| Objective: The chemical shift in/opposed phase imaging of Magnetic Resonance (MR) is a technique which has the ability to detect small amount of fat in the lesions. The fat content in lesions was highly correlated to the decreased signal intensity on the opposed-phase image. We established in vitro fat-water chemical-shift opposed-phased imaging phantom on 1.5T and 3.0T MRI scanner in order to evaluate the relationship between the lipid fraction and the SI index in the phantom and to demonstrate the exact fat content when the lowest signal intensity on the opposed-phased image.Materials and methods: The phantom was made up of water and salad oil,2 measurements were performed on the phantom using FSPGR to achieve the in/opposed phase images.1. A 20mm oblique slice was chosen at the fat-water interface which sliding along from left to right, according to the geometry, there was a linear change in fat/water from one end of the long axis of the phantom to the other end which can demonstrate the continuous variation of signal intensity with the fat content changing. Signal intensity evaluation of different fat-water values was measured by placing continuous, square-shaped regions of interest of 180mm2 along the phantom.2. Images were obtained in the 20mm transverse plane chosen at the fat-water interface, which was contained 0%,5%,10%,15%,20%,25%,30%, 35%,40%,45%,50%,55%,60%,65%,70%,75%,80%,85%,90%,95% and 100% fat fraction. Quantitative SI changes between in-phase and opposed-phase images of two methods were measured, and SI index were calculated as follows: SI index=(SIIP-SlOP)/Slip where Slip is SI on in-phase images and Slop is SI on opposed-phase images. Then fat fraction versus SI on in-phased and opposed-phased images and SI index were figured.Results: Two methods both showed: The signal intensity on the opposed-phased images continuatively decreased when the fat content was comparatively low, and then kept increasing with the fat content increasing. On 3.0T scanner the first method demonstrated the inflection range was within 36%-42%, in order to achieve the exact point of the lipid fraction, we use the density equipment to scale the darkest portion on the opposed-phased image, the inflection point was 39%. The second method showed the inflection range was at 35-40% of the fat content, but the exact point could not obtained. On 1.5T scanner showed the inflection range was at 29% of the fat content.Conclusions:We initiated the in-and opposed-phased phantom in domestic, and improved on the phantom overseas. The feature of the phantom was:in one image, the continuous variation of signal intensity with the fat content changing can be observed very clearly, thus advanced this technique application clinically.1. This experiment contained sufficient basis of theories, and compared with former cultural heritage. Its result was more dependable and precise, namely the fat contain was within 39%, the signal intensity on opposed-phase image decreased with the fat fraction increasing; the fat contain was above 39% the signal intensity on opposed-phase image decreased with the fat fraction increasing. On 1.5T scanner showed the inflection range was at 29% of the fat content.2. We adopted another methods similar to the primary research to demonstrate the result: when the fat content was low, the signal intensity on the opposed-phase decreased rapidly and then it would increase with the fat content increasing. The result was resemble to the first one, but the exact inflection point could not be achieved. It was more confirmed that the first method we used was better than the others. |
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