In Vitro Phantom Study of Chemical Shift Opposed-Phased Imaging on 1.5T and 3.0T
|School||Tianjin Medical University|
|Course||Medical Imaging and Nuclear Medicine|
|Keywords||Magnetic resonance imaging Chemical shift Model|
Objective: MRI chemical shift with anti-phase imaging can contain a considerable amount of fat and water components of the lesion or tissue-specific imaging techniques. The fat content of the tissue or lesion can produce the signal dropped its key factors related to the anti-phase, this study attempts with by 3.0T and 1.5TMR devices, anti-phase check vitro model to explore different equipment on signal strength changes and fat content of the anti-phase correlation, significant decrease of the signal on the exact fat content of the standard and to determine an anti-phase, and that the clinical application of this technique to provide better experimental basis. Materials and Methods: Take a rectangular plastic tanks, inside diameter size of 20cm X 8cm X 6cm. Slowly pour the distilled water 300ml and 300ml salad oil has made the same anti-phase model. Prepared above water - fat, anti-phase imaging model is placed in the same phase GE Signa HDx 3.0T and GE Excite Ⅱ 1.5T MRI machine using a fast spoiled gradient echo sequence (FSPGR), respectively, the line of the model (in -phase, IP) and anti-phase (out-phase, OP) imaging. Two devices first method checks: in order to continuously observe the different water - lipid content with an anti-phase change of the signal intensity on the inclined surface of the layer thickness of 20mm in the the water - Grease interface taken MRI with anti-phase one end of the scan, it is completely water, while the other end as an oil, and so one end of the model along the major axis to the other end of the water - lipid content rendered linear changes. In MRI with the anti-phase image corresponds to take continuous square interest the District (ROI), each the size of an ROI is 180mm2, the ROI were measured MRI signal intensity (SI), to calculate the signal intensity decreased index (SI index), Plot graph of the fat content and the SI, and the SI index. 3.0T apparatus further second method checks: in water - grease at the interface is to take 20mm thick, respectively mobile level center position, so that the levels formed within 0%, 5%, 10%, 15%, 20%, 25 %, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% and 100%, 21 different The proportion of water - oil content. Were each water - level of lipid levels in the same anti-phase imaging, measured 21 group of images in the same anti-phase image on the signal intensity (SI) values ??to calculate the signal strength falling index (SI index), draw the fat content and the SI, and the SI index graph. Model the degree of decline in anti-phase imaging signal the sI index: SI index = [(Si-SI of the phase with an anti-phase) / (SI same phase)] × 100% Results: The two methods are shown in the initial fat lower proportion to increase the signal strength of the anti-phase with the fat content showed a gradual decline in performance, when the fat ratio reaches a certain level, the signal strength is increased as the fat content increases. At 3.0T, the first method to this change inversion range is equivalent to 36% -42% of the fat content. Order to obtain relatively accurate reversal point of the fat content corresponding to this change in the image of the fat content in the range of 36% -42% of the anti-phase, the use of the densitometer to measure the lowest point of the image gray obtained results of the fat content of 39 %; while the second method is equivalent to the fat content of this change Inversion range 35% -40%, compared with the first method, the reversal point is difficult to be accurately measured. The first method displays the reversal point of this change is equivalent to 29% of the fat content at 1.5T. Conclusion: This study is the first time in the domestic application of 3.0T MR chemical shift with anti-phase experimental model with 1.5T MR chemical shift with anti-phase comparator. Characteristics of the experimental model, to select a single inclined level, the level ministries water - the fat percentage was a continuous linear variation in water - lipid interface;, respectively obtained on the same image signal in the same anti-phase imaging strength with a continuous change of the fat content of drift, so that the same, the correlation characteristics of the anti-phase imaging and fat content clearly show, more intuitive, easy to understand, and thus contributing to the clinical application of this technology. Has its theoretical basis of an experimental model in this study, compared to the previous literature, the results are more precise, i.e. the fat content is less than 39% at 3.0T in anti-phase on the signal strength decreases with the degree of significant increase in the fat content increases from time to time when the fat content of more than 39%, the extent to which the signal intensity decreased with increasing fat content decreases; at 1.5T on this change reversal point is equivalent to 29% of the fat content . 2 of this study Another experimental method i.e. in water - Grease interface respectively mobile level center position, to obtain different water - the fat content of the same anti-phase images, and is similar to the design model of the previous literature, the results also shows that when the fat content is relatively low, the anti-phase to the degree of decrease of the signal intensity is increased as the fat content increases, and when the fat content is relatively high, the degree of decline in anti-phase signal intensity decreases with increasing fat content , but is difficult to accurately obtain the position of the reversal point, which further demonstrates the experimental model of the deficiencies of the previous literature.