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. 2022 Jan 3;23(1):16.
doi: 10.1186/s12891-021-04970-7.

Sweep imaging with Fourier transform as a tool with MRI for evaluating the effect of teriparatide on cortical bone formation in an ovariectomized rat model

Yasutaka Sotozono  1 , Kazuya Ikoma  2 , Masamitsu Kido  1 , Okihiro Onishi  1 , Masataka Minami  1 , Hiroaki Wada  1 , Shunji Yamada  3 , Ken-Ichi Matsuda  3 , Masaki Tanaka  3 , Kenji Takahashi  1
Affiliations

Sweep imaging with Fourier transform as a tool with MRI for evaluating the effect of teriparatide on cortical bone formation in an ovariectomized rat model

Yasutaka Sotozono et al. BMC Musculoskelet Disord. .

Abstract

Background: Teriparatide (TPTD) is a drug for osteoporosis that promotes bone formation and improves bone quality. However, the effects of TPTD on cortical bone are not well understood. Sweep imaging with Fourier transform (SWIFT) has been reported as a useful tool for evaluating bound water of cortical bone, but it has yet to be used to investigate the effects of TPTD on cortical bone. This study aimed to evaluate the consequences of the effect of TPTD on cortical bone formation using SWIFT.

Methods: Twelve-week-old female Sprague-Dawley rats (n = 36) were reared after ovariectomy to create a postmenopausal osteoporosis model. They were divided into two groups: the TPTD and non-TPTD groups. Rats were euthanized at 4, 12, and 24 weeks after initiating TPTD treatment. Tibial bones were evaluated using magnetic resonance imaging (MRI) and bone histomorphometry. In MRI, proton density-weighted imaging (PDWI) and SWIFT imaging were performed. The signal-to-noise ratio (SNR) was calculated for each method. The same area evaluated by MRI was then used to calculate the bone formation rate by bone histomorphometry. Measurements were compared using the Mann-Whitney U-test, and a P-value of < 0.05 was considered significant.

Results: PDWI-SNR was not significantly different between the two groups at any time point (P = 0.589, 0.394, and 0.394 at 4, 12, and 24 weeks, respectively). Contrarily, SWIFT-SNR was significantly higher in the TPTD group than in the non-TPTD group at 4 weeks after initiating treatment, but it was not significantly different at 12 and 24 weeks (P = 0.009, 0.937, and 0.818 at 4, 12, and 24 weeks, respectively). The bone formation rate assessed by histomorphometry was significantly higher in the TPTD group than in the non-TPTD group at all timepoints (P < 0.05, all weeks). In particular, at 4 weeks, the bone formation rate was markedly higher in the TPTD group than in the non-TPTD group (P = 0.028, 1.98 ± 0.33 vs. 0.09 ± 0.05 μm3/μm2/day).

Conclusions: SWIFT could detect increased signals of bound water, reflecting the effect of TPTD on the cortical bone. The signal detected by SWIFT reflects a marked increase in the cortical bone formation rate.

Keywords: Osteoporosis; Sweep imaging with Fourier transform; Teriparatide.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Regions of interest for MRI. a The regions are set 2 mm proximal to the tibiofibular union. b Two regions, including all the areas of cortical bone, are set in the cortical bone of the tibia in the axial plane (proton density-weighted image). Ant. = anterior, Post. = posterior, Med. = medial, Lat. = lateral
Fig. 2
Fig. 2
The signal-to-noise ratio (SNR) within the tibial cortical bone measured by (a) proton density-weighted imaging (PDWI) and (b) sweep imaging with Fourier transform (SWIFT) for the teriparatide (TPTD) and non-TPTD groups. Values are expressed as means ± standard deviations. There was no significant difference in the PDWI-SNR between the two groups at any time point (P = 0.589, 0.394, and 0.394 at 4, 12, and 24 weeks, respectively). The SWIFT-SNR was significantly higher in the TPTD group than in the non-TPTD group at 4 weeks after the initiation of treatment, but no significant difference was observed at 12 and 24 weeks (P = 0.009, 0.937, and 0.818 at 4, 12, and 24 weeks, respectively). *: P < 0.05
Fig. 3
Fig. 3
Representative images obtained via proton density-weighted imaging (PDWI) and sweep imaging with Fourier transform (SWIFT) for the teriparatide (TPTD) and non-TPTD groups. SWIFT can detect proton signals in the cortical bone, which PDWI is unable to detect. Ant. = anterior, Post. = posterior, Med. = medial, Lat. = lateral
Fig. 4
Fig. 4
Representative 2D and 3D images obtained via microcomputed tomography (μCT) for the teriparatide (TPTD) and non-TPTD groups. Ant. = anterior, Post. = posterior, Med. = medial, Lat. = lateral
Fig. 5
Fig. 5
a Porosity area/cortical area (Po Ar/Ct Ar) and b bone formation rate (BFR/BS) in the tibial cortical bone measured by bone histomorphometry. There was no significant difference in Po Ar/Ct Ar between the teriparatide (TPTD) and non-TPTD groups at any time point (P = 0.857, 0.486, and 0.0571 at 4, 12, and 24 weeks, respectively). BFR/BS was significantly higher in the TPTD group than in the non-TPTD group at all timepoints (P < 0.05 at all weeks). In particular, at 4 weeks, BFR/BS was markedly higher in the TPTD group than in the non-TPTD group. *: P < 0.05
Fig. 6
Fig. 6
Representative images of the areas of the new bone in the endosteum when observed under fluorescent light. The thin arrow indicates calcein injected at 10 days before tibial removal, and the thick arrow indicates calcein injected at 4 days before tibial removal. A marked increase in the bone formation rate in the teriparatide (TPTD) group was observed at 4 weeks after the initiation of TPTD treatment
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