Evaluation of measurement uncertainties in human diffusion tensor imaging (DTI)‐derived parameters and optimization of clinical DTI protocols with a wild bootstrap analysis

Purpose

To quantify measurement uncertainties of fractional anisotropy, mean diffusivity, and principal eigenvector orientations in human diffusion tensor imaging (DTI) data acquired with common clinical protocols using a wild bootstrap analysis, and to establish optimal scan protocols for clinical DTI acquisitions.

Materials and Methods

A group of 13 healthy volunteers were scanned using three commonly used DTI protocols with similar total scan times. Two important parameters—the number of unique diffusion gradient directions (NUDG) and the ratio of the total number of diffusion‐weighted (DW) images to the total number of non‐DW images (DTIR)—were analyzed in order to investigate their combined effects on uncertainties of DTI‐derived parameters, using results from both the Monte Carlo simulation and the wild bootstrap analysis of uncertainties in human DTI data.

Results

The wild bootstrap analysis showed that uncertainties in human DTI data are significantly affected by both NUDG and DTIR in many brain regions. These results agree with previous predictions based on error‐propagations as well as results from simulations.

Conclusion

Our results demonstrate that within a clinically feasible DTI scan time of about 10 minutes, a protocol with number of diffusion gradient directions close to 30 provides nearly optimal measurement results when combined with a ratio of the total number of DW images over non‐DW images equal to six. Wild bootstrap can serve as a useful tool to quantify the measurement uncertainty from human DTI data. J. Magn. Reson. Imaging 2009;29:422–435. © 2009 Wiley‐Liss, Inc.     

3D diffusion tensor MRI with isotropic resolution using a steady‐state radial acquisition

Purpose

To obtain diffusion tensor images (DTI) over a large image volume rapidly with 3D isotropic spatial resolution, minimal spatial distortions, and reduced motion artifacts, a diffusion‐weighted steady‐state 3D projection (SS 3DPR) pulse sequence was developed.

Materials and Methods

A diffusion gradient was inserted in a SS 3DPR pulse sequence. The acquisition was synchronized to the cardiac cycle, linear phase errors were corrected along the readout direction, and each projection was weighted by measures of consistency with other data. A new iterative parallel imaging reconstruction method was also implemented for removing off‐resonance and undersampling artifacts simultaneously.

Results

The contrast and appearance of both the fractional anisotropy and eigenvector color maps were substantially improved after all correction techniques were applied. True 3D DTI datasets were obtained in vivo over the whole brain (240 mm field of view in all directions) with 1.87 mm isotropic spatial resolution, six diffusion encoding directions in under 19 minutes.

Conclusion

A true 3D DTI pulse sequence with high isotropic spatial resolution was developed for whole brain imaging in under 20 minutes. To minimize the effects of brain motion, a cardiac synchronized, multiecho, DW‐SSFP pulse sequence was implemented. Motion artifacts were further reduced by a combination of linear phase correction, corrupt projection detection and rejection, sampling density reweighting, and parallel imaging reconstruction. The combination of these methods greatly improved the quality of 3D DTI in the brain. J. Magn. Reson. Imaging 2009;29:1175–1184. © 2009 Wiley‐Liss, Inc.     

Robust GRAPPA‐accelerated diffusion‐weighted readout‐segmented (RS)‐EPI

Readout segmentation (RS‐EPI) has been suggested as a promising variant to echo‐planar imaging (EPI) for high‐resolution imaging, particularly when combined with parallel imaging. This work details some of the technical aspects of diffusion‐weighted (DW)‐RS‐EPI, outlining a set of reconstruction methods and imaging parameters that can both minimize the scan time and afford high‐resolution diffusion imaging with reduced distortions. These methods include an efficient generalized autocalibrating partially parallel acquisition (GRAPPA) calibration for DW‐RS‐EPI data without scan time penalty, together with a variant for the phase correction of partial Fourier RS‐EPI data. In addition, the role of pulsatile and rigid‐body brain motion in DW‐RS‐EPI was assessed. Corrupt DW‐RS‐EPI data arising from pulsatile nonlinear brain motion had a prevalence of ～7% and were robustly identified via k‐space entropy metrics. For DW‐RS‐EPI data corrupted by rigid‐body motion, we showed that no blind overlap was required. The robustness of RS‐EPI toward phase errors and motion, together with its minimized distortions compared with EPI, enables the acquisition of exquisite 3 T DW images with matrix sizes close to 512². Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Quality assessment of high angular resolution diffusion imaging data using bootstrap on Q-ball reconstruction

Purpose:

To develop a bootstrap method to assess the quality of High Angular Resolution Diffusion Imaging (HARDI) data using Q‐Ball imaging (QBI) reconstruction.

