316L医用不锈钢材料加载低浓度三氯生抑菌效果评价

目的评价三氯生药物在体外低浓度下对胆道常见感染细菌大肠杆菌和粪肠球菌的抑菌效果,并了解胆汁浸泡下三氯生涂层后对胆道支架材料表面细菌黏附及蛋白吸附的影响。方法抑菌环法检测三氯生在低浓度下抑菌效果,并与左氧氟沙星相比较,评价联合紫杉醇后三氯生抑菌效果;通过免疫荧光标定及电镜扫描比较一定细菌浓度的人胆汁浸泡下,316L医用不锈钢裸材料及表面涂层三氯生与聚乳酸-羟基乙酸共聚物(poly-lactic-co-glycolic acid,PLGA)药物后细菌黏附和层黏连蛋白吸附情况。结果三氯生在1、0.5、0.25、0.125、0.0625、0.03125mg/ml浓度下均有明显的抑菌效果,并且优于相同浓度下的左氧氟沙星(P<0.005),但联合紫杉醇后,其抑菌效果明显降低(P<0.005);在胆汁浸泡环境下,三氯生药物涂层组表面吸附的细菌量及吸附的层黏连蛋白均明显少于裸材料组,两者均有显著性差异(P<0.05)。结论 316医用不锈钢加载低浓度三氯生能良好抑制胆道细菌的生长,适用于胆道感染性疾病。     

Characterization of and correction for artifacts in linogram MRI

Chemical shift differences, field inhomogeneity, and gradient nonlinearity result in artifacts in magnetic resonance imaging. Three artifacts are characterized for linogram imaging and it is shown that, based on computer simulations and theory, linogram MRI behaves similarly to 2DFT. A correction technique similar to a scheme for 2DFT imaging based on the Dixon technique and coordinate transform methods is proposed. The algorithm is applied to correct for field inhomogeneity and gradient nonlinearity-induced artifacts in both simulations and images of a clinical phantom. The results show good correlation with the theory. It is concluded that linogram imaging offers certain attractive features of both 2DFT and PR imaging techniques, and is a potentially viable alternative to PR imaging in the presence of field inhomogeneity.     

The diminishing variance algorithm for real-time reduction of motion artifacts in MRI

A technique has been developed whereby motion can be detected in real time during the acquisition of data. This enables the implementation of several algorithms to reduce or eliminate motion effects from an image as it is being acquired. One such algorithm previously described is the acceptance/rejection method. This paper deals with another real-time algorithm called the diminishing variance algorithm (DVA). With this method, a complete set of preliminary data is acquired along with information about the relative motion position of each frame of data. After all the preliminary data are acquired, the position information is used to determine which data frames are most corrupted by motion. Frames of data are then reacquired, starting with the most corrupted one. The position information is continually updated in an iterative process; therefore, each subsequent reacquisition is always done on the worst frame of data. The algorithm has been implemented on several different types of sequences. Preliminary in vivo studies indicate that motion artifacts are dramatically reduced.     

The effect of 3 T MRI on microleakage of amalgam restorations

Objectives:

To evaluate the effects of 3 T magnetic field on microleakage of amalgam restorations containing three different types of silver (Ag).

Methods:

60 extracted teeth were restored with three different types of amalgam filling materials. Restored teeth were sectioned mesiodistally and divided into experimental and control groups. Experimental groups were exposed to a magnetic field of 3 T for 20 min. All samples were plunged into 2% basic fuchsin solution and examined under a digital microscope by three different observers with regard to microleakage.

Results:

Statistical analysis showed significant differences in microleakage between the groups exposed to MRI and controls, whereas differences in microleakage between amalgam types were insignificant.

Conclusions:

The primary risk of MRI systems arises from the effects of its strong magnetic field on objects containing ferromagnetic materials. An MRI of 1.5 T is known to be safe for amalgam restorations. However, our research indicates that MRI is not completely devoid of any effects on amalgam restorations.     

The effect of quality control on the function of magnetic resonance imaging (MRI), using American College of Radiology (ACR) phantom

Objective

To study image quality of MRI scanner using the American College of Radiology (ACR) phantom.

The effect of magnetization transfer on functional MRI signals

A magnetization transfer (MT)-prepared echo-planar imaging (EPI) pulse sequence was developed to study motor cortex activation, using a finger tapping paradigm. MT weighting resulted in a reduction of both the activated area and, in the majority of activated pixels, the functional MRI signal, regardless of the correlation coefficient threshold used in generating the activation map. The magnetization transfer ratio (MTR) was higher during task activation than during rest. Because the MT effect is strongly tissue-dependent, these results support the hypothesis that incorporation of MT into functional MRI will help to understand the origin of the functional MRI signal.     

