Whole-body magnetic resonance angiography at 3.0 Tesla

The quality of magnetic resonance (MR) angiography could be substantially improved over the past several years based on the introduction and application of parallel imaging, new sequence techniques, such as, e.g., centric k-space trajectories, dedicated contrast agents, and clinical high-field scanners. All of these techniques have played an important role to improve image resolution or decrease acquisition time for the dedicated examination of a single vascular territory. However, whole-body MR angiography may be the application with the potential to profit most from these technical advances. The present review article describes the technical innovations with a focus on parallel imaging at high field strength and the impact on whole-body MR angiography. The clinical value of advanced whole-body MR angiography techniques is illustrated by characteristic cases.     

Comparison of 3.0-and 1.5-tesla diffusion-weighted imaging in the visibility of breast cancer

Purpose The aim of this study was to compare diffusion-weighted imaging (DWI) at 3.0 T and 1.5 T by evaluating the apparent diffusion coefficient (ADC) value and visibility of breast cancer in the same patients. Materials and methods A total of 13 patients (16 lesions) with breast cancer underwent DWI at 3.0 T and 1.5 T. Tumors were classified into two groups based on the lesion size. The ADC values were measured, and visibility of the tumors was scored blindly. Results No significant difference was found for ADC values between 3.0 T and 1.5 T in either group (P > 0.05). All of the large lesions were visible clearly at both magnetic field strengths, and image scores were not different (P > 0.05). In contrast, small lesions were more clearly visible and had better image scores at 3.0 T than at 1.5 T (P < 0.001). Conclusion Small cancers were more clearly visible on DWI at 3.0 T than 1.5 T.     

Comparison of image quality in magnetic resonance imaging of the knee at 1.5 and 3.0 Tesla using 32-channel receiver coils

We examined to what degree the visualization of anatomic structures in the human knee is improved using 3.0-T magnetic resonance imaging (MRI) and many element RF receive coils as compared to 1.5 T. We imaged 20 knees at 1.5 and 3.0 T using T2-weighted STIR, T2-weighted gradient echo, T1-weighted spin-echo, true-FISP and T2-weighted fast spin echo techniques in conjunction with 32-element RF coil arrays. The 3.0-T examination was considerably faster than its 1.5-T counterpart. A superior subjective visibility at 3.0 T vs 1.5 T was found in 27 of 50 evaluated structures (meniscus, ligaments) with the exception of true-FISP techniques. The 3.0-T examination provided a better visibility (evaluated by blinded consensus-reading by two radiologists) of small structures such as the ligamentum transversum genu. Also, cartilage was better delineated at 3.0 T. A 23% increased average signal-to-noise ratio as assessed using a temporal filter was observed at 3.0 T as compared to 1.5 T. At 3.0 T, imaging of the human knee is faster and results in a subjective visibility of anatomic structures that is superior to and competitive with 1.5 T.     

不同MR脉冲序列在乳腺癌中的应用

MRI经历了从结构成像到功能成像,从单纯T1WI、T2WI序列到多脉冲序列成像的发展过程。利用多个MR脉冲序列成像可获得乳腺癌病变的定性、定量信息,在乳腺癌的早期诊断、生物学评价、疗效和预后评估等方面可发挥重要作用,但其也存在敏感性高而特异性相对较低且费用较高的问题。就乳腺癌MRI的应用现状、存在的问题及前景进行综述。     

Preoperative breast magnetic resonance imaging: controversies arising in the quest to evaluate clinical benefit

Breast magnetic resonance imaging (MRI) is indisputably the highest sensitivity test available to detect breast cancer, revealing more extensive cancer in the ipsilateral and otherwise occult cancer in the contralateral breasts when used before surgery. The use of preoperative breast MRI has become somewhat controversial, because the clinical benefit of the heightened detection provided by MRI has been questioned in the context of multidisciplinary breast cancer treatment, relatively low local recurrence, and metachronous contralateral cancer rates. Also, MRI detection rates have been compared with the high rates reported in the pathology literature. The emerging clinical outcome literature is showing conflicting results to demonstrating actual overall benefit. Critical review of this literature reveals several misconceptions about MRI detection rates and limitations of many of the published outcome studies to date, which render the results not necessarily generalizable to contemporary optimized breast MRI practices. This article addresses some of the misconceptions raised by critics, provides a critical review of the clinical outcome literature, reviews patient subgroups anticipated to have the highest yield when using preoperative MRI, makes recommendations for optimizing breast MRI practice, and suggests areas for potential future research.     

