11/7/2011
MRI Techniques for
Cardiovascular Imaging
Declaration of Conflict of Interest or
Relationship
Chen Lin PhD DABR
Indiana University School of Medicine
& IU Health
Research support from Siemens
Healthcare
Cardiac MRI
Basic Cardiac MR Techniques
• Morphology
• Acquisition Techniques for cardiac motion
– Wall movement
– Valve movement
– Blood vessel (aorta, pulmonary vein, coronary artery)
• Function
– Blood volume, flow and cardiac output
• Tissue Property
– Perfusion and delay enhancement
– Tumor / Mass
Chen Lin PhD 09/11
– Breath hold and Navigator (Respiratory motion)
– Prospective and retrospective ECG triggering (Sync with
cardiac motion)
– Segmented Acquisition and View sharing (Faster scan)
– Single-shot and radial sampling
• Magnetization preparation and pulse sequences for
optimal contrast
– Double IR (Dark Blood) and Triple IR (DB + STIR)
– Tagging (Wall Motion)
– 2D SSFP (TruFi versus FLASH) (CINE image for cardiac
function)
Chen Lin PhD 09/11
Unique Cardiac MR Applications
• Myocardium Perfusion
– IR (Delay Enhancement)
– IR/SR-SSFP/EPI (Myocardial Perfusion)
• Cardiac Function
– Phase Contrast (Flow Quantification)
• Cardiac MRA
– 3D SSFP (Coronary Arteries)
– Time Resolved MR Angiography (Large Vessel)
• Cardiac Mass
ECG TRIGGERING & GATING
– DB TSE sequence w. and w/o contrast (Tumor/Mass)
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ECG Triggering/Gating
• Prospective Triggering
Retrospective vs Prospective Triggering
• Retrospective Gating
– Data acquisition take
place after
predetermined delay
from trigger signal.
– Arbitrary timing of data
acquisition.
– Acquired data is sorted
into different cardiac
phase determined by
the delay from trigger
signal.
ECG
Acquisition
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 . . . .
Retrospective
Sorted based on the phase in cardiac cycle
1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 4 5 6 7 8 9 10 11 12 13
Prospective
1 2 3 4 5 6.......
Trigger Delay
Acquisition window
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Chen Lin PhD 09/11
Prospective Triggering Setup
Retrospective Triggering Setup
•
•
•
1 2 3 4 5 6.......
User defined Calculated phases ( typically 20-30 )
Trigger Delay + Acquisition Window = ~ 90% Average Cycle
TR (Temporal Resolution) X (Phases+1) = Acquisition Window
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Chen Lin PhD 09/11
Prospective versus Retrospective
Retrospectively Gated FLASH Examples
• Prospective Triggering
• Retrospective Gating
– Cover less than entire
cardiac cycle
– Sensitive to arrhythmia
– Acquisition window
manually adjusted
– Cine frame-rate
determined by data
segments
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– Measures through entire
cardiac cycle
– Arrhythmia rejection is
available
– Acquisition Window
automatically adjusted
– Variable user-defined
cine frame-rate
Flash
Flash + Grid Tagging
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k-space and Raw Data
Echo/Line/View
Kx
DATA ACQUISITION SCHEME
Phase Encoding Steps (Yres = 4)
Ky
Frequency Encoded Points (Xres = 8)
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Chen Lin PhD 09/11
Non-segmented
Segmented
ECG
ECG
Acquisition Window
Acquisition Window
Acquisition Window
Echoes
Cardiac Phases
a a a a a a a a a a a a a
| | | | | | | | | | | | |
N
1 2 3
Echoes
a a a a a a a a a a a a a
| | | | | | | | | | | | |
Cardiac Phases
N
1 2 3
aaaaaaaaaa
...
aaaaa
aaaaaaaaaa
...
aaaaa
1234512345
. . .
12345
1234512345
. . .
12345
1
2
N
Heartbeat 1
Echoes 1-5
Heartbeat 2
Echo 2
Heartbeat 1
Echo 1
•
•
•
Acquisition Window
TR
TR
1
2
N
Heartbeat 2
Echoes 6-10
• Multiple echoes combined for each phase
• Short scan duration but lower temporal resolution
One echo (k-space line/view) measured for each cardiac phase
Large number of cardiac phases -> High temporal resolution (< 10ms)
Long scan time ( # of phase encodes x RR)
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Chen Lin PhD 09/11
View sharing
View sharing Setup
ECG
Acquisition Window
Acquisition
TR
Echoes
Cardiac Phases
a a a a a a a a a a a a a . . .
a a a
a a a a a a a a a a a
1 2 3 4 5 3 1 2 3 4 5 3 1 . . .