Quantitative determination of magnetic force on a coronary stent in MRI

Purpose:

To introduce an analytical method for a quantitative determination of magnetic force on a coronary stent in the magnetic resonance imaging (MRI) magnet that is generally applicable to metallic implants. Magnetic forces on metallic implants in the MRI magnets are traditionally determined empirically by measuring deflection from the vertical plane at the central axis of the magnet and at the point of the largest force along the longitudinal axis of the magnet.

Materials and Methods:

Magnetic and chemical characterization of the stents was performed by a commercial magnetometer and energy‐dispersive X‐ray spectroscopy. Magnetic force on the stents fabricated of paramagnetic alloys (surgical stainless steel and cobalt–chromium) was determined by measuring the stent's magnetic dipole moment and employing the on‐axis magnetic field profile of an MRI magnet.

Results:

The maximum force on the stainless steel stent was found to be F_S,max = 0.18 mN, whereas on the cobalt–chromium stent it was F_C,max = 0.06 mN.

Conclusion:

The magnetic force on the investigated paramagnetic stents is even smaller than the gravitational force acting on the stents in the Earth's gravity field, so that it has no physiological impact on the stented vessels. J. Magn. Reson. Imaging 2013;37:391–397. © 2012 Wiley Periodicals, Inc.     

MRI diagnosis of brown tumor based on magnetic susceptibility

A 56-year-old male with chronic renal failure was incidentally found to have lytic bone lesions in the pubic symphysis, left femoral head, left acetabulum, left iliac bone, and L1 vertebra on computed tomography (CT). Subsequent magnetic resonance imaging (MRI) of the abdomen was performed (for evaluation of a renal lesion) which demonstrated marked loss of signal intensity in the L1 bone lesion on increasing TE gradient echo images, consistent with magnetic susceptibility effect due to hemosiderin. Brown tumor was confirmed at biopsy. The susceptibility imaging probes one particular histological characteristic of tissues and allows a restricted differential of lytic tumors that contain significant hemosiderin, including brown tumor.     

Cancellation of metal-induced MRI artifacts with dual-component paramagnetic and diamagnetic material: Mathematical modelization and experimental verification

A mathematical model of dual-component paramagnetic and diamagnetic material to cancel metal-induced MRI artifacts was developed and verified experimentally. The magnetization produced by metallic material and then the gradient linearity distortion can be cancelled by using such materials with opposing paramagnetic and diamagnetic properties. This concept of dual-component materials provides a novel solution to the problem of MRI artifacts.     

High magnetic susceptibility coatings for visualisation of optical fibres on a specialised interventional MRI system

The aim of this study was to develop methods of visualising optical fibres on MRI scans for monitoring interstitial laser therapy. Scans were performed on a specialised MRI extremity scanner at 0.17 T. Optical fibres of 0.4 mm diameter used for delivering laser energy were coated with iron particles from a superferromagnetic contrast agent. MR images of the fibres were acquired using gradient echo sequences (TR/TE = 300/10, 1 mm in-plane, 3 mm slice) and assessed for fibre visibility. Coated fibres could be resolved as lines 2 ± 1 mm wide using the gradient echo sequence. Uncoated fibres were invisible on the sequences used for in vivo therapy monitoring due to partial volume averaging. It is concluded that optical fibre visualisation by MRI may be improved by coating with ferromagnetic particles. Biocompatibility requires further assessment, but direct coating appears to be a promising method for fibre visualisation in MR-guided laser therapy.     

The role of magnetic resonance imaging (MRI) in assessment of ACL graft failure

Objective

The aim of this work is to assess the role of MRI in the diagnosis of ACL graft failure and detection of complications that may follow ACL reconstruction.

On the nature and reduction of plaque-mimicking flow artifacts in black blood MRI of the carotid bifurcation

Cardiac-gated black blood MRI of the carotid artery bifurcation in normal human subjects shows signal within the lumen suggesting wall thickening or atherosclerotic plaque. This signal was believed to be artifactual, arising from complex flow patterns present at the carotid bifurcation. Computer simulation of the hemodynamics and black blood multislice image acquisition in a model of the carotid bifurcation showed that these artifacts arise from spins recovering their signal within the slow, recirculating flow of the carotid bulb. The computed hemodynamics also suggested that these artifacts could be minimized or eliminated entirely by gating the acquisition of slices in the most artifact-prone region of the carotid bulb within a 250-ms window after peak systole. Application of these predictions to studies of normal volunteers showed that, in most cases, these flow artifacts in black blood MRI can be eliminated simply by altering the phase of the cardiac cycle to which the image acquisition is gated. The observation that the size and placement of the saturation slabs had little effect on these artifacts suggested that, in those cases in which recirculation persists throughout the cardiac cycle, either inversion-recovery or presaturation within the bulb itself would be required to suppress them.     

