In vivo diffusion MRI detects early spinal cord axonal pathology in a mouse model of amyotrophic lateral sclerosis

Diffusion magnetic resonance imaging (MRI) exhibits contrast that identifies macro‐ and microstructural changes in neurodegenerative diseases. Previous studies have shown that MR diffusion tensor imaging (DTI) can observe changes in spinal cord white matter in animals and humans affected with symptomatic amyotrophic lateral sclerosis (ALS). The goal of this preclinical work was to investigate the sensitivity of DTI for the detection of signs of tissue damage before symptoms appear. High‐field MRI data were acquired using a 9.4‐T animal scanner to examine the spinal cord of an ALS mouse model at pre‐ and post‐symptomatic stages (days 80 and 120, respectively). The MRI results were validated using yellow fluorescent protein (YFP) via optical microscopy of spinal cord tissue slices collected from the YFP,G93A‐SOD1 mouse strain. DTI maps of diffusion‐weighted imaging (DWI) signal intensity, mean diffusivity (MD), fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD) were computed for axial slices of the lumbar region of the spinal cord. Significant changes were observed in FA (6.7% decrease, p < 0.01), AD (19.5% decrease, p < 0.01) and RD (16.1% increase, p < 0.001) at postnatal day 80 (P80). These differences were correlated with changes in axonal fluorescence intensity and membrane cellular markers. This study demonstrates the value of DTI as a potential tool to detect the underlying pathological progression associated with ALS, and may accelerate the discovery of therapeutic strategies for patients with this disease.     

Spatiotemporal microstructural white matter changes in diffusion tensor imaging after transient focal ischemic stroke in rats

Structural reorganization in white matter (WM) after stroke is a potential contributor to substitute or to newly establish the functional field on the injured brain in nature. Diffusion tensor imaging (DTI) is an imaging modality that can be used to evaluate damage and recovery within the brain. This method of imaging allows for in vivo assessment of the restricted movements of water molecules in WM and provides a detailed look at structural connectivity in the brain. For longitudinal DTI studies after a stroke, the conventional region of interest method and voxel‐based analysis are highly dependent on the user‐hypothesis and parameter settings for implementation. In contrast, tract‐based spatial statistics (TBSS) allows for reliable voxel‐wise analysis via the projection of diffusion‐derived parameters onto an alignment‐invariant WM skeleton. In this study, spatiotemporal WM changes were examined with DTI‐derived parameters (fractional anisotropy, FA; mean diffusivity, MD; axial diffusivity, DA; radial diffusivity, RD) using TBSS 2 h to 6 weeks after experimental focal ischemic stroke in rats (N = 6). FA values remained unchanged 2–4 h after the stroke, followed by a continuous decrease in the ipsilesional hemisphere from 24 h to 2 weeks post‐stroke and gradual recovery from the ipsilesional corpus callosum to the external capsule until 6 weeks post‐stroke. In particular, the fibers in these areas were extended toward the striatum of the ischemic boundary region at 6 weeks on tractography. The alterations of the other parameters in the ipsilesional hemisphere showed patterns of a decrease at the early stage, a subsequent pseudo‐normalization of MD and DA, a rapid reduction of RD, and a progressive increase in MD, DA and RD with a decreased extent in the injured area at later stages. The findings of this study may reflect the ongoing processes on tissue damage and spontaneous recovery after stroke.     

Multiband diffusion‐weighted MRI of the eye and orbit free of geometric distortions using a RARE‐EPI hybrid

