Noncollinear Directions Research Articles

Continuing the search for MR imaging biomarkers for MGMT promoter methylation status: conventional and perfusion MRI revisited

Continuing the search for MR imaging biomarkers for MGMT promoter methylation status: conventional and perfusion MRI revisited

Diffusion tensor imaging of normal prostate at 3 T: effect of number of diffusion-encoding directions on quantitation and image quality

The purpose of this study was to prospectively investigate differences of diffusion tensor imaging (DTI) using a different number of diffusion-encoding directions and to evaluate the feasibility of tractography in healthy prostate at 3 T. 12 healthy volunteers underwent DTI with single-shot echo-planar imaging at 3 T using a phased-array coil. Diffusion gradients of each DTI were applied in 6 (Group 1), 15 (Group 2) and 32 (Group 3) non-collinear directions. For each group, the mean apparent diffusion coefficient (ADC), fractional anisotrophy (FA) and signal-to-noise ratio (SNR) were measured in the peripheral zone (PZ) and central gland (CG). The quality of diffusion-weighted and tractographic images were also evaluated. In all three groups, the mean ADC value of the CG was statistically lower than that of the PZ (p<0.01) and the mean FA value of the CG was statistically greater than that of the PZ (p<0.01). For the mean FA value of the CG, no statistical difference was seen among the three groups (p=0.052). However, the mean FA value of the PZ showed a statistical difference among the three groups (p=0.035). No significant difference in SNR values was seen among the three groups (p>0.05). Imaging quality of diffusion-weighted tractographic images was rated as satisfactory or better in all three groups and was similar among the three groups. In conclusion, prostate DTI at 3 T was feasible with different numbers of diffusion-encoding directions. The number of diffusion-encoding directions did not have a significant effect on imaging quality.

Assessment of White Matter Microstructural Integrity in Children with Syndromic Craniosynostosis: A Diffusion-Tensor Imaging Study

To assess whether architectural alterations exist in the white matter of patients with syndromic and complex craniosynostosis. The medical ethics committee approved this study. Written informed consent was obtained from parents or guardians before imaging. A prospective study was performed in children with syndromic and complex craniosynostosis aged 6-14 years. Forty-five patients were included: four had Apert syndrome, 14 had Crouzon-Pfeiffer syndrome, eight had Muenke syndrome, 11 had Saethre-Chotzen syndrome, and eight had complex craniosynostosis. In addition, seven control subjects were evaluated. For diffusion-tensor imaging, an echo-planar sequence was used with a diffusion gradient (b = 1000 sec/mm(2)) applied in 25 noncollinear directions. Regions of interest (ROIs) were placed in the following white matter structures: pontine crossing tract, corticospinal tracts, medial cerebral peduncles, uncinate fasciculus (measured bilaterally), anterior commissure, frontal and occipital white matter (measured bilaterally), fornix, corpus callosum (measured in the genu and splenium), and corpus cingulum (measured bilaterally). Eigenvalues were measured in all ROIs and fractional anisotropy (FA) was calculated. Across all measured ROIs, FA values were generally lower in all patients combined than in the control subjects (P < .001). There were no significant differences among subgroups of patients. Diffusion-tensor imaging measurements of white matter tracts reveal significant white matter integrity differences between children with craniosynostosis and healthy control subjects. This could imply that the developmental delays seen in these patients could be caused by the presence of a primary disorder of the white matter microarchitecture.

Biexponential Analysis of Diffusion-Tensor Imaging of the Brain in Patients with Cirrhosis before and after Liver Transplantation

