Spiral MR Imaging with Variable Radial Sampling
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Solution Overview
Problem
Spiral MR imaging techniques face challenges with image quality due to magnetic field inhomogeneities, particularly at high field strengths, leading to blurring and undefined T2 weighting in reconstructed images.
Innovation Solution
The method involves generating spin echoes along spiral trajectories in k-space with varying radial distance speeds, where at least one spin echo has a different rate of radial distance variation compared to others, allowing for dense sampling of the central k-space region to achieve well-defined T2 weighting in MR images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spiral imaging is used to achieve fast MR imaging with efficient k-space coverage, then imaging speed is improved, but image quality deteriorates due to blurring from magnetic field inhomogeneities
Solution Approach 1:
The patent segments the k-space sampling into multiple spiral trajectories with different sampling densities. Specifically, the central region of k-space is sampled with higher density using multiple interleaved spirals, while peripheral regions use standard sampling. This segmentation allows efficient coverage for speed while maintaining quality in the contrast-dominant central region.
Solution Approach 2:
The patent applies different sampling strategies to different regions of k-space. The central region, which dominates image contrast, receives enhanced sampling density through multiple spiral passes, while peripheral regions use conventional sampling. This local quality enhancement improves image quality where it matters most without sacrificing overall imaging speed.
2Strength
If spiral imaging is used at high main magnetic field strengths, then signal strength is improved, but image quality deteriorates due to increased sensitivity to magnetic field inhomogeneities
Solution Approach 1:
The patent changes the sampling parameters of the spiral trajectories, specifically varying the radial distance sampling rate. By adjusting how rapidly the spiral trajectories move through different radial distances in k-space, the method optimizes the balance between utilizing high field strength signal and mitigating the increased sensitivity to field inhomogeneities that causes blurring.
3Device complexity
If standard spiral trajectories are used for all spin echoes, then acquisition simplicity is maintained, but T2 weighting becomes undefined due to mixing of different T2 weightings in the acquired signal
Solution Approach 1:
The patent applies different trajectory characteristics to different spin echoes based on their T2 weighting. Specifically, at least one spin echo uses a modified spiral trajectory with different radial distance sampling to capture data primarily from the central k-space region, which provides well-defined T2 weighting. Other echoes use standard trajectories, maintaining overall acquisition simplicity while achieving defined T2 contrast.
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 enables fast and robust control of image contrast, providing well-defined T2 weighting and improved image quality by selectively weighting the MR signal data from the central k-space region, which dominates the image contrast.
Implementation Method 1
a main magnet coil for generating a uniform static magnetic field within an examination volume
Implementation Method 2
a number of gradient coils for generating time-varying magnetic field gradients in different spatial directions within the examination volume
Implementation Method 3
at least one RF coil for generating RF pulses within the examination volume and/or for receiving MR signals from an object positioned in the examination volume
Data Source
AI summary
The invention relates to a method of MR imaging of an object (10) positioned in an examination volume of a MR device (1). It is an object of the invention to enable fast spiral MR imaging with a defined T2 contrast. The method of the invention comprises the following steps: —generating a number of spin echoes by subjecting the object (10) to one or 5 more shots of an imaging sequence, each shot comprising an RF excitation pulse (21) followed by a number of RF refocusing pulses (22), wherein modulated readout magnetic field gradients (23, 24) are applied in each interval between successive RF refocusing pulses (22), —acquiring MR signal data, wherein each spin echo is recorded along a spiral trajectory (31-33, 41-43) in k-space which winds around the k-space origin with varying radial distance, wherein the trajectory (31, 41) of at least one spin echo has a different rate of variation of the radial distance at least in a central k-space region compared to the trajectories (32, 33, 42, 43) of the other spin echoes, and—reconstructing an MR image from the acquired MR signal data. Moreover, the invention relates to an MR device (1) and to a computer program for an MR device (1).