Pulse Design for Parallel MR Transmission Outline Kspace analysis of small tipangle excitation RF shimming and Parallel MR Transmission B 1 mapping Accelerated MR excitations Homogeneity and SAR minimization ID: 277431 Download Presentation
RF Coils’ Evaluation. Outline. Quality factor of an RF coil. Definition of SNR. Determinants of SNR in MRI. Methods to measure SNR in MRI. Ultimate intrinsic SNR. Coil performance maps. Quality Factor.
The Fourier Transform. Development of Fourier Analysis. In 1748 Leonhard Euler used linear combinations of “normal modes” to describe the motion of a vibrating string. If the configuration at some point in time is a linear combination of normal modes, so is the configuration at any subsequent time.
Receive Arrays. Receive Arrays Are Critical in MRI. Advantages. SNR. Speed (parallel MRI). Volumetric coverage. Image quality. Simplicity. Disadvantages. Cost. Complexity. Data load. …. How many elements do we need?.
Volume and Surface Coils. MR Coils. An MR coil is an inductor capable of producing and/or detecting a time-varying magnetic field. It can be represented as an inductance . L. , with a series resistance .
Gradients (Continued), Signal Acquisition and K-Space Sampling. Spin Echo and Gradient Echo. When the . prephasing. gradient is applied the spins accumulate phase (differently with location). After the 180° pulse, they will continue to accumulate phase under the influence of the readout gradient and will refocus at the echo time..
Basic pulse sequences. Gradient Echo (GRE). A class of pulse sequences that is primarily used for fast scanning. 3D volume imaging. Cardiac imaging. Gradient reversal on the frequency-encoded axis forms the echo.
Magnetization, . Relaxation, Bloch Equation, . Basic Radiofrequency . (RF) Pulse Shapes. Felix Bloch. “ The magnetic moments of nuclei in normal matter will results in a nuclear paramagnetic polarization upon establishment of equilibrium in a constant magnetic field. It is shown that a radio-frequency (RF) field at right angles to the constant field causes a forced precession of the total polarization around the constant field with decreasing latitude as the .
Pulse Design for Parallel MR Transmission. Outline. K-space analysis of small tip-angle excitation. RF shimming and Parallel MR Transmission. B. 1. mapping. Accelerated MR excitations. Homogeneity and SAR minimization.
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G16.4427 Practical MRI 1
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G16.4427 Practical MRI 1
Pulse Design for Parallel MR TransmissionSlide2
K-space analysis of small tip-angle excitation
RF shimming and Parallel MR Transmission
Accelerated MR excitations
Homogeneity and SAR minimizationSlide3
K-Space Interpretation of Small Tip Angle Excitation
New point of view for analyzing selective excitation
Similar approach as that of data acquisition and reconstruction
Strictly valid only for small tip angles excitations but holds also for flip angles ~ 90°
Bloch equation in the rotating frame
(parametrically describes a path through the spatial frequency space)
Parametric description of the unit-weight trajectory (