A comparison between the patella and the calcaneus using ultrasound velocity and attenuation as predictors of bone mineral density

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.

A Comparison of Ultrasonic and X-ray Methods for Imaging the Growth Plate

The purpose of this study was to assess a systematic and scientific method for measuring children's growth development, in which the accuracy of the existing diagnostic method has not yet been concretely examined. The most popular method for diagnosis of children's growth is to analyse the opening degree of the growth plate in each joint by an X-ray image. However, the X-ray method has some disadvantages; it is impossible to measure the diagnosis of growth periodically and repeatedly due to the radiation problem. Hence, this study introduced a profile analysis and the algorithm of analysing the image of the growth plate using the broadband ultrasound attenuation (BUA) of calcaneus, to verify the possibility of using an alternative ultrasonic method harmless to the human body. The images of the growth plate in the proximal tibiae, phalanges, and calcanei of 269 children (7–16 years old) were obtained using X-ray. The image of the growth plate in the calcanei was also obtained from these children using ultrasound. The results showed that the time of the opening degree of the growth plate in each joint was almost consistent between X-ray and ultrasonic images. Also, the images of the growth plate measured using X-ray and ultrasound showed a high correlation. Therefore, it is expected that the algorithm of ultrasonic profile analysis introduced in this study can replace the existing X-ray method to measure the growth plate correctly.