Synopsis

3 tesla derived MRCA has a limitation of low contrast for coronary arteries because of setting lower flip angles due to high SAR. Therefore, the signal contrast of for coronary arteries becomes low. 3D non-selective balanced TFE (3D nsbTFE) has the possibility to solve this problem. We examine image quality of MRCA obtained from 3 tesla and 3D nsbTFE.

INTRODUCTION

Coronary MR angiography (MRCA) is widely used for the assessment of coronary artery disease, and has big merits of no radiation exposure and unnecessary of contrast media. (REF.1）From the view point of magnetic field strength, 1.5 tesla scanner for coronary MRA is more used in clinical than 3 tesla scanner because MRCA from balanced sequence with 1.5 tesla has a good contrast in signal intensity between blood and myocardium. On the other hand, 3 tesla has to set up lower flip angles for MRCA due to a limitation of high SAR. Therefore, the signal contrast of for coronary arteries becomes low (REF.2) if T1TFE sequence is used. Furthermore, MRCA at 3 tesla has a serious problem of the banding artifacts due to B0 inhomogeneity (REF.3）. 3D non-selective balanced TFE (3D nsbTFE) has the possibility to solve this problem. 3D nsbTFE enables shorter TR by not using the slice selective excitation (Fig.1), leading to setting up high flip angles. Therefore, we hypothesized that 3D nsbTFE can obtain high contrast for coronary arteries without artifact and less local shimming.

Methods

Using 3.0T MR system (Ingenia, Philips Electronics Japan) and torso-cardiac coil, data of MRCA for 5 healthy volunteers was analyzed. We compared image quality among three sequences of the conventional method (TFE), the balanced SSFP combined with T1 TFE (b-TFE), and 3D nsbTFE. Three sequences were acquired with navigator and cardiac triggering using the following parameters; TFE, FOV (mm) = 180×180, slice thickness (mm) = 1.5×1.5×1.5, TR/TE (ms) =3.4/1.51, flip angle (°) = 12, TFE factor = 29, NSA = 1, SENSE factor = 1×1, Slice = 160, Slice orientation = transverse, 100% gathering time (min) = 5:38; b-TFE, FOV (mm) = 180×180, slice thickness (mm) = 1.5×1.5×1.5, TR/TE (ms) = 4.5/2.2, flip angle (°) = 70, TFE factor = 22, NSA = 1, SENSE factor = 1×1, Slice = 160, Slice orientation = transverse, 100% gathering time (min) = 8:11; nsbTFE, FOV (mm) = 280×280, slice thickness (mm) = 1.5×1.5×1.5, TR/TE (ms) = 2.3/0.93, flip angle (°) = 70, TFE factor=41, NSA=1, C-SENSE factor=7, Slice=330, Slice orientation = coronal,100% gathering time (min) = 3:04 (Fig.2). Curved Planer Reconstructions (CPRs) of MRCA were reconstructed using available software (Ziostation 2, Ziosoft Co, Tokyo) and image quality was evaluated by visual score at 10 places (RCA: #1,2,3,4 LAD: #5,6,7,8 CX: #11,13) based on American Heart Association classification (Fig. 3). The visual evaluation items were three items of overall image quality, sharpness, noise and artifacts, we evaluated them as 4-point grades (grade “4” was excellent, “1” was severe) by two blinded readers (one radiologist and one radiological technologist).

Results & Discussion

Overall image quality and sharpness for 3D nsbTFE were significantly higher than those for TFE and bTFE. On the other hand, the noise artifact for 3D nsbTFE was significantly decreased than that for TFE and bTFE. The signal noise ratio for 3D nsbTFE was higher than TFE and bTFE. The banding artifacts were often seen on bTFE. Three branches of coronary arteries could not be detected on bTFE. 3D nsbTFE successes to shorten and can set up high flip angle. Consequently, contrast for coronary arteries improved.

Conclusion

MRCA using nsbTFE can overcome weak points in conventional balanced SSFP with 3 tesla while while ensuring the image quality and high signal to noise ratio.

Acknowledgements

No acknowledgements found.

References

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