Magnetic field strength dependent SNR gain at the center of a spherical phantom and up to 11.7T

Abstract

Purpose The SNR at the center of a spherical phantom of known electrical properties was measured in quasi‐identical experimental conditions as a function of magnetic field strength between 3 T and 11.7 T. Methods The SNR was measured at the center of a spherical water saline phantom with a gradient‐recalled echo sequence. Measurements were performed at NeuroSpin at 3, 7, and 11.7 T. The phantom was then shipped to Maastricht University and then to the University of Minnesota for additional data points at 7, 9.4, and 10.5 T. Experiments were carried out with the exact same type of birdcage volume coil (except at 3 T, where a similar coil was used) to attempt at isolating the evolution of SNR with field strength alone. Phantom electrical properties were characterized over the corresponding frequency range. Results Electrical properties were found to barely vary over the frequency range. Removing the influence of the flip‐angle excitation inhomogeneity was crucial, as expected. After such correction, measurements revealed a gain of SNR growing as B01.94 ± 0.16 compared with B02.13 according to ultimate intrinsic SNR theory. Conclusions By using quasi‐identical experimental setups (RF volume coil, phantom, electrical properties, and protocol), this work reports experimental data between 3 T and 11.7 T, enabling the comparison with SNR theories in which conductivity and permittivity can be assumed to be constant with respect to field strength. According to ultimate SNR theory, these results can be reasonably extrapolated to the performance of receive arrays with greater than about 32 elements for central SNR in the same spherical phantom.

Commissioning of the Iseult CEA 11.7 T whole-body MRI: current status, gradient–magnet interaction tests and first imaging experience

“…More quantitative measurements followed. The same (traveling) spherical phantom was scanned at 3 T, 7 T and 11.7 T at NeuroSpin CEA, at 7 T and 9.4 T at the University of Maastricht, and finally at 7 T and 10.5 T at the Center for Magnetic Resonance Research of the University of Minnesota [9]. SNR measurements at the center of the phantom were performed in quasi-identical conditions (phantom, positioning, MR protocol, temperature and volume coil).…”

“…MRI at ultra-high field (UHF) is a promising technology to explore the human brain at the mesoscopic scale and with unprecedented details enabled by the supra-linear gain in signal-to-noise (SNR) and contrast-to-noise ratio (CNR) with field strength [1][2][3][4][5][6][7][8][9]. The first UHF magnet was an 8 T 800 mm bore system developed by Magnex Scientific Limited for Ohio State University in 1998 [10].…”

Scaling the mountains: what lies above 7 Tesla magnetic resonance?

“…With 7 T human MRI now present in the clinic, there is increasing interest in exploring ever higher magnetic field strengths. This includes pioneering reports on 9.4 T, 10.5 and 11.7 T MRI which lead the way to even higher fields [8][9][10]. This has generated the momentum to drive MR science to take even more ambitious steps into the future, envisioning human MR at 14 T and even 20 T [11][12][13][14][15].…”

Multi-scale structural alterations of the thalamus and basal ganglia in focal epilepsy as demonstrated by 7T MRI

“…It has been shown that 7T allows detection of epileptogenic lesions not visible at 3T 23 . Therefore, based on typical acquisitions performed at 3T and 7T, differences in the signal- and contrast-to-noise ratios of T 1 data will impact sensitivity to segment individual nuclei as well as the power to detect patient-control morphometric and T 1 differences at lower field strengths 25,82 .…”