人脑磁共振弹性成像的初步研究

目的探讨MR弹性成像（MRE）在正常人脑的应用。方法研制用于人脑的激发装置，激发装置附加于头线圈上，并固定在志愿者头部，激发装置产生的低频率（f）振荡波经颅骨传至颅内，引起剪切波在脑组织内传播；设计成像脉冲序列，脉冲序列以梯度回波序列为基础，在X、Y或Z轴上施加运动敏感梯度（MSG）。剪切波导致的脑组织内周期性移位可使接收信号产生周期性相位位移，获得相位图像，从而显示脑组织内剪切波的传播。通过调整相位偏置，获得1个周期内剪切波的动态传播图像；相位图像经局部f估算法处理后获得局部剪切波的波长（γ），计算出剪切模量，获得弹性图像；激发f采用100、150和200Hz。结果MRE的相位图清楚显示了剪切波在脑组织内的传播，剪切波从脑表面向中心传播。剪切波γ随激发f而变化，γ与激发f呈反比。脑白质内剪切波γ大于脑灰质；弹性图像显示脑白质的剪切模量大于脑灰质的剪切模量。结论MRE的相位图可显示剪切波在脑组织内的传播，弹性图像显示了脑灰质与白质之间的弹性变化。     

Magnetic resonance imaging of the brain with gadopentetate dimeglumine-DTPA: Comparison of T1-weighted spin-echo and 3D gradient-echo sequences

Short TR, short TE, high resolution, 3D gradient-recalled echo (GRE) imaging was evaluated for lesion detection in the brain. High resolution 3D GRE data acquisition was used to reduce partial volume effects and flow artifacts, to better visualize smaller structures, to minimize signal losses caused by field inhomogeneities, and to allow better image reformatting. Spin-echo (SE) and 3D GRE approaches were compared for lesion detection after the administration of an MR contrast agent, gadopentetate dimeglumine. Preliminary clinical studies demonstrated that the signal-to-noise ratio (SNR) in each slice of the GRE scan was worse than that of the SE scan because of the much thicker slices acquired with the SE technique. However, by averaging two adjacent 3D slices, the SNR of the two methods was essentially equivalent. In the averaged GRE slices, large lesions were seen just as well as in the SE images. More importantly, small lesions were better visualized in the thin 3D GRE images than in the thick SE images for the lesions studied in this work and the protocols used. These observations were confirmed by theoretical simulations.     

Magnetic resonance elastography of brain tumors: preliminary results

PURPOSE: To investigate the potential value of magnetic resonance elastography (MRE) in evaluating the consistency of brain tumors. MATERIAL AND METHODS: Six patients with known solid brain tumor underwent brain MRE studies. Consistency of brain tumors was evaluated at surgery. Correspondence of MRE evaluation with operative result was studied. RESULTS: The elasticity of tumors in six patients evaluated by MRE agreed with the tumor consistency given by the operative results. CONCLUSION: MRE could be used as an imaging technique for noninvasive assessment of the consistency of brain tumor in vivo.     

Sequential dynamic gadolinium magnetic resonance perfusion-weighted imaging: effects on transit time and cerebral blood volume measurements

Purpose: To evaluate if two gadolinium perfusion studies can be performed during the same table occupancy without degradation of the derived data in the second study.

Material and Methods: Magnetic resonance (MR) perfusion studies of the whole brain were performed on 12 patients during the administration of two gadolinium boluses separated by 8 min. In six patients, gadolinium was given as two 20-ml administrations of standard 0.5 M chelate (Magnevist), whilst the other six patients received two 10-ml administrations of 1.0 M chelate (Gadovist).

Results: There were no significant differences in subjective quality between the time-intensity curves of the first and second perfusion studies using either the 0.5 M or 1.0 M gadolinium chelate. The objective measurements in quality of the time-intensity curves (maximum signal change and full width at half maximum) changed by less than 5% of the original values on the second perfusion study. The first-moment mean transit times did not change significantly on the sequential studies. The regional cerebral blood volume tended to increase on the second study (by 15% on average), but this did not reach statistical significance.

Conclusion: The results from two sequential dynamic gadolinium-based perfusion studies can be compared in a meaningful manner using the technique described.     

