1H‐MR spectroscopy and diffusion tensor imaging of normal‐appearing temporal white matter in patients with nasopharyngeal carcinoma after irradiation: Initial experience

Purpose:

To detect radiation‐induced changes of temporal lobe normal‐appearing white mater (NAWM) following radiation therapy (RT) for nasopharyngeal carcinoma (NPC).

Materials and Methods:

Seventy‐five H¹‐MR spectroscopy and diffusion‐tensor imaging (DTI) examinations were performed in 55 patients before and after receiving fractionated radiation therapy (total dose; 66–75GY). We divided the dataset into six groups, a pre‐RT control group and five other groups based on time after completion of RT. N‐acetylaspartic acid (NAA)/choline (Cho), NAA/creatine (Cr), Cho/Cr, mean diffusibility (MD), functional anisotropy (FA), radial diffusibility (λ_?), and axial diffusibility (λ_||) were calculated.

Results:

NAA/Cho and NAA/Cr decreased and λ_? increased significantly within 1 year after RT compared with pre‐RT. After 1 year, NAA/Cho, NAA/Cr, and λ_? were not significantly different from pre‐RT. In all post‐RT groups, FA decreased significantly. λ_|| decreased within 9 months after RT compared with pre‐RT, but was not significantly different from pre‐RT more than 9 months after RT.

Conclusion:

DTI and H¹‐MR spectroscopy can be used to detect early radiation‐induced changes of temporal lobe NAWM following radiation therapy for NPC. Metabolic alterations and water diffusion characteristics of temporal lobe NAWM in patients with NPC after RT were dynamic and transient. J. Magn. Reson. Imaging 2013;37:101–108. © 2012 Wiley Periodicals, Inc.

     

Proton MR spectroscopy in patients with pyogenic brain abscess: MR spectroscopic imaging versus single-voxel spectroscopy

Purpose

Single-voxel spectroscopy (SVS) has been the gold standard technique to diagnose the pyogenic abssess. Two-dimensional magnetic resonance spectroscopic imaging (MRSI) is able to provide spatial distribution of metabolic concentration, and is potentially more suitable for differential diagnosis between abscess and necrotic tumors. Therefore, the purpose of this study was to evaluate the equivalence of MRSI and SVS in the detection of the metabolites in pyogenic brain abscesses.

Materials and methods

Forty-two patients with pyogenic abscesses were studied by using both SVS and MRSI methods. Two neuroradiologists reviewed the MRS data independently. A κ value was calculated to express inter-reader agreement of the abscesses metabolites, and a correlation coefficient was calculated to show the similarity of two spectra. After consensus judgment of two readers, the binary value of metabolites of pyogenic abscesses (presence or absence) was compared between SVS and MRSI.

Results

The consistency of spectral interpretation of the two readers was very good (κ ranged from 0.95 to 1), and the similarity of two spectra was also very high (cc = 0.9 ± 0.05). After consensus judgment of two readers, the sensitivities of MRSI ranged from 91% (acetate) to 100% (amino acids, succinate, lactate, lipid), and the specificities of MRSI were 100% for detecting all metabolites with SVS as reference.

Conclusion

SVS and MRSI provide similar metabolites in the cavity of pyogenic brain abscess. With additional metabolic information of cavity wall and contralateral normal-appearing brain tissue, MRSI would be a more suitable technique to differentiate abscesses from necrotic tumors.     

Metachromatic leukodystrophy. Diffusion MR imaging and proton MR spectroscopy

Metachromatic leukodystrophy is characterized by dysmyelination caused by a deficiency of arylsulfatase-A. In a 17-month-old boy with metachromatic leukodystrophy, an echo-planar diffusion MR sequence revealed a restricted diffusion pattern in the deep white matter, manifested by high-signal on b = 1000 s/mm² images, and low ADC values (0.56 × 10^-3 mm²/s). Proton MR spectroscopy revealed a marked decrease in choline, a metabolite related to myelin turnover. These observations consisting of a restricted diffusion pattern on diffusion MR imaging, and decreased choline peaks on proton spectroscopy, likely represented dysmyelination in metachromatic leukodystrophy.     

