1. 1 W. Rooney May 20, 2004 Imaging the Awake Animal MRI Efforts Overview

2. 2 MRI Environment I.Static Magnetic Field II. Radiofrequency Field III.Magnetic Field Gradients Frequency encode Phase encode

3. 3 Motion through magnetic field gradients Larmor relation:  =  B magnetic field gradients render B is spatially dependent Frequency encode Phase encode kxkx kyky

4. 4 Motion Induced R 2 * changes ΔR 2 * (Hz) -3.0 +2.6 -2.8 -0.5 +7.5 +0.3 ΔR 2 * (Hz) +1.3 +1.4 -0.3 +0.5 -1.8 +1.9 5.8 degrees 1.5 degrees Rotations as small as 1.5° may cause R 2 * changes similar to those during brain activation Lateral slices show larger R 2 * changes. R 2 * changes increase for larger angles. ΔR 2 * change during brain activation: ~ 2- 3Hz Caparelli, et al 2003

5. 5 Quantitative MRI - Difficulties  Signal changes are often small (<5%)  Subject motion causes signal changes of similar magnitude, due to: Rigid body transformation (translations & rotations) Magnetic field changes– geometric distortions & susceptibility  Even the most advanced retrospective motion correction algorithms fail if motion is excessive  Therefore, it is very difficult or impossible to perform MRI in  awake animals  sick patients and children

6. 6 Overall Goal - MRI Increase 5 to 10-fold the range of motion acceptable for susceptibility- based functional MRI techniques.

7. 7 MRI Projects I.Prospective motion correction in MRI (Lead: Rooney, BNL Chemistry) II. Dynamic prospective adjustment of main magnetic field during MRI (Lead: Wanderer, BNL Magnet Division) III.Retrospective motion correction (Lead: Ernst, BNL Medical)

8. 8 W. Rooney, X. Li, J. Mead, R. Wang May 20, 2004 Imaging the Awake Animal Prospective Motion Correction in MRI

9. 9 - MRI is extremely motion sensitive - Post-acquisition corrections have limitations - Dynamic adjustment of MRI acquisition possible Specific Aims: - develop and validate an MRI compatible motion sensing device - design and construct electronic module to synthesize sensor output - integrate motion sensor and electronic module into MRI instrument

10. 10 time lab frame “brain” frame 4 1 2 3 MRI is Motion Sensitive Y Z X

11. 11 spatial real frequency space lab frame “brain” frame lab frame “brain” frame Image Quality Restoration motion corrupted hybrid corrected 2 4 4 2

12. 12 Laser PSD 2 T R PSD 1 ADC-DSP Motion Tracking Compensation Circuit X INPUT Y Z RF Acquisition parameters X' Y' Z' RF PSD 3 Dynamic Adjustment of MRI Acquisitions Position sensing detectors (PSDs) Output to MRI instrument

13. 13 Detector array performs superbly in MRI environment: 4 T B 0, gradients (  B 0 /  t = 30 T/s), and RF (170MHz) 20 μm vibration “noise” output during MRI operation Detector Validation in MRI B 0 = ~0 B 0 = 4 T beam flexion (mechanical resonance) vibration “noise”

14. 14 - LabView System (2 ADC/DAC boards, 2.4 GHz PC) - PSD sensor array - Inputs 3 gradient waveforms 6 PSD sensor signals 2 trigger signals -Outputs 3 modified gradient waveforms RF modifying signals Motion Detection/Compensation System

15. 15 Motion Compensation System Integration

16. 16 Motion Compensation Control Panel

17. 17 Baseline MRI 5-compartment phantom 4 T whole-body MRI (GRE sequence) Scan acquired with MRI instrument in normal configuration Baseline 0 Test Phantom

18. 18 Baseline MRI 5-compartment phantom 4 T whole-body MRI (GRE sequence) Scan acquired with motion detection & compensation unit in-line Detector in-line Detector System Integration

19. 19 Detector in-line & analog filter & digital filter Detector System Integration

20. 20 Baseline 0 Rotate 90º z & invert z y x Gradient Mixing

21. 21 8º Wobble Rotation 8º Wobble w/Correction z y x Rotational Image Correction

22. 22 D. Schlyer, C. Woody, P. Vaska, W. Rooney May 20, 2004 PET-MRI Instrumentation

23. 23 PET Detector System Test

24. 24 Detector Test in MRI Environment Benchtop4 T, RF dB 0 /dt

25. 25 PET/MRI Detector Configurations

26. 26 W. Rooney, X. Li, J. Mead, R. Wang May 20, 2004 Animal Position Tracking

27. 27 Position Sensing Detectors (PSDs) PSDs are silicon photodiodes Sensitive to 400-1100 nm light Analog signal output proportional to position of light spot Excellent linearity, resolution and response time

28. 28 Rigid Body Transformation Algorithm 3 translations & 3 rotations t = 0 t > 0

29. 29 Rotation Matrix - Accuracy (%) Translation Accuracy (%) 0.00160.00030.0002 0.000020.00270.019 0.000040.000021.938 0.000121.9540.00003  Angular accuracy < 0.1°  Accuracy < 1μm y x z Computer-controlled precision motion platform (R.Ferrieri) Precision: 0.8  m and 0.0005º Programmable movements at 200 μm/s Provides motion “gold standard” Rigid Body Transformation Algorithm

30. 30 123456123456 Rigid-Body Motion Sensor Sensor arraySensor output

31. 31 Sensor Input Algorithm Output XYZXYZ 123456123456 Rotations Translations Motion Tracking Algorithm