Transurethral prostate magnetic resonance elastography: Prospective imaging requirements

Tissue stiffness is known to undergo alterations when affected by prostate cancer and may serve as an indicator of the disease. Stiffness measurements can be made with magnetic resonance elastography performed using a transurethral actuator to generate shear waves in the prostate gland. The goal of this study was to help determine the imaging requirements of transurethral magnetic resonance elastography and to evaluate whether the spatial and stiffness resolution of this technique overlapped with the requirements for prostate cancer detection. Through the use of prostate‐mimicking gelatin phantoms, frequencies of at least 400 Hz were necessary to obtain accurate stiffness measurements of 10 mm diameter inclusions, but the detection of inclusions with diameters as small as 4.75 mm was possible at 200 Hz. The shear wave attenuation coefficient was measured in vivo in the canine prostate gland, and was used to predict the detectable penetration depth of shear waves in prostate tissue. These results suggested that frequencies below 200 Hz could propagate to the prostate boundary with a signal to noise ratio (SNR) of 60 and an actuator capable of producing 60 μm displacements. These requirements are achievable with current imaging and actuator technologies, and motivate further investigation of magnetic resonance elastography for the targeting of prostate cancer. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Precise and accurate measurement of proton T1 in human brain in vivo: Validation and preliminary clinical application

Precise and accurate inversion-recovery (PAIR) magnetic resonance (MR) measurements of T1 were obtained in eight brain regions and cerebrospinal fluid of 26 healthy volunteers. Accuracy of the technique was assessed by measuring T1 in small fluid volumes with the PAIR technique and with two independent spectroscopic techniques. The mean difference between T1 measured with PAIR and with the two spectroscopic techniques was 3.1% ± 1.3. The precision (reproducibility) of measurements with the PAIR technique was excellent. The coefficient of variation (CV) across 16 measurements in a head phantom was 2.0%, compared with a CV of 2.7% across 45 separate measurements in a single subject. The within-subject CV was 1.8% ± 0.6 in white matter and 1.4% ± 1.0 in basal ganglia. The between-subject CV in 26 healthy volunteers was 3.6% ± 0.6 in white matter and 4.1% ± 1.9 in basal ganglia. Comparison between a patient with an active recurrent brain tumor and an agematched patient with an inactive brain tumor showed that T1 was significantly elevated throughout the brain of the active-tumor patient, especially in white matter tracts, even though no tumor or edema was detected in the white matter on standard MR images. Comparisons between five brain tumor patients and four healthy volunteers of similar age showed that T1 was significantly and substantially elevated throughout the white matter tracts and in the caudate nucleus, putamen, and thalamus. These results are consistent with the hypothesis that white matter tracts are selectively vulnerable to edema and that T1 increases in white matter are a sensitive indicator of patient status or tumor aggressiveness.     

Magnetic resonance imaging of malignant soft tissue neoplasms in the adult

This review addresses the spectrum of malignant soft tissue tumors frequently found in adults. Rather than presenting a complete review, the focus of this discussion is on common lesions or lesions in which the diagnosis may be suggested on the basis of imaging. Diagnoses covered include undifferentiated high-grade pleomorphic sarcoma, fibrosarcoma, dermatofibrosarcoma protuberans, liposarcoma, synovial sarcoma, malignant peripheral nerve sheath tumor, clear cell sarcoma, hemangioendothelioma, hemangiopericytoma, angiosarcoma, and leiomyosarcoma.     

脑肿瘤MR弹性成像的初步临床研究

目的 探讨MR弹性成像(MRE)在脑肿瘤手术前评价其硬度的价值.方法 14例常规影像检查确定为实性脑肿瘤患者(男5例、女9例,年龄16～63岁),术前接受脑MRE检查,以脑白质为参照对肿瘤硬度进行评价.采用自行研制的用于脑MRE成像的激发装置,固定于头线圈上,并与患者头部固定,产生低频率振荡经颅骨传至颅内,引起剪切波在脑组织内传播;脉冲序列采用相位对比梯度回波序列,获得相位图像,从而显示脑组织内剪切波的传播.相位图像经局部频率估算法(LFE)处理后获得弹性图像;肿瘤的硬度在术中与正常脑白质对比,由术者判断分为偏软、中等和偏硬.将MRE的评价结果与手术结果作对照.结果 MRE检查结果显示,1例肿瘤的弹性模量低于正常脑白质、11例高于正常脑白质、2例与正常脑白质相似;术中检查1例肿瘤硬度偏软、11例偏硬,2例中等.14例由MRE评估的肿瘤弹性均与手术结果相符.结论 MRE可以无创地显示脑肿瘤的弹性,在术前对脑肿瘤的硬度进行评价.     

