磁共振DWI和PWI在超急性脑梗死诊治中的应用

目的评价磁共振弥散加权成像（DWI）和灌注加权成像（PWI）在超急性脑梗死诊断及指导临床早期溶栓治疗中的应用价值。方法 56例发病在6 h以内且临床提示处于超急性期脑梗死患者均行急诊MRI检查,扫描序列包括T1WI、T2WI、FLAIR、DWI及PWI,部分病例行MRA检查。结果 56例患者T1WI均未见异常信号,35例患者T2WI、FLAIR发现有轻微异常信号影。56例DWI和PWI均发现异常,但在DWI上显示的高信号急性脑梗死区域与在PWI上显示的脑灌注延长区域不匹配,PWI显示的病灶范围更大。图像后处理显示平均通过时间（MTT）、达峰时间（TTP）均有不同程度的延长,脑血流量（CBF）出现不同程度的减少。结论急诊MRI,特别是DWI和PWI序列对超急性脑梗死患者可以作出准确的诊断,可以安全、迅速、有效地指导临床进行早期溶栓治疗。     

Evolution of hyperacute stroke over 6 hours using serial MR perfusion and diffusion maps

Purpose

To develop an appropriate method to evaluate the time‐course of diffusion and perfusion changes in a clinically relevant animal model of ischemic stroke and to examine lesion progression on MR images. An exploration of acute stroke infarct expansion was performed in this study by using a new methodology for developing time‐to‐infarct maps based on the time at which each voxel becomes infarcted. This enabled definition of homogeneous regions from the heterogeneous stroke infarct.

Materials and Methods

Time‐to‐infarct maps were developed based on apparent diffusion coefficient (ADC) changes. These maps were validated and then applied to blood flow and time‐to‐peak maps to examine perfusion changes.

Results

ADC stroke infarct showed different evolution patterns depending on the time at which that region of tissue infarcted. Applying the time‐to‐infarct maps to the perfusion maps showed localized perfusion evolution characteristics. In some regions, perfusion was immediately affected and showed little change over the experiment; however, in some regions perfusion changes were more dynamic.

Conclusion

Results were consistent with the diffusion‐perfusion mismatch hypothesis. In addition, characteristics of collateral recruitment were identified, which has interesting stroke pathophysiology and treatment implications. J. Magn. Reson. Imaging 2009;29:1262–1270. © 2009 Wiley‐Liss, Inc.     

Using a 2D multibreath-hold susceptibility-weighted imaging to visualize intratumoral hemorrhage of hepatocellular carcinoma at 3T MRI: Correlation with pathology

Purpose:

To assess the value of 2D multibreath‐hold susceptibility‐weighted imaging (SWI) for visualizing intratumoral hemorrhage of hepatocellular carcinoma (HCC) and correlate with pathological results.

Materials and Methods:

Fifty‐eight patients with 65 HCCs underwent T1‐, T2‐, T2*‐weighted imaging and SWI. The ability to detect intratumoral hemorrhage for each imaging technique was evaluated. A radiologic‐pathological correlation was performed.

Results:

The area under the receiver operator characteristic (ROC) curve (Az value) for SWI (Az = 0.941) was significantly greater than that for T1WI (Az = 0.748) and T2WI (Az = 0.700) (P = 0.000). When compared with T2*, SWI had slightly higher sensitivity and equal specificity, but the Az value was not significantly different (P = 0.768). The total number of hemorrhages detected by SWI was greatest by factors of 13.3, 6.7, and 2.2 compared to T1WI, T2WI, and T2*, respectively. SWI detected more microbleeds (585 in 25 HCCs) than T1WI (13 in 5 HCCs), T2WI (66 in 11 HCCs), and T2* (238 in 21 HCCs).

Conclusion:

SWI can accurately visualize internal hemorrhages and provide valuable information regarding the internal architecture of HCC. J. Magn. Reson. Imaging 2012;36:900–906. © 2012 Wiley Periodicals, Inc.     

Characterization of chondroblastic osteosarcoma: Gadolinium‐enhanced versus diffusion‐weighted MR imaging

Purpose

To detect differences in magnetic resonance imaging (MRI) between chondroblastic osteosarcoma and the other types of osteosarcomas or chondrosarcomas using gadolinium‐enhanced versus diffusion‐weighted sequences.

Materials and Methods

Contrast‐enhanced MRI and diffusion‐weighted imaging (DWI) were performed in five chondroblastic osteosarcoma (CO) cases, 17 other types of osteosarcomas (OS), and 18 chondrosarcomas (CS). DWI was obtained with a single‐shot echo‐planar imaging (EPI) sequence using a 1.5T MR imager. The apparent diffusion coefficients (ADCs) of the minimum and maximum values were also obtained. The contrast‐enhancement pattern was evaluated and minimum‐maximum ADC value of CO was compared with other types of OS and CS.

