Tilt optimized flip uniformity (TOFU) RF pulse for uniform image contrast at low specific absorption rate levels in combination with a surface breast coil at 7 Tesla

Kalleveen, Irene M. L. van; Boer, Vincent O.; Luijten, Peter R.; Klomp, Dennis W. J.

doi:10.1002/mrm.25415

Cited by 8 publications

(9 citation statements)

References 19 publications

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“…Even though R1 achieved higher specificity, PPV and NPV rates at 7T, the same observer rated the image quality of the dynamic series at 3T significantly better, which indicates that there is still room for improvement. Current technical developments, such as dynamic B0 field monitoring and correction (Boer et al 2012 ), and RF pulses designed to compensate the linear decreasing B1+ field(van Kalleveen et al 2015 ) may improve the image quality at 7T. As an example, Boer et al developed a simple field probe that proved to be useful to monitor temporal B0 field variations.…”

Section: Discussionmentioning

confidence: 99%

“…The acquired temporal B0 field information could drive a dynamic module to correct the B0 magnetic field in real time (Boer et al 2012 ). In a recent study, van Kalleveen et al were able to compensate the inhomogeneous B1+ field (while keeping the specific absorption rate low) by applying tilt optimized flip uniformity RF pulses to the breast surface coil (van Kalleveen et al 2015 ).…”

Section: Discussionmentioning

confidence: 99%

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Dynamic contrast-enhanced breast MRI at 7T and 3T: an intra-individual comparison study

et al. 2016

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The aim of this study is to compare the current state of lesion identification, the BI-RADS classification and the contrast-enhancement behavior at 7T and 3T breast MRI in the same patient group. Twenty-seven patients with thirty suspicious lesions were selected for this prospective study and underwent both 7T and 3T MRI. All examinations were rated by two radiologists (R1 and R2) independently on image quality, lesion identification and BI-RADS classification. We assessed sensitivity, specificity, NPV and PPV, observer agreement, lesion sizes, and contrast-enhancement-to-noise ratios (CENRs) of mass lesions. Fifteen of seventeen histopathological proven malignant lesions were detected at both field strengths. Image quality of the dynamic series was good at 7T, and excellent at 3T (P = 0.001 for R1 and P = 0.88 for R2). R1 found higher rates of specificity, NPV and PPV at 7T when compared to 3T, while R2 found the same results for sensitivity, specificity, NPV and PPV for both field strengths. The observers showed excellent agreement for BI-RADS categories at 7T (κ = 0.86) and 3T (κ = 0.93). CENRs were higher at 7T (P = 0.015). Lesion sizes were bigger at 7T according to R2 (P = 0.039). Our comparison study shows that 7T MRI allows BI-RADS conform analysis. Technical improvements, such as acquisition of T2w sequences and adjustment of B1+ field inhomogeneity, are still necessary to allow clinical use of 7T breast MRI.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Dynamic contrast-enhanced breast MRI at 7T and 3T: an intra-individual comparison study

et al. 2016

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“…The use of local transmit coils is essential for this method. The coils used in this study are known to have a strong but decaying

{normalB}_{1}^{+}

field in the posterior direction, which can be compensated with tilt‐optimized flip uniformity pulses . As the proposed method only consists of a frequency offset, both methods can be combined to overcome the limitation of the decaying

{normalB}_{1}^{+}

field, while at the same time enabling discretized frequency shimming.…”

Section: Discussionmentioning

confidence: 99%

Improved fat suppression of the breast using discretized frequency shimming

Velden

Luijten

Klomp

2017

Magnetic Resonance in Med

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Purpose: Robust fat suppression is essential in bilateral breast MRI at 7 Tesla. The lack of good fat suppression can result in errors when calculating the enhancement curve from dynamic contrast-enhanced acquisitions. In this work we propose discretized frequency shimming to improve the quality of fat suppression by exploiting the capabilities of a parallel transmit setup. Methods: With discretized frequency shimming, different resonance frequencies are used for the different transmitters of the radiofrequency coil. This can be particularly useful for frequency-selective radiofrequency pulses, such as water excitation. The potential of this method has been investigated by simulations on seven acquired B 0 maps. Prospective experiments on phantoms and four healthy volunteers were performed to illustrate the performance of discretized frequency shimming.Results: Simulations show a decrease in off-resonance excitation for all subjects when discretized frequency shimming is used. This decrease is highly subject-dependent, but can result in up to 30% better fat suppression, as observed in phantom and volunteer experiments. Conclusions: Discretized frequency shimming improves fat suppression in bilateral breast MRI at 7 Tesla. Magn Reson Med 79:593-599,

