Although shown as rectangles, the gradient waveforms are actually trape. The proposed tiny golden angle radial sparse parallel mri method strongly reduces eddy current related artifacts for both applications. Travis b smith ming hsieh department of electrical engineering university of southern california 3740 mcclintock avenue. Although this distortion is negligible in most echo. Eddy current effects can severely degrade image quality when using balanced steadystate free precession imaging with rapidly varying phase encode ordering schemes, which have common use in cardiac cine mri. Reduction of eddycurrentinduced distortion in diffusion. The parts of the body outside the fov in this case, the arms will be exposed to certain magnetic field gradients. Artifacts in magnetic resonance imaging from metals. The presence of eddy currents was assessed for these. The authors have observed such artifacts caused by eddy currents generated in the conducting frame of the device by the radiofrequency excitation field. Maximizing rf efficiency and minimizing eddy current. Elimination of eddy current artifacts in diffusion. Therefore, the main goal of this work is to correct phase errors induced by eddy currents in radial mri. Characterization of and correction for eddy current artifacts in echo.
Eddy currents can cause artifacts in images and may seriously degrade overall magnet performance. Considering these artifacts appear substantial in cartgr and random pe scans, they are most likely caused by the zero order spatially independent ec field. Evaluating the performances of these cor rection strategies is a challenging task for eddy. Eddy current artifacts varying magnetic field from gradients can induce electrical currents in conductors such as the cryostat causing distortion of the gradient waveforms.
Throughslice dephasing is highly effective in suppressing eddy current induced artifacts in bssfp imaging. Correction of b 0 eddy current effects in spiral mri. A method for reducing eddy current artifacts of a magnetic resonance imaging mri system having a main magnet that generates a substantially uniform magnetic field to image a subject placed therein, the method comprising. The 4um double layer particularly patterned shielding images e was highly effective in almost negating all of the eddy current artifacts and maintaining the rfcoil rf characteristics as shown in fig. Correction of b0 eddy current effects in spiral mri. Eddy currents are a common source of artifacts in spiral mri.
System and method to correct eddy current artifacts in. Elimination of eddy current artifacts in diffusionweighted echoplanar images. Secondorder eddycurrent correction is beneficial even for bipolar sequence. The eddy current distortion in the multiband diffusion images arxiv. Multi physics modeling of eddy current vibration damping in mri systems kishore venkata mogatadakala 1, ming yao, sampath telikicherla kandala, longzhi jiang, and timothy havens1 1magnet and gradient engineering, ge health care, florence, sc, united states introduction.
Eddy current artifact is due to eddy currents generated by magnetic field. Chapter 26 sequence design, artifacts and nomenclature yongquan ye, ph. Characterization and correction of eddycurrent artifacts in unipolar. A new eddycurrent compensation method in mri piers. Image guidance common uses to reduce the influence of eddy currents on gradient fields are eddy current compensation and shielded gradient coils active or passive. Optimization of diffusion mri processing pipelines is still an active area of research, with novel strategies for artifact removal, denoising, and distortion correction still being proposed. In diffusion tensor imaging dti, spatial and temporal variations of the static magnetic field b 0 caused by susceptibility effects and timevarying eddy currents result in severe distortions, blurring, and misregistration artifacts, which in turn lead to errors in dti metrics and in fiber tractography. Mri artifacts magnetic resonance imaging medical imaging. Optimization of diffusionweighted singlerefocused spin. Some artifacts affect the quality of the mri exam while others do not affect the diagnostic quality but may be confused with pathology when encountering an unfamiliar artifact, it is useful to systematically examine general features of the artifact to try and understand its general class.
One arm will receive a magnetic field that will generate a frequency higher than f max for the fov. Eddy current compenstation to regain the ideal gradientwaveform, an mr systemcompensates for the distortion in the gradient field causedby the eddy currents. Eddy currents may also be induced in some metal objects. Aapm summer school 2001 troubleshooting the acr mri. Pdf throughslice dephasing for eddy current artifact. Mri artifacts and correction strategies open access journals. Reduction of eddycurrentinduced distortion in diffusion mri using a twicerefocused spin echo. Artifacts and pitfalls in diffusion mri meteore service. Artifacts caused by eddy current in diffusion mri semantic scholar. The physics of mri are complicated and much harder to understand than those underpinning image generation in plain radiography, ct or ultrasound what follows is a very abbreviated, broad strokes description of the process.
This work explains in detail the artifacts in projection reconstruction pr imaging arising from eddy currents and describes an effective eddy current compensation based on. Chapter 26 sequence design, artifacts and nomenclature. However, the spatially uniform but timevarying b0 eddy currents can also be a subtle but important source of artifacts in spiral images. Any mri sequence is more or less prone to motion artifacts, but diffusion mri is extremely sensitive to motion. In particular, we show and explain how increasing the length of a ti rod can decrease the mri artifact a similar e. Any information contained in this pdf file is automatically generated from digital.
Mri artifacts are numerous and give an insight into the physics behind each sequence. While several methods have been proposed to correct the effect of linear eddycurrent in radial mri3,4, b0 eddy currents have usually been neglected. Data of the proposed method showed a marked increase in snr. Characterization of and correction for eddy current artifacts in echo planar diffusion imaging. Artifacts not only increase the variability of diffusion mri measures but also, most importantly, introduce bias, resulting in. Implanted device industry perspective ross venook, ph. Glassy carbon microelectrodes minimize induced voltages. Characterization of and correction for eddy current. It may be possible to control the eddy current artifact by. Wav eform of a gradient field that has been modified using grafidy to compensate for eddy currents.
