How do you choose phase encoding?

Three factors are considered in selecting phase- and frequency-encode directions: 1) reducing artifacts, 2) minimizing scanning time, and 3) accommodating restrictions imposed by coil design or parallel imaging. The phase-encoding direction is associated with two major artifacts: wrap-around and flow/motion.

What does phase mean in MRI?

Spatial encoding in MRI The second step of spatial localization is called phase encoding. A magnetic gradient field is applied briefly in one direction. As the change in frequency is very brief, when the gradient is switched off, it causes a change in phase that is proportional to the distance.

What is the purpose of the phase encoding gradient?

The phase encoding gradient is used to position the spin system at a specific line in k-space. Application of the frequency encoding gradient and recording signal as a function of time moves the spin system across a line in k-space.

What is spatial localization in MRI?

Spatial localization is based on magnetic field gradients, applied successively along different axes. Magnetic gradient causes the field strength to vary linearly with the distance from the center of the magnet.

Why does adding more phase encoding steps lead to more lines in k space?

The number of phase encoding steps are selected by the technologist. This means that need to active our phase encoding gradient as many times as the selected phase encoding value in our image matrix. Therefore, when increasing the image matrix, we are adding more lines to our K space increasing our resolution.

How do MRI gradients work?

Gradients are simply loops of wire or thin conductive sheets on a cylindrical shell that lies just inside the bore of an MRI Scanner. When an electrical current passes through these coils, the result is a secondary magnetic field. This gradient field distorts the main magnetic field in a slight but predictable pattern.

What does in and out of phase mean in MRI?

In-phase (IP) and out-of-phase (OOP) sequences correspond to paired MRI gradient echo (GRE) sequences obtained with the same repetition time (TR) but with two different echo time (TE) values.

What is in phase out of phase?

If two things are happening in/out of phase they are reaching the same or related stages at the same time/at different times.

How do gradient coils work in MRI?

What directions should the slice phase and frequency encoding gradients be applied in?

What directions should the slice, phase, and frequency encoding gradients be applied in? The slice selection gradient must be perpendicular to the imaged plane, or along y. The phase encoding gradient can be along either z or x. The frequency encoding gradient is along the remaining direction x or z.

How does the scanner know the locations of all the MR signals?

Proximity to surface receiver coils provides information about a voxel’s position. Coils near a voxel record stronger signals than coils farther away. This difference in signal intensity among receiver coils can be used as an aid to signal localization.

What is phase encoding and frequency encoding in MRI?

– Phase Encoding • You have to encode 1 of 2 dimensions within the slice. – Frequency Encoding (aka readout) • You have to encode the other dimension within the slice.