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“…The B 1 þ field decayed in the posterior direction, which was a direct result of using a quadrature surface coil. Specially designed RF pulses can compensate for most of the B 1 þ inhomogeneities, as shown recently, with tilt optimized flip uniformity pulses (24). Different techniques have been suggested for correcting inhomogeneities in the receive field of the receiver array, such as the homogenization of T 1 -weighted images by incorporating a proton density-weighted image (25).…”

Section: Discussionmentioning

confidence: 99%

Radiofrequency configuration to facilitate bilateral breast³¹P MR spectroscopic imaging and high-resolution MRI at 7 Tesla

Velden

Italiaander²,

Kemp

et al. 2014

Magn. Reson. Med.

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Purpose: High-resolution MRI combined with phospholipid detection may improve breast cancer grading. Currently, configurations are optimized for either high-resolution imaging or 31 P spectroscopy. To be able to perform both imaging as well as spectroscopy in a single session, we integrated a 1 H receiver array into a 1 H-31 P transceiver at 7T. To ensure negligible signal loss due to coupling between elements, we investigated the use of a floating decoupling loop to enable bilateral MRI and 31 P MRS. Methods: Two quadrature double-tuned radiofrequency coils were designed for bilateral breast MR with active detuning at the 1 H frequency. The two coils were placed adjacent to each other and decoupled for both frequencies with a single resonant floating loop. Sensitivity of the bilateral configuration, facilitating space for a 26-element 1 H receive array, was compared with a transceiver configuration. Results: The floating loop was able to decouple the elements over 20 dB for both frequencies. Enlargement of the elements, to provide space for the receivers, and the addition of detuning electronics altered the 31 P sensitivity by 0.4 dB. Conclusion: Dynamic contrast-enhanced scans of 0.7 mm isotropic, diffusion-weighted imaging, and 31 P MR spectroscopic imaging can be acquired at 7T in a single session as demonstrated in a patient with invasive ductal carcinoma. Magn

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Tilt optimized flip uniformity (TOFU) RF pulse for uniform image contrast at low specific absorption rate levels in combination with a surface breast coil at 7 Tesla

Abstract: By applying TOFU RF pulses to the breast surface coil, we are able to compensate the inhomogeneous B1+ field, while keeping the SAR low. Therefore stronger T1 -weighting in FFE sequences can be obtained, while pulse durations can remain short, as shown in the human breast at 7T.

Cited by 8 publications

References 19 publications

Dynamic contrast-enhanced breast MRI at 7T and 3T: an intra-individual comparison study

Dynamic contrast-enhanced breast MRI at 7T and 3T: an intra-individual comparison study

Improved fat suppression of the breast using discretized frequency shimming

Radiofrequency configuration to facilitate bilateral breast³¹P MR spectroscopic imaging and high-resolution MRI at 7 Tesla

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Tilt optimized flip uniformity (TOFU) RF pulse for uniform image contrast at low specific absorption rate levels in combination with a surface breast coil at 7 Tesla

Abstract: By applying TOFU RF pulses to the breast surface coil, we are able to compensate the inhomogeneous B1+ field, while keeping the SAR low. Therefore stronger T1 -weighting in FFE sequences can be obtained, while pulse durations can remain short, as shown in the human breast at 7T.

Cited by 8 publications

References 19 publications

Dynamic contrast-enhanced breast MRI at 7T and 3T: an intra-individual comparison study

Dynamic contrast-enhanced breast MRI at 7T and 3T: an intra-individual comparison study

Improved fat suppression of the breast using discretized frequency shimming

Radiofrequency configuration to facilitate bilateral breast31P MR spectroscopic imaging and high-resolution MRI at 7 Tesla

Contact Info

Product

Resources

About

Radiofrequency configuration to facilitate bilateral breast³¹P MR spectroscopic imaging and high-resolution MRI at 7 Tesla