Dual-Source Parallel Radiofrequency Excitation Body MR Imaging Compared with Standard MR Imaging at 3.0 T: Initial Clinical Experience

Willinek, Winfried A.; Gieseke, Jürgen; Kukuk, G; Nelles, Michael; König, R.; Morakkabati-Spitz, N; Träber, Frank; Thomas, Daniel; Kuhl, Christiane K.; Schild, Hans H.

doi:10.1148/radiol.10092127

Cited by 127 publications

(114 citation statements)

References 29 publications

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“…Regarding centrallylocated regions, the dpTX 3.0T system produced significantly higher SNR values in images in the left lobe of the liver (followed by measurements from the 1.5T scanner) and the pancreas, which is consistent with published data on T2-weighted imaging [34] . The non-dpTX 3.0T system suffered from severe artifacts in these central regions.…”

Section: Discussionsupporting

confidence: 89%

“…Feeding the two ports of the transmit array with different amplitudes and a phase shift not equivalent to 90 degrees can potentially result in a more homogeneous B1 distribution and less signal shading. Recent studies revealed improved image quality in the liver with T2 and DWI sequences when comparing dpTX 3.0T scanners with their non-dpTX counterparts [33,34] . The assessment in these studies was performed subjectively and no controls were used i.e., without volunteers, different patients received examinations.…”

Section: Discussionmentioning

confidence: 99%

“…The parallel RF excitation aims to reduce the effects of B1 inhomogeneity seen in early generation 3.0T scanners (non-dpTX 3.0T). Initial studies by Kukuk et al [33] and Willinek et al [34] have suggested reduced dielectric effects and an improved homogeneity of the B1 induction field, particularly over the liver, when comparing these dpTX 3.0T scanners with their non-dpTX counterparts.…”

Section: Introductionmentioning

confidence: 99%

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Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

Riffel¹,

Rao²,

Haneder³

et al. 2013

WJR

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AIM:To retrospectively and prospectively compare diffusion-weighted (DW) images in the abdomen in a 1.5T system and 3.0T systems with and without twochannel functionality for B1 shimming.METHODS: DW images of the abdomen were obtained on 1.5T and 3.0T (with and without two-channel functionality for B1 shimming) scanners on 150 patients (retrospective study population) and 10 volunteers (prospective study population). Eight regions were selected for clinical significance or artifact susceptibility (at higher field strengths). Objective grading quantified signal-to-noise ratio (SNR), and subjective evaluation qualified image quality, ghosting artifacts, and diagnostic value. Statistical significance was calculated using χ 2 tests (categorical variables) and independent two-sided t tests or Mann-Whitney U tests (continuous variables). RESULTS:The 3.0T using dual-source parallel transmit (dpTX 3.0T) provided the significantly highest SNRs in nearly all regions. In regions susceptible to artifacts at higher field strengths (left lobe of liver, head of pancreas), the SNR was better or similar to the 1.5T system. Subjectively, both dpTX 3.0T and 1.5T systems provided higher image quality, diagnostic value, and less ghosting artifact (P < 0.01, most values) compared to the 3.0T system without dual-source parallel transmit (non-dpTX 3.0T). CONCLUSION:The dpTX 3.0T scanner provided the highest SNR. Its image quality, lack of ghosting, and diagnostic value were equal to or outperformed most currently used systems. © 2013 Baishideng. All rights reserved.Key words: Abdominal imaging; Diffusion weighted; 3.0T; Radiofrequency excitation; Signal-to-noise ratio Core tip: With the popularity of 3.0T imaging systems, radiologists have commonly found limitations in abdominal imaging with diffusion-weighted imaging (DWI) secondary to B1 in homogeneity artifacts at these higher magnet strengths. Because artifacts disturb diagnostic value of abdominal DWI, 1.5T systems have been mainly used for this particular purpose. However, newer techniques involving 3.0T using dual-source parallel radiofrequency (RF) excitation with parallel transmission and independent RF shimming have recently been developed which may succeed in addressing such limitations. Our study illustrates both the objective and subjective utility in the abdominal distribution while imaging under a 3.0T system which incorporates dualsource RF excitation.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

Riffel¹,

Rao²,

Haneder³

et al. 2013

WJR

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“…15,16 According to Willinek et al, dual-source parallel RF excitation body MRI enables reduced dielectric shading and improved homogeneity of the RF magnetic induction field when compared with single-source imaging at 3T. 17 In 3T spine imaging, it has been reported to reduce the total examination time, and to improve B 1 1 homogeneity and flip angle accuracy by using RF shimming. 18,19 The drawback of these methods are requirements for specialized hardware and software.…”

