Biomedical implants and devices: assessment of magnetic field interactions with a 3.0-Tesla MR system

PURPOSE: To evaluate magnetic field interactions for 109 different biomedical implants and devices in association with exposure to a 3.0-Tesla magnetic resonance (MR) system. MATERIALS AND METHODS: A total of 109 implants and devices (aneurysm clips, 32; clips, fasteners, and staples, 10; coils and stents, 10; heart valve prostheses and annuloplasty rings, 12; orthopedic implants, five; suture materials, 13; vascular access ports and accessories, 13; miscellaneous implants and devices, 14) were tested for magnetic field interactions at 3.0-Tesla using previously-described, standardized techniques to assess magnetic field translational attraction and torque. RESULTS: The deflection angles and torque measurements ranged, respectively, from 0 to 16 degrees and 0 to +2 for the aneurysm clips; 0 to 90 degrees and 0 to +4 for the clips, fasteners, and staples; 0 to 47 degrees and 0 to +4 for the coils and stents; 0 to 4 degrees and 0 to +1 for the heart valve prostheses and annuloplasty rings; 0 to 12 degrees and 0 to +2 for the orthopedic implants; 0 to 13 degrees and 0 to +2 for the suture materials; 0 to 52 degrees and 0 to +4 for the vascular access ports and accessories; and 0 to 28 degrees and 0 to +3 for the miscellaneous implants and devices. CONCLUSION: Of the 109 implants and devices assessed for magnetic field interactions at 3.0-Tesla, four (4%) are potentially unsafe based on deflection angle criteria. The implications of these results for patients undergoing MR procedures at 3.0-Tesla is discussed. Notably, these results are specific to the 3.0-Tesla MR system used for this evaluation.     

Parallel imaging improves the image quality and duct visibility of breathhold two‐dimensional thick‐slab MR cholangiopancreatography

MRI has become a reliable tool in medical imaging for assessing morphological and functional details of the human body in a noninvasive manner. Perfusion is an important parameter to assess status and functionality of tissue and organs. This review summarizes the different approaches to measure perfusion based on MRI. Some basics of the theoretical background are provided as well as measurement techniques with and without contrast media are described. J. Magn. Reson. Imaging 2014;40:269–279 . © 2013 Wiley Periodicals, Inc .     

MR Imaging in the 21st Century: Technical Innovation over the First Two Decades

Clinical MRI systems have continually improved over the years since their introduction in the 1980s. In MRI technical development, the developments in each MRI system component, including data acquisition, image reconstruction, and hardware systems, have impacted the others. Progress in each component has induced new technology development opportunities in other components. New technologies outside of the MRI field, for example, computer science, data processing, and semiconductors, have been immediately incorporated into MRI development, which resulted in innovative applications. With high performance computing and MR technology innovations, MRI can now provide large volumes of functional and anatomical image datasets, which are important tools in various research fields. MRI systems are now combined with other modalities, such as positron emission tomography (PET) or therapeutic devices. These hybrid systems provide additional capabilities.In this review, MRI advances in the last two decades will be considered. We will discuss the progress of MRI systems, the enabling technology, established applications, current trends, and the future outlook.     

The present state of NMR tomography and its future

The use of nuclear magnetic resonance (NMR) tomography requires close co-operation between radiologists and doctors working in nuclear medicine, so that experience gained in computed tomography and diagnostic function programmes can be exchanged. With regard to the technology of the magnets, the main demand at the moment is for imaging. In this area, special magnetic-field strengths, spools and evaluation procedures should be developed and optimised for the various applications. A list of guidelines must be worked out, and a strategy for the application of NMR tomography within general diagnostic procedures must be drawn up. Further progress will be brought about by developments such as breath and cardiac gating, as well as by the the introduction of contrast media. In order to keep the cost of examinations within certain limits, it is necessary that plans are made to install an appropriate number of NMR devices.     

