IMAGE FORMATION PULSE SEQUENCES MRI QUIZ

What is an MRI pulse sequence?

Timed instructions controlling how MRI images represent sampled tissue.

What creates the echo in gradient echo (GRE)?

Gradient coils refocus protons; an RF pulse and gradient field are used.

Which pulse is absent in GRE?

The 180° refocusing RF pulse.

Why is GRE more sensitive to field inhomogeneities?

It lacks a 180° RF refocusing pulse.

Why are GRE sequences generally fast?

They can use shorter TR because they lack 180° refocusing pulses.

What contrast can GRE produce?

T1 or T2* characteristics.

What can influence GRE contrast?

Susceptibility, chemical shift, and field inhomogeneities.

When does steady state occur in GRE?

When TR is shorter than T2 or T2*, leaving residual transverse magnetization.

Which GRE type provides high fluid signal?

T2* steady-state, coherent, or steady-state gradient echo.

What does spoiled GRE do?

Removes residual transverse magnetization before the next excitation.

How does RF spoiling work?

Additional or phase-shifted RF pulses spoil residual transverse magnetization.

What is BTFE?

A balanced steady-state sequence with high T2 signal and mixed T2/T1 contrast.

What are BTFE image characteristics?

High SNR and bright fluids; useful for cranial nerve evaluation.

What is GE's vendor name for BTFE-like imaging?

Fiesta.

What is Siemens' vendor name for BTFE-like imaging?

TrueFISP.

What is Hitachi's vendor name for BTFE-like imaging?

BASG.

What is Toshiba's vendor name for BTFE-like imaging?

True SSFP.

What is Philips' name for the sequence?

BTFE.

What is a common use of T1 spoiled GRE?

Dynamic organ imaging and contrast-enhanced MRA.

What is one example of T1 spoiled GRE acquisition?

SPGR coronal oblique imaging to evaluate the hippocampus in a patient with seizures.

What pulse begins conventional spin echo?

A 90° RF excitation pulse.

What does the 180° pulse do in spin echo?

Refocuses the decaying spin echo.

How many k-space lines does conventional spin echo acquire per TR?

One line.

How many k-space lines can fast spin echo acquire per TR?

Multiple lines, approximately 2 to 50 or more.

What is tau in spin echo?

The interval between the 90° and 180° RF pulses; half of TE.

How is a spin echo produced?

By a combination of two or more RF pulses.

What is dual-echo spin echo?

Two images per slice with different TEs but the same TR.

What weightings are commonly obtained with dual-echo spin echo?

Short TE: proton density; long TE: T2 weighting.

With TEs of 25 ms and 90 ms, which has more T2 contrast?

The second echo at 90 ms.

How does the second dual echo compare in SNR?

It has lower SNR than the first echo.

If 20 slices are planned for dual-echo imaging, how many images result?

40 images: one at each TE for every slice.

How does fast spin echo reduce scan time?

It collects several echoes and fills multiple k-space lines during each TR.

What is TSE factor?

Echo train length in fast spin echo; the term used by Philips.

If ETL increases by a factor of 3, how does scan time change?

It becomes about three times faster, as described in the document.

What are two fast spin echo trade-offs?

Lower SNR and increased patient SAR absorption.

What can increasing ETL do to image appearance?

Increase blurring.

What is effective TE in fast spin echo?

The echo encoded closest to the center of k-space (k0).

How are fast spin echo shots calculated?

Number of phase encodings divided by ETL.

What does a 'shot' mean in fast spin echo?

The number of non-redundant RF excitations.

What is single-shot imaging?

One excitation and an echo train fill the entire k-space matrix.

Why can single-shot imaging help in abdominal MRI?

It can reduce respiratory motion or improve temporal resolution.

What is multi-shot imaging?

Each excitation fills only part of k-space, allowing opportunity for higher spatial resolution.

What pulse begins inversion recovery (IR)?

A 180° inversion pulse followed by a 90° excitation pulse.

What is the purpose of the initial 180° IR pulse?

