Browse Prior Art Database

Publication Date: 2015-Apr-13
Document File: 4 page(s) / 57K

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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.

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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. 


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...