Search

The magnetization transfer ratio (MTR) and diffusion tensor imaging (DTI) correlates of early brain development were examined in cohort of 18 very preterm neonates (27-31 gestational weeks) presenting with normal radiological findings scanned within 2weeks after birth (28-32 gestational weeks). A combination of non-linear image registration, tissue segmentation, and voxel-wise regression was used to map the age dependent changes in MTR and DTI-derived parameters in 3D across the brain based on the cross-sectional in vivo preterm data. The regression coefficient maps obtained differed between brain regions and between the different quantitative MRI indices. Significant linear increases as well as decreases in MTR and DTI-derived parameters were observed throughout the preterm brain. In particular, the lamination pattern in the cerebral wall was evident on parametric and regression coefficient maps. The frontal white matter area (subplate and intermediate zone) demonstrated a linear decrease in MTR. While the intermediate zone showed an unexpected decrease in fractional anisotropy (FA) with age, with this decrease (and the increase in mean diffusivity (MD)) driven primarily by an increase in radial diffusivity (RD) values, the subplate showed no change in FA (and an increase in MD). The latter was the result of a concomitant similar increase in axial diffusivity (AD) and RD values. Interpreting the in vivo results in terms of available histological data, we present a biophysical model that describes the relation between various microstructural changes measured by complementary quantitative methods available on clinical scanners and a range of maturational processes in brain tissue.

Aim The aim of this study was to determine the feasibility of undertaking visual functional magnetic resonance imaging (fMRI) in very preterm children. Method Forty-seven infants born at less than 32 weeks gestational age (25 males, 22 females; mean (SD) age at birth 28.8wks [1.9]) were scanned using 1.5T MRI as part of a longitudinal neuroimaging study. These infants were scanned at preterm age (within 2wks of birth) and at term-equivalent age. Quantitative T2* data and fMRI in response to visual stimuli (flashing strobe) were acquired in this population. T2* values were compared at preterm age and at term-equivalent age using a two-tailed t-test. A general linear model was used to evaluate occipital lobe response to visual stimuli. Results T2* values were significantly higher at preterm age than at term-equivalent age in both the medial and lateral occipital lobes (preterm infants: 187.2ms and 198.4ms respectively; term infants: 110.9ms and 133.2ms respectively; p

To elucidate the relationship between gestational age, pathologic findings, and magnetic resonance (MR) imaging measures of tissue maturation-myelination in deep gray matter areas in very preterm neonates imaged at birth.The study was approved by the research ethics board. Written informed consent was given by the infants' parents. Forty-two preterm neonates (19 boys; median gestational age, 28.7 weeks) with normal-appearing gray matter structures at presentation underwent MR imaging within 2 weeks of birth that included T1- and T2-weighted, magnetization transfer, and T1 relaxometry sequences. Neonates were separated into the following groups: those with normal findings (n = 23), those with white matter injury (WMI) (n = 9), those with grade I germinal matrix hemorrhage (GMH) (n = 3), and those with grade II GMH and WMI (n = 7). Analysis of covariance was used to determine regional effects of age and pathologic findings on magnetization transfer ratio (MTR) and to assess the relationship between MTR and T1.MTR increased linearly with age (P ≤ .0265), with a similar rate of change of 0.32% per week (95% confidence interval [CI]: 0.16, 0.49) in the basal ganglia (BG) and thalami. A lower trend (0.11% per week; 95% CI: -0.05, 0.28) was seen in the pons. Higher MTRs were seen in the thalami and pons than in the BG (P.05), indicating earlier maturation. Accordingly, higher T1 values were observed in the BG relative to the thalami (P.0001). Higher MTRs in the BG were observed in the group of neonates with normal findings at presentation than in the group with WMI (P = .02).MTR measurements can be used to monitor early myelination in the developing brain and to help detect changes in tissue that are not shown on T1- and T2-weighted MR images.