MRI评分对星形细胞瘤病理分级的相关性研究

目的：本文分析了42例经病理证实的幕上星形细胞瘤MRI表现，用MRI评分对肿瘤特征的一致性进行了研究。材料和方法：包括16例低级星形细胞瘤，13例分化不良性星形细胞瘤，13例多形性星形胶质母细胞瘤。所有病例检查均采用GEVectra0．5T超导型MR成像机。分别采用9个标准进行MRI评分：（1）信号不均匀性；（2）囊变与坏死；（3）出血；（4）穿越中线；（5）水肿与占位效应；（6）边缘界限；（7）流空效应；（8）增强程度；（9）增强形态。Gd－DTPA增强用T1WI。结果：每一个评分标准分别经统计学分析。MRI均值：低级星形细胞瘤为0．49±0．20，分化不良性星形细胞瘤为1．2±0．17，多形性胶质母细胞瘤为1．47±0．34。随着病理级别的增加，MRI评分亦随之增加（P＜0．01－0．001）。增强程度、信号不均匀性、水肿与占位效应、囊变与坏死和增强形态已被证明与病理级别良恶性程度密切相关。经多元线性偏回归分析P＜0．001。结论：MR影像学分级可为临床选择治疗方法提供重要依据。     

Parallel acquisition techniques in cardiac cine magnetic resonance imaging using TrueFISP sequences: comparison of image quality and artifacts

PURPOSE: To compare image quality, artifacts, and signal-to-noise ratio (SNR) in cardiac cine TrueFISP magnetic resonance imaging (MRI) with and without parallel acquisition techniques (PAT). MATERIALS AND METHODS: MRI was performed in 16 subjects with a TrueFISP sequence (1.5 T; Magnetom Sonata, Siemens): TR, 3.0 msec; TE, 1.5 msec; flip angle (FA), 60 degrees. Three axes were scanned without PAT (no PAT) and using the generalized autocalibrating partially parallel acquisition (GRAPPA) and modified sensitivity encoding (mSENSE) reconstruction algorithms with an autocalibration mode to reduce scan time. A conventional spine array and a body flex array were used. Artifacts, image noise, and overall image quality were classified on a 4-point scale by an observer blinded to the implemented technique; for quantitative comparison, SNR was measured. RESULTS: With a PAT factor of two, acquisition time could be reduced by 39%. No PAT did not show artifacts, and GRAPPA revealed fewer artifacts than mSENSE. PAT provided inferior-quality scores concerning image noise and overall image quality. In quantitative measurements, GRAPPA and mSENSE (20.1 +/- 6.2 and 15.6 +/- 6.2, respectively) yielded lower SNR than no PAT (30.6 +/- 20.1; P < 0.05) and P < 0.001). CONCLUSION: Time savings in PAT are accompanied by artifacts and an increase in image noise. The GRAPPA algorithm was superior to mSENSE concerning image quality, noise, and SNR.     

Evaluation of quantitative magnetic resonance imaging, biochemical and mechanical properties of trypsin-treated intervertebral discs under physiological compression loading

PURPOSE: To investigate the influence of targeted trypsin digestion and 16 hours compression loading on MR parameters and the mechanical and biochemical properties of bovine disc segments. MATERIALS AND METHODS: Twenty-two 3-disc bovine coccygeal segments underwent compression loading for 16 hours after the nucleus pulposus (NP) of each disc was injected with a solution of trypsin or buffer. The properties of the NP and annulus fibrosus (AF) tissues of each disc were analyzed by quantitative MRI, biochemical tests, and confined compression tests. RESULTS: Loading had a significant effect on the MR properties (T(1), T(2), T(1rho), MTR, ADC) of both the NP and AF tissues. Loading had a greater effect on the MR parameters and biochemical composition of the NP than trypsin. In contrast, trypsin had a larger effect on the mechanical properties. Our data also indicated that localized trypsin injection predominantly affected the NP. T(1rho) was sensitive to loading and correlated with the water content of the NP and AF but not with their proteoglycan content. CONCLUSION: Our studies indicate that physiological loading is an important parameter to consider and that T(1rho) contributes new information in efforts to develop quantitative MRI as a noninvasive diagnostic tool to detect changes in early disc degeneration.     

Evaluation of the anatomical and functional properties of deglutition with various kinetic high-speed MRI sequences

We evaluated various fast MR sequences for obtaining anatomical and dynamic functional information during deglutition. Seven healthy volunteers underwent MRI of the oropharynx during swallowing of an oral positive-contrast agent. Single-slice imaging was performed in the median sagittal plane while subjects were in a supine position. Twenty serial images were obtained using EPI, FLASH, and turbo-FLASH sequences. The dynamic (movement-related) information and the anatomical resolution of the soft tissues were evaluated during deglutition. The FLASH sequence provided high-quality images at rest. During swallowing, however, the images were significantly degraded by movement artifacts and had inferior temporal resolution. The EPI evidenced better temporal resolution, but was degraded by strong distortions and movement artifacts. The turbo-FLASH sequence provided the best temporal resolution and sufficient spatial resolution during motion. This sequence proved optimal for the investigation of swallowing function, and is expected to be of value for the documentation of functional disturbances in patients with oropharyngeal pathology.