Impacts of the Early COVID-19 Pandemic on Depressive Symptoms and Mental Health Among Student-Athletes.

Objective: Social distancing protocols due to the COVID-19 pandemic resulted in premature ending of athletic seasons and cancellation of upcoming seasons, placing significant stress on young athletes. Inability to play or forced early retirement has significant consequences on athlete's mental health, as demonstrated by an extensive body of injury literature. We hypothesize that premature suspension and cancellation of athletic events due to the COVID-19 pandemic leads to higher incidence of depressive symptoms among high-school and collegiate athletes. Further, athletes who strongly derive their sense of self-worth centered around athletics would have higher rates of depressive symptoms. Methods: High school and collegiate athletes were evaluated for depressive symptoms, emotional health and athletic identity measures through validated assessment instruments from May 2020 through July 2020. The Patient-Reported Outcomes Measurement Information System Depression Computer Adaptive Test (PROMIS-10 Depression CAT), Veterans RAND-12 (VR-12), which comprises both a physical and mental health component, and Athletic Identity Measurement Scale (AIMS) were utilized. Results: Mental health assessments were completed by 515 athletes (52.4% male, 47.6% female; .84.5% collegiate, 15.5% high school). Female athletes scored significantly worse than males on VR-12 mental health assessments, as well as PROMIS-10 Depression scores; however, males scored significantly lower than females on VR-12 physical health assessments, irrespective of education level. Athletes who had strong associations with athletics as central to their personal identity exhibited worse psychologic impact on VR-12 mental health and PROMIS-10 Depression measures and female athletes in this cohort reported greater depressive symptoms than males. Conclusion: Social distancing protocols due to the COVID-19 pandemic have limited athlete's ability to participate in sports at the training and competition level. Higher rates of depressive symptoms in high school and college athletes have resulted among female athletes and those who identify strongly as an athlete.

Post-operative Baseplate Radiographic Evaluation Using Routine pre-Operative CT.

Background: There is limited data evaluating post-operative component position and fixation in reverse shoulder arthroplasty (RSA). Therefore, the purpose of this study was to evaluate baseplate position and fixation using routine pre-operative CT and post-operative radiographs. Methods: A retrospective analysis of a series consecutive patient who underwent primary RSA was performed. Pre-operative and post-operative glenoid retroversion and inclination were measured using radiographs aligned with projection silhouettes of 3D scapula models in Mimics software. Baseplate retroversion and inclination were measured followed by evaluating for the presence of radiolucent lines (RLLs). Results: Twenty-four patients met inclusion criteria. The average age was 73.4 ± 10.7 years (range, 45-89 years). Radiographic follow-up was 3.4 ± 1.3 years. Post-operative glenoid baseplate retroversion was 2 ± 10 degrees (range, 30 to -9). Post-operative glenoid baseplate inclination was 3.8 ± 9.1 (range, -13 to 19). Five (21%) RSAs had baseplate retroversion >10 degrees. Follow-up radiographs revealed no RLLs around the baseplate, central post, or peripheral screws in any patient. Conclusions: Pre-operative CT imaging enabled evaluation of baseplate component placement and fixation on post-operative radiographs. Baseplate version was within 10 degrees of neutral in 79% (19/24) of patients. No RLLs or loss of fixation were found in any cases. Level of Evidence: Level IV: Diagnostic Study.

Factors Important to Patient Decision-Making After Ulnar Collateral Ligament Injury in Competitive High School and Collegiate Baseball Players.

