evaluation

The vascular lab is an essential tool in diagnosing intracranial and extracranial disease including vasospasm from subarachnoid hemorrhage and carotid artery stenosis in the setting of stroke or transient ischemic attack. This article discusses the indications, protocol, and diagnostic criteria for transcranial doppler (TCD) and carotid artery duplex ultrasound. Intracranial and extracranial arterial testing by way of TCD and carotid imaging carries enormous implications and can provide life or death information. The learning curve for these techniques is steep but can be mastered with repetition and precise technique.

Role of Nimodipine and Milrinone in Delayed Cerebral Ischemia

OBJECTIVE

The role of nimodipine and milrinone in the management of delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (SAH) was studied using clinical and TCD (transcranial Doppler) parameters.

METHODS

In this prospective observational study, patients with DCI after aneurysmal SAH presenting between November 2020 and June 2021 who were treated by either intra-arterial nimodipine (IAN) or intravenous milrinone (IVM) were included after excluding patients in whom both IAN and IVM had been given or mechanical angioplasty was performed. Twelve-hourly TCD was performed during the course of the therapy. Clinical improvement and the development of new brain infarcts were also assessed. A P value <0.05 was considered statistically significant.

RESULTS

Thirty-four patients fulfilled the inclusion criteria (IVM, 13/34 [38%]; IAN, 21/34 [62%]); patients in the IVM group (vs. IAN group) had poorer median Glasgow Coma Scale score (12 vs. 13), poorer motor response (<M6 response, 5/13 [38%] vs. 5/21 [24%]; P = 0.36) and higher grades (modified Fisher grade ≥3) of SAH (12/13 [92%] vs. 8/21 [86%]; P = 0.56). More patients in the IAN group (vs. IVM group) showed clinical improvement (17/21 [81%] vs. 10/13 [77%]; P = 0.77), development of new infarcts (15/21 [71%] vs. 7/13 [54%]; P = 0.29] and discharged to home (13/21 [62%] vs. 6/13 [46%]; P = 0.36) with less mortality (1/21 [9%] vs. 4/13 [23%]; P = 0.037). On TCD analysis, both IAN and IVM protocols showed similar effects in middle cerebral artery vasospasm; however, IAN proved better over time. In group-effect analysis, the IAN protocol was significantly better in anterior cerebral artery and posterior cerebral artery vasospasm compared with IVM protocol.

CONCLUSIONS

In this single-center small study, patients in the IAN group had significantly less mortality compared with the IVM group in the management of DCI after aneurysmal SAH.

Accelerated 2-D Real-Time Refraction-Corrected Transcranial Ultrasound Imaging

In a recent study, we proposed a technique to correct aberration caused by the skull and reconstruct a transcranial B-mode image with a refraction-corrected synthetic aperture imaging (SAI) scheme. Given a sound speed map, the arrival times were calculated using a fast marching technique (FMT), which solves the Eikonal equation and, therefore, is computationally expensive for real-time imaging. In this article, we introduce a two-point ray tracing method, based on Fermat's principle, for fast calculation of the travel times in the presence of a layered aberrator in front of the ultrasound probe. The ray tracing method along with the reconstruction technique is implemented on a graphical processing unite (GPU). The point spread function (PSF) in a wire phantom image reconstructed with the FMT and the GPU implementation was studied with numerical synthetic data and experiments with a bone-mimicking plate and a sagittally cut human skull. The numerical analysis showed that the error on travel times is less than 10% of the ultrasound temporal period at 2.5 MHz. As a result, the lateral resolution was not significantly degraded compared with images reconstructed with FMT-calculated travel times. The results using the synthetic, bone-mimicking plate, and skull dataset showed that the GPU implementation causes a lateral/axial localization error of 0.10/0.20, 0.15/0.13, and 0.26/0.32 mm compared with a reference measurement (no aberrator in front of the ultrasound probe), respectively. For an imaging depth of 70 mm, the proposed GPU implementation allows reconstructing 19 frames/s with full synthetic aperture (96 transmission events) and 32 frames/s with multiangle plane wave imaging schemes (with 11 steering angles) for a pixel size of [Formula: see text]. Finally, refraction-corrected power Doppler imaging is demonstrated with a string phantom and a bone-mimicking plate placed between the probe and the moving string. The proposed approach achieves a suitable frame rate for clinical scanning while maintaining the image quality.

3D transcranial ultrasound localization microscopy for discrimination between ischemic and hemorrhagic stroke in early phase

Early diagnosis is a critical part of the emergency care of cerebral hemorrhages and ischemia. A rapid and accurate diagnosis of strokes reduces the delays to appropriate treatments and a better functional recovery. Currently, CTscan and MRI are the gold standards with constraints of accessibility, availability, and possibly some contraindications. The development of Ultrasound Localization Microscopy (ULM) has enabled new perspectives to conventional transcranial ultrasound imaging with increased sensitivity, penetration depth, and resolution. The possibility of volumetric imaging has increased the field-of-view and provided a more precise description of the microvascularisation. In this study, rats (n = 9) were subjected to thromboembolic ischemic stroke or intracerebral hemorrhages prior to volumetric ULM at the early phases after onsets. Although the volumetric ULM performed in the early phase of ischemic stroke revealed a large hypoperfused area in the cortical area of the occluded artery, it showed a more diffused hypoperfusion in the hemorrhagic model. Respective computations of a Microvascular Diffusion Index highlighted different patterns of perfusion loss during the first 24 h of these two strokes’ subtypes. Our study provides the first proof that this methodology should allow early discrimination between ischemic and hemorrhagic stroke with a potential toward diagnosis and monitoring in clinic.