3 4 5
1 2 3 4 5 3 1 2 3 4 5
1
3
2
4
N
1
3
2
• Some of the data are shared for two adjacent cardiac phases.
• Short scan duration and good temporal resolution
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Segmentation Trade-off
• Calculations:
– “TR” = segments x time between excitation (TR)
– Scan time = # of phase encodes / segments x RR
• Increasing # of segments:
– Longer “TR”, Lower temporal resolution, Blurring
– Shorter scan time, Shorter the breath-hold or
more slices.
“DARK” BLOOD TECHNIQUE
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Chen Lin PhD 09/11
“Double IR” or Dark Blood (DB)
Dark Blood Setup
Aquisition Window
Nonselective
IR
Myocardium signal
Slice
Selective IR
Blood signal
Null
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Double IR (Dark Blood) Example
Triple IR (TIR)
Aquisition Window
Myocardium
W/O DB
With DB
W/O DB
With DB
Non-sel
IR
Sel IR
Fat
Sel IR
Blood
Null
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Null
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Dark Blood Optimization
Triple IR Example
DIR
TR too short :
systolic motion reduces
myocardial signal
TIR
TR optimized
TR too long :
blood signal begins
to recover
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Chen Lin PhD 09/11
Adjust TI According to Heart Rate (HR)
Acquisition Timing
TI
TI
TR
TI
Data
Faster HR
-> Shorter RR
-> Less Recovery Time
-> Shorter TI
HR (BPM)
RR (ms)
TR (ms)
TI (ms)
60
1000
2000
630
80
750
1500
550
100
600
1200
420
• TI = TR – Data Acq; Data Acq = TRmin
• Trigger Delay = 0
• Adjust TR so that Data Acq is in late Diastole.
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Chen Lin PhD 09/11
TI, TR Setup
DB TSE: T1w versus T2w
TI
TR
Data Acq = TRmin = 100 ms
TI = TR - TRmin = 600 ms
100
TRmin
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For T2 Weighting:
• 2-3 RR
• Long ETL
• Long TE
• + FS ?
For T1 Weighting:
• 1 RR
• Short ETL
• Short TE
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Bright Blood Sequences (bSSFP)
a(f)
a(f)
a
-a
TR
TR
“BRIGHT” BLOOD TECHNIQUE
Gslice
Gslice
Gread
Gread
Gphase
Gphase
SSFP
(FLASH)
Balanced SSFP
(TrueFISP)
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SSFP versus bSSFP
Tips for TrueFISP Cine
Finn, J. P. et al. Radiology 2006;241:338-354
• Image contrast relies on Steady state effects (Ratio of T2/T1)
– Use large flip angle
• TR and TE are set automatically
– Use min. TR.
– TE is half of the TR with the exception of asymmetric
echo.
• Position heart near iso-center to improve field homogeneity
and reduce off-resonance artifact.
• Common uses of TrueFISP cine are wall motion, valve motion,
ventricular function.
