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Updated: May 5, 2026

RNA Secondary Structure Prediction Using High-throughput SHAPE

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Published on: May 31, 2013

Signal formation in echo-shifted sequences.

Y C Chung¹, J L Duerk

¹Departments of Radiology and Biomedical Engineering, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106-5056, USA.

Magnetic Resonance in Medicine

|November 5, 1999

Summary

This summary is machine-generated.

Echo shifted (ES) sequences offer enhanced MRI capabilities for fMRI and thermometry. This study differentiates ES-FLASH and ES-GRE, clarifying their mechanisms and explaining prior experimental inconsistencies.

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Area of Science:

Magnetic Resonance Imaging (MRI)
Biomedical Engineering
Physics

Background:

Echo shifted (ES) gradient-recalled echo sequences (TE > TR) are vital for functional MRI (fMRI) and MR thermometry.
These sequences enhance T2* weighting in BOLD imaging and temperature sensitivity in phase-based thermometry compared to FLASH sequences.
Previous studies reported inconsistent observations with ES variants due to insufficient understanding of their mechanisms.

Purpose of the Study:

To provide an in-depth investigation into various Echo Shifted (ES) sequences.
To differentiate between ES-FLASH and ES-GRE sequences and elucidate their distinct echo formation mechanisms.
To reconcile previously reported inconsistent experimental observations related to ES sequences.

Main Methods:

Characterization of two distinct types of ES sequences: ES-FLASH (spoiling coherent transverse magnetization) and ES-GRE (based on SSFP signals).
Derivation of a signal expression for the TR-periodic ES-GRE sequence with a single echo shift.
Analysis using the resonance offset angle methodology for short TR imaging sequences.

Main Results:

Identification of two fundamental types of ES sequences: ES-FLASH and ES-GRE.
Development of a signal expression for the ES-GRE sequence, which simplifies to the 'FLASH-like' model under specific conditions.
Explanation of previously observed experimental inconsistencies through a clearer understanding of ES echo formation.

Conclusions:

The study clarifies the distinct mechanisms of ES-FLASH and ES-GRE sequences, resolving prior ambiguities.
The derived signal expression and resonance offset angle analysis provide valuable tools for understanding and optimizing ES sequences.
This work enhances the application of ES sequences in fMRI and MR thermometry by providing a robust theoretical framework.