Temperature dependency of quantitative ultrasound

Influence of the osteosynthesis plate on ultrasound propagation in the bone

Objective:

To analyze the influence of steel plates for osteosynthesis on the velocity of ultrasound propagation (VU) through the bone.

Methods:

The transverse coronal and sagittal velocity of ultrasound propagation underwater were measured on the intact bone and then on assemblies of the same bone with two types of osteosynthesis plates (DCP and semi tubular), fixed onto the dorsal side of the bones. The first arriving signal (FAS) was the ultrasound parameter used, taking the coronal and sagittal diameters as the distances to calculate velocity. Intergroup statistical comparisons were made at significance level of 1% (p<0.01).

Results:

Velocity was higher on the intact bones than on the bone-plate assemblies and higher for the semitubular than for the compression plates, although differences were not statistically significant for most comparisons (p=0.0132 to 0.9884), indicating that the steel plates do not interfere significantly with ultrasound wave propagation through the bone-plate assemblies.

Conclusion:

The velocity reduction effect was attributed to the greater reflection coefficient of the steel as compared to that of bone and water. Ultrasonometry can, thus, be used in the evaluation of healing of fractures fixed with steel plates. Experimental Study.

Influence of cortical bone thickness on the ultrasound velocity

OBJECTIVE

An experimental in vitro study was carried out to evaluate the influence of cortical bone thickness on ultrasound propagation velocity.

METHODS

Sixty bone plates were used, made from bovine femurs, with thickness ranging from 1 to 6 mm (10 of each). The ultrasound velocity measurements were performed using a device specially designed for this purpose, in an underwater acoustic tank and with direct contact using contact gel. The transducers were positioned in two ways: on opposite sides, with the bone between them, for the transverse measurement; and parallel to each other, on the same side of the bone plates, for the axial measurements.

RESULTS

In the axial transmission mode, the ultrasound velocity speed increased with cortical bone thickness, regardless of the distance between the transducers, up to a thickness of 5 mm, then remained constant thereafter. There were no changes in velocity when the transverse measures were made.

CONCLUSION

Ultrasound velocity increased with cortical bone thickness in the axial transmission mode, until the thickness surpasses the wavelength, after which point it remained constant.

LEVEL OF EVIDENCE

Experimental Study.

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.

Noncontact ultrasound imaging applied to cortical bone phantoms

PURPOSE

The purpose of this paper was to take the first steps toward applying noncontact ultrasound (NCU) to the tasks of monitoring osteoporosis and quantitative ultrasound imaging (QUS) of cortical bone. The authors also focused on the advantages of NCU, such as its lack of reliance on a technologist to apply transducers and a layer of acoustical coupling gel, the ability of the transducers to operate autonomously as specified by preprogrammed software, and the likely reduction in statistical and systematic errors associated with the variability in the pressure applied by the clinician to the transmitting transducer that NCU might provide. The authors also undertook this study in order to find additional applications of NCU beyond its past limited usage in assessing the severity of third degree burns.

METHODS

A noncontact ultrasound imaging system using a pair of specially designed broadband, 1.5 MHz noncontact piezoelectric transducers and cortical bone phantoms, were used to determine bone mineral density (BMD), speed of sound (SOS), integrated response (IR), and ultrasonic transmittance. Air gaps of greater than 3 cm, two transmission and two reflection paths, and a digital signal processor were also used in the collection of data from phantoms of nominal mass densities that varied from 1.17 to 2.25 g/cm(3) and in bone mineral density from 0 to 1.7 g/cm(3).

RESULTS

Good correlations between known BMD and measured SOS, IR, and transmittance were obtained for all 17 phantoms, and methods for quantifying and minimizing sources of systematic errors were outlined. The BMD of the phantom sets extended through most of the in vivo range found in cortical bone. A total of 16-20 repeated measurements of the SOS, thickness, and IR for the phantom set that were conducted over a period of several months showed a small variation in the range of measurements of ±1%-2%. These NCU data were shown to be in agreement with similar results using contact ultrasound to be within 1%-2%. Transmittance images of cortical bone phantoms showed differences in the nominal overall BMD values of the phantoms that were large enough to be distinguished by a visual examination. A list of possible sources of errors in quantitative NCU was also included in this study.

CONCLUSIONS

The results of this paper suggest that NCU might find additional applications in medical imaging, beyond its original and only previous usage in assessing third degree burns. The fact that the authors' phantom measurements using conventional, gel coupled ultrasound are in agreement with those obtained with NCU demonstrates that in spite of large additional levels of attenuation of up to 150 dB and new error sources, NCU could have comparable levels of accuracy to those of conventional quantitative ultrasound, while providing the medical and patient comfort-related advantages of not involving direct contact.

