Simultaneous <i>B</i> homogenization and specific absorption rate hotspot suppression using a magnetic resonance phased array transmit coil

Berg, Cornelis A.T. van den; Bergen, B. van den; Kamer, Jeroen B. van de; Raaymakers, B W; Kroeze, H.; Bartels, Lambertus W.; Lagendijk, J J W

doi:10.1002/mrm.21149

Cited by 85 publications

(69 citation statements)

References 21 publications

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“…However, we did not take this approach in our study because the gain in SNR was not so prominent for 3.0 T imaging in our preliminary experience. By using recent techniques such as parallel excitation (multitransmitter system) (34) or phased array transmit coils (35), image homogeneity may be improved, and therefore there is a possibility that diagnostic performance of 3.0 T imaging can be much better than that in this study.…”

Section: T Mri Of the Abdomen And Pelvis In Clinical Settingsmentioning

confidence: 85%

MR imaging of endometrial carcinoma for preoperative staging at 3.0 T: Comparison with imaging at 1.5 T

Hori

Kim

Murakami

et al. 2009

Magnetic Resonance Imaging

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Purpose:To prospectively compare magnetic resonance imaging (MRI) at 3.0 T and 1.5 T in the same patients for preoperative evaluation of endometrial carcinoma. Materials and Methods:Thirty consecutive patients with endometrial carcinoma underwent MRI at both 3.0 T and 1.5 T as well as surgery. Quantitative and qualitative analyses were performed. Two radiologists independently evaluated images. MR findings were compared with surgicopathologic findings.Results: Image homogeneity of T2-weighted images at 3.0 T was significantly inferior to that at 1.5 T (P ϭ 0.007). The scores of image homogeneity and susceptibility artifacts were not significantly different between 3.0 T gadoliniumenhanced imaging and 1.5 T imaging (P ϭ 0.09 and 0.36). Kappa statistics showed good interobserver agreement between the two radiologists for local-regional staging on T2-weighted images ( Ͼ0.6). The area under the receiver operating characteristic curve (Az) values for T2-weighted imaging in terms of myometrial invasion, cervical invasion, and lymph node metastases were 0.88 (3.0 T) versus 0.91 (1.5 T), 0.84 versus 0.83, and 0.94 versus 0.95 for reader 1, respectively. There were no significant differences between imaging at 3.0 T and at 1.5 T in Az values for either reader (P Ͼ 0.35).Conclusion: 3.0 T MRI is an equivalent imaging modality to 1.5 T imaging for presurgical evaluation of endometrial carcinoma, although not significantly superior to 1.5 T imaging.

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Section: T Mri Of the Abdomen And Pelvis In Clinical Settingsmentioning

confidence: 85%

MR imaging of endometrial carcinoma for preoperative staging at 3.0 T: Comparison with imaging at 1.5 T

Hori

Kim

Murakami

et al. 2009

Magnetic Resonance Imaging

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“…Though at least one initial attempt to consider SAR while optimizing magnetic field homogeneity with numerical calculations looks promising (13), the general application of such an approach is yet uncertain as local SAR levels and locations are patient specific (14,15) and it is not practical to create patient-specific numerical models of every patient before MRI imaging. The results in this article demonstrate that the superposition of electric and magnetic fields is valid when using current source driving methods, a fundamental step toward future developments of considering SAR for transmit arrays.…”

Section: Discussionmentioning

confidence: 99%

Calculation of SAR for transmit coil arrays

Mao

Wang

Smith

et al. 2007

Concepts Magn Reson

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Transmit coil arrays allowing independent control of individual coil drives facilitate adjustment of the B 1 field distribution, but when the B 1 field distribution is changed the electric field and SAR distributions are also altered. This makes safety evaluation of the transmit array a challenging problem because there are potentially an infinite number of possible field distributions in the sample. Local SAR levels can be estimated with numerical calculations, but it is not practical to perform separate full numerical calculations for every current distribution of interest. Here we evaluate superposition of separate electric field calculations-one for each coil-for predicting SAR in a full numerical calculation where all coils are driven simultaneously. It is important to perform such an evaluation because the effects of coil coupling may alter the result. It is shown that while there is good agreement between the superimposed and simultaneous drive results when using current sources in the simulations, the agreement is not as good when voltage sources are used. Finally, we compare maximum local SAR levels for B 1 field distributions that are either unshimmed or shimmed over one of three regions of interest. When B 1 field homogeneity is improved in a small region of interest without regard for SAR, the maximum local SAR can become very high.

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“…However, at high frequencies the radiofrequency (RF) wavelength approaches the dimension of the head and complex wave behavior occurs within the heterogeneous brain tissue (1). Destructive and constructive interferences of the RF field can cause transmit field (B þ 1 ) inhomogeneities (2)(3)(4), as well as local regions of increased power deposition (5). Transmit arrays have been developed to mitigate sample-dependent RF inhomogeneities (6,7).…”

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confidence: 99%

A conformal transceive array for 7 T neuroimaging

Gilbert

Belliveau

Curtis

et al. 2011

Magnetic Resonance in Med

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The first 16-channel transceive surface-coil array that conforms to the human head and operates at 298 MHz (7 T) is described. Individual coil elements were decoupled using circumferential shields around each element that extended orthogonally from the former. This decoupling method allowed elements to be constructed with arbitrary shape, size, and location to create a three-dimensional array. Radiofrequency shimming achieved a transmit-field uniformity of 20% over the whole brain and 14% over a single axial slice. During radiofrequency transmission, coil elements couple tightly to the head and reduce the amount of power necessary to achieve a mean 90°flip angle (660-ms and 480-ms pulse lengths were required for a 1-kW hard pulse when shimming over the whole brain and a single axial slice, respectively). During reception, the close proximity of coil elements to the head increases the signal-to-noise ratio in the periphery of the brain, most notably at the superior aspect of the head. The sensitivity profile of each element is localized beneath the respective shield. When combined with the achieved isolation between elements, this results in the capacity for low geometry factors during both transmit and receive: 1.04/1.06 (mean) and 1.25/1.54 (maximum) for 3-by-3 acceleration in the axial/sagittal plane. High cortical signal-tonoise ratio and parallel imaging performance make the conformal coil ideal for the study of high temporal and/or spatial cortical architecture and function.

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Simultaneous B homogenization and specific absorption rate hotspot suppression using a magnetic resonance phased array transmit coil

Abstract: In high-field MRI severe problems with respect to B + 1 uniformity and specific absorption rate (SAR) deposition pose a great challenge to whole-body imaging. In this study the potential of a phased array transmit coil is investigated to simultaneously reduce B

Cited by 85 publications

References 21 publications

MR imaging of endometrial carcinoma for preoperative staging at 3.0 T: Comparison with imaging at 1.5 T

MR imaging of endometrial carcinoma for preoperative staging at 3.0 T: Comparison with imaging at 1.5 T

Calculation of SAR for transmit coil arrays

A conformal transceive array for 7 T neuroimaging

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