In diffusion weighted MRI, subject motion and brain pulsation lead both to signal drop-outs and image misalignment. Unsedated neonates, with their higher heart rate and propensity for motion are particularly prone to degraded scan quality that impairs diffusion tensor estimation. Retrospective registration and robust estimators are two methods that have previously been demonstrated to address motion and intensity outliers, respectively, in diffusion data. However, when taken together, the resampling of images to correct for misalignment can have the effect of averaging outlier voxels with uncorrupted voxels, thereby making outliers more difficult to detect. This article presents a method to remove outliers prior to resampling while taking misalignment into account so that this averaging of outliers with good data can be avoided. The proposed method is compared to other processing pipelines using simulations and data from unsedated preterm neonates. These results demonstrate advantages to the proposed method, particularly in subjects with high motion. Magn Reson Med 66:92‐101, 2011. V C 2011 Wiley-Liss, Inc.

T1- and T2-W MR sequences used for obtaining diagnostic information and morphometric measurements in the neonatal brain are frequently acquired using different imaging protocols. Optimizing one protocol for obtaining both kinds of information is valuable. To determine whether high-resolution T1- and T2-W volumetric sequences optimized for preterm brain imaging could provide both diagnostic and morphometric value. Thirty preterm neonates born between 24 and 32 weeks’ gestational age were scanned during the first 2 weeks after birth. T1- and T2-W high-resolution sequences were optimized in terms of signal-to-noise ratio, contrast-to-noise ratio and scan time and compared to conventional spin-echo-based sequences. No differences were found between conventional and high-resolution T1-W sequences for diagnostic confidence, image quality and motion artifacts. A preference for conventional over high-resolution T2-W sequences for image quality was observed. High-resolution T1 images provided better delineation of thalamic myelination and the superior temporal sulcus. No differences were found for detection of myelination and sulcation using conventional and high-resolution T2-W images. High-resolution T1- and T2-W volumetric sequences can be used in clinical MRI in the very preterm brain to provide both diagnostic and morphometric information.

The influence of diffusion time (), gradient duration (), and TE on the appearance of high b-value q-space diffusion MR images of excised rat spinal cord (SC) was evaluated. The water signal decays in the white (WM) and gray matter (GM) were analyzed when the diffusion was measured perpendicular () and parallel (||) to the fibers of the SC, using three different approaches: single-component q-space analysis, the biexponential model, and the bi-Gaussian fit of the displacement distribution profile. Probability and displacement contrast and anisotropy indices were calculated for the WM and GM. It was found that WM/GM contrast increases as the diffusion time is increased when diffusion is measured perpendicular to the long axis of the SC. At a diffusion time of 50 ms, when diffusion was measured parallel to the fibers of the SC, the displacement was found to be higher for GM as compared to WM. For this direction the WM/GM contrast increased when diffusion time was increased, although here the changes were much less pronounced than for the perpendicular direction. The WM/GM displacement contrast nearly disappears for a diffusion time of 150 ms, when diffusion is measured parallel to the fibers of the SC. As expected, the anisotropy indices were found to be higher in WM than in GM, and increased with the increase in diffusion time. Both and TE affected the extracted parameters. It was found that long and long TE overemphasizes the apparent slowdiffusing water component of the SC, which is also the more restricted one. It is demonstrated that the single-component q-space analysis best describes diffusion in WM when diffusion is measured perpendicular to the fibers of the SC. In other cases, a more complete description is obtained by using twocomponent models. Magn Reson Med 54:96 –104, 2005.

Background Magnetic resonance spectroscopy allows for the noninvasive study of brain metabolism and therefore may provide useful information about brain injuries. We examined the associations of brain metabolite ratios in very preterm infants with white matter lesions and overall health status at birth. Methods Spectroscopy data were obtained from 99 very preterm infants (born ≤32wk gestation) imaged shortly after birth and from 67 of these infants at term-equivalent age. These data were processed using LC Model. Multiple regression was used to examine the association of metabolite ratios with focal non cystic white matter lesions visible on conventional magnetic resonance imaging (MRI) and with at-birth illness severity scores. Results Within 2wk of birth, the ratio of N-acetylaspartate + N-acetylaspartylglutamate to creatine + phosphocreatine was significantly lower in those infants showing white matter abnormalities on conventional MRI. Increased lactate to creatine + phosphocreatine and lactate to glycerophosphocholine + phosphocholine ratios were significantly associated with increasing severity of Clinical Risk Index for Babies II and Apgar scores taken at 1 and 5min after birth. Conclusion Both overall health status at birth and white matter injury in preterm neonates are reflected in metabolite ratios measured shortly after birth. Long-term follow-up will provide additional insight into the prognostic value of these measures.

