Gradient Coils: Types and Function PDF

Gradient Coils: types and function Hayder Jasim Taher PhD of Medical Imaging Outline of my presentation ✓ Gradient Coil. ✓ RF coils. ✓ Volume coils. ✓ Surface coils ✓ Phrased Array coils  Gradient Coil These are used to produce deliberate var...

Gradient Coils: types and function Hayder Jasim Taher PhD of Medical Imaging Outline of my presentation ✓ Gradient Coil. ✓ RF coils. ✓ Volume coils. ✓ Surface coils ✓ Phrased Array coils  Gradient Coil These are used to produce deliberate variation in the main magnetic field(Bo). There are usually three sets of gradient coils, one for each direction. The variation in the m.f permits localization of image slices as well as phase encoding and frequency encoding. These sets of gradient coil for the z-axis are helmholtz pairs, and for the x and y axes are paired saddle coils. 3  How gradient coils are produced? Magnetic field strength is proportional to the amount of current passed through the loop of wire, number of loops in wire, the size of the loop and how closely the loops are spaced. By changing these parameters coil can be produced, which increases or decreases magnetic field strength in particular direction. Gradient strength (stiffness) is measured in units of G/cm or mT/m. This means that the magnetic field strength changes by one Gauss over each centimeter or 10 milliTesla over each meter. Stronger gradients (15 or 20 mT/m) allow high speed and high resolution imaging  How gradient coils are produced? Gradient coils are a set of wires in the magnet, which enable us to create additional magnetic fields, which are, in a way, superimposed on the main magnetic field B0. There are 3 sets of wires. Each set can create a magnetic field in a specific direction: Z, X or Y. When a current is fed into the Z gradient, then a magnetic field is generated in the Z direction. 5 How gradient coils are produced? 6  How gradient coils are produced? Gradient coil provide linear gradation or slope of the magnetic field strength from one end of the solenoid to the other end. The gradient are applied by passing current through the gradient coil in certain direction. This either increases or decreases the magnetic field on either side of isocentre. The magnetic field, which is generated, is very strong. Although the gradient coils are very tightly fixed in a kind of resin, the forces, exhibited by the gradient coil, are enough to make them vibrate, hence the noise.  How gradient coils are produced? Figure shows schematically how the 3 gradient coils form a cylinder. This cylinder is then placed in the magnet bore. 8 MR systems use three sets of gradient coils the x-, y- and z gradients.