DTI has shown increased MD of water molecules in the brain of patients with cirrhosis, consistent with low-grade edema. This study further characterizes this edema by using biexponential analysis of DTI data, a technique that may differentiate cytotoxic and vasogenic edema. A total of 41 patients with cirrhosis awaiting liver transplantation and 16 healthy controls were studied by DTI by using a single-shot echo-planar technique with 11 b-values (range, 0-7500 s/mm(2)) and 6 noncollinear directions. Measurements were fitted to biexponential function to determine MD and FA for the fast and slow diffusion components. Regions of interest were selected in the parietal white matter and corticospinal tract. The assessment was repeated 1 year after liver transplantation in 24 of these patients. In parietal white matter, patients with cirrhosis showed an increase in fast MD and a decrease in fast FA that normalized after liver transplantation. In the corticospinal tract, there was an increase in fast and slow MD that normalized after transplantation, and a decrease in FA that persisted posttransplantation. There was no association of DTI parameters with minimal HE (n =12). Biexponential analysis of DTI supports the presence of edema in the brain of patients with cirrhosis that reverts after transplantation. In parietal white matter, the increase in brain water was mainly located in the interstitial compartment, while the corticospinal tract showed a mixed pattern (intra- and extracellular). In addition, the findings on posttransplantation were consistent with microstructural damage along the corticospinal tract.

Pre- and Intraoperative Tractographic Evaluation of Corticospinal Tract Shift

Magnetic resonance with diffusion tensor image (DTI) may be able to estimate trajectories compatible with subcortical tracts close to brain lesions. A limit of DTI is brain shifting (movement of the brain after dural opening and tumor resection). To calculate the brain shift of trajectories compatible with the corticospinal tract (CST) in patients undergoing glioma resection and predict the shift directions of CST. DTI was acquired in 20 patients and carried out through 12 noncollinear directions. Dedicated software "merged" all sequences acquired with tractographic processing and the whole dataset was sent to the neuronavigation system. Preoperative, after dural opening (in 11) and tumor resection (in all) DTI acquisitions were performed to evaluate CST shifting. The extent of shifting was considered as the maximum distance between the preoperative and intraoperative contours of the trajectories. An outward shift of CST was observed in 8 patients and an inward shift in 10 patients during surgery. In the remaining 2 patients, no intraoperative displacement was detected. Only peritumoral edema showed a statistically significant correlation with the amount of shift. In those patients in which DTI was acquired after dural opening as well (11 patients), an outward shifting of CST was evident in that phase. The use of intraoperative DTI demonstrated brain shifting of the CST. DTI evaluation of white matter tracts can be used during surgical procedures only if updated with intraoperative acquisitions.

Step-shape angular spin distribution in layered systems by 57Fe Mössbauer spectroscopy: A general treatment

In the so-called ‘step-shape’ angular spin distribution model for layered systems, the non-collinear directions of the atomic magnetic moments are confined to the film plane and form a homogeneous fan spanning inside an (in-plane) angular interval Δφ centered at an angle φ0. A general approach for deriving the two parameters φ0 and Δφ via 57Fe Mössbauer spectroscopy measurements is discussed. The analysis extends our previously reported treatment, which assumed that the angular aperture Δφ develops symmetrically versus a fixed direction φ0 (e.g., the in-plane easy axis of magnetization) oriented either along or perpendicular to the in-plane projection of the Mössbauer γ-ray direction. The proposed approach is also applicable for those cases when not only the spin aperture Δφ is changing but also the aperture center φ0 is rotating under the influence of different external parameters, such as applied field, temperature, stress, etc. The method is suitable for applications to nanoscale layered heterostructures with in-plane uniaxial or unidirectional magnetic anisotropy. The method is applied to experimental data obtained on a 2-nm thick defected Fe layer with in-plane magnetic texture.

Asymmetric double-shifted characteristics in epitaxial (002) exchange-biased IrMn/CoFe bilayers

Symmetric and asymmetric double-shifted loops were observed at room temperature in epitaxial (002) Ir20Mn80/Co50Fe50 samples placed in a setting field applied along collinear and noncollinear directions with the deposition-field direction, respectively. A coherent rotation model with extra unidirectional exchange and uniaxial anisotropies induced by the noncollinear setting field is proposed to explain the asymmetric double-shifted loops. Due to the existence of the biaxial magnetocrystalline anisotropy, the noncollinear setting field results in two interfacial Ir20Mn80 spin orientations, where the major spins determine the direction to observe double-shifted loops and the minor spins determine the field-shift and the asymmetry of double-shifted loops.

