Health Inequity and Time From Pediatric Stroke Onset to Arrival

BACKGROUND

Time from stroke onset to hospital arrival determines treatment and impacts outcome. Structural, socioeconomic, and environmental factors are associated with health inequity and onset-to-arrival in adult stroke. We aimed to assess the association between health inequity and onset-to-arrival in a pediatric comprehensive stroke center.

METHODS

A retrospective observational study was conducted on a consecutive cohort of children (>28 days-18 years) diagnosed with acute arterial ischemic stroke (AIS) between 2004 and 2019. Neighborhood-level material deprivation was derived from residential postal codes and used as a proxy measure for health inequity. Patients were stratified by level of neighborhood-level material deprivation, and onset-to-arrival was categorized into 3 groups: <6, 6 to 24, and >24 hours. Association between neighborhood-level material deprivation and onset-to-arrival was assessed in multivariable ordinal logistic regression analyses adjusting for sociodemographic and clinical factors.

RESULTS

Two hundred and twenty-nine children were included (61% male; median age [interquartile range] at stroke diagnosis 5.8-years [1.1-11.3]). Over the 16-year study period, there was an increase in proportion of children diagnosed with AIS living in the most deprived neighborhoods and arriving at the emergency room within 6 hours (P=0.01). Among Asian patients, a higher proportion lived in the most deprived neighborhoods (P=0.02) and level of material deprivation was associated with AIS risk factors (P=0.001).

CONCLUSIONS

Our study suggests an increase in pediatric stroke in deprived neighborhoods and certain communities, and earlier arrival times to the emergency room over time. However, whether these changes are due to an increase in incidence of childhood AIS or increased awareness and diagnosis is yet to be determined. The association between AIS risk factors and material deprivation highlights the intersectionality of clinical factors and social determinants of health. Finally, whether material deprivation impacts onset-to-arrival is likely complex and requires further examination.

The development of the pediatric stroke neuroimaging platform (PEDSNIP)

Childhood stroke occurs from birth to 18 years of age, ranks among the top ten childhood causes of death, and leaves lifelong neurological impairments. Arterial ischemic stroke in infancy and childhood occurs due to arterial occlusion in the brain, resulting in a focal lesion. Our understanding of mechanisms of injury and repair associated with focal injury in the developing brain remains rudimentary. Neuroimaging can reveal important insights into these mechanisms. In adult stroke population, multi-center neuroimaging studies are common and have accelerated the translation process leading to improvements in treatment and outcome. These studies are centered on the growing evidence that neuroimaging measures and other biomarkers (e.g., from blood and cerebrospinal fluid) can enhance our understanding of mechanisms of risk and injury and be used as complementary outcome markers. These factors have yet to be studied in pediatric stroke because most neuroimaging studies in this population have been conducted in single-centred, small cohorts. By pooling neuroimaging data across multiple sites, larger cohorts of patients can significantly boost study feasibility and power in elucidating mechanisms of brain injury, repair and outcomes. These aims are particularly relevant in pediatric stroke because of the decreased incidence rates and the lack of mechanism-targeted trials. Toward these aims, we developed the Pediatric Stroke Neuroimaging Platform (PEDSNIP) in 2015, funded by The Brain Canada Platform Support Grant, to focus on three identified neuroimaging priorities. These were: developing and harmonizing multisite clinical protocols, creating the infrastructure and methods to import, store and organize the large clinical neuroimaging dataset from multiple sites through the International Pediatric Stroke Study (IPSS), and enabling central searchability. To do this, developed a two-pronged approach that included building 1) A Clinical-MRI Data Repository (standard of care imaging) linked to clinical data and longitudinal outcomes and 2) A Research-MRI neuroimaging data set acquired through our extensive collaborative, multi-center, multidisciplinary network. This dataset was collected prospectively in eight North American centers to test the feasibility and implementation of harmonized advanced Research-MRI, with the addition of clinical information, genetic and proteomic studies, in a cohort of children presenting with acute ischemic stroke. Here we describe the process that enabled the development of PEDSNIP built to provide the infrastructure to support neuroimaging research priorities in pediatric stroke. Having built this Platform, we are now able to utilize the largest neuroimaging and clinical data pool on pediatric stroke data worldwide to conduct hypothesis-driven research. We are actively working on a bioinformatics approach to develop predictive models of risk, injury and repair and accelerate breakthrough discoveries leading to mechanism-targeted treatments that improve outcomes and minimize the burden following childhood stroke. This unique transformational resource for scientists and researchers has the potential to result in a paradigm shift in the management, outcomes and quality of life in children with stroke and their families, with far-reaching benefits for other brain conditions of people across the lifespan.

Abstract 159: Impact Of Health Inequities On Outcomes Of Stroke In Children

Introduction: Recent studies have reported access to initial imaging and underlying chronic disorders to be associated with post-stroke outcome in children. However, the influence of sociodemographic factors is yet to be investigated within the Canadian context. Our study explored the role of health inequities while considering the influence of clinical and radiological factors on post-stroke outcomes.

Methods: A consecutive cohort of children &gt;28 days-18 years of age diagnosed with arterial ischemic stroke between 2004 and 2019 at a comprehensive stroke centre in Ontario were included. Patient residential postal codes were linked to the Ontario Marginalization Index including area-level data on income, education, single-parent families, and housing quality. Post-stroke outcomes were assessed using the validated Pediatric Stroke Outcome Measure - Severity Classification System (PSOM-SCS). Poor outcome was defined as moderate-to-severe deficit at discharge or at 18 months from the onset of stroke. Univariable and multivariable logistic regression models were developed to examine the influence of material deprivation on neurological outcomes while controlling for demographic, clinical, and radiological factors.

Results: Amongst 234 children, predictors of poor outcome at discharge included moderate-to-severe stroke at presentation (OR = 4.00, p &lt; 0.05) while the presence of a single infarct may protect the patient from poor outcome at discharge (OR = 0.32, p &lt; 0.05). Predictors of poor outcome at 18 months post-stroke included patients from moderately deprived neighborhoods (OR = 5.36, p &lt; 0.05), stroke onset between 2014 and 2019 (OR = 7.44, p &lt; 0.05), or presence of a left cerebral hemispheric infarction (OR = 8.20, p &lt; 0.05).

Conclusion: Our study demonstrated that stroke severity and the number of infarcts were important in determining outcome at discharge whereas neighbourhood-level material deprivation, year of onset, and infarct location predicted outcome at 18 months from the onset of stroke. Further research is needed to explore the role of broader social determinants of health in predicting stroke outcomes longitudinally over time.

The ARVC causing TMEM43-p.S358L mutation has impact on the lipid metabolism

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 450999875

Background

Transmembrane protein 43 (TMEM43) is a phylogenetically highly conserved and ubiquitously expressed protein with unknown function. The protein contains four transmembrane domains located in the inner nuclear envelope and the endoplasmic reticulum (ER). A large acidic domain located between the first and second transmembrane domains, with unknown function, is exposed to the ER lumen. TMEM43-c.1073C&gt;T is a rare fully penetrant mutation that leads to arrhythmogenic right ventricular cardiomyopathy type 5 (ARVC5). ARVC5 is associated with myocardial fibrosis, fibrofatty replacement and progressive loss of right ventricular myocardial tissue and severe arrhythmias causing sudden cardiac death (SCD) especially in males. The pathomechanism of ARVC5 is not well understood.

Methods

We isolated and cultivated primary dermal fibroblasts of three different individuals carrying TMEM43-c.1073C&gt;T (p.S358L). Proteins were isolated from cell cultures and analysed by Orbitrap mass spectrometry. Proteome data of the mutation carriers were compared to TMEM43 wildtype control fibroblasts. Additionally, TMEM43-p.S358L and control fibroblasts were investigated by transmission electron microscopy (TEM).