Refraction-Corrected Transcranial Ultrasound Imaging Through the Human Temporal Window Using a Single Probe

Transcranial ultrasound imaging (TUI) is a diagnostic modality with numerous applications, but unfortunately, it is hindered by phase aberration caused by the skull. In this article, we propose to reconstruct a transcranial B-mode image with a refraction-corrected synthetic aperture imaging (SAI) scheme. First, the compressional sound velocity of the aberrator (i.e., the skull) is estimated using the bidirectional headwave technique. The medium is described with four layers (i.e., lens, water, skull, and water), and a fast marching method calculates the travel times between individual array elements and image pixels. Finally, a delay-and-sum algorithm is used for image reconstruction with coherent compounding. The point spread function (PSF) in a wire phantom image and reconstructed with the conventional technique (using a constant sound speed throughout the medium), and the proposed method was quantified with numerical synthetic data and experiments with a bone-mimicking plate and a human skull, compared with the PSF achieved in a ground truth image of the medium without the aberrator (i.e., the bone plate or skull). A phased-array transducer (P4-1, ATL/Philips, 2.5 MHz, 96 elements, pitch = 0.295 mm) was used for the experiments. The results with the synthetic signals, the bone-mimicking plate, and the skull indicated that the proposed method reconstructs the scatterers with an average lateral/axial localization error of 0.06/0.14 mm, 0.11/0.13 mm, and 1.0/0.32 mm, respectively. With the human skull, an average contrast ratio (CR) and full-width-half-maximum (FWHM) of 37.1 dB and 1.75 mm were obtained with the proposed approach, respectively. This corresponds to an improvement of CR and FWHM by 7.1 dB and 36% compared with the conventional method, respectively. These numbers were 12.7 dB and 41% with the bone-mimicking plate.

Detection of a pituitary macroadenoma with transcranial ultrasonography: Principles and potential clinical applications

Transcranial color-coded duplex sonography (TCCS) allows to study intracranial vessels through the intact skull, but the visualization of normal and pathologic brain structures in adults is often suboptimal due to inadequate acoustic window. The full potential of TCCS for clinical practice remains unfulfilled. Here, we describe the ability of TCCS to detect a non-functioning pituitary macroadenoma in a 58-year-old man affected by headache. The macroadenoma was visualized as a roundish, well-defined mass, mildly hyperechogenic compared to the hypoechogenic mesencephalic brainstem but mainly hypoechogenic compared to the surrounding intracranial structures. Intracranial vessels represented useful landmarks. Using tissue harmonic imaging mode, the borders of the macroadenoma were visualized more clearly. Macroadenoma characteristics were confirmed by magnetic resonance imaging. Neurosonologists should be aware of the possibility to incidentally find, during routinary TCCS, pituitary macroadenomas or other brain tumors (as incidentalomas), worthy to be recognized and referred for further investigations.

Noninvasive quantification of cerebrovascular pressure changes using 4D Flow MRI

PURPOSE

Hemodynamic alterations are indicative of cerebrovascular disease. However, the narrow and tortuous cerebrovasculature complicates image-based assessment, especially when quantifying relative pressure. Here, we present a systematic evaluation of image-based cerebrovascular relative pressure mapping, investigating the accuracy of the routinely used reduced Bernoulli (RB), the extended unsteady Bernoulli (UB), and the full-field virtual work-energy relative pressure ( ν WERP) method.

METHODS

Patient-specific in silico models were used to generate synthetic cerebrovascular 4D Flow MRI, with RB, UB, and ν WERP performance quantified as a function of spatiotemporal sampling and image noise. Cerebrovascular relative pressures were also derived in 4D Flow MRI from healthy volunteers ( n = 8 ), acquired at two spatial resolutions (dx = 1.1 and 0.8 mm).

RESULTS

The in silico analysis indicate that accurate relative pressure estimations are inherently coupled to spatial sampling: at dx = 1.0 mm high errors are reported for all methods; at dx = 0.5 mm ν WERP recovers relative pressures at a mean error of 0.02 ± 0.25 mm Hg, while errors remain higher for RB and UB (mean error of -2.18 ± 1.91 and -2.18 ± 1.87 mm Hg, respectively). The dependence on spatial sampling is also indicated in vivo, albeit with higher correlative dependence between resolutions using ν WERP (k = 0.64, R2 = 0.81 for dx = 1.1 vs. 0.8 mm) than with RB or UB (k = 0.04, R2 = 0.03, and k = 0.07, R2 = 0.07, respectively).

CONCLUSION

Image-based full-field methods such as ν WERP enable cerebrovascular relative pressure mapping; however, accuracy is directly dependent on utilized spatial resolution.

Delayed Cerebral Ischemia after Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) is the most feared complication of aneurysmal subarachnoid hemorrhage (aSAH). It increases the mortality and morbidity associated with aSAH. Previously, large cerebral artery vasospasm was thought to be the sole major contributing factor associated with increased risk of DCI. Recent literature has challenged this concept. We conducted a literature search using PUBMED as the prime source of articles discussing various other factors which may contribute to the development of DCI both in the presence or absence of large cerebral artery vasospasm. These factors include microvascular spasm, micro-thrombosis, cerebrovascular dysregulation, and cortical spreading depolarization. These factors collectively result in inflammation of brain parenchyma, which is thought to precipitate early brain injury and DCI. We conclude that diagnostic modalities need to be refined in order to diagnose DCI more efficiently in its early phase, and newer interventions need to be developed to prevent and treat this condition. These newer interventions are currently being studied in experimental models. However, their effectiveness on patients with aSAH is yet to be determined.

