Observer Agreement on Computed Tomography Perfusion Imaging in Acute Ischemic Stroke.

Background and Purpose- Computed tomography (CT) perfusion (CTP) provides potentially valuable information to guide treatment decisions in acute stroke. Assessment of interobserver reliability of CTP has, however, been limited to small, mostly single center studies. We performed a large, internet-based study to assess observer reliability of CTP interpretation in acute stroke. Methods- We selected 24 cases from the IST-3 (Third International Stroke Trial), ATTEST (Alteplase Versus Tenecteplase for Thrombolysis After Ischaemic Stroke), and POSH (Post Stroke Hyperglycaemia) studies to illustrate various perfusion abnormalities. For each case, observers were presented with noncontrast CT, maps of cerebral blood volume, cerebral blood flow, mean transit time, delay time, and thresholded penumbra maps (dichotomized into penumbra and core), together with a short clinical vignette. Observers used a structured questionnaire to record presence of perfusion deficit, its extent compared with ischemic changes on noncontrast CT, and an Alberta Stroke Program Early CT Score for noncontrast CT and CTP. All images were viewed, and responses were collected online. We assessed observer agreement with Krippendorff-α. Intraobserver agreement was assessed by inviting observers who reviewed all scans for a repeat review of 6 scans. Results- Fifty seven observers contributed to the study, with 27 observers reviewing all 24 scans and 17 observers contributing repeat readings. Interobserver agreement was good to excellent for all CTP. Agreement was higher for perfusion maps compared with noncontrast CT and was higher for mean transit time, delay time, and penumbra map (Krippendorff-α =0.77, 0.79, and 0.81, respectively) compared with cerebral blood volume and cerebral blood flow (Krippendorff-α =0.69 and 0.62, respectively). Intraobserver agreement was fair to substantial in the majority of readers (Krippendorff-α ranged from 0.29 to 0.80). Conclusions- There are high levels of interobserver and intraobserver agreement for the interpretation of CTP in acute stroke, particularly of mean transit time, delay time, and penumbra maps.

Vascular effects of caffeine found in BOLD fMRI.

The blood oxygen level-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI) measures neuronal activation indirectly. Previous studies have found aperiodic, systemic low-frequency oscillations (sLFOs, ~0.1 Hz) in BOLD signals from resting state (RS) fMRI, which reflects the non-neuronal cerebral perfusion information. In this study, we investigated the possibility of extracting vascular information from the sLFOs in RS BOLD fMRI, which could provide complementary information to the neuronal activations. Two features of BOLD signals were exploited. First, time delays between the sLFOs of big blood vessels and brain voxels were calculated to determine cerebral circulation times and blood arrival times. Second, voxel-wise standard deviations (SD) of LFOs were calculated to represent the blood densities. We explored those features on the publicly available Myconnectome data set (a 2-year study of an individual subject (Male)), which contains 45 RS scans acquired after the subject had coffee, and 45 coffee-free RS scans, acquired on different days. Our results showed that shorter time delays and smaller SDs were detected in caffeinated scans. This is consistent with the vasoconstriction effects of caffeine, which leads to increased blood flow velocity. We also compared our results with previous findings on neuronal networks from the same data set. Our finding showed that brain regions with the significant vascular effect of caffeine coincide with those with a significant neuronal effect, indicating close interaction. This study provides methods to assess the physiological information from RS fMRI. Together with the neuronal information, we can study simultaneously the underlying correlations and interactions between vascular and neuronal networks, especially in pharmacological studies.

A New Technique for the Assessment of Cerebral Vasodilatory Capacity as Part of Catheter-Based Cerebral Angiography.

BACKGROUND: Previous studies have demonstrated the value of cerebral vasodilatory capacity assessment for risk stratification in patients with extracranial arterial stenosis or occlusion. We describe a new method that assesses cerebral vasodilatory capacity as part of catheter-based cerebral angiography. METHODS: We assessed regional cerebral blood volume (rCBV) in the arterial distribution of interest using a controlled contrast injection through a diagnostic catheter placed in the common carotid or the subclavian artery. rCBV maps were created using predefined algorithm based on contrast distribution in the venous phase (voxel size 0.466 mm3) into high, intermediate, low, and no detectable rCBV regions. rCBV maps were acquired again after the administration of intra-arterial nicardipine (1.5-2.5 mg), and percentage increases of the area of various grades of rCBV were calculated. RESULTS: Three patients with internal carotid artery stenosis (32% - 64% in severity) and 1 patient with extracranial vertebral artery stenosis (46% in severity) were assessed. There was a variable but consistent increase in the area of high rCBV in the ipsilateral hemisphere in 3 patients with internal carotid artery flow (5.5%-24.5%) and the cerebellum (9.6%) in 1 patient with vertebral artery flow assessments. The increase in high rCBV was most prominent in the patient who received 2.5 mg (24.5%) and least prominent in a patient who received 1.5 mg (5.5%) of intra-arterial nicardipine. There was a concurrent reduction in areas of intermediate and low rCBV (shift) in 3 patients, and there was an increase in all areas of rCBV grades (addition) in 1 patient. CONCLUSIONS: Selective assessment of cerebral vasodilatory response in the affected arterial distribution is feasible during catheter-based cerebral angiography.