Review and evaluate the possible issues that can affect the accuracy of measurements regarding dynamic susceptibility contrast dscmri measurements of cerebral blood. Electrical currents running in the superstructure of the mri can counteract the. Eddycurrentinduced artifacts caused by an mrcompatible. The eddy current artifact can be corrected using a software tool provided that the snr is good enough or a set of specially designed diffusion gradients. Comparison of eddycurrent corrected images with affine image registration shows that eddycurrent correction with phases from the field camera performs better than image registration. Diffusionweighted imaging dwi and diffusiontensor imaging dti are noninvasive mri techniques with broad clinical applications. If persistent, it must be addressed by a service representative to verify the magnet performance. Highresolution diffusion imaging using a radial turbo. Artifacts caused by eddy current in diffusion mri xi tan abstract magnetic resonance diffusion imaging is potentially an important tool for the noninvasive characterization of normal and pathological tissue. Parker small gradient fields resulting from incompletely canceled eddy currents can cause geometric distortion in echoplanar images. Dynamic correction of artifacts due to susceptibility. Diffusion mri usually suffers from the susceptibility artifact and eddy current artifact.
Balcoma a unb mri centre, department of physics, university of new brunswick, fredericton, new brunswick, e3b. Particularly a problem with echoplanar imaging that uses strong, rapidly changing gradients. Magnetic resonance diffusion imaging is potentially an important tool for the noninvasive. There has been less attention paid to mri artifacts caused by eddy currents, but such effects have been observed 5,6. Vibration of mri systems induces eddy currents in surrounding materials including thermal shield, helium vessel, etc. What is an artifact an image artifact is a structure not normally present. But visible as a result of a limitation or malfunction in the hardware or software in the mri device. Mri artifacts and correction strategies open access journal. Artifacts from susceptibility can be controlled by reducing the objects susceptibility. Shielded gradients active shielding coils between gradient coils and maingradients. This study illustrates the importance of addressing these artifacts and presents a system response. Some affect the quality of the mri exam while others do not affect the diagnostic quality but may be confused with pathology. Mr image artifacts 16jul2015 venook aapm mri safety 19.
Localized eddy current compensation using quantitative. The gradient is going to keep going because we still have magnetic fields outside the space designated by the fov. Fast switching of diffusionencoding gradients induces eddy currents in conducting components the shifts are directiondependent, i. Reduction of eddy current induced distortion in diffusion mri using a twicerefocused spin echo t. The severity of the artifact depends on the orientation of the device in the mr unit and can be effectively eliminated by disrupting the electrical continuity of the supporting frame of the. Zebra artifacts eddy current artifacts varying magnetic field from gradients can induce electrical currents in conductors such as the cryostat causing distortion of the gradient waveforms. Aapm summer school 2001 troubleshooting the acr mri accreditation phantom tests p. The following qualitative scale was applied to the eddy current assessm ent. Other sequences that may be most affected by eddycurrents include diffusionweighted imaging, mr spectroscopy, mr angiography, balanced gradient echo sequences, and any sequence with a very short te. However, eddy currents and pulsatile brain motion cause severe artifacts when strong diffusion weighting is applied. In this work, we explore and characterize a previouslyproposed technique, throughslice dephasing, as the sole technique for eddy current.
Flow and gradient switching induced eddy currents are important sources of such phase errors, especially under offresonant condition. Changes proposed for the dwsrse sequence and for the parameter setting of the postprocessing ecc algorithm considerably reduced eddycurrent artifacts and provided a higher snr. Eddy currents that effect the kspace trajectory are often the focus of eddy current correction. Motion artifacts the second major source of artifacts, which is still related to the use of strong gradient pulses, is patient motion. Essentially, the process can be broken down into four parts. The importance of the objects geometry on the extent of the susceptibilityinduced artifact is also demonstrated. It is shown that by using the eddy current correction scheme outlined, the eddy current. In the presence of higherorder eddycurrent distortions, it was expected that affine image registration would leave residual misalignment artifacts. Characterization and correction of eddycurrent artifacts. Request pdf correction of b 0 eddy current effects in spiral mri purpose b0 eddy currents are a subtle but important source of artifacts in spiral mri. Grafidy is the tool used to calibratethe compensation values. Review the artifacts and pitfalls of diffusion mri on a qualitative basis, especially in terms of eddy currents and sensitivity to motion. Diffusion imaging is particularly prone to eddycurrent artifacts due to.
However, the phantom images were shifted by half of the slice due to the eddy current. These eddy currents are problematic for the imaging portion of the sequence that follows, especially for epirelated sequences. Pdf on may 26, 2016, michael hoff and others published artifacts in magnetic. In addition, there is a significant improvement in the quality of the resulting diffusion tensor maps. In smallbore highfield mri systems, the artifacts caused b0 eddy currents become more severe. Multi physics modeling of eddy current vibration damping. Various correction methods have been proposed, but typically assume that the eddy. Coronary magnetic resonance angiography mra acquired using steadystate free precession ssfp sequences tend to suffer from image artifacts caused by local magnetic field inhomogeneities. Truncation gibbs artifact appears as lines of alternating darkness and brightness occurs in both readout and phaseencoding directions gibbs artifacts most problematic in slice select and low contrast detectability inserts. The presence of eddy currents was assessed for these relatively large products by moving it around the entrance of the bore of the 7tesla mr system. Coupled circuit numerical analysis of eddy currents in an. Echoplanar imaging sequences are especially affected where a characteristic eddy current artifact nyquist n2 ghost is commonly seen. Pdf artifacts in magnetic resonance imaging researchgate. B 0 eddy currents are a subtle but important source of artifacts in spiral mri.