Results

A total of 9 proteins were upregulated in fibroblasts expressing TMEM43-p.S358L (p&lt;0.003). Of note, proteins involved in fatty acid metabolism, such as acyl-coenzym A (CoA) thioesterase 1 encoded by the gene ACOT1, and Malonate-CoA ligase encoded by ACSF3 were strongly upregulated (FC&gt;3 or &gt;2, respectively). ACOT1 catalyses hydrolysis acyl-CoAs to long chain fatty acids and CoA. ACSF3 catalyses the formation of thioesters between fatty acids and CoA. ACOT1 and ACSF3 regulate the intracellular levels of free fatty acids and are expressed in the cardiomyocytes of the human myocardium. TEM images of TMEM43-p.S358L carriers show an accumulation of multilamellar vesicles, which may support the dysregulation of the lipid metabolism.

Conclusion

The differentially regulated proteins in dermal fibroblasts and the accumulation of multilamellar vesicles suggest a dysregulation of the lipid metabolism by TMEM43-p.S358L, which may also have relevance for the development of myocardial fibrofatty replacement contributing to ARVC5.

Fronto-Parietal and White Matter Haemodynamics Predict Cognitive Outcome in Children with Moyamoya Independent of Stroke

Moyamoya disease is a major arteriopathy characterised by progressive steno-occlusion of the arteries of the circle of Willis. Studies in adults with moyamoya suggest an association between abnormal fronto-parietal and white matter regional haemodynamics and cognitive impairments, even in the absence of focal infarction. However, these associations have not been investigated in children with moyamoya. We examined the relationship between regional haemodynamics and ratings of intellectual ability and executive function, using hypercapnic challenge blood oxygen level-dependent magnetic resonance imaging of cerebrovascular reactivity in a consecutive cohort of children with confirmed moyamoya. Thirty children were included in the final analysis (mean age: 12.55 ± 3.03 years, 17 females, 15 idiopathic moyamoya and 15 syndromic moyamoya). Frontal haemodynamics were abnormal in all regardless of stroke history and comorbidity, but occipital lobe haemodynamics were also abnormal in children with syndromic moyamoya. Executive function deficits were noted in both idiopathic and syndromic moyamoya, whereas intellectual ability was impaired in syndromic moyamoya, even in the absence of stroke. Analysis of the relative effect of regional abnormal haemodynamics on cognitive outcomes demonstrated that executive dysfunction was predominantly explained by right parietal and white matter haemodynamics independent of stroke and comorbidity, while posterior circulation haemodynamics predicted intellectual ability. These results suggest that parietal and posterior haemodynamics play a compensatory role in overcoming frontal vulnerability and cognitive impairment.

Abstract TP97: White Matter And Deep Grey Matter Structural Variations In Childhood Moyamoya Disease

Background: Moyamoya disease is a progressive steno-occlusive arteriopathy that increases stroke risk. Clinically, cognitive decline is known to occur over time, even in the absence of stroke. MRI measures of cerebrovascular reactivity (CVR) provide an in vivo assessment of cerebrovascular reserve and stroke risk. Typically, in normal-appearing white matter (WM) lower (quantified as negative) CVR is associated with increased apparent diffusion coefficient (ADC). However, the association between negative CVR and ADC in children is not well understood.

Objectives: To determine (i) whether negative CVR is associated with changes in ADC in normal-appearing WM of children with Moyamoya, ii) whether there is an association between CVR and ADC with structural damage to the brain (by measuring the volume of subcortical structures).

Methods: Retrospective analysis of a consecutive cohort of nine children with Moyamoya (male = 4, median age = 12.1) with no history of stroke, and seven age and sex-matched controls. ADC values and fractional negativity (fneg), calculated from CVR parametric maps as the fraction of negative CVR voxels within a region of interest (ROI), were extracted from WM and subcortical GM ROIs. Volumes from the subcortical GM regions were extracted and normalized for head size. Analyses of differences was calculated per hemisphere (n=18, bilateral disease n = 4, unilateral n=5) and categorized as affected and unaffected and compared to controls.

Results: Mean (m) ADC in WM of affected hemispheres (m=807.05, p<0.01) and unaffected (m=814.68, p<0.05) hemispheres were significantly larger compared to controls (m=761.04). A positive relationship was found between fneg and ADC in affected (r=0.37, p=0.24) and unaffected (r=0.26, p=0.62) hemispheres, but with no statistical significance. Increased ADC in the caudate was associated with smaller volume in the affected hemisphere of patients (r =-0.83, p=0.02).

Conclusions: ADC in normal appearing WM in children with Moyamoya is elevated, and is associated with volume of the caudate in this cohort demonstrating the association between abnormal CVR, perfusion and structural damage in children with Moyamoya and no stroke.

Abstract TP168: Quantitative Cerebrovascular Reactivity Atlas In Children

Introduction: Cerebrovascular reactivity (CVR) can be measured by inducing carbon dioxide (CO 2 ) changes in the circulation and measuring subsequent changes in blood flow with functional MRI blood oxygen level dependent sequences (BOLD). In clinical practice, abnormalities in CVR imaging can serve as a biomarker of ischemic risk. To characterize pathological aberrations in CVR, it is essential to have quantitative reference data as to what constitutes normal CVR across brain regions at various stages of development.

Methods: Prospective enrollment of healthy children ages 6 to 18. Target N of 40. Two datasets are being generated within the atlas using two different methods of administering the vasoactive stimulus (CO 2 ): a breath-hold CVR dataset (endogenous stimulus) and a RespirAct TM CVR dataset (exogenous). A test of normality is performed on CVR values for each voxel across subjects, with mean and standard deviation calculations. This will allow for generation of a Z-score for each CVR value per voxel in any clinical CVR study. Voxel-wide validation of breath-hold CVR values against the gold standard RespirAct TM CVR values will be performed using within subject t-test and between group comparisons. Subgroup analysis based on gender and age will also be performed.

Results: Preliminary CVR data for 8 healthy right-handed children is presented (4 female, median age 13, range 9 -14 years). All participants tolerated CVR studies well and no side effects were reported. Group datasets acquired to date passed tests of normality with no significant differences in CVR values between the two methods found.

Conclusions: This study will generate the first atlas of quantitative CVR-fMRI data in healthy children. Normative physiological data on CVR changes throughout childhood, and associations between CVR, blood pressure, age, and gender will be obtained. CVR imaging is performed clinically in patients with a risk of recurrent arterial ischemic stroke such as those with intracranial arteriopathies, sickle cell disease and other genetic and metabolic disorders. Our atlas can provide clinicians with objective measures regarding extent and distribution of CVR abnormalities, allow for stroke risk stratification, and aid in determining the optimal time for intervention.

Abstract TMP94: Health Inequity And Time From Stroke Onset To Arrival Trends: A Single-centre Experience

Introduction: Clinical outcomes post childhood stroke have been shown to largely depend on age at the time of stroke, and the size and location of the infarct. However, the impact of health inequities on time to hospital arrival and outcomes remain inadequately addressed. This study examined trends in material deprivation and its impact on time from stroke onset to arrival in the ER for children with arterial ischemic stroke.

Methods: A consecutive cohort of children >28 days-18 years of age diagnosed with arterial ischemic stroke between 2004 and 2019 at a comprehensive stroke centre were included. The Ontario Marginalization Index data for each child was derived from their residential postal code using validated mapping techniques. Within the index, material deprivation measures the income, education, single-parent families, and housing quality in a region. Patients were stratified into 3 cohorts by year of presentation; Cohort 1: 2004-2008, Cohort 2: 2009-2013, and Cohort 3: 2014-2019, while their postal codes were dichotomized into low or highly deprived neighbourhoods. The time from stroke onset to arrival was stratified into < 6 hours, 6 to 24 hours, and > 24 hours.