Announcement of Meetings

Magnetization transfer (MT) techniques have been shown to significantly reduce background soft-tissue signal in time-of-flight magnetic resonance angiography. To achieve sufficient suppression, radio frequency (RF) pulses with tip angles on the order of 1000 degrees are typically used, resulting in significant RF power deposition in the patient. Although these power deposition levels do not exceed the FDA guidelines, they are significantly higher than those used in typical imaging techniques. The use of these same magnetization transfer pulses in applications at field strengths higher than 1.5 T will require MT power levels which exceed FDA safety standards. This report demonstrates that the total power deposition required to achieve background tissue suppression can be significantly reduced by the application of the saturation pulses only during the phase-encoding steps corresponding to the central portion of “k space.” This technique allows equivalent soft tissue suppression with approximately 10% of the energy deposition of conventional magnetization transfer techniques.     

Clinical Evaluation of Respiratory-triggered 3D MRCP with Navigator Echoes Compared to Breath-hold Acquisition Using Compressed Sensing and/or Parallel Imaging

Purpose:To compare the image quality of three-dimensional magnetic resonance cholangiopancreatography (MRCP) acquired with respiratory triggering against breath-hold 3D MRCP with compressed sensing (CS) and parallel imaging (PI) in a clinical setting.Methods:This study included 93 patients (45 men, mean age: 69.7 ± 9.3 years), in whom three types of 3D MRCP were performed: 3D breath-hold MRCP with CS and PI reconstruction (BH-CS-MRCP) and PI only reconstruction (BH-PI-MRCP) additionally to 3D respiratory triggered MRCP with navigator echoes (Nav-MRCP). Duct visualization and overall image quality were blindly evaluated on a four-point scale by two independent radiologists. Quantitative analysis was performed by calculating the relative duct-to-periductal contrast (RC) of three main biliary segments. Comparison between the methods was performed using paired t-test.Results:Acquisition time was 23 s for both breath-hold MRCP protocols and 1 min 29 s for Nav-MRCP. Mean grading (Nav/CS/PI) for common bile duct (2.74/2.87/2.94), common hepatic duct (2.82/2.92/3.00), central right hepatic duct (2.75/2.85/2.98), central left hepatic duct (2.75/2.85/2.92) and cystic duct (2.22/2.34/2.42) was higher in BH-CS- and BH-PI-MRCP, whereas Nav-MRCP showed higher grading in the peripheral segments (peripheral right hepatic duct: 2.24/2.01/2.12; peripheral left hepatic duct: 2.23/2.02/2.13). Overall image quality of Nav-MRCP (2.91 ± 0.7) was not different from BH-PI-MRCP (2.92 ± 0.6) (P = 0.163), but higher than BH-CS-MRCP (2.80 ± 0.7) (P = 0.031). Quantitative analysis showed lower RC values for CS- and PI-MRCP than Nav-MRCP (P < 0.001).Conclusion:Breath-hold 3D MRCP were feasible using PI and CS. Visualization of the greater ductal system was even superior in breath-hold MRCP than in Nav-MRCP by considerably reducing acquisition time. Both breath-hold methods are suitable for revised MRI protocols notably in patients with irregular respiratory cycle.     

Intraoperative MR-guided neurosurgery

For more than a decade neurosurgeons have become increasingly dependent on image guidance to perform safe, efficient, and cost-effective surgery. Neuronavigation is frame-based or frameless and requires obtaining computed tomography or magnetic resonance imaging (MRI) scans several days or immediately before surgery. Unfortunately, these systems do not allow the neurosurgeon to adjust for the brain shift that occurs once the cranium is open. This technical inability has led to the development of intraoperative MRI (ioMRI) systems ranging from 0.12-3.0T in strength. The advantages of ioMRI are the excellent soft tissue discrimination and the ability to view the operative site in three dimensions. Enhanced visualization of the intracranial lesion enables the neurosurgeon to choose a safe surgical trajectory that avoids critical structures, to maximize the extent of the tumor resection, and to exclude an intraoperative hemorrhage. All ioMRI systems provide basic T1- and T2-weighted imaging capabilities but high-field (1.5T) systems can also perform MR spectroscopy (MRS), MR venography (MRV), MR angiography (MRA), brain activation studies, chemical shift imaging, and diffusion-weighted imaging. Identifying vascular structures by MRA or MRV may prevent injury during surgery. Demonstrating elevated phosphocholine within a tumor may improve the diagnostic yield of brain biopsy. Mapping out neurologic function may influence the surgical approach to a tumor. The optimal strength for MR-guided neurosurgery is currently under investigation.     

