outline: contrast-enhanced mra - advanced body imaging...outline: contrast-enhanced mra •...
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Outline: ContrastOutline: Contrast--enhanced enhanced MRAMRA
•• BackgroundBackground•• TechniqueTechnique•• Clinical IndicationsClinical Indications•• Future DirectionsFuture Directions
Disclosures:GE Health Care: Research supportConsultant: Bracco, Bayer
The BasicsThe Basics•• During rapid IV infusion, Gadolinium During rapid IV infusion, Gadolinium
concentrated in arteries for 1 min.concentrated in arteries for 1 min.
•• Gadolinium is a potent T1 relaxation agent Gadolinium is a potent T1 relaxation agent in bloodin blood——T1T1bloodblood 1200 ms <100 ms 1200 ms <100 ms
•• Arterial MR signal enhancement is Arterial MR signal enhancement is proportional to T1 shorteningproportional to T1 shortening
OffOff--label use of Gadolinium Contrast Agentlabel use of Gadolinium Contrast Agent
THE KEY TO MRTHE KEY TO MR--ANGIOANGIO
SI
TR (ms)
T1 = 10
T1 = 100 ms
T1 = 50 msT1-shortening
with
paramagnetic contrast
Pre During Post
ContrastContrast--enhanced MRAenhanced MRA
ContrastContrast--enhanced MRAenhanced MRA
During Post
ContrastContrast--enhanced MRA enhanced MRA methodmethod
•• T1 weighted fast GRET1 weighted fast GRE•• 3D acquisition3D acquisition•• Tr < 5 msTr < 5 ms•• Te < 1 ms Te < 1 ms •• Flip = 30 degreesFlip = 30 degrees•• Gadolinium Dose: 20 cc at 2 cc/sGadolinium Dose: 20 cc at 2 cc/s
Common features of technique:Common features of technique:
Nikola TeslaNikola Tesla
HOW MUCH CONTRAST?
Dose mmol/kg• Aorta 0.1 - 0.2 (20cc)• Renal arteries/SMA 0.1 - 0.2 (30cc)• Runoff 0.2 (40cc)
MRA is an off-label use of Gd
flow rate = 3 ml/sec for renals
Pitfalls: TimingPitfalls: Timing
-5
0
5
10
15
20
0 20 40 60 80 100 120 140
Time (s)
ArterialArterial
VenousVenousTissueTissue
Timing ArtifactsTiming Artifacts
echo45°
Fourier
Transform
kx
ky
k-Space Signal Image
DetailDetail
ContrastContrast
A = 1% A = 99% A = 100%
+
+
=
=
→ k-space sampling and image reconstruction strategies help to achieve high spatial resolution time-resolved MR angiograms.
Spatial Resolution
Temporal Resolution
SNR CNR
MRA Remains A Balancing Act MRA Remains A Balancing Act
3D3D TTime ime RResolved esolved IImaging of maging of CContrast ontrast KKineticsinetics(TRICKS)(TRICKS)
aka: TREAT, DIRKSaka: TREAT, DIRKS
AD C CB B D ky
kz
Korosec et al.,Magn. Reson. Med. 1996
ky
kz
3D TRICKS: Technique3D TRICKS: Technique
C(I)D(I)
B(I)A
... ...D A C A B A D A C A B A D10 11 12 13 14 15 16 17 18 19 20 21 22Time frame
FFTImage attime frame 15
Contrast curve ArteryVein
3D TRICKs Acquisition3D TRICKs Acquisition
kx
ky
kz
k-space
Scan Time = TR × (PE × Slice) × Ave
image-space3D FFT⇒A
CB
Korosec, et al., MRM 36:345-51;1996
Time-Resolved Imaging of Contrast Kinetics
3D TRICKs Acquisition3D TRICKs Acquisition
ΔT = TR × (PE × Slice)/3ΔT = 5 ms × (128 × 32)/3 = 6.8 sec
A A AB C
A B A C A B A C A B
Frame Time 5.6 s
TR = 10.8 (1996)
3D TRICKS
512 x 128 x16
construction time 1996: 6 hours, one graduate stude
Outline: TimeOutline: Time--resolved MRAresolved MRA
•• BackgroundBackground•• TechniqueTechnique•• Clinical IndicationsClinical Indications•• Future DirectionsFuture Directions
Clinical IndicationsClinical Indications
