A comparative analysis between ultrasonometry and computer-aided tomography to evaluate bone healing

Ex vivo vibro-acoustography characterization of osteoporosis in an experimental mice model

Background

Osteoporosis is a highly prevalent multifactorial osteometabolic disease, classically diagnosed, in vivo, by dual energy X-ray absorptiometry (DXA). This study evaluated osteoporosis, ex vivo, using vibro-acoustography (VA), an elastographic technique based on ultrasound radiation force.

Methods

Three groups of mice femurs were used: (I) control group (CG), (II) osteoporosis group (OG) and (III) treated osteoporosis group (TOG), in which the animals received pamidronate, an antiresorptive drug. Evaluation was performed in an acoustic tank, using two high frequency focused beams produced by a confocal ultrasonic transducer. A hydrophone registered the low frequency acoustic response (AR) of bone samples. We used micro-computed tomography (microCT) as the reference standard and evaluated the correlation between VA and microCT parameters.

Results

The spectral analyses of the ARs with estimated area under the curve (AUC) values (mean; st. dev.) were, respectively, 1.29e^-07 and 9.32e^-08 for the CG, 3.25e^-08 and 2.16e^-08 for the OG, and 1.50e^-07 and 8.37e^-08 for the TOG. VA differentiated the experimental groups (P<0.01) and the results were reproducible [interclass correlation coefficient (ICC): 0.43 (95% CI: 0.15-0.71)]. There was also a statistically significant association between VA and microCT connectivity (Conn.) (r=0.80; P<0.01) and connectivity density (Conn. D) (r=0.76; P<0.01).

Conclusions

These results encourage further studies aimed at evaluating the potential use of VA for the diagnosis of osteoporosis as a relatively low-cost and radiation-free alternative to DXA.

Monitoring bone changes due to calcium, magnesium, and phosphorus loss in rat femurs using Quantitative Ultrasound

Bone mineral density is an important parameter for the diagnosis of bone diseases, as well as for predicting fractures and treatment monitoring. Thus, the aim of the present study was to evaluate the potential of Quantitative Ultrasound (QUS) to monitor bone changes after calcium, phosphorus, and magnesium loss in rat femurs in vitro during a demineralization process. Four quantitative ultrasound parameters were estimated from bone surface echoes in eight femur diaphysis of rats. The echo signals were acquired during a decalcification process by Ethylenediaminetetraacetic Acid (EDTA). The results were compared to Quantitative Computed Tomography (QCT) and inductively coupled plasma optical emission spectrometry measurements for validation. Integrated Reflection Coefficient (IRC) reflection parameters and Frequency Slope of Reflection Transfer Function (FSRTF) during demineralization tended to decrease, while the backscattering parameter Apparent Integrated Backscatter (AIB) increased and Frequency Slope of Apparent Backscatter (FSAB) showed an oscillatory behavior with no defined trend. Results indicate a clear relation between demineralization and the corresponding decrease in the reflection parameters and increase in the scattering parameters. The trend analysis of the fall curve of the chemical elements showed a better relationship between IRC and QCT. It was possible to monitor bone changes after ions losses, through the QUS. Thus, it is an indication that the proposed protocol has potential to characterize bone tissue in animal models, providing consistent results towards standardization of bone characterization studies by QUS endorsing its use in humans.

Preliminary results of vibro-acoustography evaluation of bone surface and bone fracture

Background

Vibro-acoustography (VA) uses two co-focused ultrasound beams with slightly different frequencies. The beams interact and generate a low-frequency focus to excite an object.

Methods

A two-element confocal ultrasound transducer with central frequency at 3.2 MHz was used to generate the low-frequency excitation (30 kHz) and the response of the bone to that excitation was acquired by a dedicated hydrophone. The face of the confocal transducer was positioned parallel to the surface of the bone at a focal length of 7 cm. The hydrophone was fixed to the side of the transducer, out of the path of the ultrasonic beam.

Results

The resulting image clearly showed the bone fracture with resolution of 0.25 mm and high contrast with well-defined borders.

Conclusions

In this paper, we present preliminary results of VA imaging of bone surface and of bone fracture using an experimental set-up. Our results encourage future studies using VA to evaluate bone fractures.

Correlation between ultrasound velocity and densitometry in fresh and demineralized cortical bone

OBJECTIVE:

To compare ultrasound propagation velocity with densitometry in the diaphyseal compact cortical bone of whole sheep metatarsals.

METHODS:

The transverse ultrasound velocity and bone mineral density of 5-cm-long diaphyseal bone segments were first measured. The bone segments were then divided into four groups of 15 segments each and demineralized in an aqueous 0.5 N hydrochloric acid solution for 6, 12, 24 or 36 hours. All measurements were repeated after demineralization for each time duration and the values measured before and after demineralization were compared.

RESULTS:

Ultrasound velocity and bone mineral density decreased with demineralization time, and most differences in the pre- and post-demineralization values within each group and between groups were significant: A moderate correlation coefficient (r=0.75956) together with a moderate agreement was determined between both post-demineralization parameters, detected by the Bland-Altman method.

