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Myocardial suppression in vivo by spin locking with composite pulses
W T Dixon1, J N Oshinski, J D Trudeau
1Frederik Philips Magnetic Resonance Research Center, Emory University Department of Radiology, Atlanta, Georgia, USA.
Insights
This study introduces T1 rho-weighting to improve cardiac MRI, enhancing the contrast between blood and myocardium. This technique offers better visualization of heart borders, especially in patients with impaired ventricular function.
Area of Science:
- Cardiovascular Magnetic Resonance Imaging
- Medical Physics
- Biomedical Engineering
Background:
- Standard cardiac MRI sequences often struggle with adequate contrast between blood pool and myocardium.
- Accurate delineation of myocardial borders is crucial for diagnosing and managing cardiac conditions, particularly in patients with poor ventricular function.
Purpose of the Study:
- To investigate the efficacy of T1 rho-weighting for improving myocardium-blood contrast in contrast-enhanced, gradient-echo, bright-blood cine cardiac MRI.
- To assess the impact of this technique on the delineation of myocardial borders.
Main Methods:
- Implementation of a composite spin-lock pulse sequence prior to each observation pulse to achieve T1 rho-weighting.
- Acquisition of standard and T1 rho-weighted gradient-echo, bright-blood cine images at 1.5T.
- Evaluation of image contrast and myocardial border delineation qualitatively and quantitatively.
Main Results:
- T1 rho-weighting significantly enhanced the contrast between blood and myocardium, increasing blood intensity relative to muscle.
- Standard images showed blood intensity 2x that of muscle, while T1 rho-weighted images showed 3-4x intensity.
- Initial clinical evaluation demonstrated improved qualitative and quantitative delineation of myocardial borders in patients with poor ventricular function.
Conclusions:
- T1 rho-weighting is an effective method for improving myocardium-blood contrast in cardiac MRI.
- This technique offers significant advantages for visualizing myocardial borders, aiding in the assessment of cardiac function.
Abstract:
Improved myocardium-blood contrast by myocardial suppression resulting from T1 rho-weighting in contrast-enhanced, gradient-echo, bright-blood cine images, acquired at 1.5T, is shown. In the standard images, blood has twice the intensity of muscle. In similar T1 rho-weighted images, it has 3-4 times the intensity of muscle. A composite spin-lock pulse before each observation pulse provides T1 rho-weighting. A typical pulse was: 90y-135x-360x-135x-90(-y) with element durations: 0.84, 1.26, 8.12, 1.26, and 0.84 ms. The tolerance of this composite pulse to shimmering and frequency errors allows spin locking with comparatively weak RF and therefore low specific absorption rate (SAR). Initial clinical evaluation on patients with poor ventricular function demonstrates both a qualitative and quantitative improvement in delineation of myocardial borders.