MRI102 week5 6-3 Ch5 - part 2

Flashcards about MRI gradients

What is the function of gradient coils in MRI?

They apply a gradient along the magnetic field.

What is magnetic field strength usually between in clinical imaging?

Between one and three Tesla

How do gradients manipulate the main magnetic field (B0)?

It manipulates the main magnetic field (B0) by increasing or decreasing its field strength in opposite directions.

What term describes locating the signal in three dimensions using gradients?

Spatial encoding or localization

What are the functions of gradients in MRI?

Slice selection, phase encoding, frequency encoding, and dephasing and rephasing nuclei

What does spatial encoding mean?

That the gradients locate the signal in three dimensions

Why would you change the phase encoding and the frequency encoding?

They create a map of phase changes and frequency changes, so that every point has a unique phase and frequency

What is the direction of the z gradient in an MRI scanner?

The length of the tunnel or bore

What is another way to describe the direction of the Z gradient?

Head to foot or superior to inferior

What direction is the x gradient?

Right to left

When viewing images on the monitor, why are the right and left sides mixed up?

Because you have to think of the image swapped, based on the patient's positioning.

What direction is the y gradient?

Anterior to posterior

What is the isocenter in MRI?

The smack dab center of the bore, B0, and gradients

How is gradient strength represented or displayed?

Represented as a slope

What does a steep slope or high amplitude gradient imply?

Implies that the gradient is strongly applied and is manipulating B0 to a great degree.

Does the MRI tech set how strong the gradient is?

The MRI tech inputs extrinsic paramters into scanner, and the computer configures the gradient strength automatically.

Explain a slice select gradient

Slice select varies based on the plane you are scanning in.

What are the imaging planes in MRI?

Coronal, sagittal, and axial or transverse.

In MRI, what is a localizer?

A grainy, low resolution starter image used to set up actual planes and slices

What gradient behaves as the slice select gradient if you want axial slices?

Z gradient

What gradient behaves as the slice select gradient if you want coronal slices?

Y gradient

What gradient behaves as the slice select gradient if you want sagittal slices?

X gradient

What is the alphabetical (and then reverse alphabetical) order of slice select gradients?

Z gradients, then Y gradients, the X gradients

When does the slice select gradient activate?

When an RF pulse is transmitted.

What does selectively exciting the nuclei mean?

Only one slice is excited at a time; adjacent slices do not get excited

What does the slice select gradient do?

It divides the anatomy into slices and allows only one slice to get excited at a time.

How does the slice select gradient determine the slice thickness and the slice gap?

By determining the slice thickness and the slice gap.