An in vivo magnetic resonance imaging technique for measurement of rat lumbar vertebral body blood perfusion

Quantitative Evaluation of Vertebral Microvascular Permeability and Fat Fraction in Alloxan-induced Diabetic Rabbits

Purpose To determine longitudinal relationships between lumbar vertebral bone marrow permeability and marrow adipose tissue in a rabbit diabetes model by using quantitative dynamic contrast agent-enhanced (DCE) magnetic resonance (MR) imaging and iterative decomposition of water and fat with the echo asymmetry and least-squares estimation quantitation (IDEAL IQ) sequence. Materials and Methods Twenty rabbits were randomly assigned to the diabetic (n = 10) or control (n = 10) group. All rabbits underwent sagittal MR imaging of the lumbar region at fixed time points (0, 4, 8, 12, and 16 weeks after alloxan injection). A linear mixed-effects model was used to analyze fat fraction (FF) and permeability parameter changes for 16 months after baseline. These parameters were compared between the two groups by using an independent-samples t test. Correlation of DCE MR imaging parameters with FF and with microvessel density (MVD) was analyzed by using the Spearman correlation coefficient. All statistical analyses were performed with software. Results Twelve weeks after injection, transfer constant (K^trans) and rate constant (K_ep) were markedly and significantly increased, while fractional plasma volume (V_p) significantly decreased. The volume of extravascular extracellular space (V_e) decreased significantly after 16 weeks in the diabetic group. MVD was negatively correlated with K^trans and K_ep and positively correlated with V_e and V_p, while FF was positively correlated with K^trans and K_ep and negatively correlated with V_e and V_p (P < .05 for all). Conclusion DCE MR imaging and the IDEAL IQ sequence can be used for quantitative evaluation of changes in vertebral microvascular permeability and vertebral fat deposition in alloxan-induced diabetic rabbits. This variation is highly associated with increased vertebral fat deposition. ^© RSNA, 2017 Online supplemental material is available for this article.

Comparison of semi-quantitative and quantitative dynamic contrast-enhanced MRI evaluations of vertebral marrow perfusion in a rat osteoporosis model

BACKGROUND

This study aims to investigate the technical feasibility of semi-quantitative and quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in the assessment of longitudinal changes of marrow perfusion in a rat osteoporosis model, using bone mineral density (BMD) measured by micro-computed tomography (micro-CT) and histopathology as the gold standards.

METHODS

Fifty rats were randomly assigned to the control group (n=25) and ovariectomy (OVX) group whose bilateral ovaries were excised (n=25). Semi-quantitative and quantitative DCE-MRI, micro-CT, and histopathological examinations were performed on lumbar vertebrae at baseline and 3, 6, 9, and 12 weeks after operation. The differences between the two groups in terms of semi-quantitative DCE-MRI parameter (maximum enhancement, E_max), quantitative DCE-MRI parameters (volume transfer constant, K^trans; interstitial volume, V_e; and efflux rate constant, K_ep), micro-CT parameter (BMD), and histopathological parameter (microvessel density, MVD) were compared at each of the time points using an independent-sample t test. The differences in these parameters between baseline and other time points in each group were assessed via Bonferroni's multiple comparison test. A Pearson correlation analysis was applied to assess the relationships between DCE-MRI, micro-CT, and histopathological parameters.

RESULTS

In the OVX group, the E_max values decreased significantly compared with those of the control group at weeks 6 and 9 (p=0.003 and 0.004, respectively). The K^trans values decreased significantly compared with those of the control group from week 3 (p<0.05). However, the V_e values decreased significantly only at week 9 (p=0.032), and no difference in the K_ep was found between two groups. The BMD values of the OVX group decreased significantly compared with those of the control group from week 3 (p<0.05). Transmission electron microscopy showed tighter gaps between vascular endothelial cells with swollen mitochondria in the OVX group from week 3. The MVD values of the OVX group decreased significantly compared with those of the control group only at week 12 (p=0.023). A weak positive correlation of E_max and a strong positive correlation of K^trans with MVD were found.

CONCLUSIONS

Compared with semi-quantitative DCE-MRI, the quantitative DCE-MRI parameter K^trans is a more sensitive and accurate index for detecting early reduced perfusion in osteoporotic bone.

