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