Evidence-based review of bone strength in children and youth with cerebral palsy

Children with cerebral palsy have various risk factors for compromised bone health. Evidence concerning their bone fragility is gathering; however, there is no consensus regarding risk factors, indications for evaluation, follow-up, or treatment. We performed an evidence-based review targeted to address the following questions concerning children with cerebral palsy: Is bone strength impaired and what are the risk factors? Are these children at increased risk for bone fractures? What are the relations between bone mineral density and fracture risk? What methods can be used for bone health assessment? How can bone strength be improved? Currently, the most acceptable method for evaluating bone status in children is dual-energy x-ray absorptiometry. Evidence demonstrates reduced bone mass in children with cerebral palsy; yet, no clear association with fractures. Preventive methods are suggested.

Instrumentation for in vivo ultrasonic characterization of bone strength

Although it has been more than 20 years since the first recorded use of a quantitative ultrasound (QUS) technology to predict bone fragility, the field has not yet reached its maturity. QUS has the potential to predict fracture risk in several clinical circumstances and has the advantages of being nonionizing, inexpensive, portable, highly acceptable to patients, and repeatable. However, the wide dissemination of QUS in clinical practice is still limited and suffering from the absence of clinical consensus on how to integrate QUS technologies in bone densitometry armamentarium. Several critical issues need to be addressed to develop the role of QUS within rheumatology. These include issues of technologies adapted to measure the central skeleton, data acquisition, and signal processing procedures to reveal bone properties beyond bone mineral quantity and elucidation of the complex interaction between ultrasound and bone structure. This article reviews the state-of-the art in technological developments applied to assess bone strength in vivo. We describe generic measurement and signal processing methods implemented in clinical ultrasound devices, the devices and their practical use, and performance measures. The article also points out the present limitations, especially those related to the absence of standardization, and the lack of comprehensive theoretical models. We conclude with suggestions of future lines and trends in technology challenges and research areas such as new acquisition modes, advanced signal processing techniques, and modelization.

A nomogram for predicting osteoporosis risk based on age, weight and quantitative ultrasound measurement

INTRODUCTION

Quantitative ultrasound measurement (QUS) or clinical risk index alone are not reliable tools for the identification of women with osteoporosis. This study examined the prognostic value of combined QUS and clinical risk index for predicting osteoporosis risk in Thai women.

METHODS

The study was designed as a cross-sectional investigation with 300 women of Thai background, aged between 38 and 85 years (mean age: 58). Femoral neck bone mineral density (BMD) was measured by DXA (Hologic QDR-4500; Bedford, MA, USA). A femoral neck BMD T-scores <or= -2.5 was defined as "osteoporosis"; otherwise, "non-osteoporosis". QUS was measured by Achilles+ (GE Lunar, Madison, WI, USA) and converted to T-score. Three models for predicting osteoporosis were considered: model I included age, weight and QUS, model II included age and weight, and model III included only QUS. The prognostic performance among the models was assessed by the area under the receiver operating characteristic curve (AUC).

RESULTS

The prevalence of osteoporosis was 12.7% (n=38/300) by femoral neck BMD. Age, weight and QUS were each significantly associated with osteoporosis risk. The AUC+/-SE value for model I was 0.86 +/- 0.03, which was significantly higher (p=0.02) than that for model II (AUC = 0.80 +/- 0.04) or model III (AUC = 0.79 +/- 0.04). Based on the estimated parameters of model I, a nomogram was constructed for predicting osteoporosis.

CONCLUSION

These data suggest that the combination of QUS and age and weight could significantly improve the prognosis of osteoporosis in Asian women, and that the nomogram can assist primary care physicians in the identification of high-risk women.

Measurement of ultrasound speed of articular cartilage in variable conditions

Ultrasound (US) imaging and measurement have been widely used for the assessment of articular cartilage (AC) in recent years. Assessment involved the measurement of acoustic properties such as US speed in AC. Those measurements were normally carried out either at room temperature or at 37 degrees C and at 0.15 M saline concentrations. The changes in the structure of AC due to the change in the concentration of bathing saline solution have been previously reported. However, the change in the US speed of AC has not been yet documented. In addition, the variation of temperature during measurements may affect the US speed in AC. The objective of this study is to investigate the change of the US speed in AC with the variations in temperature and the bathing saline concentration. Results demonstrated that the US speed significantly increased with the increase of temperature (15 degrees C to 40 degrees C) and saline concentration (0 M to 2.5 M).

