Meta-analysis of apparent diffusion coefficients in the newborn brain

Cerebral microstructural changes in children suffering from hemolytic uremic syndrome

To evaluate microstructural cerebral changes in children suffering from typical hemolytic uremic syndrome (HUS) based on apparent diffusion coefficient (ADC) maps. For 12 pediatric HUS patients (0.8 - 14.6 years of age) conventional magnetic resonance imaging (cMRI) at 1.5 T was retrospectively analyzed. ADC values were measured in 35 different brain regions and compared with age-related, previously published ADC reference values from a healthy pediatric control group. The HUS cohort was divided into 2 subgroups depending on clinical outcome. Subgroup A showed poor neurological outcome whereas subgroup B demonstrated improvement without lasting neurological deficits. Qualitative analysis revealed lesions by diffusion-weighted imaging (DWI) with hypointense correlate on the ADC map in basal ganglia and/or thalami and corresponding T2 hyperintensities in the majority of patients in Subgroup A (80%). Those in Subgroup B did not show qualitative DWI alterations with ADC correlate even when T2 hyperintense lesions were detected in basal ganglia and/or thalami. Quantitative analysis demonstrated abnormal ADC values in all HUS patients with a trend to a greater number of affected regions in Subgroup A compared to Subgroup B (16 versus 11 median number of regions respectively, p = 0.56).   Conclusion: Using DWI qualitative and quantitative differences were found between HUS patients showing poor neurological outcome and those without neurological deficits at discharge. While ADC values indicated more extensive cerebral changes than conventional qualitative findings, both may provide early prognostic indicators for neurological outcome in pediatric HUS patients. What is Known: • In patients with STEC-HUS and neurological symptoms, MRI may show hyperintense signals on T2 and altered diffusivity mostly affecting basal ganglia, thalami and periventricular white matter. What is New: • In such patients, early MRI including quantitative ADC measurements over different brain regions may allow for detection of signal alterations possibly reflecting microstructural changes in such patients.

Brain injury patterns in hypoxic ischemic encephalopathy of term neonates

BACKGROUND AND PURPOSE

Topographic patterns of brain injury in neonates can help with differentiation and prognostic categorization of hypoxic ischemic encephalopathy (HIE). In this study, we quantitatively and objectively characterized the location of hypoxic ischemic lesions in term neonates with varying severity of HIE.

METHODS

We analyzed term neonates (born ≥37 postmenstrual gestational weeks) with MRI diffusion-weighted imaging (DWI) and diagnoses of HIE. Neonates' HIE was categorized into mild, moderate, and severe. The hypoxic ischemic lesions were segmented on DWI series with attention to T1- and T2-weighted images and then co-registered onto standard brain space to generate summation maps for each severity category. Applying voxel-wise general linear models, we also identified cerebral regions more likely to infarct with increasing severity of HIE, after correction for lesion volume and time-to-scan as covariates.

RESULTS

We included 33 neonates: 20 with mild, eight with moderate, and five with severe HIE. Infarct volumes (p = .00052) and Appearance, Pulse, Grimace, Activity, and Respiration scores at 1 minute (p = .032) differed between HIE severity categories. Hypoxic ischemic lesions in neonates with mild and moderate HIE were predominant in subcortical and deep white matter along the border zones of arterial supply territories, while severe HIE also involved basal ganglia, hippocampus, and thalamus. In voxel-wise analysis, higher severity of HIE was associated with the presence of lesions in hippocampus, thalamus, and lentiform nucleus.

CONCLUSIONS

In term neonates, mild/moderate HIE is associated with infarctions of arterial territory watershed zones, whereas severe HIE distinctively involves basal ganglia, thalami, and hippocampi.

