Yi Hsun Lin

Quantitative assessments of burn degree by high-frequency ultrasonic backscattering and statistical model

An accurate and quantitative modality to assess the burn degree is crucial for determining further treatments to be properly applied to burn injury patients. Ultrasounds with frequencies higher than 20 MHz have been applied to dermatological diagnosis due to its high resolution and noninvasive capability. Yet, it is still lacking a substantial means to sensitively correlate the burn degree and ultrasonic measurements quantitatively. Thus, a 50 MHz ultrasound system was developed and implemented to measure ultrasonic signals backscattered from the burned skin tissues. Various burn degrees were achieved by placing a 100 °C brass plate onto the dorsal skins of anesthetized rats for various durations ranged from 5 to 20 s. The burn degrees were correlated with ultrasonic parameters, including integrated backscatter (IB) and Nakagami parameter (m) calculated from ultrasonic signals acquired from the burned tissues of a 5 × 1.4 mm (width × depth) area. Results demonstrated that both IB and m decreased exponentially with the increase of burn degree. Specifically, an IB of -79.0 ± 2.4 (mean ± standard deviation) dB for normal skin tissues tended to decrease to -94.0 ± 1.3 dB for those burned for 20 s, while the corresponding Nakagami parameters tended to decrease from 0.76 ± 0.08 to 0.45 ± 0.04. The variation of both IB and m was partially associated with the change of properties of collagen fibers from the burned tissues verified by samples of tissue histological sections. Particularly, the m parameter may be more sensitive to differentiate burned skin due to the fact that it has a greater rate of change with respect to different burn durations. These ultrasonic parameters in conjunction with high-frequency B-mode and Nakagami images could have the potential to assess the burn degree quantitatively.

Monitoring tissue inflammation and responses to drug treatments in early stages of mice bone fracture using 50 MHz ultrasound

Bone fracture induces moderate inflammatory responses that are regulated by cyclooxygenase-2 (COX-2) or 5-lipoxygenase (5-LO) for initiating tissue repair and bone formation. Only a handful of non-invasive techniques focus on monitoring acute inflammation of injured bone currently exists. In the current study, we monitored in vivo inflammation levels during the initial 2 weeks of the inflammatory stage after mouse bone fracture utilizing 50 MHz ultrasound. The acquired ultrasonic images were correlated well with histological examinations. After the bone fracture in the tibia, dynamic changes in the soft tissue at the medial-posterior compartment near the fracture site were monitored by ultrasound on the days of 0, 2, 4, 7, and 14. The corresponding echogenicity increased on the 2nd, 4th, and 7th day, and subsequently declined to basal levels after the 14th day. An increase of cell death was identified by the positive staining of deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) assay and was consistent with ultrasound measurements. The increases of both COX-2 and Leukotriene B4 receptor 1 (BLT1, 5-LO-relative receptor), which are regulators for tissue inflammation, in the immunohistochemistry staining revealed their involvement in bone fracture injury. Monitoring the inflammatory response to various non-steroidal anti-inflammatory drugs (NSAIDs) treatments was investigated by treating injured mice with a daily oral intake of aspirin (Asp), indomethacin (IND), and a selective COX-2 inhibitor (SC-236). The Asp treatment significantly reduced fracture-increased echogenicity (hyperechogenicity, p<0.05) in ultrasound images as well as inhibited cell death, and expression of COX-2 and BLT1. In contrast, treatment with IND or SC-236 did not reduce the hyperechogenicity, as confirmed by cell death (TUNEL) and expression levels of COX-2 or BLT1. Taken together, the current study reports the feasibility of a non-invasive ultrasound method capable of monitoring post-fracture tissue inflammation that positively correlates with histological findings. Results of this study also suggest that this approach may be further applied to elucidate the underlying mechanisms of inflammatory processes and to develop therapeutic strategies for facilitating fracture healing.

