PROPELLER WITH ECHO STABILIZATION
Publication Date: 2015-Apr-13
The IP.com Prior Art Database
The proposed invention proposes a model that predicts a phase error at various blade angles of a propeller. The phase error is measured only at a limited number, typically, 6~7 of blade angles in a pre-scan. The measured phase error is fitted to the model. During a normal scan, the phase error at each blade angle is determined and adjusted to compensate the phase error to make the echo signal more stable.
The present invention relates generally to imaging techniques and more particularly to a technique for improving an image quality of a propeller scan with an acceptable pre-scan time.
A propeller utilizes principles of fast spin-echo (FSE). Conventional propeller faces issues related to degradation of signal in an echo train. The degradation is due to violation of Carr-Purcell-Meiboom-Gill (CPMG) condition. Though, the FSE measures phase error and adjust the phase error accordingly. However, the FSE is not feasible with a propeller due to unacceptable increase in a pre-scan time. The pre-scan time is increased as the phase error is measured for each blade angle. This condition is impractical for body and musculoskeletal (MSK) studies which demand minimal pre-scan time.
It would be desirable to have a technique for improving image quality of the propeller scan with an acceptable pre-scan time.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 shows a graph depicting a constant phase error.
Figure 2 depicts in vivo images a) without phase correction, b) with the proposed phase correction and c) FSE image with phase correction as reference.
The present invention proposes a model to stabilize an echo train signal for a propeller. The model predicts a phase error at various blade angles. The model measures the phase error only at a limited number (6-7) of blade angles, instead of measuring the phase error at all blade angles. The model determines the phase error at each blade angle in a quick scan and compensates the phase error to provide more stable echo signal.
Based on experimental data, the following model is proposed:
, where Gi is the gradient amplitude on a physical axis,
c’s are the 0th and 1st order coefficients.
The dependence of 1st order coefficients on polarity of a physical gradient is partially contributed to B0 field inhomogeneity, eddy current, gradient fidelity. For a normal scan, angles of 6 blades are measured for estimation where one axis is kept at the same polarity by choosing appropriate rotation angles. The model is able to predict the p...