Results: Amongst 285 children, more lived in a highly deprived neighbourhood in the later cohort (Cohort 3: 2014-2019) than the earlier cohort (Cohort 1: 2004-2008) (47.5% vs. 40.3%). Compared to Cohort 1, more patients in Cohort 3 arrived in the ER within 6 hours of stroke onset (28.3% vs 52.5%) while a similar trend was found in patients arriving 6 to 24 hours post onset of stroke (10.1% vs. 23.2%). From Cohorts 1 to 3, a significant increase in the proportion of patients arriving in the ER within 6 hours of stroke onset was found (χ 2 = 10.9, p = 0.027).

Conclusion: Our study demonstrated an increasing trend toward more patients with stroke coming from highly deprived neighbourhoods. This is a cause for concern. However, whether this has an impact on stroke severity and outcomes is yet to be determined. Over the same period, more patients within the later cohort arrived in the ER within 6 hours of stroke onset. These findings may be attributed to sustained community-based education and primary-care initiatives that have led to increased awareness of childhood stroke symptoms over the past 15 years.

Hyperpolarized 129 Xe MRI of the rat brain with chemical shift saturation recovery and spiral-IDEAL readout

PURPOSE

To demonstrate the feasibility of ¹²⁹ Xe chemical shift saturation recovery (CSSR) combined with spiral-IDEAL imaging for simultaneous measurement of the time-course of red blood cell (RBC) and brain tissue signals in the rat brain.

METHODS

Images of both the RBC and brain tissue ¹²⁹ Xe signals from the brains of five rats were obtained using interleaved spiral-IDEAL imaging following chemical shift saturation pulses applied at multiple CSSR delay times, τ. A linear fit of the signals to τ was used to calculate the slope of the signal for both RBC and brain tissue compartments on a voxel-by-voxel basis. Gas transfer was evaluated by measuring the ratio of the whole brain tissue-to-RBC signal intensities as a function of τ. To investigate the relationship between the CSSR images and gas transfer in the brain, the experiments were repeated during hypercapnic ventilation.

RESULTS

Hypercapnia, affected the ratio of the tissue-to-RBC signal intensity (p = 0.026), consistent with an increase in gas transfer.

CONCLUSION

CSSR with spiral-IDEAL imaging is feasible for acquisition of ¹²⁹ Xe RBC and brain tissue time-course images in the rat brain. Differences in the time-course of the signal intensity ratios are consistent with gas transfer changes expected under hypercapnic conditions.

Distinct Clinical and Radiographic Phenotypes in Pediatric Patients With Moyamoya

BACKGROUND

Given the expanding evidence of clinico-radiological differences between moyamoya disease (MMD) and moyamoya syndrome (MMS), we compared the clinical and radiographic features of childhood MMD and MMS to identify predictors of ischemic event recurrence.

METHODS

We reviewed a pediatric moyamoya cohort followed between 2003 and 2019. Clinical and radiographic characteristics at diagnosis and follow-up were abstracted. Comparisons between MMD and MMS as well as between MMD and two MMS subgroups (neurofibromatosis [MMS-NF1] and sickle cell disease [MMS-SCD]) were performed.

RESULTS

A total of 111 patients were identified. Patients with MMD presented commonly with transient ischemic attacks (TIAs) (35 % MMD versus 13% MMS-NF1 versus 9.5% MMS-SCD; P = 0.047). Symptomatic stroke presentation (MMD 37% versus MMS-NF1 4% versus 33%; P = 0.0147) and bilateral disease at diagnosis (MMD 73% versus MMS-NF1 22 % versus MMS-SCD 67%; P = 0.0002) were uncommon in MMS-NF1. TIA recurrence was common in MMD (hazard ratio 2.86; P = 0.001). The ivy sign was absent on neuroimaging in a majority of patients with MMS-SCD (MMD 67% versus MMS-NF1 52% versus MMS-SCD 9.5%; P = 0.0002). Predictors of poor motor outcome included early age at diagnosis (odds ratio [OR] 8.45; P = 0.0014), symptomatic stroke presentation (OR 6.6; P = 0.019), and advanced Suzuki stage (OR 3.59; P = 0.019).

CONCLUSIONS

Moyamoya exhibits different phenotypes based on underlying etiologies. Frequent TIAs is a common phenotype of MMD and symptomatic stroke presentation a common feature of MMD and MMS-SCD, whereas unilateral disease and low infarct burden are common in MMS-NF1. In addition, absence of ivy sign is a common phenotype in MMS-SCD.

Effect of inhaled oxygen concentration on 129 Xe chemical shift of red blood cells in rat lungs

PURPOSE

To investigate the dependence of dissolved ¹²⁹ Xe chemical shift on the fraction of inhaled oxygen, F_i O₂ , in the lungs of healthy rats.

METHODS

The chemical shifts of ¹²⁹ Xe dissolved in red blood cells, δ_RBC , and blood plasma and/or tissue, δ_Plasma , were measured using MRS in 12 Sprague Dawley rats mechanically ventilated at F_i O₂ values of 0.14, 0.19, and 0.22. Regional effects on the chemical shifts were controlled using a chemical shift saturation recovery sequence with a fixed delay time. MRS was also performed at an F_i CO₂ value of 0.085 to investigate the potential effect of the vascular response on δ_RBC and δ_Plasma .

RESULTS

δ_RBC increased with decreasing F_i O₂ (P = .0002), and δ_Plasma showed no dependence on F_i O₂ (P = .23). δ_RBC at F_i CO₂ = 0 (210.7 ppm ± 0.1) and at F_i CO₂ = 0.085 (210.6 ppm ± 0.2) were not significantly different (P = .67). δ_Plasma at F_i CO₂ = 0 (196.9 ppm ± 0.3) and at F_i CO₂ = 0.085 (197.0 ppm ± 0.1) were also not significantly different (P = .81).

CONCLUSION

Rat lung δ_RBC showed an inverse relationship to F_i O₂ , opposite to the relationship previously demonstrated for in vitro human blood. Rat lung δ_RBC did not depend on F_i CO₂ .

Positional obstructive sleep apnea in an obese pediatric population

STUDY OBJECTIVES

Positional obstructive sleep apnea (POSA) is a phenotype of obstructive sleep apnea (OSA) where sleep-related obstructive events occur predominantly in the supine position. Limited knowledge exists regarding the presence of POSA in children with obesity. The study objective was to determine the prevalence of POSA while identifying factors associated with POSA in children with obesity.

METHODS

This was a cross-sectional study of children with obesity, aged 8 to 18 years, with a diagnostic polysomnogram (PSG) between 2012 to 2019, who were referred for the evaluation of sleep-related breathing. POSA was defined as an overall obstructive apnea-hypopnea index (OAHI) ≥5 events/h and a supine OAHI to nonsupine OAHI ratio of ≥2. Patient demographics, anthropometrics, and PSG data were recorded.

RESULTS

Of the 112 children with obesity with a diagnostic PSG, 43 (38%) had OSA. Among those with OSA, 25 of 43 (58%) had POSA (mean age: 14.6 ± 2.3 years; mean body mass index: 37.7 ± 7.6 kg/m²; 68% male) and 18 of 43 (42%) had non-POSA (mean age: 13.9 ± 2.8 years; mean body mass index: 37.9 ± 7.2 kg/m²; 78% male). Among those with POSA, 13 of 25 (52%) had mild OSA, 7 of 25 (28%) had moderate OSA, and 5 of 25 (20%) had severe OSA. No significant differences were found in age, sex, and anthropometric measures between POSA and non-POSA groups. Time spent in supine and nonsupine sleep did not differ significantly between groups.

CONCLUSIONS

In children with obesity and OSA, POSA occurs frequently. Identifying POSA allows for potential targeted positional therapy for children with obesity.

0873 Obstructive Sleep Apnea Impacts Brain Development in Obese Children and Adolescents: An MRI Study

Introduction

Obstructive sleep apnea (OSA) is a breathing disorder characterized by episodes of nocturnal hypoxia and chronic systemic inflammation, affecting more than 50% of obese youths. Both obesity and OSA independently have a negative impact on brain structure and function, but their combined effect on the developing brain is unknown. The purpose of this study was to assess MRI measurements of cortical thickness (CT) in obese youths with various degrees of OSA severity. We hypothesized that CT is abnormal in obese adolescents with OSA.

