Regular chondrocyte spacing is a potential cause for coherent ultrasound backscatter in human articular cartilage

Advanced Topics in Quantitative Acoustic Microscopy

Quantitative acoustic microscopy (QAM) reconstructs two-dimensional (2D) maps of the acoustic properties of thin tissue sections. Using ultrahigh frequency transducers (≥ 100 MHz), unstained, micron-thick tissue sections affixed to glass are raster scanned to collect radiofrequency (RF) echo data and generate parametric maps with resolution approximately equal to the ultrasound wavelength. 2D maps of speed of sound, mass density, acoustic impedance, bulk modulus, and acoustic attenuation provide unique and quantitative information that is complementary to typical optical microscopy modalities. Consequently, many biomedical researchers have great interest in utilizing QAM instruments to investigate the acoustic and biomechanical properties of tissues at the micron scale. Unfortunately, current state-of-the-art QAM technology is costly, requires operation by a trained user, and is accompanied by substantial experimental challenges, many of which become more onerous as the transducer frequency is increased. In this chapter, typical QAM technology and standard image formation methods are reviewed. Then, novel experimental and signal processing approaches are presented with the specific goal of reducing QAM instrument costs and improving ease of use. These methods rely on modern techniques based on compressed sensing and sparsity-based deconvolution methods. Together, these approaches could serve as the basis of the next generation of QAM instruments that are affordable and provide high-resolution QAM images with turnkey solutions requiring nearly no training to operate.

Quantitative Ultrasound Assessment of Early Osteoarthritis in Human Articular Cartilage Using a High-Frequency Linear Array Transducer

Quantitative ultrasound (QUS) assessment of osteoarthritis (OA) using high-frequency, research-grade single-element ultrasound systems has been reported. The objective of this ex vivo study was to assess the performance of QUS in detecting early OA using a high-frequency linear array transducer. Osteochondral plugs (n = 26) of human articular cartilage were scanned with ExactVu Micro-Ultrasound using an EV29L side-fire transducer. For comparison, the samples were also imaged with SAM200Ex, a custom 40-MHz scanning acoustic microscope with a single-element, focused transducer. Thirteen QUS parameters were derived from the ultrasound data. Magnetic resonance imaging (MRI) data, with T1 and T2 extracted as the quantitative parameters, were also acquired for comparison. Cartilage degeneration was graded from histology and correlated to all quantitative parameters. A maximum Spearman rank correlation coefficient (ρ) of 0.75 was achieved using a combination of ExactVu QUS parameters, while a maximum ρ of 0.62 was achieved using a combination of parameters from SAM200Ex. A maximum ρ of 0.75 was achieved using the T1 and T2 MRI parameters. This study illustrates the potential of a high-frequency linear array transducer to provide a convenient method for early OA screening with results comparable to those of research-grade single-element ultrasound and MRI.

HIGH-FREQUENCY ULTRASOUND FOR DETECTING CHRONIC KNEE JOINT LESIONS IN MINERS: AN EXPLORATORY CONTROLLED STUDY

Objective: To explore the clinical value of high-frequency ultrasound in the detection of chronic knee injuries in miners. Methods: A total of 53 Chinese coal miners from the China, as well as 33 nonminers without history of knee conditions were prospectively examined using high-frequency ultrasound. Blood flow was observed using color Doppler flow imaging (CDFI) and power Doppler ultrasound (PDUS). In the event of slow blood flow, parameters for color Doppler were set to maximal gain and minimal noise. Results: Chronic knee joint injuries were detectable as lesions in bursa around the joint and infrapatellar soft tissues. Various proportions of miners had nodular, finger-like or focal protrusions extending from the bursa synovium into the synovial cavity. Such protrusions were observed in the suprapatellar bursa (15, 28.3%), prepatellar bursa (17, 32.1%), and deep infrapatellar bursa (4, 7.5%). Infrapatellar soft tissues were significantly thicker in miners ([Formula: see text][Formula: see text]mm) than of controls ([Formula: see text][Formula: see text]mm; [Formula: see text], [Formula: see text]). Miners showed substantial thickening of the synovia, as well as nodular, finger-like and focal protrusions in the synovia of suprapatellar bursa and/or prepatellar bursa (infrapatellar bursa). Synovium in miners showed more blood flow signals, especially in the supra- and prepatellar bursae, than synovium in controls. Echoes from the interior of infrapatellar soft tissues were enhanced and uneven in 47 of 53 miners, showing hyperecho patterns of scattered dots, short lines or flakes. Conclusion: Ultrasound can complement X-ray imaging and magnetic resonance imaging for detecting and characterizing chronic knee joint injuries in miners.

Autoregressive Signal Processing Applied to High-Frequency Acoustic Microscopy of Soft Tissues

Quantitative acoustic microscopy (QAM) at frequencies exceeding 100 MHz has become an established imaging tool to depict acoustical and mechanical properties of soft biological tissues at microscopic resolutions. In this study, we investigate a novel autoregressive (AR) model to improve signal processing and parameter estimation and to test its applicability to QAM. The performance of the AR model for estimating acoustical parameters of soft tissues (i.e., acoustic impedance, speed of sound, and attenuation) was compared to the performance of the Hozumi model using simulated ultrasonic QAM signals and using experimentally measured signals from thin (i.e., 12 and ) sections of human lymph-node and pig-cornea tissue specimens. Results showed that the AR and Hozumi methods performed equally well (i.e., produced an estimation error of 0) in signals with low, linear attenuation in the tissue and high impedance contrast between the tissue and the coupling medium. However, the AR model outperformed the Hozumi model in estimation accuracy and stability (i.e., parameter error variation and number of outliers) in cases of 1) thin tissue-sample thickness and high tissue-sample speed of sound, 2) small impedance contrast between the tissue sample and the coupling medium, 3) high attenuation in the tissue sample, and 4) nonlinear attenuation in the tissue sample. Furthermore, the AR model allows estimating the exponent of nonlinear attenuation. The results of this study suggest that the AR model approach can improve current QAM by providing more reliable, quantitative, tissue-property estimates and also provides additional values of parameters related to nonlinear attenuation.

