Purpose

iterative decomposition of water and fat with echo asymmetric and least-squares estimation(IDEAL) are often used to achieve uniform water–fat separation that is insensitive to Bo inhomogeneities. but in boundaries of different magnetic substances such as bone, gas and soft tissue surface will lead to signal loss or fat-water “swapping”. Which serious impacts on MR image quality. Periodically rotated overlapping parallel lines with enhanced reconstruction(Propeller) scanning technique, acquire images using a specific filling pattern to collect data spirally by radial blades till all data in K space are acquired. Propeller technique reduces signal loss artifacts caused by magnetic-susceptibility at a great extent.

Methods

A total of 30 patients were performed routine sinus MR examination (17 males and 13 females, age:51.9 ± 16.5) were enrolled in this study with ethic committee approved. underwent Propeller T2WI and the images were compared with IDEAL T2WI sequence. An eight-channel head coil was used for axial Propeller T2WI sequence of the sinus: TR 4058ms, TE 115 ms, slice thickness 5 mm, slice gap 1.5 mm, bandwidth 50KHz, Field of view 24 cm×24 cm, No.of excitation 3, and scanning time 97 s; axial IDEAL T2WI sequence: TR 2225 ms, TE 69.3 ms, scanning matrix 384×224, bandwidth 62.5KHz, Field of view 24 cm×18 cm, slice thickness 5 mm, slice gap 1.5 mm, No.of excitation 3, scanning time 135 s. Images were evaluated using a 4-point Likert scale (1, nondiagnostic; 4, outstanding).Bland-Altman analysis was used to analyze the consistency of image quality score of two observers（95% LOA）.The data were analyzed by SPSS 17.0 statistical software, and the samples were compared by non-parametric statistics. The results were compared with the Wilcoxon paired sign rank test, and the results were compared by the Friedman test. P <0.05 was considered as statistically significant.

Results

The signal loss artifacts of 30 cases were significantly reduced by Propeller T2WI scanning, and the SNR and CNR, image quality were significantly improved, and pathological changes were well presented on the images (Figures 1,2).It is seen that the difference of the quality grading of sinus images obtained was within the 95% consistency interval, and the two observers showed good consistency(Figures 3). (P <0.001).The total scores for Propeller T2WI and IDEAL T2WI images, respectively, were as follows: 115 and 81. Statistically significant difference was observed between Propeller T2WI and IDEAL T2WI (Z=-4.540，P=0.000).

Discussion

MRI has become an important medical imaging approach in sinus. How to reduce signal loss artifacts caused by magnetic susceptibility, and how to acquire MR images meeting the demands for diagnosis are important. Magnetic susceptibility artifacts appear in boundaries of different magnetic substances such as the sinus,which including bone, gas and soft tissue surface. Because magnetic susceptibility is different, these substances will produce varied magnet effects after entering magnetic field, and the regional uneven magnetic fields will lead to signal loss in the tissue surfaces. and magnetic susceptibility artifacts are increased with magnetic intensity. Propeller technique employs spiral data collection, which fills the data in k-space using a leaf blade with certain thickness. During k-space filling, the center of the blade was fixed, rotated along one direction, and connected with other blades to form an integral circle. Therefore, the data collection of every time can correct signal loss artifacts, During once data collection, although the blade only rotates a period, the data in central region of k-space is sampled for every strip. Therefore, during once data collection, the SNR and CNR of Propeller T2WI are significantly higher than IDEAL T2WI. Propeller technique producing high-resolution images with no signal loss artifacts, which are significant for clinical diagnosis

Acknowledgements

The authors thank zha yun fei,PhD, for her assistance