Background: Patients are faced with several treatment decisions after an ulnar collateral ligament (UCL) injury: nonoperative versus operative treatment, repair versus reconstruction, and immediate versus delayed surgery. Purpose/Hypothesis: The aim of this study was to investigate the factors important to patients when deciding which treatment to pursue after a UCL injury. We hypothesized that (1) length of time away from sports and seasonal timing would be important to patients and (2) treatment decision-making would be heavily influenced by how many and which seasons of their baseball career would be missed. Study Design: Cross-sectional study. Methods: High school and collegiate baseball players with UCL tears treated at an academic institution were surveyed retrospectively on their sports participation at the time of injury and their UCL injury treatment decisions. Respondents rated the influence of various factors on a 5-point Likert scale, and they selected the top 3 factors and the single most important factor influencing their treatment decisions. Multiple logistic regression analysis was used to assess the relationship between player characteristics and factors important to their treatment decision. Results: A total of 83 athletes completed the survey; 40 were in high school and 43 were in college at the time of injury; 7 were treated nonoperatively and 76 underwent surgery (66 immediately and 10 in a delayed fashion), 10 with UCL repair and 66 with UCL reconstruction. The ability to play competitive baseball in the long term was very important or extremely important to 90% of players, while the ability to play in the short term was very important or extremely important to 17%. Length of recovery and seasonal timing were also important factors for 53% and 54% of players, respectively, and almost all (90%) highly valued advice from a surgeon. Possible failure of nonoperative treatment leading to increased time away and the possible loss of 2 consecutive baseball seasons heavily influenced decision-making in 41% of respondents. Conclusion: Survey respondents were driven by the desire to play baseball in the long term. Treatment decisions were influenced by the length of recovery and by the seasonal timing of their injury, both of which affect how many and which seasons of baseball a player may miss. Patients found advice from their surgeon to be extremely important to decision-making.

Large-Array Deep Abdominal Imaging in Fundamental and Harmonic Mode.

Deep abdominal images suffer from poor diffraction-limited lateral resolution. Extending the aperture size can improve resolution. However, phase distortion and clutter can limit the benefits of larger arrays. Previous studies have explored these effects using numerical simulations, multiple transducers, and mechanically swept arrays. In this work, we used an 8.8-cm linear array transducer to investigate the effects of aperture size when imaging through the abdominal wall. We acquired channel data in fundamental and harmonic modes using five aperture sizes. To avoid motion and increase the parameter sampling, we decoded the full-synthetic aperture data and retrospectively synthesized nine apertures (2.9-8.8 cm). We imaged a wire target and a phantom through ex vivo porcine abdominal samples and scanned the livers of 13 healthy subjects. We applied bulk sound speed correction to the wire target data. Although point resolution improved from 2.12 to 0.74 mm at 10.5 cm depth, contrast resolution often degraded with aperture size. In subjects, larger apertures resulted in an average maximum contrast degradation of 5.5 dB at 9-11 cm depth. However, larger apertures often led to visual detection of vascular targets unseen with conventional apertures. An average 3.7-dB contrast improvement over fundamental mode in subjects showed that the known benefits of tissue-harmonic imaging extend to larger arrays.

Comparison of glenoid bone grafting vs. augmented glenoid baseplates in reverse shoulder arthroplasty: a systematic review.

BACKGROUND: Management of bone loss and glenoid deformity can present a significant challenge to surgeons. The purpose of this review was to compare outcomes of reverse shoulder arthroplasty (RSA) using either bone graft or augmented baseplates for the management of glenoid bone loss and deformity. METHODS: A comprehensive search of MEDLINE, Embase, and Cochrane indices was performed for studies reporting clinical outcomes following primary RSA with bone grafting or use of augmented baseplates. Pooled and frequency-weighted means, standard deviations, and ranges were calculated and reported for comparison. RESULTS: Overall, 19 studies and 652 patients with bone grafting (n = 401) and augmented baseplates (n = 251) were included in the study. Mean patient age and gender were 70.3 ± 3.1 years and 47% female in the bone grafting group and 72.9 ± 3.7 years and 59.0% female in the augmented baseplate group. Mean follow-up for the augmented baseplate group was 23.1 ± 8.2 months and 29.5 ± 10.1 months for the bone grafting group. Overall complication and revision rates were 11.7% and 4.5% for the bone grafting group and 11.8% and 3.7% for the augmented baseplate group. Range of motion as well as patient-reported and functional outcome scores were similar between both techniques. Infections, component loosening, and notching were 1.9%, 3.6%, and 24.6% in the bone grafting group and 0.7%, 1.6%, and 4.7% in the augmented baseplate group. CONCLUSIONS: Glenoid bone grafting and augmented baseplates are effective treatment options for the management of bone loss and glenoid deformity. Both treatments improve overall clinical outcomes with relatively low complication rates and revision rates.