Ultrasonometric evaluation of bone healing: Experimental study using a model of diaphyseal transverse osteotomy of sheep tibiae

Noninvasive ionizing-radiation-free methods of evaluation, such as ultrasonometry, are desirable in any medical situation. An in vitro ultrasonometric study was undertaken to evaluate the bone healing process of sheep tibiae submitted to a diaphyseal transverse osteotomy at different times after the procedure. Fifteen sheep weighing an average of 37 kg had surgery for a transverse mid-diaphyseal osteotomy of the right tibia; they were divided postoperatively into three groups of five for periods of observation at 30, 45 and 60 days. The intact left tibiae of the 15 animals were used for control. The healing process was monitored with conventional radiographs taken at two-week intervals, and the animals were killed at the end of the period of observation of each group. Both surgical and intact tibiae were removed, their diameters were measured and they were submitted to measurement of underwater ultrasound propagation velocities (USPV) at the osteotomy sites in both the sagittal and frontal planes. The diameters of the surgical tibiae decreased with time in both planes (from 26.9 mm to 22.0 mm and to 20.9 mm in the sagittal plane, and from 29.3 mm to 23.9 mm and to 23 mm in the frontal plane), with significant differences between the periods of observation (p < or = 0.018 and p < or = 0.003 between 30 and 45 days and 30 and 60 days, respectively, for the sagittal plane and p < or = 0.006 and p < or = 0.003 between 30 and 45 days and 30 and 60 days, respectively, for the frontal plane) and between surgical and intact tibiae at all time points (p < or = 0.0005 for each comparison). USPV increased with time from 2290 m/s to 2399 m/s and to 2382 m/s in the sagittal plane, and from 2376 m/s to 2472 m/s and to 2466 m/s in the frontal plane, accounting for an approximate 5% difference between 30 and 60 days Differences between the surgical and intact tibiae were significant at all time points (p < or = 0.0005 for both sagittal and frontal planes) but not between periods for either plane. There was a strong negative correlation between diameter and USPV (Pearson's correlation coefficient of -0.8998 for the sagittal plane and -0.9192 for the frontal plane). It was concluded that ultrasonometric evaluation of the bone healing process is feasible, yielding precise and reliable results, with a potential for clinical application.

Contralateral differences in quantitative ultrasound of the heel: the importance of side in clinical practice

Quantitative ultrasound (QUS) of the heel is becoming increasingly popular for the assessment of skeletal status, although there appears to be a general lack of agreement regarding which side to measure. The purpose of the present study was to evaluate possible side differences (right versus left) in heel QUS within the general population, including children (10-15 years old, n=406), adults (26-33 years old, n=339), and elderly subjects (60-75 years old, n=455) of both genders (818 females and 382 males), and to examine the impact of these differences on prevalence estimates of osteoporosis and individual fracture risk assessment. All participants had both their heels measured twice with the Sahara device, which measures broadband ultrasound attenuation (BUA) and speed of sound (SOS) through the os calcis; a composite parameter, that is, quantitative ultrasound index (QUI) and an estimate of heel BMD (eBMD) were also derived. Significant side differences were detected for BUA and SOS (P<0.05), but not for QUI or eBMD. Contralateral differences were rather small in absolute terms, but were in the order of 12.6% for BUA, 0.72% for SOS, 7.9% for QUI, and 9.9% for eBMD, when expressed as percentage of the mean values for the two heels. Bilateral differences appeared to vary across age and gender. Significant correlations between QUS indices of the right and left heel were observed (r=0.75-0.85; P<0.001), which seemed to be stronger among the elderly and among male individuals. Prevalence rates of osteopenia and osteoporosis were not significantly different when estimated from eBMD T-scores for the one or the other foot (chi(2)=1.781, df=2, P=0.410). However, cross-classification analysis revealed that only 84% of the subjects classified into each risk category by the two calcanei were actually the same persons. In conclusion, results from the present study strongly suggest that QUS measurements of opposite heels may not be equivalent with respect to the evaluation of bone status and classification of individual fracture risk assessment, although the degree of discrepancy appears to be related to the primary outcome of interest.

Older women track and field athletes have enhanced calcaneal stiffness

Vigorous weight-bearing exercise is recommended to women as a method of osteoporosis prevention. This study examined older women athletes to see if they indeed were less likely to develop osteoporosis than those in the general population, and to investigate which factors could have contributed to these results. One hundred and thirty-nine women 40-88 years old, all competitors in a USA National Masters Track and Field Championships, volunteered for the study. Masters refers to competitors > or =40 years old. Their calcaneal stiffness (SI) was measured by a Lunar Achilles+ ultrasonometer. Subjects were also measured for height and weight, and completed a questionnaire on exercise history, diet, lifestyle factors, medical and menopausal issues, and use of hormone replacement therapy (HRT). The women, mean age 57.3 years, had an overall average SI of 99.5 (T-score = 0.04) which is equivalent to that of a 20-year-old woman and 20.8% higher than expected for women of their age. Their median SI remained not different from expected peak bone SI until the age of 70. For analysis, this cohort of women was divided into two groups: premenopausal and postmenopausal athletes. The SI of both groups was correlated with the earliest age at which they had first participated in sports or exercises that impart moderate to high strain rates to the lower limbs and with current participation in high impact track and field events. Variables correlated with SI in the general population, such as weight, HRT, previous fracture, hysterectomy, and current menopausal status, did not predict SI in this cohort. In conclusion, women competing in Masters track and field at the national level had calcaneal stiffness substantially higher than expected for women of their age in the general population, and their participation in vigorous sports and activities, either currently or at a younger age, was predictive of this association.

