• Korean Journal of Radiology
• /
• v.20 no.1
• /
• pp.126-133
• /
• 2019

Objective: To compare the lumbar vertebral bone marrow fat-signal fractions obtained from six-echo modified Dixon sequence (6-echo m-Dixon) with those from single-voxel magnetic resonance spectroscopy (MRS) in patients with low back pain. Materials and Methods: Vertebral bone marrow fat-signal fractions were quantified by 6-echo m-Dixon (repetition time [TR] = 7.2 ms, echo time (TE) = 1.21 ms, echo spacing = 1.1 ms, total imaging time = 50 seconds) and single-voxel MRS measurements in 25 targets (23 normal bone marrows, two focal lesions) from 24 patients. The point-resolved spectroscopy sequence was used for localized single-voxel MRS (TR = 3000 ms, TE = 35 ms, total scan time = 1 minute 42 seconds). A 2 × 2 × 1.5 cm³ voxel was placed within the normal L2 or L3 vertebral body, or other lesions including a compression fracture or metastasis. The bone marrow fat spectrum was characterized on the basis of the magnitude of measurable fat peaks and a priori knowledge of the chemical structure of triglycerides. The imaging-based fat-signal fraction results were then compared to the MRS-based results. Results: There was a strong correlation between m-Dixon and MRS-based fat-signal fractions (slope = 0.86, R² = 0.88, p < 0.001). In Bland-Altman analysis, 92.0% (23/25) of the data points were within the limits of agreement. Bland-Altman plots revealed a slight but systematic error in the m-Dixon based fat-signal fraction, which showed a prevailing overestimation of small fat-signal fractions (< 20%) and underestimation of high fat-signal fractions (> 20%). Conclusion: Given its excellent agreement with single-voxel-MRS, 6-echo m-Dixon can be used for visual and quantitative evaluation of vertebral bone marrow fat in daily practice.

• Investigative Magnetic Resonance Imaging
• /
• v.16 no.1
• /
• pp.16-24
• /
• 2012

Purpose : The purpose of this study was to determine whether there is a significant correlation between vertebral marrow fat fraction measured using Dixon quantitative chemical shift MRI (QCSI) and BMD on dual-energy X-ray absorptiometry (DXA). Materials and Methods: This retrospective study included 68 healthy individuals [mean age, 50.7 years; range, 25-76; male/female (M/F) = 36/32] who underwent DXA of the L-spine and whole body MRI including QCSI of the L-spine and chemical shift MRI of the liver. The enrolled individuals were divided into subgroups according to sex and T-score [i.e., normal bone density (M/F=27/23) and osteopenia (M/F=9/9)]. Vertebral marrow (Dixon QCSI, TR/TE 10.2/4.8 ms) and hepatic fat fractions (chemical shift technique, TR/TE 110/4.9 and 2.2 ms) were calculated on MRI. We evaluated whether there were significant differences in age, body mass index (BMI), vertebral marrow fat fraction, or hepatic fat fraction among the subgroups. Whether or not the participant had reached menopause was also evaluated in females. The correlations among variables (i.e., age, BMI, vertebral marrow and hepatic fat fractions, BMD) were evaluated using Spearman's correlation method. Results: There were no significant differences in age, BMI, or vertebral marrow and hepatic fat fractions between the two male subgroups (normal bone density vs. osteopenia). In female subjects, mean age in the osteopenic subgroup was greater than that in the normal subgroup (p=0.01). Presence of menopause was more common in the osteopenic subgroup [77.8% (7/9)] than the normal subgroup [26.1% (6/23), p<0.05]. The other variables showed no significant difference between female subgroups. The only significant correlation with marrow fat fraction after partial correlation analysis was that with age in the female subjects (r=0.43, p<0.05). Conclusion: The vertebral marrow fat fraction calculated using the Dixon QCSI does not precisely reflect the mild decrease in BMD for either sex.

• Investigative Magnetic Resonance Imaging
• /
• v.21 no.1
• /
• pp.28-33
• /
• 2017

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.

