Diffusion tensor imaging of the brain: effects of distortion correction with correspondence to numbers of encoding directions

Hippocampal impairment in patients with Essential Tremor

INTRODUCTION

There is growing evidence that a proportion of patients with Essential Tremor (ET) may develop a memory impairment over time. However, no studies have evaluated whether hippocampal damage really occur in ET. This study investigated the macro and micro-structural integrity of the hippocampus in ET subjects using a multimodal MRI approach.

METHODS

Neuropsychological and MRI data were acquired from 110 participants (60 patients with ET and 50 age-, sex-, and education-matched healthy controls [HC]). Whole-brain T1-weighted and Diffusion Tensor Imaging (DTI) were performed to assess macro-and microstructural alterations. MRI parameters (volume; mean diffusivity [MD]; fractional anisotropy [FA]) of bilateral hippocampi were obtained. In order to evaluate the relationship between MRI alterations and neurocognitive impairment, hippocampal parameters were also correlated with cognitive test scores.

RESULTS

Compared to controls, ET patients showed a subclinical memory impairment with significantly lower memory scores, but within the normal ranges. Despite the subclinical damage, however, ET patients showed a significant increase in MD values in the bilateral hippocampi in comparison with HC. A significant correlation was also found between MD and memory scores in ET.

CONCLUSION

This study improves the knowledge on memory impairment in ET, as our results demonstrate for the first time the hippocampal microstructural damage related to subclinical memory impairment in ET patients. Further studies are needed before these findings can be considered predictive of a distinct ET subtype or suggestive of a co-occurent dementia.

Periventricular white matter changes in idiopathic intracranial hypertension

Objective

To evaluate whether increased cerebrospinal fluid (CSF) pressure causes alteration of periventricular white matter (WM) microstructure in patients with idiopathic intracranial hypertension (IIH).

Methods

In a prospective study, patients with refractory chronic headache with and without IIH performed a neuroimaging study including 3T MRI, 3D Phase Contrast MR venography, and diffusion tensor imaging (DTI) of the brain. Whole‐brain voxel‐wise comparisons of DTI abnormalities of WM were performed using tract‐based spatial statistics. A correlation analysis between DTI indices and CSF opening pressure, highest peak, and mean pressure was also performed in patients with IIH.

Results

We enrolled 62 consecutive patients with refractory chronic headaches. Thirty‐five patients with IIH, and 27 patients without increased intracranial pressure. DTI analysis revealed no fractional anisotropy changes, but decreased mean, axial, and radial diffusivity in body (IIH_MD = 0.80 ± 0.04, non‐IIH_MD = 0.84 ± 0.4, IIH_AD = 1.67 ± 0.07, non‐IIH_AD = 1.74 ± 0.05, IIH_RD = 0.38 ± 0.04, non‐IIH_RD = 0.42 ± 0.05 [mm²/sec × 10⁻³]) of corpus callosum, and in right superior corona radiata (IIH_MD = 0.75 ± 0.04, non‐IIH_MD = 0.79 ± 0.05, IIH_AD = 1.19 ± 0.07, non‐IIH_AD = 1.28 ± 0.09, IIH_RD = 0.59 ± 0.03, non‐IIH_RD = 0.53 ± 0.03 [mm²/sec × 10⁻³]) of 35 patients with IIH compared with 27 patients without increased intracranial pressure. DTI indices were negatively correlated with high CSF pressures (P < 0.05). After medical treatment, eight patients showed incremented MD in anterior corona radiata left and right and superior corona radiata right.

Conclusions

There is significant DTI alteration in periventricular WM microstructure of patients with IIH suggesting tissue compaction correlated with high CSF pressure. This periventricular WM change may be partially reversible after medical treatment.

Prediction of Neurological Impairment in Cervical Spondylotic Myelopathy using a Combination of Diffusion MRI and Proton MR Spectroscopy

PURPOSE

In the present study we investigated a combination of diffusion tensor imaging (DTI) and magnetic resonance spectroscopic (MRS) biomarkers in order to predict neurological impairment in patients with cervical spondylosis.

