Real-Time MRI using NLINV
For recent applications see Real-Time MRI in the applications section.
MRI - The Speed Problem
Spatial Encoding | Image Reconstruction |
Magnetic Field Gradient G | Inverse Fourier Transformation |
Rapid MRI - FLASH
No Waiting Periods
Low Flip Angle Gradient-Echo MRI
Applications
Continuous Acquisitions @0.5-2s
ECG-synchronized Cardiac MRI
MR Angiography & Susceptibility
Three-Dimensional MRI
J Frahm et al, German Patent P 3504734.8, February 12, 1985
Real-Time MRI - FLASH + NLINV
Extreme Data Undersampling
Radial Gradient-Echo MRI
Advanced Parallel Imaging (NLINV)
Temporal Regularization
Applications
Continuous Acquisitions @≥ 10 ms
Dynamic MRI in Real Time
Frahm, Uecker & Zhang, US Patent 8, 384, 383 B2, March 23, 2010
Real-Time MRI - Radial Gradient-Echo MRI
Rapid Gradient-Echo Sequences
- RF Spoiled FLASH (T1)
- Refocused FLASH (T2/T1)
- Fully Balanced SSFP (T2/T1)
Radial Encoding
Robust against Motion
- No Phase Encoding
- Central Oversampling
Equivalence of Spokes
- Tolerant against Undersampling
Different Spokes for Serial Acquisitions
S Zhang et al, J Magn Reson Imaging 31:101-109, 2010 [Online Version]
Parallel MRI - Image Reconstruction by Nonlinear Inversion (NLINV)
Joint Estimation of Image & Coil Sensitivities
Spatial Encoding | Image Reconstruction | |
Magnetic Field Gradient G | Inverse Fourier Transformation | |
M Uecker et al, Magn Reson Med 60:674-682, 2008 [Online Version]
Real-Time MRI - NLINV with Temporal Regularization
Joint Estimation of Image & Coil Sensitivities
Minimization of Cost Function ( =Image/Coils, =Measured Data)
$$\Phi (x) = \frac{1}{2} ||Ax-y||_2^2 + \sum_i \lambda_i \cdot R_i(x) \qquad x = argmin_x \Phi (x)$$
Data Consistency |
Temporal Regularization |
M Uecker et al, NMR Biomed 23:986-994, 2010 [Online Version]
Real-Time MRI - Accelerated Computing
Online Reconstruction with Integrated GPU-Computer
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Parallelization of the NLINV Reconstruction Algorithm
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Implementation on Server with 2 × 4 Graphical Processing Units (Supermicro, NVIDIA Titan X)
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Development of a Unique Library for Multiple GPU Programming
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Full Integration into Commercial MRI System (Siemens VD13)
- Up to 50 Frames per Second
Schaetz & Uecker, Lect Notes Comput Sci 7439:114-128, 2012 [Online Version]
Real-Time MRI - Temporal Fidelity
Experimental details: RF-Spoiled Radial FLASH , 1.6 × 1.6 × 6 mm3, Acquisition Time 33.3 / 10.0 ms, 30 / 100 Frames per Second
J Frahm et al, The Open Med Imaging J 8:1-7, 2014 [Online Version]