Materials and Methods:

HARDI data were re‐shuffled using regular bootstrap with jackknife sampling. For each bootstrap dataset, the diffusion orientation distribution function (ODF) was estimated voxel‐wise using QBI reconstruction based on spherical harmonics functions. The reproducibility of the ODF was assessed using the Jensen‐Shannon divergence (JSD) and the angular confidence interval was derived for the first and the second ODF maxima. The sensitivity of the bootstrap method was evaluated on a human subject by adding synthetic noise to the data, by acquiring a map of image signal‐to‐noise ratio (SNR) and by varying the echo time and the b‐value.

Results:

The JSD was directly linked to the image SNR. The impact of echo times and b‐values was reflected by both the JSD and the angular confidence interval, proving the usefulness of the bootstrap method to evaluate specific features of HARDI data.

Conclusion:

The bootstrap method can effectively assess the quality of HARDI data and can be used to evaluate new hardware and pulse sequences, perform multifiber probabilistic tractography, and provide reliability metrics to support clinical studies. J. Magn. Reson. Imaging 2011;33:1194–1208. © 2011 Wiley‐Liss, Inc.     

Cerebral asymmetry in patients with schizophrenia: A voxel‐based morphometry (VBM) and diffusion tensor imaging (DTI) study

Purpose:

To evaluate the differences in gray‐ and white‐matter asymmetry between schizophrenia patients and normal subjects.

Materials and Methods:

Forty‐eight right‐handed patients with chronic schizophrenia (24 males and 24 females) and 48 right‐handed age‐ and sex‐matched healthy controls (24 males and 24 females) were included in this study. The effects of diagnosis on gray‐matter volume asymmetry and white‐matter fractional anisotropy (FA) asymmetry were evaluated with use of voxel‐based morphometry (VBM) and voxel‐based analysis of FA maps derived from diffusion tensor imaging (DTI), respectively.

Results:

The mean gray‐ and white‐matter volumes were significantly smaller in the schizophrenia group than in the control group. The voxel‐based morphometry (VBM) showed no significant effect of diagnosis on gray‐matter volume asymmetry. The voxel‐based analysis of DTI also showed no significant effect of diagnosis on white‐matter FA asymmetry.

Conclusion:

Our results of voxel‐based analyses showed no significant differences in either gray‐matter volume asymmetry or white‐matter FA asymmetry between schizophrenia patients and normal subjects. J. Magn. Reson. Imaging 2010;31:221–226. © 2009 Wiley‐Liss, Inc.     

Toward a practical protocol for human optic nerve DTI with EPI geometric distortion correction

Purpose

To develop a practical protocol for diffusion tensor imaging (DTI) of the human optic nerve with echo planar imaging (EPI) geometric distortion correction.

Materials and Methods

A conventional DTI protocol was modified to acquire images with fat and cerebrospinal fluid (CSF) suppression and field inhomogeneity maps of contiguous coronal slices covering the whole brain. The technique was applied to healthy volunteers and multiple sclerosis patients with and without a history of unilateral optic neuritis. DTI measures and optic nerve tractography before and after geometric distortion correction were compared. Diffusion measures from left and right or from affected and unaffected eyes in different subject cohorts were reported.

Results

The image geometry after correction closely resembled reference anatomical images. Optic nerve tractography became feasible after distortion correction. The diffusion measures from the healthy volunteers were in good agreement with the literature. Statistically significant differences were found in the fractional anisotropy and orthogonal eigenvalues between affected and unaffected eyes in optic neuritis patients with poor recovery. The diffusion measures before and after geometric distortion correction were not significantly different. For cohorts without optic neuritis, the difference between diffusion measures from left and right eyes was not statistically significant.

Conclusion

The proposed technique could provide a practical DTI protocol to study the human optic nerve. J. Magn. Reson. Imaging 2009;30:699–707. © 2009 Wiley‐Liss, Inc.     