Quantitative assessment on the orientation and distribution of carbon fibers in a conductive polymer composite using high-frequency ultrasound

Conductive polymer composites, typically fabricated from a mix of conductive fillers and a polymer substrate, are commonly applied as bipolar plates in a fuel cell stack. Electrical conductivity is a crucial property that greatly depends on the distribution and orientation of the fillers. In this study, a 50-MHz ultrasound imaging system and analysis techniques capable of nondestructively assessing the properties of carbon fibers (CFs) in conductive polymer composites were developed. Composite materials containing a mix of polycarbonate substrates and 0 to 0.3 wt% of CFs were prepared using an injection molding technique. Ultrasonic A-line signals and C-scan images were acquired from each composite sample in regions at a depth of 0.15 mm beneath the sample surface (region A) and those at a depth of 0.3 mm (region B). The integrated backscatter (IB) and the Nakagami statistical parameter were calculated to quantitatively assess the samples. The area ratio, defined as the percentage of areas composed of CF images normalized by that of the whole C-scan image, was applied to further quantify the orientation of CFs perpendicular to the sample surface. Corresponding to the increase in CF concentrations from 0.1 to 0.3 wt%, the average IB and Nakagami parameter (m) of the composite samples increased from -78.10 ± 2.20 (mean ± standard deviation) to -72.66 ± 1.40 dB and from 0.024 ± 0.012 to 0.048 ± 0.011, respectively. The corresponding area ratios were respectively estimated to be 0.78 ± 0.35%, 2.33 ± 0.66%, and 2.20 ± 0.60% in region A of the samples; those of CFs with a perpendicular orientation were 0.04 ± 0.03%, 0.08 ± 0.02%, and 0.12 ± 0.05%. The area ratios in region B of the samples were calculated to be 1.19 ± 0.54%, 2.81 ± 0.42%, and 2.64 ± 0.76%, and those of CFs with a perpendicular orientation were 0.07 ± 0.04%, 0.12 ± 0.04%, and 0.14 ± 0.03%. According to the results of the orientations and ultrasonic images, CFs tended to distribute more uniformly in the deeper regions of the samples. This study validates that the distribution and orientation of CFs in conductive polymer composites could be sensitively and quantitatively assessed by high-frequency ultrasound in conjunction with current analysis methods.

In vivo measurements of ultrasonic backscatter from blood

Ultrasonic backscatter from whole blood has been studied extensively in vitro. It has found to be related to hematocrit, plasma protein, and flow disturbance. To validate these in vitro results, in vivo backscatter measurements have been made on whole blood flowing in the abdominal aorta and the inferior vena cava using a 10 MHz intravascular transducer in pigs. The probe was inserted into vessels of interest via a peripheral vein or artery. Backscattering coefficient (BSC) of blood was measured using a newly developed approach in which backscattered power acquired from a 6% porcine red cell suspension was used as a reference to extract the BSC from a dense scattering medium. Results from three pigs showed that BSC of blood in the vein and artery is respectively 3.7-10/sup -5/ and 1.2/spl times/10/sup -5/ (cm-sr)/sup -1/ at 10 MHz and 34% hematocrit which are slightly larger than BSC from the porcine red cell suspension of the same hematocrit and frequency at 6.5/spl times/10/sup -6/ (cm-sr)/sup -1/. One important reason for the higher backscatter in veins is that red cell aggregation is more pronounced in veins where blood flow is less pulsatile and slower than that in arteries. Moreover, previous in vitro measurements also showed that disturbed flow may increase ultrasonic backscatter of blood. This observation was confirmed by the current in vivo measurements in which stenosis were created by ligating the artery. Backscatter of blood measured downstream of the stenosis as a function of distance from the stenosis indicates that the closer the site where the measurement was made to the stenosis, the higher the backscatter, presumably resulted from the higher degree of flow disturbance.