Age-related topographic map of magnetic resonance diffusion metrics in neonatal brains

Accelerated maturation of brain parenchyma close to term-equivalent age leads to rapid changes in diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) metrics of neonatal brains, which can complicate the evaluation and interpretation of these scans. In this study, we characterized the topography of age-related evolution of diffusion metrics in neonatal brains. We included 565 neonates who had MRI between 0 and 3 months of age, with no structural or signal abnormality-including 162 who had DTI scans. We analyzed the age-related changes of apparent diffusion coefficient (ADC) values throughout brain and DTI metrics (fractional anisotropy [FA] and mean diffusivity [MD]) along white matter (WM) tracts. Rate of change in ADC, FA, and MD values across 5 mm cubic voxels was calculated. There was significant reduction of ADC and MD values and increase of FA with increasing gestational age (GA) throughout neonates' brain, with the highest temporal rates in subcortical WM, corticospinal tract, cerebellar WM, and vermis. GA at birth had significant effect on ADC values in convexity cortex and corpus callosum as well as FA/MD values in corpus callosum, after correcting for GA at scan. We developed online interactive atlases depicting age-specific normative values of ADC (ages 34-46 weeks), and FA/MD (35-41 weeks). Our results show a rapid decrease in diffusivity metrics of cerebral/cerebellar WM and vermis in the first few weeks of neonatal age, likely attributable to myelination. In addition, prematurity and low GA at birth may result in lasting delay in corpus callosum myelination and cerebral cortex cellularity.

Three-Dimensional Magnetic Resonance Fingerprinting in Neonates: Quantifying Regional Difference and Maturation in the Brain

OBJECTIVES

Magnetic resonance fingerprinting (MRF) allows the simultaneous measurement of multiple tissue properties in a single acquisition. Three-dimensional (3D) MRF with high spatial resolution can be used for neonatal brain imaging. The aim of this study is to apply 3D MRF to neonates and show regional differences and maturation in the brain.

MATERIALS AND METHODS

In this prospective study, 3D MRF using hybrid radial-interleaved acquisition was performed on phantoms and neonates from December 2019 to October 2020. For the reconstruction of 3D MRF, singular value decomposition was applied to reduce reconstruction time, and the iterative reconstruction technique was applied to improve image quality. The accuracies of T1 and T2 values derived from 3D MRF were evaluated in a phantom experiment. Regional T1 and T2 values were obtained from neonates' brain T1 and T2 maps derived from 3D MRF. Regional T1 and T2 values were compared, and their changes according to corrected gestational age were evaluated.

RESULTS

The acquisition time for 3D MRF with a spatial resolution of 0.7 × 0.7 × 2 mm3 was less than 5 minutes. The phantom study showed high correlation between T1 and T2 values derived from 3D MRF and those from conventional spin echo sequences (T1, R2 = 0.998, P < 0.001; T2, R2 = 0.998, P < 0.001). Three-dimensional MRF was performed in 25 neonates (15 boys, 10 girls; median corrected gestational age, 263 days; interquartile range, 10 days). In neonates, T1 and T2 values differed in the frontal (median [interquartile range], 2785 [2684-2888] milliseconds and 189.8 [176.7-222.9] milliseconds), parietal (2849 [2741-2950] milliseconds and 191.6 [167.5-232.9] milliseconds), and occipital white matter (2621 [2513-2722] milliseconds and 162.9 [143.5-186.1] milliseconds), showing lower values in occipital white matter (P < 0.001). Regional T1 values showed a negative relationship with corrected gestational age (coefficient, -0.775 to -0.480; P < 0.05).

CONCLUSIONS

Fast and high spatial resolution 3D MRF was applied to neonates. T1 and T2 maps derived from 3D MRF enabled the quantification of regional differences and maturation in the neonatal brain.

Role of the noninvasive imaging techniques in monitoring and understanding the evolution of brain edema

Human brain injury elicits accumulation of water within the brain due to a variety of pathophysiological processes. As our understanding of edema emerged two temporally (and cellular) distinct processes were identified, cytotoxic and vasogenic edema. The emergence of both types of edema is reflected by the temporal evolution and is influenced by the underlying pathology (type and extent). However, this two-edema compartment model does not adequately describe the transition between cytotoxic and vasogenic edema. Hence, a third category has been proposed, termed ionic edema, that is observed in the transition between cytotoxic and vasogenic edema. Magnetic resonance neuroimaging of edema today primarily utilizes T2-weighted (T2WI) and diffusion-weighted imaging (DWI). Clinical diagnostics and translational science studies have clearly demonstrated the temporal ability of both T2WI and DWI to monitor edema content and evolution. DWI measures water mobility within the brain reflecting cytotoxic edema. T2WI at later time points when vasogenic edema develops visualizes increased water content in the brain. Clinically relevant imaging modalities, including ultrasound and positron emission tomography, are not typically used to assess edema. In sum, edema imaging is an important cornerstone of clinical diagnostics and translational studies and can guide effective therapeutics manage edema and improve patient outcomes.