bSSFP Contrast
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Chen Lin PhD 09/11
Motion Dependent Phase Difference
G
t
A
Bipolar Gradient
t
A
Moving spins
f
Z
Df = gAt V
FLOW QUANTIFICATION
t
Y
Stationary spins
MXY
X
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Velocity ENCoding
VENC Optimization
+180
+180
+170
+200
+180
+90
+180 deg
+4096 pix
+90 deg
Df
-90
0 pix
0 deg
-200
-170
-180
-180
-180
-90 deg
-4096 pix
-180 deg
Velocity = VENC / 1800 * Df
VENC too large
VENC optimal
Poor Contrast
VENC too small
Aliasing
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Chen Lin PhD 09/11
VENC Optimization
Interleaved Acquisition of Flow Compensated
and Flow Encoded Echoes
Pulmonary Artery
70-130
Aorta
100 – 175
Carotid Artery
80 – 120
External Iliac Artery
81 – 120
Carotid Syphon
55
Common Femoral Artery
115
Basilar Artery
40
ECG
Acq Window
Echoes
s1 s2 s1 s2 s1 s2 s1 s2 s1 s2
Superficial Femoral Artery 90
Vertebral Artery
40
Popliteal Artery
70
Sagittal Sinus Vein
10
Peripheral Veins
5 – 10
Acq Window
s1 s2 s1 s2 s1 s2 s1 s2 s1 s2
s1 = flow compensated
s2 = flow encoded
Velocity ~ fs2 - fs1
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Chen Lin PhD 09/11
Phase Contrast Acquisition
VENC, Reconstruction and Direction Setup
Need to acquire two images: 1) w/o flow encoding and 2)
flow encoded
Re-phased
Magnitude
|M1|
magnitude of flow
compensated signal
|M2 – M1|
magnitude of signal
difference
flow bright
background visible
flow bright
background suppressed
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Phase
f2-f1
phase angle of
signal difference
forward flow bright
reverse flow black
background mid-gray
* Always minimize TE/TR after increasing VENC
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Velocity Encoding Direction
Measuring Pulsatile Flow with Cardiac Trigger
In-Plane
Sagittal
Aorta
Thru-Plane
Axial Aorta
Aorta
CSF
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Chen Lin PhD 09/11
Normal aortic valve
Aortic Value Stenosis
Velocity
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Flow
Flow
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Finn, J. P. et al. Radiology 2006;241:338-354
Finn, J. P. et al. Radiology 2006;241:338-354
Human Vascular System
•
•
•
•
•
•
•
•
Intra cranial
Carotid
Aortic
Coronary
Pulmonary
Abdominal
Renal
Peripheral
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Velocity
Vascular Abnormities
•
•
•
•
•
•
•
Stenosis
Aneurysm
Arterial Venous Malformation (AVM)
Thrombus
Plaque
Internal bleeding
…
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MRA Related Properties of Blood
MR Angiography Techniques
• Flow
• Contrast Enhanced MRA (CE-MRA)
– Velocity: 100 – 150 cm/sec in abdominal aorta; 10 – 20
cm/sec in peripheral arteries
– Steady versus Pulsatile: Peak arterial flow @ 150 – 200 ms
after ventricular contraction
– Laminar versus Turbulent
–
–
–
–
–
• T1
• Non-Enhanced MRA (NCE-MRA)
– ~ 1200ms @ 1.5T; ~ 1500ms @ 3T
– Quantitative
– Prone to artifacts
– Different techniques specific to region
• T2
– ~ 250ms for arterial blood; ~ 30ms for venous blood
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Chen Lin PhD 09/11
Basic CE-MRA Technique
CE-MRA Considerations
• 0.1-0.2 mM/kg (2040ml) of Gd contrast
injected at 2-3 ml/sec.
• Flush with 20-30ml of
saline.
• T1w 3D spoiled gradient
echo based sequence.
• Min. TE and Min. TR.
• Partial k-space
acquisition.
1. Amount of Gd Contrast (dose) and Injection rate
2. Proper acquisition window and timing
– Accurate bolus timing by test bolus or fluro-trigger
– Centric view ordering
3. Acceleration with partial k-space acquisition
– Partial Echo, Partial Fourier, Parallel imaging, Radial
sampling
4. Time resolved MRA with view sharing
– Key-hole, TRICKS/TWIST, 4D-TRAK
5. Multi-station bolus chasing and continuous moving
table acquisition for peripheral MRA (pMRA)
0.8 x 0.9 x 0.6 mm3
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1. Amount of Contrast
2. Acquisition Window and Timing
Pulmonary arteries
Aorta
Renal arteries
Portal vein
Peripheral arteries
0.1 mmol/kg
0.1 - 0.2 mmol/kg
0.1 - 0.2 mmol/kg
0.2 mmol/kg
0.3 mmol/kg
Injection
Chen Lin PhD 09/11
Courtesy of M. Prince, Cornell, NY
•
•
•
•
•
High contrast to noise ratio
No flow induced de-phasing and signal lost
Fast acquisition -> Time-resolved MRA
Acquisition timing is important
Gd related NSF is a concern
Artery
Vein
Gd: 20ml
Gd: 40ml
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0 sec
12 sec
18 sec
24 sec
30 sec
Time
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Timing Bolus
Injection
• 1 – 2 ml of Gd with 20ml Saline and same
injection rate.
• Plot signal intensity versus time in the feeding
artery.
