By Gerrit Schultz
Within the earlier few a long time MRI has turn into essentially the most vital imaging modalities in medication. For a competent prognosis of pathologies additional technological advancements are of basic value. This examine bargains with a appreciably new strategy of photo encoding. Gradient linearity has ever because been an unquestioned technological layout criterion. With the appearance of parallel imaging, this strategy might be wondered, making method of a lot a extra versatile gradient that makes use of encoding fields with an arbitrary geometry. The theoretical foundation of this new imaging modality – PatLoc imaging – are comprehensively awarded, compatible photograph reconstruction algorithms are constructed for a number of imaging sequences and imaging effects – together with in vivo information – are explored in accordance with novel designs.
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Within the earlier few a long time MRI has turn into the most vital imaging modalities in drugs. For a competent analysis of pathologies extra technological advancements are of fundamental value. This research bargains with a extensively new process of picture encoding. Gradient linearity has ever due to the fact that been an unquestioned technological layout criterion.
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Extra info for Magnetic Resonance Imaging with Nonlinear Gradient Fields: Signal Encoding and Image Reconstruction
G. 2 in ) are therefore of great interest to the RF engineer with important consequences for the optimal coil geometries. At the same time, the coils should be placed as near as possible to the measured object in order to enhance the SNR. These and other concerns explain why modern whole-body MR scanners are often equipped with a multitude of different RF-receiver arrays, where each array is optimized for a different medical application. For example, there are cardiac, spine or knee arrays.
For a constant ﬁeld B0 ez the energy levels E(m) are, according to Eqs. 2, given by: E(m) = m γB0 , where m is the quantum number of the z-angular momentum Sˆz . In NMR, the Boltzmann factor B = γB0/kB T is typically only about 10−5 . Therefore, the exponentials in Eq. 6 can be simpliﬁed using a Taylor series expansion and for a spin 1/2 system with only two Zeeman states (m = ±1/2) the equilibrium density operator reduces to: 1 2 σ ˆ eq = + 14 B 0 1 2 0 . − 14 B The initial magnetization M eq is then found with the relations presented in Eqs.
21) V This phase factor can be manipulated by the gradient ﬁelds in two different ways: application of a gradient ﬁeld during signal readout or before. Reconsider Fig. 7b. There, it is shown that the application of a SEM during signal readout alters the frequency content of the signal. Therefore, this strategy is denoted as frequency encoding. The frequency content is different only for spins experiencing a different ﬁeld strength - therefore localization with pure frequency encoding is only feasible along one spatial direction.