Targeted single-shot methods for diffusion-weighted imaging in the kidneys

Purpose:

To investigate the feasibility of combining the inner‐volume‐imaging (IVI) technique with single‐shot diffusion‐weighted (DW) spin‐echo echo‐planar imaging (SE‐EPI) and DW‐SPLICE (split acquisition of fast spin‐echo) sequences for renal DW imaging.

Materials and Methods:

Renal DWI was performed in 10 healthy volunteers using single‐shot DW‐SE‐EPI, DW‐SPLICE, targeted‐DW‐SE‐EPI, and targeted‐DW‐SPLICE. We compared the quantitative diffusion measurement accuracy and image quality of these targeted‐DW‐SE‐EPI and targeted DW‐SPLICE methods with conventional full field of view (FOV) DW‐SE‐EPI and DW‐SPLICE measurements in phantoms and normal volunteers.

Results:

Compared with full FOV DW‐SE‐EPI and DW‐SPLICE methods, targeted‐DW‐SE‐EPI and targeted‐DW‐SPLICE approaches produced images of superior overall quality with fewer artifacts, less distortion, and reduced spatial blurring in both phantom and volunteer studies. The apparent diffusion coefficient (ADC) values measured with each of the four methods were similar and in agreement with previously published data. There were no statistically significant differences between the ADC values and intravoxel incoherent motion (IVIM) measurements in the kidney cortex and medulla using single‐shot DW‐SE‐EPI, targeted‐DW‐EPI, and targeted‐DW‐SPLICE (P > 0.05).

Conclusion:

Compared with full‐FOV DWI methods, targeted‐DW‐SE‐EPI and targeted‐DW‐SPLICE techniques reduced image distortion and artifacts observed in the single‐shot DW‐SE‐EPI images, reduced blurring in DW‐SPLICE images, and produced comparable quantitative DW and IVIM measurements to those produced with conventional full‐FOV approaches. J. Magn. Reson. Imaging 2011;33:1517–1525. © 2011 Wiley‐Liss, Inc.     

Diffusion-weighted MRI: role in detecting abdominopelvic internal fistulas and sinus tracts

Purpose:

To retrospectively determine the incremental value of diffusion‐weighted MR‐imaging (DW‐MRI) to T2‐weighted (T2w) images in diagnosis of internal fistulas (IFs) and sinus tracts (STs).

Materials and Methods:

Fourteen patients with 25 IFs and STs arising from the small bowel ( 20 ), colon ( 4 ) and biliary tract ( 1 ) were included. Two independent observers reviewed T2w images, T2w+DW‐MRI images and T2w+contrast enhanced T1‐weighted (CE T1w) images at three sessions to detect IF/ST based on a confidence scale of five. Sensitivity and confidence score of each session was compared.

Results:

10/25 (40%) and 9/25 (36%) IFs and STs were detected on T2w images by observer 1 and 2, respectively. Both observers detected 19/25 (76%) and 24/25(96%) IFs and STs on T2w+DW‐MRI and T2w+CE T1w images, respectively. Detection rate and confidence score improved significantly by combining T2w images with DW‐MRI or CE T1w images (reader 1 + 2: P ≤ 0.01). There was no significant difference between the IF/ST detection rate of T2w+DW‐MRI and T2w+CE T1 image combinations. Confidence scores with T2w+CE T1w images were significantly greater than DW‐MRI+T2w images (reader 1:P = 0.01; reader 2: P = 0.03).

Conclusion:

DW‐MRI showed additional value to T2w imaging for diagnosis of IF and ST. DW‐MRI can be a useful adjunct, especially for patients with renal failure. J. Magn. Reson. Imaging 2012;35:125‐131. © 2011 Wiley Periodicals, Inc.     

Human cervical spinal cord funiculi: Investigation with magnetic resonance diffusion tensor imaging

Purpose:

To use spinal cord diffusion tensor imaging (DTI) for investigating human cervical funiculi, acquire axial diffusion magnetic resonance imaging (MRI) data with an in‐plane resolution sufficient to delineate subquadrants within the spinal cord, obtain corresponding DTI metrics, and assess potential regional differences.

Materials and Methods:

Healthy volunteers were studied with a 3 T Siemens Trio MRI scanner. DTI data were acquired using a single‐shot spin echo EPI sequence. The spatial resolution allowed for the delineation of regions of interest (ROIs) in the ventral, dorsal, and lateral spinal cord funiculi. ROI‐based and tractography‐based analyses were performed.

