Zhang, Xiaoming

Abstract Objective . Penile vibro-elastography (PVE) is complicated by reverberant shear wavefields from the cylindrical geometry of the corpus cavernosum (CC), which bias shear wave speed (SWS) estimates. This study evaluated local phase velocity imaging with wavefield-based filtering (LPVI-WBF) for CC stiffness assessment in post-prostatectomy erectile dysfunction (ED), compared against phase gradient (PG) and time-of-flight (TOF) methods. Approach . Six patients with post-prostatectomy ED underwent PVE at four longitudinal visits (902 acquisitions). SWS was estimated in flaccid and erect states at 100, 150, and 200 Hz using LPVI-WBF, PG, and TOF. Wavefield composition was quantified via the standing wave index. Simulations evaluated accuracy and frequency stability under clean and reverberant conditions. Main results . Reverberant components dominated penile acquisitions, with traveling wave energy absent in 59% of acquisitions and mean standing wave fraction of 57 ± 17%. LPVI-WBF was the only method producing physiologically consistent estimates, with erect SWS exceeding flaccid (3.59 ± 0.48 vs 3.25 ± 0.58 m s −1 , p < 0.0001). PG and TOF yielded reversed results ( E < F, p < 0.0001). The dispersion exponent was near-zero for LPVI-WBF ( α = 0.048, p = 0.21), consistent with weakly viscoelastic tissue, while PG ( α = 0.184) and TOF ( α = 0.321) showed significant frequency dependence from reverberant contamination. Simulations confirm PG accuracy in clean wavefields but collapse under reverberant ones. Significance . LPVI-WBF produced SWS estimates consistent with expected CC biomechanics across all patients and frequencies, a criterion PG and TOF failed to satisfy. Phantom validation and multi-directional wavefield simulation are needed to establish accuracy.

Excess extravascular lung water (EVLW) is a common consequence for patients with congestive heart failure, inflammatory conditions, or acute respiratory distress syndrome. Computed tomography (CT) is widely used to assess EVLW, but with a higher radiation dose and logistical complexity. Lung ultrasound (LUS) using B-line artifacts demonstrates a reasonable correlation with EVLW, but user experience with the acquisition technique, equipment-dependent factors and the subjective analysis of the B-line artifacts results in significant inter-observer variability. We propose a technique to automatically detect lung ultrasound B-lines over heart cycles. The method first extracts B-mode image features from videos in a region of interest (ROI). A ResNet50-UNet network is then applied to segment regions of B-lines. This technique was performed on 8 videos (i.e., 4 patients versus 4 controls with the duration of each video 2–3 s, resolution 1024 × 758 pixels, and frame rate 28 fps). The training accuracy and lossvalue of proposed models were 96.5% and 0.05, respectively. The paired t-test statical analysis shows that there is significant difference (p-value = 0.0035) of total number of B-line between normal and lungs with edema. The proposed method improves the accuracy for counting the B-lines and reduces the labor work and intra-observer variability from different users.

Many lung diseases are associated with dramatic changes in mechanical properties of the lung. Chest radiographs and computed tomography (CT) are the most common clinical methods for evaluating lung disease, but they are expensive, use radiation, and do not measure lung stiffness. Shear wave elastography (SWE) uses ultrasound radiation force (URF) to generate wave propagation in the tissue. However, URF should not be applied to the lung, because there are air and blood in the alveoli. Relatively high-intensity ultrasound can cause alveolar hemorrhage and lung injury. We have developed a noninvasive, and clinically feasible technology, lung ultrasound surface wave elastography (LUSWE), that is capable of measuring lung elastic properties with speed and accuracy. LUSWE uses a handheld shaker to generate a local small harmonic vibration on the chest surface. The resulting wave propagates through the intercostal muscle and propagates on the lung. The surface wave speed is noninvasively measured using an ultrasound technique. LUSWE is safe because diagnostic ultrasound is only used to detect the wave propagation along the lung duo to mechanical wave generation on the chest. LUSWE may be used to assess multiple lung disorders such as lung fibrosis or lung edema.

The evaluation of diffuse lung disease invariably involves chest computerized tomography (CT). The detailed information obtained is often equivalent to that from lung biopsies. It, however, involves exposure to ionising radiation which limits its repeated application in monitoring and follow up. Ultrasound techniques offer potentially safer/cheaper alternatives and lung ultrasound surface wave elastography (LUSWE) is a novel, noninvasive, and clinically feasible technique to quantify lung stiffness, an important biomechanical property that changes in diffuse fibrotic and infiltrative lung diseases. We have developed a sensitive, accurate and reproducible technique to measure changes in lung surface stiffness by using surface wave transmission speed and demonstrated its value in detecting and staging the degree of fibrosis in diffuse interstitial lung diseases, specifically idiopathic pulmonary fibrosis and progressive systemic sclerosis associated lung disease, as well as changes in heart failure. The technique consists of ultrasound detection of the propagation speed of a wave generated by the vibrations from an indenting shaker in multiple intercostal spaces to provide a representative assessment of both lungs. It offers the prospect of simple, radiation-free, repetitive assessment of changes in acute and chronic diffuse lung diseases with the potential for easy and rapid bedside use, all important considerations in clinical practice.