Effect of temperature on the longitudinal variability of quantitative ultrasound variables

It is unclear whether longitudinal change in phantom measurements bears any relation to the long-term in vivo instrument performance of quantitative ultrasound devices. Longitudinal quantitative ultrasound phantom data were obtained by measuring the manufacturer-provided phantom at ambient temperature and two different sets of Leeds phantoms at either ambient temperature or following a phantom temperature-control protocol. Measurements were performed using the Achilles Plus bone densitometer. Changes in longitudinal phantom data were compared to in vivo quantitative ultrasound data obtained from seven healthy, young volunteers. A cosinor model with linear trend and Hotelling's T2-test were used to quantify seasonal rhythms and long-term drift in quantitative ultrasound variables. Temperature effects and marked seasonal rhythms on quantitative ultrasound phantom measurements were evident but were far less apparent in vivo. Longitudinal precision of quantitative ultrasound variables was poorer for the manufacturer-provided phantom than for phantoms that were subjected to a temperature-control protocol or for healthy volunteers. This study has shown that longitudinal precision and longitudinal change differs between in vivo and phantom data. Longitudinal quantitative ultrasound measurements for monitoring change in skeletal status cannot, as yet, be properly controlled.

Avaliação ultra-sonométrica da consolidação de osteotomias mediodiafisárias transversas em diferentes períodos: estudo experimental em tíbias de carneiro

Foi realizado um estudo experimental sobre a avaliação ultra-sonométrica da consolidação de tíbias de carneiros submetidas a osteotomia transversal mediodiafisária, utilizando 15 carneiros, com pêso médio de 37 Kg, divididos em três grupos experimentais de cinco animais cada, conforme o período de observação pós-operatória de 30, 45 e 60 dias. As osteotomias foram realizadas nas tíbias direitas dos animais, ficando as tíbias esquerdas como controle. Foi feita avaliação radiográfica da consolidação a cada duas semanas e, ao fim do período de observação, os animais foram sacrificados e as tíbias, removidas para a análise ultra-sonométrica. Foram medidos e correlacionados o diâmetro da tíbia e a velocidade de propagação transversal do ultra-som na região da osteotomia, em duas direções diferentes (perpendicular e paralela ao plano da tuberosidade anterior da tíbia). A velocidade de propagação do ultra-som aumentou com o avançar da consolidação (±5%), sendo as diferenças significantes em relação ao grupo-controle, mas não entre os grupo experimentais. Os diâmetros diminuíram nas duas direções medidas, sendo as diferenças significantes entre os grupos, com forte correlação negativa com a velocidade. Concluiu-se que o método de avaliação da consolidação pela ultra-sonometria é factível, com resultados confiáveis e precisos.

In vivo performance evaluation of the Achilles Insight QUS device

Achilles plus (GE, Lunar) has been widely used worldwide for more than a decade, and for its precision, ability to predict fragility fractures and comparability to central DXA, it can be considered a reference standard among quantitative ultrasound devices. As a water-bath system, Achilles plus has obvious practical drawbacks. Achilles Insight is a new-generation device that gives ultrasound parameters in less than 1 min, providing real-time imaging of the os calcis. The aim of this study was to evaluate the in vivo performance of Achilles Insight in comparison to Achilles plus. The precision showed a coefficient of variation (CV) of 0.5 and 0.4%, 4.1 and 3.0%, 2.7 and 2.1%, respectively, for speed of sound (SOS), broadband ultrasound attenuation (BUA), and Stiffness obtained with Achilles plus and Achilles Insight. We also studied 117 postmenopausal women (mean age: 67.1+/-8.8 yr), 47 with and 70 without fragility fractures. Ultrasound parameters obtained by the two devices significantly (p<0.001) correlated and resulted in agreement according to the Bland and Altman method. Achilles plus and Achilles Insight showed similar values of areas under receiver operating characteristics (ROC) curves in discriminating patients with or without fractures (0.884, 0.82, and 0.879 for SOS, BUA, and Stiffness, respectively, with Achilles plus, and 0.882, 0.828, and 0.889, respectively, for Achilles Insight). In conclusion, the better precision of the Achilles Insight with respect to Achilles plus could be explained by the fact that the measurement with Achilles Insight needs less time and gives a consequent reduction in motion artifacts. The high correlation and the similar ability to identify postmenopausal women with vertebral fracture suggest the possibility of using the database of Achilles plus for Achilles Insight.