Management of breast magnetic resonance imaging-detected lesions

Breast magnetic resonance imaging (MRI) has become an essential component of breast imaging. Whether it is used as a problem-solving tool or a screening test or for staging patients with breast cancer, it detects many lesions in the breast. The challenge for the radiologist is to distinguish significant from insignificant lesions and to direct their management. A brief summary of the terminology according to the American College of Radiologists lexicon will be provided. This review article will cover the differential diagnosis of enhancing lesions, including masses and nonmass enhancement, from benign and malignant causes. Some of the specific morphologic and kinetic features that help to differentiate benign from malignant lesions will be illustrated, and positive predictive values of these features will be reviewed. The various methods of investigating enhancing lesions of the breast will be discussed, including second-look ultrasound, ultrasound-guided biopsy, stereotactic biopsy, and MRI-guided biopsy. A practical approach to the management of MRI-detected lesions will include timing of follow-up, when to biopsy and when to ignore enhancing lesions in the breast.     

MR liver imaging and cholangiography in the presence of surgical metallic clips at 1.5 and 3 Tesla

To evaluate whether clips from prior cholecystectomy impair image quality during magnetic resonance cholangiography (MRC) at 3 Tesla (T) compared with 1.5 T, surgical clips were embedded in a gel phantom and positioned at predefined distances from a fluid-filled tube designed to simulate the bile duct. The maximum clip distance was noted where susceptibility artifacts obscured the fluid-filled tube at 1.5 T and 3 T. Susceptibility artifact size was calculated for each sequence within each magnet class. In vivo analysis included 42 patients postcholecystectomy who underwent MRC at either 1.5 T or 3 T. In vitro, mean area of susceptibility artifacts was 104 mm² on 3-T and 75 mm² on 1.5-T MR imaging (MRI). While surgical clips within a 2-mm range impaired visualization of the fluid-filled tube on 1.5-T MRI, this range increased to 4 mm on 3-T MRI. In vivo, MRC image quality was impaired by susceptibility artifacts in three of 21 cases at 3 T and in two of 21 cases at 1.5 T. Overall, biliary pseudo-obstructions due to susceptibility artifacts from cholecystectomy surgical clips were not substantially more common on 3-T MRC in clinical practice, and patients with a history of prior cholecystectomy should not be excluded from a 3-T MRC.     

多模态MRI对乳腺癌化疗相关认知功能障碍的研究进展

乳腺癌病人化疗相关认知功能障碍（CRCI）发生的重要神经基础是化疗引起的脑结构、代谢、灌注和功能的改变。多模态MRI可以通过基于体素的形态学测量、扩散张量成像、磁共振波谱、磁敏感加权成像、动脉自旋标记灌注成像和基于血氧水平依赖的功能MRI等技术从局部或全局显示脑灰质体积和密度改变、脑白质纤维损伤、脑代谢改变、脑血流灌注以及脑区激活和功能连接变化等,从而为进一步探索乳腺癌CRCI的发病机制、早期诊断和症状研究提供依据。就多模态MRI在乳腺癌CRCI中的研究进展予以综述。     

乳腺癌新辅助化疗的动态增强磁共振成像评价

目的:探讨乳腺癌患者新辅助化疗(NAC)后通过动态增强MRI评估肿瘤边界的准确性;观察NAC前、后时间-信号强度曲线(TIC)变化。方法:搜集57例行NAC乳腺癌患者,化疗前后均行病理及MRI检查,以病理结果作为金标准,将NAC后MRI所测肿瘤最大径与其进行比较;观察记录NAC前、后TIC类型。结果:化疗后MRI测量的肿瘤最大径与病理量出的最大径有很高的相关性(r=0.926,P<0.005);NAC后TIC类型变化多样。结论:动态增强MRI可以对乳腺癌NAC后进行有效评价。化疗前、后的TIC变化可以为临床评价NAC疗效提供丰富的信息。     