颅脑磁共振弥散张量成像应用进展

磁共振弥散张量成像技术是利用水分子的弥散运动各向异性进行成像,是目前唯一反映人体活体组织空间组成信息及病理状态下各组织成分之间水分子交换功能状况的检查方法,可以从细胞及分子水平来研究疾病状况。本文回顾DTI的原理和潜在的临床应用,如脑缺血性疾病、脑发育、脑肿瘤、外伤性脑损伤和癫痫、多发性硬化、代谢性疾病等。     

In vivo diffusion tensor imaging of the rat spinal cord at 9.4T

PURPOSE: To determine differences in diffusion measurements in white matter (WM) and gray matter (GM) regions of the rat cervical, thoracic, and cauda equina spinal cord using in vivo diffusion tensor imaging (DTI) with a 9.4T MR scanner. MATERIALS AND METHODS: DTI was performed on seven rats in three slices at the cervical, thoracic, and cauda equina regions of the spinal cord using a 9.4T magnet. Axial diffusion weighted images (DWIs) were collected at a b-value of 1000 seconds/mm(2) in six directions. Regions of interest were identified via T2-weighted images for the lateral, dorsal, and ventral funiculi, along with GM regions. RESULTS: Analysis of variance (ANOVA) results indicated significant differences between every WM funiculus compared to GM for longitudinal apparent diffusion coefficient (lADC), transverse apparent diffusion coefficient (tADC), fractional anisotropy (FA), measured longitudinal anisotropy (MA1), and anisotropy index (AI). A significant difference in mean diffusivity (MD) between regions of the spinal cord was not found. Diffusion measurements were significantly different at each spinal level. In general, GM regions were significantly different than WM regions; however, there were few significant differences between individual WM regions. CONCLUSION: In vivo DTI of the rat spinal cord at 9.4T appears sensitive to the architecture of neural structures in the rat spinal cord and may be a useful tool in studying trauma and pathologies in the spinal cord.     

Diffusion tensor imaging and MR spectroscopy in hypertension and presumed cerebral small vessel disease.

In patients with cerebral small vessel disease (SVD) diffusion tensor imaging (DTI) is sensitive to white matter damage and correlates better with cognitive function than conventional imaging. It has been proposed as a surrogate marker for treatment trials. However, the pathological changes underlying DTI are not known. The purpose of this study was to use magnetic resonance spectroscopy (MRS) to determine the pathological changes underlying DTI abnormalities in a range of patients from asymptomatic white matter hyperintensities to symptomatic cerebral SVD. 29 SVD patients, 63 hypertensive subjects, and 42 normotensive controls were recruited. The relationship between the DTI and MRS parameters in the centrum semiovale white matter was determined. There was a significant reduction in N-acetylaspartate (NAA; 2.067 +/- 0.042 vs 2.299 +/- 0.029 and 2.315 +/- 0.036, P = 9 x 10(-6)) and increase in mean diffusivity (mm2/s x 10(-3); 0.942 +/- 0.123 vs 0.822 +/- 0.064 and 0.792 +/- 0.057, P = 1 x 10(-8)) in symptomatic SVD patients compared with the other two groups. DTI parameters correlated with NAA in all three groups, in a graded manner depending on severity of disease (r -SVD -0.827, hypertensive subjects -0.457, controls -0.317). NAA is a marker of axonal loss/dysfunction. These findings are consistent with axonal loss/dysfunction being the principal process causing the DTI changes found in cerebral SVD and ageing.     

Generalized diffusion tensor imaging and analytical relationships between diffusion tensor imaging and high angular resolution diffusion imaging.

A new method for mapping diffusivity profiles in tissue is presented. The Bloch-Torrey equation is modified to include a diffusion term with an arbitrary rank Cartesian tensor. This equation is solved to give the expression for the generalized Stejskal-Tanner formula quantifying diffusive attenuation in complicated geometries. This makes it possible to calculate the components of higher-rank tensors without using the computationally-difficult spherical harmonic transform. General theoretical relations between the diffusion tensor (DT) components measured by traditional (rank-2) DT imaging (DTI) and 3D distribution of diffusivities, as measured by high angular resolution diffusion imaging (HARDI) methods, are derived. Also, the spherical tensor components from HARDI are related to the rank-2 DT. The relationships between higher- and lower-rank Cartesian DTs are also presented. The inadequacy of the traditional rank-2 tensor model is demonstrated with simulations, and the method is applied to excised rat brain data collected in a spin-echo HARDI experiment.     