Prophylactic infusion of phenylephrine is effective in attenuating the decrease in regional cerebral blood volume and oxygenation during spinal anesthesia for cesarean section.

BACKGROUND: Hypotension induced by spinal anesthesia for cesarean section causes a decrease in maternal regional cerebral blood volume and oxygenation. We used near-infrared spectroscopy to determine whether prophylactic infusion of phenylephrine attenuates these decreases. METHODS: Sixty patients undergoing bupivacaine spinal anesthesia for cesarean section were randomly divided into one of three intravenous infusion groups: saline (P0), phenylephrine 25 (P25) or 50 µg/min (P50). Mean arterial pressure, heart rate and near-infrared spectroscopy measurements were made at one-minute intervals for 20 minutes, and oxyhemoglobin, deoxy-hemoglobin and total-hemoglobin concentrations and tissue oxygenation index were determined. Mean changes in the values between baseline and each measurement time after intrathecal injection were compared. RESULTS: Significant decreases in mean arterial pressure were seen in group P0 compared to P25 and P50 (P <0.01). Heart rate decreased in a dose-dependent manner during phenylephrine infusion (P0 vs. P25 and P50, P25 vs. P50; P <0.05). Significantly higher total-hemoglobin levels were observed in the phenylephrine groups versus the P0 group (P <0.01). The largest decrease in tissue oxygenation index was found in the P50, followed by P0 and P25 groups (P0 vs. P25 and P50, P25 vs. P50; P <0.05). CONCLUSION: Prophylactic infusion of phenylephrine, especially at 25 µg/min, can effectively suppress decreases in regional cerebral blood volume and regional cerebral blood oxygenation after induction of spinal anesthesia for cesarean section.

Cerebral blood volume and apparent diffusion coefficient - Valuable predictors of non-response to bevacizumab treatment in patients with recurrent glioblastoma.

BACKGROUND: Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. The core of standard of care for newly diagnosed GBM was established in 2005 and includes maximum feasible surgical resection followed by radiation and temozolomide, with subsequent temozolomide with or without tumor-treating fields. Unfortunately, nearly all patients experience a recurrence. Bevacizumab (BV) is a commonly used second-line agent for such recurrences, but it has not been shown to impact overall survival, and short-term response is variable. METHODS: We collected MRI perfusion and diffusion images from 54 subjects with recurrent GBM treated only with radiation and temozolomide. They were subsequently treated with BV. Using machine learning, we created a model to predict short term response (6 months) and overall survival. We set time thresholds to maximize the separation of responders/survivors versus non-responders/short survivors. RESULTS: We were able to segregate 21 (68%) of 31 subjects into unlikely to respond categories based on Progression Free Survival at 6 months (PFS6) criteria. Twenty-two (69%) of 32 subjects could similarly be identified as unlikely to survive long using the machine learning algorithm. CONCLUSION: With the use of machine learning techniques to evaluate imaging features derived from pre- and post-treatment multimodal MRI, it is possible to identify an important fraction of patients who are either highly unlikely to respond, or highly likely to respond. This can be helpful is selecting patients that either should or should not be treated with BV.

Increased cerebral blood volume pulsatility during head-down tilt with elevated carbon dioxide: the SPACECOT Study.

Astronauts aboard the International Space Station (ISS) have exhibited hyperopic shifts, posterior eye globe flattening, dilated optic nerve sheaths, and even optic disk swelling from spaceflight. Elevated intracranial pressure (ICP) consequent to cephalad fluid shifts is commonly hypothesized as contributing to these ocular changes. Head-down tilt (HDT) is frequently utilized as an Earth-based analog to study similar fluid shifts. Sealed environments like the ISS also exhibit elevated CO2, a potent arteriolar vasodilator that could further affect cerebral blood volume (CBV) and cerebral blood flow, intracranial compliance, and ICP. A collaborative pilot study between the National Space Biomedical Research Institute and the German Aerospace Center tested the hypotheses that 1) HDT and elevated CO2 physiologically interact and 2) cerebrovascular pulsatility is related to HDT and/or elevated CO2 In a double-blind crossover study (n = 6), we measured CBV pulsatility via near-infrared spectroscopy, alongside noninvasive ICP and intraocular pressure (IOP) during 28-h -12° HDT at both nominal (0.04%) and elevated (0.5%) ambient CO2 In our cohort, CBV pulsatility increased significantly over time at cardiac frequencies (0.031 ± 0.009 µM/h increase in total hemoglobin concentration pulsatility amplitude) and Mayer wave frequencies (0.019 ± 0.005 µM/h increase). The HDT-CO2 interaction on pulsatility was not robust but rather driven by one individual. Significant differences between atmospheres were not detected in ICP or IOP. Further work is needed to determine whether individual differences in pulsatility responses to CO2 relate to visual changes in space.NEW & NOTEWORTHY Cerebral blood volume (CBV) pulsatility-as measured by near-infrared spectroscopy-increases over time during -12° head-down tilt at both cardiac and Mayer wave frequencies. CBV pulsatility appeared to increase more under elevated (0.5%) CO2 at Mayer wave frequencies in some individuals. If similar dynamic pulsatility increases occur in astronauts, there is the potential to initiate vascular and possibly other remodeling processes that lead to symptoms associated with sustained increases in intracranial pressure.

