MRI102 week4 5-27 Ch5

Flashcards about MRI gradients, spatial encoding, and related concepts, based on lecture notes.

What are gradients in MRI?

Hardware used to locate signals within the body during an MRI scan.

What is the purpose of mapping signals during an MRI?

Mapping out where signals are coming from in order to generate a proper image.

What is spatial encoding?

The process of locating a signal from any given point in the anatomy being scanned.

What are gradient coils?

Cylindrical electromagnets used for spatial encoding.

What do gradients do?

They generate magnetic fields themselves; there are three of them.

What are the three gradients in MRI?

X, Y, and Z.

How are the X, Y, and Z gradients named?

Based on the direction in which they generate a magnetic field.

What direction does the X gradient go?

Right to left.

What direction does the Y gradient go?

Anterior to posterior.

What direction does the Z gradient go?

Superior to inferior (head to foot).

How do gradients help with spatial location?

They alter the main magnetic field (B0) in a linear fashion.

What is isocenter?

The center of the magnetic field where the gradients don't change the field strength.

Why do we alter B0 with gradients?

They create a graded Larmor frequency across the anatomy being scanned.

What is gradient amplitude?

Determines the rate of change in B0.

What are the logical names for gradients based on their function?

Slice select, phase encoding, and frequency encoding.

What does the slice select gradient do?

Locates the slice within the scan plane.

What does the phase encoding gradient do?

Spatially locates the signal along the short axis of the anatomy.

What does the frequency encoding gradient do?

Spatially locates the signals along the long axis of the anatomy.

Briefly describe the spatial encoding process.

Locating a slice and then locating the signal within the slice.

What performs spatial encoding?

The gradients.

Why are there 3 gradient coils, labeled X, Y, and Z ?

Because there are three of them.

What is the function of gradient coils?

They generate magnetic fields and alter the main magnetic field (B0).

What do gradients affect by altering the magnetic field?

The processional frequency of hydrogen nuclei.