To null fat or fluid signal, depending on TI and field strength.

What is inversion time (TI)?

The interval between the 180° inversion pulse and the 90° excitation pulse.

What IR sequence types are listed?

STIR, FLAIR, and 3D-IR.

What TI relationship is given for nulling a tissue?

TI is approximately 69% of that tissue's T1 relaxation time.

What does STIR stand for?

Short TI inversion recovery.

At 1.5 T, what is the approximate STIR fat null point?

About 140–160 ms.

What STIR applications are listed?

Compression fractures, retro-orbital fat lesions, musculoskeletal contusions, and fat suppression.

What does FLAIR stand for?

Fluid-attenuated inversion recovery.

What TI is given to null CSF in FLAIR at 1.5 T?

Approximately 2000 ms.

What is T2-weighted FLAIR commonly used to evaluate?

Periventricular white matter.

What does SPGR stand for?

Spoiled Gradient Recalled echo.

How does SPGR spoil transverse magnetization?

It phase-shifts the RF excitation pulse to prevent residual transverse magnetization from accumulating.

Why does SPGR use a short TE?

To reduce T2 effects so T1 effects predominate.

What is Siemens' name for the SPGR-type sequence?

FLASH (Fast Low Angle SHot).

What is Philips' name for the SPGR-type sequence?

T1-FFE (Fast Field Echo).

What is Hitachi's name for the SPGR-type sequence?

SARGE (Steady state Acquisition Rewound Gradient Echo).

What is TR?

Time between two RF excitation pulses; described in the document as between two 90° pulses.

What is TE?

Time from the 90° RF pulse to the peak signal in the receiver coil.

What happens to PD weighting when TR lengthens and TE stays short?

Proton-density weighting increases.

What happens to available slices when TE increases?

The number decreases because fewer slices fit within TR.

What happens when TR increases?

SNR and the number of available slices increase, according to the document.

What is the basic scan-time formula?

TR × phase matrix × NEX gives milliseconds; divide by 1000 for seconds.

What scan-time formula includes ETL?

TR × matrix × NEX ÷ ETL.

What controls image contrast through pulse sequence timing?

The timing of RF pulses.

Why are spin echo sequences less sensitive to inhomogeneity?

Their 180° RF refocusing pulses help correct local field inhomogeneities.

What happens when flip angle is reduced?

Images contain less T1 information.

What determines scan plane and slice thickness?

The slice-selection gradient.

How can oblique slice orientations be acquired?

By using two gradients for slice selection.

Which gradient is active during echo production?

The frequency-encoding (readout) gradient.

What is echo-planar imaging (EPI)?

A very fast technique that can acquire an entire MR image in a fraction of a second.

Which sequence is described as the fastest commonly available?

Echo-planar imaging (EPI).

What is the basic spin echo pulse pattern?

90° RF followed by 180° RF.

What is the basic fast spin echo pulse pattern?

90° RF followed by a train of 180° RF pulses.

What is the basic inversion recovery pulse pattern?

180° inversion pulse followed by a 90° excitation pulse.

How does gradient echo create an echo?

A variable flip-angle RF pulse followed by gradient-based refocusing.

Which GRE settings are listed for T2* weighting?

TR 450 ms with a 30° flip angle.

Which GRE settings are listed for T1* weighting?

TR 45 ms with a 90° flip angle.

What happens to T2 information when TE is reduced?

T2 information decreases.

How does increasing flip angle affect SNR?

SNR increases up to the Ernst angle.

What changes tend to lengthen scan time?

Increase TR, decrease ETL, increase NEX, and decrease parallel-imaging factor.

What changes tend to shorten scan time?

Decrease TR, increase ETL, decrease NEX, enable half-scan, and increase parallel-imaging factor.

Which changes can improve SNR?

Increase TR, reduce phase matrix, increase FOV, narrow receive bandwidth, increase NEX/NSA, and reduce ETL.

Which changes can reduce SNR?

Decrease TR or pixel size/FOV, widen receive bandwidth, decrease NEX, or increase ETL.