MRI Gradient Measurement via Single-Point Imaging
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Solution Overview
Problem
Current MRI systems face challenges in accurately determining actual gradient fields due to distortions caused by eddy currents, mechanical/thermal vibrations, and physiologically induced magnetic fields, leading to image artifacts such as blurriness and phase errors, especially in non-Cartesian acquisitions and long readout durations.
Innovation Solution
A single point imaging (SPI) technique is implemented to measure gradients without slice selection or additional equipment, by linearly scaling gradient amplitude with each repetition time and using k-space and/or image domain data to estimate the k-space trajectory, allowing for improved image quality through adaptive FOV scaling factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gradient fields are used for spatial encoding in MRI, then image acquisition is enabled, but gradient distortions cause image artifacts such as blurriness and phase errors
Solution Approach 1:
The system performs preliminary measurement of the actual k-space trajectory using single-point imaging before the main image acquisition. This allows the system to characterize gradient distortions in advance and apply corrections during reconstruction, preventing image artifacts rather than correcting them after they occur.
Solution Approach 2:
The invention creates a copy of the k-space trajectory information through single-point imaging measurements. By acquiring separate trajectory data without full image content, the system obtains a simplified representation that can be used for correction without interfering with the main imaging process.
2Measurement precision
If external field probes are added to measure gradients, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The MRI system uses its own imaging capabilities to measure gradient fields. By employing single-point imaging sequences, the system leverages its existing RF coils, gradient system, and signal processing hardware to perform self-diagnosis and calibration, eliminating the need for external measurement devices.
Solution Approach 2:
The imaging system is designed to perform multiple functions: it can acquire full images for diagnosis and simultaneously perform single-point imaging for gradient measurement and characterization. This multi-functionality allows the same hardware to serve both imaging and calibration purposes without requiring dedicated measurement equipment.
3Measurement precision
If phase encoding with multiple RF pulses is used, then gradient measurement resolution is improved, but measurement time increases
Solution Approach 1:
The invention extracts gradient measurement information from single-point imaging data without requiring multiple RF pulses. By using phase encoding with a single RF pulse and acquiring data at different phase encoding steps, the system obtains gradient measurement information more efficiently, separating the measurement function from time-consuming multi-pulse sequences.
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 method provides accurate measurement of actual gradient fields, reducing geometric distortions and improving image quality in MRI systems, particularly in non-Cartesian acquisitions and long readout sequences, without the need for additional hardware or knowledge about the imaged subject.
Implementation Method 1
a plurality of gradient coils configured to apply a gradient field to the polarizing magnetic field
Implementation Method 2
If, however, the substance, or tissue, is subjected to a magnetic field (excitation field B1; also referred to as the radiofrequency (RF) field) which is in the x-y plane and which oscillates near the Larmor frequency, the net aligned moment, Mz, may be rotated, or 'tipped', into the x-y plane
Implementation Method 3
The emitted MRI signals are detected using a receiver coil. The MRI signals are then digitized and processed to reconstruct the image
Data Source
AI summary
A system and method for determining an actual gradient field generated by a magnetic resonance imaging (MRI) system when controlled to produce a prescribed gradient field is provided. The techniques include using the prescribed gradient field, controlling the MRI system to perform a phase encoding including a gradient that is scaled along each direction desired to be measured over a selected number of encoding times and acquiring one-dimensional (1D) data using a prescribed k-space trajectory during the phase encoding. The 1D data is used to determine scaling factors between encoding times that correlate to actual k-space trajectories achieved when controlling the gradient coils to perform the phase encoding based on the desired gradient field and a report is generated that provides a measure of the actual gradient field generated when controlling the MRI system to produce the prescribed gradient field.