Interleaved MR Data Acquisition for Quiet Scanning
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Solution Overview
Problem
Magnetic resonance (MR) examinations using quiet measurement sequences face challenges in averaging measurements due to susceptibility to patient movements and unwanted refocusing of residual magnetization, which leads to artifacts in the image, especially when using the 'outer averages' method.
Innovation Solution
The method involves acquiring each measurement data set in multiple partial measurements, with successive partial measurements covering different regions of k-space, thereby reducing movement sensitivity and avoiding refocusing artifacts, while keeping gradient jumps small to minimize noise and maintain the quiet character of the measurement sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the 'outer averages' method is used to average measurements, then the signal-to-noise ratio is improved, but the measurement becomes very susceptible to patient movements and unwanted refocusings of residual magnetization lead to artifacts
Solution Approach 1:
The measurement process is divided into multiple partial measurements (e.g., 6 partial measurements) that are interleaved between different measurement data sets. Each partial measurement covers a different partial region of k-space, and successive partial measurements are associated with different data sets. This segmentation allows averaging to be performed on partial measurements from different data sets, reducing movement sensitivity while maintaining signal-to-noise ratio improvement.
2Measurement precision
If the 'inner averages' method is used to average measurements, then the signal-to-noise ratio is improved, but unwanted refocusings of residual magnetization between two identical partial measurements lead to artifacts in the MR image
Solution Approach 1:
The measurement sequence is designed with asymmetric ordering where successive partial measurements are associated with different measurement data sets rather than identical repetitions. Specifically, partial measurements from different data sets are interleaved (e.g., MDS1_1, MDS2_1, MDS1_2, MDS2_2), breaking the symmetry of repeated identical measurements and preventing unwanted refocusings of residual magnetization while still enabling averaging.
3Measurement precision
If gradient fields are rapidly switched to achieve spatial coding, then measurement precision is improved, but mechanical measures for noise reduction are required due to distortions and oscillation in the gradient coil
Solution Approach 1:
The gradient switching is dynamically optimized by controlling the order of partial measurements to minimize gradient jumps between successive measurements. The system dynamically adjusts the measurement sequence (interleaving different data sets) to reduce dG/dt while maintaining the necessary spatial coding capability, thereby reducing noise from gradient coil oscillation without sacrificing measurement precision.
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 allows for effective averaging of measurements in quiet sequences, reducing noise and artifacts, and is less sensitive to patient movements, while maintaining the quiet nature of the measurements by ensuring gradient jumps remain within manageable limits.
Implementation Method 1
the examination subject is positioned in a strong, static, homogeneous basic magnetic field (also called a B0 field) with a field strength from 0.2 Tesla to 7 Tesla or more in a magnetic resonance apparatus, such that the nuclear spins of the examination subject orient along the basic magnetic field
Implementation Method 2
To trigger nuclear magnetic resonance signals, radio-frequency excitation pulses (RF pulses) are radiated into the examination subject, and the triggered nuclear magnetic resonance signals are measured
Implementation Method 3
For spatial coding of the measurement data, rapidly switched magnetic gradient fields are superimposed on the basic magnetic field
Data Source
AI summary
In a magnetic resonance data acquisition of at least two measurement data sets of an examination subject, each of the at least two measurement data sets is acquired in at least three partial measurements. Each partial measurement covers a partial region of k-space corresponding to the examination subject to be examined, and the partial measurements are executed in series in an order such that two successive partial measurements are associated with different data sets of the at least two measurement data sets, and such that two successive partial measurements respectively do not measure the same partial region. A reduced movement sensitivity is achieved by the acquisition of the interleaved partial measurements associated with different measurement data sets. Unwanted refocusings (and therefore echo signals of residual magnetization) are also avoided by avoiding successive partial measurements that measure the same partial region.