Methods

55 obese subjects (26 females, 29 males, mean 14.3 ± 2.4 years) were included in the analysis. All subjects were assessed with polysomnography (PSG) to evaluate presence and severity of OSA. T1-weighted MPRAGE images were acquired using a 3T MRI scanner following PSG. CT was extracted using the CIVET 2.1.1 pipeline, and statistical analysis was performed on SurfStat to examine global and regional CT in relation to age using a general linear model.

Results

Based on PSG outcome, subjects were divided into 3 groups, no OSA (OAHI &lt; 1.5 events/hr., n = 15), mild OSA (OAHI &lt; 5, n = 14), and moderate/severe OSA (OAHI &#8805; 5, n = 26). Cortical thickness analysis revealed a negative-trending correlation between global CT and age in no OSA (T = -0.49, P &gt; 0.6), as seen in typical development. This correlation weakened in the presence of mild OSA (T = -0.20, P &gt; 0.8) and became significantly positive in moderate/severe OSA (T = 3.87, P = 0.001), affecting several cortical areas.

Conclusion

These results indicate that brain development in obese adolescents with moderate/severe OSA significantly deviates from the typical trajectory of cortical thinning. This thickening could be due to exacerbated inflammation from the combined effect of both diseases, or a neurotrophic effect of leptin. More data is needed to validate these findings.

Support

None

Ultrasound Detection of Abnormal Cerebrovascular Morphology in a Mouse Model of Sickle Cell Disease Based on Wave Reflection

Sickle cell disease (SCD) is associated with a high risk of stroke, and affected individuals often have focal brain lesions termed silent cerebral infarcts. The mechanisms leading to these types of injuries are at present poorly understood. Our group has recently demonstrated a non-invasive measurement of cerebrovascular impedance and wave reflection in mice using high-frequency ultrasound in the common carotid artery. To better understand the pathophysiology in SCD, we used this approach in combination with micro-computed tomography to investigate changes in cerebrovascular morphology in the Townes mouse model of SCD. Relative to controls, the SCD mice demonstrated the following: (i) increased carotid artery diameter, blood flow and vessel wall thickness; (ii) elevated pulse wave velocity; (iii) increased reflection coefficient; and (iv) an increase in the total number of vessel segments in the brain. This study highlights the potential for wave reflection to aid the non-invasive clinical assessment of vascular pathology in SCD.

Hydroxycarbamide treatment in children with Sickle Cell Anaemia is associated with more intact white matter integrity: a quantitative MRI study

Sickle cell anaemia (SCA) is a devastating genetic blood disorder leading to chronic anaemia, impaired cerebrovascular dilatory capacity and cerebral infarctions. Our aim was to assess the relationship between microstructural properties of the white matter (WM) and both cerebrovascular reactivity (CVR) and cerebral blood flow, as well as the effects of hydroxycarbamide on these relationships. Our results demonstrate that mean CVR was increased in hydroxycarbamide-treated patients compared to untreated patients. Moreover, untreated SCA patients had increased skew and kurtosis of mean diffusivity histograms in the WM compared to hydroxycarbamide-treated patients and healthy age-matched controls, indicating disruption of WM integrity. Regression analysis of CVR and WM mean diffusivity (MD) revealed a significant linear relationship between CVR and MD histogram skew and kurtosis in healthy controls, but not in either of the two SCA groups. These findings suggest that patients treated with hydroxycarbamide possess white matter MD histogram parameters which more closely resemble those of healthy controls.

Quantification of pathophysiological alterations in venous oxygen saturation: A comparison of global MR susceptometry techniques

The purpose of this study was to compare the Infinite Cylinder and Forward Field methods of quantifying global venous oxygen saturation (Y_v) in the superior sagittal sinus (SSS) from MRI phase data, and assess their applicability in systemic cerebrovascular disease.15 children with sickle cell disease (SCD) and 10 healthy age-matched controls were imaged on a 3.0 T MRI system. Anatomical and phase data around the superior sagittal sinus were acquired from a clinically available susceptibility weighted imaging sequence and converted to Y_v using the Infinite Cylinder and Forward Field methods. Y_v was significantly higher when calculated using the Infinite Cylinder method compared to the Forward Field method in both patients (p = 0.003) and controls (p < 0.001). A significant difference in Y_v was observed between patients and controls for the Forward Field method only (p = 0.006). While various implementations of Y_v quantification can be used in practice, the results can differ significantly. Simplistic models such as the Infinite Cylinder method may be easier to implement, but their dependence on broad assumptions can lead to an overestimation of Y_v, and may reduce the sensitivity to pathophysiological changes in Y_v.

Breath-Hold Blood Oxygen Level-Dependent MRI: A Tool for the Assessment of Cerebrovascular Reserve in Children with Moyamoya Disease

BACKGROUND AND PURPOSE

There is a critical need for a reliable and clinically feasible imaging technique that can enable prognostication and selection for revascularization surgery in children with Moyamoya disease. Blood oxygen level-dependent MR imaging assessment of cerebrovascular reactivity, using voluntary breath-hold hypercapnic challenge, is one such simple technique. However, its repeatability and reliability in children with Moyamoya disease are unknown. The current study sought to address this limitation.

MATERIALS AND METHODS

Children with Moyamoya disease underwent dual breath-hold hypercapnic challenge blood oxygen level-dependent MR imaging of cerebrovascular reactivity in the same MR imaging session. Within-day, within-subject repeatability of cerebrovascular reactivity estimates, derived from the blood oxygen level-dependent signal, was computed. Estimates were associated with demographics and intellectual function. Interrater reliability of a qualitative and clinically applicable scoring scheme was assessed.

RESULTS

Twenty children (11 males; 12.1 ± 3.3 years) with 30 MR imaging sessions (60 MR imaging scans) were included. Repeatability was "good" on the basis of the intraclass correlation coefficient (0.70 ± 0.19). Agreement of qualitative scores was "substantial" (κ = 0.711), and intrarater reliability of scores was "almost perfect" (κ = 0.83 and 1). Younger participants exhibited lower repeatability (P = .027). Repeatability was not associated with cognitive function (P > .05). However, abnormal cerebrovascular reactivity was associated with slower processing speed (P = .015).

CONCLUSIONS

Breath-hold hypercapnic challenge blood oxygen level-dependent MR imaging is a repeatable technique for the assessment of cerebrovascular reactivity in children with Moyamoya disease and is reliably interpretable for use in clinical practice. Standardization of such protocols will allow further research into its application for the assessment of ischemic risk in childhood cerebrovascular disease.

Assessment of cerebral blood flow with magnetic resonance imaging in children with sickle cell disease: A quantitative comparison with transcranial Doppler ultrasonography

INTRODUCTION

Transcranial Doppler ultrasonography (TCD) is a clinical tool for stratifying ischemic stroke risk by identifying abnormal elevations in blood flow velocity (BFV) in the middle cerebral artery (MCA). However, TCD is not effective at screening for subtle neurologic injury such as silent cerebral infarcts. To better understand this disparity, we compared TCD measures of BFV with tissue-level cerebral blood flow (CBF) using arterial spin-labeling MRI in children with and without sickle cell disease, and correlated these measurements against clinical hematologic measures of disease severity.

METHODS

TCD and MRI assessment were performed in 13 pediatric sickle cell disease patients and eight age-matched controls. Using MRI measures of MCA diameter and territory weight, TCD measures of BFV in the MCA [cm/s] were converted into units of CBF [ml min^-1100 g^-1] for comparison.