Contrast-enhanced 3.0-T breast MRI for characterization of breast lesions: increased specificity by using vascular maps

Purpose: To assess the diagnostic accuracy of contrast-enhanced 3.0-T breast magnetic resonance imaging (MRI) for differentiating benign from malignant breast masses and subsequently to test if specificity could be further improved by scoring of the overall ipsilateral breast vascularity. Materials and methods: Fifty-four patients were prospectively enrolled in the study and underwent contrast-enhanced 3.0-T breast MRI. MR images were evaluated and classified according to the MRI BI-RADS lexicon criteria. Lesion size, number of lesions, and localization in the breast were systematically assessed. Maximum intensity projections (MIPS) were obtained by using high-resolution contrast-enhanced (0.1 mmol/kg gadobutrol) fat-saturated T1-weighted images. Breast vascularization was scored according to the methods from Sardanelli et al. by measuring the number, diameter, and length of the vessels on the MIPS. The score ranged from 0 (indicating absent or low breast vascularity) to 3 (indicating high breast vascularity). Results: Final analysis of 56 lesions revealed 25 (45%) malignant lesions and 31 (55%) benign lesions. Correlation with the MRI BI-RADS classification revealed cancer in none (0%) of the BI-RADS II lesions, in 1 (12%) of the BI-RADS III lesions, in 5 (83%) of the BI-RADS IV lesions, and in 19 (100%) of the BI-RADS V lesions. Based on morphologic and kinetic data analysis, the sensitivity and specificity of 3.0-T breast MRI was 100% (25/25) and 74% (23/31), respectively. After adjustment for the breast vascularity score, specificity significantly (p = 0.048) increased to 87% (27/31) without affecting sensitivity. Conclusion: Diagnostic accuracy of contrast-enhanced 3.0-T breast MRI increased significantly when the vascularity score was added to the standard morphologic and kinetic data analysis, resulting in a specificity of 87% without affecting sensitivity, which remained 100%.     

Clinical significance of magnetic resonance imaging findings in rectal cancer

Staging of rectal cancer is essential to help guide clini-cians to decide upon the correct type of surgery and determine whether or not neoadjuvant therapy is indicated. Magnetic resonance imaging (MRI) is currently one of the most accurate modalities on which to base treatment decisions for patients with rectal cancer. MRI can accurately detect the mesorectal fascia, assess the invasion of the mesorectum or surrounding organs and predict the circumferential resection margin. Although nodal disease remains a difficult radiological diagnosis, new lymphographic agents and diffusion weighted imaging may allow identification of metastatic nodes by criteria other then size. In light of this, we have reviewed the literature on the accuracy of specific MRI findings for staging the local extent of primary rectal cancer. The aim of this review is to establish a correlation between MRI findings, prognosis, and available treatment options.     

磁共振波谱技术在乳腺癌诊断中的应用

乳腺癌是临床常见的恶性肿瘤之一,MR在乳腺癌的诊断中发挥着重要的作用。磁共振波谱技术是能检测体内生化代谢的微创性检查方法,本文介绍磁共振波谱在乳腺癌诊断和评价治疗效果中的应用现状。     

MR在乳腺肿瘤中的应用

随着MR成像技术的不断发展，MRI诊断乳腺疾病的敏感性有了很大的提高。近年来MRS及MR引导的乳腺定向活检技术的临床应用，进一步提高了腿诊断乳腺疾病的特异性。就近年文献中有关乳腺肿瘤的腿应用予以综述。     

Preoperative breast magnetic resonance imaging: applications in clinical practice

