Ultrasonic backscatter measurements at the calcaneus: An in vivo study

Osteoporosis is a systemic skeleton disease that has already been a major public health issue. As a traditional clinical method, dual-energy X-ray absorptiometry (DXA) measures the bone mineral density (BMD) to evaluate the bone status. However, the X-ray based method has the disadvantages of ionizing radiation and high cost. Quantitative ultrasound has played a role in the bone diagnostics with the advantages of non-ionizing radiation, portability, low cost and ease of use. This paper presents an in vivo approach of measuring the calcaneus using ultrasonic backscatter method, a total of 523 subjects were involved. The ultrasonic backscattered signals were acquired using a custom designed ultrasonic backscatter bone diagnostic (UBBD) instrument with a 5.0 MHz transducer. The time slope of apparent backscatter (TSAB) parameter was calculated and compared with the BMD measured from DXA. The TSAB and BMD showed a negative correlation (R = −0.65 ∼ −0.52, p < 0.05). Discrimination analysis was performed using receiver operating characteristic (ROC) curves to discriminate people who have been diagnosed with osteoporosis from people without osteoporosis using DXA. The area under the curve (AUC) for ultrasound backscatter parameter TSAB was 0.8 with p < 0.05. By means of the ROC analysis, the optimum thresholds of TSAB were determined to be −0.81 dB/µs. The sensitivity and specificity of TSAB for the optimum threshold were 77% and 74%, respectively. The Youden index and accuracy was 51% and 75% for the TSAB at 5.0 MHz, respectively. These results indicate that ultrasonic backscatter is promising in the in vivo bone characterization.