Results:

Significant fractional anisotropy (FA) differences were found between ROIs in the dorsal and ventral funiculi (P = 0.0001), dorsal and lateral funiculi (P = 0.015), and lateral and ventral funiculi (P = 0.0002). Transverse diffusivity was significantly different between ROIs in the ventral and dorsal funiculi (P = 0.003) and the ventral and lateral funiculi (P = 0.004). Tractography‐based quantifications revealed DTI parameter regional differences that were generally consistent with the ROI‐based analysis.

Conclusion:

Original contributions are: 1) the use of a tractography‐based method to quantify DTI metrics in the human cervical spinal cord, and 2) reported DTI values in various funiculi at 3 T. J. Magn. Reson. Imaging 2010;31:829–837. ©2010 Wiley‐Liss, Inc.     

Diffusion tensor imaging (DTI) with retrospective motion correction for large-scale pediatric imaging

Purpose:

To develop and implement a clinical DTI technique suitable for the pediatric setting that retrospectively corrects for large motion without the need for rescanning and/or reacquisition strategies, and to deliver high‐quality DTI images (both in the presence and absence of large motion) using procedures that reduce image noise and artifacts.

Materials and Methods:

We implemented an in‐house built generalized autocalibrating partially parallel acquisitions (GRAPPA)‐accelerated diffusion tensor (DT) echo‐planar imaging (EPI) sequence at 1.5T and 3T on 1600 patients between 1 month and 18 years old. To reconstruct the data, we developed a fully automated tailored reconstruction software that selects the best GRAPPA and ghost calibration weights; does 3D rigid‐body realignment with importance weighting; and employs phase correction and complex averaging to lower Rician noise and reduce phase artifacts. For select cases we investigated the use of an additional volume rejection criterion and b‐matrix correction for large motion.

Results:

The DTI image reconstruction procedures developed here were extremely robust in correcting for motion, failing on only three subjects, while providing the radiologists high‐quality data for routine evaluation.

Conclusion:

This work suggests that, apart from the rare instance of continuous motion throughout the scan, high‐quality DTI brain data can be acquired using our proposed integrated sequence and reconstruction that uses a retrospective approach to motion correction. In addition, we demonstrate a substantial improvement in overall image quality by combining phase correction with complex averaging, which reduces the Rician noise that biases noisy data. J. Magn. Reson. Imaging 2012;36:961–971. © 2012 Wiley Periodicals, Inc.     

Predicting survival in glioblastomas using diffusion tensor imaging metrics

Purpose

To retrospectively correlate various diffusion tensor imaging (DTI) metrics in patients with glioblastoma multiforme (GBM) with patient survival analysis and also degree of tumor proliferation index determined histologically.

Materials and Methods

Thirty‐four patients with histologically confirmed treatment naive GBMs underwent DTI on a 3.0 Tesla (T) scanner. Region‐of‐interest was placed on the whole lesion including the enhancing as well as nonenhancing component of the lesion to determine the various DTI metrics. Kaplan‐Meier estimates and Cox proportional hazards regression methods were used to assess the relationship of DTI metrics (minimum and mean values) and Ki‐67 with progression free survival (PFS). To study the relationship between DTI metrics and Ki‐67, Pearson's correlation coefficient was computed.

Results

Univariate analysis showed that patients with fractional anisotropy (FA)_mean ≤ 0.2, apparent diffusion coefficient (ADC)_min ≤ 0.6, planar anisotropy (CP)_min ≤ 0.002, spherical anisotropy (CS)_mean > 0.68 and Ki‐67 > 0.3 had lower PFS rate. The multivariate analysis demonstrated that only CP_min was the best predictor of survival in these patients, after adjusting for age, Karnofsky performance scale and extent of resection. No significant correlation between DTI metrics and Ki‐67 were observed.

Conclusion

DTI metrics can be used as a sensitive and early indicator for PFS in patients with glioblastomas. This could be useful for treatment planning as high‐grade gliomas with lower ADC_min, FA_mean, CP_min, and higher CS_mean values may be treated more aggressively. J. Magn. Reson. Imaging 2010;32:788–795. © 2010 Wiley‐Liss, Inc.     

