Contrast Enhanced MRA Using Phase Contrast Composite Image for HYPR Reconstruction
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Solution Overview
Problem
Current magnetic resonance angiography (MRA) techniques face challenges in achieving high spatial resolution and signal-to-noise ratio (SNR) due to the need for extensive data acquisition, often resulting in lengthy scan times and artifacts from undersampling.
Innovation Solution
The method employs a highly constrained backprojection reconstruction (HYPR) using a phase contrast composite image generated from a separate scan, allowing for improved distribution of signal samples across pixels and reducing the number of required projection views, thereby enhancing image quality and SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the number of projection views is reduced to shorten scan time, then scan time is reduced, but image quality and SNR deteriorate
Solution Approach 1:
A phase contrast composite image is acquired and processed in advance to create a mask image that defines vascular structures before the actual contrast-enhanced imaging. This preliminary action allows the mask to guide subsequent reconstruction, enabling reduced sampling without loss of image quality.
Solution Approach 2:
The mask image provides spatially varying constraints that allow different regions of the image to be reconstructed with different sampling densities. Vascular regions are prioritized for accurate reconstruction while non-vascular regions can use lower sampling, optimizing the trade-off between scan time and image quality.
2Device complexity
If conventional backprojection reconstruction is used, then reconstruction is simple, but spatial resolution and SNR are limited
Solution Approach 1:
The reconstruction method changes the parameters of the backprojection process by incorporating mask-based weighting factors that modulate the contribution of each projection view. This transforms the standard backprojection into a constrained backprojection that achieves superior resolution and SNR.
Solution Approach 2:
The mask image serves as an intermediary element that mediates between the raw projection data and the final reconstructed image. It translates anatomical knowledge into reconstruction constraints, enabling enhanced image quality without requiring complex iterative methods.
3Loss of time
If highly undersampled data is used to reduce scan time, then scan time is reduced, but artifacts increase
Solution Approach 1:
The method converts the harmful effect of undersampling (which causes artifacts) into a beneficial constraint-based reconstruction approach. By using the mask image to guide the backprojection, the reconstruction process actively compensates for missing data, transforming artifact-prone undersampled data into high-quality images.
Solution Approach 2:
The mask image provides feedback information about the expected signal distribution in vascular structures. This feedback is used to weight and prioritize certain projection views during reconstruction, allowing the system to correct for undersampling effects and minimize artifacts in the final image.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the reconstruction of contrast-enhanced MRA images with unprecedented spatial resolution and SNR, reducing scan time while minimizing artifacts, and provides valuable flow direction information typically not available in standard CEMRA or DSA scans.
Implementation Method 1
Magnetic resonance imaging (MRI) uses the nuclear magnetic resonance (NMR) phenomenon to produce images. When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency.
Implementation Method 2
When utilizing these signals to produce images, magnetic field gradients (Gx Gy and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used.
Implementation Method 3
MR methods have also been developed that encode motion into the phase of the acquired signal as disclosed in U.S. Pat. No. Re. 32,701. These form the second class of MRA techniques and are known as phase contrast (PC) methods.
Data Source
AI summary
Mask projection views are obtained prior to the arrival of a contrast agent during a dynamic contrast enhanced MRA study. After the arrival of the contrast agent, a set of undersampled contrast enhanced projection views are obtained for each of a plurality of time frames. Corresponding mask projection views are subtracted from the contrast enhanced projection views to provide sparse contrast enhanced projection view sets. A phase contrast scan of a region of interest is performed prior to or after the arrival of the contrast agent. The phase contrast image is used as a composite image in a HYPR reconstruction of the sparse projection view sets to produce first pass contrast enhanced images. Iterative HYPR reconstructions can also be performed to remove venous information from the reconstructed images.