RESULTS

There was no significant association between TCD measures of BFV in the MCA and corresponding MRI measures of CBF in patients (r = .28, p = .39) or controls (r = .10, p = .81). After conversion from BFV into units of CBF, a strong association was observed between TCD and MRI measures (r = .67, p = .017 in patients, r = .86, p = .006 in controls). While BFV in the MCA showed a lack of correlation with arterial oxygen content, an inverse association was observed for CBF measurements.

CONCLUSIONS

This study demonstrates that BFV in the MCA cannot be used as a surrogate marker for tissue-level CBF in children with sickle cell disease. Therefore, TCD alone may not be sufficient for understanding and predicting subtle pathophysiology in this population, highlighting the potential clinical value of tissue-level CBF.

The Potential for Advanced Magnetic Resonance Neuroimaging Techniques in Pediatric Stroke Research

BACKGROUND

This article was written to provide clinicians and researchers with an overview of a number of advanced neuroimaging techniques in an effort to promote increased utility and the design of future studies using advanced neuroimaging in childhood stroke. The current capabilities of advanced magnetic resonance imaging techniques provide the opportunity to build on our knowledge of the consequences of stroke on the developing brain. These capabilities include providing information about the physiology, metabolism, structure, and function of the brain that are not routinely evaluated in the clinical setting.

METHODS

During the Proceedings of the Stroke Imaging Laboratory for Children Workshop in Toronto in June 2015, a subgroup of clinicians and imaging researchers discussed how the application of advanced neuroimaging techniques could further our understanding of the mechanisms of stroke injury and repair in the pediatric population. This subgroup was established based on their interest and commitment to design collaborative, advanced neuroimaging studies in the pediatric stroke population.

RESULTS

In working toward this goal, we first sought to describe here the magnetic resonance imaging techniques that are currently available for use, and how they have been applied in other stroke populations (e.g., adult and perinatal stroke).

CONCLUSIONS

With the continued improvement in advanced neuroimaging techniques, including shorter acquisition times, there is an opportunity to apply these techniques to their full potential in the research setting and learn more about the effects of stroke in the developing brain.

Cerebrovascular Reactivity and Intellectual Outcome in Childhood Stroke With Transient Cerebral Arteriopathy

BACKGROUND

Hypercapnic-challenge blood oxygen level-dependent magnetic resonance imaging cerebrovascular reactivity (CVR), measures the regional perfusion response to altered carbon dioxide. CVR correlates with the tissue-level microvascular dysfunction and ischemic risk. Among children with arterial ischemic stroke, transient cerebral arteriopathy (TCA) is a frequent, nonprogressive unilateral intracranial arteriopathy, which typically results in basal ganglia infarction and chronic cerebral artery stenosis. Therefore TCA provides a model for studying the consequences of chronic nonprogressive stenosis using CVR and intellectual outcome. We hypothesized that children with TCA and chronic nonprogressive intracranial artery stenosis have impaired CVR distal to the stenosis and associated cognitive impairment.

METHODS

We studied children with a prior diagnosis of TCA as defined by infarction limited to the basal ganglia, internal capsule, or both; and significant (greater than 50% diameter) residual stenosis of the supraclinoid internal carotid artery, its proximal branches or both. All children had CVR, intellectual function, and infarct volumes quantified.

RESULTS

We performed CVR studies in five children at mean 8.96 years (3.33 to 14.58 years) poststroke. Impaired CVR was limited to the infarct zone and adjacent white matter in most children. Intellectual function was broadly average in all but one subject.

CONCLUSIONS

In children with typical TCA, ipsilateral cortical CVR and intellectual function seem to be preserved despite persistent arterial stenosis in the majority. These findings suggest that chronic revascularization strategies in these children may not be indicated and require further exploration in a larger cohort of children.

Functional and anatomical evidence of cerebral tissue hypoxia in young sickle cell anemia mice

Cerebral ischemia is a significant source of morbidity in children with sickle cell anemia; however, the mechanism of injury is poorly understood. Increased cerebral blood flow and low hemoglobin levels in children with sickle cell anemia are associated with increased stroke risk, suggesting that anemia-induced tissue hypoxia may be an important factor contributing to subsequent morbidity. To better understand the pathophysiology of brain injury, brain physiology and morphology were characterized in a transgenic mouse model, the Townes sickle cell model. Relative to age-matched controls, sickle cell anemia mice demonstrated: (1) decreased brain tissue pO₂ and increased expression of hypoxia signaling protein in the perivascular regions of the cerebral cortex; (2) elevated basal cerebral blood flow , consistent with adaptation to anemia-induced tissue hypoxia; (3) significant reduction in cerebrovascular blood flow reactivity to a hypercapnic challenge; (4) increased diameter of the carotid artery; and (5) significant volume changes in white and gray matter regions in the brain, as assessed by ex vivo magnetic resonance imaging. Collectively, these findings support the hypothesis that brain tissue hypoxia contributes to adaptive physiological and anatomic changes in Townes sickle cell mice. These findings may help define the pathophysiology for stroke in children with sickle cell anemia.

MRI-based cerebrovascular reactivity using transfer function analysis reveals temporal group differences between patients with sickle cell disease and healthy controls

OBJECTIVES

Cerebrovascular reactivity (CVR) measures the ability of cerebral blood vessels to change their diameter and, hence, their capacity to regulate regional blood flow in the brain. High resolution quantitative maps of CVR can be produced using blood-oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) in combination with a carbon dioxide stimulus, and these maps have become a useful tool in the clinical evaluation of cerebrovascular disorders. However, conventional CVR analysis does not fully characterize the BOLD response to a stimulus as certain regions of the brain are slower to react to the stimulus than others, especially in disease. Transfer function analysis (TFA) is an alternative technique that can account for dynamic temporal relations between signals and has recently been adapted for CVR computation. We investigated the application of TFA in data on children with sickle cell disease (SCD) and healthy controls, and compared them to results derived from conventional CVR analysis.

MATERIALS AND METHODS

Data from 62 pediatric patients with SCD and 34 age-matched healthy controls were processed using conventional CVR analysis and TFA. BOLD data were acquired on a 3 Tesla MRI scanner while a carbon dioxide stimulus was quantified by sampling the end-tidal partial pressures of each exhaled breath. In addition, T1 weighted structural imaging was performed to identify grey and white matter regions for analysis. The TFA method generated maps representing both the relative magnitude change of the BOLD signal in response to the stimulus (Gain), as well as the BOLD signal speed of response (Phase) for each subject. These were compared to CVR maps calculated from conventional analysis. The effect of applying TFA on data from SCD patients versus controls was also examined.

RESULTS

The Gain measures derived from TFA were significantly higher than CVR values based on conventional analysis in both SCD patients and healthy controls, but the difference was greater in the SCD data. Moreover, while these differences were uniform across the grey and white matter regions of controls, they were greater in white matter than grey matter in the SCD group. Phase was also shown to be significantly correlated with the amount that TFA increases CVR estimates in both the grey and white matter.

CONCLUSIONS

We demonstrated that conventional CVR analysis underestimates vessel reactivity and this effect is more prominent in patients with SCD. By using TFA, the resulting Gain and Phase measures more accurately characterize the BOLD response as it accounts for the temporal dynamics responsible for the CVR underestimation. We suggest that the additional information offered through TFA can provide insight into the mechanisms underlying CVR compromise in cerebrovascular diseases.

Reduced cerebrovascular reserve is regionally associated with cortical thickness reductions in children with sickle cell disease

Sickle cell disease (SCD) is a genetic disorder which adversely affects cerebrovascular health. Previous studies have demonstrated regional cortical thinning in SCD. However, the reason behind regional reductions in cortical thickness remains unclear. Therefore, we aimed to explore the possible link between the state of cerebrovascular health and cortical thickness. In this study, we obtained magnetic resonance (MR) based measures of cerebrovascular reactivity (CVR), a measure of vascular health, and cortical thickness in SCD patients (N=60) and controls of similar age and similar gender ratio (N=27). The group comparison analysis revealed significant regionally specific reductions in CVR and cortical thickness in the SCD group compared to the controls. In addition, a regional association analysis was performed between CVR and cortical thickness in the SCD group which revealed a significant regional association in several brain regions with the highest strength of association observed in the left cuneus, right post central gyrus and the right temporal pole. The regional association analysis revealed that significant associations were found in brain regions with high metabolic activity (anterior cingulate, posterior cingulate, occipital gyrus, precuneus) thus demonstrating that these regions could be most vulnerable to structural damage under hypoxic conditions.

