Magnetic Resonance Materials in Physics, Biology and Medicine

, Volume 26, Issue 5, pp 477–490

Alleviating artifacts in 1H MRI thermometry by single scan spatiotemporal encoding

Authors

  • Rita Schmidt
    • Chemical Physics DepartmentWeizmann Institute of Science
    • Chemical Physics DepartmentWeizmann Institute of Science
Research Article

DOI: 10.1007/s10334-013-0372-9

Cite this article as:
Schmidt, R. & Frydman, L. Magn Reson Mater Phy (2013) 26: 477. doi:10.1007/s10334-013-0372-9

Abstract

Objective

Recent years have seen an increased interest in combining MRI thermometry with devices capable of destroying malignancies by heat ablation. Expected from the MR protocols are accurate and fast thermal characterizations, providing real time feedback on restricted tissue volumes and/or rapidly moving organs like liver. This article explores the potential advantages of relying on spatiotemporally encoded (SPEN) sequences for retrieving real-time thermometric images based on the water’s proton resonance frequency (PRF) shifts.

Materials and methods

Hybrid spatiotemporal/k-space encoding single-scan MRI experiments were implemented on animal and human scanners, and their abilities to deliver single- and multi-slice real-time thermometric measurements based on PRF-derived phase maps in phantoms and in vivo, were compared against echo planar imaging (EPI) and gradient-echo counterparts.

Results

Under comparable acquisition conditions, SPEN exhibited advantages vis-à-vis EPI in terms of dealing with inhomogeneous magnetic field distortions, with shifts arising due to changes in the central frequency offsets, with PRF distributions, and for zooming into restricted fields-of-view without special pulse sequence provisions.

Conclusion

This work confirms the ability of SPEN sequences, particularly when implemented under fully-refocused conditions, to exploit their built-in robustness to shift- and field-derived inhomogeneities for monitoring thermal changes in real-time under in vitro and in vivo conditions.

Keywords

Spatiotemporal encodingReal-time MRI1H-based thermometryIn vivo PRFRestricted FOV

Abbreviations

MRI

Magnetic resonance imaging

NMR

Nuclear magnetic resonance

FOV

Field of view

FT

Fourier transform

SPEN

SPatio-temporal ENcoding

PRF

Proton resonance frequency

STD

Standard deviation

SNR

Signal-to-noise ratio

SR

Super-resolution

SAR

Specific absorption rate

RF

Radio frequency

RO

Readout

PE

Phase-encode

SS

Slice-select

TE

Echo time

TR

Repetition time

EPI

Echo-planar imaging

Supplementary material

10334_2013_372_MOESM1_ESM.docx (540 kb)
Magnitude images (top row) and temperature maps derived from spin-echo EPI and Hybrid SPEN thermometry experiments in an inhomogeneous environment. Distortions in Bo were achieved by placing a titanium non-magnetic plate next to bigger water tube; a smaller one kept at constant temperature and a bigger one undergoing cooling. The vertical progression shows temperature maps at time = 0, 3, 10 min into the process. Common scan parameters: FOVs = 25 mm, resolution 0.35 × 0.35 mm (pixel matrix 70 × 70), τo = 5 ms, Tacq = 30.8 ms. For the 90° chirp Hybrid SPEN Texc = 26.8 ms, Gexc = 0.92 G/cm. (DOCX 539 kb)

Copyright information

© ESMRMB 2013