Robust correction of spike noise: Application to diffusion tensor imaging

Echo‐planar imaging (EPI) ‐based diffusion tensor imaging (DTI) is particularly prone to spike noise. However, existing spike noise correction methods are impractical for corrupted DTI data because the methods correct the complex MRI signal, which is not usually stored on clinical MRI systems. The present work describes a novel Outlier Detection De‐spiking technique (ODD) that consists of three steps: detection, localization, and correction. Using automated outlier detection schemes, ODD exploits the data redundancy available in DTI data sets that are acquired with a minimum of six different diffusion‐weighted images (DWIs) with similar signal and noise properties. A mathematical formulation, describing the effects of spike noise on magnitude images, yields appropriate measures for an outlier detection scheme used for spike detection while a normalization‐dependent outlier detection scheme is used for spike localization. ODD performs accurately on diverse DTI data sets corrupted by spike noise and can be used for automated control of DTI data quality. ODD can also be extended to other MRI applications with data redundancy, such as dynamic imaging and functional MRI. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Smoothing that does not blur: Effects of the anisotropic approach for evaluating diffusion tensor imaging data in the clinic

Purpose:

To compare the effects of anisotropic and Gaussian smoothing on the outcomes of diffusion tensor imaging (DTI) voxel‐based (VB) analyses in the clinic, in terms of signal‐to‐noise ratio (SNR) enhancement and directional information and boundary structures preservation.

Materials and Methods:

DTI data of 30 Alzheimer's disease (AD) patients and 30 matched control subjects were obtained at 3T. Fractional anisotropy (FA) maps with variable degrees and quality (Gaussian and anisotropic) of smoothing were created and compared with an unsmoothed dataset. The two smoothing approaches were evaluated in terms of SNR improvements, capability to separate differential effects between patients and controls by a standard VB analysis, and level of artifacts introduced by the preprocessing.

Results:

Gaussian smoothing regionally biased the FA values and introduced a high variability of results in clinical analysis, greatly dependent on the kernel size. On the contrary, anisotropic smoothing proved itself capable of enhancing the SNR of images and maintaining boundary structures, with only moderate dependence of results on smoothing parameters.

Conclusion:

Our study suggests that anisotropic smoothing is more suitable in DTI studies; however, regardless of technique, a moderate level of smoothing seems to be preferable considering the artifacts introduced by this manipulation. J. Magn. Reson. Imaging 2010;31:690–697. © 2010 Wiley‐Liss, Inc.     

Effect of cerebral spinal fluid suppression for diffusional kurtosis imaging

Purpose:

To evaluate the cerebral spinal fluid (CSF) partial volume effect on diffusional kurtosis imaging (DKI) metrics in white matter and cortical gray matter.

Materials and Methods:

Four healthy volunteers participated in this study. Standard DKI and fluid‐attenuated inversion recovery (FLAIR) DKI experiments were performed using a twice‐refocused‐spin‐echo diffusion sequence. The conventional diffusion tensor imaging (DTI) metrics of fractional anisotropy (FA), mean, axial, and radial diffusivity (MD, D_‖, D_?) together with DKI metrics of mean, axial, and radial kurtosis (MK, K_‖, K_?), were measured and compared. Single image slices located above the lateral ventricles, with similar anatomical features for each subject, were selected to minimize the effect of CSF from the ventricles.

Results:

In white matter, differences of less than 10% were observed between diffusion metrics measured with standard DKI and FLAIR‐DKI sequences, suggesting minimal CSF contamination. For gray matter, conventional DTI metrics differed by 19% to 52%, reflecting significant CSF partial volume effects. Kurtosis metrics, however, changed by 11% or less, indicating greater robustness with respect to CSF contamination.

Conclusion:

Kurtosis metrics are less sensitive to CSF partial voluming in cortical gray matter than conventional diffusion metrics. The kurtosis metrics may then be more specific indicators of changes in tissue microstructure, provided the effect sizes for the changes are comparable. J. Magn. Reson. Imaging 2013;37:365–371. © 2012 Wiley Periodicals, Inc.

     

Diffusion-weighted MRI as an adjunct to mammography in women under 50 years of age: an initial study

Purpose:

To evaluate diffusion‐weighted magnetic resonance (DW) imaging as an adjunct to mammography for the detection of small invasive breast cancer.

Materials and Methods:

Institutional review board standards were followed for this retrospective study. We performed both breast DW imaging and mammography on 25 women under 50 years of age with pathologically proven T1 breast cancer and on 21 healthy women under 50 years of age. Four offsite radiologists blind to the clinical information independently interpreted the mammograms and DW images and then classified their confidence level regarding the presence of breast cancer. The composite area under receiver operating characteristic curve (AUC), of mammography alone, DW imaging alone, and the combination of DW imaging and mammography (DWI/Cal) were calculated.

