MR colonography: 1.5T versus 3T

MR colonography is a powerful noninvasive method to image colorectal masses and inflammatory bowel disease. This article describes current techniques of MR colonography and compares its implementation at 1.5T and 3T.     

Liver MR imaging: 1.5T versus 3T

This article focuses on technical challenges in transferring 1.5T liver protocols to 3T systems and the overall comparison of MR sequences, highlighting the advantages and disadvantages of imaging at the higher field strength. An important benefit is the capacity of acquiring high-quality, thin-section postgadolinium T1-weighted three-dimensional gradientecho sequences, most clinically relevant for the detection and characterization of small hypervascular malignant diseases. Further research and development is necessary to overcome disadvantages, such as with in- and out-of phase T1-weighted gradient-echo sequences, and to minimize artifacts that appear at 3T.     

Small bowel MR imaging: 1.5T versus 3T

This article provides practical information regarding patient preparation schemes for small bowel MR imaging, and offers dedicated pulse sequence protocols for 1.5-T and 3-T MR imaging scanners, with specific emphasis on the advantages and remaining limitations of the higher field strength.     

MR imaging of the pancreas: 1.5T versus 3T

Pancreatic cancer has an almost uniformly grim prognosis. Early detection has the potential to improve survival, however. One promising approach to increase detection rates is the use of MR imaging at 3T. Imaging at 3T improves temporal or spatial resolution for pancreatic evaluation. Known challenges of imaging at 3T, such as increased power deposition and B1 field inhomogeneity, are not significant limitations for pancreatic imaging. Preliminary results suggest that the signal-to-noise ratio can be as much as twice as high as at 1.5T, particularly after contrast administration. Evaluation of the hepatobiliary ducts is comparable or superior to that at 1.5T. Additional studies are needed to determine if the improved image quality translates into improved sensitivity for disease.     

MR imaging of the prostate: 1.5T versus 3T

Over the past several years, evidence supporting the use of MR imaging in the evaluation of prostate cancer has grown. Almost all this work has been performed at 1.5T. The gradual introduction of 3T scanners into clinical practice provides a potential opportunity to improve the quality and usefulness of prostate imaging. Increased signal to noise allows for imaging at higher resolution, higher temporal resolution, or higher bandwidth. Although this may improve the quality of conventional T2-weighted prostate imaging, which has been the standard sequence for detecting and localizing prostate cancer for years, the real potential for improvement at 3T involves more advanced techniques, such as spectroscopy, diffusion-weighted imaging, dynamic contrast imaging, and susceptibility imaging. This review presents the current data on 3T MR imaging of the prostate as well as the authors' impressions based on their experience at Yale-New Haven Hospital.     

A review of MR physics: 3T versus 1.5T

This article illustrates changes in the underlying physics concepts related to increasing the main magnetic field from 1.5T to 3T. The effects of these changes on tissue constants and practical hardware limitations is discussed as they affect scan time, quality, and contrast. Changes in susceptibility artifacts, chemical shift artifacts, and dielectric effects as a result of the increased field strength are also illustrated. Based on these fundamental considerations, an overall understanding of the benefits and constraints of signal-to-noise ratio and contrast-to-noise ratio changes between 1.5T and 3T MR systems is developed.     

MR imaging of the adrenal glands: 1.5T versus 3T

MR imaging at 1.5T is considered the prime cross-sectional imaging modality for characterization of adrenal lesions. This is of utmost clinical importance, because non-functioning adenoma and adrenal metastasis are fairly common. The differentiation of these two tumor entities primarily is based on chemical shift imaging, also known as dual echo in-phase and opposed-phase imaging. At 3.0 T, the echo time pairs for in-phase and opposed-phase MR imaging need to be adjusted because the frequency difference is double that of standard 1.5T MR systems. Unfortunately, the acquisition of the first opposed-phase echo at 1.1 milliseconds and the first in-phase echo at 2.2 milliseconds within the same breath-hold requires unacceptably high receiver bandwidths at 3.0 T. Therefore, alternative data collection schemes have been implemented. This article reviews the current literature regarding adrenal imaging at 3.0 T with a focus on the chemical shift technique.     

