共查询到20条相似文献,搜索用时 0 毫秒
1.
Purpose
To evaluate MRI artifacts at 3-Tesla for 38 commonly used cosmetics.Materials and Methods
Thirty-eight cosmetics (16, nail polishes; 5, eyeliners; 3, mascaras; 10, eye shadows; 1, lip gloss; 1, body lotion; 1, body glitter, and 1, hair loss concealer) underwent evaluation for MRI artifacts at 3-Tesla. The cosmetics were applied a copper-sulfate-filled, phantom and initially assessed using a “screening” gradient echo (GRE) pulse sequence. Of the 38 different cosmetics, 14 (37%) exhibited artifacts. For these 14 cosmetics, additional characterization of artifacts was performed using a GRE pulse sequence. A qualitative scale was applied to characterize the artifact size.Results
Artifacts were observed, as follows: 2, nail polishes; 5, eyeliners; 3, mascaras; 3, eye shadows; 1, hair loss concealer. Artifact size ranged from small (eye shadow) to very large (hair loss concealer) and tended to be associated with the presence of iron oxide or other metal-based ingredient.Conclusions
Commonly used cosmetics caused artifacts that may create issues if the area of interest is the same as where the cosmetic was applied or if its presence was unknown, thus, potentially causing it to be construed as pathology. Therefore, these findings have important implications for patients referred for MRI examinations. 相似文献2.
梯度回波序列是磁共振成像中常用的脉冲序列,然而梯度回波对主磁场波动非常敏感,呼吸等生理运动引起的信号波动会导致图像伪影.该文报道了采用导航回波技术获取呼吸运动导致的局部磁场波动,用以矫正图像回波中随时间变化的相位波动,并将该技术应用于三维多回波梯度回波成像和T2*定量图研究.研究结果显示:矫正前,相位波动幅度随回波时间增长而增大,模图和T2*定量图在相位编码方向有明显伪影,并且男女呼吸伪影水平有显著性差异;矫正后,相位波动幅度大幅下降,图像伪影水平有显著性下降. 相似文献
3.
Three-dimensional numerical simulations of the static magnetic field in the human head were carried out to assess the field inhomogeneity due to magnetic susceptibility differences at tissue interfaces. We used a finite difference method and magnetic permeability distributions obtained by segmentation of computed tomography images. Computations were carried out for four models, consisting of the head and the neck; the head, neck, and shoulders; the head, neck, and thorax; and the head tilted backwards, including the neck and the shoulders. Considerable magnetic field inhomogeneities were observed in the inferior frontal lobes and inferior temporal lobes, particularly near the sphenoid sinus and the temporal bones. Air/tissue interfaces at the shoulders were found to induce substantial magnetic field inhomogeneities in the occipital lobes and the cerebellum, whereas air/tissue interfaces in the lungs appeared to have less influence on the magnetic field in the brain. Tilting the head backwards could significantly reduce the field inhomogeneities superior to the planum sphenoidale as well as in the occipital lobes and the cerebellum. 相似文献
4.
Aljallad MH Yuan J Pilatou MC McDannold NJ Panych LP 《Magnetic resonance imaging》2011,29(9):1205-1214
Purpose
The purpose was to develop a new magnetic resonance imaging technique for fast temperature monitoring with extended volume coverage.Materials and Methods
The Multiple Resolutions Along Phase-Encode and Slice-Select Dimensions (MURPS) method was implemented in both a two-dimensional (2D) spoiled gradient echo (SPGR) sequence and a multishot echo-planar imaging (EPI) sequence. Both modified sequences were used to acquire image data from three slices with variable phase-encode resolution and slice thickness. In the SPGR sequence, a 2D resonant frequency pulse was also implemented to enable imaging within a reduced field of view, and this was used to monitor (at 1.5 T) the temperature changes in a live rabbit and in gel phantoms heated by focused ultrasound. A modified EPI sequence was tested during heating of a phantom undergoing motion.Results
The in vivo experiments demonstrated that temperature changes in unexpected locations away from the focal plane, such as near bone structures, could be detected due to the extra volume coverage afforded by the MURPS method. Temperature changes in a moving phantom were resolved using the MURPS EPI sequence with an acquisition rate of three slices every 300 ms.Conclusion
The MURPS method enables temperature monitoring over multiple slices without loss of temporal resolution compared with single-slice imaging and, if combined with multishot EPI, enables volume temperature monitoring in moving organs. 相似文献5.