Assessment of the Kinetic Trajectory of the Median Nerve in the Wrist by High-Frequency Ultrasound

Carpal tunnel syndrome (CTS) is typically diagnosed by physical examination or nerve conduction measurements. With these diagnostics however it is difficult to obtain anatomical information in the carpal tunnel. To further improve the diagnosis of CTS, an attempt using 30 MHz high-frequency ultrasound to noninvasively detect the local anatomical structures and the kinetic trajectory of the median nerve (MN) in the wrist was explored. Measurements were performed on the right wrist of 14 asymptomatic volunteers. The kinetic trajectory of the MN corresponding to flexion (from 0° to 90°) and extension (from 90° to 0°) movements of the fingers were detected by a cross correlation-based motion tracking technique. The average displacements of the MN according to finger movements were measured to be 3.74 and 2.04 mm for male and female subjects, respectively. Moreover, the kinetic trajectory of the MN in both the ulnar-palmar and total directions generally follows a sigmoidal curve tendency. This study has verified that the use of high-frequency ultrasound imaging and a motion tracking technique to sensitively detect the displacement and kinetic trajectory of the MN for the assessment of CTS patients is feasible.

Effect of scanning direction on the statistical parameters of ultrasonic signals backscattered from the annular pulley and tendon

Previous studies have demonstrated that quantitative parameters estimated from backscattering signals are capable of characterizing pulley and tendon tissues for being applied to diagnose the trigger finger syndrome. Yet, the probability density functions (PDFs) of the envelope signals were found to vary significantly between those acquired from the transverse and sagittal views of samples. To extensively explore these effects, this study used a 30 MHz high-frequency ultrasound and theoretical considerations, to further comprehend the effect of the ultrasonic scanning direction on the estimated statistical parameters from the annular pulley and tendon. The ex vivo experiments began with the preparations of pulley and superficial digital flexor tendon (SDFT) excised from the first annular (A1) pulley region of cadavers. The tissue samples were then immersed in a saline solution tank. The ultrasound system was arranged to allow the scanning of tissues from the direction parallel to the fiber axis, at 0°, to that of perpendicular direction, at 90°, in which the increment of scanning angle is 5°. Statistical parameters, including Nakagami parameter (m) and scaling parameter, were estimated from regions of the acquired backscattering signals. Histological slices were also made for results verification. The scaling parameters associated with A1 pulley and SDFT of different scanning angles did not vary significantly; while those of the corresponding m was decreased significantly, as the scanning angle increased. The m of SDFT tended to decline with the increase of scanning angle faster than that of A1 pulley. Specifically, the m parameters of A1 pulley and SDFT decreased respectively from 1.06 ± 0.10 to 0.88 ± 0.07 and from 1.03 ± 0.06 to 0.78 ± 0.03. The empirical results are consistent with Nakagami statistical distribution, and which demonstrate that m could be applied to quantitatively assess to characterize the PDF of high-frequency ultrasonic envelopes from the A1 pulley and SDFT at various scanning angles.

Quantitative Assessment of First Annular Pulley and Adjacent Tissues Using High-Frequency Ultrasound

Due to a lack of appropriate image resolution, most ultrasound scanners are unable to sensitively discern the pulley tissues. To extensively investigate the properties of the A1 pulley system and the surrounding tissues for assessing trigger finger, a 30 MHz ultrasound system was implemented to perform in vitro experiments using the hypodermis, A1 pulley, and superficial digital flexor tendon (SDFT) dissected from cadavers. Ultrasound signals were acquired from both the transverse and sagittal planes of each tissue sample. The quantitative ultrasonic parameters, including sound speed, attenuation coefficient, integrated backscatter (IB) and Nakagami parameter (m), were subsequently estimated to characterize the tissue properties. The results demonstrated that the acquired ultrasound images have high resolution and are able to sufficiently differentiate the variations of tissue textures. Moreover, the attenuation slope of the hypodermis is larger than those of the A1 pulley and SDFT. The IB of A1 pulley is about the same as that of the hypodermis, and is very different from SDFT. The m parameter of the A1 pulley is also very different from those of hypodermis and SDFT. This study demonstrated that high-frequency ultrasound images in conjunction with ultrasonic parameters are capable of characterizing the A1 pulley system and surrounding tissues.

