MR Imaging of the Newborn: a technical perspective

This article discusses neonatal magnetic resonance (MR) imaging and reviews equipment and procedures for MR-related transport, sedation, monitoring, and scanning. MR is gaining importance in the diagnosis and clinical management of critically ill, and often very low birth weight infants, so research is ongoing to make transport and examination safer and imaging more successful. Efforts are focused on integration of dedicated neonate MR scanners in neonatal intensive care units, improvements in incubator technology and handling, and more efficient use of scan/sedation time by choosing dedicated neonate coil arrays that improve the signal-to-noise-ratio and facilitate the choice of modern imaging techniques.     

Endoluminal MR imaging of diseases of the anus and rectum

Endoluminal MRI of the rectum and anus was introduced in the first half of this decade to overcome the limitations of endoluminal sonography and body coil MRI. Endoluminal MRI is the imaging method of choice for fecal incontinence and anal tumors, whereas it is a competitive imaging method to phased array coil MRI in patients with perianal fistulas or rectal tumor. The purpose of this article is to describe the technique and major indications of endoluminal MR imaging of the anus and rectum.     

syngo骨关节成像技术

Siemens磁共振设备硬件方面提供各个骨关节专用线圈以提高图像分辨率,多通道设计支持并行采集,局部发射接收线圈避免卷折伪影并降低射频沉积;高级应用序列包括可以去除运动伪影的syngoBLADE、可以减弱金属导致的伪影的三点tseDIXON、可以得到各向同性数据的SPACE;除形态学检查外,syngoMaplt提供实时生化成像的简单工具;针对临床需要,综合现有技术,提供完备的各关节优化扫描协议。     

Parallel imaging in MR angiography

The recently developed techniques of parallel imaging with phased array coils are rapidly becoming accepted for magnetic resonance angiography (MRA) applications. This article reviews the various current parallel imaging techniques and their application to MRA. The increased scan efficiency provided by parallel imaging allows increased temporal or spatial resolution, and reduction of artifacts in contrast-enhanced MRA (CE-MRA). Increased temporal resolution in CE-MRA can be used to reduce the need for bolus timing and to provide hemodynamic information helpful for diagnosis. In addition, increased spatial resolution (or volume coverage) can be acquired in a breathhold (eg, in renal CE-MRA), or in otherwise limited clinically acceptable scan durations. The increased scan efficiency provided by parallel imaging has been successfully applied to CE-MRA as well as other MRA techniques such as inflow and phase contrast imaging. The large signal-to-noise ratio available in many MRA techniques lends these acquisitions to increased scan efficiency through parallel imaging.     

基于射频场测量的去耦技术在磁共振相控阵线圈中的应用

目的将基于射频场测量的去耦技术应用于核磁共振相控阵线圈以消除核磁共振图像由于阵列单元之间耦合引起的伪影.方法利用测量得到的单个线圈和阵列单元的射频场计算阵列中各个单元之间的耦合系数矩阵以及相应的去耦系数矩阵,并将后者作用于阵列中各单元线圈射频场,以消除各个单元之间的耦合.结果此方法用基于有限元的高频结构仿真软件HFSS进行了仿真,并对仿真结果用计算机模拟核磁共振图像进行了验证, 两者之间具有很好的一致性.结论证明该方法有效驱除了阵列单元之间的耦合效应.     

临床用肢端柔性表面线圈和相控阵线圈在小动物磁共振成像中的性能比较

目的对比肢端柔性线圈和相控阵线圈非并行采集及并行采集技术在小动物实验中对图像质量的影响。方法10只Wistar大鼠,分别用西门子标配的临床用正交柔性肢端线圈和相控阵肢端线圈在同一扫描参数的条件下用于头部信号采集,同时在肢端相控阵线圈采集中采用并行采集技术再获得相同的图像,然后对三组图像选择同一层面进行SNR的比较。结果正交柔性线圈和4通道肢端相控阵线圈采集的图像信噪比有明显的差异,正交柔性线圈能获得更高的图像信噪比,而肢端相控阵线圈非并行采集与并行采集技术(R=2)所获得的图像信噪比没有差异,但采用并行采集技术能极大地减少扫描时间。结论小动物实验在线圈的选用上,线圈的填充因数对图像质量的影响更大,但相控阵线圈与并行采集技术合用可以极大地减少成像时间。     

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.     