Multidelay Arterial Spin-Labeling MRI in Neonates and Infants: Cerebral Perfusion Changes during Brain Maturation

BACKGROUND AND PURPOSE

Arterial spin-labeling with multiple postlabeling delays can correct transit times. We tried to evaluate CBF in neonates and infants using multidelay arterial spin-labeling.

MATERIALS AND METHODS

Multidelay arterial spin-labeling was applied to 13 preterm neonates (mean postmenstrual age, 34.9 weeks), 13 term-equivalent-age neonates (mean postmenstrual age, 39.2 weeks), and 6 infants (mean postmenstrual age, 57.8 weeks). Transit time-corrected CBF in the caudate, thalamus, frontal GM, occipital GM, frontal WM, and occipital WM was measured, and relative CBF compared with the whole-brain CBF was calculated. Inter- and intragroup comparisons were performed among the 3 age groups. A correlation and nonlinear regression analysis were performed between postmenstrual age and CBF.

RESULTS

Intergroup comparisons showed significantly higher whole-brain CBF in infants (38.3 mL/100 g/min) compared with preterm (15.5 mL/100 g/min) and term-equivalent-age (18.3 mL/100 g/min) neonates (P < .001). In the intragroup comparison, all 3 groups showed significantly higher relative CBF values in the occipital WM (63.6%-90.3%) compared with the frontal WM (46.3%-73.9%). In term-equivalent-age neonates, the occipital GM (120.8%) had significantly higher relative CBF values than the frontal GM (103.5%). There was a significant negative correlation between postmenstrual age and the relative CBF of the thalamus (r = - 0.449, P = .010). There were significant positive relationships between postmenstrual age and the relative CBF of the frontal WM (R ² = 0.298, P = .001) and occipital WM (R ² = 0.452, P < .001).

CONCLUSIONS

Multidelay arterial spin-labeling with transit time-corrected CBF showed developmental changes and regional differences of CBF in neonates and infants.

Early Imaging and Adverse Neurodevelopmental Outcome in Asphyxiated Newborns Treated With Hypothermia

BACKGROUND

Brain injury can be identified as early as day two of life in asphyxiated newborns treated with hypothermia, when using diffusion magnetic resonance imaging (MRI). However, it remains unclear whether these diffusion changes can predict future neurodevelopment. This study aimed to determine whether abnormal early diffusion changes in newborns treated with hypothermia are associated with adverse neurodevelopmental outcome at age two years.

METHODS

Asphyxiated newborns treated with hypothermia were enrolled prospectively. They underwent magnetic resonance imaging (MRI) at specific time points over the first month of life, including diffusion-weighted imaging and diffusion-tensor imaging. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in different regions of interest. Adverse neurodevelopmental outcome was defined as cerebral palsy, global developmental delay, and/or seizure disorder around age two years. ADC and FA values were compared between the newborns developing or not developing adverse outcome.

RESULTS

Twenty-nine asphyxiated newborns treated with hypothermia were included. Among the newborns developing adverse outcome, ADC values were significantly decreased on days two to three of life and increased around day ten of life in the thalamus, posterior limb of the internal capsule, and the lentiform nucleus. FA values decreased in the same regions around day 30 of life. These newborns also had increased ADC around day ten of life and around day 30 of life, and decreased FA around day 30 of life in the anterior and posterior white matter.

CONCLUSIONS

Diffusion changes that were evident as early as day two of life, when the asphyxiated newborns were still treated with hypothermia, were associated with later abnormal neurodevelopmental outcome.

Can cerebellar and brainstem apparent diffusion coefficient (ADC) values predict neuromotor outcome in term neonates with hypoxic-ischemic encephalopathy (HIE) treated with hypothermia?

Background and purpose

To determine the apparent diffusion coefficient (ADC) in specific infratentorial brain structures during the first week of life and its relation with neuromotor outcome for Hypoxic-ischemic encephalopathy (HIE) in term neonates with and without whole-body hypothermia (TH).

Materials and methods

We retrospectively evaluated 45 MRI studies performed in the first week of life of term neonates born between 2010 and 2013 at Boston Children's Hospital. Selected cases were classified into three groups: 1) HIE neonates who underwent TH, 2) HIE normothermics (TN), and 3) controls. The neuromotor outcome was categorized as normal, abnormal and death. The ADC_mean was calculated for six infratentorial brain regions.

