Francisco Contijoch1,2, Yuchi Han3, Srikant Kamesh Iyer4, Peter Kellman5, Gene Gualtieri6, Mark A Elliott4, Sebastian Berisha4, Joseph H Gorman7, Robert C Gorman7, James J Pilla4, Walter R T Witschey4. 1. Department of Bioengineering, Jacobs School of Engineering, University of California, San Diego, CA, United States of America. 2. Department of Radiology, School of Medicine, University of California, San Diego, CA, United States of America. 3. Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America. 4. Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America. 5. National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD, United States of America. 6. AJO, Philadelphia, PA, United States of America. 7. Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America.
Abstract
BACKGROUND: Segmented cine cardiac MRI combines data from multiple heartbeats to achieve high spatiotemporal resolution cardiac images, yet predefined k-space segmentation trajectories can lead to suboptimal k-space sampling. In this work, we developed and evaluated an autonomous and closed-loop control system for radial k-space sampling (ARKS) to increase sampling uniformity. METHODS: The closed-loop system autonomously selects radial k-space sampling trajectory during live segmented cine MRI and attempts to optimize angular sampling uniformity by selecting views in regions of k-space that were not previously well-sampled. Sampling uniformity and the ability to detect cardiac phase in vivo was assessed using ECG data acquired from 10 normal subjects in an MRI scanner. The approach was then implemented with a fast gradient echo sequence on a whole-body clinical MRI scanner and imaging was performed in 4 healthy volunteers. The closed-loop k-space trajectory was compared to random, uniformly distributed and golden angle view trajectories via measurement of k-space uniformity and the point spread function. Lastly, an arrhythmic dataset was used to evaluate a potential application of the approach. RESULTS: The autonomous trajectory increased k-space sampling uniformity by 15±7%, main lobe point spread function (PSF) signal intensity by 6±4%, and reduced ringing relative to golden angle sampling. When implemented, the autonomous pulse sequence prescribed radial view angles faster than the scan TR (0.98 ± 0.01 ms, maximum = 1.38 ms) and increased k-space sampling mean uniformity by 10±11%, decreased uniformity variability by 44±12%, and increased PSF signal ratio by 6±6% relative to golden angle sampling. CONCLUSION: The closed-loop approach enables near-uniform radial sampling in a segmented acquisition approach which was higher than predetermined golden-angle radial sampling. This can be utilized to increase the sampling or decrease the temporal footprint of an acquisition and the closed-loop framework has the potential to be applied to patients with complex heart rhythms.
BACKGROUND: Segmented cine cardiac MRI combines data from multiple heartbeats to achieve high spatiotemporal resolution cardiac images, yet predefined k-space segmentation trajectories can lead to suboptimal k-space sampling. In this work, we developed and evaluated an autonomous and closed-loop control system for radial k-space sampling (ARKS) to increase sampling uniformity. METHODS: The closed-loop system autonomously selects radial k-space sampling trajectory during live segmented cine MRI and attempts to optimize angular sampling uniformity by selecting views in regions of k-space that were not previously well-sampled. Sampling uniformity and the ability to detect cardiac phase in vivo was assessed using ECG data acquired from 10 normal subjects in an MRI scanner. The approach was then implemented with a fast gradient echo sequence on a whole-body clinical MRI scanner and imaging was performed in 4 healthy volunteers. The closed-loop k-space trajectory was compared to random, uniformly distributed and golden angle view trajectories via measurement of k-space uniformity and the point spread function. Lastly, an arrhythmic dataset was used to evaluate a potential application of the approach. RESULTS: The autonomous trajectory increased k-space sampling uniformity by 15±7%, main lobe point spread function (PSF) signal intensity by 6±4%, and reduced ringing relative to golden angle sampling. When implemented, the autonomous pulse sequence prescribed radial view angles faster than the scan TR (0.98 ± 0.01 ms, maximum = 1.38 ms) and increased k-space sampling mean uniformity by 10±11%, decreased uniformity variability by 44±12%, and increased PSF signal ratio by 6±6% relative to golden angle sampling. CONCLUSION: The closed-loop approach enables near-uniform radial sampling in a segmented acquisition approach which was higher than predetermined golden-angle radial sampling. This can be utilized to increase the sampling or decrease the temporal footprint of an acquisition and the closed-loop framework has the potential to be applied to patients with complex heart rhythms.
Authors: Christoph Moenninghoff; Lale Umutlu; Christian Kloeters; Adrian Ringelstein; Mark E Ladd; Antje Sombetzki; Thomas C Lauenstein; Michael Forsting; Marc Schlamann Journal: Acad Radiol Date: 2013-03-07 Impact factor: 3.173
Authors: Michael Markl; Andreas Harloff; Thorsten A Bley; Maxim Zaitsev; Bernd Jung; Ernst Weigang; Mathias Langer; Jürgen Hennig; Alex Frydrychowicz Journal: J Magn Reson Imaging Date: 2007-04 Impact factor: 4.813