3.0T MR扩散张量成像在脑梗死诊断中的应用

目的：探讨3.0T磁共振扩散张量成像（DTI）对脑梗死的诊断价值。方法：对75例不同时期脑梗死患者进行MRI常规检查、扩散加权成像（DWI）及DTI检查,重建平均扩散系数（DCavg）图及部分各向异性（FA）图。以T2WI与DWI图像为参照,测定各期脑梗死灶及对侧正常脑组织的平均DCavg值、平均FA值,并进行统计学处理。结果：与对侧正常脑组织相比,脑梗死平均DCavg值在超急性期及急性期显著减低（P〈0.01）,随着时间延长呈逐渐恢复升高的变化趋势;脑梗死平均FA值在超急性期无一致性变化,与对侧正常脑组织相比差异无统计学意义（P〉0.05）,可轻度升高或轻度降低,随着病程进展呈不可恢复持续减低规律。结论：联合DCavg值与FA值可对脑梗死进行更精确的临床分期,有助于及时准确了解脑梗死的病理生理改变,为临床治疗及预后判断提供依据。     

van der Knaap syndrome: MR imaging findings including FLAIR, diffusion imaging, and proton MR spectroscopy

A patient is reported with diffuse leukoencephalopathy associated with cystic degeneration of the white matter of the brain (van der Knaap syndrome). The changes were studied by fluid attenuated inversion recovery (FLAIR), and diffusion-weighted MR imaging. The FLAIR sequence revealed suppressed signal of the cysts, and widespread high-signal white matter changes associated with thinned cortices. On diffusion-weighted MR imaging, apparent diffusion coefficient (ADC) values ranged from 3.0 × 10^–3 to 2.7 × 10^–3 mm²/s in the temporal cysts, similar to that of CSF. The ADC values within the parenchyma ranged between 2 × 10^–3 and 2.1 × 10^–3 mm²/s, a value falling between normal parenchyma and cerebrospinal fluid, compared with a control group of three healthy subjects. The changes were also evaluated by proton MR spectroscopy, and were compared with a control group of 12 cases. Magnetic resonance spectroscopy revealed apparently increased NAA/Cr ratios in most parts of the brain. The NAA/Cho ratios were either high or low, and the Cho/Cr ratios were increased or normal in different regions. Received: 27 October 1999; Revised: 9 December 1999; Accepted: 20 December 1999     

MR imaging and spectroscopy in Lhermitte-Duclos disease

Lhermitte-Duclos disease is a rare abnormality occurring in the cerebellum with only 130 cases reported in the literature. There is debate as to whether this abnormality is a hamartoma, a malformation or a tumour. In this case report we discuss the spectroscopy findings from two patients presenting with this disease. The patients, one 40-year-old Caucasian woman with a 6-year history of headaches, unsteady gait and falls, deterioration in vision and another 28-year-old Caucasian man with a 1-year history of headaches and a previous history of a transient stroke, were found to have this lesion in the cerebellum. Proton spectroscopic data were obtained using a single-voxel PRESS technique (TE=135 ms, TR=1600 ms), from the region of the abnormality. The results were expressed as ratios under the three prominent resonances representing choline (Cho), creatine (Cr), and N-acetyl (NA) moieties. The metabolite ratios were compared to normative data. The two cases demonstrated reduced ratios in NA/Cho and NA/Cr in relation to the controls. The ratios of Cho/Cr appeared closer to the normal mean ratio. There were peaks attributable to lactate in both cases. The low NA/Cr and NA/Cho ratios could be due to the apparent lack of neuronal architecture and the presence of embryonic neural tissue, which does not express NA, indicating more favourably towards a benign hamartoma rather than a tumour.     

磁共振扩散张量成像在正常颈髓中的应用研究

目的：比较不同b值及不同数量梯度场方向对正常人颈髓扩散张量成像（DTI）的影响,探讨正常人颈髓最佳DTI技术、扩散及各向异性特点。方法：分别施加6个和25个方向的扩散敏感梯度磁场,选择不同b值（0、100、200、400、600、800、1000s/mm2）,对25名健康志愿者行颈髓DTI成像,分析比较各自影像特点并分别在颈髓相对宽的C2～C3水平、颈髓相对窄的C4～C7水平选择感兴趣区（ROI）测量表观扩散系数（ADC）与部分各向异性（FA）值及第一、二、三本征值（1、2、3）。结果：①在其它参数不变的情况下,6个与25个方向相应部位的ADC值、FA值及本征值1、2、3无显著差异（P〉0.05）。②随着b值的增大,颈髓平均质量指数变小,b=100、200、400、600s/mm2间的质量指数差异无统计学意义（P〉0.05）,b=1000s/mm2时的质量指数与信噪比均较差,b=600s/mm2时与b=100、200、800、1000s/mm2之间差异有统计学意义（P〈0.01）,而b=600、400s/mm2间差异无统计学意义（P〉0.05）。③同一参数情况下,颈髓C4～C7水平所测的ADC值与FA值分别低于C2～C3水平所测值（P〈0.05）,本征值1〉2〉3（P〈0.05）。结论：运用GE1.5T超导磁共振系统,b值取0与600s/mm2,采集方向为6时可获得较好的颈髓DTI图像,颈髓具有明显的各向异性,平行于白质纤维方向的扩散梯度可得到较高的ADC值。     

In vivo diffusion tensor imaging of the human prostate.