Does the timing of tenotomy during biceps tenodesis affect the incidence of Popeye deformity and clinical outcome? An analysis of short-term follow-up of 2 techniques.

BACKGROUND: There are multiple techniques that attempt to maintain anatomic length-tension relationship during biceps tenodesis. However, no direct comparison has been performed with respect to the timing of biceps tenotomy during biceps tenodesis. This study aims to assess the incidence of Popeye deformity and clinical outcomes of 2 all-arthroscopic techniques for biceps tenodesis based on timing of the biceps tenotomy. METHODS: A consecutive series of patients undergoing arthroscopic biceps tenodesis with concomitant rotator cuff tears were enrolled from 2019 to 2021. Biceps tenodesis performed after tenotomy formed the first cohort (group 1). The other cohort had biceps tenodesis performed prior to biceps tenotomy (group 2). Postoperative anterior arm pain, biceps muscle spasms, and patient perceptions of the appearance of the bicep muscle were assessed. In addition, patient-reported outcomes (PROs) were collected at 3 months and minimum 6 months postoperatively. RESULTS: A total of 71 patients were eligible for participation and 62 patients (53% female, age 58.7 ± 9.0 years) were enrolled (n = 33 in group 1, and n = 29 in group 2). There were no differences between groups with respect to gender, age, and laterality of biceps tenodesis, as well as type and size of rotator cuff repair. At 3-month follow-up, Veterans RAND 12-Item Health Survey (VR-12) physical health summary scores were significantly improved in group 2 (44.8 ± 9.7) compared with group 1 (34.1 ± 3.4) (P = .03). In addition, patients in group 2 experienced significantly less pain in their anterior arm than patients in group 1 (19% vs. 33%, P = .02). There were no differences in biceps muscle spasm (3.4% vs. 5.2%, P = .21) and no other differences in PROs between groups. Final follow-up averaged 11.6 ± 3.3 months in group 1 and 11.8 ± 5.5 months in group 2. There were no significant differences in patient-perceived biceps Popeye deformity between group 1 (12.1%) and group 2 (0%) (P = .652). Furthermore, there were no differences in American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, EuroQol-5 Dimension, Patient-Reported Outcomes Measurement Information System Global Health (PROMIS 10) physical health, PROMIS 10 depression, VR-12 physical health summary, and Single Assessment Numeric Evaluation scores between the 2 technique groups. CONCLUSION: Patients with tenotomy performed after tenodesis had better VR-12 physical health summary scores and less arm pain than patients with tenotomy performed before tenodesis at 3-month follow-up. However, there were no differences in any outcome at final follow-up of nearly 1-year. In addition, there were no differences in perceived Popeye deformity between groups at any time period.

Incidental Pulmonary Nodules Found on Shoulder Arthroplasty Preoperative CT Scans.

With current emphasis on preoperative templating of anatomical and reverse shoulder arthroplasty (aTSA and rTSA, respectively), patients often receive thin slice (<1.0 mm) computerized tomography (CT) scans of the operative shoulder, which includes about two-thirds of the ipsilateral lung. The purpose of this study is to evaluate the prevalence and management of incidentally detected pulmonary nodules on preoperative CT scans for shoulder arthroplasty. In this single-center retrospective study, we queried records of aTSA and rTSA patients from 2015 to 2020 who received preoperative CT imaging of the shoulder. Compared to patients with negative CT findings, there were significantly more females (63.8% vs. 46.4%; P = .011), COPD (13.0% vs. 4.7%; P = .015), and asthma (18.8% vs. 6.9%; P = .003) among the patients with incidental nodules on CT. Binary logistic regression confirmed that female sex (odds ratio = 2.00; 95% CI = 1.04 to 3.88; P = .037), COPD history (OR = 3.02; 95% CI = 1.05 to 8.65; P = .040), and asthma history (OR = 3.17; 95% CI = 1.30 to 7.77; P = .011) were significantly associated with an incidental nodule finding. Incidental pulmonary nodules found on shoulder arthroplasty preoperative CT scans are often low risk in size with low risk of malignancy, and do not require further workup. This study may provide guidance to orthopedic surgeons on how to manage patients with incidental pulmonary nodules to increase chances of early cancer detection, avoid unnecessary referrals, reduce potentially harmful radiation exposure of serial CT scans, and improve cost efficiency.

