Magnetic resonance imaging phantom-based S1 vertebral scores are indicators of fat-water-like osteoporotic changes in postmenopausal women: a pilot study

Abstract

Study design: A prospective study.

Purpose: To assess fat-water-like tissue changes on the 1st sacral vertebra using novel magnetic resonance imaging (MRI) phantombased F- and W-scores and evaluate their diagnostic performances in osteoporosis detection.

Overview of literature: Using an uncommonly advanced MRI technique, previous studies have found that fat-water changes were consistent with osteoporosis. The role of routine MRI sequences can be extended in this regard. The S1 vertebra is considered a crucial anatomical site in spine surgeries because it seldom suffers from fractures. Thus, S1 could indicate osteoporotic fat-water changes.

Methods: Forty-two female volunteers (aged 62.3±6.3 years) underwent spine examination with both MRI (including a phantom) and dual-energy X-ray absorptiometry (DXA) following ethical approval. MRI phantom-based F- and W-scoreS1 were defined by normalizing S1 vertebral signal intensities (SIs) by coconut oil and water SIs of the phantom on T1- and T2-weighted imaging, respectively. Using receiver operating characteristic analysis, the diagnostic performances of the new scores for evaluating osteoporosis and vertebral fractures were investigated against standard areal bone mineral density measured with DXA (DXA-aBMD).

Results: The F-scoreS1 and W-scoreS1 were greater (4.11 and 2.43, respectively) in patients with osteoporosis than those without osteoporosis (3.25 and 1.92, respectively) and achieved areas under the curve (AUCs) of 0.82 and 0.76 (p<0.05), respectively, for osteoporosis detection. Similarly, the mean F-scoreS1 and W-scoreS1 were higher (4.11 and 2.63, respectively) in patients with vertebral fractures than in those without fractures (3.30 and 1.82, respectively) and had greater AUCs (0.90 for W-scoreS1 and 0.74 for F-scoreS1) than DXA-aBMD (AUC, 0.26; p<0.03). In addition, the F- and W-scoreS1 demonstrated a strong correlation (r=0.65, p<0.001).

Conclusions: The new S1 vertebral-based MRI scores were developed to detect osteoporotic changes and demonstrated improvements over DXA-aBMD in differentiating patients with vertebral fractures.

Keywords: Magnetic resonance imaging; Osteoporosis; Osteoporotic fracture; Phantom; Sacral region.

Fig. 1

Patient selection diagram: 42 female volunteers consented to undergo both magnetic resonance imaging (MRI) and dual-energy X-ray absorptiometry (DXA) examinations following the inclusion and exclusion criteria.

Fig. 2

An acrylic phantom was designed and developed consisting of coconut oil as a good T1 reference control and deionized water as a good T2 reference control. The phantom shape was consistent and well-fit for the lumbar lordotic space and was used during magnetic resonance imaging (MRI) scanning.

Fig. 3

Magnetic resonance (MR) images were analyzed with free MircoDicom software. (A) To calculate the F-score_S1, regions of interest (ROI) indicated by white arrowheads were selected on S1 vertebra and on coconut oil to calculate the signal intensity (SI) using T1-weighted images, while a small ROI was selected for cerebrospinal fluid (as a control) at L3 level to calculate the vertebral bone quality (VBQ) score; (B) similarly, to calculate the W-score_S1, T2-weighted images were used to measure SI at S1 vertebra and SI of deionized water (T2 reference control), indicated by white arrowheads.

Fig. 4

(A, B) Negative and strong correlations were found between F-score_S1, W-score_S1, and areal bone mineral density (aBMD), compared to (C) the vertebral bone quality score (VBQ) showed similar negative correlation; however, the strongest correlation was reported between the two new scores, (D) Additionally, a positive and significant correlation was found between the S1 F-score and W-score, which shows that with an increase in fat content, there could be an increase in water-like contents. CI, confidence interval.

Fig. 5

The performances of the F-score_S1 and W-score_S1 were assessed for osteoporosis (A), low bone mass (B), and vertebral fractures (C). The receiver operating characteristic area under the curve (AUC) for F-score_S1 and W-score_S1 shows significant differences in F-score_S1, W-score_S1, and areal bone mineral density (aBMD) identified between non-osteoporosis and osteoporosis, normal and low bone mass, as well as between non-fracture and fracture cases. Compared to the vertebral bone quality (VBQ) score and the current standard dual-energy X-ray absorptiometry-aBMD in detecting osteoporosis, low bone mass, and vertebral fractures, the new scores showed improved results. CI, confidence interval.