Craniopharyngiomas: identification of different semiological patterns with MRI

Our objectives were to analyze different semiological patterns in craniopharyngiomas studied with CT and MR sequences. Retrospective study of 26 patients with confirmed craniopharyngiomas. All cases were examined with CT and MR imaging using a variety of pulse sequences (spin echo, inversion recovery, gradient echo in-phase and opposed-phase). The analyzed component patterns were classified as solid, calcium, proteic-like, cerebrospinal fluid (CSF)-like, hematic-like, and fatty patterns. The different patterns were related by means of contingency tables and the Fisher exact test and also to epidemiological findings and tumor size. A solid pole was detected in all patients, whereas a cystic component was present in 92.3% of the cases. Calcification was visualized in 65.3%, proteic-like in 53.8%, CSF-like in 23%, hematic-like in 19.2%, and fatty component in 15.3%. There were no statistical associations between patterns, with the exception that in no case did CSF-like and proteic-like patterns coexist ( P=0.004). Tumor size was related to components. Hematic-like (17.0+/-18.9 vs 3.9+/-2.6 mm, non-present vs present) and CSF-like (16.9+/-19.6 vs 6.5+/-4.0 mm) patterns were observed most frequently in smaller tumors, whereas larger tumors usually had proteic-like (5.9+/-5.4 vs 21.1+/-21.0 mm) and calcified (4.6+/-1.9 vs 19.1+/-19.9 mm) patterns. Computed tomography and a combination of different MR images frequently allow the detection of different semiological patterns in these tumors. Semiological patterns were correlated only to tumor size.     

Magnetic resonance imaging of articular cartilage: ex vivo study on normal cartilage correlated with magnetic resonance microscopy

The aims of this study were (a) to compare the MR appearance of normal articular cartilage in ex vivo MR imaging (MRI) and MR microscopy (MRM) images of disarticulated human femoral heads, (b) to evaluate by MRM the topographic variations in articular cartilage of disarticulated human femoral heads, and subsequently, (c) to compare MRM images with histology. Ten disarticulated femoral heads were examined. Magnetic resonance images were obtained using spin-echo (SE) and gradient-echo (GE) sequences. Microimages were acquired on cartilage–bone cylindrical plugs excised from four regions (superior, inferior, anterior, posterior) of one femoral head, using a modified SE sequence. Both MRI and MRM images were obtained before and after a 90 ° rotation of the specimen, around the axis perpendicular to the examined cartilage surface. Finally, MRM images were correlated with histology. A trilaminar appearance of articular cartilage was observed with MRI and with a greater detail with MRM. A good correlation between MRI and MRM features was demonstrated. Both MRI and MRM showed a loss of the trilaminar cartilage appearance after specimen rotation, with greater evidence on MRM images. Cartilage excised from the four regions of the femoral head showed a different thickness, being thickest in the samples excised from the superior site. The MRM technique confirms the trilaminar MRI appearance of human articular cartilage, showing good correlation with histology. The loss of the trilaminar appearance of articular cartilage induced by specimen rotation suggests that this feature is partially related to the collagen-fiber orientation within the different layers. The MRM technique also shows topographic variations in thickness of human articular cartilage. Received 28 July 1997; Revision received 31 December 1997; Accepted 6 January 1998     

Magnetic resonance imaging of benign soft tissue neoplasms in adults

This article reviews a spectrum of benign soft tissue tumors found in adults. Rather than presenting a complete review, the focus of this article is on benign tumors for which the diagnosis may be confidently made or strongly suggested on the basis of imaging. Diagnoses presented include nodular fasciitis, superficial and deep fibromatosis, elastofibroma, lipomatous lesions, giant cell tumor of the tendon sheath, pigmented villonodular synovitis, peripheral nerve sheath tumors, Morton neuroma, hemangioma, and myxoma.     

