Evaluation of image analysis according to changing breath hold methods of B1 calibration .
Purpose
Single RF sources, dielectric shading artifacts occur from the image signal imbalance according to the anatomic differences among patients. Therefore, dual RF sources are used to improve this. In this theses, we discuss how the image is affected by the changes in B1 calibration scan and breathing method needed when using dual RF sources.
Materials and methods
The tests were performed on healthy 14 volunteers, the test equipment used was Archieva 3.0T TX(Philips medical system, Netherlands) and used coil was a 32-channel sense cardiac coil. The breath hold methods were expiration as in the actual examinations and the modified method of free breathing and inspiration. B1 calibration scans were performed on each method. According to the change in breathing method, the axial images were acquired by 3D dual echo and e-THRIVE sequence. The images were evaluated by a quantitative method of dividing the liver into 9 sections and comparing the measured SNR and CNR, and a qualitative method in which 3 radiologists carried out a relative evaluation of the images' homogeneity and background noise occurrence according to a 3-point scale. The evaluation values were statistically processed using Wilcoxon signed rank test(SPSS 18.0K for windows).
Results
The quantitative results were as follows: the SNR values for 3D dual echo and e-THRIVE were 251.05/167.07/183.53 and 161.08/117.22/128.38, respectively expiration and free breathing and inspiration while the CNR values for 3D dual echo and the e-THRIVE were 73.68/56.4/55.69 and 62.61/40.34/35. The qualitative results for 3D dual echo and e-THRIVE were 2.30/1.76/1.94 and 2.56/1.46/1.98. The statistics results were expiration(p<0.05) but not statistically significant for free breathing and inspiration(p>0.05).
Conclusion
The B1 calibration scan results using the breathing method, after expiration which is identical to that used in real examinations, showed that the images were best. When B1 calibration scan was performed using a breathing method different, an imbalance in image homogeneity occurred resulting in deterioration of SNR and CNR and, in severe cases, dielectric shading artifacts occurred, thereby deteriorating the image quality. Therefore, we could confirm that the B1 calibration scan obtained by using a breathing method identical to that used act actual abdominal MRI examinations implemented the images with higher diagnostic value.
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