Results

Both CO and CS showed a similar enhancement pattern; both showed septonodular and peripheral rim enhancement. The minimum ADC value of CO (1.24 ± 0.10 × 10^?3mm²/sec) was significantly higher than that of other types of OS (0.84 ± 0.15 × 10^?3mm²/sec) and was significantly lower than that of CS (1.64 ± 0.20 × 10^?3mm²/sec). In addition, the maximum ADC value of CO (2.28 ± 0.20 × 10^?3mm²/sec) was significantly higher than that of other types of OS (1.33 ± 0.26 × 10^?3mm²/sec).

Conclusion

DWI appears to be more useful for differentiating between chondroblastic osteosarcoma and chondrosarcoma or other types of osteosarcoma than Gd‐enhanced MRI. J. Magn. Reson. Imaging 2009;29:895–900. © 2009 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 and perfusion of the breast

This article is a review of the current published clinical applications of DWI and perfusion of breast MR explaining possibilities and limits of both techniques.DWI in a fast time acquisition and without contrast medium gives information as regards cellularity of breast lesions. The technique can be used for distinguishing between benign and malignant breast lesions and monitoring therapies in locally advanced breast cancer.Perfusion can give additional information as regards vascularization of breast lesions, useful in the characterization of breast lesions doubt at DCE-MRI and also in monitoring chemotherapic effect.     

MRI弥散和灌注成像诊断超早期脑梗死的实验研究

目的评价磁共振弥散成像(DWI)和灌注成像(PWI)技术在超早期脑梗死中的诊断价值。方法新西兰白兔42只,随机分为7组,其中6组为实验组,1组为假手术组。采用改良O’Brein法闭塞兔一侧大脑中动脉制作局灶性脑缺血模型,对照组仅暴露同侧大脑中动脉,不予电凝。术后0.5、1、2、3、4、6 h不同时间段进行MRI扫描。结果常规MR序列显示缺血病灶明显晚于DWI和PWI。随着时间延长病灶各参数有特征性变化规律。在DWI和PWI中缺血区体积均随时间的延长不断扩大,两者不匹配区随时间延长逐渐缩小。结论DWI和PWI在诊断超早期脑梗死上优于常规MR序列。     

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.

     

Adrenal hemorrhage after orthotopic liver transplantation: MR appearance

The purpose of this paper is to describe the MR imaging findings of right adrenal hemorrhage after orthotopic liver transplantation. Twenty-seven orthotopic liver transplantation patients underwent MR studies of the liver and/or biliary system. Patients were referred to MR examination because of suspected biliary complications ( n=22) or for evaluation of mass lesions ( n=5). The standard MR protocol included T1-weighted spin-echo (SE) or gradient-recalled echo (GRE) images and T2-weighted turbo SE (TSE) images with fat suppression. In addition, cholangiography pulse sequences and/or contrast-enhanced T1-weighted images were obtained according to specific indications. In 2 patients a right adrenal mass was detected at MR imaging. Three to 4 weeks after transplantation, the lesions were markedly hyperintense on T2-weighted images and showed a hypointense capsule. Follow-up MR examinations revealed a slight decrease in size and a change in morphology. Computed tomography examinations of these 2 patients, obtained 10 weeks after transplantation, showed resolution of the hemorrhage and transformation into a cystic lesion in one case and a complete resolution of the hemorrhage and a normal right adrenal gland in the other case. Adrenal hemorrhage after liver transplantation shows typical MR features and should not be mistaken for an adrenal tumor or a postoperative abscess.     

MRI在脑动静脉畸形合并自发性出血诊断中的应用

目的探讨磁共振成像（MRI）在诊断脑动静脉畸形（CAVM）合并自发性出血的可行性。方法13例临床怀疑CAVM合并自发性出血患者，其中，5例经手术证实，7例经DSA证实，1例患儿因具有典型MRI表现直接接受γ刀放射治疗。所有病例均接受常规MRI检查，8例又经增强扫描。结果常规MRI显示血肿周围细小供血动脉及粗大引流静脉8例，仅发现粗大引流静脉3例，未发现明显畸形血管2例。增强扫描后，血肿已部分吸收，可见细小扭曲的供血动脉及引流静脉。血肿位于额叶4例，枕叶3例，顶叶3例，颞叶2例，基底节区1例。CAVM合并蛛网膜下腔出血3例，硬膜下出血2例，血肿破入脑室1例，大部分病灶位于脑实质内近脑表面和静脉窦旁。结论MRI可清晰显示CAVM的供血动脉、瘤体、引流静脉，并在病灶的确切解剖关系与证实治疗后病灶消失的程度方面具有明显优势，因而，它能为选择最佳治疗提供重要依据。     

Simultaneous acquisition of MR angiography and venography (MRAV).