Test–retest reliability and repeatability of renal diffusion tensor MRI in healthy subjects

This study assessed test-retest reliability and repeatability of diffusion tensor imaging (DTI) in the kidneys. Seven healthy volunteers (age range, 19-31 years), were imaged three consecutive times on the same day (short-term reliability) and the same imaging protocol was repeated after a month (long-term reliability). Diffusion-weighted magnetic resonance imaging scans in the coronal-oblique projection of the kidney were acquired on a 1.5 T scanner using a multi-section echo-planar sequence; six contiguous slices each 5 mm thick, diffusion sensitisation along 20 non-collinear directions, TR=730 ms, TE=73 ms and 2 b-values (0 and 400 s mm(-2)). Volunteers were asked to hold their breath throughout each data acquisition (approx. 20 s). The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were obtained from maps generated using dedicated software MIStar (Apollo Medical Imaging, Melbourne, Australia). Statistical analyses of both short- and long-term repeats were carried out from which the within-subject coefficient of variation (wsCV) was calculated. The wsCV obtained for both the ADC and FA values were less than 10% in all the analyses carried out. In addition, paired (repeated measures) t-test was used to measure the variation between the diffusion parameters collected from the two scanning sessions a month apart. It showed no significant difference and the wsCV obtained after comparing the first and second scans were found to be smaller than 15% for both ADC and FA. Renal DTI produces reliable and repeatable results which make longitudinal investigation of patients viable.

Diffusion tensor imaging in the cervical spinal cord

There are discrepancy between MR findings and clinical presentations. The compressed cervical cord in patients of the spondylotic myelopathy may be normal on conventional MRI when it is at the earlier stage or even if patients had severe symptoms. Therefore, it is necessary to take a developed MR technique--diffusion tensor imaging (DTI)--to detect the intramedullary lesions. Prospective MR and DTI were performed in 53 patients with cervical compressive myelopathy and twenty healthy volunteers. DTI was performed along six non-collinear directions with single-shot spin echo echo-planar imaging (EPI) sequence. Intramedullary apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in four segments (C2/3, C3/4, C4/5, C5/6) for volunteers, in lesions (or the compressed cord) and normal cord for patients. DTI original images were processed to produce color DTI maps. In the volunteers' group, cervical cord exhibited blue on the color DTI map. FA values between four segments had a significant difference (P < 0.01), with the highest FA value (0.85 ± 0.03) at C2/3 level. However, ADC value between them had no significant difference (P > 0.05). For patients, only 24 cases showed hyperintense on T2-weighted image, while 39 cases shown patchy green signal on color DTI maps. ADC and FA values between lesions or the compressed cord and normal spinal cord of patients had a significant difference (both P < 0.01). FA value at C2/3 cord is the highest of other segments and it gradually decreases towards the caudal direction. Using single-shot spin echo EPI sequence and six non-collinear diffusion directions with b value of 400 s mm(-2), DTI can clearly show the intramedullary microstructure and more lesions than conventional MRI.

The effect of axial loading to the lumbar intervertebral discs MR diffusion characteristics

Objective To analysis the effect of axial loading to ADC value, FA of lumbar intervetebral discs. Methods Forty five patients with low back pain (age range, 25 to 54 years) were evaluated with MR T2WI, MR T1WI and diffusion tensor imaging (DTI) of the lumbar spine. Following axial loading with 40% to 50% body weight for 10 minutes, a repeat DTI was performed. DTI were obtained by using an echo-planar imaging ( EPI ) sequence, TE 89 ms, TR 2500 ms, b value of 400 s/mm2,6 noncollinear diffusion directions. Scan time was approximately 4 min 10 s. An isotropic ADC map, FA map and bo map were calculated from DTI sequence. The mean ADC value, FA prior to and following axialloading were analyzed with t test and Rank Sum test. Results Forty five patients with 225 discs were evaluated and 223 discs were included in the study except for 2 calcified discs. The Pfirrmann grading results were as following: 100 Grade Ⅱ , 48 Grade Ⅲ, 59 Grade Ⅳ, and 16 Grade Ⅴ. No significant difference existed in the mean ADC value before [ ( 1666 ± 252 ) × 10-3 mm2/s ] and after [ ( 1662 ± 253 ) ×10 -3 mm2/s ] axial loading ( Z = - 1.363, P ＞ 0.05 ), but the mean FA [ ( 301 ± 104 ) × 10 -3, ( 316 ±112) × 10-3 ] value increased ( Z = - 2.794, P ＜ 0.05 ). The paired-samples t test show that the mean ADC value [ ( 1685 ± 190) × 10-3 mm2/s, ( 1624 ± 180) × 10-3mm2/s] of Grade Ⅲ discs decreased after axial loading, t=3.513, P＜0. 05, Grade Ⅲ, Ⅳdiscs mean FA value [(300±87) ×10-3, (326±87) ×10-3 for Grade Ⅲ and (348 ±67) × 10-3, (351 ± 71 ) × 10-3 for Grade Ⅳ ] increased, t = - 2. 210,- 2.006, P ＜ 0.05. No significant difference existed in Grade Ⅱ , Ⅳ and Ⅴ discs ADC value, all the P ＞0.05. No significant difference existed in Grade Ⅱ and Ⅴ discs FA value, both the P ＞ 0.05. Conclusions Short time axial loading mainly affect the mildly degenerated discs, the ADC value decreases and the disc diffusion ability decreases. No obvious change in ADC value or disc diffusion ability existed in the normal and severely degenerated discs. Key words: Intervertebral disc; Lumbar vertebrae; Magnetic resonance imaging