Results of large randomized trials have shown that survival rates after breast conserving surgery are equivalent to those obtained by radical mastectomy. Breast conserving surgery with wide local excision in women with early stage breast cancer who are thought to have a single and resectable tumour as determined by clinical examination and conventional imaging followed by postoperative irradiation is the standard of care in early breast cancer. Mapping of local disease is the key element to guide optimal surgery to obtain tumour-free margins, thereby decreasing risk of local recurrence. The usual preoperative workup of breast malignancy consists of clinical breast examination and mammography with or without ultrasound. However, mammography and ultrasound fail to accurately assess tumour extent in as many as a third of patients eligible for breast conserving therapy. It is well established that magnetic resonance imaging is far superior to mammography (with and without ultrasound) for mapping the local extent of breast cancer. Experts advocate its use despite its high costs, high number of false positive findings, and lack of evidence from randomized prospective trials and, notably, fear of "overtreatment." This article discusses the current role of breast magnetic resonance imaging with its clinical advantages and applications.     

Diffusion-weighted magnetic resonance imaging in the characterization of axillary lymph nodes in patients with breast cancer

Purpose:

To assess prospectively the accuracy of diffusion‐weighted magnetic resonance imaging (DWI) in differentiating between metastatic and benign axillary lymph nodes in patients with breast cancer.

Materials and Methods:

In all, 215 patients with histologically proven breast cancer, prior to axillary dissection, underwent breast and axillary 1.5 T MRI. In 102 patients in whom at least one axillary lymph node with a short axis of 6 mm or more was found the apparent diffusion coefficient (ADC) was measured in one lymph node per patient by means of an echo planar, parallel imaging DWI sequence. Forty‐three lymph nodes were finally included which, on histological examination, either contained a metastasis larger than 5 mm or were metastasis‐free; nodes with metastases smaller than 5 mm were excluded.

Results:

From histological examination, 19/43 lymph nodes had a metastasis at least 5 mm, while in 24/43 no malignant cells were found. The ADC values of the lymph nodes with metastases (mean: 0.878 × 10^?3 mm²/s; range: 0.30 –1.20) were significantly lower (P < 0.001) than those of the benign lymph nodes (mean: 1.494; range: 0.60 –2.50). Adopting a threshold value of 1.09 × 10^?3 mm²/s DWI resulted in 94.7% sensitivity, 91.7% specificity, and 93.0% accuracy in the identification of metastasis in this series of lymph nodes.

Conclusion:

From these preliminary data DWI seems a promising method in the differential diagnosis between metastatic and benign axillary lymph nodes in patients with breast cancer. J. Magn. Reson. Imaging 2012;36:858–864. © 2012 Wiley Periodicals, Inc.

     

Cardiac magnetic resonance parallel imaging at 3.0 Tesla: technical feasibility and advantages

PURPOSE: To quantify changes in signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), specific absorption rate (SAR), RF power deposition, and imaging time in cardiac magnetic resonance imaging with and without the application of parallel imaging at 1.5 T and 3.0 T. MATERIALS AND METHODS: Phantom and volunteer data were acquired at 1.5 T and 3.0 T with and without parallel imaging. RESULTS: Doubling field strength increased phantom SNR by a factor of 1.83. In volunteer data, SNR and CNR values increased by factors of 1.86 and 1.35, respectively. Parallel imaging (reduction factor = 2) decreased phantom SNR by a factor of 1.84 and 2.07 when compared to the full acquisition at 1.5 T and 3.0 T, respectively. In volunteers, SNR and CNR decreased by factors of 2.65 and 2.05 at 1.5 T and 1.99 and 1.75 at 3.0 T, respectively. Doubling the field strength produces a nine-fold increase in SAR (0.0751 to 0.674 W/kg). Parallel imaging reduced the total RF power deposition by a factor of two at both field strengths. CONCLUSIONS: Parallel imaging decreases total scan time at the expense of SNR and CNR. These losses are compensated at higher field strengths. Parallel imaging is effective at reducing total power deposition by reducing total scan time.     

