Retrospective MRI Gating with Navigator-Derived Time Offsets
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Solution Overview
Problem
Existing gated magnetic resonance imaging (MRI) techniques assume a fixed correlation between physiological signals and internal organ motion, which may not accurately represent individual patient or examination-specific conditions, leading to suboptimal image quality.
Innovation Solution
A method that determines a patient-specific and examination-specific gating time offset by comparing physiological signals with motion signals from anatomical features, using a navigator pulse sequence to adjust the timing of MR imaging data acquisition, ensuring better correlation with the desired state of the internal organ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fixed correlation between physiological signals and internal organ motion is assumed for gating, then the gating process is simple and fast, but the image quality deteriorates due to inaccurate timing alignment with individual patient variations
Solution Approach 1:
The patent applies preliminary action by acquiring navigator echo data before the main imaging sequence to determine patient-specific gating time offsets. The navigator echoes are acquired continuously during the imaging sequence, and the gating parameters are determined in advance from this preliminary data, allowing the main imaging to proceed with accurate timing without real-time delays.
Solution Approach 2:
The patent uses a reduced number of navigator echoes (partial action) compared to full real-time monitoring, acquiring navigator data at selected intervals to determine gating offsets. This partial acquisition approach maintains sufficient accuracy for timing alignment while avoiding the productivity loss of continuous real-time navigator acquisition.
2Manufacturing precision
If real-time navigator echoes are acquired continuously to determine accurate gating timing, then image quality improves, but the scanning time increases due to additional data acquisition
Solution Approach 1:
The patent acquires navigator echoes only at selected intervals and positions rather than continuously throughout the entire imaging sequence. This partial acquisition provides sufficient information to determine gating time offsets without the time penalty of continuous navigator acquisition, resolving the contradiction between timing accuracy and scanning duration.
Solution Approach 2:
The gating time offsets are determined from navigator echoes acquired in advance and during the sequence, but the actual gating timing is applied retrospectively to the already-acquired imaging data. This allows accurate gating determination without requiring real-time delays in the main imaging acquisition.
3Ease of operation
If physiological sensors are used to measure respiration or cardiac signals for gating, then the gating process is straightforward to implement, but the fidelity to the actual internal organ motion state deteriorates due to surrogate measurement limitations
Solution Approach 1:
The patent introduces navigator echoes as an intermediary measurement that directly probes the position of the imaged organ or a correlated anatomical structure. Instead of relying on surrogate physiological signals, the navigator echoes serve as a direct mediator to measure actual organ position, which is then used to determine accurate gating time offsets.
Data Source
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AI summary
A magnetic resonance (MR) imaging device (10) repeatedly executes a navigator pulse sequence (40) to generate navigator data in image space as a function of time, and a motion signal (44) of an anatomical feature that moves with a physiological cycle (e.g. respiration) as a function of time is extracted from the navigator data. A concurrent physiological signal (16) as a function of time is generated by a physiological monitor (12, 14) concurrently with the repeated execution of the navigator pulse sequence. A gating time offset (50) is determined by comparing the motion signal of the anatomical feature as a function of time and the concurrent physiological signal as a function of time. The MR imaging device performs a prospective or retrospective gated MR imaging sequence (36) using gating times defined as occurrence times of gating events detected by the physiological monitor modified by the gating time offset.