Investig Magn Reson Imaging.  2017 Mar;21(1):28-33. 10.13104/imri.2017.21.1.28.

Measurement and Compensation of Respiration-Induced B0 Variations in Lumbar Spine Bone Marrow Fat Quantification

• Nam Y
• Hwang E
• Jung JY

• KMID: 2376266
• DOI: http://doi.org/10.13104/imri.2017.21.1.28

Abstract

PURPOSE
To investigate and compensate the effects of respiration-induced B0 variations on fat quantification of the bone marrow in the lumbar spine.
MATERIALS AND METHODS
Multi-echo gradient echo images with navigator echoes were obtained from eight healthy volunteers at 3T clinical scanner. Using navigator echo data, respiration-induced B0 variations were measured and compensated. Fat fraction maps were estimated using T2*-IDEAL algorithm from the uncompensated and compensated images. For manually drawn bone marrow regions, the estimated B0 variations and the calculated fat fractions (before and after compensations) were analyzed.
RESULTS
An increase of temporal B0 variations from inferior level to superior levels was observed for all subjects. After compensation using navigator echo data, the effects of the B0 variations were reduced in gradient echo images. The calculated fat fractions show significant differences (P < 0.05) in L1 and L3 between the uncompensated and the compensated.
CONCLUSION
The results of this study raise the need for considering respiration-induced B0 variations for accurate fat quantification using gradient echo images in the lumbar spine. The use of navigator echo data can be an effective way for the reduction of the effects of respiratory motion on the quantification.

Keyword

Marrow fat; Lumbar spine; IDEAL; Respiration; B0 navigator; Physiological noise

MeSH Terms

Bone Marrow*
Compensation and Redress*
Healthy Volunteers
Respiration
Spine*

Figure

• 

  Fig. 1 Pulse sequence diagram for GRE-based fat quantification with respiration-induced B0 compensation. Navigator echoes (DC lines, ky = 0) were obtained after last imaging echo and phase rewinding gradients.

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  Fig. 2 Processing steps for navigator echo compensation. Each k-space line was compensated by phase differences (relative to 1st TR) in the readout direction.

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  Fig. 3 (a) A representative six-echo combined magnitude image of a healthy volunteer (root sum of squares). (b) The estimated B0 variations for 5 vertebral levels from a healthy volunteer. (c) Standard deviations of B0 variations for all 8 volunteers.

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  Fig. 4 Comparison of the uncompensated and compensated results. (a) The magnitude images at TE = 10.2 ms and (b) the estimated fat fraction maps.

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  Fig. 5 The estimated fat fractions of the uncompensated (blue) and compensated (red) data (average and standard deviation for eight volunteers, *: P < 0.05).

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