Real-Time MRI – Outline
Biomed NMR JF11/59
Technical Considerations
- Data Acquisition
- Image Reconstruction
Preliminary Applications
- Joint Movements, Swallowing, Speaking
- Heart Function
A First Extension
- Cardiovascular Blood Flow
3D MRI Movies ?!
- An (Almost) Unbelievable Story …
Real-Time MRI – Robust, Fast, and Continuous
Biomed NMR JF11/52
Echo-Planar and Spiral Imaging
- Limited Spatial Resolution (single-shot version)
- Not Continuous (unless gradient-echo version with low flip angle)
- T2* and Off-Resonance Problems
Fast Spin-Echo (RARE) MRI
- High SAR (high field), Not Continuous
STEAM MRI
- Low SNR, Not Continuous
FLASH MRI
- Very Short TR/TE (high bandwidth), Low SAR, Continuous
- Fast? Undersampling!
Real-Time MRI – Radial vs Cartesian Encoding
Biomed NMR JF11/42
Cartesian
Simple Image Reconstruction
- Inverse Fourier Transformation
Radial
Robust Against Motion
- No Phase Encoding
- Central Sampling of k Space
Equivalence of Individual Spokes
- Tolerance Against Undersampling
- Minor Loss of Spatial Resolution
Parallel MRI as Regularized Nonlinear Inverse Problem
M Uecker et al, Magn Reson Med 60:674-682, 2008; Magn Reson Med 63:1456-1462, 2010 Biomed NMR JF11/65
Real-Time MRI – Outline
Biomed NMR JF11/59
Technical Considerations
- Data Acquisition
- Image Reconstruction
Preliminary Applications
- Joint Movements, Swallowing, Speaking
- Heart Function
A First Extension
- Cardiovascular Blood Flow
3D MRI Movies ?!
- An (Almost) Unbelievable Story …
Real-Time MRI of the Knee
Reconstructions Using Nonlinear Inversion
Biomed NMR JF11/51
Lifting of the Lower Leg in Prone Position
Central Section Lateral Section
Refocused Radial FLASH, TR/TE = 4.4/2.3 ms, 25o , 0.75 × 0.75 × 5 mm3
75 Spokes, 256 × 256 Matrix, Acquisition Time 333 ms, 3 Frames per Second
Real-Time MRI of the Temporomandibular Joint
Reconstructions Using Nonlinear Inversion
Collaboration: N Gersdorff Biomed NMR JF11/44
Voluntary Opening and Closing of the Mouth
Refocused Radial FLASH, TR/TE = 4.3/2.2 ms, 20o , 0.75 × 0.75 × 5 mm3
77 Spokes, 256 × 256 Matrix, Acquisition Time 333 ms, 3 Frames per Second
Real-Time MRI of Normal Swallowing
Reconstructions Using Nonlinear Inversion
S Zhang et al, 2011 Biomed NMR JF11/46
Voluntary Swallowing of 5 ml Pineapple Juice
RF-Spoiled Radial FLASH, TR/TE = 2.17/1.44 ms, 5o, 1.5 × 1.5 × 10 mm3, FOV 192 × 192 mm2
19 Spokes, 128 × 128 Matrix, Acquisition Time 41.2 ms, 24 Frames per Second
Real-Time MRI of Speaking – Sentences
Reconstructions Using Nonlinear Inversion
A Niebergall et al, 2011 Biomed NMR JF11/45
“You are watching a presentation about MRI in real time …”
RF-Spoiled Radial FLASH, TR/TE = 2.22/1.44 ms, 5o, 1.5 × 1.5 × 10 mm3, FOV 192 × 192 mm2
15 Spokes, 128 × 128 Matrix, Acquisition Time 33 ms, 30 Frames per Second
Real-Time MRI of the Heart – Short-Axis View
Reconstructions Using Nonlinear Inversion
M Uecker et al, NMR Biomed 23:986-994, 2010 Biomed NMR JF11/53
15 Spokes 11 Spokes
30 ms 22 ms
RF-Spoiled Radial FLASH, TR/TE = 2.0/1.3 ms, 8o, 2 × 2 × 8 mm3, FOV 256 × 256 mm2
15 / 11 Spokes, 128 × 128 Matrix, Acquisition Time 30 / 22 ms, 33 / 45 Frames per Second
Real-Time MRI of the Heart – Short-Axis View
Reconstructions Using Nonlinear Inversion
M Uecker et al, NMR Biomed 23:986-994, 2010 Biomed NMR JF11/54
9 Spokes 7 Spokes
18 ms 14 ms