Relationship between Microstructural Degeneration of the Corpus Callosum, White Matter Hyperintensities, and Motor Function in Cognitively Intact Elderly

Age-related changes in cerebral white matter, such as decreased corpus callosum (CC) volume and the presence of periventricular white matter hyperintensities (PVWMH) on fluid attenuated inversion recovery (FLAIR) MRI sequences have been demonstrated in nondemented elderly and are associated with motor impairment. Diffusion tensor imaging (DTI) can potentially detect microstructural white matter changes prior to macrostructural volume change. Examination of the relationship of microstructual CC degeneration detected by DTI, PVWMH's and motor function in cognitively intact elderly may suggest a structural-functional connection to this pathology. 14 cognitive intact (CDR = 0, mean MMSE 29.5) elderly men and women (mean age 80.2, range 70 - 92) underwent 3T MRI and detailed neurological evaluation, including fine motor and balance testing. WMH volumes were obtained with FLAIR sequences and were adjusted for intracranial volume. CC microstructural integrity was assessed using fractional anisotrophy (FA) from DTI (TR = 9500 ms; TE = 95 ms; slice thickness 2.0 mm; 20 non-collinear directions). For each subject, a 24 mm2 region of interest was placed in the CC genu (figure) . Relationships between WMHs, CC integrity, and motor function were examined using multivariate analyses adjusted for age. Greater age was associated with decreased CC genu FA (R2 = 0.41, p = 0.01) and total CC volume (R2 = 0.37, p = 0.02). Neither total nor anterior CC volume was associated with motor test performance. %PVWMH volume was associated with slower finger tapping (R2 = 0.23, p = 0.08), but was not associated with one leg standing (OLS). After adjusting for age and %PVWMH, decreased CC genu FA was associated with slower finger tapping (p = 0.02). After adjusting for age, decreased CC genu FA was associated with OLS with eyes open (p = 0.03 left; p = 0.02 right), and OLS with eyes closed (p = 0.07). Advanced age is associated with microstructural degeneration of the anterior corpus callous that disrupts fine motor skills and balance function in cognitively intact elderly, independent of WMH's or CC atrophy. Identification of risk factors to prevent such white matter change is needed to preserve motor abilities in our elderly population

Assessment of Brain White Matter Fiber Bundle Atrophy in Patients with Friedreich Ataxia