•• Lower extremity runoff evaluationLower extremity runoff evaluation•• Asymmetric flow statesAsymmetric flow states•• Upper extremity MRAUpper extremity MRA•• Mass evaluation and characterizationMass evaluation and characterization•• Congenital heart diseaseCongenital heart disease•• Venous diseaseVenous disease•• Aortic diseaseAortic disease
R BACKGROUND TISSUE SUPPRESSION
Benefits of 3D CE MRA with subtractionBenefits of 3D CE MRA with subtraction2D TOF 3D CEMRA
1. Distal StationTime-resolved MRA10 cc Gd at 1 cc/sec
20 cc Gd Single Phase3. Pelvis: Centric
1
3
22. Thighs: TRICKS 10 cc at 1 cc/sec
Improved Peripheral MRAImproved Peripheral MRA
•• Significantly more arteries Significantly more arteries diagnostic withdiagnostic with TRICKS TRICKS
•• Significantly more venous Significantly more venous contamination with moving contamination with moving SmartStepSmartStep in lower stationin lower station
••n=20, p < 0.05n=20, p < 0.05
Smartstep TRICKS
Hany TF, et al Radiology 2001;221:266-272.
Benefits of timeBenefits of time--resolved imaging resolved imaging protocolprotocol
Left Popliteal Occlusion
Benefits of timeBenefits of time--resolved imagingresolved imaging
Thromboangitis ObliteransThromboangitis Obliterans
13 y/o with Tetrology of Fallot post13 y/o with Tetrology of Fallot post--repairrepair
Right PA enlargement causes SVC Right PA enlargement causes SVC obstructionobstruction
Sagittal reformatSagittal reformat
Vascular Access EvaluationVascular Access Evaluation
Rotate MIPCollapsed Time Frames
Secondary PAH due to chronic thromboembolic diseaseSecondary PAH due to chronic thromboembolic disease
Courtesy of Stephan Schoenberg et al
Outline: TimeOutline: Time--resolved MRAresolved MRA
•• BackgroundBackground•• TechniqueTechnique•• Clinical IndicationsClinical Indications•• Future DirectionsFuture Directions
Spatial Resolution
Temporal Resolution
SNR CNR
Traditional Traditional ““CartesianCartesian”” sampling of ksampling of k--spacespace
2D-FFT
Alternate Trajectories: Radial Alternate Trajectories: Radial SamplingSampling•• Sampling along radial spokes (2DSampling along radial spokes (2D--PR)PR)
2D-FFT
Characteristics of Radial SamplingCharacteristics of Radial Sampling
kx
ky
HYPR HYPR –– Radial Acquisition Radial Acquisition –– FootFootFOV = 300 mm
512 x 512 x 26 (ZIP 52)
Voxel size0.59 x 0.59 x 3.0 (-1.5) mm
Frame Time = 2.0 Sec
16 proj/frame
Speedup(Cartesian) = 32512 PE/16 proj
Speedup(radial) = 50804 proj/16 proj3D HYPR
3D TOF CE MRA DSA
Pitfalls: ResolutionPitfalls: Resolution
Summary: TimeSummary: Time--resolved MRA resolved MRA
•• Eliminates need for accurate timing of contrast Eliminates need for accurate timing of contrast injection injection –– less need for radiologist supervisionless need for radiologist supervision
•• Allows high temporal and spatial resolution Allows high temporal and spatial resolution simultaneouslysimultaneously
•• Allows detection of nonAllows detection of non--uniform or asymmetric flowuniform or asymmetric flow
•• Automated process with essentially no postAutomated process with essentially no post--processing processing
•• Clinical indications expanding beyond arterial Clinical indications expanding beyond arterial disease onlydisease only
•• Need for visualization with 4D processing to take full Need for visualization with 4D processing to take full f fd t f ll th i f ti