The aim of this study was to determine the feasibility of undertaking visual functional magnetic resonance imaging (fMRI) in very preterm children.Forty-seven infants born at less than 32 weeks gestational age (25 males, 22 females; mean (SD) age at birth 28.8 wks [1.9]) were scanned using 1.5 T MRI as part of a longitudinal neuroimaging study. These infants were scanned at preterm age (within 2 wks of birth) and at term-equivalent age. Quantitative T2* data and fMRI in response to visual stimuli (flashing strobe) were acquired in this population. T2* values were compared at preterm age and at term-equivalent age using a two-tailed t-test. A general linear model was used to evaluate occipital lobe response to visual stimuli.T2* values were significantly higher at preterm age than at term-equivalent age in both the medial and lateral occipital lobes (preterm infants: 187.2 ms and 198.4 ms respectively; term infants: 110.9 ms and 133.2 ms respectively; p0.002). Significant positive occipital lobe activation (q0.01) was found in 3 out of 65 (5%) fMRIs carried out at preterm age and in 19 out of 26 (73%) scans carried out at term-equivalent age.Visual stimuli do not elicit a reliable blood oxygen level-dependent (BOLD) response in very preterm infants during the preterm period. This suggests that BOLD fMRI may not be the appropriate modality for investigating occipital lobe function in very preterm infants.

In diffusion weighted MRI, subject motion and brain pulsation lead both to signal drop-outs and image misalignment. Unsedated neonates, with their higher heart rate and propensity for motion are particularly prone to degraded scan quality that impairs diffusion tensor estimation. Retrospective registration and robust estimators are two methods that have previously been demonstrated to address motion and intensity outliers, respectively, in diffusion data. However, when taken together, the resampling of images to correct for misalignment can have the effect of averaging outlier voxels with uncorrupted voxels, thereby making outliers more difficult to detect. This article presents a method to remove outliers prior to resampling while taking misalignment into account so that this averaging of outliers with good data can be avoided. The proposed method is compared to other processing pipelines using simulations and data from unsedated preterm neonates. These results demonstrate advantages to the proposed method, particularly in subjects with high motion.

Spinal cord injury (SCI) is a major cause of disability for many living persons. Therefore, several experimental models and handful of techniques were developed to study and characterize the damage evolution following SCI. In the present study, high b-value q-space diffusion-weighted imaging (DWI) was used to follow the spatial and temporal damage evolution in excised rat spinal cords following hemi-crush injury. The DWI results were correlated with behavioral testing. It was found that the damage depends, as expected, on the severity of the insult. Significant spontaneous recovery was observed, six weeks following the insult, only for the mild hemi-crush injury but not following the severe injury. The damage was found to be more severe in the area caudal to the trauma site as compared to the rostral section of the cord.

The development of the damage following hemi-crush trauma in rat spinal cord was studied ex vivo using high b value ( b max = 1 × 10 7 s cm −2 ) q -space diffusion weighted MRI (DWI) at five days, ten days and six weeks post-trauma. Rat spinal cord trauma, produced by hemi-crush of 15s and 60s duration, was studied. The water signal decay in these diffusion experiments was found to be non mono-exponential and was analyzed using the q -space approach. The q -space MRI parameters were compared with T1 and T2 MR images, behavioral tests and histopathological osmium staining. A very good anatomical correlation was found between the q -space MRI parameters and the osmium staining. Interestingly, we found that in the 15s hemi-crush model significant recovery was observed in both the q -space MR images and the osmium staining six weeks post-trauma. However, in the 60s hemi-crush trauma model very little recovery was observed. These results paralleled those obtained from behavioral tests demonstrating that partial spontaneous recovery seems to occur in the 15s hemi-crush spinal cord model, which should be taken in consideration when using it to evaluate new therapies.

Magnetic Resonance Imaging (MRI) is currently the most important imaging modality of the central nervous system (CNS) (Stark and Bradley Jr. 1999, Young 2000). The main reasons for that is the non-invasiveness of the method, the many physical parameters that can be used to obtain such MR images, the safeness of the technique and the fact that morphological information can be coupled with biochemical information using magnetic resonance spectroscopy (MRS).