To investigate in vivo severity and topographic distribution of brain white matter (WM) fiber bundle atrophy in patients with Friedreich ataxia, a condition characterized by an uneven involvement of brain WM, and to correlate such findings with the clinical status of the patients. The study was conducted with institutional review board approval. Written informed consent was obtained from each participant. Sixteen patients with Friedreich ataxia and 15 healthy control subjects were studied by using a 1.5-T magnetic resonance (MR) imager and 3-mm-thick diffusion-tensor images with 15 noncollinear directions. The size of WM fiber bundles was examined at a voxel level by using a recently developed method, which relies on production of anisotropy maps and nonlinear registration. Data were analyzed by using statistical parametric mapping software and an analysis of covariance model adjusted for age and sex. Compared with control subjects, patients with Friedreich ataxia had WM atrophy in (a) the central portion of the medulla oblongata, (b) the dorsal upper pons, (c) the superior cerebellar peduncles, (d) the central portion of the midbrain, (e) the medial portion of the right cerebral peduncle, (f) the peridentate region, bilaterally, and (g) the optic chiasm. The severity of the neurologic deficits correlated significantly with atrophy of the peridentate WM, bilaterally, and that of the superior cerebellar peduncle decussation. Findings of this study show that it is feasible to obtain in vivo atrophy estimates of specific brain WM fiber bundles in patients with Friedreich ataxia and that such estimates correlate with patients' clinical status. This approach has the potential to provide new information that is likely to improve the understanding of the pathophysiology of inherited ataxias.

Diffusion Tensor Imaging in a Human PET/MR Hybrid System

The aim of this study was to test and demonstrate the feasibility of diffusion tensor imaging (DTI) with a hybrid positron emission tomography (PET)/magnetic resonance imaging system for simultaneous PET and magnetic resonance (MR) data acquisition. All measurements were performed with a prototype hybrid PET/MR scanner dedicated for brain and head imaging. The PET scanner, which is inserted into a conventional 3.0-Tesla high field MR imager equipped with a transmit/receive birdcage head coil, consists of 192 block detectors with a matrix of 12 x 12 lutetium oxyorthosilicate scintillation crystals combined with MR-compatible 3 x 3 avalanche photodiode arrays. In 7 volunteers and 4 patients with brain tumors, DTI was performed during simultaneous PET data readout applying a diffusion weighted echo planar sequence (12 noncollinear directions, echo time (TE)/repetition time (TR) 98 ms/5300 ms, b-value 800 s/mm). Image quality and accuracy of DTI were assessed in comparison with DTI images acquired after removal of the PET insert. The diffusion images showed good image quality in all volunteers regardless of simultaneous PET data readout or after removal of the PET scanner; however, significantly (P < 0.01) stronger rim artifacts were found in fractional anisotropy images computed from DTI images recorded during simultaneous PET acquisition, demonstrating higher eddy-current effects. In region of interest analysis, no notable differences were found in the computation of the direction of the principal eigenvector (P > 0.05) and fractional anisotropy values (P > 0.05). In the assessment of pathologies, in all 4 patients PET and DTI provided important clinical information in addition to conventional magnetic resonance imaging. Diffusion tensor imaging may be combined with simultaneous PET data acquisition, offering additional important morphologic and functional information for treatment planning in patients with brain tumors.

Efficiency of Fractional Anisotropy and Apparent Diffusion Coefficient on Diffusion Tensor Imaging in Prognosis of Neonates with Hypoxic-Ischemic Encephalopathy: A Methodologic Prospective Pilot Study

The DTI parameters (FA and ADC) reflect the properties of the brain microstructure. Decreased anisotropy is a common feature of cerebral tissue abnormalities. Our study investigates the neurologic prognostic efficiency of these parameters in white (PLIC, CP) and gray matter (PP) in the first days of life in term neonates with HIE. We hypothesize that lesions in related brain areas could be part of a physiopathologic substratum supporting neurologic deficiencies in this population. A total of 22 neonates (13 girls and 9 boys; mean gestational age, 40 weeks +/- 9 days; birth weight, 3203 +/- 584 g) underwent brain MR imaging between day 1 and day 6 after birth; 6-noncollinear direction DTI was performed. FA and ADC were measured on specific brain areas. Amiel-Tison score was performed on day 8.5 +/- 4 (group A, favorable outcome [n = 16]; group B, unfavorable outcome [n = 6]). Intraobserver and interobserver comparison in DTI parameter measurements showed a coefficient of variability of less than 5%. In PLIC and PP, the ADC values were lower in group B compared with group A (P = .000027), whereas in PLIC and CP, the FA values were lower in group B compared with group A (P < .02). These findings indicate that a poor early neurologic outcome in neonates with HIE is associated with lower FA or ADC values in specific areas of white or gray matter. The difference in ADC/FA changes in the different brain areas explored may support possibly different pathologic processes.