• Allows individual measurement of arterial and
venous enhancement kinetics
Contrast Concentration
Fluoro Triggering and Centric View Order
Time to
k-space
Center
Recessed Elliptical
Centric View Order
Artery
Patient
Specific Delay
Vein
Time
• Fluoro Triggering : Realtime 2D scan of ~1 fps)
• Test Bolus: 2D fast scan with small dose
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P.Finn et al., UCLA, Los Angeles, USA
tMRA with High Accelaration Factor
Injection
Contrast Concentration
4. Time-resolved CE-MRA (tMRA)
Artery
Vein
One volume per sec
with iPAT = 4
Time
Combined
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Acceleration by Sharing of k-space Data
TWIST (Time-resolved imaging WIth Stochastic Trajectories)
• Divide k-space into central and peripheral
regions.
• Sample central k-space region more
frequently than peripheral region.
• Share peripheral k-space data in multiple
reconstructions.
Size (%) Density (%)
Contrast
A
B
A
B
A
B
• Maintain the same SNR.
• Increase frame rate, but temporal base
remains same (temporal interpolation).
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Dynamic Series
MIP
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EC-TRICKS
4D (Spatial & Temporal) Information
Time-resolved MRA
Ky
D
C
B
Kz
A
Kx
ABCD AB AC AD AB AC AD AB AC AD AB …
Courtesy of Y. Zhou, PhD
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Chen Lin PhD 09/11
Summary
Major Non-CE MRA Techniques
• CE MRA is a fast and robust technique.
• Acquisition timing is critical to ensure optimal
SNR and prevent venous contamination.
• Proper screening of high risk patients is
needed to avoid NSF caused by Gd contrast
agent.
1.
Time of Flight (TOF)
–
–
2.
3D TOF: Intra-cranial
2D TOF: Carotid, Pelvic, Peripheral
Phase Contrast (PC)
–
3.
Intra-cranial, Renal
IR Prepared Balanced SSFP
–
4.
Coronary, Renal
ECG Triggered Multi-(cardiac)-phase FSE
–
Abdominal, Pelvic, Peripheral
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Chen Lin PhD 09/11
Non-CE MRA Application from Major Vendors
Magnetization Preparations in Renal bSSFP
MRA
GE
TOF
PC
[IR-] bSSFP
Inhance 2D
Inflow
Inhance 3D
Velocity
Inhance / Inflow
IR
Philips
TOF
Siemens
TOF
Toshiba
FBI (Fresh
Blood
Imaging)
Balanced FFE
PC
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[ET-] MP-FSE
1. Apply IR to suppress
background tissue
2. Allow Inflow of arterial
blood
3. Apply SAT band to
eliminate venous signal
4. Acquire data with
balanced SSFP sequence
TRANCE
(Triggered
Angiography.
Non-Contrast
Enhanced)
NATIVE Tru-FISP
NATIVE SPACE
Time-SLIP:
(Spatial Labeling
Inversion Pulse)
CIA (ContrastFree Improved
Angiography)
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IR-bSSFP MRA of Renal Artery
Typical Renal IR-bSSFP MRA Protocols
• Basic Sequence: Balanced SSFP
• Contrast:
–
–
–
–
TE = Min.
TR = Min.
FA: 60-70 deg.
TI = 600 ms
• Orientation: Axial slab for renal
• Coverage:
– FOV/PFOV/SLAB: 340 mm / 70-80% / 70-80 mm
• Resolution:
– Base/phase/slice thickness: 304 / 80% / 0.8 mm
• Options:
– FATSAT, ECG Triggering and Resp Gating
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IR-bSSFP MRA of Portal Vein
Principles of Triggered FSE MRA
Planning
Shimada, K. et al. Am. J. Roentgenol. 2009;193:106-112
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MIP
Diastolic
phase
Systolic
phase
ECG
1
Arterial
flow
velocity
Fast arterial flow
Option 1
Use SPACE1
acquisition in a
short window
ECG delay time
1
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Chen Lin PhD 09/11
Principles of Triggered FSE MRA
Velocity Contrast
Diastolic
phase
Systolic
phase
ECG
2
Arterial
flow
velocity
Fast arterial flow
Option 2
Use FSE
acquisition in a
long window
2
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ECG delay time
Diastolic (V+A)
=
Systolic (V)
MRA (A)
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FSE MRA Technique
NATIVE versus CE for pMRA
• Signal lost due to fast flow during systole.
• Requires ECG triggering and correct setting of
acquisition delays.
• Independent of flow direction.
Courtesy of LMU, Munich, Germany
Chen Lin PhD 09/11
Chen Lin PhD 09/11
Native vs CE MRA for Aortic Artery
Thank You!
Source
Image
MIP
Chen Lin PhD 09/11
clin1@iupui.edu
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