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. 2016 May;75(5):1958-66.
doi: 10.1002/mrm.25789. Epub 2015 Jun 16.

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

Ryan M Davis  1 , Zijian Zhou  1 , Hyunkoo Chung  2 , Warren S Warren  1
Affiliations

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

Ryan M Davis et al. Magn Reson Med. 2016 May.

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.

Keywords: Carr-Purcell-Meiboom-Gill; intermolecular multiple quantum coherence; red bone marrow; temperature imaging.

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Figures

Figure 1
Figure 1
The MSE-HOT pulse sequence used for imaging RBM temperature.
Figure 2
Figure 2
The CPMG pulse sequence used for testing how the number of refocusing pulses given in a fixed echo time affects the methylene signal.
Figure 3
Figure 3
A representative MSE-HOT dataset. a) T2-weighted image of porcine RBM sample. b) magnitude of d(x,y). c) temperature image overlaid on T2-weighted image. d) fat SQC image for the 16 SQC echoes created by MSE-HOT. e) methylene-water iZQC magnitude image for the 16 iZQC echoes. f) SSE-HOT precision map overlaid on T2-weighted image. g) MSE-HOT precision map overlaid on T2-weighted image. h) histogram of the precision data in f&g.
Figure 4
Figure 4
The iZQC signal as a function of echo time. All error bars are the standard deviation of 9 voxels total from 3 different porcine RBM samples. a) iZQC signal magnitude vs echo time for MSE and SSE pulse sequences. b) The uncorrected phase of iZQC and SQC echoes and φMSE for the MSE sequence. c) The corrected phase of the iZQC echo (φ̄MSE) as a function of echo time.
Figure 5
Figure 5
Simulations and experiments of methylene protons on lipids under a CPMG experiment. Error bars are the standard deviation of all water data-points at the same field strength. a) Experimental methylene signal of water, palmitic acid (PA), oleic acid (OA), and cholesteryl benzoate (CB) at 7T. b) Experimental methylene signal of water, PA, OA, and CB at 1T. c) high resolution spectra of alkane region of PA, OA, and CB at 360 MHz. Solvent linewidths were less than 3 ppb. d) Simulated methylene signal under CPMG pulse sequence with Hamiltonian H1 at 7 T. e) simulated and experimental methylene signal of OA at 7 T. f) simulated and experimental methylene signal of OA at 1T.
Figure 6
Figure 6
Precision summary of MSE-HOT. a) Temperature precision within the marrow region for MSE and SSE sequences (N=3 marrow samples). b) Mean and median precision as a function of number of echoes averaged. For example for the data point with value “5” on the x axis, the first 5 MSE echoes were averaged. Each data point is generated from a separate histogram similar to the one in part a.
Figure 7
Figure 7
Representative dataset for the mock hyperthermia treatment. a) T2-weighted image of RBM sample. The ROI used to calculate temperature is outlined in red. b) the fiberoptic and MSE-HOT temperature measurements obtained during heating and cooling of the RBM sample. c) temperature maps overlaid on T2-weighted images during heating and cooling of RBM sample.
Figure 8
Figure 8
Images of emulsions. a) a RARE image of emulsions at 23 °C. b) iZQC frequency maps of emulsions.
See this image and copyright information in PMC

References

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