B1 Field Mapping Using Orthogonal Virtual Coils
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Solution Overview
Problem
Current B1 transmit field mapping in magnetic resonance imaging is inefficient, requiring a large number of sequences that prolong imaging session times due to the subject loading effect and non-uniformity of the B1 field, especially at higher static magnetic fields.
Innovation Solution
A method that reduces the number of B1 field mapping sequences by using a set of radio frequency transmit coils and determining coil sensitivities based on acquired data, employing a linear transform to select virtual coils with lower frequency components, and encoding these to mimic the B1 field mapping, thereby enhancing B1 shimming efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If B1 field mapping sequences are performed for each individual transmit coil in two- or three-dimensions, then complete B1 mapping information is acquired, but imaging session time is significantly prolonged
Solution Approach 1:
The patent combines B1 mapping measurements from multiple transmit coils into a single unified measurement process. Instead of performing separate 2D or 3D mapping sequences for each coil, the method encodes coil sensitivity information into a single 2D or 3D measurement, thereby reducing total imaging time while preserving complete B1 mapping information for all coils.
Solution Approach 2:
The patent transitions from multiple separate 2D/3D measurements per coil to a compressed encoding approach where coil sensitivity information is embedded in an additional dimension (encoding domain). This allows reconstruction of individual coil B1 maps from a reduced number of measurements by applying decoding algorithms that exploit the encoding structure.
2Measurement precision
If a large number of B1 field mapping sequences are performed to account for subject loading effect, then accurate B1 uniformity correction is achieved, but imaging efficiency deteriorates
Solution Approach 1:
The patent performs a preliminary encoding of coil sensitivity information into the measurement process itself. By pre-defining encoding schemes that capture the essential B1 field characteristics across all coils, the method enables accurate uniformity correction without requiring multiple sequential measurements for each coil, thereby maintaining imaging efficiency.
Solution Approach 2:
The patent changes the measurement parameters by transitioning from individual coil measurements to a multi-coil encoded measurement framework. This parameter change allows the system to capture B1 field information for multiple coils simultaneously by modifying how the measurement data is structured and encoded, rather than changing the physical measurement process itself.
3Manufacturing precision
If multiple B1 mapping sequences are executed to ensure uniformity at higher static magnetic fields, then B1 field uniformity is improved, but the complexity of the imaging protocol increases
Solution Approach 1:
The patent segments the B1 mapping process into two distinct stages: an encoding stage where coil sensitivity information is embedded in the measurement design, and a decoding stage where individual coil B1 maps are reconstructed from the encoded data. This segmentation simplifies the actual imaging protocol by reducing the number of sequences needed, while the computational decoding process handles the complexity of extracting individual coil information.
Data Source
AI summary
A method comprises: performing a number of B i field mapping sequences (24) using a set of radio frequency transmit coils (11) to acquire a B1 field mapping data set wherein said number is less than a number of radio frequency transmit coils in the set of radio frequency transmit coils; and determining coil sensitivities (30) for the set of radio frequency transmit coils based on the acquired B1 field mapping data set. In some embodiments, the performed B1 field mapping sequences are defined by (i) performing a linear transform (40) on the set of radio frequency transmit coils to generate a set of orthogonal virtual radio frequency transmit coils (42) and (ii) selecting (44) a sub-set (46) of the set of orthogonal virtual radio frequency transmit coils that define the performed B1 field mapping sequences.