Simulation of susceptibility artifacts in 2D and 3D fourier transform spin-echo and gradient-echo magnetic resonance imaging

doi:10.1016/0730-725X(94)92201-2

Magnetic Resonance Imaging

Volume 12, Issue 5, 1994, Pages 767-774

https://doi.org/10.1016/0730-725X(94)92201-2 Get rights and content

Abstract

A method is presented for simulating susceptibility artifacts in 2D and 3D spin-echo and gradient-echo imaging of arbitrary susceptibility distributions. The method incorporates object induced field perturbations in the time domain (k-space) and is demonstrated for spherical nonuniformities in susceptibility. Both simulations and experimental results for multi-slice 2D and 3D imaging of phantoms and human subjects are provided.

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Cited by (71)

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Citation Excerpt :
In addition, the time domain (k-space) DBS electrode simulation is a powerful tool that helped us understand and predict the effect of electrode-induced and inherent static field inhomogeneity in MRI. The method offers flexibility in studying the effects of various experimental conditions and parameter settings on the appearance of susceptibility artifacts in both SE and GRE imaging and may be employed to provide insight into a number of related artifacts familiar from clinical practice and reported in the literature [27,28]. Examples include geometry and intensity distortions associated with air cavities, foreign bodies, blood vessels, hemangiomas, trabecular bone, etc.
Deep brain stimulation (DBS) has become a widely performed surgical procedure for patients with medically refractory movement disorders and mental disorders. It is clinically important to set up a MRI protocol to map the brain targets and electrodes of the patients before and after DBS and to understand the imaging artifacts caused by the electrodes.
Five patients with DBS electrodes implanted in the habenula (Hb), fourteen patients with globus pallidus internus (GPi) targeted DBS, three pre-DBS patients and seven healthy controls were included in the study. The MRI protocol consisted of magnetization prepared rapid acquisition gradient echo T1 (MPRAGE T1W), 3D multi-echo gradient recalled echo (ME-GRE) and 2D fast spin echo T2 (FSE T2W) sequences to map the brain targets and electrodes of the patients. Phantom experiments were also run to determine both the artifacts and the susceptibility of the electrodes. Signal to noise ratio (SNR) on T1W, T2W and GRE datasets were measured. The visibility of the brain structures was scored according to the Rose criterion. A detailed analysis of the characteristics of the electrodes in all three sequence types was performed to confirm the reliability of the postoperative MRI approach. In order to understand the signal behavior, we also simulated the corresponding magnitude data using the same imaging parameters as in the phantom sequences.
The mean ± inter-subject variability of the SNRs, across the subjects for T1W, T2W, and GRE datasets were 20.1 ± 8.1, 14.9 ± 3.2, and 43.0 ± 7.6, respectively. High resolution MPRAGE T1W and FSE T2W data both showed excellent contrast for the habenula and were complementary to each other. The mean visibility of the habenula in the 25 cases for the MPRAGE T1W data was 5.28 ± 1.11; and the mean visibility in the 20 cases for the FSE T2W data was 5.78 ± 1.30. Quantitative susceptibility mapping (QSM), reconstructed from the ME-GRE sequence, provided sufficient contrast to distinguish the substructures of the globus pallidus. The susceptibilities of the GPi and globus pallidus externa (GPe) were 0.087 ± 0.013 ppm and 0.115 ± 0.015 ppm, respectively. FSE T2W sequences provided the best image quality with smallest image blooming of stimulator leads compared to MPRAGE T1W images and GRE sequence images, the measured diameters of electrodes were 1.91 ± 0.22, 2.77 ± 0.22, and 2.72 ± 0.20 mm, respectively. High resolution, high bandwidth and short TE (TE = 2.6 ms) GRE helped constrain the artifacts to the area of the electrodes and the dipole effect seen in the GRE filtered phase data provided an effective mean to locate the end of the DBS lead.
The imaging protocol consisting of MPRAGE T1W, FSE T2W and ME-GRE sequences provided excellent pre- and post-operative visualization of the brain targets and electrodes for patients undergoing DBS treatment. Although the artifacts around the electrodes can be severe, sometimes these same artifacts can be useful in identifying their location.
Removing unwanted background phase with a reference phantom for applications in susceptibility quantification
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A method of removing the background phase with a reference phantom but without overcorrecting the induced phase from objects of interest is proposed. Several factors during the imaging procedure and post-processing are investigated for their accuracies.
A method using a reference phantom to remove eddy currents as well as using the least squares fit to quantify susceptibility and to remove the background phase is proposed. Phase induced from simulated spheroids was fitted and compared to their true magnetic moments, an important concept for the proposed method. A cylindrical phantom and its simulation, a phantom with straws filled with Gd-DTPA, and a simulated head model were used to study systematic errors due to some confounding factors. The feasibility for in vivo applications was demonstrated from an actual human head. Susceptibility and remaining phase after removing the background phase were measured in all cases.
Simulations show that magnetic moments of various spheroids and phantoms can be accurately quantified from images, regardless of the partial volume effect. All measured susceptibility values are within ±0.16 ppm of −9.4 ppm for agarose and 0.05 ppm of 1 ppm for Gd-DTPA. Most residual phase is within ±0.1 rad from the phantom center. Susceptibilities close to −9.4 ppm are also obtained for the simulated and actual head. Correspondingly, the remaining phase has a mean value less than two standard deviations.
