Assignment 4 (Ch5) review

Flashcards about MRI coding and spatial encoding

Why is locating the signal in three dimensions important when coding an MRI?

You can't create an image without locating the signal from different parts of the body.

What is a pixel in the context of imaging?

A two-dimensional element of a picture.

What is a voxel?

A three-dimensional pixel.

What role do gradient coils play in spatial encoding?

They perform it, meaning they are charged with locating the signal in three dimensions.

How are gradient coils oriented in the MR system?

In the x, y, and z directions.

How does altering the main magnetic field (B0) using gradients affect Larmor frequency?

Gradients create a grade of change in B0, leading to a grade of change in precessional frequency according to the Larmor equation.

What is the effect when gradients affect B0?

They increase the magnetic field on one side and decrease it on the other, creating a grade of change.

What is the magnetic isocenter and why is it important in MRI?

It's the center of the magnet (B0) and the center of the gradients. The gradients are oriented in such a way that their center falls at the isocenter.

How do gradient amplitude and slope affect the MR signal's spatial location?

They cause a grade of change in precessional frequencies, enabling the mapping and pinpointing of nuclei based on their differences in precessional frequency in all three directions (x, y, z).

What do physical gradients refer to?

How the gradients are physically oriented in the magnet (x, y, and z directions).

What are logical gradients?

The same three gradients (as physical gradients) named based off their function: slice select, phase, and frequency.

What is the function of the slice select gradient?

Helps us select slices.

What does the phase encoding gradient control?

Controls (or determines) the phase of the nuclei per TR.

What does the frequency encoding gradient control?

Controls the precessional frequency shift during echo collection.

How does the change in precessional frequency along a gradient access help determine the position?

If there's a difference in precessional frequencies, we can map those out and pinpoint the location based on gradients activated in different directions.

How is a grid created from change in processional frequency?

Changes in precessional frequency is mapped in different directions allowing the accurate picture of the anatomy.