Diffusion‐weighted imaging (DWI) provides information on tissue microstructure. Single‐shot echo planar imaging (EPI) is the most common technique for DWI applications in the brain, but is prone to geometric distortions and signal voids. Rapid acquisition with relaxation enhancement [RARE, also known as fast spin echo (FSE)] imaging presents a valuable alternative to DWI with high anatomical accuracy. This work proposes a multi‐shot diffusion‐weighted RARE‐EPI hybrid pulse sequence, combining the anatomical integrity of RARE with the imaging speed and radiofrequency (RF) power deposition advantage of EPI. The anatomical integrity of RARE‐EPI was demonstrated and quantified by center of gravity analysis for both morphological images and diffusion‐weighted acquisitions in phantom and in vivo experiments at 3.0 T and 7.0 T. The results indicate that half of the RARE echoes in the echo train can be replaced by EPI echoes whilst maintaining anatomical accuracy. The reduced RF power deposition of RARE‐EPI enabled multiband RF pulses facilitating simultaneous multi‐slice imaging. This study shows that diffusion‐weighted RARE‐EPI has the capability to acquire high fidelity, distortion‐free images of the eye and the orbit. It is shown that RARE‐EPI maintains the immunity to B₀ inhomogeneities reported for RARE imaging. This benefit can be exploited for the assessment of ocular masses and pathological changes of the eye and the orbit.     

High‐resolution diffusion tensor imaging of the human kidneys using a free‐breathing,multi‐slice,targeted field of view approach

Fractional anisotropy (FA) obtained by diffusion tensor imaging (DTI) can be used to image the kidneys without any contrast media. FA of the medulla has been shown to correlate with kidney function. It is expected that higher spatial resolution would improve the depiction of small structures within the kidney. However, the achievement of high spatial resolution in renal DTI remains challenging as a result of respiratory motion and susceptibility to diffusion imaging artefacts. In this study, a targeted field of view (TFOV) method was used to obtain high‐resolution FA maps and colour‐coded diffusion tensor orientations, together with measures of the medullary and cortical FA, in 12 healthy subjects. Subjects were scanned with two implementations (dual and single kidney) of a TFOV DTI method. DTI scans were performed during free breathing with a navigator‐triggered sequence. Results showed high consistency in the greyscale FA, colour‐coded FA and diffusion tensors across subjects and between dual‐ and single‐kidney scans, which have in‐plane voxel sizes of 2 × 2 mm² and 1.2 × 1.2 mm², respectively. The ability to acquire multiple contiguous slices allowed the medulla and cortical FA to be quantified over the entire kidney volume. The mean medulla and cortical FA values were 0.38 ± 0.017 and 0.21 ± 0.019, respectively, for the dual‐kidney scan, and 0.35 ± 0.032 and 0.20 ± 0.014, respectively, for the single‐kidney scan. The mean FA between the medulla and cortex was significantly different (p < 0.001) for both dual‐ and single‐kidney implementations. High‐spatial‐resolution DTI shows promise for improving the characterization and non‐invasive assessment of kidney function. © 2014 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.     

Quantitative MRI of skeletal muscle in a cross‐sectional cohort of patients with spinal muscular atrophy types 2 and 3

The aim of this study was to document upper leg involvement in spinal muscular atrophy (SMA) with quantitative MRI (qMRI) in a cross‐sectional cohort of patients of varying type, disease severity and age. Thirty‐one patients with SMA types 2 and 3 (aged 29.6 [7.6‐73.9] years) and 20 healthy controls (aged 37.9 [17.7‐71.6] years) were evaluated in a 3 T MRI with a protocol consisting of DIXON, T2 mapping and diffusion tensor imaging (DTI). qMRI measures were compared with clinical scores of motor function (Hammersmith Functional Motor Scale Expanded [HFMSE]) and muscle strength. Patients exhibited an increased fat fraction and fractional anisotropy (FA), and decreased mean diffusivity (MD) and T2 compared with controls (all P < .001). DTI parameters FA and MD manifest stronger effects than can be accounted for the effect of fatty replacement. Fat fraction, FA and MD show moderate correlation with muscle strength and motor function: FA is negatively associated with HFMSE and Medical Research Council sum score (τ = ?0.56 and ?0.59; both P < .001) whereas for fat fraction values are τ = ?0.50 and ?0.58, respectively (both P < .001). This study shows that DTI parameters correlate with muscle strength and motor function. DTI findings indirectly indicate cell atrophy and act as a measure independently of fat fraction. Combined these data suggest the potential of muscle DTI in monitoring disease progression and to study SMA pathogenesis in muscle.     

