Effect of intervening tissues on ultrasonic backscatter measurements of bone: An in vitro study

Abstract

Ultrasonic backscatter techniques are being developed to diagnose osteoporosis. Tissues that lie between the transducer and the ultrasonically interrogated region of bone may produce errors in backscatter measurements. The goal of this study is to investigate the effects of intervening tissues on ultrasonic backscatter measurements of bone. Measurements were performed on 24 cube shaped specimens of human cancellous bone using a 5 MHz transducer. Measurements were repeated after adding a 1 mm thick plate of cortical bone to simulate the bone cortex and a 3 cm thick phantom to simulate soft tissue at the hip. Signals were analyzed to determine three apparent backscatter parameters (apparent integrated backscatter, frequency slope of apparent backscatter, and frequency intercept of apparent backscatter) and three backscatter difference parameters [normalized mean backscatter difference (nMBD), normalized slope of the backscatter difference, and normalized intercept of the backscatter difference]. The apparent backscatter parameters were impacted significantly by the presence of intervening tissues. In contrast, the backscatter difference parameters were not affected by intervening tissues. However, only one backscatter difference parameter, nMBD, demonstrated a strong correlation with bone mineral density. Thus, among the six parameters tested, nMBD may be the best choice for in vivo backscatter measurements of bone when intervening tissues are present.

Characterization of a polymer, open-cell rigid foam that simulates the ultrasonic properties of cancellous bone

“…FSAB is another backscatter parameter that has been identified as potentially useful for ultrasonic bone assessment. 26,[29][30][31]33,35 Measured values of FSAB from the OCRF specimens are similar, but slightly greater (less negative) than values reported for cancellous bone. nMBD is a relatively new backscatter parameter that may be less sensitive to the effects of gate duration and position because it is corrected (normalized) for these effects.…”

“…Two types of ultrasonic transducers were used. A 0.5 MHz diameter planar transducer (Panametrics V301, Waltham, MA) with a 25.4 mm element diameter, 53.8 mm near field length, and 6 mm beam diameter was used to perform SOS and attenuation Cellular aluminum foam Velocity, attenuation, B/A a Ji et al 11 Le et al 12 Zhang et al 13 Lee [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] The beam diameters of both transducers were determined from technical notes provided by the manufacturer. 40 Measurement configurations are illustrated in Fig.…”

“…[24][25][26][29][30][31][32]37,38,[42][43][44] A third backscatter parameter, called the normalized mean of the backscatter difference (nMBD), has been investigated in recent studies as another potentially useful bone assessment parameter. 26,[34][35][36] Unlike AIB and FSAB, which are based on the power in a single gated portion of the backscatter signal, nMBD is based on the power difference between two gated portions of the same signal. nMBD was determined from 36 nMBD ¼ 1…”

Effect of gate choice on backscatter difference measurements of cancellous bone

“…For example, intervening tissues that lie between the transducer and ultrasonically interrogated region may produce errors in AIB measurements of bone. 31 In addition, recent studies have shown that AIB may depend strongly on the portion of the backscatter signal that is analyzed. 32,33 AIB is determined by measuring the power in a portion of the backscatter signal defined by a "gate" that is used to select that portion for analysis.…”

“…Parameters based on this technique have been shown to correlate strongly with bone density, and to be relatively insensitive to errors caused by intervening tissues that lie between the transducer and ultrasonically interrogated region of bone. 31,35 In addition, theoretical considerations have led to a concept called "normalization" that may reduce the dependence of backscatter difference parameters on the size and location of analysis gates applied to the backscatter signal. 35 These features address the major limitations of AIB as a bone assessment parameter, while preserving conveniences associated with AIB such as ease of measurement, especially in vivo.…”