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High performance gradient coils used in MRI are typically capable of producing a gradient magnetic field of approximate 30 mT/m or higher for a 1.5 T MRI. The slew rate of a gradient system is a measure of how quickly the gradients can be ramped on or off. Typical higher performance gradients have a slew rate of up to 100–200 T·m −1 ·s ...
A Maxwell coil is a device for producing a large volume of almost constant (or constant-gradient) magnetic field. It is named in honour of the Scottish physicist James Clerk Maxwell . A Maxwell coil is an improvement of a Helmholtz coil : in operation it provides an even more uniform magnetic field (than a Helmholtz coil), but at the expense of ...
It is also the term that is behind MRI: it is generated by the gradient coil system. The i γ B xy ′(t) M z (t) describes the effect of RF field (the B xy ′(t) factor) on nuclear magnetization. For an example see below. - M xy ′(t) / T 2 describes the loss of coherency of transverse magnetization.
Equation for calculating the slew rate and accompanying diagram. In general, real time MRI relies on gradient echo sequences, efficient k-space sampling, and fast reconstruction methods to speed up the image acquisition process. [11] Gradient echo sequences present shorter echo times since only one RF pulse is required for each sequence. [12]
The three coils are driven with each set 120 degrees in phase from the others. For the purpose of this example, the magnetic field is taken to be the linear function of the coil's current. The result of adding three 120-degree phased sine waves on the axis of the motor is a single rotating vector that always remains constant in magnitude. [ 17 ]
For an open surface Σ, the electromotive force along the surface boundary, ∂Σ, is a combination of the boundary's motion, with velocity v, through a magnetic field B (illustrated by the generic F field in the diagram) and the induced electric field caused by the changing magnetic field.
A Helmholtz coil Helmholtz coil schematic drawing. A Helmholtz coil is a device for producing a region of nearly uniform magnetic field, named after the German physicist Hermann von Helmholtz. It consists of two electromagnets on the same axis, carrying an equal electric current in the same direction. Besides creating magnetic fields, Helmholtz ...
Nuclear magnetic resonance (NMR) experiments are often performed with surface transceiver coils that have desirable sensitivity, but have the disadvantage of producing an inhomogeneous excitation field. This inhomogeneous field causes spatial variations in spin flip angles, which, in turn, causes errors and degrades the receiver's sensitivity.