The proposed method from phantom studies can reliably remove the background phase without overcorrections. The in vivo example demonstrates the feasibility of the method.
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Magnetic resonance imaging has proven its potential application in bread dough and gas cell monitoring studies, and dynamic processes such as dough proving and baking can be monitored. However, undesirable magnetic susceptibility effects often affect quantification studies, especially at high fields. A new low-field method is presented based on local assessment of porosity in spin-echo imaging, local characterization of signal loss in gradient-echo imaging and prediction of relaxation times by simulation to estimate bubble radii in bread dough during proving. Maps of radii showed different regions of dough constituting networks which evolved during proving. Mean radius and bubble distribution were assessed during proving.
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Susceptibility artifacts due to metallic prostheses are a major problem in clinical magnetic resonance imaging. We theoretically and experimentally analyze slice distortion arising from susceptibility differences in a phantom consisting of a stainless steel ball bearing embedded in agarose gel. To relate the observed image artifacts to slice distortion, we simulate images produced by 2D and 3D spin-echo (SE) and a view angle tilting (VAT) sequence. Two-dimensional SE sequences suffer from extreme slice distortion when a metal prosthesis is present, unlike 3D SE sequences for which — since slices are phase-encoded — distortion of the slice profile is minimized, provided the selected slab is larger than the region of interest. In a VAT sequence, artifacts are reduced by the application of a gradient along the slice direction during readout. However, VAT does not correct for the excitation slice profile, which results in the excitation of spins outside the desired slice location and can lead to incorrect anatomical information in MR images. We propose that the best sequences for imaging in the presence of a metal prosthesis utilize 3D acquisition, with phase encoding replacing slice selection to minimize slice distortion, combined with excitation and readout gradient strengths at their maximum values.
Metal Artifact Reduction in Musculoskeletal Magnetic Resonance Imaging
2006, Orthopedic Clinics of North America
Citation Excerpt :
The magnitude of local misregistration artifact also is inversely proportional to the frequency encoding (readout) gradient strength used in the imaging acquisition [18]. Misregistration artifacts occur only in the frequency encoding direction and are not seen in the phase encoding direction because of the type of phase encoding used in clinical sequences (variable amplitude encoding) [23–25]. Because misregistration artifacts occur only in the frequency encoding direction, orientation of the frequency and phase encoding gradients can be selected such that misregistration artifacts are directed away from areas of anticipated clinical diagnostic interest.
Magnetic resonance imaging of microstructure transition in stainless steel
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Magnetic resonance images are prone to artifacts caused by metallic objects. Such artifacts may not only hamper image interpretation, but also have been shown to provide information about the magnetic properties of the substances involved. In this work, we aim to explore the potential of MRI to detect, localize and characterize changes in magnetic properties that may occur when certain alloys have been exposed to a thermomechanical stress. For this purpose, stainless steel 304L wires were drawn to induce a change from paramagnetic austenitic into ferromagnetic martensitic microstructure. The changes in magnetic behavior were quantified by analyzing the geometric distortion in spin echo and the geometric distortion and intravoxel dephasing in gradient echo images at 0.5, 1.5 and 3 T. The results of both imaging strategies were in agreement and in accordance with independent measurements with a vibrating sample magnetometer. Drawing wire to 2% of its cross-sectional area was found to increase the volume fraction of the ferromagnetic martensite from 0.3% to 80% and to enhance the magnetization up to two or three orders of magnitude. The results demonstrate the potential of MRI to locate and quantify stress-induced changes in the magnetic properties of alloys in a completely noninvasive and nondestructive way.

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Original contributionSimulation of susceptibility artifacts in 2D and 3D fourier transform spin-echo and gradient-echo magnetic resonance imaging

Abstract

Magn. Reson. Imaging

Magn. Reson. Imaging

Susceptibility artifacts in NMR imaging

Magn. Reson. Imaging

Reduction of T2∗ dephasing in gradient field-echo imaging

Radiology

Superparamagnetic contrast agents: predicting signal loss in gradient-echo imaging

JMRI

Magnetic field distribution in models of trabecular bone

Magn. Reson. Med.

Potential hazards and artifacts of ferromagnetic and nonferromagnetic surgical and dental materials and devices in nuclear magnetic resonance imaging

Radiology

Artifacts in MR imaging after surgical intervention

J. Comput. Assist. Tomogr.

Comparison of MR imaging and CT in patients with intracranial aneurysm clips

AJNR

Original contribution
Simulation of susceptibility artifacts in 2D and 3D fourier transform spin-echo and gradient-echo magnetic resonance imaging

Reduction of $T_{2}^{∗}$ dephasing in gradient field-echo imaging