Results

A total of 45 infants were included: 28 HIE TH treated, 8 HIE TN, and 9 controls. The mean gestational age was 39 weeks; 57.8% were male; 11.1% were non-survivors. The median age at MRI was 3 days (interquartile range, 1–4 days). A statistically significant relationship was shown between motor outcome or death and the ADC_mean in the vermis (P = 0.002), cerebellar left hemisphere (P = 0.002), midbrain (P = 0.009), pons (P = 0.014) and medulla (P = 0.005). In patients treated with TH, the ADC _mean remained significantly lower than that in the controls only in the hemispheres (P = 0.01). In comparison with abnormal motor outcome, ADC_mean was lowest in the left hemisphere (P = 0.003), vermis (P = 0.003), pons (P = 0.0036) and medulla (P = 0.008) in case of death.

Conclusion

ADC_mean values during the first week of life in the left hemisphere, vermis, pons and medulla are related to motor outcome or death in infants with HIE either with or without hypothermic therapy. Therefore, this objective tool can be assessed prospectively to determine if it can be used to establish prognosis in the first week of life, particularly in severe cases of HIE.

Changes in brain microstructure during infancy and childhood using clinical feasible ADC-maps

PURPOSE

The purpose of this study was to examine age-related changes in apparent diffusion coefficient (ADC) during infancy and childhood using routine MRI data.

METHODS

A total of 112 investigations of patients aged 0 to 17.2 years showing a normal degree of myelination and no signal abnormalities on conventional MRI were retrospectively selected from our pool of pediatric MRI examinations at 1.5T. ADC maps based on our routinely included axial diffusion weighted sequence were created from the scanner. ADC values were measured in 35 different brain regions investigating normal age-related changes during the maturation of the human brain in infancy and childhood using clinical feasible sequences at 1.5T.

RESULTS

The relationship between ADC values and age in infancy and childhood can be described as an exponential function. With increasing age, the ADC values decrease significantly in all brain regions, especially during the first 2 years of life. Except in the peritrigonal white matter, no significant differences were found between both hemispheres. Between 0 and 2 years of life, no significant gender differences were detected.

CONCLUSIONS

Using ADC maps based on a routinely performed axial diffusion weighted sequence, it was possible first to describe the relationship between ADC values and age in infancy and childhood as exponential function in the whole brain and second to determine normative age-related ADC values in multiple brain regions.

Automatic quantification of ischemic injury on diffusion-weighted MRI of neonatal hypoxic ischemic encephalopathy

A fully automatic method for detection and quantification of ischemic lesions in diffusion-weighted MR images of neonatal hypoxic ischemic encephalopathy (HIE) is presented. Ischemic lesions are manually segmented by two independent observers in 1.5 T data from 20 subjects and an automatic algorithm using a random forest classifier is developed and trained on the annotations of observer 1. The algorithm obtains a median sensitivity and specificity of 0.72 and 0.99 respectively. F1-scores are calculated per subject for algorithm performance (median = 0.52) and observer 2 performance (median = 0.56). A paired t-test on the F1-scores shows no statistical difference between the algorithm and observer 2 performances. The method is applied to a larger dataset including 54 additional subjects scanned at both 1.5 T and 3.0 T. The algorithm findings are shown to correspond well with the injury pattern noted by clinicians in both 1.5 T and 3.0 T data and to have a strong relationship with outcome. The results of the automatic method are condensed to a single score for each subject which has significant correlation with an MR score assigned by experienced clinicians (p < 0.0001). This work represents a quantitative method of evaluating diffusion-weighted MR images in neonatal HIE and a first step in the development of an automatic system for more in-depth analysis and prognostication.

The Value of Diffusion-Weighted Imaging in the Differential Diagnosis of Ovarian Lesions: A Meta-Analysis

OBJECTIVES

The ability of contrast-enhanced MRI to distinguish between malignant and benign ovarian masses is limited. The aim of this meta-analysis is to evaluate the diagnostic performance of diffusion-weighted imaging (DWI) in differentiating malignant from benign ovarian masses.

METHODS

A comprehensive literature search was performed in several authoritative databases to identify relevant articles. The weighted mean difference (WMD) and corresponding 95% confidence interval (95% CI) were calculated. We also used subgroup analysis to analyze study heterogeneity, and evaluated publication bias.

