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Coronary flow and flow reserve in canines using MR phase difference and complex difference processing
K L Wedding1, T M Grist, J D Folts
1Department of Medical Physics, University of Wisconsin-Madison, USA.
Insights
Magnetic resonance imaging (MRI) accurately measures coronary blood flow in canine circumflex arteries. This study validates MRI flow measurements against ultrasound, identifying processing techniques and error sources for improved heart disease diagnosis.
Area of Science:
- Cardiovascular Imaging
- Medical Physics
- Diagnostic Technology
Background:
- Coronary artery disease remains a leading cause of death in the US.
- Magnetic resonance imaging (MRI) offers noninvasive assessment of cardiac anatomy and physiology.
- Previous research established MRI accuracy for flow in the left anterior descending artery.
Purpose of the Study:
- To validate MRI-derived coronary flow measurements in canine circumflex arteries.
- To compare phase difference and complex difference MR velocity processing techniques.
- To identify sources of error in MR flow quantification using ultrasound as a standard.
Main Methods:
- MR flow measurements in canine circumflex arteries.
- Validation against transit time ultrasound measurements.
- Comparison of phase difference (PD) and complex difference (CD) MR data processing.
- Analysis of error sources including motion and signal-to-noise ratio.
Main Results:
- Phase difference processing (30% magnitude threshold) showed strong correlation with ultrasound (r=0.94) but was sensitive to vessel boundary identification.
- Complex difference processing correlated well with ultrasound, despite systematic underestimations.
- Identified error sources include ultrasound variability, low MR signal-to-noise, boundary detection issues, and motion artifacts.
Conclusions:
- MRI is a viable tool for noninvasive coronary flow measurement, with PD and CD methods offering different trade-offs in accuracy and robustness.
- Further optimization of MR techniques and processing is needed to minimize errors and enhance diagnostic utility for coronary artery disease.
- This study provides critical insights into the validation and limitations of MR flow quantification in a challenging anatomical region.
Abstract:
Coronary artery disease continues to be the leading cause of death for adults in the United States. Magnetic resonance imaging (MR) has the potential to dramatically impact the diagnosis of heart disease by noninvasively providing a wide range of anatomic and physiologic information. Previous research has shown that coronary flow, one component of a complete examination, can be accurately measured in the left anterior descending artery in vivo. The current work validates MR flow measurements in canine circumflex arteries using transit time ultrasound as a standard. The circumflex artery experiences greater in-plane motion and is a more stringent test for flow measurement accuracy. This work also compares two methods of processing MR velocity data, phase difference and complex difference techniques, and examines the sources of error present in the animal validation model. Phase difference processing with a 30% magnitude threshold best matched the mean ultrasound flow values (30% PD = 1.04 x US + 1.49, r = 0.94), but it was very sensitive to vessel boundary identification. The complex difference process was less sensitive to vessel boundary identification and correlated well with the transit time ultrasound despite systematic underestimations. The reasons for the discrepancies are shown to stem from a number of possible sources including variability of the ultrasound standard, low signal-to-noise ratios in the MR images, sensitivity of the MR technique to vessel boundary identification, and motion artifacts in the images.