• Korean Journal of Radiology
• /
• v.22 no.10
• /
• pp.1671-1679
• /
• 2021

Objective: We quantitatively measured the fat fraction (FF) in the vertebrae of patients with ankylosing spondylitis (AS) using magnetic resonance imaging (MRI) and investigated the role of FF as an indicator of both active inflammation and chronicity. Materials and Methods: A total of 52 patients with AS who underwent spinal MRI were retrospectively evaluated. The FF values of the anterosuperior and anteroinferior corners of the bone marrow in the L1-S1 spine were assessed using the modified Dixon technique. AS activity was measured using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), AS Disease Activity Score (ASDAS), and serum inflammatory marker levels. AS disease chronicity was assessed by AS disease duration and the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). Univariable and multivariable regression analyses were conducted to investigate the correlation between FF and other clinical characteristics. Results: The mean FF ± standard deviation of the total lumbar spine was 43.0% ± 11.3%. At univariable analysis, spinal FF showed significant negative correlation with BASDAI (β = -0.474, p = 0.002) and ASDAS with C-reactive protein (ASDAS-CRP; β = -0.478, p = 0.002) and a significant positive correlation with AS disease duration (β = 0.440, p = 0.001). After adjusting for patient age, sex, and total mSASSS score, spinal FF remained significantly negatively correlated with BASDAI (β = -0.543, p < 0.001), ASDAS-CRP (β = -0.568, p < 0.001), and ASDAS with erythrocyte sedimentation rate (β = -0.533, p = 0.001). Spinal FF was significantly lower in patients with very high disease activity (ASDAS-CRP > 3.5) than in those with only high disease activity (2.1 ≤ ASDAS-CRP ≤ 3.5) (p = 0.010). Conclusion: Spinal FF may help assess both AS disease activity and chronicity.

• Korean Journal of Radiology
• /
• v.20 no.6
• /
• pp.916-930
• /
• 2019

Objective: To investigate the relationships of T₂^*-corrected 6-echo Dixon volumetric interpolated breath-hold examination (VIBE) imaging-based fat fraction (FF) and R₂^* values with bone mineral density (BMD); determine their associations with sex, age, and menopause; and evaluate the diagnostic performance of the FF and R₂^* for predicting osteopenia and osteoporosis. Materials and Methods: This study included 153 subjects who had undergone magnetic resonance (MR) imaging, including MR spectroscopy (MRS) and T₂^*-corrected 6-echo Dixon VIBE imaging. The FF and R₂^* were measured at the L4 vertebra. The male and female groups were divided into two subgroups according to age or menopause. Lin's concordance and Pearson's correlation coefficients, Bland-Altman 95% limits of agreement, and the area under the curve (AUC) were calculated. Results: The correlation between the spectroscopic and 6-echo Dixon VIBE imaging-based FF values was statistically significant for both readers (p_c = 0.940 [reader 1], 0.908 [reader 2]; both p < 0.001). A small measurement bias was observed for the MRS-based FF for both readers (mean difference = -0.3% [reader 1], 0.1% [reader 2]). We found a moderate negative correlation between BMD and the FF (r = -0.411 [reader 1], -0.436 [reader 2]; both p <0.001) with younger men and premenopausal women showing higher correlations. R₂^* and BMD were more significantly correlated in women than in men, and the highest correlation was observed in postmenopausal women (r = 0.626 [reader 1], 0.644 [reader 2]; both p < 0.001). For predicting osteopenia and osteoporosis, the FF had a higher AUC in men and R₂^* had a higher AUC in women. The AUC for predicting osteoporosis was highest with a combination of the FF and R₂^* in postmenopausal women (AUC = 0.872 [reader 1], 0.867 [reader 2]; both p < 0.001). Conclusion: The FF and R₂^* measured using T₂^*-corrected 6-echo Dixon VIBE imaging can serve as predictors of osteopenia and osteoporosis. R₂^* might be useful for predicting osteoporosis, especially in postmenopausal women.