RF-Spoiled Radial FLASH, TR/TE = 2.0/1.3 ms, 8o, 2 × 2 × 8 mm3, FOV 256 × 256 mm2
9 / 7 Spokes, 128 × 128 Matrix, Acquisition Time 30 / 22 ms, 55 / 71 Frames per Second
Real-Time MRI of the Heart – 100 Frames per Second
Reconstructions Using Nonlinear Inversion
M Uecker et al, NMR Biomed 23:986-994, 2010 Biomed NMR JF11/55
5 Spokes 5 Spokes
Short-Axis View Three-Chamber View
RF-Spoiled Radial FLASH, TR/TE = 2.0/1.3 ms, 8o, 2 × 2 × 8 mm3, FOV 256 × 256 mm2
5 Spokes, 128 × 128 Matrix, Acquisition Time 10 ms, 100 Frames per Second
Real-Time MRI of the Heart – 1.5 mm Resolution
Reconstructions Using Nonlinear Inversion
M Uecker et al, NMR Biomed 23:986-994, 2010 Biomed NMR JF11/56
15 Spokes, 34 ms 15 Spokes, 34 ms
Short-Axis View Three-Chamber View
RF-Spoiled Radial FLASH, TR/TE = 2.28/1.46 ms, 8o, 1.5 × 1.5 × 6 mm3, FOV 256 × 256 mm2
15 Spokes, 176 × 176 Matrix, Acquisition Time 34 ms, 30 Frames per Second
Real-Time MRI – Outline
Biomed NMR JF11/59
Technical Considerations
- Data Acquisition
- Image Reconstruction
Preliminary Applications
- Joint Movements, Swallowing, Speaking
- Heart Function
A First Extension
- Cardiovascular Blood Flow
3D MRI Movies ?!
- An (Almost) Unbelievable Story …
Real-Time MRI of the Heart – Turbulent Flow
Reconstructions Using Nonlinear Inversion
S Zhang et al, J Cardiovasc Magn Reson 12:39, 2010 Biomed NMR JF11/57
18 ms 18 ms
Four-Chamber View Two-Chamber View
RF-Spoiled Radial FLASH, TR/TE = 2.0/1.3 ms, 8o, 2 × 2 × 8 mm3, FOV 256 × 256 mm2
9 Spokes, 128 × 128 Matrix, Acquisition Time 18 ms, 55 Frames per Second
Velocity-Encoded Phase-Contrast MRI in Real Time
Reconstructions Using Nonlinear Inversion
AA Joseph et al, NMR Biomed, 2011 Biomed NMR JF11/41
Two Acquisitions Using Highly Undersampled Radial FLASH (interleaved or sequential) with
Two Bipolar Phase-Contrast Gradients Gvenc of Opposite Polarity (through-plane flow)
Velocity-Encoded Phase-Contrast MRI in Real Time
Reconstructions Using Nonlinear Inversion
AA Joseph et al, NMR Biomed, 2011 Biomed NMR JF11/37
Ascending Aorta, Through-Plane Flow, venc = 150 cm s-1
Anatomy Magnitude Image
RF-Spoiled Radial FLASH, TR/TE = 3.44/2.76 ms, 10o, 1.8 × 1.8 × 6 mm3, FOV 256 × 256 mm2
2 × 7 Spokes, 144 × 144 Matrix, Total Acquisition Time 48 ms, 21 Frames per Second
Velocity-Encoded Phase-Contrast MRI in Real Time
Reconstructions Using Nonlinear Inversion
AA Joseph et al, NMR Biomed, 2011 Biomed NMR JF11/38
Ascending Aorta, Through-Plane Flow, venc = 150 cm s-1
Phase-Contrast Map Velocity Profile (20 Heartbeats)
RF-Spoiled Radial FLASH, TR/TE = 3.44/2.76 ms, 10o, 1.8 × 1.8 × 6 mm3, FOV 256 × 256 mm2
2 × 7 Spokes, 144 × 144 Matrix, Total Acquisition Time 48 ms, 21 Frames per Second
Velocity-Encoded Phase-Contrast MRI in Real Time
Reconstructions Using Nonlinear Inversion
AA Joseph et al, NMR Biomed, 2011 Biomed NMR JF11/76
Ascending Aorta, Through-Plane Flow, venc = 150 cm s-1
Dynamic Velocities During Single Heartbeat (12 Frames = 512 ms)
RF-Spoiled Radial FLASH, TR/TE = 3.05/2.29 ms, 10o, 1.8 × 1.8 × 6 mm3, FOV 256 × 256 mm2
2 × 7 Spokes, 144 × 144 Matrix, Total Acquisition Time 42.5 ms, 23 Frames per Second
Real-Time MRI – Outline
Biomed NMR JF11/59
Technical Considerations
- Data Acquisition
- Image Reconstruction
Preliminary Applications
- Joint Movements, Swallowing, Speaking
- Heart Function
A First Extension
- Cardiovascular Blood Flow
3D MRI Movies ?!
