Description of how MRI sequences spatially encode nuclei in the read and phase direction
Differences that occur in an induced magnetization in biological tissues in a magnetic field cause image contrast in MRI. A signal measured by the receiver coils is the integral of an induced magnetization over the whole imaged volume. To construct a three-dimensional distribution of magnetization, a spatially varying field pattern is generated in the volume, such that voxels at various parts generate a signal that is tagged with data on the location. Standard techniques for spatial encoding in MRI create high-quality images.
In magnetic resonance imaging technique, two main methods (SVD MRI and SMASH MRI) are used to modify the k-space sampling to reduce the encoding steps reducing the total acquisition time of the image. The SVD MRI improves the imaging time in situations where numerous pictures of the same patient are acquired. SMASH MRI is based on parallel acquisition by the use of several receiver coils at the same time. SMASH is created with speed-up factors of up to six on cardiac and other images.
The slice signals are then recorded on the K-space and processed to create an image of the slice plane. Reading of the signal by the spatial frequency encoding takes only milliseconds. The phase spatial encoding involves subsequently imaging the sequence. One phase encoding step in a spin echo sequence occurs in every repetitive time (TR). As the TR, values can be of up to three seconds where the phase encoding is longer that frequency encoding (Bright, 2011).
Application of frequency encoding gradient is the final step in spatial encoding once the signal is received in the last direction. This modifies the frequencies in a horizontal direction throughout the encoding period.
Discussion of how two Fourier transforms are required to convert k-space data to an image
A Fourier transform is a mathematical technique for converting a time domain data into a frequency domain data. An inverse Fourier transform is the reverse of Fourier transform, that is, changes from the frequency domain to time domain. It is a principal method of decomposition of cofounded sign and complicated signal that enables mathematicians to discover the frequency and amplitude properties of a signal. A Fourier change is the operation that changes over capacities from time to time. During the creation of MRI images, the Fourier transform determines the frequency and stage MR flags that form K-space (Mangrum, 2012). On the other hand, the two-dimensional opposite Fourier change of the K-space is the MR image seen. A grip of the Fourier transform is the fundamental to comprehension a few MR antiques and procedures for sign procurement in the modern world.
References
Bright, A. (2011). Planning and Positioning in MRI. Sydney, Churchill Livingstone Elsevier. Mangrum, W. (2012). Duke review of MRI principles. Philadelphia, PA, Elsevier/Mosby.