A Highly Predictive MicroRNA Panel for Determining Delayed Cerebral Vasospasm Risk Following Aneurysmal Subarachnoid Hemorrhage

Approximately one-third of aneurysmal subarachnoid hemorrhage (aSAH) patients develop delayed cerebral vasospasm (DCV) 3-10 days after aneurysm rupture resulting in additional, permanent neurologic disability. Currently, no validated biomarker is available to determine the risk of DCV in aSAH patients. MicroRNAs (miRNAs) have been implicated in virtually all human diseases, including aSAH, and are found in extracellular biofluids including plasma and cerebrospinal fluid (CSF). We used a custom designed TaqMan Low Density Array miRNA panel to examine the levels of 47 selected brain and vasculature injury related miRNAs in CSF and plasma specimens collected from 31 patients with or without DCV at 3 and 7 days after aSAH, as well as from eight healthy controls. The analysis of the first 18-patient cohort revealed a striking differential expression pattern of the selected miRNAs in CSF and plasma of aSAH patients with DCV from those without DCV. Importantly, this differential expression was observed at the early time point (3 days after aSAH), before DCV event occurs. Seven miRNAs were identified as reliable DCV risk predictors along with a prediction model constructed based on an array of additional 19 miRNAs on the panel. These chosen miRNAs were then used to predict the risk of DCV in a separate, testing cohort of 15 patients. The accuracy of DCV risk prediction in the testing cohort reached 87%. The study demonstrates that our novel designed miRNA panel is an effective predictor of DCV risk and has strong applications in clinical management of aSAH patients.

Vasospasm: Role of Imaging in Detection and Monitoring Treatment

Cerebral vasospasm (VS) and delayed cerebral ischemia (DCI) are important complications of aneurysmal subarachnoid hemorrhage (ASAH). Imaging approaches to VS monitoring include noninvasive bedside assessment with transcranial Doppler ultrasonography, angiographic evaluation with digital subtraction angiography, and computed tomography (CT) angiography. DCI is a clinical diagnosis and is not fully explained by the presence of angiographic VS. CT perfusion has shown clinical utility and implications for future research in the evaluation of DCI in patients with ASAH. This review article discusses the common approaches to diagnosis and monitoring of VS and DCI, current treatment strategies, and future research directions.

Intrathecal chemotherapy-associated cerebral vasospasm in children with hematologic malignancies

BACKGROUND

Mechanisms of chemotherapy-associated neurotoxicity are poorly understood, and therefore, prevention strategies have not been developed. We hypothesized that a subgroup of children receiving intrathecal cytarabine develops subclinical vasospasm, which may contribute to long-term neurocognitive sequelae of cancer.

METHODS

We used transcranial Doppler ultrasound to serially evaluate cerebral blood flow velocities in participants ≤25 years old receiving intrathecal cytarabine for hematologic malignancies.

RESULTS

Four of 18 participants (22%) met the criteria for subclinical vasospasm within 4 days of intrathecal cytarabine administration. The distribution of oncologic diagnoses differed between the vasospasm and non-vasospasm groups (p = 0.02). Acute myeloid leukemia was identified as a potential risk factor for vasospasm. Children with vasospasm were more likely to have received intravenous cytarabine (75% versus 0%, p = 0.01) and less likely to have received steroids (25% versus 100%, p = 0.01).

CONCLUSIONS

A subpopulation of children with hematologic malignancies develops subclinical vasospasm after intrathecal cytarabine treatment. Future research is needed to determine the long-term clinical consequences of cerebral vasospasm in this population.

IMPACT

A subset of children with hematologic malignancies who receive intrathecal cytarabine experience subclinical cerebral vasospasm, as measured by transcranial Doppler ultrasound. Of children receiving intrathecal cytarabine, those who develop cerebral vasospasm are more likely to have diagnosis of acute myeloid leukemia, more likely to receive concurrent intravenous cytarabine, and less likely to receive steroids as part of their chemotherapy regimen, as compared with children without vasospasm. Future research is needed to determine if vasospasm during chemotherapy is associated with higher rates of neurocognitive dysfunction, and if so, to focus on prevention of these long-term sequelae of childhood cancer.

From 2D to 4D Phase-Contrast MRI in the Neurovascular System: Will It Be a Quantum Jump or a Fancy Decoration?

Considering the crosstalk between the flow and vessel wall, hemodynamic assessment of the neurovascular system may offer a well-integrated solution for both diagnosis and management by adding prognostic significance to the standard CT/MR angiography. 4D flow MRI or time-resolved 3D velocity-encoded phase-contrast MRI has long been promising for the hemodynamic evaluation of the great vessels, but challenged in clinical studies for assessing intracranial vessels with small diameter due to long scan times and low spatiotemporal resolution. Current accelerated MRI techniques, including parallel imaging with compressed sensing and radial k-space undersampling acquisitions, have decreased scan times dramatically while preserving spatial resolution. 4D flow MRI visualized and measured 3D complex flow of neurovascular diseases such as aneurysm, arteriovenous shunts, and atherosclerotic stenosis using parameters including flow volume, velocity vector, pressure gradients, and wall shear stress. In addition to the noninvasiveness of the phase contrast technique and retrospective flow measurement through the wanted windows of the analysis plane, 4D flow MRI has shown several advantages over Doppler ultrasound or computational fluid dynamics. The evaluation of the flow status and vessel wall can be performed simultaneously in the same imaging modality. This article is an overview of the recent advances in neurovascular 4D flow MRI techniques and their potential clinical applications in neurovascular disease. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY STAGE: 3.