自旋回波及其改良序列在肺实质磁共振成像中的应用

目的　选择肺实质磁共振功能成像合适的序列。方法　选择健康志愿者 8人 ,健康家犬 8条 ,对自旋回波及其改良序列进行调试、组合。结果　选择的序列是单激发快速自旋回波序列和单激发反转快速自旋回波序列。结论　适合肺实质磁共振功能成像的序列是中心相位编码方式的单激发快速自旋回波序列和单激发反转快速自旋回波序列     

Direct comparison of sensitivity encoding (SENSE) accelerated and conventional 3D contrast enhanced magnetic resonance angiography (CE‐MRA) of renal arteries: Effect of increasing spatial resolution

Purpose:

To assess the effect of attaining higher spatial resolution in contrast‐enhanced magnetic resonance angiography (MRA) of renal arteries using parallel imaging, sensitivity encoding (SENSE), by comparing the SENSE contrast‐enhanced (CE) MRA against a conventional CE‐MRA protocol with identical scan times, injection protocol, and other acquisition parameters.

Materials and Methods:

Numerical simulations and a direct comparison of SENSE‐accelerated versus conventional acquisitions were performed. A total of 41 patients (18 male) were imaged using both protocols for a direct comparison. Both protocols used fluoroscopic triggering, centric encoding, breath‐holding, equivalent injection protocol, and lasted ≈30 seconds.

Results:

Simulated point‐spread functions were narrower for the SENSE protocol compared to the conventional protocol. In the patient study, although the SENSE protocol produced images with lower signal‐to‐noise ratio (SNR), image quality was better for all segments of the renal arteries. In addition, ringing of kidney parenchyma and renal artery blurring were significantly reduced in the SENSE protocol. Finally, reader confidence improved with the SENSE protocol.

Conclusion:

Despite a reduction in SNR, the higher‐resolution SENSE CE‐MRA provided improved image quality, reduced artifacts, and increased reader confidence compared to the conventional protocol. J. Magn. Reson. Imaging 2010;31:149–159. © 2009 Wiley‐Liss, Inc.     

磁共振脑血管血流分析的临床应用——脑血栓、脑缺血与正常组对比研究

目的：测定脑血栓、脑缺血患者和正常人的颅内动脉血流，为临床提供进一步的诊断资料。材料和方法：应用ＭＲ血流分析技术，对４２例大脑中动脉（ＭＣＡ）、颅内动脉（ＩＣＡ）及基底动脉（ＢＡ）血流进行了测量与分析。结果：（１）ＭＣＡ脑梗塞组血流速度峰值增高而平均血流量值降低；脑缺血组血流速度峰值增高或正常而平均血流量值正常或降低，二者必居其一；正常组之ＭＲ血流分析无异常。（２）ＩＣＡ和ＢＡ二者均未见明显异常。结论：推测ＭＲ脑血流分析技术在预测中风方面可能是有效的检测手段。     

Low b-value diffusion-weighted imaging: emerging applications in the body

Thanks to recent advances in magnetic resonance imaging technology, it has become possible to perform intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) in any part of the body. Extracranial applications of DWI are currently under active investigation, especially for oncological imaging. However, the use of non-quantitative low b-value (10-100 s/mm(2)) DWI in the body is still a relatively unexplored field, and its potential is not fully recognized. Non-quantitative low b-value DWI may especially be useful for the evaluation of structures that have an inherently low signal at high b-value DWI, including (but not limited to) the liver, heart, and small bowel. This article will review and discuss the basic principles and potential applications of nonquantitative low b-value DWI in the body.     

