MRI Image Processing Fundamentals

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Questions and Answers

What determines a T1-weighted image?

Repetition Time (TR) (correct)

Time to Echo (TE)

Length of RF pulses

Signal decay rate

A longer TR allows for better differentiation between tissues in T1-weighted imaging.

False

What is the time between the delivery of the RF pulse and the receipt of the echo signal called?

Time to Echo (TE)

If TR is ____, tissue A and B cannot be differentiated due to equal longitudinal magnetization.

long Signup and view all the answers

Match the following terms with their definitions:

TR = The time between successive RF pulse sequences applied TE = The duration from RF pulse delivery to echo signal receipt T1-weighted imaging = Determines tissue contrast based on longitudinal relaxation T2-weighted imaging = Focuses on transversal relaxation differences Signup and view all the answers

What is one way to alter the slice thickness during imaging?

By changing the band width of the RF pulse Signup and view all the answers

The frequency encoding gradient is applied along the x-axis.

False Signup and view all the answers

What is the main purpose of the slice selection gradient?

To excite the protons in the specific slice intended for imaging. Signup and view all the answers

What effect does a 180-degree pulse have on protons during a Spin Echo sequence?

Protons change direction and become in phase. Signup and view all the answers

A longer TE results in a stronger spin echo signal.

False Signup and view all the answers

To increase image resolution, one can use a ______ slice, given there are enough protons.

thinner Signup and view all the answers

Match the following gradients with their functionality:

Slice selection gradient = Excites specific slice of protons Frequency encoding gradient = Applies different precession frequencies along y-axis Phase encoding gradient = Creates varying frequencies along x-axis Gradient field = Modifies strength of the magnetic field Signup and view all the answers

What is the purpose of a 90-degree RF pulse in Spin Echo sequences?

To initiate transverse magnetization by tipping protons into the transverse plane. Signup and view all the answers

What happens if the slice is too thin?

There is not enough signal due to insufficient protons. Signup and view all the answers

Protons in ________ dephase slower than protons in fatty tissue, resulting in a stronger signal.

fluid Signup and view all the answers

Match the TE conditions to their corresponding image quality:

Short TE = Weaker overall signal Long TE = Stronger spin echo signal Short TR, Short TE = T1-weighted image Long TR, Long TE = T2-weighted image Signup and view all the answers

The phase encoding gradient is activated after the slice selection gradient.

True Signup and view all the answers

What is the result of applying multiple 180-degree pulses in a Spin Echo sequence?

The signal intensity gradually decreases. Signup and view all the answers

What factor can help to obtain a thicker slice when employing a gradient field?

Using a wider band width of the RF pulse. Signup and view all the answers

T2-curve is a representation of signal intensity over time in an MRI.

True Signup and view all the answers

What happens if no 180-degree pulse is applied during the imaging process?

The signal decays faster, producing a T2*-curve. Signup and view all the answers

Study Notes

Patient Signal Processing in MRI

MRI uses pulse sequences to differentiate tissues
Image creation varies with RF pulse sequences
Repetition Time (TR) is the time between RF pulses for a slice
Time to Echo (TE) is the time between RF pulse and echo signal receipt

Tissue Differentiation

Different tissues have different relaxation times
Short TR—shows T1 weighted image
Long TR—shows T2 weighted image
Short TE— stronger spin echo signal of tissue A compared to tissue B, good for differentiating between the two tissues
Long TE— weaker spin echo signal, harder to differentiate tissues visually

Spin Echo Sequences

Consist of a 90° RF pulse and at least one 180° pulse
Longitudinal magnetization increases after the 90° pulse, then dephased
180° pulse reverses the dephasing of protons , leading to a spin echo signal
Signal strength depends on T2 properties of tissue
T2 signal decreases with time
Short TE results in stronger signal
Long TE results in weaker signal, harder to distinguish tissues

Slice Selection

Using gradients in the magnetic field to select a specific slice for imaging
Slice thickness altered by RF pulse band width or gradient steepness
Thinner slices require higher magnetic field strength for better resolution

Signal Location for Image Reconstruction

Frequency encoding gradient applied in the y-direction; creates varied precession frequencies
Phase encoding gradient applied in the x-direction; temporal variations in precession frequency
Spatial locations determined by frequency and phase of signals
Fourier transformation analyzes the combined signal information to map location and intensity of voxels in an image

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Description

This quiz explores the key principles of patient signal processing in MRI, including pulse sequences, repetition time (TR), and echo time (TE). Understand how these factors influence tissue differentiation and image creation. Test your knowledge on T1 and T2 weighted images and spin echo sequences.