High angular resolution diffusion imaging reveals intravoxel white matter fiber heterogeneity.

Magnetic resonance (MR) diffusion tensor imaging (DTI) can resolve the white matter fiber orientation within a voxel provided that the fibers are strongly aligned. However, a given voxel may contain a distribution of fiber orientations due to, for example, intravoxel fiber crossing. The present study sought to test whether a geodesic, high b-value diffusion gradient sampling scheme could resolve multiple fiber orientations within a single voxel. In regions of fiber crossing the diffusion signal exhibited multiple local maxima/minima as a function of diffusion gradient orientation, indicating the presence of multiple intravoxel fiber orientations. The multimodality of the observed diffusion signal precluded the standard tensor reconstruction, so instead the diffusion signal was modeled as arising from a discrete mixture of Gaussian diffusion processes in slow exchange, and the underlying mixture of tensors was solved for using a gradient descent scheme. The multitensor reconstruction resolved multiple intravoxel fiber populations corresponding to known fiber anatomy. Ma     

Magnetic resonance diffusion characteristics of histologically defined prostate cancer in humans

The contrast provided by diffusion‐sensitive magnetic resonance offers the promise of improved tumor localization in organ‐confined human prostate cancer (PCa). Diffusion tensor imaging (DTI) measurements of PCa were performed in vivo, in patients undergoing radical prostatectomy, and later, ex vivo, in the same patients' prostatectomy specimens. The imaging data were coregistered to histological sections of the prostatectomy specimens, thereby enabling unambiguous characterization of diffusion parameters in cancerous and benign tissues. Increased cellularity, and hence decreased luminal spaces, in peripheral zone PCa led to approximately 40% and 50% apparent diffusion policy (ADC) decrease compared with benign peripheral zone tissues in vivo and ex vivo, respectively. In contrast, no significant diffusion anisotropy differences were observed between the cancerous and noncancerous peripheral zone tissues. However, the dense fibromuscular tissues in prostate, such as stromal tissues in benign prostatic hyperplasia in central gland, exhibited high diffusion anisotropy. A tissue classification method is proposed to combine DTI and T2‐weighted image contrasts that may provide improved specificity of PCa detection over T2‐weighted imaging alone. PCa identified in volume rendered MR images qualitatively correlates well with histologically determined PCa foci. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Diffusion MRI predicts transrectal ultrasound biopsy results in prostate cancer detection

Purpose

To evaluate the ability of diffusion tensor imaging (DTI) to predict the transrectal ultrasound (TRUS) biopsy outcomes in persons who have no history of previous TRUS biopsy and present with elevated prostate‐specific antigen (PSA) levels.

Materials and Methods

Thirty‐seven participants underwent DTI, followed by 12‐core TRUS‐guided needle biopsy within 2 weeks. DTI was performed using endorectal coils on a 1.5 Tesla scanner at 1‐mm³ spatial resolution. By comparing with the TRUS biopsy results, the optimum thresholds of the trace apparent diffusion coefficient (tADC) and of the nodular size were investigated. The diagnostic performance of both criteria, the tADC threshold (Criteria A) and the tADC threshold combined with nodular size threshold (Criteria B), were evaluated.

Results

The optimum tADC threshold was 1.0 μm²/ms. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of prostate cancer (PCA) detection for Criteria A were 98%, 89%, 73%, 99%, and 91%, respectively, and were 97%, 98%, 92%, 99% and 98% for Criteria B.

Conclusion

Owing to high negative predictive value, the tADC threshold could be used to exclude subjects with clinically undetectable PCA. Adding the nodular size threshold, the combined threshold could identify the tADC‐positive segments that are likely to yield positive biopsy results. J. Magn. Reson. Imaging 2011;33:356–363. © 2011 Wiley‐Liss, Inc.     

磁共振扩散峰度成像预测食管癌放疗敏感性的实验研究

目的 从动物模型层面探讨扩散峰度成像（DKI）在预测食管癌放疗敏感性方面的应用价值。方法 建立人食管癌Eca-109裸鼠移植瘤模型,实验组给予单次剂量15 Gy（6 MV X射线）照射,对照组不接受任何处理。比较两组移植瘤体积及表观弥散系数（ADC）、平均扩散峰度（MK）、平均扩散系数（MD）的变化情况,观察实验组与对照组在相应时间点的细胞密度和坏死比例。结果 实验组裸鼠移植瘤在照射后明显出现了生长延迟现象,从照后第7天开始实验组移植瘤体积明显小于对照组（t=3.206~6.149,P<0.05）。照后第3天开始实验组ADC值及MD值明显高于对照组,MK值明显低于对照组（t_ADC=-11.018~-2.049,t_MD=-6.609~-2.052,t_MK=2.492~9.323,P<0.05）。照后第3天开始对照组细胞密度高于实验组,实验组的坏死比例高于对照组（t_密度=-8.387~-2.239,t_坏死比例=2.980~17.430,P<0.05）。结论 单次大剂量照射可以抑制荷瘤裸鼠肿瘤生长,ADC、MK、MD值均可以先于肿瘤形态学变化而发生改变,移植瘤细胞密度及坏死比例的变化与ADC、MK、MD值的变化基本吻合。DKI具有早期预测食管癌放疗敏感性的价值。     