High resolution carotid black-blood 3T MR with parallel imaging and dedicated 4-channel surface coils

Background

Most of the carotid plaque MR studies have been performed using black-blood protocols at 1.5 T without parallel imaging techniques. The purpose of this study was to evaluate a multi-sequence, black-blood MR protocol using parallel imaging and a dedicated 4-channel surface coil for vessel wall imaging of the carotid arteries at 3 T.

Materials and methods

14 healthy volunteers and 14 patients with intimal thickening as proven by duplex ultrasound had their carotid arteries imaged at 3 T using a multi-sequence protocol (time-of-flight MR angiography, pre-contrast T1w-, PDw- and T2w sequences in the volunteers, additional post-contrast T1w- and dynamic contrast enhanced sequences in patients). To assess intrascan reproducibility, 10 volunteers were scanned twice within 2 weeks.

Results

Intrascan reproducibility for quantitative measurements of lumen, wall and outer wall areas was excellent with Intraclass Correlation Coefficients >0.98 and measurement errors of 1.5%, 4.5% and 1.9%, respectively. Patients had larger wall areas than volunteers in both common carotid and internal carotid arteries and smaller lumen areas in internal carotid arteries (p < 0.001). Positive correlations were found between wall area and cardiovascular risk factors such as age, hypertension, coronary heart disease and hypercholesterolemia (Spearman''s r = 0.45-0.76, p < 0.05). No significant correlations were found between wall area and body mass index, gender, diabetes or a family history of cardiovascular disease.

Conclusion

The findings of this study indicate that high resolution carotid black-blood 3 T MR with parallel imaging is a fast, reproducible and robust method to assess carotid atherosclerotic plaque in vivo and this method is ready to be used in clinical practice.     

相控线圈在上腹部磁共振检查中的作用

目的 选择合适的脉冲线圈以获得清晰的腹部磁共振图像。方法 14例病人采用体线圈和体部相控阵线圈分别进行腹部磁共振扫描，两种线圈 的扫描序列完全一致，比较两种线圈所获图像的质量。结果 用相控阵线圈采集的腹部磁共振图像的平均信噪比明显高于体线圈所获图像（P＜0．05）。结论 利用体部相控阵线圈可明显提高腹部磁共振图像的质量。     

Dynamic MR urography in urinary tract obstruction: implementation and preliminary results

Background Recent studies have demonstrated magnetic resonance (MR) capabilities in evaluating renal morphology and function in patients with urinary obstruction. The objective of this report is to support the introduction of dynamic MR renography on any MR equipment. Methods A custom-made device of vials filled with different concentrations of gadolinium was studied by combinations of T1-weighted gradient-echo sequences and coils. We compared the capabilities of two coils (phased array vs. standard body), the properties of dynamic sequences, and the effects of increasing concentrations of gadolinium on signal intensity. In a second section, we designed MR urography plug-ins of Image J (DICOM image software) for the analysis of dynamic studies. Results Optimized gradient-echo sequences acquired with a phased array body coil produced acceptable quality images with a linear relation between signal intensity and the lowest concentrations of gadolinium. In vitro measurements showed loss of linearity above 8 mmol/L. Conclusion Theoretical calculation and data from the literature suggest that the gadolinium dose to the patient should not exceed one-fourth of the usual one (0.025 mmol/kg). Postprocessing using Image J software and the specifically designed plug-ins was validated. The collection of plug-ins is now available on the Internet.     

Universal radio‐frequency receive‐coil connector: Concept and validation at 3 T

In most clinical magnetic resonance imaging systems, only commercial receive coils with the appropriate connector and encoding can be plugged in. When willing to use a dedicated receive coil for a specific study which cannot be achieved with commercial coils, the researcher faces the connecting issue related to the specificity of the proprietary connector. In this work, a universal device is proposed which allows for the connection of any single channel dedicated coil on any magnetic resonance (MR) system, as long as it is provided with at least one commercial receive coil. Technical feasibility of the universal connecting device was demonstrated on a 3 T MR clinical imager. The device included an independent active decoupling circuit while signal transmission to the data cabinet was achieved by electromagnetic coupling with a commercial receive coil plugged to the MR device. The universal connecting device was notably characterized in terms of signal‐to‐noise ratio (SNR) and compared to the standard connection. Image SNR was comparable using both means of connection. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 125–133, 2015     