Section: Discussionmentioning

confidence: 99%

Simple modification of arm position improves B₁⁺ and signal homogeneity in the thoracolumbar spine at 3T

Ishizaka

Kudo

Harada

et al. 2017

Magnetic Resonance Imaging

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Purpose: To evaluate the homogeneity of the radiofrequency magnetic field (B 1 1 ) and signal intensity using different arm positions during 3T thoracolumbar spinal imaging. Materials and Methods: Twenty volunteers were scanned with a four-channel radiofrequency (RF) transmit coil at 3T, with arms on the bed (conventional), arms elevated by 100 mm (arm lift), or with the arms-up position (elevated arm). Axial B 1 1 maps and sagittal T 1 -weighted image (T 1 WI)-performed RF shimming were obtained for each arm position. The mean and standard deviation (SD) of the flip angle (FA) at the center of the vertebra on each B 1 1 map, and contrast noise ratios (CNRs) between the spinal cord and cerebrospinal fluid of sagittal T 1 WI, were calculated and compared among the different arm positions. Results: Mean FA values (degrees) for the arm lift and elevated arm positions were significantly larger than for the conventional position (P < 0.001 for both) at the twelfth thoracic vertebra (Th12). FA SD values for the arm lift and elevated arm position were significantly smaller than for the conventional position (P < 0.001 for both) at Th12. CNR for the arm lift and elevated arm position were significantly higher than for the conventional position (P 5 0.007 and 0.002, respectively). The mean and SD of the FA and the CNR did not differ significantly for the arm lift and elevated arm positions (P 5 0.591, 0.958, and 0.927, respectively). 3Tmagnetic resonance imaging (MRI) has several advantages such as higher spatial and temporal resolution. Based on such advantages, many clinical applications of 3T MRI have been reported. 1-3 Spine imaging has been among the more frequent applications. [4][5][6] However, the RF distribution becomes more inhomogeneous in body imaging at 3T than at 1.5T, because the RF wavelength at 3T is only half as large as that at 1.5T. 7,8 In particular, the signal decrease due to local RF field inhomogeneity in abdominal imaging is caused by the dielectric resonance effect or standing-wave effect. 8,9 These B 1 1 inhomogeneities have been also reported at the thoracolumbar junction in spine imaging.10

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“…Therefore, body coils with two [34] or more channels [35] were introduced to enhance image quality and SAR performance. These approaches allow the usual clinical workflow and the use of standard receive arrays, while at the same time increasing the degrees of freedom for transmit field manipulation.…”

Section: Introductionmentioning

confidence: 99%

Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI

et al. 2017

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Object:In this work an 8-channel array integrated into the gap between the gradient coil and bore liner of a 7-Tesla whole-body magnet is presented that would allow a workflow closer to that of systems at lower magnetic fields that have a built-in body coil; this integrated coil is compared to a local 8-channel array built from identical elements placed directly on the patient. Results: While the remote array shows a slightly better performance in terms of (B + 1 ) homogeneity, the power efficiency and the SAR efficiency are inferior to those of the local array: the transmit voltage has to be increased by a factor of 3.15 to achieve equal flip angles in a central axial slice. The g-factor calculations show a better parallel imaging g-factor for the local array. The field of view of the integrated array is larger than that of the local array. First in vivo images with the integrated array look subjectively promising. Conclusion:Although some RF performance parameters of the integrated array are inferior to a tight-fitting local array, these disadvantages might be compensated by the use of amplifiers with higher power and the use of local receive arrays. In addition, the distant placement provides the potential to include more elements in the array design.

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Dual-Source Parallel Radiofrequency Excitation Body MR Imaging Compared with Standard MR Imaging at 3.0 T: Initial Clinical Experience

Abstract: Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.

Cited by 127 publications

References 29 publications

Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

Simple modification of arm position improves B₁⁺ and signal homogeneity in the thoracolumbar spine at 3T

Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI

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Dual-Source Parallel Radiofrequency Excitation Body MR Imaging Compared with Standard MR Imaging at 3.0 T: Initial Clinical Experience

Abstract: Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.

Cited by 127 publications

References 29 publications

Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

Simple modification of arm position improves B1+ and signal homogeneity in the thoracolumbar spine at 3T

Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI

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Simple modification of arm position improves B₁⁺ and signal homogeneity in the thoracolumbar spine at 3T