CONCLUSION:

We conclude that both ultrasound velocity and bone mineral density decrease as a result of demineralization, thus indicating that bone mineral content is of great importance for maintaining the acoustic parameters of cortical bone, as observed for cancellous bone. Ultrasound velocity can be used to evaluate both compact cortical bone quality and bone mineral density.

Ultrasound method applied to characterize healthy femoral diaphysis of Wistar rats in vivo

A simple experimental protocol applying a quantitative ultrasound (QUS) pulse-echo technique was used to measure the acoustic parameters of healthy femoral diaphyses of Wistar rats in vivo. Five quantitative parameters [apparent integrated backscatter (AIB), frequency slope of apparent backscatter (FSAB), time slope of apparent backscatter (TSAB), integrated reflection coefficient (IRC), and frequency slope of integrated reflection (FSIR)] were calculated using the echoes from cortical and trabecular bone in the femurs of 14 Wistar rats. Signal acquisition was performed three times in each rat, with the ultrasound signal acquired along the femur's central region from three positions 1 mm apart from each other. The parameters estimated for the three positions were averaged to represent the femur diaphysis. The results showed that AIB, FSAB, TSAB, and IRC values were statistically similar, but the FSIR values from Experiments 1 and 3 were different. Furthermore, Pearson's correlation coefficient showed, in general, strong correlations among the parameters. The proposed protocol and calculated parameters demonstrated the potential to characterize the femur diaphysis of rats in vivo. The results are relevant because rats have a bone structure very similar to humans, and thus are an important step toward preclinical trials and subsequent application of QUS in humans.

A comparative in vivo ultrasonometric evaluation of normal and delayed fracture healing in sheep tibiae

OBJECTIVE

To compare normal and delayed bone healing by measuring ultrasound conduction velocity across the bone callus.

METHODS

A model of transverse linear and 5 mm resection osteotomies of sheep tibiae was used. Fourteen sheep were operated on and were divided into two groups of seven according to osteotomy type. The procedure was performed on the right tibiae and the intact left tibiae were used as controls. The transverse and axial ultrasound velocities were measured at 30-day intervals for 90 days, after which the animals were killed and both the right and left tibiae were resected for in vitro biomechanical analysis.

RESULTS

Both the transverse and axial ultrasound velocities progressively increased, but the increase was smaller for the delayed union that resulted from the resection osteotomy. The mechanical resistance was higher for the normally healed tibiae that resulted from a linear osteotomy; this result closely correlated with the ultrasound velocity results. Significant differences were found for the comparisons between the intact and operated tibiae in both groups and between the groups for both the transverse and axial ultrasound velocities, but the differences were greater for the latter.

CONCLUSION

We conclude that in vivo transverse and axial ultrasound velocities provide highly precise information about the healing state of both linear and resection diaphyseal osteotomies, but the axial ultrasound velocity most likely has greater discriminatory power. This method has the potential for clinical application in humans.

The early phases of bone healing can be differentiated in a rat osteotomy model by focused transverse-transmission ultrasound

Here we describe the use of a 5-MHz focused transmission system to image the bone repair region and to distinguish the early healing phases in a rat osteotomy (OT) model. Twelve-month-old female rats underwent a 2-mm OT. After 6 wk of consolidation, 2-D projection images of time-of-flight, speed of sound, and ultrasound attenuation were measured in vitro. The tissue types in the OT gap region were assessed by site-matched histology sections and micro-computed tomography (μCT). In the cases investigated, OT gap regions containing fibrous tissue (group A) were found to have similar properties compared with adjacent muscle tissue, whereas regions filled with cartilage and mineralized callus tissues (group B) differed significantly. Analysis of variance revealed that the healing group had a stronger effect on acoustic parameters (F < 35) than on μCT-based parameters (F < 22). This pilot study reports the feasibility of transverse transmission quantitative ultrasound in assessment of the onset of cartilage formation during callus formation.

Ultrasonometry evaluation of axial compression osteosinthesis. An experimental study

OBJECTIVE:

To measure the ultrasound propagation velocity (UV) through a tibial transverse osteotomy in sheep, before and after the fixation with a DCP plate.

MATERIAL AND METHODS:

Ten assemblies of a DCP plate with the diaphyseal segment of tibiae, in which a transverse osteotomy was made, were used. Both coronal and sagittal transverse and the axial UV were measured, first with the intact bone assembled with the plate and then with the uncompressed and compressed osteotomy; statistical comparisons were made at the 1% (p<0.01) level of significance.

RESULTS:

Compared with the intact bone assembly, axial UV significantly decreased with the addition of the osteotomy and significantly increased with compression, presenting the same behavior for the other modalities, although not significantly.

DISCUSSION AND CONCLUSION:

In accordance with the literature data on the ultrasonometric evaluation of fracture healing, underwater UV measurement was able to demonstrate the efficiency of DCP plate fixation. The authors conclude that the method has a potential for clinical application in the postoperative follow-up of DCP plate osteosinthesis, with a capability to demonstrate when it becomes ineffective. Laboratory investigation.