pMRI Calibration via Cartesian Continuous Sampling
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Solution Overview
Problem
Conventional Parallel Magnetic Resonance Imaging (pMRI) techniques require additional auto-calibration signal (ACS) lines to estimate coil sensitivities, which increases scan time due to the need for extra k-space data acquisition, reducing the benefits of under-sampling.
Innovation Solution
The method employs Cartesian continuous sampling with an extended acquisition window and overlapping phase-encoding gradients, allowing for calibration without additional ACS lines by continuously sampling during gradient changes, thereby reducing the need for extra data acquisition and shortening the imaging session.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional ACS lines are acquired for calibration, then coil sensitivity estimation accuracy is improved, but scan time increases
Solution Approach 1:
The patent combines the calibration data acquisition with the actual imaging data acquisition by using overlapping phase-encoding gradients. The ACS lines are acquired during the same scan session as the imaging data, merging two previously separate processes into one unified acquisition sequence, thereby eliminating dedicated calibration time while maintaining sensitivity estimation accuracy
Solution Approach 2:
The patent implements continuous sampling during gradient changes and transitions between k-space lines. By continuously acquiring data during what would traditionally be idle gradient transition periods, the system maintains useful data acquisition throughout the entire scan session, eliminating wasted time while ensuring sufficient calibration data is collected
2Productivity
If under-sampling is applied to reduce scan time, then productivity is improved, but calibration data quality deteriorates
Solution Approach 1:
The patent segments the k-space acquisition into multiple interleaved sequences with different phase-encoding steps. By distributing the under-sampled acquisitions across multiple segments and combining them through the overlapping gradient technique, sufficient calibration data is accumulated from multiple sources, maintaining data quality despite reduced sampling density in any single sequence
Solution Approach 2:
The patent changes the timing and phasing parameters of the gradient waveforms to create overlapping acquisition windows. By adjusting gradient durations and timing offsets, the system transforms the acquisition parameters to enable continuous sampling during transitions, ensuring adequate calibration data is captured even with under-sampling of the main imaging data
Data Source
AI summary
Example systems, methods, and apparatus control a pMRI apparatus to produce a pulse sequence having an extended acquisition window, and overlapping phase-encoding gradients and read gradients. One example method controls a pMRI apparatus to produce a trajectory having Cartesian and radial segments that sample in a manner that satisfies the Nyquist criterion in at least one region of a volume to be imaged. The pMRI apparatus is controlled to apply radio frequency energy to the volume according to the pulse sequence and following the trajectory and to acquire MR signal from the volume in response to the application of the RF energy. The MR signal includes a first component associated with the Cartesian segment of the trajectory and a second component associated with the radial segment of the trajectory. The example method includes calibrating a reconstruction process using Nyquist-satisfying data from the second component.