Theoretical analysis of magnetic wall decoupling method for radiative antenna arrays in ultrahigh magnetic field MRI

Radiative antenna techniques, e.g., dipole and monopole, have been proposed for radiofrequency (RF) coil array designs in ultrahigh field MRI to obtain stronger B₁ field and higher signal‐to‐noise ratio (SNR) gain in the areas deep inside human head or body. It is known that element decoupling performance is crucial to SNR and parallel imaging ability of array coil and has been a challenging issue in radiative antenna array designs for MR imaging. Magnetic wall or induced current elimination (ICE) technique has proven to be a simple and effective way of achieving sufficient decoupling for radiative array coils experimentally. In this study, this decoupling technique for radiative coil array was analyzed theoretically and verified by a simulation study. The decoupling conditions were derived and obtained from the theory. By applying the predicated decoupling conditions, the isolation of two radiative elements could be improved from about ? 8 dB to better than ? 35 dB. The decoupling performance has also been validated by current distribution along the radiative elements and magnetic field profiles in a water phantom. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 183–190, 2015     

Advances in pediatric MR imaging

This article describes the considerable technical achievements that have been made in MR imaging in the evaluation of pediatric patients. The latest techniques in improving signal intensity, resolution, and speed are discussed. The multitude of new options for pediatric MR imaging are illustrated, including higher field strength imaging, multi-channel coil technology coupled with parallel imaging, and new pulse sequence designs. Several future directions in the field of pediatric body and musculoskeletal imaging also are highlighted.     

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.     

High-resolution magnetic resonance imaging of the anorectal region without an endocoil

Background: To evaluate the feasibility of a high-resolution magnetic resonance imaging (MRI) technique in detailed imaging of the anal sphincter and lower pelvic region without the use of an endoluminal coil. Methods: MRIs with an external phased array coil (T1- and T2-weighted turbo spin echo) were performed in 22 volunteers and 12 patients with an anal fistula, an anal sphincter defect, or a rectal tumor. The normal scans were evaluated by three independent observers. The scans of the patients were compared with surgical and/or histologic findings. Results: The anal sphincter was visualized with detail. In the anal canal, hemorrhoidal tissue and the submucosae ani muscle could be seen. The MRI technique also allowed detailed imaging of anatomical structures above the pelvic floor. The MR findings in the 12 patients showed exact correlation with surgery and/or histology. Conclusions: High-resolution MRI of the anorectal region without an endoluminal coil is feasible. The MR technique with an external phased array coil allows detailed imaging of the anal sphincter at rest, the rectum, and the surrounding pelvic structures with one single investigation. The results are promising and suggest useful applications in the management of anorectal diseases.     

Future horizons in MR imaging

In this article, we defined the major areas of active research in clinical MR imaging. Further increases in the number of parallel coils within an imaging array and in advances in parallel imaging pulse sequences and postprocessing will lead to further reductions in imaging time analogous to the impact of multidetector CT on helical CT. The synergism between parallel and high-field imaging will aid the development of high-field imaging. The combined dynamic and hepatic parenchymal enhancement of new contrast agents that have or may soon receive FDA approval will enable improved detection and characterization of liver lesions. The lymphotropic SPIO agents will remain an active area of clinical research to further assess their role in oncologic staging. Molecular imaging contrast research using magnetic particles and MR microscopy will continue to flourish. Screening examinations by MR imaging will re-main an area of research for the short- and intermediate term, with the final outcome dependent more on socioeconomic costs than the underlying capability of achieving high-quality screening studies.     

Simulation of B-scan images from two-dimensional transducer arrays: Part II--Comparisons between linear and two-dimensional phased arrays.