6.
Dirk H.J. Poot Wouter Pintjens Marleen Verhoye Annemie Van Der Linden Jan Sijbers 《Magnetic resonance imaging》2010
Echo planar imaging (EPI) is an ultrafast magnetic resonance imaging (MRI) technique that allows one to acquire a 2D image in about 100 ms. Unfortunately, the standard EPI images suffer from substantial geometric distortions, mainly originating from susceptibility differences in adjacent tissues. To reduce EPI distortions, correction methods based on a field map, which is a map of the off-resonance frequencies, have been developed. In this work, a nonlinear least squares estimator is used to optimize the estimation of the field map of the B0 field. The model of the EPI and reference data includes parameters for the phase evolution, the complex magnitude, the relaxation of the MRI signal and the EPI-specific phase difference between odd and even echoes, and from these parameters, additional corrections might be computed. The reference data required to estimate the field map can be acquired with a modified EPI-sequence. The proposed method is tested on simulated as well as experimental data and proves to be significantly more robust against noise, compared to the previously suggested method. 相似文献
7.
P. Cantillon-Murphy L.L. Wald M. Zahn 《Journal of magnetism and magnetic materials》2010,322(6):727-733
In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ. As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad/s. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4 and 7 degree Centigrade above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B0. Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B0. Results are presented for the expected temperature increase in small tumors (approximately 1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002-0.01 solid volume fraction) and nanoparticle radii (1-10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful selection of the rotating or sinusoidal field parameters (field frequency and amplitude). The work indicates that it may be feasible to combine low-field MRI with a magnetic hyperthermia system using superparamagnetic iron oxide nanoparticles. 相似文献
8.
Weiland JD Faraji B Greenberg RJ Humayun MS Shellock FG 《Magnetic resonance imaging》2012,30(3):382-389
Objective
The objective was to evaluate magnetic resonance imaging (MRI) issues (magnetic field interactions, heating, artifacts and functional alterations) at 1.5 T and 3 T for the Argus II Retinal Prosthesis (Second Sight Medical Products, Sylmar, CA, USA).Materials and Methods
Standardized protocols were used to assess magnetic field interactions (translational attraction and torque; 3 T, worst case), MRI-related heating (1.5 and 3 T), artifacts (3 T; worst case) and functional changes (1.5 and 3 T) associated with MRI.Results
The magnetic field interactions were acceptable. MRI-related heating, which was studied at a relatively high, MR system-reported whole body averaged specific absorption rates, will not pose a hazard to the patient under the conditions used for testing. While artifacts were “moderate” in relation to the dimensions of the Argus II Retinal Prosthesis, optimization of MRI parameters can reduce the size of the artifacts. Exposures to MRI conditions at 1.5 and 3 T did not damage or alter the functional aspects of the Argus II Retinal Prosthesis.Conclusions
In consideration of the test results, a patient with the Argus II Retinal Prosthesis may undergo MRI at 1.5 T or 3 T when specific guidelines and MRI conditions are followed, including those advised by the manufacturer. 相似文献9.
Eleftherios Lavdas Panayiotis Mavroidis Spiros Kostopoulos Dimitrios Glotsos Violeta Roka Theofilos Topalzikis Athanasios Bakas Georgia Oikonomou Nikos Papanikolaou Georgios Batsikas Ioannis Kaffes Dimitrios Kechagias 《Magnetic resonance imaging》2013
The purpose of this study is to compare two types of sequences in brain magnetic resonance (MR) examinations of uncooperative and cooperative patients. For each group of patients, the pairs of sequences that were compared were two T2-weighted (T2-W) fluid attenuated inversion recovery sequences with different k-space trajectories (conventional Cartesian and BLADE) and two T2-TSE weighted with different k-space trajectories (conventional Cartesian and BLADE). Twenty-three consecutive uncooperative patients and 44 cooperative patients, who routinely underwent brain MR imaging examination, participated in the study. Both qualitative and quantitative analyses were performed based on the signal-to-noise ratio, contrast-to-noise ratio (CNR), and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of motion, other (e.g., Gibbs, susceptibility artifacts, phase encoding from vessels) artifacts and pulsatile flow artifacts was evaluated. 相似文献
10.