METHODS

Twenty-seven patients with cervical spondylosis were evaluated. DTI and single voxel MRS were performed in the cervical cord. N-acetylaspartate (NAA) and choline (Cho) metabolite concentration ratios with respect to creatine were quantified, as well as the ratio of choline to NAA. The modified mJOA scale was used as a measure of neurologic deficit. Linear regression was performed between DTI and MRS parameters and mJOA scores. Significant predictors from linear regression were used in a multiple linear regression model in order to improve prediction of mJOA. Parameters that did not add value to model performance were removed, then an optimized multiparametric model was established to predict mJOA.

RESULTS

Significant correlations were observed between the Torg-Pavlov ratio and FA (R2 = 0.2021, P = 0.019); DTI fiber tract density and FA, MD, Cho/NAA (R2 = 0.3412, P = 0.0014; R2 = 0.2112, P = 0.016; and R2 = 0.2352, P = 0.010 respectively); along with FA and Cho/NAA (R2 = 0.1695, P = 0.033). DTI fiber tract density, MD and FA at the site of compression, along with Cho/NAA at C2, were significantly correlated with mJOA score (R2 = 0.05939, P < 0.0001; R2 = 0.4739, P < 0.0001; R2 = 0.7034, P < 0.0001; R2 = 0.4649, P < 0.0001). A combination biomarker consisting of DTI fiber tract density, MD, and Cho/NAA showed the best prediction of mJOA (R2 = 0.8274, P<0.0001), with post-hoc tests suggesting fiber tract density, MD, and Cho/NAA were all significant contributors to predicting mJOA (P = 0.00053, P = 0.00085, and P = 0.0019, respectively).

CONCLUSION

A linear combination of DTI and MRS measurements within the cervical spinal cord may be useful for accurately predicting neurological deficits in patients with cervical spondylosis. Additional studies may be necessary to validate these observations.

Diffusion tensor imaging predicts functional impairment in mild-to-moderate cervical spondylotic myelopathy

BACKGROUND CONTEXT

Magnetic resonance imaging (MRI) is the standard imaging modality for the assessment of cervical spinal cord; however, MRI assessment of the spinal cord in cervical spondylotic myelopathy patients has not demonstrated a consistent association with neurologic function or outcome after surgical or medical intervention. Thus, there is a need for sensitive imaging biomarkers that can predict functional impairment in patients with advanced cervical spondylosis.

PURPOSE

To implement diffusion tensor imaging (DTI) as an imaging biomarker for microstructural integrity and functional impairment in patients with cervical spondylosis.

STUDY DESIGN

Nonrandomized, single institution study.

PATIENT SAMPLE

Forty-eight cervical spondylosis patients with or without spinal cord signal change underwent DTI of the spinal cord along with functional assessment.

OUTCOME MEASURES

Functional measures of neurologic function via modified Japanese Orthopedic Association (mJOA) score.

METHODS

A zoomed-echoplanar imaging technique and two-dimensional spatially selective radiofrequency excitation pulse were used for DTI measurement. Fractional anisotropy (FA), mean diffusivity (MD), radial and axial diffusion (AD) coefficient, AD anisotropy, ψ, defined as AD-MD, and the standard deviation (SD) of primary eigenvector orientation were evaluated at the site of compression.

RESULTS

Results suggest average FA, transverse apparent diffusion coefficient, ψ, and SD of primary eigenvector orientation at the spinal level of highest compression were linearly correlated with mJOA score. Receiver-operator characteristic analysis suggested FA and ψ could identify stenosis patients with mild-to-moderate symptoms with a relatively high sensitivity and specificity.

CONCLUSIONS

The results of this study support the potential use of DTI as a biomarker for predicting functional impairment in patients with cervical spondylosis.

