1. Artifacts in Cardiac MRI Andreas Sigfridsson, IMV/IMT/CMIV Andreas Sigfridsson, IMV/IMT/CMIV 2007-04-27

2. sigge@imv.liu.se Dynamic imaging Images are acquired line-by-line in k- space Motion during acquisition causes artifacts, not blurring Motion during acquisition causes artifacts, not blurring Special care must be taken Special care must be takenTriggering Acquisition ordering

3. sigge@imv.liu.se Example Simulation example 256x256, TR=20 ms, total scan time ~5 s 256x256, TR=20 ms, total scan time ~5 s Image domaink-space

4. sigge@imv.liu.se Signal saturation Signal recovery - relaxation

5. sigge@imv.liu.se Signal saturation Progress to steady-state

6. sigge@imv.liu.se Varying signal during inflow The MR signal is increased during inflow Signal increase related to flow velocity More magnetization because of T1 decay/recovery More magnetization because of T1 decay/recovery Static spins, saturated signal Flowing spins, fresh signal

7. sigge@imv.liu.se Varying signal intensity Simulated six sinusoidal heart beats Intensity Image (animation)

8. sigge@imv.liu.se Varying signal intensity, results Reconstructed image High contrastNormal contrast

9. sigge@imv.liu.se Varying signal intensity, k-space Image artifacts because of k-space sampling Different lines are acquired with different signal intensity Different lines are acquired with different signal intensity

10. sigge@imv.liu.se Varying signal intensity, analysis Analyze signal

11. sigge@imv.liu.se Slow sine variation IntensityFT(Intensity)

12. sigge@imv.liu.se Varying signal intensity, results Reconstructed image High contrastNormal contrast

13. sigge@imv.liu.se Fast sine variation IntensityFT(Intensity)

14. sigge@imv.liu.se Fast sine variation IntensityFT(Intensity)

15. sigge@imv.liu.se “Physiological” variation Aortic flow (handcrafted, not actual data) Intensity (one beat) Intensity (whole scan)

16. sigge@imv.liu.se “Physiological” variation Intensity variation (animation)

17. sigge@imv.liu.se “Physiological” variation Intensity FT(Intensity)

18. sigge@imv.liu.se “Physiological” variation Reconstructed images High contrast Normal contrast

19. sigge@imv.liu.se Remedies Triggering Wait for ECG R-tag Wait for ECG R-tag Wait additional trigger delay time Wait additional trigger delay time Acquire one (or several) k-space lines Acquire one (or several) k-space lines Acquisition reordering Measure current cardiac (or respiratory phase) Measure current cardiac (or respiratory phase) Choose k-space line to acquire Choose k-space line to acquire Creates a slow varying intensity curve along k-space Creates a slow varying intensity curve along k-space

20. sigge@imv.liu.se Triggering - random phase If triggering is not accurate, random variations will still be left Intensity FT(Intensity)

21. sigge@imv.liu.se Random phase, reconstructed Normal contrastHigh contrast

22. sigge@imv.liu.se Acquisition reordering IntensityFT(Intensity)

23. sigge@imv.liu.se Acquisition reordering OrderedRandom

24. sigge@imv.liu.se Acquisition reordering Reconstructed images High contrastNormal contrast

25. sigge@imv.liu.se Actual examples ECG triggering failed

26. sigge@imv.liu.se Dynamic imaging Images are acquired line-by-line in k- space Motion during acquisition causes artifacts, not blurring Motion during acquisition causes artifacts, not blurring Special care must be taken Special care must be takenTriggering Acquisition ordering Artifacts might be predictable through use of Fourier transform Artifacts might be predictable through use of Fourier transform