Ibrahim SharifiH. Shokrollahi S. Amiri 《Journal of magnetism and magnetic materials》2012,324(6):903-915
Magnetic ferrofluids (magnetic nanofluids) have received special attention due to their various biomedical applications such as drug delivery and hyperthermia treatment for cancer. The biological applications impose some special requirements. For example, the well-known iron oxide ferrofluids become undesirable because their iron atoms are poorly distinguishable from those of hemoglobin. A conceivable solution is to use mixed-ferrites (MFe2O4 where M=Co, Mn, Ni, Zn) to have a range of magnetic properties. These ferrites have attracted special attention because they save time, and because of their low inherent toxicity, ease of synthesis, physical and chemical stabilities and suitable magnetic properties. Based on the importance of ferrite particles in ferrofluids for hyperthermia treatment, this paper gives a summary on the physical concepts of ferrofluids, hyperthermia principal, magnetic properties and synthesis methods of nanosized ferrites. 相似文献
11.
12.
射频场映像是通过一定算法对磁共振射频线圈的发射场进行重建的方法.高场下的射频场经过生物组织时会发生明显变化,在其基础上可以反演生物组织体内电特性,进而对癌症等疾病进行早期诊断,是对生物组织的磁共振结构成像的有力补充.目前为止,射频场映像和电特性研究都以高场鸟笼线圈为主,对低场下的相控阵研究较少.本文主要研究了低场永磁体磁共振射频场的均匀度.有限元仿真和实验验证了在17.8 MHz激励下,射频场在空载和负载下均匀度均发生较大变化.射频场均匀度在负载下的改变在一定程度上可以反映负载生物组织的电特性,对磁共振电特性实用化研究提供了一定的参考价值. 相似文献
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14.
The purpose of this study was to demonstrate and evaluate the performance of real-time color-flow MRI at 3 T using variable-density spiral (VDS) phase contrast. Spiral phase contrast imaging was implemented within a flexible real-time interactive MRI system that provided continuous image reconstruction and an intuitive user interface. The pulse sequence consisted of a spectral-spatial excitation, bipolar gradient, spiral readout and gradient spoiler. VDSs were utilized to increase spatial and/or temporal resolution relative to uniform-density spirals (UDSs). Parameter choices were guided by specific applications. Sliding window reconstruction was used to achieve a maximum display rate of 40 frames/s. No breath-holding or gating was used. Our results demonstrated that real-time color-flow movies using UDS and VDS provided adequate visualization of intracardiac flow, carotid flow and proximal coronary flow in healthy volunteers. Average aortic outflow velocity measured at the aortic valve plane using VDS was 29.4% higher than that using UDS. Peak velocity measured in the common carotid artery using VDS was 9.8% higher than that using UDS. 相似文献
15.
Monrudee LiangruksaRanjan Ganguly Ishwar K. Puri 《Journal of magnetism and magnetic materials》2011,323(6):708-716
Magnetic fluid hyperthermia (MFH) is a cancer treatment that can selectively elevate the tumor temperature without significantly damaging the surrounding healthy tissue. Optimal MFH design requires a fundamental parametric investigation of the heating of soft materials by magnetic fluids. We model the problem of a spherical tumor and its surrounding healthy tissue that are heated by exciting a homogeneous dispersion of magnetic nanoparticles infused only into the tumor with an external AC magnetic field. The key dimensionless parameters influencing thermotherapy are the Péclet, Fourier, and Joule numbers. Analytical solutions for transient and steady hyperthermia provide correlations between these parameters and the portions of tumor and healthy tissue that are subjected to a threshold temperature beyond which they are damaged. Increasing the ratio of the Fourier and Joule numbers also increases the tumor temperature, but doing so can damage the healthy tissue. Higher magnetic heating is required for larger Péclet numbers due to the larger convection heat loss that occurs through blood perfusion. A comparison of the model predictions with previous experimental data for MFH applied to rabbit tumors shows good agreement. The optimal MFH conditions are identified based on two indices, the fraction IT of the tumor volume in which the local temperature is above a threshold temperature and the ratio IN of the damaged normal tissue volume to the tumor tissue volume that also lies above it. The spatial variation in the nanoparticle concentration is also considered. A Gaussian distribution provides efficacy while minimizing the possibility of generating a tumor hot spot. Varying the thermal properties of tumor and normal tissue alters ITand IN but the nature of the temperature distribution remains unchanged. 相似文献
16.
