MRI Physics Chapter 3 & 4

A technique used to visualize the morphology of the heart and great vessels is:

Double IR

What is the name of the signal detected in the receiver coil at the time TE after application of a 180 degree RF rephrasing pulse?

Echo

A balanced gradient-echo sequence does not correct the phase shift errors created by flowing CSF or blood.

False

In a fast or turbo gradient-echo sequence, very short TEs are achieve by two methods : ramped sampling and use of broad receive bandwidth.

False

In STIR sequences, which tissue is being suppressed?

Fat

Which statement is not true about FSE pulse sequences?

Fat is brighter than on SE pulse sequences

STIR sequences can suppress the signal from all of the following EXCEPT:

Fluid (CSF)

The gradient that is on during the production of the echo is the:

Frequency

The point in a tissue's longitudinal recovery where there is no component of magnetization and therefore no signal created on an IR pulse sequence is called:

Null Point

Fluid attenuated inversion recovery (FLAIR) sequences are typically used for the evaluation of:

Periventricular white matter disease

Imaging parameters in GRE PD-weighted sequences should have:

Small flip angle, long TR, short TE

Imaging parameters in GRE T2*-weighted sequences should have:

Small flip angle, long, TR, long TE

A pulse sequence with a 90⁰ RF excitation pulse followed by a 180⁰ RF rephasing pulse is known as a(an):

Spin echo

In a steady state which tissue will demonstrate a high signal intensity?

Tissue where T1 recovery and T2 decay times are similar

EPI often run in conjunction with single-shot imaging and the TR is set at infinity.

True

Gradient echo sequences can yield either T1 or T2* characteristics.

True

In EPI with single-shot imaging, we may see blurring and ghosting artifacts

True

In a gradient-echo sequence, Flip angle and TR determine whether vectors are saturated or not and, therefore, the degree of T1 contrast in the image.

True

In an EPI sequence, PD weighting is achieved by selecting short TE.

True

In the steady state, image contrast is not due to differences in recovery and T2 decay times of tissues but rather due to the ratio recovery time to T2 decay time

True

The steady state is equal amounts of longitudinal and transverse magnetization.

True

What is the extrinsic contrast parameter unique to TSE/FSE

Turbo factor or echo train length

In FLAIR sequences, which tissue is being suppressed?

CSF

In the multi-echo spin-echo sequence shown below, the number of SHORT TE images created with a 20-slice sequence will be:

20

IR pulse sequences are characterized by:

A 180⁰ inversion RF pulse followed by a 90⁰ excitation RF pulse

The pulse sequence consisting of a variable flip angle RF excitation pulse followed by a pulse of the magnetic field gradients is called:

Gradient echo

Gradient echo T1-weighted sequences use:

Gradient or RF spoiling

The process of dephasing magnetic moments with use of gradients is called:

Gradient spoiling

Spin echo sequences:

Have a 90-degree excitation pulse followed by 180-degree rephasing pulse

Gradient echo sequences acquired for high signal from fluid are known as all of the following EXCEPT

Incoherent gradient echoes

Gradient echo sequences acquired for high signal from fluid are known as all of the following EXCEPT:

Incoherent gradient echoes

The time between 180⁰ inversion pulse and the 90⁰ excitation pulse is known as:

Inversion time

Imaging parameters in GRE T1-weighted sequences should have:

Large flip angle, short TR, short TE

What is gradient rewinding

Process by which NMVs are rephrased

What are the consequences of generating a steady state in a gradient-echo sequence?

Residual transverse magnetization that is rephased to produce a stimulated echo. Images where contrast is dependent on T1/T2 rather than absolute values of T1 recovery time and T2 decay time. (A and B were both correct)

What is the scan time for a sequence with the following parameters? TR=2000ms, NSA=2, Phase encoding matrix= 256, Freq matrix= 512

Scan time = TR x NSA x PE matrix 2000ms x 2 x 256 =1024000ms =1024sec =17 min

What are the consequences of increasing ETL parameter

Shorter scan time, more T2 weighting, less magnetic susceptibility, more J coupling more MTC, fewer slices and possibly some blurring if the turbo factor is very long

A technique that allows k-space to fill from a single echo train is known as:

Single shot imaging

Gradient echo sequences acquired for the evaluation of hemorrhagic lesions rely on:

Susceptibility

Coherent GRE sequences are typically:

T2*-weighted

Short tau inversion recovery images are:

T2-weighted, fat saturated images

Which combination of TR and TE create a T2-weighted image?

TE 90ms, TR 4000ms

How is the TI required to null the signal be calculated

TI required to null the signal from a tissue is always 0.69 times its T1 relaxation time

What parameters are suitable in a FLAIR sequence and why?

TI to suppress CSF, Long TE to enhance T2 weighting, and Long TR to allow full recovery of spins from saturation

Which TR is considered appropriate to maintain a steady state

TR below 50ms

Why should STIR sequences not be used after administering gadolinium

The T1 recovery times of enhancing structures are shortened by gadolinium so that they approach the T1 recovery time of fat. In a STIR sequence, therefore, enhancing tissue may be nulled

Black blood acquisitions produce images where blood flow is dark and are based on:

spin echo sequences