This study demonstrates the feasibility of in vivo prostate diffusion tensor imaging (DTI) in human subjects. We implemented an EPI-based diffusion-weighted (DW) sequence with seven-direction diffusion gradient sensitization, and acquired DT images from six subjects using cardiac gating with a phased-array prostate surface coil operating in a linear mode. We calculated two indices to quantify diffusion anisotropy. The direction of the eigenvector corresponding to the leading eigenvalue was displayed by means of a color-coding scheme. The average diffusion values of the prostate peripheral zone (PZ) and central gland (CG) were 1.95 +/- 0.08 x 10(-3) mm2 s and 1.53 +/- 0.34 x 10(-3) mm2 s, respectively. The average fractional anisotropy (FA) values for the PZ and CG were 0.46 +/- 0.04 and 0.40 +/- 0.08, respectively. The diffusion ellipsoid in prostate tissue was anisotropic and approximated a prolate model, as shown in the color maps of the anisotropy. Consistent with the tissue architecture, the prostate fiber orientations were predominantly in the superior-inferior (SI) direction for both the PZ and CG. This study shows the feasibility of in vivo DTI and establishes normative DT values for six subjects.     

Accelerating MR diffusion tensor imaging via filtered reduced-encoding projection-reconstruction.

MR diffusion tensor imaging (DTI) is a promising tool for characterizing the microstructure of ordered tissues. However, its practical applications are hampered by relatively low signal-to-noise-ratio and spatial and temporal resolution. Reduced-encoding imaging (REI) via k-space sharing with constrained reconstruction has previously been shown to be effective for accelerating DTI, although the implementation was based on rectilinear k-space sampling. Due to the intrinsic oversampling of central k-space and allowance for isotropic downsampling, projection-reconstruction (PR) imaging may be better suited for REI. In this study, regularization procedures, including radial filtering and baseline signal correction to adequately reconstruct reduced encoded PR imaging data, are investigated. The proposed filtered reduced-encoding projection-reconstruction (FREPR) technique is applied to DTI tissue fiber orientation and fractional anisotropy (FA) measurements. Results show that FREPR offers improved reconstructions of the reduced encoded images and on an equal total scan-time basis provides more accurate fiber orientation and FA measurements compared to rectilinear k-space sampling-based REI methods or a control experiment consisting of only fully encoded images. These findings suggest a potentially significant role of FREPR in accelerating repeated imaging and improving the data acquisition-time efficiency of DTI experiments.     

Comparison of 3 Tesla proton MR spectroscopy, MR perfusion and MR diffusion for distinguishing glioma recurrence from posttreatment effects

Purpose:

To compare 3 Tesla (3T) multi‐voxel and single‐voxel proton MR spectroscopy (MRS), dynamic susceptibility contrast perfusion MRI (DSC), and diffusion‐weighted MRI (DWI) for distinguishing recurrent glioma from postradiation injury.

Materials and Methods:

We reviewed all 3T MRS, DSC and DWI studies performed for suspicion of malignant glioma recurrence between October 2006 and December 2008. Maximum Cho/NAA and Cho/Cr peak‐area and peak‐height ratios were recorded for both multi‐voxel and single‐voxel MRS. Maximum cerebral blood volume (CBV) and minimum apparent diffusion coefficient (ADC) were normalized to white matter. Histopathology and clinical‐radiologic follow‐up served as reference standards. Receiver operating characteristic curves for each parameter were compared.

Results:

Forty lesions were classified as glioma recurrence (n = 30) or posttreatment effect (n = 10). Diagnostic performance was similar for CBV ratio (AUC = 0.917, P < 0.001), multi‐voxel Cho/Cr peak‐area (AUC = 0.913, P = 0.002), and multi‐voxel Cho/NAA peak‐height (AUC = 0.913, P = 0.002), while ADC ratio (AUC = 0.726, P = 0.035) did not appear to perform as well. Single‐voxel MRS parameters did not reliably distinguish tumor recurrence from posttreatment effects.

