Jocelyne S. Lapointe MD FRCPC

KBTH Visiting Radiology Consultant

Demystify MRI sequences

Familiarize clinicians with common

usages of each type of sequence

Help clinicians determine if the MRI

techniques used are adequately

answering their question(s)

Will be explained in the presentation

T1W or T2W: T1 weighted

GRE: gradient recalled echo

Some names are manufacturer specific =

know your MRI machine(s)

Fat on T1 Clotted blood (intracellular methemoglobin

on T1 and T2 sequences) CSF on T2W Arteries on FFE T1 type of T1 sequence

used on KBTH Phillips Achieva (called FLASH on Siemens, SPGR on GE machines)

Vessels and enhancing lesions on post contrast T1 (N.B. enhancement only detectable on T1)

Melanin (melanoma)

Calcification (sometimes)

Hemosiderin (on T1, T2, GRE sequences;

GRE called FFE T2 on Philips MRI)

Flowing blood (i.e. oxyhemoglobin)

Deoxyhemoglobin (on GRE)

Melanin on T2

Ordered combination of radiofrequency

(RF) and gradient pulses designed to

acquire the data to form the MRI image

Computer program that controls all

hardware aspects of the MRI

measurement process (and thus the

resultant images)

T1, T2, FLAIR are standard names Other names at “whim” of manufacturer

or sequence developer (i.e. no “standard”)

Over one hundred named sequences ************************* Main MRI manufacturers: Siemens, GE, Philips,

Hitachi, Toshiba

KBTH & 37 Military: Philips Achieva 1.5T Teaching Hospitals new MRIs: Toshiba 1.5T

SE , TSE, FSE: spin echo, turbo spin echo,

fast spin echo

FFE: fast field echo (Philips MRI)

PD: proton density

IR: inversion recovery:

- FLAIR: fluid attenuated IR

- STIR: short tau IR

- SPIR: spectral saturation with IR

DWI: diffusion weighted imaging

ADC: apparent diffusion coefficient

GE, GRE: gradient (recalled) echo

SWI: susceptibility weighted imaging

EPI: echo planar imaging

BOLD: blood oxygen level dependent

Name Full Name Synonyms T1 or T2 Weighing

SE Spin Echo T1 or T2

TSE Turbo Spin Echo FSE: Fast Spin Echo T1 or T2

FFE T2 T2 Fast Field Echo FISP: Fast Imaging with

Steady State

GRE: Gradient Recalled Echo

GE: Gradient Echo

GRASS: Gradient Recalled

Acquisition of Steady State

T2

FFE T1 T1 Fast Field Echo FLASH: Fast Low Angle Shot

SPGR: Spoiled GRASS

T1 (Vessels white)

FLAIR (T2) Fluid Attenuated Inversion

Recovery

T2 FLAIR usually used

TIRM Turbo Inversion Recovery

Measurement

Turbo FLAIR

CISS (balanced FFE) Constructive Interference in

Steady State

(3D high resolution

sequence) Fiesta (General

Electric)

T2

HASTE Half Fourier Acquisition

Single Shot Turbo Spin Echo

T2

PD Proton Density Not T1W or T2W

RARE Refocused Acquisition in

Readout Direction

Contrast depends predominantly on the

differences in the T1 times between

tissues e.g. fat and water.

Simplistically, T1 is a function of TR (i.e.

time of repetition) and represents

longitudinal relaxation of Hydrogen

protons

Grey -white different because of window setting

Contrast predominantly depends on the

differences in the T2 times between

tissues e.g. fat and water.

Simplistically, T2 is a function of the TE

(i.e. time to echo) and represents

transverse relaxation of Hydrogen

proton

Quantitative summary of the number of

protons per unit tissue.

The higher the number of H+ protons in a

given unit of tissue, the brighter the

signal on the PD image.

