MR Echo Signal Filtering and Oversampling to Prevent Image Cropping
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Solution Overview
Problem
Existing magnetic resonance imaging techniques suffer from wrap-around artifacts and cropping effects due to non-linearities in gradient fields, leading to incomplete data acquisition and increased computing effort, particularly in off-center measurements.
Innovation Solution
A method involving the use of optimized filter parameters and oversampling factors, determined using distortion maps of gradient units, to ensure complete data acquisition within a desired field of view while preventing aliasing and cropping artifacts, without significantly increasing computing or measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oversampling is applied in the readout direction to prevent wrap-around artifacts, then aliasing is reduced, but computing effort and measurement time increase
Solution Approach 1:
The patent dynamically adjusts the oversampling factor based on the specific examination protocol and gradient non-linearity characteristics. Instead of applying fixed oversampling, the system calculates an optimal oversampling factor that provides sufficient aliasing prevention while minimizing unnecessary data acquisition, thereby reducing measurement time and computing effort.
Solution Approach 2:
The patent applies partial oversampling only where and when needed, rather than uniformly oversampling the entire k-space. By calculating the required oversampling factor based on protocol-specific parameters and gradient non-linearity, the system applies just enough oversampling to prevent aliasing without the excessive action of uniform oversampling throughout.
2Manufacturing precision
If gradient non-linearity is corrected using distortion maps, then image accuracy is improved, but cropping effects occur at image boundaries
Solution Approach 1:
The patent performs preliminary calculation of the oversampling factor before data acquisition, taking into account the gradient non-linearity characteristics and the specific examination protocol. This preliminary action allows the system to prepare appropriate oversampling parameters that will prevent cropping effects while maintaining image accuracy, avoiding the need for post-processing corrections.
Solution Approach 2:
The patent creates an expanded k-space representation that copies and extends the sampling pattern beyond the standard field of view boundaries. This copying approach ensures that boundary regions are adequately sampled even after gradient non-linearity correction, preventing information loss at image edges.
3Area of stationary object
If field of view is increased to accommodate off-center measurements, then complete object coverage is achieved, but data acquisition time increases
Solution Approach 1:
The patent dynamically changes the oversampling factor parameter based on the relationship between the desired field of view and the object position. For off-center measurements where complete coverage is needed, the system calculates an appropriate oversampling factor that ensures adequate sampling without requiring a uniform increase in the entire field of view, thereby maintaining efficient data acquisition.
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
Enables high-quality MR images with minimal artifacts and reduced computing effort by optimizing data recording and reconstruction processes, ensuring all relevant regions are represented without excessive data discard.
Implementation Method 1
The magnetic alternating field generated by the excitation pulses irradiated by means of at least one transmit coil is also referred to as a B1 field. In order to spatially encode the measurement data, fast-switched magnetic gradient fields, called gradients for short, are overlaid on the basic magnetic field.
Implementation Method 2
before recording the measurement data a band-pass filter can be applied to the received echo signal, which filter suppresses frequencies which are too high and too low, that is to say frequencies which are outside of a field of view band specified by the selected field of view.
Data Source
AI summary
Techniques are described for recording of magnetic resonance data to prevent cropping effects. A loss factor indicates an expected reduction of an image reconstructed on the basis of measurement data recorded using the loaded measurement protocol and determines filter parameters for a frequency filter for filtering frequencies of echo signals, received when recording measurement data with the measurement protocol, on the basis of the loss factor and on the basis of the desired field of view, and determines an oversampling factor on the basis of the filter parameters of the frequency filter. The oversampling factor specifies an oversampling to be applied when recording of measurement data. Oversampled measurement data is recorded using the determined filter parameters and the oversampling factor when implementing the loaded measurement protocol.