Gradient

Gradient is a term used in mathematics and physics to describe a directional rate of change. In the context of medical imaging, a gradient often refers to a magnetic field gradient used in Magnetic Resonance Imaging (MRI).

Definition

A gradient is a vector field that points in the direction of the greatest rate of increase of a scalar field, and whose magnitude is that rate of increase.

In Medical Imaging

In medical imaging, particularly in Magnetic Resonance Imaging (MRI), gradients play a crucial role. The gradient fields are used to spatially encode the location of signal from the patient. This is achieved by superimposing a linear gradient field on the static magnetic field. This results in a variation in magnetic field strength depending on the position within the field. The variation in magnetic field strength allows for the spatial encoding of signal.

Gradient Coils

Gradient coils are used in MRI machines to create the gradient fields. These coils carry a current of electricity, creating a magnetic field that varies linearly across the imaging volume. The gradient coils are typically located within the bore of the magnet and are driven by dedicated amplifiers for each gradient axis.

Gradient Strength

The strength of a gradient is measured in milliteslas per meter (mT/m). The strength of the gradient field determines the resolution of the image; stronger gradients allow for higher resolution imaging.

Safety Concerns

The rapid switching of gradient fields can cause peripheral nerve stimulation, which can be uncomfortable for the patient. Additionally, the gradient fields can induce currents in conductive materials, including implanted medical devices such as pacemakers.

See Also

• Magnetic Resonance Imaging (MRI)
• Medical Imaging
• Physics
• Mathematics

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