Design of 2D Sparse Array Transducers for Anomaly Detection in Medical Phantoms

Aperiodic sparse 2D ultrasonic array configurations, including random array, log spiral array, and sunflower array, have been considered for their potential as conformable transducers able to image within a focal range of 30-80 mm, at an operating frequency of 2 MHz. Optimisation of the imaging performance of potential array patterns has been undertaken based on their simulated far field directivity functions. Two evaluation criteria, peak sidelobe level (PSL) and integrated sidelobe ratio (ISLR), are used to access the performance of each array configuration. Subsequently, a log spiral array pattern with -19.33 dB PSL and 2.71 dB ISLR has been selected as the overall optimal design. Two prototype transducers with the selected log spiral array pattern have been fabricated and characterised, one using a fibre composite element composite array transducer (CECAT) structure, the other using a conventional 1-3 composite (C1-3) structure. The CECAT device demonstrates improved coupling coefficient (0.64 to 0.59), reduced mechanical cross-talk between neighbouring array elements (by 10 dB) and improved operational bandwidth (by 16.5%), while the C1-3 device performs better in terms of sensitivity (~50%). Image processing algorithms, such as Hough transform and morphological opening, have been implemented to automatically detect and dimension particles located within a fluid-filled tube structure, in a variety of experimental scenarios, including bespoke phantoms using tissue mimicking material. Experiments using the fabricated CECAT log spiral 2D array transducer demonstrated that this algorithmic approach was able to detect the walls of the tube structure and stationary anomalies within the tube with a precision of ~0.1 mm.

Surface Point Cloud Ultrasound with Transcranial Doppler: Coregistration of Surface Point Cloud Ultrasound with Magnetic Resonance Angiography for Improved Reproducibility, Visualization, and Navigation in Transcranial Doppler Ultrasound

Transcranial Doppler (TCD) ultrasound is a standard tool used in the setting of recent sub-arachnoid hemorrhage (SAH). By tracking velocity in the circle-of-Willis vessels, vasospasm can be detected as interval velocity increase. For this disease process, repeated TCD velocity measurements over many days is the basis for its usefulness. However, a key limitation to TCD is its user dependence, which is itself largely due to the fact that exact information about probe positioning is lost between subsequent scans. Surface point cloud ultrasound (SPC-US) was recently introduced as a general approach combining ultrasound and three-dimensional surface imaging of patient + probe. In the present proof-of-principle demonstration, we have applied SPC-US to TCD and co-registered the skin surface with that from MRA images to provide a roadmap of the vasculature in 3D space for better speed, accuracy, reproducibility, and potential semi-automation of TCD. Collating the acronyms, we call the combined approach SPC-US-TCD. TCD of the M1 was obtained while three-dimensional photographic images were obtained with the Structure Sensor camera. MRA imaging was also obtained. SPC-US-TCD and corresponding MRA 3D reconstruction images were co-registered in MeshMixer using the skin surfaces for alignment. A cylinder the width of the TCD probe was placed over the fused images and aligned with the direction and orientation of the TCD probe to demonstrate the acoustic beam. In the fused images, the acoustic beam intersects the right M1 segment of the middle cerebral artery (MCA). The angle of insonation is well demonstrated and measurable in various planes. Distance measurements made in Blender localized the TCD probe position based on three skin surface landmarks, and tabulated orientation based on three angles along the corresponding directions. SPC-US-TCD provides valuable information that is otherwise not present in TCD studies. By co-registering SPC-US-TCD data with that from cross sectional vessel imaging, precise probe location relative to external skin surface landmarks as well as 3D vessel location relative to TCD probe placement offers the potential to provide a roadmap that improves exam reproducibility, speed of acquisition, and accuracy. The goal of future work is to demonstrate this improvement statistically by application to multiple patients and scans.

Investigation of the Effect of the Skull in Transcranial Photoacoustic Imaging: A Preliminary Ex Vivo Study

Although transcranial photoacoustic imaging (TCPAI) has been used in small animal brain imaging, in animals with thicker skull bones or in humans both light illumination and ultrasound propagation paths are affected. Hence, the PA image is largely degraded and in some cases completely distorted. This study aims to investigate and determine the maximum thickness of the skull through which photoacoustic imaging is feasible in terms of retaining the imaging target structure without incorporating any post processing. We identify the effect of the skull on both the illumination path and acoustic propagation path separately and combined. In the experimental phase, the distorting effect of ex vivo sheep skull bones with thicknesses in the range of 0.7~1.3 mm are explored. We believe that the findings in this study facilitate the clinical translation of TCPAI.

Neurovascular coupling is not influenced by lower body negative pressure in humans

Cerebral blood flow is tightly coupled with local neuronal activation and metabolism, i.e., neurovascular coupling (NVC). Studies suggest a role of sympathetic nervous system in the regulation of cerebral blood flow. However, this is controversial, and the sympathetic regulation of NVC in humans remains unclear. Since impaired NVC has been identified in several chronic diseases associated with a heightened sympathetic activity, we aimed to determine whether reflex-mediated sympathetic activation via lower body negative pressure (LBNP) attenuates NVC in humans. NVC was assessed using a visual stimulation protocol (5 cycles of 30 s eyes closed and 30 s of reading) in 11 healthy participants (aged 24 ± 3 yr). NVC assessments were made under control conditions and during LBNP at -20 and -40 mmHg. Posterior (PCA) and middle (MCA) cerebral artery mean blood velocity (V_mean) and vertebral artery blood flow (VA_flow) were simultaneously determined with cardiorespiratory variables. Under control conditions, the visual stimulation evoked a robust increase in PCA_Vmean (∆18.0 ± 4.5%), a moderate rise in VA_flow (∆9.6 ± 4.3%), and a modest increase in MCA_Vmean (∆3.0 ± 1.9%). The magnitude of NVC response was not affected by mild-to-moderate LBNP (all P > 0.05 for repeated-measures ANOVA). Given the small change that occurred in partial pressure of end-tidal CO₂ during LBNP, this hypocapnia condition was matched via voluntary hyperventilation in absence of LBNP in a subgroup of participants (n = 8). The mild hypocapnia during LBNP did not exert a confounding influence on the NVC response. These findings indicate that the NVC is not influenced by LBNP or mild hypocapnia in humans.NEW & NOTEWORTHY Visual stimulation evoked a robust increase in posterior cerebral artery velocity and a modest increase in vertebral artery blood flow, i.e., neurovascular coupling (NVC), which was unaffected by lower body negative pressure (LBNP) in humans. In addition, although LBNP induced a mild hypocapnia, this degree of hypocapnia in the absence of LBNP failed to modify the NVC response.

