Outline: Contrast-enhanced MRA Background Technique Clinical Indications Future Directions Disclosures: GE Health Care: Research support Consultant: Bracco, Bayer
The Basics During rapid IV infusion, Gadolinium concentrated in arteries for 1 min. Gadolinium is a potent T1 relaxation agent in blood T1 blood 1200 ms <100 ms T1 blood Arterial MR signal enhancement is proportional to T1 shortening Off-label use of Gadolinium Contrast Agent
THE KEY TO MR-ANGIO SI T1 = 10 T1 = 50 ms T1 = 100 ms T1-shortening with paramagnetic contrast TR (ms)
Contrast-enhanced MRA Pre During Post
Contrast-enhanced MRA During Post
Contrast-enhanced MRA method Common features of technique: T1 weighted fast GRE 3D acquisition Tr < 5 ms Te < 1 ms Flip = 30 degrees Gadolinium Dose: 20 cc at 2 cc/s Nikola 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: Timing 20 15 10 Arterial Venous Tissue 5 0-5 0 20 40 60 80 100 120 140 Time (s)
Timing Artifacts
Fourier Transform 45 echo
k-space Signal Image k y Detail k x Contrast
+ = A = 1% A = 99% A = 100% + =
MRA Remains A Balancing Act Spatial Resolution SNR CNR Temporal Resolution k-space sampling and image reconstruction strategies help to achieve high spatial resolution time-resolved MR angiograms.
3D Time Resolved Imaging of Contrast Kinetics (TRICKS) aka: TREAT, DIRKS k z k z k y DC B A BCD ky Korosec et al., Magn. Reson. Med. 1996
3D TRICKS: Technique Contrast curve Artery Vein Time frame 10 11 12 13 14 15 16 17 18 19 20 21 22 D A C A B A D A C A B A D...... A B(I) C(I) D(I) FFT Image at time frame 15
3D TRICKs Acquisition Time-Resolved Imaging of Contrast Kinetics k y k x k z C B A k-space 3D FFT image-space Scan Time = TR (PE Slice) Ave Korosec, et al., MRM 36:345-51;1996
3D TRICKs Acquisition A B A C A B A C A B A B A C A ΔT = TR (PE Slice)/3 ΔT = 5 ms (128 32)/3 = 6.8 sec
3D TRICKS TR = 10.8 (1996) 512 x 128 x16 Frame Time 5.6 s onstruction time 1996: 6 hours, one graduate stude
Outline: Time-resolved MRA Background Technique Clinical Indications Future Directions
Clinical Indications Lower extremity runoff evaluation Asymmetric flow states Upper extremity MRA Mass evaluation and characterization Congenital heart disease Venous disease Aortic disease
Benefits of 3D CE MRA with subtraction 2D TOF 3D CEMRA BACKGROUND TISSUE SUPPRESSION
20 cc Gd Single Phase 3. Pelvis: Centric 3 2. Thighs: TRICKS 10 cc at 1 cc/sec 2 1. Distal Station Time-resolved MRA 10 cc Gd at 1 cc/sec 1
Improved Peripheral MRA Significantly more arteries diagnostic with TRICKS Significantly more venous contamination with moving SmartStep in lower station n=20, p < 0.05 Hany TF, et al Radiology 2001;221:266-272. Smartstep TRICKS
Benefits of time-resolved imaging protocol Left Popliteal Occlusion
Benefits of time-resolved imaging
Thromboangitis Obliterans
13 y/o with Tetrology of Fallot post-repair
Right PA enlargement causes SVC obstruction Sagittal reformat
Vascular Access Evaluation Collapsed Time Frames Rotate MIP
Secondary PAH due to chronic thromboembolic disease Courtesy of Stephan Schoenberg et al
Outline: Time-resolved MRA Background Technique Clinical Indications Future Directions Spatial Resolution SNR CNR Temporal Resolution
Traditional Cartesian sampling of k-k space 2D- FFT
Alternate Trajectories: Radial Sampling Sampling along radial spokes (2D-PR) 2D- FFT
Characteristics of Radial Sampling k x k y
HYPR Radial Acquisition Foot FOV = 300 mm 512 x 512 x 26 (ZIP 52) Voxel size 0.59 x 0.59 x 3.0 (-1.5) mm Frame Time = 2.0 Sec 16 proj/frame Speedup(Cartesian) = 32 512 PE/16 proj 3D HYPR Speedup(radial) = 50 804 proj/16 proj
Pitfalls: Resolution 3D TOF CE MRA DSA
Summary: Time-resolved MRA Eliminates need for accurate timing of contrast injection less need for radiologist supervision Allows high temporal and spatial resolution simultaneously Allows detection of non-uniform or asymmetric flow Automated process with essentially no post- processing Clinical indications expanding beyond arterial disease only Need for visualization with 4D processing to take full d t f ll th i f ti