- An (Almost) Unbelievable Story …
Spatially Encoded Phase-Contrast MRI
3D MRI of 2D Objects Using 2 Projection Images
KD Merboldt et al, Magn Reson Med 66:950-957, 2011 Biomed NMR JF11/25
Two Acquisitions of a Projection Image (nonselective RF excitation) with
Two Monopolar Phase-Contrast Gradients Gpc of Opposite Polarity (perpendicular encoding)
Spatially Encoded Phase-Contrast MRI
3D MRI of 2D Objects Using Two Projection Images
KD Merboldt et al, Magn Reson Med 66:950-957, 2011 Biomed NMR JF11/26
Three-Dimensional Visualization of the 2D Phase-Contrast Projection Map
2D Phase-Contrast Projection Map Using Radial FLASH (color = phase difference)
Spatially Encoded Phase-Contrast MRI in Real Time
3D MRI of the Acting Human Hand – 40 ms Resolution
KD Merboldt et al, Magn Reson Med 66:950-957, 2011 Biomed NMR JF11/47
RF-Spoiled Radial FLASH, TR/TE = 2.88/2.25 ms, 5o (nonselective), 2 × 2 mm2, FOV 256 × 256 mm2
2 × 7 Spokes (FOV 256 mm), 128 × 128 Matrix, Total Acquisition Time 40 ms, 25 Frames per Second
Reconstructions Using Nonlinear Inversion and Phase Difference
Spatially Encoded Phase-Contrast MRI in Real Time
3D MRI of 1D Objects Using 3 MRI Signals
KD Merboldt et al, Magn Reson Med 66:950-957, 2011 Biomed NMR JF11/27
Three Acquisitions of a Frequency-Encoded MRI Signal (nonselective RF excitation)
Two Orthogonal Monopolar Phase-Contrast Gradients Gpc1 and Gpc2 (two phase-encodings)
Reconstructions Using Fourier Transformation and Phase Difference
Spatially Encoded Phase-Contrast MRI in Real Time
3D MRI of a Rotating Water-Filled Tube – 5 ms Resolution
KD Merboldt et al, Magn Reson Med 66:950-957, 2011 Biomed NMR JF11/22
Frequency-Encoded Gradient Echoes, TR/TE = 1.68/1.15 ms, 12o (nonselective), 2 × 2 mm2
3 Gradient Echoes, 128 × 128 Matrix, Total Acquisition Time 5 ms, 200 Frames per Second
Reconstructions Using Fourier Transformation and Phase Difference
Real-Time MRI – Summary
Biomed NMR JF11/58
Data Acquisition – Low-Flip Angle Gradient Echo MRI (FLASH)
- Radial Encoding with Pronounced Undersampling
- Multi-Coil Data for Parallel MRI
Image Reconstruction – Regularized Nonlinear Inversion
- Joint Estimation of Image Content and Coil Sensitivities
- Regularization with Previous Frame
- Temporal and Spatial Filtering
Current Projects
- Reduction of Reconstruction Time (GPU Implementation)
- Adaptation of Post-Processing Software (Cardiovascular MR)
- Improvement of the Algorithm (Regularization, Filtering)
- Many More Applications and Extensions