Antiangiogenic Effect of Bevacizumab: Application of Arterial Spin-Labeling Perfusion MR Imaging in a Rat Glioblastoma Model.

BACKGROUND AND PURPOSE: The usefulness of arterial spin-labeling for the evaluation of the effect of the antiangiogenic therapy has not been elucidated. Our aim was to evaluate the antiangiogenic effect of bevacizumab in a rat glioblastoma model based on arterial spin-labeling perfusion MR imaging. MATERIALS AND METHODS: DSC and arterial spin-labeling perfusion MR imaging were performed by using a 9.4T MR imaging scanner in nude rats with glioblastoma. Rats were randomly assigned to the following 3 groups: control, 3-day treatment, and 10-day treatment after bevacizumab injection. One-way analysis of variance with a post hoc test was used to compare perfusion parameters (eg, normalized CBV and normalized CBF from DSC MR imaging and normalized CBF based on arterial spin-labeling) with microvessel area on histology. The Pearson correlations between perfusion parameters and microvessel area were also determined. RESULTS: All of the normalized CBV from DSC, normalized CBF from DSC, normalized CBF from arterial spin-labeling, and microvessel area values showed significant decrease after treatment (P < .001, P < .001, P = .005, and P < .001, respectively). In addition, normalized CBV and normalized CBF from DSC and normalized CBF from arterial spin-labeling strongly correlated with microvessel area (correlation coefficient, r = 0.911, 0.869, and 0.860, respectively; P < .001 for all). CONCLUSIONS: Normalized CBF based on arterial spin-labeling and normalized CBV and normalized CBF based on DSC have the potential for evaluating the effect of antiangiogenic therapy on glioblastomas treated with bevacizumab, with a strong correlation with microvessel area.

Acute hypercarbia increases the lower limit of cerebral blood flow autoregulation in a porcine model.

OBJECTIVES: In the present study, our objective was to determine if hypercarbia would alter cerebral blood flow (CBF) autoregulation and reduce the ability of cerebrovascular reactivity monitoring to identify the lower limit of cerebrovascular autoregulation (LLA). METHODS: Anaesthetised juvenile pigs were assigned between two groups: normocarbia (control group, n = 10) or hypercarbia [high carbon dioxide (CO2) group, n = 8]. Normocarbia subjects were maintained with an arterial CO2 of 40 Torr, while the hypercarbia subjects had an increase of inspired CO2 to achieve an arterial pCO2 of >80 Torr. Gradual hypotension was induced by continuous haemorrhage from a catheter in the femoral vein, and the LLA was determined by monitoring cortical laser Doppler flux (LDF). Vascular reactivity monitoring was performed using the pressure reactivity index (PRx) and haemoglobin volume index (HVx). RESULTS: There were no sustained differences in ICP between groups. Autoregulation was present in both groups, despite elevation in pCO2.The control group had an average LLA of 45 mmHg (95% CI: 43-47 mmHg) and the high CO2 group had a LLA of 75 mmHg (95% CI: 73-77 mmHg). The detected LLA for each subject correlated with the level of pCO2 (spearman R = 0.8243, P < 0.0001). Both the PRx and HVx accurately detected the LLA despite the presence of hypercarbia. DISCUSSION: Hypercarbia without acidosis increases the observed LLA independent of alterations in ICP. Elevations in CO2 can impair cerebrovascular autoregulation, but if there is a sufficient increase in blood pressure above the CO2 altered LLA, then autoregulation persists.

Assessment of early response to tumor-treating fields in newly diagnosed glioblastoma using physiologic and metabolic MRI: initial experience.

Tumor-treating fields (TTFields) is a novel antimitotic treatment modality for patients with glioblastoma. To assess response to TTFields, a newly diagnosed patient with glioblastoma underwent diffusion, perfusion and 3D echo-planar spectroscopic imaging prior to initiation of TTFields plus temozolamide (baseline) and at 1- and 2-month follow-up periods. Increased mean diffusivity along with decreased fractional anisotropy and maximum relative cerebral blood volume were noted at 2 months relative to baseline suggesting inhibition of tumor growth and angiogenesis. Additionally, a reduction in choline/creatine was also noted during this period. These preliminary data indicate the potential of physiologic and metabolic MRI in assessing early treatment response to TTFields in combination with temozolamide.