Chemical shift imaging

As mentioned earlier, chemical shift imaging, oil and water protons in the oscillation frequency are based on the difference. Methylene peak oil, peak water with this method, the relative chemical shift between the TE is determined according to phase in and out, and accordingly (IOP) is generated images. This relative chemical shift, 1.5T unit, the body temperature of -217 Hz. According to the oil molecules in water are 217 Hz slower than water and fat signals from the 1.5 T unit to be in the same direction every 4.6 msec, 2.3 sec in the opposite direction makes a. Accordingly, the total signal in-phase images obtained in water + fat, out-phase images can be obtained from water-fat signal. Out-of-phase images faz'a fat tissue contains relatively watched shows loss of signal.


In 1984, the two-point method described by Dixon for the first time the magnetic field (B0) to avoid the sensitivity of the technique in 1991, Glover 3 three-point method developed by adding an image. This method is reported on the many different studies and to reduce the effects of this method is not only B0 at the same time receive a combination of water and fat images that contain information for the quantitative measurement of oil has shown promise. Colleagues carried out by the first comprehensive noise analysis work, "Fast Spin Echo" (FSE), 3-point water-fat separation appropriate examination of water and oil phases-n / 6, n / 2, 7H / 6 phase has been shown to . However, the calculation of the appropriate amount of fat present in the liver, but all of the deviations from MR images can be corrected. These deviations and the correction methods are as follows:


1. Prediction of T1: T1-weighted viewport long T1 relaxation of the proton (water), the shorter one (oil) increases the signal. To eliminate this effect should reduce the weight of the T1 image and the flip angle (FA), achieved by 5 °.


2. T2 * (T2 relaxation time appears) impact: Oil-water separation methods such as T2 * effect leads to the use of different echo times. Especially this effect increases the accumulation of iron and may lead to incorrect measurements. For this reason, examination, T2 * is done by calculating correction.


3. Spectral complexity of the oil: NMR spectrum of the peak of the oil is at least 6 must be evaluated and appropriate for the calculation of the peaks of all the oil.


4. Noise prediction: Separate oil and water is calculated as the images of the errors that may occur when bringing together in order to calculate the percentage of fat. This phase also developed by Liu and colleagues, or magnetic separation techniques limited.


5. Vortex: Different from the complex in gradient echo times lead to a rapid opening and closing phase, it can distort the calculation of the percentage of fat. This effect was also developed by Yu and colleagues solved with hybrid-complex magnetic approach.


Developed with the chemical shift correction of the effects described by the effect of oil-water separation methods described in the last one-quant method IDEAL MR.