RESULTS

The meta-analysis is based on 21 studies, which reported the findings for 731 malignant and 918 benign ovarian masses. There was no significant difference in apparent diffusion coefficient (ADC) values for DWI between benign and malignant lesions (WMD = 0.22, 95% CI = -0.02-0.47, p = 0.08). Subgroup analysis by benign tumor type revealed higher ADC values (or a trend toward higher values) for cysts, cystadenomas and other benign tumors compared to malignant masses (cyst: WMD = 0.54, 95% CI = -0.05-1.12, p = 0.07; cystadenoma: WMD = 0.73, 95% CI = 0.38-1.07, p < 0.0001; other benign tumor: WMD = 0.16, 95% CI = -0.13-0.46, p = 0.28). On the other hand, lower ADC values (or a trend toward lower values) were observed for endometrioma and teratoma compared to malignant masses (endometrioma: WMD = -0.09, 95% CI = -0.47-0.29, p = 0.64; teratoma: WMD = -0.49, 95% CI = -0.85-0.12, p = 0.009). Subgroup analysis by mass property revealed higher ADC values in cystic tumor types than in solid types for both benign and malignant tumors. Significant study heterogeneity was observed. There was no notable publication bias.

CONCLUSIONS

Quantitative DWI is not a reliable diagnostic method for differentiation between benign and malignant ovarian masses. This knowledge is essential in avoiding misdiagnosis of ovarian masses.

Evolution of Apparent Diffusion Coefficient and Fractional Anisotropy in the Cerebrum of Asphyxiated Newborns Treated with Hypothermia over the First Month of Life

The objective of this study was to assess the evolution of diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI) over the first month of life in asphyxiated newborns treated with hypothermia and to compare it with that of healthy newborns. Asphyxiated newborns treated with hypothermia were enrolled prospectively; and the presence and extent of brain injury were scored on each MRI. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in the basal ganglia, in the white matter and in the cortical grey matter. Sixty-one asphyxiated newborns treated with hypothermia had a total of 126 ADC and FA maps. Asphyxiated newborns developing brain injury eventually had significantly decreased ADC values on days 2-3 of life and decreased FA values around day 10 and 1 month of life compared with those not developing brain injury. Despite hypothermia treatment, asphyxiated newborns may develop brain injury that still can be detected with advanced neuroimaging techniques such as DWI and DTI as early as days 2-3 of life. A study of ADC and FA values over time may aid in the understanding of how brain injury develops in these newborns despite hypothermia treatment.

Diffusion-weighted imaging of focal renal lesions: a meta-analysis

OBJECTIVES

Contrast-enhanced MRI can only distinguish to a limited extent between malignant and benign focal renal lesions. The aim of this meta-analysis is to review renal diffusion-weighted imaging (DWI) to compare apparent diffusion coefficient (ADC) values for different renal lesions that can be applied in clinical practice.

METHODS

A PubMed search was performed to identify relevant articles published 2004-2011 on renal DWI of focal renal lesions. ADC values were extracted by lesion type to determine whether benign or malignant. The data table was finalised in a consensus read. ADC values were evaluated statistically using meta-regression based on a linear mixed model. Two-sided P value <5 % indicated statistical significance.

RESULTS

The meta-analysis is based on 17 studies with 764 patients. Renal cell carcinomas have significant lower ADC values than benign tissue (1.61 ± 0.08 × 10(-3) mm(2)/s vs 2.10 ± 0.09 × 10(-3) mm(2)/s; P < 0.0001). Uroepithelial malignancies can be differentiated by lowest ADC values (1.30 ± 0.11 × 10(-3) mm(2)/s). There is a significant difference between ADC values of renal cell carcinomas and oncocytomas (1.61 ± 0.08 × 10(-3) mm(2)/s vs 2.00 ± 0.08 × 10(-3) mm(2)/s; P < 0.0001).

CONCLUSIONS

Evaluation of ADC values can help to determine between benign and malignant lesions in general but also seems able to differentiate oncocytomas from malignant tumours, hence potentially reducing the number of unnecessarily performed nephrectomies.

