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MRA studies of arterial stenosis: improvements by diastolic acquisition
D Saloner1, K Selby, C M Anderson
1Department of Radiology, VA Medical Center, San Francisco, CA 94121.
Abstract:
Cardiac-phase-specific data acquisition is used to reduce signal loss in MR Angiography resulting from disturbed flow. RF pulses are delivered continuously throughout the cardiac cycle, but incrementation of phase-encoding gradients and data storage are enabled only during the chosen part of the cycle. Studies in a stenotic pulsatile flow phantom demonstrate that poststenotic signal loss is primarily determined by the mean flow velocity, and is not appreciably affected by acceleration or deceleration of the mean flow rate. The signal loss is least in diastole. In vivo studies in patients with carotid artery disease show that data acquisition in diastole reduces the apparent degree and extent of carotid bifurcation stenosis and provides a crisper definition of the vascular lumen. The additional time required for cardiac-phase-specific acquisition can be reduced by gating only the lower-order phase-encoding lines while retaining acceptable image quality.
Insights
Cardiac-phase-specific MRI reduces signal loss in MR Angiography from disturbed flow. Acquiring data during diastole minimizes stenosis effects and improves vascular imaging, especially in carotid artery disease patients.
Area of Science:
- Medical Imaging
- Cardiovascular Imaging
- Magnetic Resonance Angiography
Background:
- Signal loss in Magnetic Resonance Angiography (MRA) is a significant challenge, particularly in areas of disturbed blood flow.
- This signal loss can lead to underestimation of stenosis severity and reduced visualization of vascular structures.
- Cardiac-phase-specific data acquisition aims to mitigate these artifacts by synchronizing image acquisition with the cardiac cycle.
Purpose of the Study:
- To investigate the impact of cardiac-phase-specific data acquisition on signal loss in MR Angiography.
- To evaluate the relationship between flow velocity and signal loss in stenotic phantom models.
- To assess the clinical utility of diastolic acquisition for imaging carotid artery stenosis.
Main Methods:
- Utilized a pulsatile flow phantom with simulated stenosis to study signal loss characteristics.
- Performed in vivo Magnetic Resonance Angiography (MRA) in patients with carotid artery disease.
- Acquired data during specific cardiac phases (diastole) and compared with conventional acquisition methods.
Main Results:
- Post-stenotic signal loss in phantoms was primarily dependent on mean flow velocity, not flow acceleration.
- Signal loss was minimized when data acquisition occurred during diastole.
- Diastolic acquisition in patients reduced the apparent severity of carotid bifurcation stenosis and enhanced lumen definition.
Conclusions:
- Cardiac-phase-specific data acquisition, particularly during diastole, effectively reduces signal loss in MR Angiography.
- This technique improves the accuracy of stenosis assessment and vascular imaging in conditions like carotid artery disease.
- Optimizing acquisition timing, such as gating lower-order phase-encoding lines, can reduce scan time while maintaining image quality.