Developmental trajectories of cerebrovascular reactivity in healthy children and young adults assessed with magnetic resonance imaging

KEY POINTS

Cerebrovascular reactivity (CVR) reflects the vasodilatory reserve of cerebral resistance vessels. Normal development in children is associated with significant changes in blood pressure, cerebral blood flow (CBF) and cerebral oxygen metabolism. Therefore, it stands to reason that CVR will also undergo changes during this period. The study acquired magnetic resonance imaging measures of CVR and CBF in healthy children and young adults to trace their changes with age. We found that CVR changes in two phases, increasing with age until the mid-teens, followed by a decrease. Baseline CBF declined steadily with age. We conclude that CVR varies with age during childhood, which prompts future CVR studies involving children to take into account the effect of development.

ABSTRACT

Cerebrovascular reactivity (CVR) reflects the vasculature's ability to accommodate changes in blood flow demand thereby serving as a critical imaging tool for mapping vascular reserve. Normal development is associated with extensive physiological changes in blood pressure, cerebral blood flow and cerebral metabolic rate of oxygen, all of which can affect CVR. Moreover, the evolution of these physiological parameters is most prominent during childhood. Therefore, the aim of this study was to use non-invasive magnetic resonance imaging (MRI) to characterize the developmental trajectories of CVR in healthy children and young adults, and relate them to changes in cerebral blood flow (CBF). Thirty-four healthy subjects (17 males, 17 females; age 9-30 years) underwent CVR assessment using blood oxygen level-dependent MRI in combination with a computer controlled CO2 stimulus. In addition, baseline CBF was measured with a pulsed arterial spin labelling sequence. CVR exhibited a gradual increase with age in both grey and white matter up to 14.7 years. After this break point, a negative correlation with age was detected. Baseline CBF maintained a consistent negative linear correlation across the entire age range. The significant age-dependent changes in CVR and CBF demonstrate the evolution of cerebral haemodynamics in children and should be taken into consideration. The shift in developmental trajectory of CVR from increasing to decreasing suggests that physiological factors beyond baseline CBF also influence CVR.

Reproducibility of cerebrovascular reactivity measures in children using BOLD MRI

PURPOSE

To evaluate the reproducibility of cerebrovascular reactivity (CVR) measurements acquired in children using magnetic resonance imaging (MRI) in combination with a computer-controlled carbon dioxide (CO2 ) stimulus.

MATERIALS AND METHODS

Ten healthy children (age 16.1 ± 1.6 years) underwent CVR imaging on a 3T scanner using a blood-oxygen level-dependent (BOLD) MRI sequence. Targeted hypercapnia was induced during imaging with a CO2 gas challenge delivered using a specialized gas sequencer (RespirAct). A total of four BOLD scans were performed over 2 separate days to test within-day and between-day consistency of the data. CVR values were computed by correlating the relative change in BOLD signal in response to the CO2 stimulus delivered to the each subject.

RESULTS

Intraclass correlation coefficients (ICCs) of within-day values show highly reproducible measures in both the gray matter (ICC = 0.857, P < 0.001) and white matter (ICC = 0.895, P < 0.001). Relatively lower between-day reproducibility was observed in both the gray matter (ICC = 0.776, P = 0.001) and white matter (ICC = 0.719, P = 0.004).

CONCLUSION

Using a computer-controlled CO2 stimulus, we have demonstrated the reliability of BOLD-CVR measurements in pediatric subjects. Within-day and between-day metrics of reproducibility were comparable to adult data.

Dynamic contrast-enhanced MRI and CT provide comparable measurement of blood-brain barrier permeability in a rodent stroke model

In the current management of acute ischemic stroke (AIS), clinical criteria are used to estimate the risk of hemorrhagic transformation (HT), which is a devastating early complication. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and computed tomography (DCE-CT) may serve as physiologically-based decision making tools to more reliably assess the risk of HT. Before these tools can be properly validated, the comparability of the blood-brain barrier (BBB) permeability measurements they generate should be assessed. Sixteen rats were subjected to a transient middle cerebral artery occlusion before successively undergoing DCE-CT and DCE-MRI at 24-hours. BBB permeability (K(trans)) values were generated from both modalities. A correlation of R=0.677 was found (p<0.01) and the resulting relationship was [DCE-CT=(0.610*DCE-MRI)+4.140]. A variance components analysis found the intra-rat coefficient of variation to be 0.384 and 0.258 for K(trans) values from DCE-MRI and DCE-CT respectively. Permeability measures from DCE-CT were 22% higher than those from DCE-MRI. The results of this study demonstrate for the first time comparability between DCE-CT and DCE-MRI in the assessment of AIS. These results may provide a foundation for future clinical trials making combined use of these modalities.

Longitudinal assessment of imatinib's effect on the blood-brain barrier after ischemia/reperfusion injury with permeability MRI

Acute ischemic stroke (AIS) often results in degeneration of the blood-brain barrier (BBB), which can lead to vasogenic edema and an increased risk of intracerebral hemorrhage. Imatinib is an agent that may be able to protect the BBB and reduce the risk of the harmful consequences of BBB degeneration. We sought to measure the effect of Imatinib on the BBB after experimental stroke longitudinally in vivo with permeability dynamic contrast-enhanced MRI. Ischemia/reperfusion injury was induced with a transient middle cerebral artery occlusion surgery. Rats were given Imatinib at 2 and 20 h after stroke onset. Post-assessment included neurologic functioning, MR imaging, Evans Blue extravasation, Western blot, and immunohistology assay. Imatinib protected the BBB by 24 h but failed to decrease BBB permeability at an earlier time-point. Imatinib also reduced infarct volume, edema, and improved neurologic functioning by 24 h. Rats treated with Imatinib also had a higher expression of the BBB structural protein Zona ocludens-1 and a reduction in nuclear factor-kappa beta (NF-κβ) activation. Imatinib is a promising agent to protect the BBB after AIS, but its effect on the BBB may not become prominent until 24 h after the onset of ischemia. This finding may help elucidate Imatinib's role in the clinical management of AIS and influence future study designs.

Physiologic characterization of inflammatory arthritis in a rabbit model with BOLD and DCE MRI at 1.5 Tesla

OBJECTIVE

Our aim was to test the feasibility of blood oxygen level dependent magnetic resonance imaging (BOLD MRI) and dynamic contrast-enhanced (DCE) MRI to monitor periarticular hypoxic/inflammatory changes over time in a juvenile rabbit model of arthritis.

METHODS

We examined arthritic and contralateral nonarthritic knees of 21 juvenile rabbits at baseline and days 1,14, and 28 after induction of arthritis by unilateral intra-articular injection of carrageenin with BOLD and DCE MRI at 1.5 Tesla (T). Nine noninjected rabbits served as controls. Associations between BOLD and DCE-MRI and corresponding intra-articular oxygen pressure (PO2) and blood flow [blood perfusion units (BPU)] (polarographic probes, reference standards) or clinical-histological data were measured by correlation coefficients.

RESULTS

Percentage BOLD MRI change obtained in contralateral knees correlated moderately with BPU on day 0 (r = -0.51, p = 0.02) and excellently on day 28 (r = -0.84, p = 0.03). A moderate correlation was observed between peak enhancement DCE MRI (day 1) and BPU measurements in arthritic knees (r = 0.49, p = 0.04). In acute arthritis, BOLD and DCE MRI highly correlated (r = 0.89, p = 0.04; r = 1.0, p < 0.0001) with histological scores in arthritic knees.

