Abstract
Osteoporosis is a critical problem during aging. Ultrasound signals backscattered from bone contain information associated with microstructures. This study proposed using entropy imaging to collect the information in bone microstructures as a possible solution for ultrasound bone tissue characterization. Bone phantoms with different pounds per cubic foot (PCF) were used for ultrasound scanning by using single-element transducers of 1 (nonfocused) and 3.5 MHz (nonfocused and focused). Clinical measurements were also performed on lumbar vertebrae (L3 spinal segment) in participants with different ages (n = 34) and postmenopausal women with low or moderate-to-high risk of osteoporosis (n = 50; identified using the Osteoporosis Self-Assessment Tool for Taiwan). The signals backscattered from the bone phantoms and subjects were acquired for ultrasound entropy imaging by using sliding window processing. The independent t-test, one-way analysis of variance, Spearman correlation coefficient rs, and the receiver operating characteristic (ROC) curve were used for statistical analysis. The results indicated that ultrasound entropy imaging revealed changes in bone microstructures. Using the 3.5-MHz focused ultrasound, small-window entropy imaging (side length: one pulse length of the transducer) was found to have high performance and sensitivity in detecting variation among the PCFs (rs = − 0.83; p < 0.05). Small-window entropy imaging also performed well in discriminating young and old participants (p < 0.05) and postmenopausal women with low versus moderate-to-high osteoporosis risk (the area under the ROC curve = 0.80; cut-off value = 2.65; accuracy = 86.00%; sensitivity = 71.43%; specificity = 88.37%). Ultrasound small-window entropy imaging has great potential in bone tissue characterization and osteoporosis assessment.
Highlights
Osteoporosis is a critical problem during aging
Speed of sound and broadband ultrasound attenuation methods are typically applied to calcaneus bone measurements; they are difficult to use for evaluating central skeletal sites, which are the most crucial sites of fracture due to o steoporosis[6]
The results revealed that ultrasound entropy imaging could be used to visualize the information uncertainty in ultrasound backscattered signals, enabling the detection of bone density and the evaluation of osteoporosis risk
Summary
Osteoporosis is a critical problem during aging. Ultrasound signals backscattered from bone contain information associated with microstructures. Radiofrequency echographic multi spectrometry (REMS) based on the frequency-domain analysis of raw ultrasound backscattered signals acquired from a transabdominal scan of the axial sites, femur, and spine has been an emerging technique and further attracts researchers’ attention in osteoporosis assessment[13,14]. This implies that the ultrasound backscattering analysis is highly compatible with B-mode imaging for screening wide populations for osteoporosis. Evidence to support the applicability of statistical distributions derived from soft-tissue assumptions to the analysis of bone microstructures (hard tissues) is insufficient Under this condition, a non-model-based approach that can collect information related to backscattered signals may be a more reliable and adaptive method for characterizing bones on a theoretical basis
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