Diffusion‐weighted MRI of the prostate without susceptibility artifacts: Undersampled multi‐shot turbo‐STEAM with rotated radial trajectories

The aim of this study was to develop and evaluate a clinically feasible approach to diffusion‐weighted (DW) MRI of the prostate without susceptibility‐induced artifacts. The proposed method relies on an undersampled multi‐shot DW turbo‐STEAM sequence with rotated radial trajectories and a multi‐step inverse reconstruction with denoised multi‐shot phase maps. The total acquisition time was below 6 min for a resolution of 1.4 × 1.4 × 3.5 mm³ and six directions at b = 600 s mm^?2. Studies of eight healthy subjects and two patients with prostate cancer were performed at 3 T employing an 18‐channel body‐array coil and elements of the spine coil. The method was compared with conventional DW echo‐planar imaging (EPI) of the prostate. The results confirm that DW STEAM MRI avoids geometric distortions and false image intensities, which were present for both single‐shot EPI (ssEPI) and readout‐segmented EPI, particularly near the intestinal wall of the prostate. Quantitative accuracy of the apparent diffusion coefficient (ADC) was validated with use of a numerical phantom providing ground truth. ADC values in the central prostate gland of healthy subjects were consistent with those measured using ssEPI and with literature data. Preliminary results for patients with prostate cancer revealed a correct anatomical localization of lesions with respect to T₂‐weighted MRI in both mean DW STEAM images and ADC maps. In summary, DW STEAM MRI of the prostate offers clinically relevant advantages for the diagnosis of prostate cancer compared with state‐of‐the‐art EPI‐based approaches. The method warrants extended clinical trials.     

Multiple‐echo diffusion tensor acquisition technique (MEDITATE) on a 3T clinical scanner

This article describes the concepts and implementation of an MRI method, the multiple‐echo diffusion tensor acquisition technique (MEDITATE), which is capable of acquiring apparent diffusion tensor maps in two scans on a 3T clinical scanner. In each MEDITATE scan, a set of RF pulses generates multiple echoes, the amplitudes of which are diffusion weighted in both magnitude and direction by a pattern of diffusion gradients. As a result, two scans acquired with different diffusion weighting strengths suffice for accurate estimation of diffusion tensor imaging (DTI) parameters. The MEDITATE variation presented here expands previous MEDITATE approaches to adapt to the clinical scanner platform, such as exploiting longitudinal magnetization storage to reduce T₂ weighting. Fully segmented multi‐shot Cartesian encoding is used for image encoding. MEDITATE was tested on isotropic (agar gel), anisotropic diffusion phantoms (asparagus) and in vivo skeletal muscle in healthy volunteers with cardiac gating. Comparisons of accuracy were performed with standard twice‐refocused spin echo (TRSE) DTI in each case and good quantitative agreement was found between diffusion eigenvalues, mean diffusivity and fractional anisotropy derived from TRSE DTI and from the MEDITATE sequence. Orientation patterns were correctly reproduced in both isotropic and anisotropic phantoms, and approximately for in vivo imaging. This illustrates that the MEDITATE method of compressed diffusion encoding is feasible on the clinical scanner platform. With future development and employment of appropriate view‐sharing image encoding, this technique may be used in clinical applications requiring time‐sensitive acquisition of DTI parameters such as dynamical DTI in muscle. Copyright © 2013 John Wiley & Sons, Ltd.     

Multi‐centre reproducibility of diffusion MRI parameters for clinical sequences in the brain