Flow-diverting stent and delayed intracranial bleeding: the case for discussing acquired von Willebrand disease

A unique feature of the flow-diverting stent (FDS) has rendered it useful in the endovascular treatment of selected intracranial aneurysms for the last decade. Delayed aneurysmal rupture and intracranial parenchymal bleeding are two leading hemorrhagic complications after FDS. It has recently been shown for the first time that there is a relationship between FDS and reduced level of vWF activity in patients undergoing endovascular cerebral aneurysm treatment. Here, the current literature is reviewed in the context of this novel finding to propose an illustrative scenario that conceptually links implantation of FDS to delayed intracranial bleeding, through the mechanism of shear-induced activation of vWF. In this scenario, after FDS implantation, sustained release of activated vWF in association with platelets plays a pivotal role in the mechanisms of delayed intracranial hemorrhages.

Assessment of Atherosclerosis in Peripheral and Central Circulation in Adult β Thalassemia Intermedia Patients by Color Doppler Ultrasound: Egyptian Experience

BACKGROUND

Atherosclerosis has been extensively studied in thalassemia major (TM) and sickle cell disease but not yet in β thalassemia intermedia (TI). Previous studies concerned with TM were performed in children. TI patients usually live longer and, thus, are more prone to complications of atherosclerosis.

AIM

In our study, we applied color Doppler for the determination of arterial conduit and flow velocities in β TI patients.

METHODS

For central circulation, we measured right and left middle cerebral arteries (MCAs) and basilar artery (BA) mean flow velocity (MFV), pulsatility index (PI), and peak systolic velocity (PSV) as well as carotid intimal media thickness, and to assess peripheral circulation, we studied ankle/brachial index and posterior and anterior tibial arteries' (ATA, PTA) pressure and PSV. This was applied for 30 adult TI patients and 20 age-, sex-, and ethnic group-matched controls.

RESULTS

Transcranial Doppler findings among cases and controls showed that the MFV, PSV of MCAs, and PSV, PI, and MFV of the BA were statistically higher in cases than controls. A comparison between splenectomized and nonsplenectomized patients showed that total leukocyte count, platelet count, lactate dehydrogenase, ferritin, PSV and MFV of the left MCA were all statistically higher in splenectomized cases. Differences between males and females with TI with respect to laboratory and Doppler findings were all statistically insignificant except for intima media thickness, PTA pressure, ATA pressure, and PSV.

CONCLUSION

More than one parameter should be applied to assess atherosclerosis in TI. There is evidence of an increased risk of central ischemia rather than peripheral ischemia in these patients.

Effectiveness of intrathecal nicardipine on cerebral vasospasm in non-traumatic subarachnoid hemorrhage: a systematic review

OBJECTIVE

The objective of this review was to determine the effectiveness of intrathecal nicardipine compared to usual care on cerebral vasospasm and its impact on the following outcome measures: mean flow velocities, angiographic and/or clinical vasospasm, and infection rates.

INTRODUCTION

The results of non-traumatic (aneurysmal) subarachnoid hemorrhage can have devastating effects on patients in terms of functional outcomes. Although other medications have been and continue to be used, Nimodipine is the only Food and Drug Administration-approved medication for treating and improving outcomes following non-traumatic subarachnoid hemorrhage, which may be caused by aneurysmal rupture or arteriovenous malformation. Cerebral vasospasm after non-traumatic subarachnoid hemorrhage is a major concern; cerebral vasospasm refers to the narrowing of the cerebral vessels, which can lead to stroke. Delayed ischemic neurological deficit, as a result of cerebral vasospasm, is the number one reason for death and disability following subarachnoid hemorrhage. This review will determine the effects that intrathecal nicardipine has on cerebral vasospam following non-traumatic subarachnoid hemorrhage.

INCLUSION CRITERIA

The participants of this review included adult patients (18 years and over) in intensive care units. The patients must have had a subarachnoid hemorrhage without history of trauma as cause of subarachnoid hemorrhage, along with the presence of an external ventricular drain. The intervention was administration of intrathecal nicardipine in patients with cerebral vasospasm as a result of non-traumatic subarachnoid hemorrhage. The comparator was usual care, which does not include use of intrathecal nicardipine as part of the treatment regimen. The current review considered both experimental and quasi-experimental study designs. The primary outcomes measured included presence of cerebral vasospasm (identified by mean flow velocities measured by transcranial Doppler and the presence of angiographic vasospasm identified on angiogram) and clinical/symptomatic vasospasm. Secondarily, infection rates as a result of intrathecal nicardipine administration were evaluated.