[Shaoyangzhugu Formula regulates p19Arf-p53-p21Cip1 signaling pathway to ameliorate cartilage degeneration in aged cynomolgus monkeys with knee osteoarthritis]

OBJECTIVE

To study the effect of Shaoyangzhugu (SYZG) Formula (a formula consisting of 9 traditional Chinese drugs) in delaying the degeneration of articular cartilage and the role p19^Arf-p53-p21^Cip1 signaling pathway in mediating this effect.

METHOD

Thirteen aged cynomolgus monkeys with degenerative knee joints were selected based on X-ray findings, and one of them was randomly selected for pathological observation. The other monkeys were randomized equally into SYZG Formula group (treated with SYZG decoction), ammonia moxime group and saline group. All the monkeys were sacrificed after 8 weeks of treatment with intragastric administration of the drugs or saline. The pathology in the knee joint articular cartilage was observed and the mRNA and protein expressions of p19^Arf, p53, and p21^Cip1 in the articular cartilage were detected using RT-qPCR and Western blotting.

RESULTS

The pathological findings of the articular cartilage in old cynomolgus monkeys were consistent with the characteristics of knee osteoarthritis (KOA). Mankin scores of the cynomolgus monkeys were 7.38∓0.52 in SYZG Formula group, 7.88∓0.83 in ammonia moxime group, and 8.38∓0.74 in saline group, showing a significant difference between SYZG Formula group and saline group (P<0.05). The expressions of p19^Arf, p53, and p21^Cip1 were the lowest in SYZG Formula group and the highest in saline group with significant differences among the 3 groups (P<0.05).

CONCLUSION

SYZG Formula can delay chondrocyte senescence by regulating p19^Arf-p53-p21^Cip1 signaling pathway to delay articular cartilage degeneration in aged cynomolgus monkeys.

[Shaoyangzhugu Formula regulates p19Arf-p53-p21Cip1 signaling pathway to ameliorate cartilage degeneration in aged cynomolgus monkeys with knee osteoarthritis]

OBJECTIVE

To study the effect of Shaoyangzhugu (SYZG) Formula (a formula consisting of 9 traditional Chinese drugs) in delaying the degeneration of articular cartilage and the role p19Arf-p53-p21Cip1 signaling pathway in mediating this effect.

METHOD

Thirteen aged cynomolgus monkeys with degenerative knee joints were selected based on X-ray findings, and one of them was randomly selected for pathological observation. The other monkeys were randomized equally into SYZG Formula group (treated with SYZG decoction), ammonia moxime group and saline group. All the monkeys were sacrificed after 8 weeks of treatment with intragastric administration of the drugs or saline. The pathology in the knee joint articular cartilage was observed and the mRNA and protein expressions of p19Arf, p53, and p21Cip1 in the articular cartilage were detected using RT-qPCR and Western blotting.

RESULTS

The pathological findings of the articular cartilage in old cynomolgus monkeys were consistent with the characteristics of knee osteoarthritis (KOA). Mankin scores of the cynomolgus monkeys were 7.38∓0.52 in SYZG Formula group, 7.88∓0.83 in ammonia moxime group, and 8.38∓0.74 in saline group, showing a significant difference between SYZG Formula group and saline group (P<0.05). The expressions of p19Arf, p53, and p21Cip1 were the lowest in SYZG Formula group and the highest in saline group with significant differences among the 3 groups (P<0.05).

CONCLUSION

SYZG Formula can delay chondrocyte senescence by regulating p19Arf-p53-p21Cip1 signaling pathway to delay articular cartilage degeneration in aged cynomolgus monkeys.

High-Frequency Ultrasound Imaging of Tidemark In Vitro in Advanced Knee Osteoarthritis

High-frequency ultrasound imaging has been widely adopted for assessment of the degenerative changes of articular cartilage in osteoarthritis (OA). Yet, there are few reports on investigating its capability to evaluate subchondral bone. Here, we employed high-frequency ultrasound imaging (25 MHz) to examine in vitro the tidemark in cylindrical osteochondral disks (n = 33) harvested from advanced OA knees of humans. We found good correspondence in morphology observed by ultrasound imaging and micro-computed tomography. Ultrasound roughness index (URI) of tidemark was derived from the raw radiofrequency signals to compare with bone quality factors, including bone volume fraction (BV/TV) and bone mineral density (BMD) measured by micro-computed tomography, using the Spearman correlation (ρ). URI of the tidemark was negatively associated with the subchondral plate BV/TV (ρ = -0.73, p <0.001), BMD (ρ = -0.40, p = 0.020), as well as the underneath trabecular bone BV/TV (ρ = -0.39, p = 0.025) and BMD (ρ = -0.43, p = 0.012). In conclusion, this preliminary study demonstrated that morphology measured by high-frequency ultrasound imaging could reflect the quality of the subchondral bone. High-frequency ultrasound is a promising imaging tool to evaluate the changes of the subchondral bone in addition to those of the overlying cartilage in OA.