Volume 87, Issue 4 pp. 1731-1741
RESEARCH ARTICLE

Phase-independent thermometry by Z-spectrum MR imaging

Alessandro M. Scotti

Corresponding Author

Alessandro M. Scotti

Radiology Department, University of Illinois at Chicago, Chicago, Illinois, USA

Bioengineering Department, University of Illinois at Chicago, Chicago, Illinois, USA

Correspondence

Alessandro M. Scotti, Radiology Department, University of Illinois at Chicago, Chicago, IL, USA.

Email: [email protected]

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Frederick Damen

Frederick Damen

Radiology Department, University of Illinois at Chicago, Chicago, Illinois, USA

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Jin Gao

Jin Gao

Bioengineering Department, University of Illinois at Chicago, Chicago, Illinois, USA

Research Resources Center, University of Illinois at Chicago, Chicago, Illinois, USA

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Weiguo Li

Weiguo Li

Radiology Department, University of Illinois at Chicago, Chicago, Illinois, USA

Research Resources Center, University of Illinois at Chicago, Chicago, Illinois, USA

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Chong Wee Liew

Chong Wee Liew

Physiology and Biophysics Department, University of Illinois at Chicago, Chicago, Illinois, USA

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Zimeng Cai

Zimeng Cai

School of Medical Engineering, Southern Medical University, Guangzhou, China

Guangdong Provincial Key Laboratory of Image Processing, Southern Medical University, Guangzhou, China

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Zhuoli Zhang

Zhuoli Zhang

Radiology Department, Northwestern University, Evanston, Illinois, USA

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Kejia Cai

Kejia Cai

Radiology Department, University of Illinois at Chicago, Chicago, Illinois, USA

Bioengineering Department, University of Illinois at Chicago, Chicago, Illinois, USA

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First published: 09 November 2021

Abstract

Purpose

Z-spectrum imaging, defined as the consecutive collection of images after saturating over a range of frequency offsets, has been recently proposed as a method to measure the fat–water fraction by the simultaneous detection of fat and water resonances. By incorporating a binomial pulse irradiated at each offset before the readout, the spectral selectivity of the sequence can be further amplified, making it possible to monitor the subtle proton resonance frequency shift that follows a change in temperature.

Methods

We tested the hypothesis in aqueous and cream phantoms and in healthy mice, all under thermal challenge. The binomial module consisted of 2 sinc-shaped pulses of opposite phase separated by a delay. Such a delay served to spread out off-resonance spins, with the resulting excitation profile being a periodic function of the delay and the chemical shift.

Results

During heating experiments, the water resonance shifted downfield, and by fitting the curve to a sine function it was possible to quantify the change in temperature. Results from Z-spectrum imaging correlated linearly with data from conventional MRI techniques like T1 mapping and phase differences from spoiled GRE.

Conclusion

Because the measurement is performed solely on magnitude images, the technique is independent of phase artifacts and is therefore applicable in mixed tissues (e.g., fat). We showed that Z-spectrum imaging can deliver reliable temperature change measurement in both muscular and fatty tissues.

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