Multi–spin echo spatial encoding provides three-fold improvement of temperature precision during intermolecular zero quantum thermometry

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Abstract

Purpose:

Intermolecular multiple quantum coherences (iMQCs) are a source of MR contrast with applications including temperature imaging, anisotropy mapping, and brown fat imaging. Because all applications are limited by signal-to-noise ratio (SNR), we developed a pulse sequence that detects intermolecular zero quantum coherences with improved SNR.

Methods:

A previously developed pulse sequence that detects iMQCs, HOMOGENIZED with off resonance transfer (HOT), was modified with a multi-spin echo spatial encoding scheme (MSE-HOT). MSE-HOT uses a series of refocusing pulses to generate a stack of images that are averaged in postprocessing for higher SNR. MSE-HOT performance was quantified by measuring its temperature accuracy and precision during hyperthermia of ex vivo red bone marrow samples.

Results:

MSE-HOT yielded a three-fold improvement in temperature precision relative to previous pulse sequences. Sources of improved precision were 1) echo averaging and 2) suppression of J-coupling in the methylene protons of fat. MSE-HOT measured temperature change with an accuracy of 0.6°C.

Conclusion:

MSE-HOT improved the temperature accuracy and precision of HOT to a level that is sufficient for hyperthermia of bone marrow. Magn Reson Med 75:1958–1966, 2016. © 2015 Wiley Periodicals, Inc.

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