Rapid increase in marrow fat content and decrease in marrow perfusion in lumbar vertebra following bilateral oophorectomy: an MR imaging-based prospective longitudinal study

Objective

Bilateral oophorectomy leads to reduced bone mineral density (BMD), and reduced BMD is associated with increased marrow fat and reduced marrow perfusion. Purpose of this study was to investigate how soon these changes occur following surgical oophorectomy.

Materials and Methods

Six patients who underwent hysterectomy and bilateral salpingo-oophorectomy were studied. At baseline, mean patient age was 49.5 years (range: 45-54 years). Third lumbar vertebral body BMD measurement using quantitative CT, marrow fat fraction (FF) using MR spectroscopy and marrow perfusion using dynamic contrast enhanced MRI were conducted immediately prior to surgery and at 3, 9, and 21 months after surgery.

Results

Reduced BMD, increased marrow FF, and reduced marrow perfusion occurred synchronously post-oophorectomy. There was a sharp decrease of 12.5 ± 7.2% in BMD (n = 6), a sharp increase of 92.2 ± 46.3% (n = 6) in FF, a sharp decrease of 23.6 ± 3.9% in maximum contrast enhancement (n = 5), and of 45.4 ± 7.7% for enhancement slope (n = 5) during the initial 3 months post surgery. BMD and marrow perfusion continued to decrease, and marrow FF continued to increase at a slower rate during the following 18 months. Friedman test showed a significant trend for these changes (p < 0.05).

Conclusion

Bilateral oophorectomy leads to a rapid decrease in lumbar BMD, an increase in marrow fat content, and a decrease in marrow blood perfusion.

Organic nitrate maintains bone marrow blood perfusion in ovariectomized female rats: a dynamic, contrast-enhanced magnetic resonance imaging (MRI) study

This study investigated the effects of nitrate on bone mineral density (BMD) and bone marrow perfusion in ovariectomized (OVX) female rats, and also the effects of nitrate on in vitro osteoblastic activity and osteoclastic differentiation of murine monocyte/macrophage RAW 264.7 cells. Female Sprague–Dawley rats were divided into OVX + nitrate group (isosorbide-5-mononitrate, ISM, 150 mg/kg/ day b.i.d), OVX + vehicle group, and control group. Lumbar spine CT bone densitometry and perfusion MRI were performed on the rats at baseline and week 8 post-OVX. The OVX rats’ BMD decreased by 22.5% ± 5.7% at week 8 (p < 0.001); while the OVX + ISM rats’ BMD decreased by 13.1% ± 2.7% (p < 0.001). The BMD loss difference between the two groups of rats was significant (p = 0.018). The OVX rats’ lumbar vertebral perfusion MRI maximum enhancement (Emax) decreased by 10.3% ± 5.0% at week 8 (p < 0.005), while in OVX + ISM rats, the Emax increased by 5.5% ± 6.9% (p > 0.05). The proliferation of osteoblast-like UMR-106 cells increased significantly with ISM treatment at 0.78 µM to 50 μM. Treatment of UMR-106 cells with ISM also stimulated the BrdU uptake. After the RAW 264.7 cells were co-treated with osteoclastogenesis inducer RANKL and 6.25 μM ~ 100 μM of ISM for 3 days, a trend of dose-dependent increase of osteoclast number was noted.

Compromised perfusion in femoral head in normal rats: distinctive perfusion MRI evidence of contrast washout delay

OBJECTIVES

The femoral head is prone to osteonecrosis. This study investigated dynamic contrast-enhanced (DCE) MRI contrast washout features of the femoral head and compared the data with data from other bony compartments in normal rats.

METHODS

7-month-old Wistar rats were used. DCE MRI of the right hip (n=18), right knee (n=12) and lumbar spine (n=10) was performed after an intravenous bolus injection of Gd-DOTA (0.3 mmol kg(-1)). Temporal resolution was 0.6 s for hip and spine, and 0.3 s for knee. The total scan duration was 8 min for hip and spine, and 4.5 min for knee. The regions of interest for enhancement measurement included femoral head, proximal femoral diaphysis, distal femoral diaphysis and epiphysis, proximal tibial epiphysis and diaphysis, and lumbar vertebrae L1-5.

RESULTS

Femoral head showed no enhancement signal decay during the DCE MRI period, while all other bony compartments showed a contrast washin phase followed by a contrast washout phase. In the knee joint, the contrast washout of the proximal tibia diaphysis was slower that of other bony compartments of the knee.

CONCLUSION

Based on the evidence of delayed contrast washout, this study showed that blood perfusion in the femoral head could be compromised in normal rats.