High resolution spectroscopic imaging of GABA at 3 Tesla

A spin echo‐based MRSI sequence was developed to acquire edited spectra of γ‐aminobutyric acid in an entire slice. Water and lipid signals were suppressed by a dual‐band presaturation sequence, which included integrated outer volume suppression pulses for additional lipid suppression. Experiments in three normal volunteers were performed at 3 T using a 32‐channel head coil. High signal‐to‐noise ratio spectra and metabolic images of γ‐aminobutyric acid were acquired from nominal 4.5 cm³ voxels (estimated actual voxel size 7.0 cm³) in a scan time of 17 min. The sequence is also expected to co‐edit homocarnosine and macromolecules, giving a composite γ‐aminobutyric acid⁺ resonance. The γ‐aminobutyric acid⁺ to water ratio was measured using a companion water MRSI scan and was found to correlate linearly with the % gray matter (GM) of each voxel (γ‐aminobutyric acid⁺/water = (1.5 × GM + 3.2) × 10^?5, R = 0.27), with higher γ‐aminobutyric acid⁺ levels in gray matter compared with white. In conclusion, high signal‐to‐noise ratio γ‐aminobutyric acid‐MRSI is possible at 3 T within clinically feasible scan times. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

A review of the safety implications of magnetic resonance imaging at field strengths of 3 Tesla and above

RationaleDiagnostic imaging is being driven by technological developments particularly so in the field of Magnetic Resonance Imaging (MRI). Electromagnetic fields used to produce images are becoming much stronger and switched more rapidly and it is essential that safety advice remains appropriate and current. Using a systematic methodology, this review aims to identify the clinical safety implications in performing MRI at field strengths of 3 Tesla (T) and above and determine whether the current clinical safety guidelines are appropriate.MethodReferences were sourced from The Cochrane Library, Centre for Reviews and Dissemination Science Direct, PubMed and Google Scholar. Related websites searched included The British Institute of Radiology, Society of Radiographers, Royal College of Radiologists, The Institution of Engineering and Technology, IMRSER (Institute for Magnetic Resonance Safety, Education, and Research), MagNet (NHS PASA). References supplied in retrieved papers were also checked for potential relevance. The use of consistent search terminology and inclusion and exclusion criteria ensured quality and provided rigour to conclusions drawn.ConclusionAccording to the literature retrieved, the current body of knowledge has allowed safety guidelines to be established for patient safety and these are both appropriate and valid at field strengths of 3 T.     

Establishing a comprehensive breast magnetic resonance imaging service in a community hospital

Advances made since the first application of breast magnetic resonance imaging (MRI) in the late 1980s have made it an integral complement to a comprehensive breast assessment centre. Incorporating breast MRI into an existing practice can appear daunting, but a structured and organized approach allows for a smoother transition. With a well thought out plan that engages all team members and experience in interpretation and performing of interventional procedures, breast MRI will serve to add valuable information in patient management.     

Multicontrast-weighted magnetic resonance imaging of atherosclerotic plaques at 3.0 and 1.5 Tesla: ex-vivo comparison with histopathologic correlation

The purpose was to analyze magnetic resonance (MR) plaque imaging at 3.0 Tesla and 1.5 Tesla in correlation with histopathology. MR imaging (MRI) of the abdominal aorta and femoral artery was performed on seven corpses using T1-weighted, T2-weighted, and PD-weighted sequences at 3.0 and 1.5 Tesla. Cross-sectional images at the branching of the inferior mesenteric artery and the profunda femoris were rated with respect to image quality. Corresponding cross sections of the imaged vessels were obtained at autopsy. The atherosclerotic plaques in the histological slides and MR images were classified according to the American Heart Association (AHA) and analyzed for differences. MRI at 3.0 Tesla offered superior depiction of arterial wall composition in all contrast weightings, rated best for T2-weighted images. Comparing for field strength, the highest differences were observed in T1-weighted and T2-weighted techniques (both P< or =0.001), with still significant differences in PD-weighted sequence (P< or =0.005). The majority of plaques were histologically classified as calcified plaques. In up to 21% of the cases, MRI at both field strengths detected signal loss characteristic of calcification although calcified plaque was absent in histology. MRI at 3.0 Tesla offers superior plaque imaging quality compared with 1.5 Tesla, but further work is necessary to determine whether this translates in superior diagnostic accuracy.