Na Chai1, Panli Zuo2, Stephan Kannengiesser3, Andre De Oliveira3, Shun Qi1, and Hong Yin1
1Department of Radiology, Xijing Hospital, Xi'an, China, People's Republic of, 2Siemens Healthcare, MR Collaborations NE Asia, Beijing, China, People's Republic of, 3Application Predevelopment, Siemens Healthcare, Erlangen, Germany
Synopsis
Using the multi-echo 1H-MRS and multi-echo Dixon VIBE, we measured the proton density fat fraction (PDFF) using MR imaging in the bone marrow of L2-L4 vertebra, and compared with the bone mineral density (BMD) measured using computed tomography (CT). The resutls showed a significant correlation between PDFF measured using the two methods, and also PDFF with BMD.Purpose
Bone mineral density (BMD) measured using computed
tomography (CT) has been used to determine fracture risk and potential for osteoporosis
in clinical practice. In previous studies, vertebral
bone marrow fat fraction showed a reliable correlation with BMD using single-voxel
proton magnetic resonance spectroscopy (1H-MRS) with single-echo. However,
the difference in T2-relaxation between water and fat induces a bias in the quantification
of fat fraction (FF) at different TE. In order to get the proton density fat
fraction (PDFF) without being influenced by other factors, in this study we
used multi-echo 1H-MRS and multi-echo Dixon to measure the PDFF in
L2-L4 spines and compared it with corresponding BMD measured by CT.
Methods
This study was approved by the local ethics committee, and all patients
gave written informed consent. 20 people (7 males and 13 females; mean age, 49.1±19.0 years old) were recruited for this study. All MR imaging was performed on a
1.5 T MR scanner (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany). A
prototype sagittal multi-echo Dixon
VIBE
sequence was used for fat
quantification with the following parameters: 6 TEs of 1.12, 2.46, 3.69, 4.92,
6.15, and 7.38 ms, a TR of 9.15 ms, a slice thickness of 4.0 mm, a flip angle of 4°, a matrix size of 160×126, and a field-of-view
of 327×261mm2. PDFF was calculated
inline using a prototype
implementation
of a multi-step adaptive fitting approach1. Single-voxel 1H
MRS of each L2-4 vertebra was performed
using a prototype multi-echo STEAM
sequence without water suppression with 5 TEs of 12, 24, 38, 48 and 72 ms; a TR
of 3000 ms, and a voxel of 15×15×15 mm3. PDFF was calculated inline using prototype peak
fitting of every TE to correct the T2 decay of each component2. Bone
mineral density (BMD) of each
L3-4 vertebra was measured
with single-energy quantitative computed tomography (CT). Linear correlation
analysis was performed using the Pearson correlation coefficient to evaluate
the association between PDFF
measured by Dixon
VIBE
and MRS with BMD.Results
L2, L3 and L4 showed no difference in BMD (124.3 mg/cm3±48.3 vs. 131.3 mg/cm3±52.6 vs. 129.9 mg/cm3±54.8; P
>0.05), PDFF measured by 1H-MRS (37.5%±8.7 vs. 41.5%±9.4 vs. 42.5%±10.3; P
>0.05), and
PDFF measured by Dixon VIBE (46.9%±10.7 vs. 50.0%±11.2 vs. 48.6%±11.1; P
>0.05). Thus, the values from L2, L3 and L4 were grouped together in the
following analysis. PDFF measured by 1H-MRS was lower than that measured by Dixon VIBE
(40.5%±9.8 vs. 48.5%±11.2, P <0.001), but had
significant correlation (r = 0.747, P
<0.001; Figure 1). PDFF measured by 1H-MRS and Dixon VIBE both showed significant correlation with BMD measured by CT
(r = -0.717 and -0.712, P <0.001 for both;
Figure 2).
Discussion
This study compared the PDFF measured by 1H-MRS and Dixon VIBE
using multiple echoes, and assessed the correlation with BMD. The results
showed significant correlation between them. FF measured by
single-echo 1H-MRS is TE dependent, and the multi-echo 1H-MRS
used in the present study corrected the T2 decay to get a reliable derivation
of FF. As 1H-MRS only measured FF in a VOI and needs to be performed
in each vertebra, Dixon VIBE has an advantage to cover a larger
FOV and get the FF map of all vertebraein one examination. Using the multi-echo Dixon VIBE,
which is insensitive to field inhomogeneity and corrected for T2* decay, the
PDFF has significant correlation with PDFF measured by 1H-MRS, and
also showsstrong correlation with BMD.
Conclusion
Multi-echo MRS and
multi-echo Dixon VIBE are useful in assessing spinal fat content, and can be used
to assess the BMD.Acknowledgements
No acknowledgement found.References
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