CONCLUSION

The proposed techniques are feasible to perform at 1.5 T, and they hold potential as surrogate measures to monitor hypoxic and inflammatory changes over time in arthritis at higher-strength MRI fields.

KEY POINTS

• BOLD and DCE MRI detect interval perisynovial changes in a rabbit knee • BOLD and DCE MRI act as surrogate markers of physiologic changes in arthritis • BOLD MRI signal represents oxygen extraction compared with intra-articular PO 2 • DCE MRI measurements estimate physiologic periarticular vascular properties • In rabbit knees with acute arthritis, BOLD/DCE MRI highly correlated with histological scores.

Neuroproteome changes after ischemia/reperfusion injury and tissue plasminogen activator administration in rats: a quantitative iTRAQ proteomics study

The thrombolytic, recombinant tissue plasminogen activator (rt-PA) is the only approved therapy for acute ischemic stroke (AIS). When administered after AIS, rt-PA has many adverse pleiotropic actions, which are currently poorly understood. The identification of proteins showing differential expression after rt-PA administration may provide insight into these pleiotropic actions. In this study we used a 2D-LC MS/MS iTRAQ proteomic analysis, western blotting, and pathway analysis to analyze changes in protein expression 24-hours after rt-PA administration in the cortical brain tissue of 36 rats that underwent a sham or transient middle cerebral artery occlusion surgery. After rt-PA administration we reported alterations in the expressions of 18 proteins, many of which were involved in excitatory neurotransmitter function or cytoskeletal structure. The expression changes of GAD2 and EAAT1 were validated with western blot. The interactions between the identified proteins were analyzed with the IPA pathway analysis tool and three proteins: DPYSL2, RTN4, and the NF-kB complex, were found to have characteristics of being key proteins in the network. The differential protein expressions we observed may reflect pleiotropic actions of rt-PA after experimental stroke, and shine light on the mechanisms of rt-PA's adverse effects. This may have important implications in clinical settings where thrombolytic therapy is used to treat AIS.

Normal-appearing white matter permeability distinguishes poor cognitive performance in processing speed and working memory

BACKGROUND AND PURPOSE

Secondary-progressive MS is characterized by reduced acute inflammation and contrast enhancement but with increased axonal degeneration and cognitive/clinical disability that worsens with advanced disease. Relative recirculation, extracted from DSC is a surrogate measure of BBB integrity. We hypothesized that normal-appearing white matter relative recirculation is reduced in cognitively impaired compared with nonimpaired secondary-progressive MS, reflecting more advanced disease.

MATERIALS AND METHODS

Cognitive performance was classified as impaired or nonimpaired by use of Minimal Assessment of Cognitive Function In MS test components. Demographic data, brain parenchymal fraction, WM lesion fraction, and weighted mean normal-appearing white matter relative recirculation were compared in cognitively dichotomized groups. Univariate and multivariate logistic regressions were used to study the association between cognitive test results and normal-appearing white matter relative recirculation.

RESULTS

The mean (SD) age of 36 patients with secondary-progressive MS studied was 55.9 ± 9.3 years; 13 of 36 (36%) patients were male. A highly significant difference between normal-appearing white matter relative recirculation and WM lesion relative recirculation was present for all patients (P < .001). Normal-appearing white matter relative recirculation in impaired patients was significantly lower than in nonimpaired subjects for the Symbol Digit Modalities Test (P = .007), Controlled Word Association Test (P = .008), and Paced Auditory Serial Addition Test (P = .024). The Expanded Disability Status Scale demonstrated an inverse correlation with normal-appearing white matter relative recirculation (r = -0.319, P = .075). After adjustment for confounders, significant normal-appearing white matter relative recirculation reduction persisted for the Symbol Digit Modalities Test (P = .023) and the Paced Auditory Serial Addition Test (P = .047) but not for the Controlled Word Association Test (P = .13) in impaired patients.

CONCLUSIONS

Significant normal-appearing white matter relative recirculation reduction exists in cognitively impaired patients with secondary-progressive MS, localizing to the domains of processing speed and working memory.

Wavelets and fuzzy relational classifiers: a novel diffusion-weighted image analysis system for pediatric metabolic brain diseases

The diffusion-weighted imaging (DWI) technique can be utilized to investigate a variety of diseases. We propose an automated pilot system, which assists in the diagnosis of metabolic brain diseases, utilizing the DWI. In this study, DWI images are preprocessed and exponential apparent diffusion coefficient (eADC) images are produced. The eADC images are later brain extracted and normalized to a standard brain template. Subsequently, we utilized wavelets to denoise the eADC images. The images are rectified, thresholded and now conspicuous abnormal regions are subsequently identified utilizing different brain atlases. Abnormal regions constitute the features that will be used by a fuzzy relational classifier in order to categorize the diseases. A sensitivity and specificity of 60% and 93.33%, respectively, in detecting metabolic brain diseases have been achieved.

Noninvasive MRI measures of microstructural and cerebrovascular changes during normal swine brain development

The swine brain is emerging as a potentially valuable translational animal model of neurodevelopment and offers the ability to assess the impact of experimentally induced neurological disorders. The goal for this study was to characterize swine brain development using noninvasive MRI measures of microstructural and cerebrovascular changes. Thirteen pigs at various postnatal ages (2.3-43.5 kg) were imaged on a 1.5-Tesla MRI system. Microstructural changes were assessed using diffusion tensor imaging measures of mean diffusivity and fractional anisotropy. Cerebrovascular changes were assessed using arterial spin labeling measures of baseline cerebral blood flow (CBF) and the cerebrovascular reactivity (CVR) of the blood-oxygen level dependent (BOLD) MRI signal to CO2. We found a positive logarithmic relationship for regional tissue volumes and fractional anisotropy with body weight, which is similar to the pattern reported in the developing human brain. Unlike in the maturing human brain, no consistent changes in mean diffusivity or baseline CBF with development were observed. Changes in BOLD CVR exhibited a positive logarithmic relationship with body weight, which may impact the interpretation of functional MRI results at different stages of development. This animal model can be validated by applying the same noninvasive measures in humans.

Measurement of cerebrovascular reactivity in pediatric patients with cerebral vasculopathy using blood oxygen level-dependent MRI

BACKGROUND AND PURPOSE

Cerebrovascular reactivity (CVR) is an indicator of cerebral hemodynamics. In adults with cerebrovascular disease, impaired CVR has been shown to be associated with an increased risk of stroke. In children, however, CVR studies are not common. This may be due to the difficulties and risks associated with current CVR study methodologies. We have previously described the application of precise control of end-tidal carbon dioxide partial pressure for CVR studies in adults. Our aim is to report initial observations of CVR studies that were performed as part of a larger observational study regarding investigations in pediatric patients with cerebral vascular disease.

METHODS

Thirteen patients between the ages of 10 and 16 years (10 with a diagnosis of Moyamoya vasculopathy and 3 with confirmed, or suspected, intracranial vascular stenosis) underwent angiography, MRI, and functional blood oxygen level-dependent MRI mapping of CVR to hypercapnia. The results of the CVR study were then related to both the structural imaging and clinical status.

RESULTS

Sixteen blood oxygen level-dependent MRI CVR studies were performed successfully in 13 consecutive patients. Twelve of the 13 patients with angiographic abnormalities also had CVR deficits in the corresponding downstream vascular territories. CVR deficits were also seen in 8 of 9 symptomatic patients and 2 of the asymptomatic patients. Notably, in patients with abnormalities on angiography, the reductions in CVR extended beyond the ischemic lesions identified with MR structural imaging into normal-appearing brain parenchyma.

CONCLUSIONS

This is the first case series reporting blood oxygen level-dependent MRI CVR in children with cerebrovascular disease. CVR studies performed so far provide information regarding hemodynamic compromise, which complements traditional clinical assessment and structural imaging.