Conclusion:

A 3T DSC and multi‐voxel MRS Cho/Cr peak‐area and Cho/NAA peak‐height appear to outperform DWI for distinguishing glioma recurrence from posttreatment effects. Single‐voxel MRS parameters do not appear to distinguish glioma recurrence from posttreatment effects reliably, and therefore should not be used in place of multi‐voxel MRS. J. Magn. Reson. Imaging 2012;35:56‐63. © 2011 Wiley Periodicals, Inc.     

Line-scan diffusion tensor MR imaging at 0.2 T: feasibility study

PURPOSE: To investigate and measure apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values using data obtained with line-scan diffusion-weighted imaging (DWI) of human brains on a 0.2 Tesla MR imager. MATERIALS AND METHODS: Diffusion-tensor imaging (DTI) was performed on eight healthy volunteers. The signal-to-noise ratios (SNRs) of white matter and cerebrospinal fluid were measured. ADC and FA were also measured from the data obtained from all subjects. Three-dimensional corticospinal fiber tracts were reconstructed from the DT images and a qualitative evaluation was done. RESULTS: The total scan time was 52 minutes 30 seconds for 18 slices with full-tensor images covering the whole brain. The ADCs and FAs show the appropriate values, in comparison with values obtained at high field strength in previous studies. Corticospinal fibers were demonstrated more clearly on images obtained at 0.2 T than at 1.5T. CONCLUSION: DTI at low field strength may be feasible for clinical use to estimate the white matter of brain with limited coverage, which often may be sufficient.     

Diffusion tensor spectroscopy (DTS) of human brain.

The diffusion tensor of N-acetyl aspartate (NAA), creatine and phosphocreatine (tCr), and choline (Cho) was measured at 3T using a diffusion weighted STEAM (1)H-MRS sequence in the healthy human brain in 6 distinct regions (4 white matter and 2 cortical gray matter). The Trace/3 apparent diffusion coefficient (ADC) of each metabolite was significantly greater in white matter than gray matter. The Trace/3 ADC values of tCr and Cho were found to be significantly greater than NAA in white matter, whereas all 3 metabolites had similar Trace/3 ADC in cortical gray matter. Fractional anisotropy (FA) values for all 3 metabolites were consistent with water FA values in the 4 white matter regions; however, metabolite FA values were found to be higher than expected in the cortical gray matter. The principal diffusion direction derived for NAA was in good agreement with expected anatomic tract directions in the white matter.     

Cerebral diffusion tensor imaging in tuberous sclerosis

Purpose

The purpose of this study was to investigate the features of the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in cortical tubers and white-matter lesions in patients with tuberous sclerosis (TS) using diffusion tensor imaging (DTI).

Materials and methods

Conventional magnetic resonance imaging (MRI) and DTI were performed in 14 patients with clinically established TS. Based on these DT images, ADC and FA maps were generated. The ADC values in 32 cortical tubers, and the ADC and FA values in 18 white-matter lesions were measured and compared with those of the corresponding contralateral regions.

Results

Compared with the corresponding contralateral regions, cortical tubers of TS patients had significantly higher ADC values (P < 0.001); white-matter lesions had significantly higher ADC values (P < 0.001) and significantly lower FA values (P < 0.001).

Conclusion

DTI is a useful tool for demonstrating changes in cortical tubers and white-matter lesions resulting from TS.     

MR tractography with diffusion tensor imaging in clinical routine

Using MRI, we demonstrated that the depiction of the cerebral white matter fiber tracts has become a routine procedure. Diffusion tensor (DT) sequences may be analyzed with combined volume analysis and tractography extraction software, giving indirect visualization of white matter connections. We obtained DT data from 20 subjects with normal MR imaging and five patients presenting cerebral diseases such as brain tumors, multiple sclerosis and stroke, with five patients explored on two different MR scanners. Data were transferred to dedicated workstations for anatomical realignment, determination of voxel eigenvectors and calculation of fiber tract orientations in a region of interest. In all subjects, axonal directions underlying the main neuronal pathways could be delineated. Comparisons between diseased regions and contralateral areas demonstrated changes in voxel anisotropy in injured regions, revealing possible preferential fiber orientations within diffuse T2 hyperintensities. Rapid data processing allows imaging of the normal and diseased fiber pathways as part of the routine MRI examination. Therefore, it appears that whenever white matter disease is suspected a tractography can be performed with this fast and simple method that we proved to be reliable and reproducible