Non-Contrast MRA Using Dynamic Slice Orientation and FOV Shifting
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Solution Overview
Problem
Current non-contrast enhanced magnetic resonance angiography (MRA) methods are limited by sensitivity to patient motion, inadequate portrayal of vessel anatomy in severe vascular disease, and excessively long scan times, with challenges in suppressing venous signals and maintaining arterial conspicuity across varying flow velocities.
Innovation Solution
The method involves orienting imaging slices away from the axial direction and shifting the field-of-view to align with the vasculature, using RF saturation pulses to suppress signals, and employing a quiescent interval to synchronize data acquisition with arterial flow, allowing for efficient acquisition of k-space data and reconstruction of angiographic images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-contrast enhanced MRA methods are used to avoid gadolinium-based contrast agents, then patient safety is improved, but scan time becomes excessively long and image quality deteriorates
Solution Approach 1:
The patent applies preliminary saturation pulses to specific imaging slices before the actual data acquisition. These saturation pulses are applied to slices that will not be imaged in the current sequence, preparing the tissue magnetization in advance to suppress venous signal in those regions during the subsequent acquisition period, thereby enabling faster scan times without compromising image quality.
Solution Approach 2:
The patent divides the imaging volume into multiple discrete imaging slices and applies saturation pulses selectively to specific slices rather than the entire volume. This segmentation allows the system to suppress venous signal in unimaged slices while maintaining arterial signal in the target slices, enabling parallel processing and reducing overall scan time.
2Object-generated harmful factors
If RF saturation pulses are applied to suppress venous signals, then venous signal suppression is improved, but arterial signal may also be suppressed if timing is not precise
Solution Approach 1:
The patent applies saturation pulses with specific timing and spatial localization to target only venous blood in regions where it flows. By carefully selecting the timing of saturation pulses relative to the cardiac cycle and by localizing them to specific imaging slices, the system suppresses venous signal while preserving arterial signal that flows through different regions or at different times.
Solution Approach 2:
The patent utilizes the periodic nature of cardiac blood flow, applying saturation pulses at specific intervals during the cardiac cycle when venous flow is present but arterial flow is minimal or absent. This periodic timing allows selective suppression of venous signal while maintaining arterial conspicuity throughout the imaging sequence.
3Ease of manufacture
If imaging slices are oriented axially for standard MRA, then anatomical coverage is simplified, but alignment with tortuous vasculature is poor
Solution Approach 1:
The patent employs dynamic reorientation of imaging slices during the scanning process. Rather than using fixed axial slices throughout, the system adjusts the orientation of imaging slices to align with the local vasculature, particularly for tortuous vessels. This dynamic adaptation allows the imaging protocol to maintain simplicity while improving anatomical accuracy by automatically adjusting slice orientation based on detected vessel paths.
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 reduces scan time, improves arterial depiction, and effectively suppresses venous signals, enabling accurate imaging of vasculature with reduced motion artifacts and improved diagnostic accuracy across a range of flow velocities.
Implementation Method 1
applying at least one radio frequency ('RF') saturation pulse to a selected region in the subject at least partially suppressing magnetic resonance signals therein
Implementation Method 2
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
the individual magnetic moments of the nuclei in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency
Implementation Method 4
If the substance, or tissue, is subjected to a magnetic field (excitation field B1) that is in the x-y plane and that is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or 'tipped', into the x-y plane to produce a net transverse magnetic moment Mxy
Data Source
AI summary
A method for performing a non-contrast-enhanced magnetic resonance angiography (“MRA”) for a subject is provided. The method includes directing a magnetic resonance imaging (“MRI”) system to perform a pulse sequence to acquire k-space data from imaging slices that are oriented away from an axial direction of the subject. The method includes repeating the pulse sequence for a plurality of imaging slices, wherein a field-of-view (“FOV”) of at least one of the plurality of imaging slices is shifted by a predetermined value. The method also includes reconstructing, using the acquired k-space data, one or more angiographic images indicative of the subject's vasculature.