Reduced-Bandwidth MR Imaging of the Head at 1.5 T

Simon, Jack H.; Foster, Thomas H.; Ketonen, Leena; Tötterman, S.; Szumowski, Jerzy; Kido, Daniel K.; Manzione, James V.; Joy, Stephen E.

doi:10.1148/radiology.172.3.771

Cited by 7 publications

(3 citation statements)

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“…14,15 Decreasing BW can be used to increase SNR at a constant imaging time or to maintain the SNR for reducing the imaging time. 18 With the parallel technique, the correction factors of 1.5 were used in our experiment for the calculation of SNR to elevate the image quality. [19][20][21] An improvement in SNR could be acquired with decreasing BW in our study.…”

Section: Discussionmentioning

confidence: 99%

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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Section: Discussionmentioning

confidence: 99%

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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“…This pixel-by-pixel misregistration along the frequency-encoding direction visibly manifests itself as a bright or dark band running perpendicular to the frequencyencoding direction. Clinically, the chemical shift artifact is most often recognized at the margins of predominantly fluid-filled structures that are embedded in fatty regions, such as the bladder (Fig 2) and orbits (2,3,5,11). The misregistration of signal along the frequency-encoding direction results from the erroneous mapping of the signal of the fatty elements relative to that of the fluid-filled structures.…”

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confidence: 99%

“…Use of a narrower bandwidth will also increase the chemical shift banding seen on the images (2,5). However, narrowing the bandwidth may increase the TE of the sequence or limit the number of sections that can be acquired.…”

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confidence: 99%

Chemical Shift: The Artifact and Clinical Tool Revisited

Hood¹,

Ho²,

et al. 1999

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The chemical shift phenomenon refers to the signal intensity alterations seen in magnetic resonance (MR) imaging that result from the inherent differences in the resonant frequencies of precessing protons. Chemical shift was first recognized as a misregistration artifact of image data. More recently, however, chemical shift has been recognized as a useful diagnostic tool. By exploiting inherent differences in resonant frequencies of lipid and water, fatty elements within tissue can be confirmed with dedicated chemical shift MR pulse sequences. Alternatively, the recognition of chemical shift on images obtained with standard MR pulse sequences may corroborate the diagnosis of lesions with substantial fatty elements. Chemical shift can aid in the diagnosis of lipid-containing lesions of the brain (lipoma, dermoid, and teratoma) or the body (adrenal adenoma, focal fat within the liver, and angiomyolipoma). In addition, chemical shift can be implemented to accentuate visceral margins (e.g., kidney and liver).

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