The purpose of this work was to assess the reproducibility of diffusion imaging, and in particular the apparent diffusion coefficient (ADC), intra‐voxel incoherent motion (IVIM) parameters and diffusion tensor imaging (DTI) parameters, across multiple centres using clinically available protocols with limited harmonization between sequences. An ice–water phantom and nine healthy volunteers were scanned across fives centres on eight scanners (four Siemens 1.5T, four Philips 3T). The mean ADC, IVIM parameters (diffusion coefficient D and perfusion fraction f) and DTI parameters (mean diffusivity MD and fractional anisotropy FA), were measured in grey matter, white matter and specific brain sub‐regions. A mixed effect model was used to measure the intra‐ and inter‐scanner coefficient of variation (CV) for each of the five parameters. ADC, D, MD and FA had a good intra‐ and inter‐scanner reproducibility in both grey and white matter, with a CV ranging between 1% and 7.4%; mean 2.6%. Other brain regions also showed high levels of reproducibility except for small structures such as the choroid plexus. The IVIM parameter f had a higher intra‐scanner CV of 8.4% and inter‐scanner CV of 24.8%. No major difference in the inter‐scanner CV for ADC, D, MD and FA was observed when analysing the 1.5T and 3T scanners separately. ADC, D, MD and FA all showed good intra‐scanner reproducibility, with the inter‐scanner reproducibility being comparable or faring slightly worse, suggesting that using data from multiple scanners does not have an adverse effect compared with using data from the same scanner. The IVIM parameter f had a poorer inter‐scanner CV when scanners of different field strengths were combined, and the parameter was also affected by the scan acquisition resolution. This study shows that the majority of diffusion MRI derived parameters are robust across 1.5T and 3T scanners and suitable for use in multi‐centre clinical studies and trials. © 2015 The Authors NMR in Biomedicine Published by John Wiley & Sons Ltd.     

Fiber type characterization in skeletal muscle by diffusion tensor imaging

Fiber type distribution within a skeletal muscle, i.e. the quantification of the relative amount of type 1 (slow‐twitching) and type 2 (fast‐twitching) muscle fibers, is of great interest for the monitoring of the effects of training or the treatment of muscle diseases. The purpose of this study was to determine the feasibility of diffusion tensor imaging (DTI) as a tool for noninvasive fiber type quantification in human skeletal muscle. The right calves of 12 healthy volunteers were examined using DTI at 1.5 T. Standard DTI parameters, including fractional anisotropy (FA), and mean, radial and parallel diffusivity (MD, RD and PD, respectively), were determined in the soleus muscle. Fiber type proportion and mean fiber diameter within the soleus muscle were quantified from tissue specimens obtained via a fine needle biopsy. Linear regression analysis tested for associations between DTI and biopsy results. FA values were correlated significantly with fiber type proportion, such that higher FA values indicated a higher proportion of type 1 fibers (R² = 0.5, p = 0.01). This was based on lower diffusivity perpendicular to the main axis of the fiber in subjects with a higher type 1 fiber proportion (RD: R² = 0.52, p = 0.008). MD was also correlated with the proportion of type 1 fibers (R² = 0.37, p = 0.037), whereas PD showed no significant correlation. DTI is a promising method for the noninvasive estimation of fiber type proportion in skeletal muscle. This technique may be used to monitor training effects or may be further developed as a biomarker in certain muscle diseases. Copyright © 2013 John Wiley & Sons, Ltd.     

An intravoxel oriented flow model for diffusion‐weighted imaging of the kidney

By combining intravoxel incoherent motion (IVIM) and diffusion tensor imaging (DTI) we introduce a new diffusion model called intravoxel oriented flow (IVOF) that accounts for anisotropy of diffusion and the flow‐related signal. An IVOF model using a simplified apparent flow fraction tensor (IVOF_f) is applied to diffusion‐weighted imaging of human kidneys. The kidneys of 13 healthy volunteers were examined on a 3 T scanner. Diffusion‐weighted images were acquired with six b values between 0 and 800 s/mm² and 30 diffusion directions. Diffusivity and flow fraction were calculated for different diffusion models. The Akaike information criterion was used to compare the model fit of the proposed IVOF_f model to IVIM and DTI. In the majority of voxels the proposed IVOF_f model with a simplified apparent flow fraction tensor performs better than IVIM and DTI. Mean diffusivity is significantly higher in DTI compared with models that account for the flow‐related signal. The fractional anisotropy of diffusion is significantly reduced when flow fraction is considered to be anisotropic. Anisotropy of the apparent flow fraction tensor is significantly higher in the renal medulla than in the cortex region. The IVOF_f model describes diffusion‐weighted data in the human kidney more accurately than IVIM or DTI. The apparent flow fraction in the kidney proved to be anisotropic.     