Difference in the numbers of H+ protons

per voxel =image contrast

Proton density weighting always present

Effects of T1 and T2 contrast must be

diminished to achieve PD

CSF isointense to grey matter on PD

Two MS cases

Pros:

Reduction of scan time, decreased

motion artefacts compared to SE

Low sensitivity to magnetic susceptibility

artifacts

Cons:

Modification of tissue contrast

Clinical use:

Almost all the organs, with T1 or T2

GRE (aka FFE T2) and now SWI

FLAIR

Fat saturation (FS) (STIR)( SPIR)

DWI

TOF MRA

PC MRA (or PCA)

Pros:

fast technique (uses less RF power)

Cons:

T2*-weighted images instead of T2

Sensitive to magnetic susceptibility

Clinical use:

Hemorrhage (haemosiderin) and

calcification; melanin

Gradient echo type sequence

More powerful than GRE:/ FFE T2; more

and smaller haemosiderin deposits

detected

Confirms that microhaemorrhages occur

in many conditions other than with axonal

injury(ex: hypertension, Alzheimer’s)

To null the signal of a particular tissue

FLAIR: (Fluid Attenuated Inversion Recovery)

nulls CSF, to better detect bright signal

in brain tissue (i.e. T2 FLAIR mainly)

STIR: (Short Tau Inversion Recovery) nulls fat in

muscle, marrow, orbit, etc., to better see

oedema or enhancement (as bright)

Better than T2 to show

abnormal signal

(i.e. “white”) in brain

tissue while CSF in

ventricles and sulci is

black

Many types: T2 Fat Sat, STIR, SPIR, SPAIR

Used to see oedema in bone marrow and

enhancement in fat filled structures(orbit,

for ex.)

Often fat saturation is incomplete , so pre

and post contrast sequences needed to

confirm enhancement

—21-year-old male athlete with acute traumatic hip injury.

Blankenbaker D G et al. AJR 2008;190:W1-W7

©2008 by American Roentgen Ray Society

—21-year-old male athlete with acute traumatic hip injury.

Blankenbaker D G et al. AJR 2008;190:W1-W7

©2008 by American Roentgen Ray Society

Figure 10a.

Sanders T G et al. Radiographics 2000;20:S135-S151

©2000 by Radiological Society of North America

T2 STIR (N.B. CSF BRIGHT) T1 STIR WITH GADOLINIUM

Ultra fast sequence, commonly used for

acquiring DWI, Perfusion and Functional

MRI (fMRI)

EPI sequences can be used when patient

motion a problem

Exploits the random

motion of H2O

molecules.

Tissue cellularity and

intact cell

membranes

determine the

impedance of water

molecule diffusion.

Fast (< 1min)

sequence in brain

Now being used in

abdomen/pelvis (1-

5min) with or without

breath holding

Brain Infarction (cytotoxic

oedema) “Blue” (i.e. cellular)

tumours (lymphoma) Abscess vs. Tumour

DTI (Diffusion

tensor imaging or tractography)

White matter tracts

Abdomen/Pelvis: Nodes in lymphoma Liver Prostate

Obtained from DWI at touch of button

(not a separate MRI sequence)

Generates quantitative data on tissues,

voxel by voxel

Used to better analyse DWI images

T1 WITH GADOLINIUM DWI

Time of Flight Angiography (TOF)

Phase Contrast Angiography(PCA)

Most protocols use a 3D TOF sequence

IV Gadolinium for optimum resolution

Same indications for imaging as catheter

angiography or CT angiography

Visible on T1W (not on T2W or FLAIR)

Fat saturation used if much fat present, to

separate fat from enhancement

Maximum enhancement : first 15 minutes

(Enhancement “half life” is 30 minutes or less (delay in

scanning affects degree of enhancement; top-up

injection may be needed)

T1W: all organs (for anatomical detail); post gadolinium, to detect enhancement

T2W: fluid structures, oedema FLAIR: oedema/increased H2O in tissue GRE/T2 FFE and SWI: calcification,

haemosiderin, melanin DWI: restricted flow of H2O/cellular tissue Fat Sat and STIR/SPIR: oedema and

enhancement (with gadolinium)in fat surrounded structures

MRA: Vessels