Distribution of microstructural damage in the brains of professional boxers: a diffusion MRI study

PURPOSE: To investigate and localize cerebral abnormalities in professional boxers with no history of moderate or severe head trauma. MATERIALS AND METHODS: Diffusion tensor imaging (DTI) was used to determine the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in the brains of 81 professional male boxers and 12 male control subjects. Voxel-based analysis (VBA) of both the diffusion and anisotropy values was performed using statistical parametric mapping (SPM). From this objective analysis, regions of microstructural abnormalities in the brains of the boxers were located. RESULTS: Increases in the ADC, and decreases in FA were identified in deep white matter (WM), while decreases in ADC were identified in cortical gray matter (GM). Regions of positive correlation between ADC and age were also found in both the boxer and control groups, although the regions and strength of the correlation were not the same in each group. CONCLUSION: Using VBA, we localized previously unreported abnormalities in the brains of professional boxers. These abnormalities are assumed to reflect cumulative (chronic) brain injury resulting from nonsevere head trauma.     

Sequential diffusion-weighted magnetic resonance imaging study of lysophosphatidyl choline-induced experimental demyelinating lesion: an animal model of multiple sclerosis

PURPOSE: To differentiate the surrounding edema from the focal demyelinating lesion during the early phase of the lesion using an apparent diffusion coefficient (ADC), and to monitor the changes in ADCs during the complete progression of a lysophosphatidyl choline (LPC)-induced experimental demyelinating lesion, an animal model of multiple sclerosis (MS). MATERIAL AND METHODS: Eighteen rats divided into two groups-demyelinating lesion (group I, N = 12) and vehicle group (saline injected; group II, N = 6)-were studied. A 0.2-microl quantity of 1% LPC solution in isotonic saline was injected in the rat brain internal capsule (IC) area to create the demyelinating lesion. Six rats were used exclusively for histology. Diffusion-weighted (DW) images were acquired at different diffusion weightings on the 3rd, 5th, 10th, 15th, and 20th days after LPC injection. ADC was measured from three regions of interest (ROIs) within the IC: focal demyelinating lesion (area A), surrounding area of the lesion (area B), and contralateral IC area (area C). RESULTS: Histology revealed demyelination of the IC area during the early phase of lesion progression up to day 10 and remyelination thereafter. Elevated ADCs were observed for the surrounding edematous area (area B), compared to the focal demyelinating lesion (area A) during the early phase of the demyelination process, while substantial reduction of ADCs was noticed during remyelination for both regions. CONCLUSION: Measurement of ADC showed clear differentiation of the surrounding edema from the LPC-induced focal demyelinating lesion in rats, especially during the early phase of the lesion progression.     

Can diffusion weighted image and apparent diffusion coefficient (ADC) differentiate benign from malignant cervical adenopathy?

Background

Cervical adenopathy is a common problem and the differentiation of benign and malignant node is of crucial importance for therapy management.

Objective

This prospective study aimed to know if Diffusion weighted images (DWI) and apparent diffusion coefficient (ADC) can differentiate benign from malignant cervical lymphadenopathy.

Patients and methods

Thirty patients with cervical adenopathy were included in this study. Doppler ultrasound, DWI and ADC maps were automatically reconstructed and used for the measurement of ADC values.

Results

The sensitivity and specificity of the RI cut-off value <0.69 in differentiation between benign and malignant cervical L.Ns was 88.8% and 71.4%, respectively. The optimal ADC cut off value for differentiation between benign and malignant lymph nodes was ?1.0 × 10⁻³ mm²/s with an accuracy 96.7%, a sensitivity 100%, a specificity 88.9%, PPV 95.4% and NPV 100% and statistically significant P-value = 0.000.

Conclusion

DWI and ADC were useful for differentiation between benign and malignant cervical lymphadenopathy and recommended to decrease the need of invasive biopsies. However, CDUS techniques can be used as preliminary technique but, they had potential pitfalls in diagnosis of malignant cervical lymphadenopathy cases.     

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.     

Ability of diffusion-weighted imaging for the differential diagnosis between chronic expanding hematomas and malignant soft tissue tumors

Purpose

To evaluate the potential of diffusion‐weighted imaging (DWI) in distinguishing chronic expanding hematomas (CEHs) from malignant soft tissue tumors.

Materials and Methods

We performed conventional MRI and DWI of six CEHs and 31 malignant soft tissue tumors from 37 patients seen between May 2000 and November 2006. DWI was obtained with a single‐shot echo‐planar imaging (EPI) sequence using a 1.5T MR imager. The mean apparent diffusion coefficient (ADC) value was also calculated. We evaluated MRI findings of CEHs and compared ADC value of CEHs with malignant soft tissue tumors.