磁共振扩散张量成像序列对脊髓型颈椎病的诊断价值

目的:分析3.0T磁共振（MR）扩散张量成像（DTI）序列对脊髓型颈椎病（CSM）的诊断价值。方法:选择福建中医药大学附属康复医院收治的30例CSM患者纳入观察组,另选择同期体检人群中年龄匹配的30例健康志愿者为对照组,均运用常规MRI序列及DTI技术进行扫描,运用DTI技术测量FA及ADC值,进行图像后处理及数据分析,观察组患者根据MR平扫结果分为A组（n=10,单纯硬膜囊受压）、B组（n=14,颈髓受压,信号正常）和C组（n=6,颈髓受压,T2WI高信号）,分析各组FA及DA值差异,评价DTI诊断脊髓型颈椎病的诊断价值。结果:对照组脊髓C2-3、C3-4、C4-5、C5-6、C6-7节段的ADC值与FA比较差异无统计学意义（P>0.05）;对照组与A、B、C组的ADC值、FA值存在显著性差异（P<0.05）,B组、C组的ADC值显著高于对照组（P<0.05）,FA值显著低于对照组（P<0.05）,A组ADC值、FA值与对照组比较差异无统计学意义（P>0.05）;从A组到C组,ADC值呈升高趋势,FA值呈降低趋势,差异显著（P<0.05）;MR T2WI、DTI序列扫描FA值、MR DTI序列扫描ADC值诊断扫描诊断CSM的敏感度与特异度为20.00%（6/30）与80.00%（24/30）,80.00%（24/30）与20.00%（6/30）,66.67%（20/30）与30.00%（9/30）。结论:DTI较常规MRI能更早期而准确地诊断CSM,是一种显示CSM病变和观察病变修复过程的有效手段。     

Multi‐center evaluation of stability and reproducibility of quantitative MRI measures in healthy calf muscles

The purpose of this study was to evaluate temporal stability, multi‐center reproducibility and the influence of covariates on a multimodal MR protocol for quantitative muscle imaging and to facilitate its use as a standardized protocol for evaluation of pathology in skeletal muscle. Quantitative T2, quantitative diffusion and four‐point Dixon acquisitions of the calf muscles of both legs were repeated within one hour. Sixty‐five healthy volunteers (31 females) were included in one of eight 3‐T MR systems. Five traveling subjects were examined in six MR scanners. Average values over all slices of water‐T2 relaxation time, proton density fat fraction (PDFF) and diffusion metrics were determined for seven muscles. Temporal stability was tested with repeated measured ANOVA and two‐way random intraclass correlation coefficient (ICC). Multi‐center reproducibility of traveling volunteers was assessed by a two‐way mixed ICC. The factors age, body mass index, gender and muscle were tested for covariance. ICCs of temporal stability were between 0.963 and 0.999 for all parameters. Water‐T2 relaxation decreased significantly (P < 10^?3) within one hour by ~ 1 ms. Multi‐center reproducibility showed ICCs within 0.879–0.917 with the lowest ICC for mean diffusivity. Different muscles showed the highest covariance, explaining 20–40% of variance for observed parameters. Standardized acquisition and processing of quantitative muscle MRI data resulted in high comparability among centers. The imaging protocol exhibited high temporal stability over one hour except for water T2 relaxation times. These results show that data pooling is feasible and enables assembling data from patients with neuromuscular diseases, paving the way towards larger studies of rare muscle disorders.     