A magnetite ferrofluid coated by dextran with a high specific absorption rate (SAR) of 75 W/g in an AC field of 55 kHz and 200 Oe was prepared by the gel crystallization method with ultrasonic treatment. For comparison, uncoated magnetite particles with a mean diameter of 50 nm were also fabricated. Several possible mechanisms such as Brownian, Neel and diffusion relaxation processes on heating effects and their influence on SAR are discussed. Several factors which can increase the value of SAR were discussed, including dextran coating, ultrasonic treatment, proper particle size and the presence of defects and disorder in the particles. 相似文献
17.
Dextran‐Coated Antiferromagnetic MnO Nanoparticles for a T1‐MRI Contrast Agent with High Colloidal Stability 下载免费PDF全文
Herbert R. Neves Rafael A. Bini Jeam H. O. Barbosa Carlos E. G. Salmon Laudemir C. Varanda 《Particle & Particle Systems Characterization》2016,33(3):167-176
A simple approach to synthesize carboxymethyl dextran‐coated MnO nanoparticles (CMDex‐MnONPs) with high colloidal stability in physiological saline solutions is described here for potential applications as a magnetic resonance imaging (MRI) T1 contrast agent. The thermal decomposition methodology is used to produce uniform MnONPs with an average size of around 20 nm, and its hydrophobic surface is modified with CMDex molecules, conferring hydrophilic properties. After CMDex coating, the nanoparticle presents high colloidal stability in concentrations ranging from 10 to 50 μg mL?1, average hydrodynamic size (Z‐average) of 130 nm, polydispersity degree of ≈12%, and negative surface charge in both simulated body fluid solutions and pure water with zeta‐potential of –20 and –40 mV, respectively. The CMDex‐MnONPs with 20 nm show antiferromagnetic behavior at room temperature, and the magnetic properties are found to be strongly dependent of the nanoparticle size, increasing the contribution of the ferromagnetic Mn3O4 phase with decreasing size for nanoparticles about 3 nm. Cytotoxicity evaluation in cancerous and noncancerous cells in the range of 5.0–50.0 μg mL?1 shows low toxicity for cancerous cells and lack of the same for healthy cells lines. Related to the magnetic properties, CMDex‐MnONP presents significant r1 relaxivity and low r2/r1 relaxivity ratio. The results suggest that these nanoparticles display characteristics for potential applications as an MRI T1 contrast agent. 相似文献
18.
Alsayed A.M. Elsherbini Mahmoud Saber Mohamed AggagAhmed El-Shahawy Hesham A.A. Shokier 《Magnetic resonance imaging》2011,29(2):272-280
Super paramagnetic iron oxide Fe3O4 nanoparticles prepared via photochemical reaction in pure form were used for inducing hyperthermia to treat subcutaneous Ehrlich carcinoma implanted in female mice. Our results indicate that the mean temperature profiles at the rectum, periphery of the tumor surface and at the center of the tumor during hyperthermia treatment increased gradually. The maximum temperature achieved in the tumor center was 47±1°C after 20 min with radiofrequency exposures at 25 kW. The acquired magnetic resonance images identified apoptotic cells in the center of the tumor which were exposed to magnetic resonance hyperthermia (MRH). Apoptotic cells presented as dark signal intensity in the T1-weighted images which were further confirmed by pathological examinations. Also, the results revealed that the tumor size in the all mice exposed to MRH is still as the same as before the treatment, but the rate of tumor growth was very slow by comparing with the growth rate of the control group. 相似文献
19.
Hassan Hejase Saleh S. Hayek Shahnaz Qadri Yousef Haik 《Journal of magnetism and magnetic materials》2012
Manganese zinc iron magnetic nanoparticles were synthesized by a co-precipitation method for application as hyperthermia inducing agents. The structure, morphology and magnetic properties of the nanoparticles are characterized using scanning electron microscopy, X-ray diffraction, and a superconducting quantum interference device. The magnetic properties being investigated include Curie temperature, saturation magnetization, remnant magnetization, coercive field, and hysteresis. The study showed that adjusting the Mn contribution to the particles contributed to the adjustment of all magnetic properties of the complex. 相似文献
20.
A simple method for obtaining images whose contrast depends only on T2 is described and tested both on phantoms and in vivo. The method works reliably and effectively under clinically realistic operating conditions using standard imaging protocols. It can result in a substantial reduction in imaging times for T2 weighted images. 相似文献