Results

On conventional MRI, two of six CEHs were difficult to differentiate from malignant soft tissue tumors based on imaging findings. The mean ADC value of CEHs and malignant soft tissue tumors was 1.55 ± 0.121 × 10^?3 mm²/sec and 0.92 ± 0.139 × 10^?3 mm²/sec (mean ± SD), respectively. The mean ADC value of CEHs was significantly higher than that of malignant soft tissue tumors (P < 0.01). There was no overlap in the minimum ADC values among CEHs and malignant soft tissue tumors.

Conclusion

DWI is useful for differentiating between CEHs and malignant soft tissue tumors. J. Magn. Reson. Imaging 2008;28:1195–1200. © 2008 Wiley‐Liss, Inc.

     

Magnetic resonance (MR) differential diagnosis of breast tumors using apparent diffusion coefficient (ADC) on 1.5‐T

To review the published reports concerning the apparent diffusion coefficient (ADC) value evaluation for the differentiation between malignant and benign breast tumors, articles were searched with the inclusion criteria: (a) a 1.5‐T unit was used; (b) the diagnostic criteria were clearly stated; (c) diffusion‐weighted images (DWIs) were obtained, and ADC value was calculated; (d) ADC values of breast tumors were reported with mean ± standard deviation (SD). Meta‐analysis from 12 articles revealed that the pooled sensitivity and specificity were 0.89 (95% confidence interval [CI], 0.85–0.91) and 0.77 (95% CI, 0.69–0.84), respectively, and that only the maximum b factor correlated with the mean ADC values of malignant and benign tumors, and the noncancerous breast tissue (P< 0.05,P < 0.01,P< 0.05, respectively). In conclusion, ADC evaluation is useful for the differentiation between malignant and benign breast tumors. J. Magn. Reson. Imaging 2009;30:249–255. © 2009 Wiley‐Liss, Inc.     

Diffusion imaging with prospective motion correction and reacquisition

A major source of artifacts in diffusion‐weighted imaging is subject motion. Slow bulk subject motion causes misalignment of data when more than one average or diffusion gradient direction is acquired. Fast bulk subject motion can cause signal dropout artifacts in diffusion‐weighted images and results in erroneous derived maps, e.g., fractional anisotropy maps. To address both types of artifacts, a fully automatic method is presented that combines prospective motion correction with a reacquisition scheme. Motion correction is based on the prospective acquisition correction method modified to work with diffusion‐weighted data. The images to reacquire are determined automatically during the acquisition from the imaging data, i.e., no extra reference scan, navigators, or external devices are necessary. The number of reacquired images, i.e., the additional scan duration can be adjusted freely. Diffusion‐weighted prospective acquisition correction corrects slow bulk motion well and reduces misalignment artifacts like image blurring. Mean absolute residual values for translation and rotation were <0.6 mm and 0.5°. Reacquisition of images affected by signal dropout artifacts results in diffusion maps and fiber tracking free of artifacts. The presented method allows the reduction of two types of common motion related artifacts at the cost of slightly increased acquisition time. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Diagnostic utility of diffusion‐weighted MR imaging and apparent diffusion coefficient value for the diagnosis of adrenal tumors

Purpose

To determine the utility of diffusion‐weighted MR imaging (DWI) for the diagnosis of adrenal tumors.

Materials and Methods

Forty‐two patients (24 men and 18 women; age, 61.5 ± 12.7 years old; range, 34–86 years) with 43 adrenal tumors (11 functioning cortical adenomas, 20 nonfunctioning cortical adenomas, 7 metastatic tumors, and 5 pheochromocytomas) were retrospectively investigated. DWIs were obtained by single‐shot spin‐echo type echo‐planar imaging sequence (1.5 Tesla [T]; TR = 8000 ms, TE = 72, b‐factor = 0 and 1000 s/mm²), and apparent diffusion coefficient (ADC) value was calculated. Chemical shift images were obtained by gradient echo sequence (TR = 161, TE = 2.38 [out‐of‐phase, OP] and 4.76 [in‐phase, IP], FA = 60), and the signal intensity index (SII; [IP‐OP]/IP *100%) was calculated.

Results

There was no difference in ADC values between adenomas (1.09 ± 0.29*10^?3 mm²/s; range, 0.52–1.64) and metastatic tumors (0.85 ± 0.26*10^?3; 0.51–1.23; p = 0.14). Pheochromocytomas showed the higher mean ADC value (1.59 ± 0.34*10^?3; 1.04–1.96) compared with those of adenomas or metastatic tumors (P < 0.05 and P < 0.005, respectively). The mean SII of adenomas (62.1 ± 17.9%; 14.5–88.4) was significantly higher than those of pheochromocytomas (4.0 ± 10.0%; ?19.6–3.3; P < 0.005) or metastatic tumors (?1.5 ± 11.7%; ?18.3–8.2; P < 0.01). There was no correlation between ADC values and SII.

Conclusion

Although pheochromocytomas showed higher ADC values, we did not find that ADC value had diagnostic utility for differentiating adenomas and metastatic tumors. J. Magn. Reson. Imaging 2009;29:112–117. © 2008 Wiley‐Liss, Inc.