Parallel MRI Calibration Using 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 understand 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 k-space data 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 accuracy is improved, but scan time increases
Solution Approach 1:
The patent combines the calibration data acquisition with the regular imaging data acquisition by using the same k-space sampling trajectory. The ACS lines are integrated into the existing Cartesian sampling pattern rather than being acquired separately, merging two functions (calibration and imaging) into a single acquisition process.
Solution Approach 2:
The sampling trajectory serves multiple purposes: it acquires both the calibration data needed for coil sensitivity estimation and the imaging data for image reconstruction. The same k-space lines are used dually for both calibration and image formation, making the acquisition process universal.
2Productivity
If under-sampling is applied to reduce scan time, then productivity is improved, but measurement precision deteriorates due to loss of k-space data
Solution Approach 1:
The patent uses feedback by acquiring ACS lines that provide information about coil sensitivities, which are then used to guide the reconstruction process. The calibration data feeds back into the reconstruction algorithm to compensate for the effects of under-sampling, allowing accurate image recovery from incomplete k-space data.
Solution Approach 2:
The calibration data is acquired preliminarily as part of the imaging sequence setup. The ACS lines are collected before or during the main imaging acquisition to establish coil sensitivity profiles that will be used throughout the reconstruction process, preparing the system in advance for accurate image formation from under-sampled 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 non-Cartesian 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 non-Cartesian segment of the trajectory. The example method includes calibrating a reconstruction process using Nyquist-satisfying data from the second component.