Results:

The AUC of composite ROC curves of mammography, DW imaging, DWI/Cal combination, was 0.79 (95% CI, 0.72–0.87), 0.86 (95% CI, 0.84–0.87), and 0.96 (95% CI, 0.92–1.00), respectively.

Conclusion:

DW imaging may be a useful adjunct to mammography in the detection of small invasive breast cancer in women under 50 years of age. J. Magn. Reson. Imaging 2012;36:139–144. © 2012 Wiley Periodicals, Inc.     

Diffusion tensor imaging of forearm nerves in humans

Purpose:

To implement a diffusion tensor imaging (DTI) protocol for visualization of peripheral nerves in human forearm.

Materials and Methods:

This Health Insurance Portability and Accountability Act (HIPAA)‐compliant study was approved by our Institutional Review Board and written informed consent was obtained from 10 healthy participants. T₁‐ and T₂‐weighted turbo spin echo with fat saturation, short tau inversion recovery (STIR), and DTI sequences with 21 diffusion‐encoding directions were implemented to acquire images of the forearm nerves with an 8 channel knee coil on a 3T MRI scanner. Identification of the nerves was based on T₁‐weighted, T₂‐weighted, STIR, and DTI‐derived fractional anisotropy (FA) images. Maps of the DTI‐derived indices, FA, mean diffusivity (MD), longitudinal diffusivity (λ_//), and radial diffusivity (λ_?) along the length of the nerves were generated.

Results:

DTI‐derived maps delineated the forearm nerves more clearly than images acquired with other sequences. Only ulnar and median nerves were clearly visualized on the DTI‐derived FA maps. No significant differences were observed between the left and right forearms in any of the DTI‐derived measures. Significant variation in the DTI measures was observed along the length of the nerve. Significant differences in the DTI measures were also observed between the median and ulnar nerves.

Conclusion:

DTI is superior in visualizing the median and ulnar nerves in the human forearm. The normative data could potentially help distinguish normal from diseased nerves. J. Magn. Reson. Imaging 2012;36:920–927. © 2012 Wiley Periodicals, Inc.

     

Diffusion tensor and tensor metrics imaging in intracranial epidermoid cysts

Purpose

To explore the utility of diffusion tensor imaging (DTI) and diffusion tensor metrics (DTM) in characterizing the structural pathology of epidermoid cysts. DTI gives information about the tissue structure; a high fractional anisotropy (FA) indicates a highly structured orientation of the tissue, fibers, or white matter tracts. Based on the tensor rank, a set of three metrics has been described that can be used to measure the directional dependence of diffusion: linear anisotropy (CL), planar anisotropy (CP), and spherical anisotropy (CS). DTM takes into account the shape of diffusion anisotropy and hence may provide better insight into the orientation of structures than FA.

Materials and Methods

DTI was performed in three patients with epidermoid cysts. FA, directionally‐averaged mean diffusivity (Dav), exponential apparent diffusion coefficient (eADC), and DTM, such as CL, CP, and CS, were measured from the tumor core as well as from the normal‐appearing white matter. Histopathological correlation was obtained.

Results

Epidermoid cysts showed high FA with Dav values similar to that of normal white matter. eADC maps did not show any restriction of diffusion. FA values were high, but not as high as that for the white matter. CP values were higher and CL values were lower than those obtained for the white matter in various regions.

Conclusion

High CP values suggest preferential diffusion of water molecules along a two‐dimensional geometry, which could be attributed to the well‐structured orientation of keratin filaments and flakes within the tumor as demonstrated by histopathology. Advanced imaging modalities like DTI with DTM can provide information regarding the microstructural anatomy of the epidermoid cysts. J. Magn. Reson. Imaging 2009;29:967–970. © 2009 Wiley‐Liss, Inc.     

Diffusion tensor imaging tractography parameters of limbic system bundles in temporal lobe epilepsy patients

Purpose:

To investigate changes in diffusion tensor imaging (DTI) measures in limbic system white matter of patients with temporal lobe epilepsy (TLE) using diffusion tensor tractography.