KEY POINTS

• This meta-analysis assesses the role of diffusion-weighted MRI in renal lesions. • ADC values obtained by DW MRI have been compared for different renal lesions. • ADC values can help distinguish between benign and malignant tumours. • Differentiating oncocytomas from malignant tumours can potentially reduce inappropriate nephrectomies.

Automated core-penumbra quantification in neonatal ischemic brain injury

Neonatal hypoxic-ischemic brain injury (HII) and arterial ischemic stroke (AIS) result in irreversibly injured (core) and salvageable (penumbral) tissue regions. Identification and reliable quantification of salvageable tissue is pivotal to any effective and safe intervention. Magnetic resonance imaging (MRI) is the current standard to distinguish core from penumbra using diffusion-perfusion mismatch (DPM). However, subtle MR signal variations between core-penumbral regions make their visual delineation difficult. We hypothesized that computational analysis of MRI data provides a more accurate assessment of core and penumbral tissue evolution in HII/AIS. We used two neonatal rat-pup models of HII/AIS (unilateral and global hypoxic-ischemia) and clinical data sets from neonates with AIS to test our noninvasive, automated computational approach, Hierarchical Region Splitting (HRS), to detect and quantify ischemic core-penumbra using only a single MRI modality (T2- or diffusion-weighted imaging, T2WI/DWI). We also validated our approach by comparing core-penumbral images (from HRS) to DPM with immunohistochemical validation of HII tissues. Our translational and clinical data results showed that HRS could accurately and reliably distinguish the ischemic core from penumbra and their spatiotemporal evolution, which may aid in the vetting and execution of effective therapeutic interventions as well as patient selection.

Cerebral white matter and neurodevelopment of preterm infants after coagulase-negative staphylococcal sepsis

OBJECTIVE

Coagulase-negative staphylococci are the most common pathogens causing late-onset sepsis in the neonatal intensive care unit. Neonatal sepsis can be associated with cerebral white matter damage in preterm infants. Neurodevelopment has been shown to be correlated with apparent diffusion coefficients, fractional anisotropy, and axial and radial diffusivities of the white matter.

DESIGN

Prospective cohort study.

SETTING

Twenty-eight-bed neonatal intensive care unit at a tertiary care children's hospital.

PATIENTS

Seventy preterm infants (gestational age <32 wks), 28 with coagulase-negative staphylococcal sepsis (group 1) and 42 without sepsis (group 2).

INTERVENTION

The values of apparent diffusion coefficients, fractional anisotropy, and axial and radial diffusivity of three white matter regions (parietal, frontal, and occipital), estimated with diffusion-tensor magnetic resonance imaging with a 3.0-T magnetic resonance imaging system, were obtained at term-equivalent age. Neurodevelopmental outcome assessments were performed at 15 months (Griffiths Mental Developmental Scales) and 24 months (Bayley Scales of Infant and Toddler Development, Third Edition) corrected age.

MEASUREMENTS AND MAIN RESULTS

Values of apparent diffusion coefficients, fractional anisotropy, and axial and radial diffusivity of the left and right white matter regions were equal in all patients. There was no significant difference in apparent diffusion coefficient values (mean of total: 1.593 ± 0.090 × 10mm(-3)/sec(2) and 1.601 ± 0.117 × 10mm(-3)/sec(2), respectively, p = .684), fractional anisotropy values (mean of total: 0.19 ± 0.04 and 0.19 ± 0.03, respectively, p = .350), radial diffusivity (mean of total: 1.420 ± 0.09 × 10mm(-3)/sec(2)and 1.425 ± 0.12 × 10mm(-3)/sec(2), respectively, p = .719), and axial diffusivity (mean of total: 1.940 ± 0.12 × 10mm(-3)/sec(2) and 1.954 ± 0.13 × 10mm(-3)/sec(2), respectively, p = .590) in the three combined regions between the two groups. No significant differences were found in neurodevelopmental outcome at 24 months.

CONCLUSIONS

No association was found between coagulase-negative staphylococcal sepsis in preterm infants and cerebral white matter damage as determined by values of apparent diffusion coefficients, fractional anisotropy, and radial and axial diffusivity at term-equivalent age, and no adverse effect was seen on early neurodevelopmental outcome.

Progression of corpus callosum diffusion-tensor imaging values during a period of signal changes consistent with myelination

OBJECTIVE

Changes in signal intensity on T1- and T2-weighted MR images consistent with myelination in the corpus callosum occur during months 3-9 of postnatal life and occur earlier in the splenium than in the genu. We hypothesized that the rate of change in diffusion-tensor imaging parameters in the first year of life would be greater in the splenium, especially during months 3-9.