Pulmonary edema is common in patients with congestive heart failure. Extravascular lung water (EVLW) correlates to the disease prognosis but the assessment is challenging. The current standard method, computed tomography (CT), poses a significant logistic burden and exposes patents to ionizing radiation. Non-invasive lung ultrasound (LUS) is introduced to subjectively evaluate B-lines for EVLW but results in significant inter-observer variability. We have developed ultrasound vibro-elastography (USVE) to safely measure lung surface wave speed quantitatively. In this abstract, we presented the technique for analyzing water content in a lung phantom model. A sponge is used as the lung phantom. Twelve water contents were injected in the phantom for different EVLW values. The mass density of the phantom was measured for each water content. Wave propagation was generated at five frequencies between 100 Hz and 300 Hz in the phantom, and the surface wave speeds were collected. The viscoelasticity was derived from the wave speed dispersion with frequency. The obtained surface wave speeds showed no clear correlation with different water content. The elasticity and viscosity, however, were found increased with water content. This research pinpoints the likelihood and possible direction for USVE to assess EVLW for patients with pulmonary edema.

Glaucoma is the leading cause of irreversible blindness worldwide. Ocular biomechanical properties have been implicated in glaucoma pathogenesis, but existing commercial devices cannot determine changes in specific tissues. We recently performed a study to compare corneal wave speed (a measure of corneal elasticity) and ocular rigidity (a whole eye measurement of ocular biomechanics) between glaucomatous and normal eyes. Twenty glaucomatous eyes from 10 patients and 20 normal eyes from 13 controls, matched for age, intraocular pressure (IOP), and axial length were included. Ocular rigidity was calculated based on the difference in supine IOP by pneumatonometry with and without a 10-g weight. Corneal wave speed was determined by ultrasound surface wave elastography in which a small, 0.1 s harmonic vibration at 100 Hz was generated through the closed eyelids. Wave propagation was captured by an ultrasound transducer, and wave speed was determined from the phase change with distance. No significant differences in corneal wave speed between glaucomatous and normal eyes were detected (P = 0.17). However, ocular rigidity was significantly lower in glaucomatous eyes (0.0218 ± 0.0033 vs 0.0252 ± 0.0050 μl−1, P = 0.01). While lower ocular rigidity is consistent with altered biomechanics in glaucoma, the lack of a difference in corneal wave speed suggests that corneal tissue may not be significantly affected, and scleral changes likely play a more important role.

Papilledema is optic nerve swelling caused by increased intracranial hypertension, which has the potential to cause significant vision loss. Papilledema from idiopathic intracranial hypertension (IIH) is typically bilateral and symmetric, but can sometimes be asymmetric and even unilateral. The cause for this asymmetry is unknown. The purpose of this study was to develop ultrasound vibro-elastography (UVE) for assessing patients with papilledema to evaluate for biomechanical differences in these eyes. Nine patients with papilledema from IIH and 9 age-matched healthy control subjects were enrolled. A local harmonic vibration was used to generate wave propagation through the eyelid. Three excitation frequencies of 100, 150, and 200 Hz were used. A 6.4 MHz ultrasound probe was used to measure wave propagation in the eye structures. Wave speeds were measured in the posterior sclera of the maculae. The magnitudes of the wave speed of the IIH patients’ posterior sclera were significantly higher than those of healthy subjects. In patients with unilateral papilledema, the wave speed of the posterior sclera were higher in the eyes with papilledema than in the contralateral eyes without papilledema. UVE provides a noninvasive technique to measure the wave speed of posterior sclera, which is stiffer in eyes with papilledema.

Precis: Ocular biomechanics were compared between treated glaucoma patients and healthy subjects matched for age, intraocular pressure (IOP), and axial length. There was no difference in corneal wave propagation speed, but ocular rigidity was lower in glaucomatous eyes. Purpose: Ocular biomechanical properties are important in understanding glaucoma pathogenesis but the affected tissues are unclear. In this study, we compared corneal wave speed (a measure of corneal elasticity) and ocular rigidity coefficient between glaucomatous and normal eyes. Materials and Methods: Twenty glaucomatous eyes from 10 patients and 20 normal eyes from 13 controls, matched for age, IOP, and axial length were included. Ocular rigidity was calculated based on the difference in supine IOP by pneumatonometry with and without a 10-g weight. Corneal wave speed was determined by ultrasound surface wave elastography. A small, 0.1-second harmonic vibration at 100 Hz was generated through the closed eyelids. Wave propagation was captured by an ultrasound transducer, and wave speed was determined from the phase change with distance. Comparisons were performed using generalized estimating equation models. Results: There were no significant differences in corneal wave speed between glaucomatous and normal eyes (2.16±0.25 vs. 2.07±0.16 m/s, P=0.17). However, ocular rigidity was significantly lower in glaucomatous eyes (0.0218±0.0033 vs. 0.0252±0.0050/μL, P=0.01). Corneal wave speed was not correlated with age and IOP in either group (P≥0.23) but was correlated with ocular rigidity (R=0.48, P=0.02) and inversely correlated with axial length (R=−0.53, P=0.01) in glaucomatous eyes. Conclusion: Glaucomatous eyes tend to have lower ocular rigidity than healthy eyes with similar age, IOP, and axial length. However, the lack of a difference in corneal wave speed suggests that corneal tissue may not be significantly affected, and scleral changes likely play a more important role in glaucoma.