MRI Gradient Pulse Timing for Arteriovenous Separation
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Solution Overview
Problem
Conventional magnetic resonance imaging (MRI) methods for non-contrast-enhanced magnetic resonance angiography (MRA) face challenges in distinguishing between arterial and venous blood flow, especially in lower limb imaging, due to low flow velocities and the limitations of gradient pulse intensity and echo train spacing, which affect time resolution and arteriovenous separation.
Innovation Solution
The MRI apparatus and method employ a sequence setting unit to apply motion probing gradient pulses with varying intensities, independent of blood vessel direction, and perform scans at specific cardiac phases to generate blood flow images, using flow encode and spoiler pulses to enhance signal differences between systole and diastole, allowing for improved arteriovenous separation without relying on contrast media.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gradient pulse intensity is increased to suppress arterial blood flow signal during systole, then arteriovenous separation is improved, but time resolution deteriorates
Solution Approach 1:
The patent divides the gradient pulse application into multiple segments: a first gradient pulse applied before the echo time to suppress arterial signal, and a second gradient pulse applied after the echo time to further suppress residual signal. This segmented approach allows better control over signal suppression timing and intensity, improving arteriovenous separation without excessively increasing total pulse duration that would harm time resolution.
Solution Approach 2:
The patent applies the first gradient pulse before the echo time (TP/2) to preemptively suppress the arterial blood flow signal during systole. This preliminary action reduces the signal strength before the actual signal acquisition, thereby improving the contrast between arterial and venous signals without requiring excessively strong gradient pulses that would extend the total imaging time.
2Measurement precision
If echo train spacing is increased to improve arteriovenous separation, then signal difference between systole and diastole is enhanced, but time resolution deteriorates
Solution Approach 1:
The patent changes the timing parameters of gradient pulse application relative to the echo time. Instead of increasing echo train spacing, the patent optimizes the timing of gradient pulses (first pulse at TP/2, second pulse at TE) to achieve better arteriovenous separation. This parameter optimization improves signal differentiation while maintaining the original echo train spacing and thus preserving time resolution.
3Measurement precision
If gradient pulse is applied in readout direction to suppress arterial signal, then arteriovenous separation is improved, but depiction accuracy of blood vessels deteriorates
Solution Approach 1:
The patent applies gradient pulses with different characteristics in different directions: a first gradient pulse in the readout direction to suppress arterial signal, and a second gradient pulse also in the readout direction but with adjusted parameters to control the suppression. This localized and directional application of gradient pulses allows precise control over which blood flow signals are suppressed, improving arteriovenous separation while maintaining accurate depiction of blood vessels through proper signal preservation in other directions.
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 more accurate and detailed blood flow imaging in blood vessels by enhancing signal differences between arterial and venous flows, improving arteriovenous separation and time resolution, even for low-velocity blood flows, without increasing echo train spacing or relying on contrast media.
Implementation Method 1
a motion probing gradient pulse which applies a gradient magnetic field in a readout direction
Implementation Method 2
facilitating flow void effect in a blood vessel of the object
Data Source
AI summary
A magnetic resonance imaging apparatus includes an imaging condition setting unit, a scan performing unit and a blood flow image generating unit. The imaging condition setting unit sets a sequence accompanying application of a motion probing gradient pulse as an imaging condition. The scan performing unit performs an imaging scan according to the sequence. The blood flow image generating unit generates a blood flow image based on data acquired by the imaging scan.