Materials and Methods:

DTI metrics including fractional anisotropy (FA), λ1, λ2, λ3, and trace (Tr) coefficients were obtained from tractography for bilateral fornix, superior and inferior cingulum fibers in 18 patients and 10 healthy controls. Hippocampal signal‐to‐noise ratio (SNR) quantitative analysis was performed in order to confirm the magnetic resonance imaging (MRI) hippocampal lesion presence or absence in TLE patients.

Results:

Nine patients presented unilateral hippocampal sclerosis (TLE+HS) and nine patients had no signal abnormalities on conventional MRI (TLE?HS). On the ipsilateral seizure side, all three investigated tracts showed significant DTI indices abnormalities in both patient groups when compared with controls, most marked on the inferior cingulum. Contralateral to the seizure side, the three tracts presented significant DTI parameters in only the TLE+HS group when compared with controls.

Conclusion:

The DTI abnormalities found in the TLE?HS group may suggest that in the inferior cingulum the structural integrity is more affected than in the fornix or superior cingulum white matter bundles. The eigenvalues taken separately add complementary information to the FA and Tr metrics and may be useful indices in better understanding the architectural reorganization of limbic system tracts in TLE patients without HS. J. Magn. Reson. Imaging 2012;36:561–568. © 2012 Wiley Periodicals, Inc.

     

Changes in cerebellar functional connectivity and anatomical connectivity in schizophrenia: a combined resting-state functional MRI and diffusion tensor imaging study

Purpose:

To examine the functional and anatomical connectivity of the cerebellum and their relationship in schizophrenia through resting‐state functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI).

Materials and Methods:

Ten subjects with schizophrenia and 10 healthy controls underwent resting‐state fMRI and DTI. Left and right cerebellar seed regions were used in a voxel‐wise functional connectivity analysis of the cerebellum. Fractional anisotropy (FA) was measured to assess white matter integrity of the middle cerebellar peduncle (MCP) and superior cerebellar peduncle (SCP). Differences in functional connectivity and FA values between the two groups were determined by two‐sample t‐tests. The relationship between functional connectivity and FA values in both groups were assessed using Pearson s correlation.

Results:

Decreased functional connectivity to the left middle temporal gyrus, bilateral middle cingulate cortex, right paracentral lobule, right thalamus, and bilateral cerebellum were found in subjects with schizophrenia when compared to healthy controls; while decreased FA values in the left SCP were found in subjects with schizophrenia compared to healthy controls. Significant correlation was observed between the functional connectivity of the left cerebellum‐right paracentral lobule and right cerebellum‐right thalamus and the FA values of the MCP in healthy controls.

Conclusion:

Findings of this multi‐modal imaging study support functional and anatomical connectivity abnormalities and the role of the cerebellum in schizophrenia. They also indicate the need for further investigation regarding the relationship between functional and anatomical connectivity and its role in neuropathophysiology. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Quantitative assessment of the cervical spinal cord damage in neuromyelitis optica using diffusion tensor imaging at 3 Tesla

Purpose:

To investigate whether quantitative MRI measures of cervical spinal cord white matter (WM) using diffusion tensor imaging (DTI) in neuromyelitis optica (NMO) differed from controls and correlated with clinical disability.

Materials and Methods:

Ten referred patients and 12 healthy volunteers were imaged on a 3 Tesla scanner and patients were clinically assessed on the Expanded Disability Status Scale (EDSS). Two raters quantified DTI‐derived indices from all participants, including fractional anisotropy (FA), mean diffusivity (MD), parallel diffusivity (lambda[parallel]) and perpendicular diffusivity (lambda[perpendicular]) at C1–C6 for lateral and dorsal columns. After the inter‐rater reliability test, univariate correlations between DTI measures and disability were assessed using the Spearman's rho correlation coefficient. Multiple regression analysis was performed to investigate which DTI measures independently correlated with the clinical score.

Results:

Statistical test results indicated high reliability of all DTI measurements between two raters. NMO patients showed reduced FA, increased MD and lambda[perpendicular] compared with controls while lambda[parallel] did not show any significant difference. The former three DTI metrics also showed significant correlations with disability scores, and especially FA was found to be sensitive to mild NMO (EDSS ≤ 3)

Conclusion:

FA is a potentially useful quantitative biomarker of otherwise normal appearing WM damage in NMO. Such damage is associated with clinical disability. J. Magn. Reson. Imaging 2011;33:1312–1320. © 2011 Wiley‐Liss, Inc.