Two-dimensional (2-D) arrays have been proposed as a solution to the degradation in medical ultrasound image quality occurring as a result of asymmetric focusing properties of linear phased array transducers. The 2-D phased transducer array is also capable of electronically steering the symmetrically focused ultrasound beam throughout a three-dimensional volume. In a companion paper the potential of 2-D transducer arrays for medical imaging has been investigated using simulated B-scan images. In this paper, the advantages of 2-D over linear transducer arrays is demonstrated by simulating images of spherical cysts embedded in a large scattering volume. The large elevation beamwidth in the nearfield of a 5 MHz linear phased transducer array results in a severe reduction in the image contrast measured between a 4 mm diameter cyst and the surrounding scattering media. By employing a 2-D array with symmetric focusing, the contrast between the cyst and surrounding scatterers is significantly improved. The use of additional elements in the elevation direction of a linear array is also investigated. In this case the additional elements are included only to focus, but not to steer the ultrasound beam. Using the contrast characteristics of a 4 mm diameter cyst, it is shown that relatively few elevation elements are required to significantly improve the nearfield imaging capability of the linear array.     

Motion artifact control in body MR imaging.

The mechanisms involved in the generation of motion artifacts in MR imaging are complex and depend both on the type and direction of motion as well as on the parameters of the imaging sequence chosen. The methods used to control or reduce motion artifacts are multiple and the appropriate method for use with any given clinical situation will depend on the particular hardware and software of the MR imaging unit, the patient's clinical status, and the specific organ or disease state to be imaged. Some general guidelines for clinical use that are applicable in most scenarios can be defined, although preferences for the different techniques vary. Appropriate T1-weighted images of the upper abdomen and liver can be obtained with breath-hold T1-weighted gradient echo. These images should be acquired with inferior-superior spatial presaturation pulses to reduce vascular pulsation artifact and ghosting. The application of GMN will depend on the individual MR imaging system. If sufficient coverage cannot be obtained with gradient-echo imaging, then conventional T1-weighted images with phase-encoding reordering is suggested. The addition of spatial presaturation pulses (inferior-superior) may be valuable. The use of fat suppression will further improve image quality by reducing ghost artifact and improving CNR, although SNR will decrease. T2-weighted imaging of the upper abdomen will depend greatly on the hardware and software of the MR imaging unit. Recent techniques of breath-hold T2-weighted imaging require faster and stronger gradients, and may not be universally available. If available, these techniques provide excellent anatomic detail, although image contrast (e.g., liver to spleen) may decrease. Respiratory-triggered FSE techniques are the preferred method of imaging in most centers, because the imaging time is considerably less than conventional T2-weighted imaging whereas the image quality is improved. Liver lesion detection capability of the various techniques is still under study. The addition of fat suppression appears to improve image quality further with an increase in lesion detection. By understanding the principles underlying motion artifacts, one can choose the appropriate method of artifact control tailored for the individual clinical situation. In addition, the recognition of the variable appearances of motion artifacts will prevent interpretive errors and misdiagnoses. Careful attention to motion artifact reduction techniques can greatly improve patient care.     

临床型MR观察多发性硬化模型大鼠中枢神经系统

目的 探索临床型MR扫描仪配备临床应用型线圈进行多发性硬化(MS)模型大鼠脑和脊髓病灶成像研究的可行性.方法 选用髓鞘少突胶质细胞糖蛋白多肽35～55致敏Lewis大鼠制备MS模型动物10只.以1.5T MR扫描仪配用小肢端表面柔线圈,分别对大鼠脑和脊髓行T1WI和T2WI扫描,层厚1～2 mm;以3.0T MR扫描仪配用正交腕关节线圈,分别对大鼠脑和脊髓行T1WI、T2WI和Gd-DTPA增强T1WI三维容积扫描,体素0.06～0.08 mm3.利用工作站专业软件获得脑和脊髓多方向重组图像. 结果 3.0T MR T2WI和T1WI显示MS大鼠脑内病灶具有较高的空间分辨力和对比度,脊髓病灶的对比度较弱.1.5T MR设备显示大鼠MS病灶的空间分辨力较低.MS模型大鼠的中枢神经系统病灶分布在脑和脊髓,斑片状,呈T2高信号、T1低信号,Gd-DTPA增强后部分病灶强化.结论 临床型3.0T MR设备能清晰显示MS模型大鼠脑以及脊髓内部的病灶,为小动物中枢神经系统疾病的实验研究提供了一种能广泛应用的无创性手段.