Diffusion anisotropy indexes are sensitive to selecting the EPI readout-encoding bandwidth at high-field MRI

Jahng, Geon‐Ho; Weiner, Michael W.; Schuff, Norbert

doi:10.1016/j.mri.2008.01.005

Cited by 8 publications

(9 citation statements)

References 24 publications

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“…They have shown that Nyquist ghost can produce severe artifacts such as regions with apparently low ADC (apparent diffusion coefficient) values, which simulate regions of reduced diffusion. Moreover, Jahng et al (41) have revealed at 4 T that diffusion anisotropic indexes are sensitive to BW of spin-echo EPI-diffusion acquisition sequence due to associated Nyquist ghost. Recently, Jahng and Schuff (42) have studied at 4 T the influence of BW on quantitative gradient-echo EPI-perfusion measurements based on arterial spin labeling (ASL) technique.…”

Section: Discussionmentioning

confidence: 99%

Characterization of Nyquist ghost in EPI‐fMRI acquisition sequences implemented on two clinical 1.5 T MR scanner systems: effect of readout bandwidth and echo spacing

Giannelli

Diciotti

Tessa

et al. 2010

J Applied Clin Med Phys

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In EPI‐fMRI acquisitions, various readout bandwidth (BW) values are used as a function of gradients' characteristics of the MR scanner system. Echo spacing (ES) is another fundamental parameter of EPI‐fMRI sequences, but the employed ES value is not usually reported in fMRI studies. Nyquist ghost is a typical EPI artifact that can degrade the overall quality of fMRI time series. In this work, the authors assessed the basic effect of BW and ES for two clinical 1.5 T MR scanner systems (scanner‐A, scanner‐B) on Nyquist ghost of gradient‐echo EPI‐fMRI sequences. BW range was: scanner‐A, 1953‐3906 Hz/pixel; scanner‐B, 1220‐2894 Hz/pixel. ES range was: scanner‐A, scanner‐B: 0.75‐1.33 ms. The ghost‐to‐signal ratio of time series acquisition false(GSRtsfalse) and drift of ghost‐to‐signal ratio false(DRGSRfalse) were measured in a water phantom. For both scanner‐A (93% of variation) and scanner‐B (102% of variation) the mean GSRts significantly increased with increasing BW. GSRts values of scanner‐A did not significantly depended on ES. On the other hand, GSRts values of scanner‐B significantly varied with ES, showing a downward trend (81% of variation) with increasing ES. In addition, a GSRts spike point at ES=1.050.2emms indicating a potential resonant effect was revealed. For both scanners, no significant effect of ES on DRGSR was revealed. DRGSR values of scanner‐B did not significantly vary with BW, whereas DRGSR values of scanner‐A significantly depended on BW showing an upward trend from negative to positive values with increasing BW. GSRts and DRGSR can significantly vary with BW and ES, and the specific pattern of variation may depend on gradients performances, EPI sequence calibrations and functional design of radiofrequency coil. Thus, each MR scanner system should be separately characterized. In general, the employment of low BW values seems to reduce the intensity and temporal variation of Nyquist ghost in EPI‐fMRI time series. On the other hand, the use of minimum ES value might not be entirely advantageous when the MR scanner is characterized by gradients with low performances and suboptimal EPI sequence calibration.PACS numbers: 87.61.‐c, 87.61.Qr, 87.61.Hk

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Section: Discussionmentioning

confidence: 99%

Characterization of Nyquist ghost in EPI‐fMRI acquisition sequences implemented on two clinical 1.5 T MR scanner systems: effect of readout bandwidth and echo spacing

Giannelli

Diciotti

Tessa

et al. 2010

J Applied Clin Med Phys

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“…Previous fMRI studies demonstrated that variable degrees of scanner noise, including variations in EPI bandwidth, affect activation patterns in fMRI [38][39][40][41][42][43]. In addition, previous investigations showed that N2 ghosting can affect measurements of diffusion anisotropy such as fractional anisotropy and the relative anisotropy whereas mean diffusivity was not affected [12,13]. The result of this study also showed that one should stay away from mechanical vibrations, which can result in artificial activation patterns in BOLD-based and ASL-based functional MRI studies [44].…”

Section: Discussionmentioning

confidence: 99%

“…Recently, the author [12] and others [13] demonstrated for DTI that the impact of N2 ghosting on diffusion measures can practically be eliminated by tuning the modulation frequency of the EPI readout gradient, i.e. the EPI bandwidth, to a range outside the harmonics of mechanical gradient vibrations so that the magnitude of the vibrations is substantially reduced.…”

Section: Introductionmentioning

confidence: 99%

Influence of selecting EPI readout-encoding bandwidths on arterial spin labeling perfusion MRI

