Abstract
Objective. Atherosclerosis is a leading cause of mortality and morbidity. Optical endoscopy, ultrasound, and X-ray offer minimally invasive imaging assessments but have limited sensitivity for characterizing disease and therapeutic response. Magnetic resonance imaging (MRI) endoscopy is a newer idea employing tiny catheter-mounted detectors connected to the MRI scanner. It can see through vessel walls and provide soft-tissue sensitivity, but its slow imaging speed limits practical applications. Our goal is high-resolution MRI endoscopy with real-time imaging speeds comparable to existing modalities. Methods. Intravascular (3 mm) transmit-receive MRI endoscopes were fabricated for highly undersampled radial-projection MRI in a clinical 3-tesla MRI scanner. Iterative nonlinear reconstruction was accelerated using graphics processor units connected via a single ethernet cable to achieve true real-time endoscopy visualization at the scanner. MRI endoscopy was performed at 6-10 frames/sec and 200-300 μm resolution in human arterial specimens and porcine vessels ex vivo and in vivo and compared with fully sampled 0.3 frames/sec and three-dimensional reference scans using mutual information (MI) and structural similarity (3-SSIM) indices. Results. High-speed MRI endoscopy at 6-10 frames/sec was consistent with fully sampled MRI endoscopy and histology, with feasibility demonstrated in vivo in a large animal model. A 20-30-fold speed-up vs. 0.3 frames/sec reference scans came at a cost of ~7% in MI and ~45% in 3-SSIM, with reduced motion sensitivity. Conclusion. High-resolution MRI endoscopy can now be performed at frame rates comparable to those of X-ray and optical endoscopy and could provide an alternative to existing modalities, with MRI's advantages of soft-tissue sensitivity and lack of ionizing radiation.
Highlights
Atherosclerosis is a prevalent factor in cardiovascular disease and a leading cause of mortality and morbidity [1,2,3]
Undersampling was previously proposed as a means of accelerating Magnetic resonance imaging (MRI) endoscopy [20]
The advance here was achieved using stand-alone hardware developed for real-time MRI that is connected to the scanner via a simple ethernet cable [21] and a modified MRI pulse sequence that replaced slice selection with adiabatic excitation to provide imaging from the viewpoint of the coil at the endoscope’s tip
Summary
Atherosclerosis is a prevalent factor in cardiovascular disease and a leading cause of mortality and morbidity [1,2,3]. Other minimally invasive imaging options include intravascular (IV) ultrasound (IVUS) and optical coherence tomography (OCT), which are clinically available but not widely used These can offer improved spatial resolution and contrast for evaluating stenoses, identifying potentially vulnerable lesions, and facilitating intervention [9,10,11]. Confounding factors are the presence of calcifications in the case of IVUS [12, 13] and optical penetration and a requirement for blood-free access to the vessel wall in the case of OCT [14, 15] All of these modalities employ X-ray guidance and expose patients and operators to ionizing radiation
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