Optimization of the parameters for diffusion tensor magnetic resonance imaging data acquisition for breast fiber tractography at 1.5 T

INTRODUCTION

Diffusion tensor MRI has emerged as a promising tool for the analysis of the microscopic properties of tissues. Optimizing image acquisition parameters is essential for producing high-quality DTI. This study aimed to optimize the parameters for DTI data acquisition for breast fiber tractography at 1.5 T.

PATIENTS AND METHODS

A total of 21 healthy volunteers received breast DTI scanning using an ASSET-based EPI technique operated under different parameters including b value, the number of diffusion gradient directions, and spatial resolution. The images were analyzed for signal-to-noise, signal intensity ratio, mean number and length of reconstructive fiber tracts, and fractional anisotropy value.

RESULTS

The optimal acquisition parameters at 1.5 T for breast DT-MRI fiber tractography were determined as follows: axial 31 direction, b = 600 seconds per mm(2), matrix 128 × 128 with slice thickness of 3 mm.

CONCLUSION

The optimization of data acquisition parameters could improve the quality of breast DT-MRI images and assist fiber tractography at 1.5 T.

Diffusion tensor tractography of the uncinate fasciculus: pitfalls in quantitative analysis due to traumatic volume changes

PURPOSE

To demonstrate the sensitivity of quantitative diffusion tensor tractography to traumatic injury of the uncinate fasciculus (UF), and to evaluate the effect of volume changes on the accuracy of quantitative analysis.

MATERIALS AND METHODS

Diffusion tensor imaging (DTI) was performed at 3 T for 110 patients with traumatic brain injury (TBI) and 60 control subjects. Volume, mean diffusivity (MD), and mean fractional anisotropy (FA) of the UF were measured by means of tractography. The influence of FA threshold on mean FA values was determined and the values were further related to the tract volume.

RESULTS

In patients with TBI, 16% of the volumes and 29% of the FA values were decreased and 25% of the MD values were increased (>2 SD from the mean of controls). Small tracts (6% of trajectories) often had normal mean FA, but low volume-related FA values. Large UFs often had decreased mean FA values, but normal volume-related central values (3% of trajectories).

CONCLUSION

Posttraumatic FA and MD changes and volume reductions are common in the tractography of UF. Trauma-induced volume changes can cause misleading whole-tract mean FA values. Therefore, additional volume-based analysis of the central part is beneficial for clinical assessment.

Visual pathway study using in vivo diffusion tensor imaging tractography to complement classic anatomy

BACKGROUND

Knowledge of the individual course of the optic radiations (ORs) is important to avoid postoperative visual deficits. Cadaveric studies of the visual pathways are limited because it has not been possible to separate the OR from neighboring tracts accurately and results may not apply to individual patients. Diffusion tensor imaging studies may be able to demonstrate the relationships between the OR and neighboring fibers in vivo in individual subjects.

OBJECTIVE

To use diffusion tensor imaging tractography to study the OR and the Meyer loop (ML) anatomy in vivo.

METHODS

Ten healthy subjects underwent magnetic resonance imaging with diffusion imaging at 3 T. With the use of a fiducial-based diffusion tensor imaging tractography tool (Slicer 3.3), seeds were placed near the lateral geniculate nucleus to reconstruct individual visual pathways and neighboring tracts. Projections of the ORs onto 3-dimensional brain models were shown individually to quantify relationships to key landmarks.

RESULTS

Two patterns of visual pathways were found. The OR ran more commonly deep in the whole superior and middle temporal gyri and superior temporal sulcus. The OR was closely surrounded in all cases by an inferior longitudinal fascicle and a parieto/occipito/temporo-pontine fascicle. The mean left and right distances between the tip of the OR and temporal pole were 39.8 ± 3.8 and 40.6 ± 5.7 mm, respectively.

CONCLUSION

Diffusion tensor imaging tractography provides a practical complementary method to study the OR and the Meyer loop anatomy in vivo with reference to individual 3-dimensional brain anatomy.