健康志愿者头部MR弹性成像研究

目的 应用MR弹性成像(MRE)技术评估健康志愿者脑组织的剪切模量,并了解脑组织剪切模量与年龄间是否存在相关性.方法 选取105名健康志愿者,其中男42名、女63名,行头部MRE检查.通过局部频率估算法(LFE)分别测量志愿者脑灰质与脑白质的剪切模量.采用独立样本t检验评估脑灰质与脑白质剪切模量间是否存在差异,以及脑实质剪切模量是否存在性别差异;应用Spearman相关分析评估剪切模量与年龄是否存在相关性,并将志愿者分为≤40岁组(76名)和>40岁组(29名),分别进行脑实质剪切模量与年龄间的相关性分析.结果 105名健康志愿者脑白质的剪切模量[(23.1±5.7)kPa]高于脑灰质[(11.3±2.6)kPa],两者间差异具有统计学意义(t=19.34,P<0.01).男性志愿者脑白质与脑灰质的剪切模量分别为(23.4±5.8)、(11.4±2.8)kPa,女性志愿者分别为(22.8±5.6)、(11.1±2.5)kPa.男、女志愿者脑组织间剪切模量值差异无统计学意义(t值分别为-0.534、-0.606,P值均>0.05).年龄相关性分析显示,灰质的剪切模量与年龄呈正相关(r=0.315,P<0.01),白质的剪切模量与年龄无相关性(r=0.183,P>0.05);≤40岁组志愿者灰、白质剪切模量与年龄呈正相关(r值分别为0.251、0.235,P值均<0.05),而>40岁组志愿者脑灰、白质剪切模量均与年龄无相关性(r值分别为0.181、-0.001,P值均>0.05).结论 健康志愿者脑白质的剪切模量明显高于脑灰质;脑实质剪切模量男女之间无差别;脑灰质剪切模量随年龄增加而增加.     

Magnetic resonance elastography as a method to estimate myocardial contractility

Purpose:

To determine whether increasing epinephrine infusion in an in vivo pig model is associated with an increase in end‐systolic magnetic resonance elastography (MRE)‐derived effective stiffness.

Materials and Methods:

Finite element modeling (FEM) was performed to determine the range of myocardial wall thicknesses that could be used for analysis. Then MRE was performed on five pigs to measure the end‐systolic effective stiffness with epinephrine infusion. Epinephrine was continuously infused intravenously in each pig to increase the heart rate in increments of 20%. For each such increase end‐systolic effective stiffness was measured using MRE. In each pig, Student's t‐test was used to compare effective end‐systolic stiffness at baseline and at initial infusion of epinephrine. Least‐square linear regression was performed to determine the correlation between normalized end‐systolic effective stiffness and increase in heart rate with epinephrine infusion.

Results:

FEM showed that phase gradient inversion could be performed on wall thickness ≈≥1.5 cm. In pigs, effective end‐systolic stiffness significantly increased from baseline to the first infusion in all pigs (P = 0.047). A linear correlation was found between normalized effective end‐systolic stiffness and percent increase in heart rate by epinephrine infusion with R² ranging from 0.86–0.99 in four pigs. In one of the pigs the R² value was 0.1. A linear correlation with R² = 0.58 was found between normalized effective end‐systolic stiffness and percent increase in heart rate when pooling data points from all pigs.

Conclusion:

Noninvasive MRE‐derived end‐systolic effective myocardial stiffness may be a surrogate for myocardial contractility. J. Magn. Reson. Imaging 2012;36:120–127. © 2012 Wiley Periodicals, Inc.     

Magnetic resonance imaging of cerebral infarction: Time course of Gd-DTPA enhancement and CT comparison

Summary Thirty-five patients (7 females and 28 males) with cerebral infarction and suspicion of cerebral infarction of 4 h to 27 months duration were studied 45 times with magnetic resonance (MR) imaging using Bd-DTPA. Spin echo (SE) images were obtained before and after the administration of Gd-DTPA (0.1 or 0.15 mmol/kg) and compared with the enhanced CT. MR imaging using Gd-DTPA was more sensitive than enhanced CT and very useful for detecting a new focus of cerebral infarction, especially in the cases with multiple infarcted areas and for showing the extent of cortical and subcortical infarction. In most cases the MR enhancement was obvious in the subacute stage, especially after cerebral embolism, and the signal intensity of the lesion tended to show a gradual increase. The diagnosis of embolism was accepted on the basis of acute onset without prior TIA, coupled with angiography showing the embolus itself and/or a capillary blush and a wide area of infarction.     

