MRI Tissue Characteristics & Image Contrast - Quizlet

What are the two categories of MRI image contrast parameters?

Intrinsic and extrinsic parameters.

What are intrinsic parameters in MRI?

Characteristics of tissues that cannot be changed, such as T1 recovery, T2 decay, and proton density.

What are extrinsic parameters in MRI?

Factors that can be controlled or manipulated by the technologist to alter image contrast.

What are examples of extrinsic parameters?

TR (repetition time), TE (echo time), TI (inversion time), flip angle, turbo factor (ETL), and pulse sequence type.

What does TR stand for?

Time to Repetition.

What does TE stand for?

Time to Echo.

What does TI stand for?

Time to Inversion.

Which pulse sequence is TI associated with?

Inversion recovery sequence (180° to 90° pulses).

What does T1 relaxation refer to?

Longitudinal or spin-lattice relaxation — recovery of magnetization along the z-axis.

How is T1 relaxation defined?

The time required for 63% of the tissue's longitudinal magnetization to recover.

How many T1 times does it take to reach full equilibrium?

Approximately 5 T1 relaxation times.

Which tissue appears bright on T1-weighted images?

Fat, due to rapid recovery.

Which tissue appears dark on T1-weighted images?

Water, due to long recovery times.

What does T2 relaxation refer to?

Transverse relaxation or spin-spin relaxation — the loss of transverse magnetization.

How is T2 relaxation defined?

Time required for 63% of the tissue's transverse magnetization to decay.

Which tissue appears dark on T2-weighted images?

Fat, due to rapid decay.

Which tissue appears bright on T2-weighted images?

Water, due to slow decay.

What is T2* relaxation?

T2 relaxation plus magnetic field inhomogeneities.

Why is T2* shorter than T2?

Because magnetic field inhomogeneities cause spins to precess at different rates, speeding up dephasing.

Is T2* a true T2 relaxation image?

No, it includes additional dephasing mechanisms and cannot be trusted as a true T2.

What is proton density (PD)?

The number of hydrogen protons in a given volume of tissue.

What tissues have high proton density and appear bright?

Fat and water.

What tissues have low or no proton density and appear dark?

Air, cortical bone, ligaments, tendons, and cartilage.

What is another term for proton density?

Spin density.

What is the appearance of tissues with low proton density on MRI?

They appear dark or black.

What does T1-weighted imaging best demonstrate?

Anatomy

What does T2-weighted imaging best demonstrate?

Pathology

Why is T2-weighted imaging useful for pathology?

Bright signals indicate areas of abnormal fluid or inflammation.

What happens to fluid on a T2 image?

It appears bright.

What happens to fluid on a T1 image?

It appears dark.

What does FLAIR stand for?

Fluid Attenuated Inversion Recovery.

What does FLAIR suppress?

Cerebrospinal fluid (CSF).

What does a FLAIR image show?

Bright abnormal lesions with dark CSF.

What does a proton density image represent?

Only the number of protons in tissue — cannot distinguish between fat and water because both are bright.

What do we use TR and TE to control?

Image contrast and weighting in MRI.

Which parameter primarily controls T1 contrast?

TR (Time to Repetition).

Which parameter primarily controls T2 contrast?

TE (Time to Echo).

What is TR in MRI timing?

Time between repetitions of the pulse sequence.

What is TE in MRI timing?

Time between the initial 90° pulse and the echo.

What TR and TE combination produces T1-weighted images?

Short TR and short TE.

What TR and TE combination produces T2-weighted images?

Long TR and long TE.

What TR and TE combination produces Proton Density-weighted images?

Long TR and short TE.

What happens when TR is short?

There is incomplete recovery of longitudinal magnetization, emphasizing T1 differences.

What happens when TR is long?

Longitudinal magnetization fully recovers, minimizing T1 contrast.

What happens when TE is short?

There is minimal T2 decay, reducing T2 weighting.

What happens when TE is long?

More T2 decay occurs, increasing T2 weighting.

How does the spinal cord appear on a T1-weighted image compared to CSF?

Hyperintense (brighter than CSF).

How does the spinal cord appear on a T2-weighted image compared to CSF?

Hypointense (darker than CSF).

Why does the CSF appear bright on T2 images?

Because of its long T2 relaxation time.

Why does the CSF appear dark on T1 images?

Because of its long T1 relaxation time.

What are the three primary intrinsic factors affecting MR image contrast?

T1 relaxation, T2 relaxation, and proton density.

What are the main extrinsic factors affecting MR image contrast?

TR, TE, TI, flip angle, ETL, and pulse sequence selection.

What happens if the technologist adjusts TR and TE values incorrectly?

The image contrast weighting may shift between T1, T2, and PD unintentionally.

Why can't intrinsic factors be changed?

They are inherent to tissue composition and molecular environment.

What is the main goal of adjusting TR and TE?

To manipulate the image contrast to emphasize specific tissue characteristics.

What type of images are best for evaluating multiple sclerosis lesions?

FLAIR images, because CSF is suppressed and lesions appear bright.

What type of image is best for musculoskeletal imaging?

Proton density-weighted images.

In MRI, what does "signal intensity" refer to?

The brightness or darkness of a structure on the image, based on how much signal is emitted.

What causes tissues to appear bright in MRI?

A high signal intensity.

What causes tissues to appear dark in MRI?

A low signal intensity

Which images are T2 weighted images?

A&E

3 multiple choice options

Which images are T1 weighted images?

B&F

3 multiple choice options

Which images are FLAIR images?

C&G

3 multiple choice options

Which images are Proton Density images?

D&H

3 multiple choice options