Jahng

Schuff

2009

Magn Reson Mater Phy

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Object The objective of this study was to investigate effects of varying readout bandwidths on the arterial spin labeling (ASL)-perfusion MRI measurements at a high magnetic field MRI system. Materials and methods Brain perfusion studies were performed on nine volunteers (four males, five females) using flow sensitive alternating inversion recovery (FAIR) ASL single-shot echo-planar imaging (EPI)-MRI. To investigate EPI bandwidth effects on the time-series perfusion-weighted imaging (PWI) data, two regions-of-interest (ROI) were placed outside the brain to determine the level of noise and another ROI inside the brain to determine the level of signal. Coefficients of variations (CoV) were calculated for the timeseries PWI data. One-way analysis of variance (ANOVA) was used to investigate voxel-wise differences in the time-series PWI data between two different bandwidth values. Results At the level of ROI, there was no significant effect of changing EPI bandwidths on the time-series PWI data in any of the volunteers (P > 0.031). In contrast, CoV values over the dynamic PWI data varied with depending on selecting EPI bandwidths and voxel-based tests showed that N2 ghosting, modulated by EPI bandwidth, can appear in some brain regions, especially in areas that overlap with the spatial distribution of N2 ghosting artifacts. Conclusions Although N2 ghosting can be reduced by adjusting the bandwidth of EPI on the time-series of PWI data, the effects cannot be entirely eliminated. In particular, N2 ghosting can bias CBF quantification if EPI control scans to determine the equilibrium-state signal are confounded by N2 ghosting. Therefore, careful tuning of the bandwidth of EPI is necessary to avoid artifacts in the ASL signal from N2-ghosting.Keywords Nyquist ghost artifact · Echo-planar imaging · Readout-encoding bandwidth · Arterial spin labeling · Human brain · High field MRI

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“…6 When an EPI DWI is selected on Magnetom® Avanto (Siemens Medical Solutions, Erlangen, Germany), the RF of Magnetom Symphony (Siemens Medical Solutions) will be picked up by the receiver coil of Avanto, resulting in RF artefacts on the images. As for the other pulse sequences with a narrower BW, including fast sequences [TrueFISP, CE-MR angiography (MRA)], no RF artefacts will be produced.…”

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confidence: 99%

“…It was reported that one practical solution to reduce EPI ghosting artefacts is to modify the BW in the frequency-encoding direction. 6 Hence, we have tested this method in this study.…”

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Radiofrequency artefacts in echoplanar imaging induced by two 1.5 T MR scanners in close proximity

Cui²,

Sp³

et al. 2014

BJR

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Objective: The purpose of this study was to assess radio frequency (RF) artefacts in echoplanar imaging (EPI) induced by two 1.5T MR scanners in close proximity and to find an effective method to correct them. Methods: Based on the intact shielding of rooms, experiments were performed by two MR scanners with similar centre frequencies. Phantom A (PA) was scanned in one scanner by EPI at different bandwidths (BWs). Simultaneously, phantom B was scanned in a fixed sequence for scanning with the other scanner. RF artefact gaps of PA, scanning time and the image signal-noise ratio (SNR) were measured and recorded. Statistical analysis was performed with the repeatedmeasures analysis of variance test. Based on findings obtained from PA, three healthy volunteers were studied at a conventional BW and a lower BW to observe the artefact variance. Results: EPI RF artefacts were symmetrically situated in both sides of the image following the phase-encoding direction. The gap size of the artefact became larger and the SNR was significantly improved with a narrower BW. RF artefacts with a lower BW in volunteers presented the same characteristic as PA. Conclusion: For EPI RF artefacts produced by two 1.5 T MR scannerswithapproximatelysimilarcentrefrequencies,wecan reduce BWs in a suitable range to minimize the effect on MRI. Advances in knowledge: MR scanners with the same field strength installed in the same vicinity might produce RF artefacts in the sequence at larger BWs. Reducing BWs properly is effective to control the position of artefacts and improve the image quality.Owing to the limited space and inappropriate planning, two 1.5 T MR scanners in our hospital were installed with their apertures facing each other at the same level. Subsequently, artefacts appeared in MR images when they were used at the same time. Artefacts that severely impaired the quality of MR images were a band or zipper of intensity perpendicular to the frequency-encoding direction. They frequently appeared in many conventional sequences, so that the scanning could not work. We and the engineers studied the characteristics of the artefacts and considered them radiofrequency (RF) artefacts. We tried our best to search for the interference source, but we could not be sure what instrument it came from. After recording and analysing artefacts, we found an apparent law. Only when two scanners were used at the same time did the RF artefacts appear in many sequences. After closing the RF coil of one scanner, RF artefacts disappeared from the images of the other. Therefore, we considered that these artefacts were produced from the interaction between two scanners. Two MR scanners have the same field strength of 1.5 T and a similar approximate centre frequency (Avanto 5 63.680982 MHz; Symphony 5 63.685914 MHz). The difference of the centre frequencies between both scanners is 4932 Hz. As soon as half of the sampling rate of the sequence is .4932 Hz, RF of the opposite scanner will be received and fill in the k-space corresponding to the frequency range whe...

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Diffusion anisotropy indexes are sensitive to selecting the EPI readout-encoding bandwidth at high-field MRI

Cited by 8 publications

References 24 publications

Characterization of Nyquist ghost in EPI‐fMRI acquisition sequences implemented on two clinical 1.5 T MR scanner systems: effect of readout bandwidth and echo spacing

Characterization of Nyquist ghost in EPI‐fMRI acquisition sequences implemented on two clinical 1.5 T MR scanner systems: effect of readout bandwidth and echo spacing

Influence of selecting EPI readout-encoding bandwidths on arterial spin labeling perfusion MRI

Radiofrequency artefacts in echoplanar imaging induced by two 1.5 T MR scanners in close proximity

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