磁共振Keyhole技术在颈动脉动态增强血管成像中的应用

目的　探讨匙孔 (Keyhole)技术在颈动脉动态增强磁共振血管成像 (dynamiccontrastechancedMRA ,DCE -MRA)中的应用优势。方法　将疑有颈部动脉疾病的 16例患者分为 2组 ,实验组 8例患者使用Keyhole技术 ;对照组 8例未使用Keyhole技术 ,直接行DCE -MRA扫描。结果　对照组 8例患者中 2例扫描在 6～ 8s时 ,只有动脉显示 ,而静脉未显影 ,3例扫描时间 8～ 9s时 ,已有静脉轻微显影。 3例扫描时间 >10s时 ,静脉已完全显影。实验组的 8例患者由于扫描时间缩短了一半 ,8例均获得了清晰、立体的颈动脉血管及分支全貌且无静脉显示的图像。结论　Keyhole技术的使用大大地缩短了扫描时间 ,可使颈动脉图像快速显影 ,不受静脉同时显示的干扰 ,提高了诊断准确性     

Three-dimensional flow-independent peripheral angiography

A magnetization-prepared sequence, T₂-Prep-IR, exploits T₁, T₂, and chemical shift differences to suppress background tissues relative to arterial blood. The resulting flow-independent angiograms depict vessels with any orientation and flow velocity. No extrinsic contrast agent is required. Muscle is the dciminant source of background signal in normal volunteers. However, long-T₂ deep venous blood and nonvascular fluids such as edema also contribute background signal in some patients. Three sets of imaging parameters are described to address patient-specific contrast requirements. A rapid, spiral-based, three-dimensional readout is utilized to generate high-resolution angiograms of the lower extremities. Comparisons with x-ray angiography and two-dimensional time-of-flight angiography indicate that this flow-independent technique has unique capabilities to accurately depict stenoses and to visualize slow flow and in-plane vessels.     

“Cystic”‐appearing soft tissue masses: What is the role of anatomic,functional, and metabolic MR imaging techniques in their characterization?

Although conventional MR imaging with contrast‐enhanced T1‐weighted sequences is of paramount importance for evaluating soft tissue masses, noncontrast MR sequences have emerged that facilitate their characterization. In this article, the utility and pitfalls of conventional MR imaging with T1‐weighted, fluid‐sensitive, and contrast‐enhanced sequences will be discussed, along with that of functional (diffusion weighted imaging) and metabolic (proton MR spectroscopy) non–contrast‐enhanced techniques for the purpose of soft tissue mass characterization. In particular, we discuss the application of these techniques to differentiating neoplastic or inflammatory masses that have high fluid content from benign cysts, as this distinction is a common pitfall of conventional sequences. J. Magn. Reson. Imaging 2014;39:504–511 . © 2013 Wiley Periodicals, Inc .     

Resistive NMR of intracranial hematomas

Summary Comparison between computed tomography and nuclear magnetic resonance imaging in 17 patients with intracranial hematomas indicates a distinct role for NMR in evaluating the stable patient with hematoma. NMR is useful for delineating the extent of the hematoma, the relationship of the hematoma to brain anatomy, and the presence of hematoma at a time when the hematoma is isodense on CT.     

磁共振成像对输尿管梗阻诊断的价值

目的目的探讨磁共振成像(MRU)在输尿管梗阻性疾病诊断中的价值。方法对44例(其中输尿管肿瘤23例,输尿管结石8例,输尿管结核及炎性狭窄5例,输尿管息肉3例,巨输尿管症5例)输尿管梗阻病人进行了MRU检查,并与B超、CT、静脉尿路造影(IVU)、输尿管逆行造影结果进行比较。结果MRU能清楚显示输尿管梗阻的部位,对输尿管梗阻的定位诊断率为100%,定性诊断率为86%。结论MRU对输尿管梗阻的诊断率高,无创且不受肾功能影响,并发症少,是对输尿管梗阻病变的最佳显示方法。     