Tract‐specific and age‐related variations of the spinal cord microstructure: a multi‐parametric MRI study using diffusion tensor imaging (DTI) and inhomogeneous magnetization transfer (ihMT)

Being able to finely characterize the spinal cord (SC) microstructure and its alterations is a key point when investigating neural damage mechanisms encountered in different central nervous system (CNS) pathologies, such as multiple sclerosis, amyotrophic lateral sclerosis or myelopathy. Based on novel methods, including inhomogeneous magnetization transfer (ihMT) and dedicated SC probabilistic atlas post‐processing, the present study focuses on the in vivo characterization of the healthy SC tissue in terms of regional microstructure differences between (i) upper and lower cervical vertebral levels and (ii) sensory and motor tracts, as well as differences attributed to normal aging. Forty‐eight healthy volunteers aged from 20 to 70 years old were included in the study and scanned at 3 T using axial high‐resolution T₂*‐w imaging, diffusion tensor imaging (DTI) and ihMT, at two vertebral levels (C2 and C5). A processing pipeline with minimal user intervention, SC segmentation and spatial normalization into a reference space was implemented in order to assess quantitative morphological and structural parameters (cross‐sectional areas, scalar DTI and MT/ihMT metrics) in specific white and gray matter regions of interest. The multi‐parametric MRI metrics collected allowed upper and lower cervical levels to be distinguished, with higher ihMT ratio (ihMTR), higher axial diffusivity (λ_∥) and lower radial diffusivity (λ_⊥) at C2 compared with C5. Significant differences were also observed between white matter fascicles, with higher ihMTR and lower λ_∥ in motor tracts compared with posterior sensory tracts. Finally, aging was found to be associated with significant metric alterations (decreased ihMTR and λ_∥). The methodology proposed here, which can be easily transferred to the clinic, provides new insights for SC characterization. It bears great potential to study focal and diffuse SC damage in neurodegenerative and demyelinating diseases. Copyright © 2016 John Wiley & Sons, Ltd.     

Diffusion tensor imaging and T2 relaxometry of bilateral lumbar nerve roots: feasibility of in‐plane imaging

Lower back pain is a common problem frequently encountered without specific biomarkers that correlate well with an individual patient's pain generators. MRI quantification of diffusion and T₂ relaxation properties may provide novel insight into the mechanical and inflammatory changes that occur in the lumbosacral nerve roots in patients with lower back pain. Accurate imaging of the spinal nerve roots is difficult because of their small caliber and oblique course in all three planes. Two‐dimensional in‐plane imaging of the lumbosacral nerve roots requires oblique coronal imaging with large field of view (FOV) in both dimensions, resulting in severe geometric distortions using single‐shot echo planar imaging (EPI) techniques. The present work describes initial success using a reduced‐FOV single‐shot spin‐echo EPI acquisition to obtain in‐plane diffusion tensor imaging (DTI) and T₂ mapping of the bilateral lumbar nerve roots at the L4 level of healthy subjects, minimizing partial volume effects, breathing artifacts and geometric distortions. A significant variation in DTI and T₂ mapping metrics is also reported along the course of the normal nerve root. The fractional anisotropy is statistically significantly lower in the dorsal root ganglia (0.287 ± 0.068) than in more distal regions in the spinal nerve (0.402 ± 0.040) (p < 10^–5). The T₂ relaxation value is statistically significantly higher in the dorsal root ganglia (78.0 ± 11.9 ms) than in more distal regions in the spinal nerve (59.5 ± 7.4 ms) (p < 10^–5). The quantification of nerve root DTI and T₂ properties using the proposed methodology may identify the specific site of any degenerative and inflammatory changes along the nerve roots of patients with lower back pain. Copyright © 2012 John Wiley & Sons, Ltd.     

MRI quantification of non‐Gaussian water diffusion in normal human kidney: a diffusional kurtosis imaging study

