J.L. Katz

Inhomogeneities in anisotropic elastic constants of cortical bone

Two different acoustic techniques were used to investigate inhomogeneity patterns in anisotropic elastic constants of the human tibia and femur using a standard transmission method, to investigate the entire cross section of the same cortical bones using a low-frequency acoustic microscope and to correlate the acoustic impedance values obtained with this microscope with the c33 (longitudinal direction) found in transmission. Eighty femoral and 120 tibial specimens prepared from 20 pairs of femur and tibia obtained via autopsy were investigated. The longitudinal elastic stiffness was significantly higher in the tibia compared to the femur, while all other elastic constants were identical. The elastic stiffness patterns were completely different for the two bones and in good agreement with the average acoustic impedance found with the acoustic microscope in the same anatomical locations.<<ETX>>

Temperature Dependence of the Ultrasonic Velocities in Bone

In orthopaedic and dental procedures involving bone cutting such as drilling, sawing, tapping and trepanning, it is desirable to know at what temperature thermal damage or thermal necrosis t akes place in bone. Changes in elastic properties appear likely to accompany such damage. Therefore, an ultrasonic r ight-angle reflector technique has been employed to measure the bulk (longitudinal and transverse) and surface wave velocities in bone in the temperature range from room temperature to 90°C. In these measurements, bovine femoral specimens were immersed in a constant temperature bath of purified water. Typical ultrasonic velocities (km/s) along the bone axis are: VL (longitudinal) = 4.29 and Vs (surface) = 1.96 at 21OC; VL - 3.99 and VS = 1.89 at 80OC. The transverse wave peaks of reflection spectra are broad, and the reflection curves at 90°C are badly distorted. From these results, there appears to be no structural change taking place below 9OOC, contrary to the tensile test results by other investigators.

Ultrasonic Characterization of Some Pathological Human Femora

For noninvasive ultrasonic diagnosis of bone abnormalities (e.g., by a modified acoustic emission technique), as well as for understanding bone formation/resorption processes, it is desirable to know the ultrasonic properties of abnormal or pathological bones relative to normal bone. As part of our long-range plan to catalog these data on various types of bone diseases and fractures, the ultrasonic velocities of some human osteoporotic and osteopetrotic femoral bones (formalin fixed and immersed in water) have been measured at room temperature and at 5 MHz based on the hexagonal system, and correlated to their respective densities and microstructures. Typical longitudinal (V ) and transverse (V ) velocities (km/s) along and perpendicular (z, or X2) to the bone axis (X ) for normal, osteoporotic and osteopetrotic bones in this order are: V = 4.01, 3.86, 3.40; V = 3.31, 3 .21, 3.10; JL = 1.86, 1.84, 1.65 anaLV = 1.65, 1.51, 1.68: The ages of the subjects (male and female) range from 12 to 87. In addition, the microhardness of these bones has been measured. L 3.

Further Studies on the Acoustic Emission of Fresh "Malian Bones"

In an extension of our previous work on bovine femora (1977 Ultrasonics Symp. Proc.), acoustic emission testinBhave been performed on bones from several different species of mammals and from different types of bone within the same species: canine skulls, femora, tibiae/fibulae, humeri, and ulnaqradii, porcine skulls and femora; and bovine tibiae and femora. Three types of acoustic emission (AE) parameters were obtained for each specimen: (1) cumulative AE counts vs. loading time, (2) number of AE events vs. pulse width, and (3) number of AE events vs. peak amplitude. The AE spectra from these bones are similar, somewhat independent of the s pecies of mammals and the type of bone, but different from those of other natural and synthetic materials. The surrounding soft tissues in canine long bones appear to attenuate AE signals, thus lowering the number of AE events in both pulse width and amplitude distributions, compared to bones without soft tissues. However, effects of the soft t issues in canine skulls seem to be insignificant. In order to simulate abnormal or defective bones, a drilled hole or EDTA treatment was introduced into the specimen.

Sonic Diagnosis of Bone Fracture and Diseases: Time Series and Frequency Analysis

Clinical a pplication of ultrasounds in diagnostic bone diseases in a noninvasive/non-traumatic way has been hampered due to effects of the surrounding soft tissues on the ultrasound propagation. In order to detect the ultrasound signal that propagated through the bone, a correlation analysis is performed on the received u ltrasound signals. It is shown that the received u ltrasound signal energy is decreased as the size of the defect is increased. Further, through the crosscorrelation a nalysis, ultrasound signals propagated through the bone and through the soft tissues can be separated.

Ultrasonic Right-Angle Reflection Measurements of Bone Abnormalities

An ultrasonic right-angle reflector technique is very convenient for studying bone diseases such as osteoporosis, since bone is anisotropic, porous, and fluid-filled in vivo as well as in wet bone. The bone abnormalities included in this study are EDTA-treated bovine bone and two types of pathological human bone (osteoporotic and osteopetrotic), as well as normal human and bovine bones. Bone specimens were prepared by the usual metallographic techniques. Bovine bone specimens were immersed in EDTA solution for gradually i ncreasing p eriods of time up to 65 hours, and the decalcification process was followed up both by measuring the anisotropic ultrasonic bulk and surface wave velocities in bone, and by comparing the characteristic wave reflection spectra at 15 MHz and room temperature. Particularly noticeable in the bone spectrum is a characteristic broad peak (or no peak at all) instead of a sharp transverse (bulk) wave peak, which has not been observed in any other porous or non-porous materials studied so far.