Outline: Contrast-enhanced MRA

Transcription

1 Outline: Contrast-enhanced MRA Background Technique Clinical Indications Future Directions Disclosures: GE Health Care: Research support Consultant: Bracco, Bayer

2 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

3 THE KEY TO MR-ANGIO SI T1 = 10 T1 = 50 ms T1 = 100 ms T1-shortening with paramagnetic contrast TR (ms)

4 Contrast-enhanced MRA Pre During Post

5 Contrast-enhanced MRA During Post

6 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

7 HOW MUCH CONTRAST? Dose mmol/kg Aorta (20cc) Renal arteries/sma (30cc) Runoff 0.2 (40cc) MRA is an off-label use of Gd flow rate = 3 ml/sec for renals

8 Pitfalls: Timing Arterial Venous Tissue Time (s)

9 Timing Artifacts

10 Fourier Transform 45 echo

11 k-space Signal Image k y Detail k x Contrast

12 + = A = 1% A = 99% A = 100% + =

13 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.

14 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

15 3D TRICKS: Technique Contrast curve Artery Vein Time frame 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

16 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

17 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

18 3D TRICKS TR = 10.8 (1996) 512 x 128 x16 Frame Time 5.6 s onstruction time 1996: 6 hours, one graduate stude

19 Outline: Time-resolved MRA Background Technique Clinical Indications Future Directions

20 Clinical Indications Lower extremity runoff evaluation Asymmetric flow states Upper extremity MRA Mass evaluation and characterization Congenital heart disease Venous disease Aortic disease

21 Benefits of 3D CE MRA with subtraction 2D TOF 3D CEMRA BACKGROUND TISSUE SUPPRESSION

22 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

23 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: Smartstep TRICKS

24 Benefits of time-resolved imaging protocol Left Popliteal Occlusion

25 Benefits of time-resolved imaging

26 Thromboangitis Obliterans

27 13 y/o with Tetrology of Fallot post-repair

28 Right PA enlargement causes SVC obstruction Sagittal reformat

29 Vascular Access Evaluation Collapsed Time Frames Rotate MIP

30 Secondary PAH due to chronic thromboembolic disease Courtesy of Stephan Schoenberg et al

31 Outline: Time-resolved MRA Background Technique Clinical Indications Future Directions Spatial Resolution SNR CNR Temporal Resolution

32 Traditional Cartesian sampling of k-k space 2D- FFT

33 Alternate Trajectories: Radial Sampling Sampling along radial spokes (2D-PR) 2D- FFT

34 Characteristics of Radial Sampling k x k y

35 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) = PE/16 proj 3D HYPR Speedup(radial) = proj/16 proj

36 Pitfalls: Resolution 3D TOF CE MRA DSA

37 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