Optimizing Abdominal MR Imaging: Approaches to Common Problems

Yang, Roberta K.; Roth, Christopher G.; Ward, Robert James; deJesus, Joseph O.; Mitchell, Donald G.

doi:10.1148/rg.301095076

Cited by 95 publications

(80 citation statements)

References 31 publications

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“…A wide variety of approaches have been developed to deal with motion artifacts at body MR imaging (22). These approaches include synchronization of image acquisition to respiratory motion, changes in the acquisition parameters to minimize the effect of motion on image quality, and accelerated image acquisition (Table).…”

Section: Motion Artifacts Physiologic Motion-related Artifactsmentioning

confidence: 99%

Body MR Imaging: Artifacts, k-Space, and Solutions

et al. 2015

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Body magnetic resonance (MR) imaging is challenging because of the complex interaction of multiple factors, including motion arising from respiration and bowel peristalsis, susceptibility effects secondary to bowel gas, and the need to cover a large field of view. The combination of these factors makes body MR imaging more prone to artifacts, compared with imaging of other anatomic regions. Understanding the basic MR physics underlying artifacts is crucial to recognizing the trade-offs involved in mitigating artifacts and improving image quality. Artifacts can be classified into three main groups: (a) artifacts related to magnetic field imperfections, including the static magnetic field, the radiofrequency (RF) field, and gradient fields; (b) artifacts related to motion; and (c) artifacts arising from methods used to sample the MR signal. Static magnetic field homogeneity is essential for many MR techniques, such as fat saturation and balanced steady-state free precession. Susceptibility effects become more pronounced at higher field strengths and can be ameliorated by using spin-echo sequences when possible, increasing the receiver bandwidth, and aligning the phase-encoding gradient with the strongest susceptibility gradients, among other strategies. Nonuniformities in the RF transmit field, including dielectric effects, can be minimized by applying dielectric pads or imaging at lower field strength. Motion artifacts can be overcome through respiratory synchronization, alternative k-space sampling schemes, and parallel imaging. Aliasing and truncation artifacts derive from limitations in digital sampling of the MR signal and can be rectified by adjusting the sampling parameters. Understanding the causes of artifacts and their possible solutions will enable practitioners of body MR imaging to meet the challenges of novel pulse sequence design, parallel imaging, and increasing field strength. © RSNA, 2015 • radiographics.rsna.org Susie Y. Huang, MD, PhD Ravi T. Seethamraju, PhD Pritesh Patel, MD Peter F. Hahn, MD, PhD John E. Kirsch, PhD Alexander R. Guimaraes, MD, PhD Abbreviations: B 0 = static magnetic field, B 1 = applied radiofrequency field, FOV = field of view, RARE = rapid acquisition with relaxation enhancement, RF = radiofrequency, SNR = signal-to-noise ratio, SSFP = steady-state free precession, STIR = short inversion time inversionrecovery, TR = repetition time

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Section: Motion Artifacts Physiologic Motion-related Artifactsmentioning

confidence: 99%

Body MR Imaging: Artifacts, k-Space, and Solutions

et al. 2015

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“…This result correlated with the SNR equation, which is inversely proportional to the square root of the receiver BW. 22,23 It was reported that decreasing the receiver BWallows an increasing TE 22 and ES. 14 Although there were changes in TE, ES and scanning time, no obvious statistically significant difference was found in our study.…”

Section: Discussionmentioning

confidence: 99%

“…Characteristics of the artefacts in the PA images were recorded. A mid-transverse section (image number 29, b2 value 5 1000 s mm 22 ) was chosen for measurement. A straight line was drawn through the centre of PA, which arrived at the inner margins of two parallel artefacts in the image.…”

Section: Phantom Studiesmentioning

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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“…Moreover, without ionizing radiation, repeated MR scans can routinely be used for observation of postoperative LN metastasis and therapeutic effects. In contrast, a relatively long scanning time makes MRI more susceptible to motion artifacts from breath or gastrointestinal peristalsis [38]. That may limit its use in evaluating regional LNs of chest and abdominal malignancies.…”

Section: Computed Tomographymentioning

confidence: 99%

Radiologic Assessment of Lymph Nodes in Oncologic Patients

2013

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Status of lymph node metastasis has important implications in deciding treatment of oncologic patients. The appropriate choice of imaging modality is crucial to obtain accurate evaluation of lymph node status. Current imaging methods are mainly divided into two categories, conventional structural imaging and more recently emerging functional imaging. In depth understanding of these imaging tools is essential in making the correct choice for individual patients, and eventually for better diagnosis and treatment.

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Optimizing Abdominal MR Imaging: Approaches to Common Problems

Cited by 95 publications

References 31 publications

Body MR Imaging: Artifacts, k-Space, and Solutions

Body MR Imaging: Artifacts, k-Space, and Solutions

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

Radiologic Assessment of Lymph Nodes in Oncologic Patients

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