Segmented EPI MRI for Beat-to-Beat Cerebrovascular Flow Measurement
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Solution Overview
Problem
Conventional MRI techniques lack sufficient spatial and temporal resolution to effectively assess cerebrovascular function, particularly in evaluating vascular flow resistance and compliance during different phases of the cardiac cycle, which is crucial for monitoring health and disease states.
Innovation Solution
The method employs ultra-fast segmented echo-planar imaging (EPI) with retrospective gating to the cardiac cycle, maximizing sensitivity to flow in the magnitude signal without velocity encoding gradients, and combines partial Fourier transform and parallel imaging to achieve high temporal and spatial resolution, allowing for dynamic measurement of pulsatile flow on a beat-to-beat basis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional MRI techniques are used to assess cerebrovascular function, then the measurement can be performed, but the temporal resolution is insufficient to evaluate different phases of cardiac cycle
Solution Approach 1:
The patent segments the EPI readout into multiple shots (first shot, second shot, etc.) acquired at different times during the cardiac cycle. Each shot captures a portion of k-space, and these segments are later combined to form complete images. This segmentation allows temporal resolution to be improved by acquiring multiple shots within one cardiac cycle, enabling evaluation of different cardiac phases while maintaining adequate spatial resolution through proper k-space sampling and combination.
2Speed
If attempts are made to increase temporal resolution, then cardiac phase evaluation becomes possible, but spatial resolution is reduced below useful level
Solution Approach 1:
The patent resolves the spatial-resolution loss by acquiring multiple shots in the time dimension (different cardiac phases) and combining them through Fourier transformation in the temporal dimension. By treating the shot index as an additional dimension (time/phase dimension) rather than trying to capture everything in a single spatial snapshot, the method recovers spatial resolution while gaining temporal information. The k-space data from multiple shots are combined using phase-corrected Fourier transformation to reconstruct high-resolution images for each cardiac phase.
3Speed
If ultra-fast segmented EPI is used with short TR, then temporal resolution is improved for beat-to-beat measurement, but the repetition time becomes shorter than cardiac cycle causing signal fluctuations
Solution Approach 1:
The patent employs periodic action by synchronizing the multi-shot EPI acquisition to the cardiac cycle rhythm. The TR is set to be shorter than the cardiac cycle, allowing multiple shots to be acquired within one cardiac period. By acquiring shots periodically at specific phases (e.g., using ECG gating or pulse synchronization), the method captures the periodic nature of cardiac pulsations while maintaining stable signal through consistent phase sampling. This periodic sampling strategy transforms the signal fluctuations into useful temporal information rather than noise.
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 provides improved clinical assessment of vascular resistance and compliance in large cerebral arteries, enabling accurate sampling of pulsatile flow and distinguishing between inflow effects, thereby enhancing the understanding of cerebrovascular health and its relation to cardiovascular risk.
Implementation Method 1
Magnetic resonance imaging (MRI) may in principle allow for dynamic measurement of cerebrovascular function for clinical appraisal, by rapidly sampling tissue magnetization changes that result from physiological brain-cardiac interactions.
Implementation Method 2
The use of an ultra-fast segmented EPI readout maximises sensitivity to flow in the magnitude signal, without the need for velocity encoding gradients, thus allowing pulsatile flow to be measured dynamically on a cardiac beat-to-beat basis.
Data Source
AI summary
A method for obtaining magnetic resonance imaging (MRI) echo-planar image (EPI) data, including providing a homogeneous, static background field; providing a gradient field to select a slice of an object for imaging; applying Radio-frequency (RF) pulses to excite magnetic resonance in the selected slice; and measuring a radio frequency signal emitted by the selected slice containing image data. The RF pulses are repeatedly applied separated by a time period shorter than a recovery time of static material in the selected slice such that the static material remains in a state of magnetic saturation, while dynamic material arriving within the slice since a previous RF pulse is not magnetically saturated.