Hepatic metastases: CT versus MR imaging at 1.5T

A prospective multi-institutional study was performed to compare the sensitivity of computed tomography (CT) and high-field magnetic resonance (MR) imaging (1.5T) in the detection of hepatic metastases, T₁-weighted and T₂-weighted spin-echo (SE) MR images were compared with noncontrast, dynamic, and delayed CT. Sixty-nine oncology patients were studied. Non-contrast CT showed an overall sensitivity of 57%, dynamic CT 71%, delayed CT 72%, T₁-weighted SE MR 47%, and T₂-weighted SE MR 78%. Although there was no statistically significant (p}<0.05) difference among dynamic CT, delayed CT, and T₂-weighted SE MR, these three methods were significantly more sensitive (p< 0.005) than non-contrast CT or T₁-weighted SE MR. T₂-weighted SE MR was significantly more sensitive (p< 0.006) than CT or T₁-weighted SE MR in the detection of small (<1 cm) lesions. CT was more sensitive in the detection of extrahepatic disease. These data confirm the superiority of T₂-weighted SE over T₁-weighted SE pulse sequences at 1.5T.     

Imaging at higher magnetic fields: 3 T versus 1.5 T

Clinical hepatobiliary magnetic resonance (MR) imaging continues to evolve at a fast rate. However, three basic requirements must still be satisfied if novel high-field MR imaging techniques are to be included in the hepatobiliary imaging routine: improvement of parenchymal contrast, suppression of respiratory motion artifact, and anatomic coverage of the entire hepatobiliary system. This article outlines the various arenas involved in MR imaging of the hepatobiliary system at 3 Tesla (T) compared with 1.5 T by (1) highlighting magnetic field-dependent MR contrast phenomena that contribute to the overall appearance of high-field hepatobiliary imaging; (2) summarizing the biodistributions of different gadolinium chelates used as MR contrast agents and their effectiveness regarding the static magnetic field; (3) showing the?implementation of advanced imaging techniques such as three-dimensional acquisition schemes and parallel acceleration techniques used in T1-, T2-, and diffusion-weighted hepatobiliary imaging; and (4) addressing artifact mechanisms exacerbated by, or originating from, increase of the static magnetic field.     

1.5T MR诊断脑结核瘤

1 材料与方法 本组26例脑结核瘤患者,男16例,女10例,年龄16～75岁,平均年龄46.5岁.胸部发现结核病灶24例,其中浸润型15例,粟粒型9例.脊柱结核1例,另外1例未发现明确的颅外结核灶.     

Differential diagnosis of periampullary carcinomas: comparison of CT with negative-contrast CT cholangiopancreatography versus MRI with MR cholangiopancreatography

Background

Negative-contrast CT cholangiopancreatography (nCTCP) has been introduced into clinical practice recently. In the present study, we compared CT with nCTCP vs. MRI with MR cholangiopancreatography (MRCP) for the differential diagnosis of periampullary carcinomas.

Methods

Fifty-nine patients with pathologically proven periampullary carcinomas who had received both CT and MR examinations before operation were reviewed retrospectively. Two reviewers independently interpreted the two image sets [the two-dimensional (2D)-CT with nCTCP set (CT set) vs. the 2D-MRI with MRCP set (MRI set)] in differentiating periampullary carcinomas, and the results were compared to the final pathologic records.

Results

An interobserver agreement with a weighed κ value of 0.868 for the CT set and 0.701 for the MRI set was obtained for both reviewers in this study. No statistically significant differences were observed in the accuracy of identifying each of the periampullary carcinomas of four origins (P values of 0.250, 0.500, 0.500, and 1.000 for reviewer 1 in comparison with 1.000, 0.625, 0.687, and 1.000 for reviewer 2 on the two image sets, respectively).

Conclusion

The CT set provides a comparable performance to that of the MRI set in differentiating periampullary carcinomas, and it may be an alternative to 2D-MRI with MRCP in assessing malignant biliary obstruction in patients who are not suitable for MR examinations.     

比较3.0T与5.0T MR胆胰管造影图像质量

目的 比较3.0T与5.0T MR胆胰管造影(MRCP)图像质量。方法 前瞻性纳入18例胆管扩张患者(胆管扩张组)和7名健康志愿者(健康组),采用3.0T和5.0T MR仪行MRCP,比较二者显示胆管树细节能力、信噪比(SNR)及图像伪影。结果 胆管扩张组中,5.0T MRCP所示胆管树分支数目、分支总长度及最大分支长度均大于3.0T MRCP(P均＜0.05);健康组中,5.0T MRCP所示胆管树分支数目及分支总长度均大于3.0T MRCP(P均＜0.05)。2组5.0T MRCP 的SNR均大于3.0T MRCP,但差异无统计学意义(P均＞0.05)。3.0T与5.0T MRCP图像伪影差异无统计学意义(P=0.054)。结论 5.0T MRCP所示胆管树解剖细节较3.0T MRCP更佳,而其SNR及图像伪影与后者相当。     

MR cholangiopancreatography techniques.