Assessment of tumor angiogenesis: dynamic contrast-enhanced MRI with paramagnetic nanoparticles compared with Gd-DTPA in a rabbit Vx-2 tumor model

The purpose of this study was to evaluate the suitability of a macromolecular MRI contrast agent (paramagnetic nanoparticles, PNs) for the characterization of tumor angiogenesis. Our aim was to estimate the permeability of PNs in developing tumor vasculature and compare it with that of a low molecular weight contrast agent (Gd-DTPA) using dynamic contrast-enhanced MRI (DCE). Male New Zealand white rabbits (n = 5) underwent DCE MRI 12-14 days after Vx-2 tumor fragments were implanted into the left hind limb. Each contrast agent (PNs followed by Gd-DTPA) was evaluated using a DCE protocol and transendothelial transfer coefficient (K(i)) maps were calculated using a two-compartment model. Two regions of interest (ROIs) were located within the tumor core and hindlimb muscle and five ROIs were placed within the tumor rim. Comparisons were performed using repeated measures analysis of variance (ANOVA). The K(i) values estimated using PNs were significantly lower than those obtained for Gd-DTPA (p = 0.018). When PNs and Gd-DTPA data were analyzed separately, significant differences were identified among tumor rim ROIs for PNs (p < 0.0001), but not for Gd-DTPA data (p = 0.34). The mean K(i) for the tumor rim was significantly greater than that of either the core or the hindlimb muscle for both contrast agents (p < 0.05 for each comparison). In summary, the extravasation of Gd-DTPA was far greater than that of PNs, suggesting that PNs can reveal regional differences in tumor vascular permeability that are not otherwise apparent with clinical contrast agents such as Gd-DTPA. These results suggest that PNs show potential for the noninvasive delineation of tumor angiogenesis.

Measuring the integrity of the human blood-brain barrier using magnetic resonance imaging

The evaluation of blood-brain barrier (BBB) integrity with contrast-enhanced magnetic resonance imaging (MRI) may prove valuable in the setting of certain brain pathologies, such as brain tumors and acute ischemic stroke. Various MRI protocols have been developed to explore the integrity of the BBB by monitoring the leakage of intravenously administered contrast medium into the brain parenchyma. In its simplest form, BBB integrity is assessed qualitatively, by determining the presence or absence of contrast-enhancement on a structural MR image. When a dynamic contrast-enhanced (DCE) MRI protocol is combined with a suitable pharmacokinetic model, DCE-MRI can map the spatial distribution of BBB integrity throughout the brain and assist with evaluating the effects of therapy. Several model-free surrogate measures of BBB permeability have been recently proposed, all of which can be readily computed from standard dynamic susceptibility contrast MRI perfusion scans. Contrast-enhanced MRI offers multiple strategies for evaluating BBB integrity.

Abstract 4318: Biomarker evaluation during an image-guided intracranial murine glioma study of radiation and sunitinib

Introduction: Tumour angiogenesis, a hallmark of glioblastoma multiforme, serves as a potential therapeutic target. Sunitinib (SU) is a multi-targeted tyrosine kinase inhibitor with antiantiogenic activity that may enhance radiation (RT) effects. In preclinical studies using intracranial (IC) mouse tumour models, a major challenge is the ability to evaluate IC tumour size, growth and vascular changes over time. This study aims to use an image-guided experimental design to evaluate the effects of RT and/or SU in an IC murine glioma model using serial micro-MRI and urine biomarkers with corresponding pathology, tumour growth delay (TGD) and survival (OS)outcomes.

Methods:

U87 glioma cells were inoculated by IC injection in the right frontal lobe of 58 NOD SCID mice. Imaging was performed on a 7-Tesla Bruker BioSpec on day 7 post-injection (treatment D0), D3, 7, 10, 14, 17 and 21. Mice with visible tumours on D0 T2-weighted (T2-w) imaging were stratified by tumour size to treatments: (1) control (CTRL) - placebo (2) RT - RT + placebo (3) SU - oral gavage SU (4) RT + SU. RT 8 Gy was delivered in 1 fraction to the right hemi-brain on D1 under image-guidance. SU 0.8 mg or placebo was administered by oral gavage. Serial imaging/analysis included: (1) T2-w imaging (2) Quantitative T1 (3) DCE-MRI - initial area under the DCE curve at 60 seconds (iAUC60) (4) diffusion weighted imaging - apparent diffusion coefficient (ADC) (5) contrast-enhanced T1-w imaging (T1-gad). Expression of angiogenesis markers were measured in serial urine samples. Pathological evaluation included tumour size, cell density, vessel density/permeability and apoptosis.

Results: Fifty-two mice with tumours were assigned to treatment arms such that mean tumour volume for each arm was 0.58 - 0.61mm3 (p&gt;0.05) on D0. No mice expired with serial contrast-enhanced imaging. OS was significantly better with RT (p=0.008) and SU+RT (p=0&lt;0.001) than CTRL, and SU+RT better than SU (p=0.018) and RT (p=0.05). Exponential tumour growth occurred in CTRLs but TGD was noted in all treatment arms until D14. Changes in iAUC60 showed trends/differences between treatment arms only at early timepoints: (1) RT - rise by D3 (2) SU - stable during SU (3) SU+RT - decrease of 30.1+6.8% by D3, maintained during SU. Baseline tumour ADC values were 8±5% above CL brain across all animals. Rise in ADC was greatest with RT and SU+RT (43±10%, 28±7%) than CTRL and SU (16±4%, 19±19%) at D10.

Conclusion: This study demonstrates the potential utility of image-guidance to augment murine intracranial tumour studies of RT and AA therapy. Survival was improved with combined SU+RT. Promising early biomarkers of response identified to date include DCE at D3, and ADC at D10, warranting further investigation in a larger cohort. Further study of these markers may improve temporal characterization of vessel normalization and enable studies to optimize scheduling of antiangiogenic therapies with radiation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4318.

Blood-oxygen level dependent MRI measures of cerebrovascular reactivity using a controlled respiratory challenge: reproducibility and gender differences

PURPOSE

To evaluate the reproducibility and gender differences in cerebrovascular reactivity (CVR) measurements obtained using the blood-oxygen level dependent (BOLD) response to controlled changes in end-tidal partial pressure of carbon dioxide (PETCO(2)).

MATERIALS AND METHODS

We obtained ethical approval to image 19 healthy volunteers (10 men, 9 women) on a 1.5 Tesla (T) MRI scanner twice on two separate days using identical procedures. CVR images were generated by collecting BOLD MRI data during controlled changes in PETCO(2) induced by a sequential gas delivery system.

RESULTS

Using the intraclass correlation coefficient (ICC), we demonstrated excellent within-day CVR measures in gray matter (GM) (ICC = 0.92) and white matter (WM) (ICC = 0.88) regions, excellent between-day reproducibility in GM (ICC = 0.81), and good between-day reproducibility in the WM (ICC = 0.66). CVR values between men and women were significantly different in the GM and WM. Men exhibited a 22 +/- 2% greater CVR in GM and a 17 +/- 2% greater CVR in WM compared with females.

CONCLUSION

Our results demonstrate the reliability of BOLD MRI CVR measurements obtained using a controlled cerebrovascular challenge. Using this technique, we also revealed significantly increased BOLD response to CO(2) in males compared with females.

Texture analysis: a review of neurologic MR imaging applications

Texture analysis describes a variety of image-analysis techniques that quantify the variation in surface intensity or patterns, including some that are imperceptible to the human visual system. Texture analysis may be particularly well-suited for lesion segmentation and characterization and for the longitudinal monitoring of disease or recovery. We begin this review by outlining the general procedure for performing texture analysis, identifying some potential pitfalls and strategies for avoiding them. We then provide an overview of some intriguing neuro-MR imaging applications of texture analysis, particularly in the characterization of brain tumors, prediction of seizures in epilepsy, and a host of applications to MS.