Investigation of Readout RF Pulse Impact on the Chemical Exchange Saturation Transfer Spectrum.

Sheng-Min Huang,Hsin-Chin Liang,Shang-Yueh Tsai,Yi-Chun Wu,Fu-Nien Wang,Chia-Hao Chang,Meei-Ling Jan

doi:10.1038/srep15062

Abstract

Chemical exchange saturation transfer magnetic resonance imaging (CEST-MRI) is capable of both microenvironment and molecular imaging. The optimization of scanning parameters is important since the CEST effect is sensitive to factors such as saturation power and field homogeneity. The aim of this study was to determine if the CEST effect would be altered by changing the length of readout RF pulses. Both theoretical computer simulation and phantom experiments were performed to examine the influence of readout RF pulses. Our results showed that the length of readout RF pulses has unremarkable impact on the Z-spectrum and CEST effect in both computer simulation and phantom experiment. Moreover, we demonstrated that multiple refocusing RF pulses used in rapid acquisition with relaxation enhancement (RARE) sequence induced no obvious saturation transfer contrast. Therefore, readout RF pulse has negligible effect on CEST Z-spectrum and the optimization of readout RF pulse length can be disregarded in CEST imaging protocol.

Highlights

To generate CEST contrast, magnetization preparation pulse is embedded in the pulse sequence
Amide proton transfer (APT) imaging has been reported to be useful for detecting lactic acidosis during acute ischemia; the chemical shift of the amide proton transfer (APT) mechanism is within 1~4 ppm[15]
Since the bandwidth of readout RF is related to the pulse length, readout RF pulse length may be a factor that influencing CEST effect due to spillover effect

Summary

Introduction

To generate CEST contrast, magnetization preparation pulse is embedded in the pulse sequence. For the saturation RF pulse, especially in small molecule contrast agents, a lot of research studies have evaluated options for shortening imaging time and gaining CEST effects. To the best of our knowledge, the issue of readout RF pulses was only briefly mentioned in Sun’s work[21] They speculated that readout RF pulse is not long enough to generate CEST contrast. The purpose of this study was to investigate if the CEST effect would be altered by readout RF including excitation and refocusing pulses. Both theoretical simulations and phantom experiments were carried out to examine this issue using steady state saturation preparation process

Objectives

Methods

Results