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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