SUBJECTS AND METHODS

Fifty-two infants (age range, 0-52 weeks) underwent one MRI examination with a six-direction diffusion-tensor imaging sequence. Fractional anisotropy, apparent diffusion coefficient, radial diffusivity, and axial diffusivity were measured in the genu and splenium of the corpus callosum. For each parameter, the slopes of change in the splenium and in the genu were measured for the entire first year of life and for the age period 3-9 months. The ratios of slope of change in the splenium to that in the genu in these two periods were compared.

RESULTS

For fractional anisotropy, the ratio of slope of change in the splenium to that in the genu was 1.67 in the first year and 4.00 for 3-9 months; apparent diffusion coefficient, 2.00 in the first year and 4.33 for 3-9 months; radial diffusivity, 1.75 in the first year and 4.40 for 3-9 months; and axial diffusivity, 3.25 in the first year and 4.86 for 3-9 months.

CONCLUSION

Rates of change were always greater in the splenium. For the age period 3-9 months, the splenium-to-genu ratio was approximately 1.5- to 2.5-fold as high as that for the entire year. These findings correspond well with the sequence of signal intensity changes in the corpus callosum.

Long-term magnetic resonance imaging of stem cells in neonatal ischemic injury

OBJECTIVE

Quantitative magnetic resonance imaging (MRI) can serially and noninvasively assess the degree of injury in rat pup models of hypoxic ischemic injury (HII). It can also noninvasively monitor stem cell migration following iron oxide prelabeling. Reports have shown that neural stem cells (NSCs) may help mediate neuroprotection or stimulate neuroreparative responses in adult and neonatal models of ischemic injury. We investigated the ability of high-field MRI to monitor and noninvasively quantify the migration, proliferation, and location of iron oxide-labeled NSCs over very long time periods (58 weeks) in real time while contemporaneously correlating this activity with the evolving severity and extent of neural damage.

METHODS

Labeled clonal murine NSCs (mNSCs) were implanted 3 days after unilateral HII in 10-day-old rat pups into the contralateral striatum or ventricle. We developed methods for objectively quantifying key aspects of dynamic NSC behavior (eg, viability; extent, and speed of migration; degree of proliferation; extent of integration into host parenchyma). MRI images were validated with histological and immunohistochemical assessments.

RESULTS

mNSCs rapidly migrated (100 μm/day) to the lesion site. Chains of migrating NSCs were observed in the corpus callosum. In pups subjected to HII, though not in intact control animals, we observed a 273% increase in the MR-derived volume of mNSCs 4 weeks after implantation (correlating with the known proliferative behavior of endogenous and exogenous NSCs) that slowly declined over the 58-week time course, with no adverse consequences. Large numbers of now quiescent mNSCs remained at the site of injury, many retaining their iron oxide label.

INTERPRETATION

Our studies demonstrate that MRI can simultaneously monitor evolving neonatal cerebral injury as well as NSC migration and location. Most importantly, it can noninvasively monitor proliferation dynamically for prolonged time periods. To be able to pursue clinical trials in newborns using stem cell therapies it is axiomatic that safety be insured through the long-term real time monitoring of cell fate and activity, particularly with regard to observing unanticipated risks to the developing brain. This study supports the feasibility of reliably using MRI for this purpose.

Magnetic resonance imaging in neonatal stroke

Neonatal stroke occurs in 1 in 2300-5000 live births, the incidence of which is lower than that in adults, but still higher than that in childhood. The higher incidence of perinatal stroke in preterm and term infants compared to stroke in childhood may be partly explained by higher detection rates using routine fetal ultrasound and postnatal cranial sonography. In addition, there is greater availability of magnetic resonance imaging (MRI) for neuroimaging in preterm and full-term infants, which is due in part to the availability of MR-compatible incubators and MR systems at or near the neonatal intensive care unit. In addition, the wide range of MR techniques, such as T2-, diffusion- and susceptibility-weighted imaging allows improved visualization and quantification of neonatal stroke or hypoxic-ischemic injury. This chapter reviews the MR neuroimaging modalities that actually assist the clinician in the detection of neonatal stroke.