METHODS

The search strategy aimed to find both published and unpublished studies. Seven databases were searched with no date limitations due to the limited amount of research on this topic.Two independent reviewers assessed the methodological validity of the papers prior to inclusion in the review using the standardized critical appraisal instruments from Joanna Briggs Institute System for the Unified Management, Assessment and Review of Information (JBI SUMARI).Quantitative data was extracted from included studies using the standardized data extraction tool from JBI SUMARI.Statistical pooling was not possible; therefore findings were presented in a narrative form.

RESULTS

Two studies examined the effect that intrathecal nicardipine has on cerebral vasospasm, clinical/symptomatic vasospasm and safety concerns (i.e. infection). The studies indicate that intrathecal nicardipine has shown potential benefits and safety in the treatment of cerebral vasospasm.

CONCLUSIONS

Although intrathecal nicardipine has shown potential to be effective in treating cerebral vasospasm, variance existed among those who received intrathecal nicardipine. In terms of safety, one study had no occurrences of associated bacterial meningitis and the other study had two reported cases of bacterial meningitis out of 50 among those who received intrathecal nicardipine. Limited studies on the use of intrathecal nicardipine following non-traumatic subarachnoid hemorrhage and lack of pooling of results for this review demonstrate the need for more research in this field.

Intravenous administration of Milrinone, as an alternative approach to treat vasospasm in subarachnoid hemorrhage: A case report of transcranial Doppler monitoring

This case illustrates the importance and potential of having TCD monitoring in intensive care. This easy-to-use, safe, low-cost, and bedside tool allows evaluation of the safety and feasibility of an alternative treatment of VSP in SCH and demonstrates the potential to avoid the use of angiography, a high cost, invasive procedure.

Incorporation of Transcranial Doppler into the ED for the neurocritical care patient

INTRODUCTION

In the catastrophic neurologic emergency, a complete neurological exam is not always possible or feasible given the time-sensitive nature of the underlying disease process, or if emergent airway management is indicated. As the neurologic exam may be limited in some patients, the emergency physician is reliant on the assessment of brainstem structures to determine neurological function. Physicians thus routinely depend on advanced imaging modalities to further investigate for potential catastrophic diagnoses. Acquiring these tests introduces the risks of transport as well as delays in managing time-sensitive neurologic processes. A more immediate, non-invasive bedside approach complementing these modalities has evolved: Transcranial Doppler (TCD).

OBJECTIVE

This narrative review will provide a description of scenarios in which TCD may be applicable. It will summarize the sonographic findings and associated underlying pathophysiology in such neurocritical care patients. An illustrated tutorial, along with pearls and pitfalls, is provided.

DISCUSSION

Although there are numerous formalized TCD protocols utilizing four views (transtemporal, submandibular, suboccipital, and transorbital), point-of-care TCD is best accomplished through the transtemporal window. The core applications include the evaluation of midline shift, vasospasm after subarachnoid hemorrhage, acute ischemic stroke, and elevated intracranial pressure. An illustrative tutorial is provided.

CONCLUSIONS

With the wide dissemination of bedside ultrasound within the emergency department, there is a unique opportunity for the emergency physician to utilize TCD for a variety of conditions. While barriers to training exist, emergency physician performance of limited point-of-care TCD is feasible and may provide rapid and reliable clinical information with high temporal resolution.

Transcranial Doppler Versus CT-Angiography for Detection of Cerebral Vasospasm in Relation to Delayed Cerebral Ischemia After Aneurysmal Subarachnoid Hemorrhage: A Prospective Single-Center Cohort Study: The Transcranial doppler and CT-angiography for Investigating Cerebral vasospasm in Subarachnoid hemorrhage (TACTICS) study

Cerebral vasospasm in the first 2 weeks after aneurysmal subarachnoid hemorrhage is recognized as a major predictor of delayed cerebral ischemia. The routine screening for cerebral vasospasm with either transcranial Doppler or CT angiography has been advocated, although its diagnostic value has not yet been determined. Our study investigated the diagnostic accuracy of detecting vasospasm by transcranial Doppler and CT angiography for the prediction of delayed cerebral ischemia and functional outcome. Additionally, agreement between transcranial Doppler and CT angiography was determined.

Design

Prospective diagnostic accuracy study.

Settings

Neurocritical care unit and neurosurgical ward at a tertiary academic medical center.

Patients

Between 2013 and 2016, 59 consenting patients were included.

Intervention

Patients undergo both transcranial Doppler and CT angiography for detection of cerebral vasospasm on days 5 and 10 after aneurysmal subarachnoid hemorrhage. Delayed cerebral ischemia was defined as secondary neurologic deterioration, not explained otherwise. Unfavorable outcome was defined modified Rankin Scale > 2 at 6 months.

Measurements and Main Results

On transcranial Doppler, cerebral vasospasm was observed in 26 patients (45%). On CT angiography, vasospasm was observed in 54 patients (95%). The agreement between transcranial Doppler and CT angiography was 0.47. Delayed cerebral ischemia occurred in 16 patients (27%); unfavorable outcome in 12 patients (20%). Transcranial Doppler predicted delayed cerebral ischemia with a sensitivity of 0.44 (day 5) and 0.50 (day 10), with a specificity of 0.67 (day 5) and 0.57 (day 10). CT angiography predicted delayed cerebral ischemia with a sensitivity of 0.81 (day 5 and 10) and with a specificity of 0.070 (day 5) and 0.00 (day 10). The highest accuracy for predicting unfavorable outcome was on day 5 (0.61 for transcranial Doppler vs 0.27 for CT angiography).

Conclusion

The diagnostic accuracy of both CT angiography and transcranial Doppler for detection of cerebral vasospasm as well as prediction of delayed cerebral ischemia and functional outcome is limited. The agreement between CT angiography and transcranial Doppler is low.