The tissue contrast principles and the technical aspects involved in the design of the imaging protocols currently used for clinical MR cholangiopancreatography are reviewed using a neutral terminology that is applicable to most of the high-field MRI equipment available from the major manufacturers. Furthermore, the technical discussions that follow are accompanied by a comprehensive set of tables listing the pulse sequence parameters used by the authors of the other articles in this issue. The tables are organized according to groups of parameters that determine the fundamental features of the protocols and of the generated images, specifically motion artifact reduction technique, scan geometry, image contrast, and recommended image post processing algorithm.     

Achieva 1.5T SE锐智磁共振的性能特点与临床应用

磁共振设备面世以来就以其无可比拟的独特优势飞速发展,但随着应用的广泛普及,其繁复的定位与参数设置、复杂的扫描序列和后处理等问题也日益突出,使扫描效率与扫描质量受到极大制约.为此,将全程智能检查与高分辨成像技术完美结合起来的Achieva 1.5T SE锐智磁共振产品应运而生.     

3D MTR measurement: from 1.5 T to 3.0 T

This study investigates some of the issues involved in magnetization transfer ratio (MTR) acquisition, and in particular aims to determine whether high quality in vivo MTR measurements can be made at 3.0 T. The dependency of the MTR white-to-grey matter contrast to noise ratio (CNR) on MT pulse characteristics at 1.5 T and at 3.0 T was investigated using an established two-pool model for MT. The simulations showed that MT pulse parameters optimizing the CNR can be derived for both field strengths. Both the SNR and the CNR of MTR maps at 3.0 T were increased compared to 1.5 T. Images obtained using a safe in vivo MTR acquisition protocol based on results of simulations at 3.0 T are presented.     

Rapid 3D navigator-triggered MR cholangiopancreatography with SPACE sequence at 3T: only one-third acquisition time of conventional 3D SPACE navigator-triggered MRCP

Abdominal Radiology - The purpose of this study was to compare the proposed rapid NT-MRCP protocol and the conventional NT-MRCP protocol with respect to image quality as well as the acquisition...     

磁共振胆胰管成像结合T1加权成像对胆总管微小结石的诊断价值

目的：研究磁共振胰胆管水成像（MRCP）结合T1加权成像（T1WI）检测胆总管微小结石的诊断价值。对象与方法：2005年1月~2006年12月共有104例胆总管结石患者，其中56例胆总管微小结石（直径≤5mm）。术前作常规MRI检查（横断位T1WI：TR/TE 155ms/3.4ms，横断位和冠状位T2WI：15000ms/81ms）。MRCP检查采用EXPRESS脂肪饱和序列，包括5组胆管路径的斜冠状45mm厚层成像采集、5mm薄层冠状成像采集（资源图像），来源于资源图像的最大信号投影重建图像。MR检查后1~5天内行胆总管外科手术或ERCP取石。分析胆总管微小结石的T1WI和MRCP表现及MRCP和T1WI对微小结石的检测、诊断。结果：56例胆总管微小结石，合并胆囊结石30例，胆囊切除7例。47例T1WI胆总管微小结石高信号改变。MRCP显示阳性结石充盈缺损33例。T1WI及T1WI结合MRCP检出胆总管微小结石阳性率明显高于单纯MRCP检查，统计学比较有显著性差异（Fisher精确检验，P＜0.01）。结论：在进行MRCP检查的同时，辅以T1WI有助于提高胆总管微小结石的诊断敏感性。     

磁共振胰胆管造影的诊断价值

目的：综合评价磁共振胰胆管造影（ＭＲＣＰ）的临床诊断价值。材料和方法：对５１例ＭＲＣＰ显示胰胆管扩张在病例进行分析,其中４７例经手术病理证实,４例经临床证实。结果：ＭＲＣＰ显示胆管梗阻的定位诊断正确率为１００％,定性诊断正确率为８６．３％。结论：ＭＲＣＰ对胆石症,恶性胆管梗阻及先天性胆总管囊肿等胆系疾病的诊断价值高于其他影像检查。