Parcelation of the White Matter Using DTI: Insights into the Functional Connectivity of the Brain

Definitions Diffusion tensor imaging (DTI) is a neuroimaging MR technique, which allows in vivo and non-destructive visualization of myeloarchitectonics in the neural tissue and provides quantitative estimates of WM integrity by measuring molecular diffusion. It is based in the phenomenon of diffusion anisotropy in the nerve tissue, in that water molecules diffuse faster along the neural fiber direction and slower in the fiber-transverse direction (figure 1) The hinderance of water diffusion in white matter is putative due to the diffusion barrier represented by the cell membrane and the myelin sheath however, it is governed by several other, yet not completely elucidated, parameters related to the diffusion physics and biophysical properties of the tissue such as, the cell membrane permeability and the free diffusion coefficients for the cellular compartments. The anisotropic diffusion of coherently oriented axonal fibers can be exploited for anatomic mapping and quantitative characterization of white matter tracts. This is done by depicting and measuring the diffusion tensor within the imaging voxels of the diffusion acquisition. Provided that 6 diffusion-encoded images sets are acquired along noncollinear directions, the diffusion tensor can be calculated. Diffusion tensor, is a mathematical model of the 3D pattern of diffusion trsjectories (a 3X3 matrix of vectors) within the white matter tracts. The three principal axes of the diffusion tensor are termed the eigenvectors. The largest eigenvector is termed the primary eigenvector and indicates the direction and magnitude of greatest water diffusion. It is important for fiber tractography because it indicates the orientation of axonal fiber bundles. The degree of directionality of intravoxel diffusivity is measured by the fractional anisotropy (FA) index. When the value of the primary eigenvector is higher than the values of the second and third eigenvectors the FA will be high, indicating diffusion along a preferred direction. The graphic representation of the three eigenvectors corresponds to a prolate shape of diffusion ellipsoid with the long axis of the ellipsoid indicating the preferred direction of diffusion (figure 2). Its value varies from 0 (isotropic diffusion) up to maximum 1, indicating perfectly linear diffusion along the primary eigenvector.

Diffusion tensor magnetic resonance imaging of glial brain tumors

Aim To evaluate the author's experience with the use of diffusion tensor magnetic resonance imaging (DTI) on patients with glial tumors. Methods A retrospective evaluation of a group of 24 patients with glial tumors was performed. There were eight patients with Grade II, eight patients with Grade III and eight patients with Grade IV tumors with a histologically proven diagnosis. All the patients underwent routine imaging including T2 weighted images, multidirectional diffusion weighted imaging (measured in 60 non-collinear directions) and T1 weighted non-enhanced and contrast enhanced images. The imaging sequence and evaluation software were produced by Massachusetts General Hospital Corporation (Boston, MA, USA). Fractional anisotropy (FA) maps were calculated in all patients. The white matter FA changes were assessed within the tumorous tissue, on the tumorous borderline and in the normally appearing white matter adjacent to the tumor. A three-dimensional model of the white matter tract was created to demonstrate the space relationship of the tumor and the capsula interna or corpus callosum in each case using the following fiber tracing parameters: FA step 0.25 and a tensor declination angle of 45 gr. An additional assessment of the tumorous tissue enhancement was performed. Results A uniform homogenous structure with sharp demargination of the Grade II tumors and the wide rim of the intermedial FA in all Grade III tumors respectively, were found during the evaluation of the FA maps. In Grade IV tumors a variable demargination was noted on the FA maps. The sensitivity and specificity for the discrimination of low- and high-grade glial tumors using FA maps was revealed to be 81% and 87% respectively. If the evaluation of the contrast enhancement was combined with the evaluation of the FA maps, both sensitivity and specificity were 100%. Conclusion Although the evaluation of the fractional anisotropy maps is not sufficient for glioma grading, the combination of the contrast enhancement pattern and fractional anisotropy maps evaluation improves the possibility of distinguishing low- and high-grade glial tumors. Three-dimensional models of the white matter fibers in the corpus callosum and the internal capsule may be used in the presurgical planning.