Cerebral Blood Flow in Polytrauma: Transcranial Doppler Analysis in a Nonhuman Primate Shock Model

BACKGROUND

In combat-related trauma, resuscitation goals are to attenuate tissue hypoxia and maintain circulation. During hemorrhagic shock, compensatory and autoregulatory mechanisms are activated to preserve cerebral blood flow. Transcranial Doppler (TCD) ultrasonography may be an ideal noninvasive modality to monitor cerebral hemodynamics. Using a nonhuman primate (NHP) model, we attempted to characterize cerebral hemodynamics during polytraumatic hemorrhagic shock using TCD ultrasonography.

MATERIALS AND METHODS

The ophthalmic artery was insonated at multiple time points during varying stages of shock. Hemorrhage was controlled and pressure targeted to 20 mmHg to initiate and maintain the shock period. Mean flow velocity (MFV), peak systolic velocity (PSV), end diastolic velocity (EDV), pulsatility index (PI), and resistance index (RI) were recorded. Results represent mean ± standard deviation; statistical significance is P < 0.05; n = 12.

RESULTS

Compared to baseline, MFV, PSV, EDV, and RI show significant changes after 60 min of hemorrhagic shock, (9.81 ± 3.60 cm/s; P < 0.01), (21.15 ± 8.59 cm/s; P < 0.01), (5.15 ± 0.21 cm/s; P < 0.01), (0.70 ± 0.11; P < 0.05), respectively. PI did not change during hemorrhagic shock. At end of prehospital care (T30), cerebral flow recovers for MFV, PSV, and RI while EDV remained decreased at T30 (6.15 ± 1.13 cm/s; P < 0.01) and 1 h of simulated transport (T90) (5.87 ± 0.62 cm/s; P < 0.01). Changes in PI at T30 and T90 were not significant. MFV diminished (16.45 ± 3.85 cm/s; P < 0.05) at T90.

CONCLUSIONS

This study establishes baseline and hemorrhagic shock values for NHP cerebral blood flow velocities and cerebrovascular indices. TCD ultrasonography may represent an important area of research for targeted resuscitation investigations using a hemorrhagic shock model in NHPs.

Noninvasive Neuromonitoring: Current Utility in Subarachnoid Hemorrhage, Traumatic Brain Injury, and Stroke

Noninvasive neuromonitoring is increasingly being used to monitor the course of primary brain injury and limit secondary brain damage of patients in the neurocritical care unit. Proposed advantages over invasive neuromonitoring methods include a lower risk of infection and bleeding, no need for surgical installation, mobility and portability of some devices, and safety. The question, however, is whether noninvasive neuromonitoring is practical and trustworthy enough already. We searched the recent literature and reviewed English-language studies on noninvasive neuromonitoring in subarachnoid hemorrhage, traumatic brain injury, and ischemic and hemorrhagic stroke between the years 2010 and 2015. We found 88 studies that were eligible for review including the methods transcranial ultrasound, electroencephalography, evoked potentials, near-infrared spectroscopy, bispectral index, and pupillometry. Noninvasive neuromonitoring cannot yet completely replace invasive methods in most situations, but has great potential being complementarily integrated into multimodality monitoring, for guiding management, and for limiting the use of invasive devices and in-hospital transports for imaging.

Understanding the neurovascular unit at multiple scales: Advantages and limitations of multi-photon and functional ultrasound imaging

Developing efficient brain imaging technologies by combining a high spatiotemporal resolution and a large penetration depth is a key step for better understanding the neurovascular interface that emerges as a main pathway to neurodegeneration in many pathologies such as dementia. This review focuses on the advances in two complementary techniques: multi-photon laser scanning microscopy (MPLSM) and functional ultrasound imaging (fUSi). MPLSM has become the gold standard for in vivo imaging of cellular dynamics and morphology, together with cerebral blood flow. fUSi is an innovative imaging modality based on Doppler ultrasound, capable of recording vascular brain activity over large scales (i.e., tens of cubic millimeters) at unprecedented spatial and temporal resolution for such volumes (up to 10μm pixel size at 10kHz). By merging these two technologies, researchers may have access to a more detailed view of the various processes taking place at the neurovascular interface. MPLSM and fUSi are also good candidates for addressing the major challenge of real-time delivery, monitoring, and in vivo evaluation of drugs in neuronal tissue.

Applications of Transcranial Color-Coded Sonography in the Emergency Department

Transcranial color-coded Doppler sonography is a noninvasive bedside ultrasound application that combines both imaging of parenchymal structures and Doppler assessment of intracranial vessels. It may aid in rapid diagnoses and treatment decision making of patients with intracranial emergencies in point-of-care settings. This pictorial essay illustrates the technical aspects and emergency department applications of transcranial color-coded Doppler sonography, and provides some rationale for implementation of this technique into the emergency department practice.