Magnetic resonance imaging of inflammatory bowel disease: evaluation in a rabbit model

PURPOSE: To correlate intestinal contrast enhancement and wall thickening with the degree of inflammation in an experimental model of inflammatory bowel disease. MATERIALS and METHODS: Inflammatory bowel disease was elicited in 39 New Zealand White rabbits by rectal instillation of 2,4,6-trinitrobenzene sulphonic acid (TNBA). Magnetic resonance imaging (MRI) was used to determine bowel wall thickness and intestinal contrast enhancement after the administration of 0.1 mmol/kg of gadodiamide intravenously. MR measurements were compared with the complete histopathologic analysis. RESULTS: MR measurements of bowel wall thickness correlated well with histopathologic measurements in vitro (r = 0.85, P < 0.0001) and with histopathologic evidence of chronic inflammatory bowel disease (P < 0.02). Chronic inflammation was characterized by increased intestinal contrast enhancement (137 +/- 25%) when compared to normal bowel (86 +/- 7%, P = 0.04). CONCLUSION: Contrast-enhanced MRI accurately reflects inflammatory bowel disease in the rabbit model.     

恶性淋巴瘤治疗前后磁共振成像信号强度的变化及临床意义

我们对20例恶性淋巴瘤患者治疗前后进行了检查,并分别测量了肿瘤、皮下脂肪及肌肉的信号强度,对所得数据进行了标准化处理.结果表明,治疗后所有病人的信号强度标准化值均明显减小,减小的程度标定着肿瘤纤维化的程度;MRI的T_2WI图像可对复发或残留瘤灶与纤维肿块间作出鉴别,因此,恶性淋巴瘤治疗前后MRI检查有着重要的临床指导意义.     

宫腔积脓的MRI表现及与病理对照分析

目的 分析宫腔积脓的MRI表现及与病理相关性.方法 回顾性分类总结12例经手术病理证实为宫腔积脓患者的常规MRI、扩散加权成像(DWI)表现特点,计算平均表观扩散系数(ADC)值,并对照分析相对应病理成分.结果 根据积脓MRI信号均匀性分类:信号均匀型2例,T1WI呈稍低信号,T2WI呈稍高信号,DWI呈高信号,脓液中各成分分布较均匀;信号混杂型5例,MRI示脓液底部或周围混杂稍短T2信号,DWI呈混杂高信号,脓液底部见沉淀物;液-液平面型5例,上层呈水样信号,下层T2WI信号较上层低,其中3例下层信号均匀,DWI呈均匀高信号,脓液中各成分分布均匀,2例下层信号混杂,为血性积脓,DWI呈高低混杂信号.12例宫腔积脓平均ADC值为0.532×10-3 mm2/s.12例子宫体积均增大,其中10例子宫壁变薄,另2例子宫壁炎性浸润、增厚;8例患有宫颈癌;5例合并盆腔积液.结论 宫腔积脓的MRI表现具有特征性,其MRI表现与病理成分高度相关,且ADC值在其诊断中具有重要价值.     

脑胶质瘤瘤周组织3.0T~1H-MRS与浸润程度的相关性分析

目的:分析未经治疗的脑胶质瘤瘤周组织的1 H-MRS表现,探讨不同代谢物比率与肿瘤浸润程度间的关系。方法:搜集未经治疗的脑胶质瘤25例,均经手术、病理证实。术前在3.0T MR仪上行常规平扫及MRI增强检查,并用点解析频谱法(PRESS)行多体素1 H-MRS成像。经MRI引导-神经导航下穿刺活检取得组织学样本并行病理学分析。结果:共得到239个组织学样本及相应1 H-MRS、病理学分析结果。Spearman分析示Cho/nCr及NAA/Cho与肿瘤的浸润程度相关性最大。结论:初步研究表明,与常规及MRI增强相比,1 H-MRS能够更准确地反映脑胶质瘤的浸润范围及程度,这对于评价肿瘤范围及制定手术计划、评价疗效都具有重要的诊断和治疗意义。