Our aim was to prospectively evaluate the feasibility of diffusional kurtosis imaging (DKI) in normal human kidney and to report preliminary DKI measurements. Institutional review board approval and informed consent were obtained. Forty‐two healthy volunteers underwent diffusion‐weighted imaging (DWI) scans with a 3‐T MR scanner. b values of 0, 500 and 1000 s/mm² were adopted. Maps of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (D_⊥), axial diffusivity (D_||), mean kurtosis (MK), radial kurtosis (K_⊥) and axial kurtosis (K_||) were produced. Three representative axial slices in the upper pole, mid‐zone and lower pole were selected in the left and right kidney. On each selected slice, three regions of interest were drawn on the renal cortex and another three on the medulla. Statistical comparison was performed with t‐test and analysis of variance. Thirty‐seven volunteers successfully completed the scans. No statistically significant differences were observed between the left and right kidney for all metrics (p values in the cortex: FA, 0.114; MD, 0.531; D_⊥, 0.576; D_||, 0.691; MK, 0.934; K_⊥, 0.722; K_||, 0.891; p values in the medulla: FA, 0.348; MD, 0.732; D_⊥, 0.470; D_||, 0.289; MK, 0.959; K_⊥, 0.780; K_||, 0.287). Kurtosis metrics (MK, K_||, K_⊥) obtained in the renal medulla were significantly (p <0.001) higher than those in the cortex (0.552 ± 0.04, 0.637 ± 0.07 and 0.530 ± 0.08 in the medulla and 0.373 ± 0.04, 0.492 ± 0.06 and 0.295 ± 0.06 in the cortex, respectively). For the diffusivity measures, FA of the medulla (0.356 ± 0.03) was higher than that of the cortex (0.179 ± 0.03), whereas MD, D_⊥ and D_|| (mm²/ms) were lower in the medulla than in the cortex (3.88 ± 0.09, 3.50 ± 0.23 and 4.65 ± 0.29 in the cortex and 2.88 ± 0.11, 2.32 ± 0.20 and 3.47 ± 0.31 in the medulla, respectively). Our results indicate that DKI is feasible in the human kidney. We have reported the preliminary DKI measurements of normal human kidney that demonstrate well the non‐Gaussian behavior of water diffusion, especially in the renal medulla. Copyright © 2014 John Wiley & Sons, Ltd.     

Diffusion tensor imaging discriminates between glioblastoma and cerebral metastases in vivo

In a prospective study, patients with a radiologically proven brain tumour underwent diffusion tensor imaging (DTI) prior to definitive diagnosis and treatment. Twenty‐eight patients with a histologically proven glioblastoma or metastasis were included in the study. Following the definition of regions of interest, DTI metrics [mean diffusivity (MD) and fractional anisotropy (FA)] were calculated for the tumour volume and the surrounding region of peritumoral oedema. These metrics were then subjected to logistic regression to investigate their ability to discriminate between glioblastomas and cerebral metastases. A cross‐validation was performed to investigate the ability of the model to predict tumour. The logistic regression analysis correctly distinguished glioblastoma in 15 of 16 cases (93.8%) and metastasis in 11 of 12 cases (91.7%). Cross‐validation resulted in the model correctly predicting 14 of 16 (87.5%) glioblastomas and 10 of 12 (83.3%) metastases studied. MD was significantly higher (p = 0.02) and FA was significantly lower (p = 0.04) within the oedema surrounding metastases than within the oedema around glioblastomas. MD was significantly higher (p = 0.02) within the tumour volume of the glioblastomas. Our results demonstrate that, when DTI metrics from the tumour volume and surrounding peritumoral oedema are studied in combination, glioblastoma can be reliably discriminated from cerebral metastases. Copyright © 2010 John Wiley & Sons, Ltd.     

Improvement of accuracy of diffusion MRI using real‐time self‐gated data acquisition

Diffusion‐weighted and diffusion tensor MR imaging (DWI, DTI) techniques are generally performed with signal averaging of multiple measurements to improve the signal‐to‐noise ratio (SNR) and the accuracy of the diffusion measurement. Any discrepancy in the images between different averages causes errors which reduce the accuracy of the diffusion MRI measurements. In this report, a motion artifact reduction scheme with a real‐time self‐gated (RTSG) data acquisition for diffusion MRI using two‐dimensional echo planar imaging (2D EPI) is described. A subject's translational and rotational motions during application of the diffusion gradients induce an additional phase term and a shift of the echo‐peak position in the k‐space, respectively. These motions also reduce the magnitude of the echo‐peak. Based on these properties, we present a new scheme which monitors the position and the magnitude of the largest echo‐peak in the k‐space. The position and the magnitude of each average is compared to those of early averaging shot to determine if the differences are within or beyond the given threshold values. Motion corrupted data are reacquired in real time. Our preliminary results using RTSG indicate an improvement of both SNR and the accuracy of diffusion MRI measurements. Copyright © 2009 John Wiley & Sons, Ltd.     