Brain connectivity in non-reading impaired children and children diagnosed with developmental dyslexia

Diffusion Tensor Imaging (DTI) was used to investigate the relationship between white matter and reading abilities in reading impaired and non-reading impaired children. Seventeen children (7 non-reading impaired, 10 reading impaired) participated in this study. DTI was performed with 2mm isotropic resolution to cover the entire brain along 30 noncollinear directions. Voxelwise analyses were conducted on data processed through Tract Based Spatial Statistics (TBSS). The data replicated previous results seen across multiple studies and extended findings to include measures of both real word and pseudoword decoding. Negative correlations were observed in the left posterior corpus callosum between fractional anisotropy (FA) values and both measures of decoding. Positive correlations between FA values and real word and pseudoword decoding were observed in the left superior corona radiata. This extension of findings regarding correlations between the corona radiata and reading skills suggests an important direction for future research into the neurological substrates of reading.

A vortex solid-to-liquid transition with fully anisotropic scaling

The vortex solid-to-liquid transition has been studied in heavy ion irradiated untwinned single crystals of YBa2Cu3O7-δ with an inclined applied magnetic field. For magnetic fields tilted at angles about 45° away from the columnar defects, we find that the electric resistivity in the vortex liquid regime approaches zero with power laws in the reduced temperature T — Tc that have different exponents in all three spatial directions. Since the symmetry in the problem has been broken in two non-collinear directions by i) the direction of the columnar defects and ii) the direction of the applied magnetic field, our findings give evidence for a new type of critical behavior with fully anisotropic critical exponents. A possible view of the vortex topology for the transition is also suggested.

Quantitative examination of a novel clustering method using magnetic resonance diffusion tensor tractography

MR diffusion tensor imaging (DTI) can measure and visualize organization of white matter fibre tracts in vivo. DTI is a relatively new imaging technique, and new tools developed for quantifying fibre tracts require evaluation. The purpose of this study was to compare the reliability of a novel clustering approach with a multiple region of interest (MROI) approach in both healthy and disease (schizophrenia) populations.DTI images were acquired in 20 participants (n=10 patients with schizophrenia: 56±15 years; n=10 controls: 51±20 years) (1.5 T GE system) with diffusion gradients applied in 23 non-collinear directions, repeated three times. Whole brain seeding and creation of fibre tracts were then performed. Interrater reliability of the clustering approach, and the MROI approach, were each evaluated and the methods compared.There was high spatial (voxel-based) agreement within and between the clustering and MROI methods. Fractional anisotropy, trace, and radial and axial diffusivity values showed high intraclass correlation (p<0.001 for all tracts) for each approach. Differences in scalar indices of diffusion between the clustering and MROI approach were minimal.The excellent interrater reliability of the clustering method and high agreement with the MROI method, quantitatively and spatially, indicates that the clustering method can be used with confidence. The clustering method avoids biases of ROI drawing and placement, and, not limited by a priori predictions, may be a more robust and efficient way to identify and measure white matter tracts of interest.

Diffusion tensor imaging and fiber tractography of C6 rat glioma

To apply diffusion tensor images using 30 noncollinear directions for diffusion-weighted gradient schemes to characterize diffusion tensor imaging (DTI) features associated with C6 glioma-bearing rat brains, and ideally visualize fiber tractography datasets. Fiber tractographies of normal male Fischer 344 rat brains were constructed from DTI datasets acquired with a 30 noncollinear diffusion gradient scheme. Cultured C6 cell were intracranially injected into the cortex of male Fischer 344 rats. The time course of the tumor growth was monitored with DTI and fiber tractography using diffusion-weighting gradients in 30 noncollinear directions. Fiber tractographies through the corpus callosum (CC) were easily visualized with the 30-direction gradient scheme, and the fiber trajectories of the motor cortex and striatum were well represented in normal rats. Fiber tractography indicated that the neuronal fibers of the CC were compressed or disappeared by growing C6 glioma, which affected surrounding brain tissue. We have demonstrated in this study that fiber tractography with the 30 noncollinear diffusion gradient scheme method can be used to help provide a better understanding regarding the influence of a tumor on the surrounding regions of normal brain tissue in vivo.