MRES7004 Essay Example | Topics and Well Written Essays - 2250 words

MRES7004 - Essay ExampleThe practise of the sequence produces a FID which is rent to get the gradient required. Multiple frequencies argon produced as the read gradient is applied. The variation of frequencies is linearly connected. The total change of frequency experienced depends on the authority within the gradient. After the FID is acquired, it is treated with a Fourier transform. This produces a spectrum that displays peaks corresponding to different frequencies. The sum total of all signal intensity set at ane single place of observation become individual peaks. A one dimensional quantity is produced by the application of the read gradient as it is supreme of time. (Weishaupt et al., 2006) Phase Direction Encoding A phase gradient is applied after applying a read gradient and slice selection. This is otherwise known as phase encoding and tends to increase the nucleis frequency such that it precesses at different angles that all match up with the Larmor frequency. The incr ease of frequency due to the application of a phase gradient directly impacts the total phase change displayed by nuclei. However there is a need to discern different nuclei which throne be done by the application of Fourier transforms. (Westbrook et al., 2005) Question Two Using the Fourier transforms helps to convert the available data from the time domain to the frequency domain. This can and then be utilised to form two dimensional or three dimensional run intos based on available data. Data is spatially encoded before become a part of the k space and so its position within the k space can be determined accordingly. Application of the first Fourier transforms back up in interpreting the data values that were encoded in the read direction. This is useful in identifying the frequency (alternatively signal intensity) within the level selected for the application of the read gradient. This makes it easy to differentiate the positions within the k spaces horizontal trajectory. The data obtained in this way has its units changed from m-1 to m. Consequently only a one dimensional image is formed. (Woodward, 2001) Application of the second Fourier transform helps to differentiate various frequencies that were encoded along the phase direction after the application of a phase gradient. This transform separates all the values and lists them accordingly. The vertical k space trajectories are dealt with this transformation. The units again change from m-1 to m and the resulting image becomes two dimensional. (IMAIOS, 2009) The total k space contains data encoded from two directions that are the read and the phase directions. The read directions data is displayed as horizontal trajectories in the k space while the phase directions data is displayed as vertical trajectories in the k space. Fourier transforms aid in creating a complete two dimensional image of the concerned nuclear reel densities in relation to the slice positions. (Hashemi et al., 2004) Question Three Various experimental factors affect transverse spin coherence as well as the k space. These factors and their effects are listed below. Radio Frequency Pulse A radio frequency pulse at 90o is utilised along with the chief magnetic issue to produce magnetism such that the Z direction vector reorients itself into the X plane the Y plane. The magnetism produced is subsequently de-phased both in the X plane and the Y plane. This requires one more re-phasing at 180o. Read Gradient Read