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Clinical Trial
. 1997 Mar;125(1):65-71.
doi: 10.1006/jmre.1996.1072.

The intrinsic signal-to-noise ratio in human cardiac imaging at 1.5, 3, and 4 T

H Wen  1 , T J Denison, R W Singerman, R S Balaban
Affiliations
Clinical Trial

The intrinsic signal-to-noise ratio in human cardiac imaging at 1.5, 3, and 4 T

H Wen et al. J Magn Reson. 1997 Mar.

Abstract

Cardiac imaging is inherently demanding on the signal-to-noise performance of the MR scanner and may benefit from high field strengths. However, the complex behavior of the radiofrequency field in the human body at high frequencies makes model-based analyses difficult. This study aims to obtain reliable comparisons of the signal-to-noise profile in the human chest in vivo at 1.5, 3, and 4 T. By using an RF-field-mapping method, it is shown that the intrinsic signal-to-noise increases with the field strength up to 4 T with a less than linear relation. The RF field profile is markedly distorted at 4 T, and the onset of this distortion is dependent on the body size. The high power deposition and the consequences of the RF field distortion are discussed.

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Figures

FIG. 1
FIG. 1
The pulse sequence used to map the B1 field of surface coils in the chest. The ratio between the partially saturated image and the reference image yields the B1 magnitude.
FIG. 2
FIG. 2
The B1 maps of a spherical water phantom with a surface coil placed above it, collected at 4 T. The gray scale is in flip angles, from 0° to 65°. The map on the left was collected with the RF frequency on resonance; the map on the right was collected with the RF frequency off resonance by 200 Hz to simulate a bad shim condition.
FIG. 3
FIG. 3
The B1 maps of a transaxial slice of volunteer 2 at 4 T, collected with TR = 3 s and TR = 5 s, respectively. The flip-angle contours are overlaid on the reference images.
FIG. 4
FIG. 4
Radiofrequency field maps of transaxial slices of volunteers 1 and 2 at 1.5, 3, and 4 T. The B1 distribution is represented as flip-angle contours overlaid on reference images which were used for the B1 calculations. In the B1 mapping experiments, the power input into the surface coils was adjusted such that the flip angle at the center of the heart was 90°.
FIG. 5
FIG. 5
The B1 profile from the anterior chest wall to the posterior portion of the heart of volunteers 1 (a) and 2 (b). The flip-angle values were taken along the arrows depicted in the transaxial images.
FIG. 6
FIG. 6
The relative ISNR (a) and total power deposition (b) of both volunteers at 1.5, 3, and 4 T.
See this image and copyright information in PMC

References

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