A dual-echo pulse sequence for simultaneous acquisition of MR angiography and venography (MRAV) is developed. Data acquisition of the second echo for susceptibility-weighted imaging-based MR venography is added to the conventional three-dimensional (3D) time-of-flight (TOF) MRA pulse sequence. Using this dual-echo acquisition approach, the venography data can be acquired without increasing the repetition time, and, therefore, the scan duration of routine TOF MRA scans is maintained. The feasibility of simultaneous acquisition of MRAV is presented in brain scans at different spatial resolutions. The effect of spatial resolution on vein-to-background contrast is also demonstrated. Venous contrast is improved in high-resolution (0.52 x 0.52 x 1.6 mm(3)) images compared to that in standard-resolution (0.78 x 0.78 x 1.6 mm(3)) images. This MRAV technique enables the acquisition of MR venography without the need of an extra scan or injection of contrast agent in routine clinical brain exams at 3T.     

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     

Detection of hyperacute parenchymal hemorrhage of the brain using echo-planar T2*-weighted and diffusion-weighted MRI

We investigated the usefulness of echo-planar imaging (EPI) as well as T2^*-weighted and diffusion-weighted MRI (DWI) to identify hyperacute hemorrhage (within 24 h after ictus) in the brain. Seven patients were examined 3.5 to 24 h after onset of symptoms using a whole-body 1.5-T MR system. Two diffusion-weighted sequences were run to obtain isotropic and anisotropic diffusion images. Apparent diffusion coefficients (ADC) were calculated from the isotropic diffusion images. All DWI images as well as the T2*-weighted EPI images showed the hematomas as either discrete, deeply hypointense homogeneous lesions, or as lesions of mixed signal intensity containing hypointense areas. We conclude that even in the early phase after hemorrhage, sufficient amounts of paramagnetic deoxyhemoglobin are present in intracerebral hemorrhages to cause hypointensity on EPI T2^*-weighted and DWI images; thus, use of ultrafast EPI allows identification of intracerebral hemorrhage. Received: 21 March 2000 Revised: 26 July 2000 Accepted: 27 July 2000     

Diffusion-weighted MR imaging (DWI) in spinal cord ischemia

Introduction Spinal cord infarction is a rare clinical diagnosis characterized by a sudden onset of paralysis, bowel and bladder dysfunction, and loss of pain and temperature perception, with preservation of proprioception and vibration sense. Magnetic resonance imaging (MRI) usually demonstrates intramedullary hyperintensity on T2-weighted MR images with cord enlargement. However, in approximately 45% of patients, MR shows no abnormality. Diffusion-weighted MR imaging (DWI) has been widely used for the evaluation of a variety of brain disorders, especially for acute stroke. Preliminary data suggest that DWI has the potential to be useful in the early detection of spinal infarction.Methods We performed DWI, using navigated, interleaved, multishot echo planar imaging (IEPI), in a series of six patients with a clinical suspicion of acute spinal cord ischemia.Results In all patients, high signal was observed on isotropic DWI images with low ADC values (0.23 and 0.86×10⁻³ cm²/s), indicative of restricted diffusion.Conclusion We analyzed the imaging findings from conventional MR sequences and diffusion-weighted MR sequences in six patients with spinal cord infarction, compared the findings with those in published series, and discuss the value of DWI in spinal cord ischemia based on current experience. Although the number of patients with described DWI findings totals only 23, the results of previously published studies and those of our study suggest that DWI has the potential to be a useful and feasible technique for the detection of spinal infarction.     

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.     

Enhanced mass on contrast-enhanced breast MR imaging: Lesion characterization using combination of dynamic contrast-enhanced and diffusion-weighted MR images

Purpose

To evaluate the diagnostic accuracy of a combination of dynamic contrast‐enhanced MR imaging (DCE‐MRI) and diffusion‐weighted MR imaging (DWI) in characterization of enhanced mass on breast MR imaging and to find the strongest discriminators between carcinoma and benignancy.

Materials and Methods

We analyzed consecutive breast MR images in 270 patients; however, 13 lesions in 93 patients were excluded based on our criteria. We analyzed tumor size, shape, margin, internal mass enhancement, kinetic curve pattern, and apparent diffusion coefficient (ADC) values. We applied univariate and multivariate analyses to find the strongest indicators of malignancy and calculate a predictive probability for malignancy. We added the corresponding categories to these prediction probabilities for malignancy and calculated diagnostic accuracy when we consider category 4b, 4c, and 5 lesions as malignant and category 4a, 3, and 2 lesions as benign. In a validation study, 75 enhancing lesions in 71 patients were examined consecutively.

Results

Irregular margin, heterogeneous internal enhancement, rim enhancement, plateau time–intensity curve (TIC) pattern, and washout TIC pattern were the strongest indicators of malignancy as well as past studies, and ADC values less than 1.1 × 10^?3 mm²/s were also the strongest indicators of malignancy. In a validation study, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 92% (56/61), 86% (12/14), 97% (56/58), 71% (12/17), and 91% (68/75), respectively.

Conclusion

The combination of DWI and DCE‐MRI could produce high diagnostic accuracy in the characterization of enhanced mass on breast MR imaging. J. Magn. Reson. Imaging 2008;28:1157–1165. © 2008 Wiley‐Liss, Inc.