Diffusion-weighted magnetic resonance imaging of treatment-associated changes in recurrent and residual medulloblastoma: preliminary observations in three children

Purpose: To emphasize a possible role of magnetic resonance (MR) diffusion-weighted imaging (DWI) for lesion conspicuity and detection of treatment effects in children with medulloblastoma.

Material and Methods: Three children with medulloblastoma (two residual and one recurrent) were examined repetitively by MR diffusion-weighted imaging. Regional assessment of the apparent diffusion coefficient (ADC) was done for tumorous lesions and periventricular white matter appearing normal on standard MR images.

Results: All lesions were clearly visible on DWI. In the case of recurrent tumor, on one scan, DWI showed lesions that were not seen on contrast-enhanced MRI. Increase (41%) of ADC was seen in one lesion, which subsequently responded completely to treatment over 27 months' follow-up. Intermediate increases (23-26%) of ADC were found with partial therapy response in three lesions. In contrast, a decrease (-11%) of ADC in two lesions was seen with tumor progression.

Conclusion: These observations may suggest a role for DWI in early detection of metastatic disease and treatment monitoring of medulloblastoma, warranting a formal study.     

Magnetic resonance imaging of the gallbladder: spectrum of abnormalities

Various pathologies involving the gallbladder can manifest clinically, producing nonspecific clinical symptoms and making diagnosis difficult and challenging. Real-time sonography is the most widely used diagnostic study for the gallbladder and the primary screening examination of choice. With increasing use of magnetic resonance imaging (MRI) and MR cholangiopancreatography (MRCP), gallbladder pathology is frequently seen. Understanding the basic patterns of various disease manifestations and appearance on MRI is the key to making an accurate diagnosis. Given its inherent tissue contrast and contrast sensitivity, MRI in conjunction with MRCP can be a very valuable test in evaluating gallbladder pathology. Gallbladder pathology can be classified into congenital (such as absence), inflammatory (acute, hemorrhagic, and chronic cholecystitis), traumatic, benign (polyps) and malignant tumors (gallbladder carcinoma and lymphoma), and other disease processes can be seen in cholelithiasis, cholesterosis, thickened gallbladder wall, and Mirrizzi syndrome.     

Marchiafava-Bignami病的磁共振DWI、DTI初步研究

目的：探讨磁共振弥散加权成像（DwI）、弥散张量成像（DTI）对Marchiafava_Bignami（MBD）的诊断及预后评价的价值。方法：对10例MBD患者行DWI检查,其中4例再行DTI检查。结果：本组急性型8例,DWI显示病灶区信号明显增高,并有4例出现弥散受限改变;胼胝体膝部、压部的各向异性分数（FA）值与正常值比较差异有统计学意义（P〈O．05）,额叶白质、半卵圆中心白质与正常值比较差异也有统计学意义（P〈O．05）。结论：MBD的DWI、DTI改变可能反映其临床及预后。     

Thin-section MR imaging of rat brain at 4.7 T.

The brains of anesthetized 7-month-old male hooded rats were imaged in coronal, sagittal, and horizontal planes at 4.7 T. Images were obtained with a section thickness of 0.6 mm and in-plane pixel size of 0.18-0.20 mm, resulting in finer combined spatial and contrast resolution than in most previously published reports. This allowed detailed anatomic assignment of many brain structures on the basis of comparison with a histologic brain atlas. T1, apparent T2, and water proton density values of gray matter, white matter, and cerebrospinal fluid (CSF) were derived from saturation-recovery and multi-echo measurements. These values were used to calculate expected contrast-to-noise ratios as a function of TR and TE in spin-echo imaging sequences. The optimal simultaneous contrast between gray and white matter and between CSF and gray matter was obtained on images with moderate T2 weighing, with a TR of 3.6 seconds and a TE of 45 msec. The use of thin sections was found to be essential for resolving many fine structures, and the improved sensitivity provided by the high magnetic field strength was crucial for imaging such thin sections at adequate signal-to-noise ratios.