The Effects of Taekwondo Training on Peripheral Neuroplasticity-Related Growth Factors, Cerebral Blood Flow Velocity, and Cognitive Functions in Healthy Children: A Randomized Controlled Trial

Although regular Taekwondo (TKD) training has been reported to be effective for improving cognitive function in children, the mechanism underlying this improvement remains unclear. The purpose of the present study was to observe changes in neuroplasticity-related growth factors in the blood, assess cerebral blood flow velocity, and verify the resulting changes in children’s cognitive function after TKD training. Thirty healthy elementary school students were randomly assigned to control (n = 15) and TKD (n = 15) groups. The TKD training was conducted for 60 min at a rating of perceived exertion (RPE) of 11–15, 5 times per week, for 16 weeks. Brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), and insulin-like growth factor-1 (IGF-1) levels were measured by blood sampling before and after the training, and the cerebral blood flow velocities (peak systolic [MCAs], end diastolic [MCAd], mean cerebral blood flow velocities [MCAm], and pulsatility index [PI]) of the middle cerebral artery (MCA) were measured using Doppler ultrasonography. For cognitive function assessment, Stroop Color and Word Tests (Word, Color, and Color-Word) were administered along with other measurements. The serum BDNF, VEGF, and IGF-1 levels and the Color-Word test scores among the sub-factors of the Stroop Color and Word Test scores were significantly higher in the TKD group after the intervention (p < 0.05). On the other hand, no statistically significant differences were found in any factors related to cerebral blood flow velocities, or in the Word test and Color test scores (p > 0.05). Thus, 16-week TKD training did not significantly affect cerebral blood flow velocities, but the training may have been effective in increasing children’s cognitive function by inducing an increase in the levels of neuroplasticity-related growth factors.

4D Flow MRI in Neuroradiology: Techniques and Applications

Assessment of the intracranial flow is important for the understanding and management of cerebral vascular diseases. From brain aneurysms and arteriovenous malformations lesions to intracranial and cervical stenosis, the appraisal of the blood flow can be crucial and influence positively on patients' management. The determination of the intracranial hemodynamics and the collateral pattern seems to play to a major role in the management of these lesions. 4D flow magnetic resonance imaging is a noninvasive phase contrast derived method that has been developed and applied in neurovascular diseases. It has a great potential if followed by further technical improvements and comprehensive and systematic clinical studies.

Informatics in neurocritical care: new ideas for Big Data

PURPOSE OF REVIEW

Big data is the new hype in business and healthcare. Data storage and processing has become cheap, fast, and easy. Business analysts and scientists are trying to design methods to mine these data for hidden knowledge. Neurocritical care is a field that typically produces large amounts of patient-related data, and these data are increasingly being digitized and stored. This review will try to look beyond the hype, and focus on possible applications in neurointensive care amenable to Big Data research that can potentially improve patient care.

RECENT FINDINGS

The first challenge in Big Data research will be the development of large, multicenter, and high-quality databases. These databases could be used to further investigate recent findings from mathematical models, developed in smaller datasets. Randomized clinical trials and Big Data research are complementary. Big Data research might be used to identify subgroups of patients that could benefit most from a certain intervention, or can be an alternative in areas where randomized clinical trials are not possible.

SUMMARY

The processing and the analysis of the large amount of patient-related information stored in clinical databases is beyond normal human cognitive ability. Big Data research applications have the potential to discover new medical knowledge, and improve care in the neurointensive care unit.

Contemporary carotid imaging: from degree of stenosis to plaque vulnerability

Carotid artery stenosis is a well-established risk factor of ischemic stroke, contributing to up to 10%-20% of strokes or transient ischemic attacks. Many clinical trials over the last 20 years have used measurements of carotid artery stenosis as a means to risk stratify patients. However, with improvements in vascular imaging techniques such as CT angiography and MR angiography, ultrasonography, and PET/CT, it is now possible to risk stratify patients, not just on the degree of carotid artery stenosis but also on how vulnerable the plaque is to rupture, resulting in ischemic stroke. These imaging techniques are ushering in an emerging paradigm shift that allows for risk stratifications based on the presence of imaging features such as intraplaque hemorrhage (IPH), plaque ulceration, plaque neovascularity, fibrous cap thickness, and presence of a lipid-rich necrotic core (LRNC). It is important for the neurosurgeon to be aware of these new imaging techniques that allow for improved patient risk stratification and outcomes. For example, a patient with a low-grade stenosis but an ulcerated plaque may benefit more from a revascularization procedure than a patient with a stable 70% asymptomatic stenosis with a thick fibrous cap. This review summarizes the current state-of-the-art advances in carotid plaque imaging. Currently, MRI is the gold standard in carotid plaque imaging, with its high resolution and high sensitivity for identifying IPH, ulceration, LRNC, and inflammation. However, MRI is limited due to time constraints. CT also allows for high-resolution imaging and can accurately detect ulceration and calcification, but cannot reliably differentiate LRNC from IPH. PET/CT is an effective technique to identify active inflammation within the plaque, but it does not allow for assessment of anatomy, ulceration, IPH, or LRNC. Ultrasonography, with the aid of contrast enhancement, is a cost-effective technique to assess plaque morphology and characteristics, but it is limited in sensitivity and specificity for detecting LRNC, plaque hemorrhage, and ulceration compared with MRI. Also summarized is how these advanced imaging techniques are being used in clinical practice to risk stratify patients with low- and high-grade carotid artery stenosis. For example, identification of IPH on MRI in patients with low-grade carotid artery stenosis is a risk factor for failure of medical therapy, and studies have shown that such patients may fair better with carotid endarterectomy (CEA). MR plaque imaging has also been found to be useful in identifying revascularization candidates who would be better candidates for CEA than carotid artery stenting (CAS), as high intraplaque signal on time of flight imaging is associated with vulnerable plaque and increased rates of adverse events in patients undergoing CAS but not CEA.

Middle cerebral artery dissection: diagnostic and prognostic value of transcranial color-coded sonography

We report 2 patients with ischemic stroke related to an initial severe focal narrowed middle cerebral artery caused by a dissection mechanism, a presentation that has received little attention to date. Diagnostic modalities and follow-up using transcranial color-coded sonography are reported and discussed. Results with transcranial color-coded sonography were correlated with computed tomographic angiography, showing the great value of this radiation-free arterial monitoring process in this setting, especially in young adults.