Cross-Sectional Nakagami Images in Passive Stretches Reveal Damage of Injured Muscles.

Muscle strain is still awanting a noninvasive quantitatively diagnosis tool. High frequency ultrasound (HFU) improves image resolution for monitoring changes of tissue structures, but the biomechanical factors may influence ultrasonography during injury detection. We aim to illustrate the ultrasonic parameters to present the histological damage of overstretched muscle with the consideration of biomechanical factors. Gastrocnemius muscles from mice were assembled and ex vivo passive stretching was performed before or after injury. After injury, the muscle significantly decreased mechanical strength. Ultrasonic images were obtained by HFU at different deformations to scan in cross and longitudinal orientations of muscle. The ultrasonography was quantified by echogenicity and Nakagami parameters (NP) for structural evaluation and correlated with histological results. The injured muscle at its original length exhibited decreased echogenicity and NP from HFU images. Cross-sectional ultrasonography revealed a loss of correlation between NP and passive muscle stretching that suggested a special scatterer pattern in the cross section of injured muscle. The independence of NP during passive stretching of injured muscle was confirmed by histological findings in ruptured collagen fibers, decreased muscle density, and increased intermuscular fiber space. Thus, HFU analysis of NP in cross section represents muscle injury that may benefit the clinical diagnosis.

Photoacoustic imaging using microstructured plastic fiber- optic illumination

We observed that photoacoustic imaging of a gelatin phantom, which consisted a graphite-filled inclusion with a 4-mm-diameter, illuminated by a microstructured plastic fiber guiding green laser light inside. This approach can effectively extend light propagation depth in tissue.

Factors affecting the statistical analysis of ultrasonic backscattering signals and imaging

Statistical distribution of ultrasonic backscattering signals has been demonstrated capable of characterizing variations of density and arrangement of scatterers in biological tissues. The statistical analysis of ultrasound signals has also found with less dependency on the attenuation effect. Yet, as the employed ultrasound frequency and pulse duration were increased, several factors could further affect the precise estimation of the statistical parameters. To further investigate the addressed issues, experiments were arranged and performed from tissue-mimicking phantoms and porcine livers. Various duty cycles, including 1, 3, 5, and 10%, of tone bursts at 1 KHz pulse repetition frequency corresponding to ultrasound frequencies of 3.5, 7.5, and 10 MHz were adjusted for driving the transducers. The tissue-mimicking phantoms were fabricated, which consisted of gelatin and glass beads of 16 and 64 scatterers/ mm3 and those of porcine livers with either healthy or pathological fibrosis were obtained from local slaughter house. Various thickness of Silicone plates with the attenuation coefficient of 1.62 dB/mm..MHz were placed on the surface of objects to be measured. Nakagami statistical model, including shape parameter (Nakagami-m) and parametric imaging, was implemented to assess variations of the probability density function (PDF) estimated from the acquired ultrasonic backscattering signals. Results of phantoms indicated that the attenuation could significantly vary the shape of PDF of backscattered envelopes. Especially, large attenuation effect was found corresponding to those broader incident ultrasound bandwidths excited by the monocycle signal; whereas the effect is substantially reduced as the tone bursts were more than 3 cycles. Results of porcine livers indicated that the Nakagami-m increased with the increasing ultrasound frequencies and bandwidth, and that those associated PDFs were nearly pre- Rayleigh distributed. Both phantoms and porcine livers results consistently demonstrated that the use of 3 cycles tone bursts for exciting transducers may achieve the most appropriate performance to accommodate a tradeoff between attenuation effect and image resolution. Current study also verified that the operational modes of incident ultrasound need to be properly assured before that the statistical model may be further applied to clinical applications.