Bilateral substantia nigra and pyramidal tract changes following experimental intracerebral hemorrhage: an MR diffusion tensor imaging study

The amelioration of secondary neurological damage is among the most important therapeutic goals for patients with intracerebral hemorrhage (ICH). Secondary injury of the ipsilateral substantia nigra (SN) and pyramidal tract (PY) is common after cerebral stroke. Such injury has been characterized previously by anatomical or diffusion MRI, but not in a comprehensive manner, and the knowledge regarding the contralateral changes is relatively poor. This study examined longitudinally both contralateral and ipsilateral SN and PY changes following experimental ICH with diffusion tensor imaging (DTI) and histology. ICH was induced in 14 Sprague‐Dawley rats by the infusion of collagenase into the right striatum. Four‐shot, spin‐echo, echo‐planar DTI was performed at 7 T with a b value of 1000 s/mm² and 30 diffusion gradient directions at 3.5 h and days 1, 3, 7, 14, 42 and 120 after ICH. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ_//) and radial diffusivity (λ_┴) were measured in SN and PY accordingly. Two to three rats were sacrificed at days 3, 7, 42 and 120 for histology. The contralateral SN showed an increase in λ_// with perivascular enlargement during the first 3 days after ICH. The ipsilateral SN showed increases in FA, λ_//, λ_┴ and MD at day 1, dramatic decreases at day 3 with neuronal degeneration and neuropil vacuolation, and subsequent gradual normalization. The contralateral PY showed diffusivity decreases at day 1. The ipsilateral PY showed early decreases and then late increases in MD and λ_┴, and continuously decreasing FA and λ_// with progressive axonal loss and demyelination. In summary, DTI revealed early bilateral changes in SN and PY following ICH. The evolution of the ipsilateral parameters correlated with the histological findings. In the ipsilateral PY, λ_// and λ_┴ changes indicated evolving and complex pathological processes underlying the monotonic FA decrease. These results support the use of quantitative multiparametric DTI for the evaluation of SN and PY injuries in clinical and preclinical investigations of ICH. Copyright © 2013 John Wiley & Sons, Ltd.     

Correlation of DTI metrics in the wall and cavity of brain abscess with histology and immunohistochemistry

Diffusion tensor imaging (DTI) was performed in eight patients with brain abscess (BA). The aim of this study was to see the difference in the relationship between intercellular cell adhesion molecule‐1 (ICAM‐1) and lymphocyte function‐associated antigen‐1 (LFA‐1) expression and DTI metrics measured in vivo in the wall and cavity of BA and its possible explanation vis‐à‐vis histology and immunohistochemistry. Neuroinflammatory molecules (NMs) were quantified from BA cavity aspirate of the patients and quantitative immunohistochemical analysis was performed for ICAM‐1 and LFA‐1 in the BA wall, showing maximal positive staining and correlated with DTI metrics. The fractional anisotropy (FA) significantly increased while mean diffusivity and spherical anisotropy significantly decreased in the BA wall compared to the BA cavity. In the BA wall, FA and linear anisotropy (CL) showed a significant positive correlation with ICAM‐1 and LFA‐1 expression whereas FA and planar anisotropy positively correlated with NMs quantified from aspirated pus respectively. Higher FA values in the BA wall compared to BA cavity, even when ICAM‐1 and LFA‐1 were expressed only in the macrophages and not in the collagen fibers, suggests that a combination of both concentric layers of collagen fibers as well as neutrophils and macrophages provide structural orientation and are responsible for increased FA. In the BA wall, increased CL was found compared to the cavity, indicating the presence of concentrically laid collagen fibers responsible for the diffusion of water molecules in the direction parallel to the collagen fibers. We conclude that in the BA, different mechanisms are operative for the changes in the DTI metrics in the wall and cavity; these conclusions are validated by histology and immunohistochemistry. Copyright © 2009 John Wiley & Sons, Ltd.