Adaptive Models for Multi-Covariate Imaging of Sub-Resolution Targets (MIST).

Multi-covariate imaging of sub-resolution targets (MIST) is a statistical, model-based image formation technique that smooths speckles and reduces clutter. MIST decomposes the measured covariance of the element signals into modeled contributions from mainlobe, sidelobes, and noise. MIST covariance models are derived from the well-known autocorrelation relationship between transmit apodization and backscatter covariance. During in vivo imaging, the effective transmit aperture often deviates from the applied apodization due to nonlinear propagation and wavefront aberration. Previously, the backscatter correlation length provided a first-order measure of these patient-specific effects. In this work, we generalize and extend this approach by developing data-adaptive covariance estimation, parameterization, and model-formation techniques. We performed MIST imaging using these adaptive models and evaluated the performance gains using 152 tissue-harmonic scans of fetal targets acquired from 15 healthy pregnant subjects. Compared to standard MIST imaging, the contrast-to-noise ratio (CNR) is improved by a median of 8.3%, and the speckle signal-to-noise ratio (SNR) is improved by a median of 9.7%. The median CNR and SNR gains over B-mode are improved from 29.4% to 40.4% and 24.7% to 38.3%, respectively. We present a versatile empirical function that can parameterize an arbitrary speckle covariance and estimate the effective coherent aperture size and higher order coherence loss. We studied the performance of the proposed methods as a function of input parameters. The implications of system-independent MIST implementation are discussed.

Disparities in Telemedicine Utilization During COVID-19 Pandemic: Analysis of Demographic Data from a Large Academic Orthopaedic Practice.

Background: The coronavirus-19 (COVID-19) pandemic has prompted a shift in health-care provision toward implementation of telemedicine. This study investigated demographic information on orthopaedic telemedicine utilization at a single academic orthopaedic institution in an effort to identify factors associated with telemedicine usage. Methods: Demographic and appointment data were collected from the electronic medical record during equivalent time periods prior to the onset of the COVID pandemic (pre-COVID) and during the COVID pandemic (peri-COVID). Multivariate analyses were performed to identify demographic and socioeconomic correlates of telemedicine utilization. Results: There was a significant increase in telemedicine visits between the eras of study, with significant differences in telemedicine usage in association with age, sex, marital status, English as the primary language, and insurance type (p < 0.001). Multivariate analyses found American Indian/Alaska Native (adjusted odds ratio [aOR] = 0.487, p = 0.004), Black/African American (aOR = 0.622, p < 0.001), Native Hawaiian/other Pacific Islander (aOR = 0.676, p = 0.003), and Asian (aOR = 0.731, p < 0.001) race to be significantly associated with decreased telemedicine usage. Additionally, male sex (aOR = 0.878, p < 0.001) and a non-commercial insurance plan (p < 0.001) were significantly associated with decreased telemedicine usage. Conclusions: Non-White race, non-commercial insurance plans, and male sex were associated with decreased telemedicine utilization. Further investigation is needed to characterize and better identify underlying factors contributing to disparities in telemedicine access and utilization.

Comparison of Glenoid Bone Grafting versus Augmented Glenoid Baseplates in Reverse Shoulder Arthroplasty: A Systematic Review.

BACKGROUND: Management of bone loss and glenoid deformity can present a significant challenge to surgeons. The purpose of this review was to compare outcomes of reverse shoulder arthroplasty (RSA) using either bone graft or augmented baseplates for the management of glenoid bone loss and deformity. METHODS: A comprehensive search of MEDLINE, Embase, Cochrane indices was performed for studies reporting clinical outcomes following primary RSA with bone grafting or use of augmented baseplates. Pooled and frequency-weighted means were calculated where applicable. Between-group comparison was also performed. RESULTS: Overall, 19 studies and 652 patients were included in the study. There were no significant differences in age or gender between the bone grafting (70.3 years; 47.8% female) and augmented baseplate (72.9 years; 59.0% female) groups (p=0.166; p=0.659). Overall complication and revision rates were similar for reverse shoulder arthroplasty (RSA) using either bone graft (11.7% complication rate; 4.5% revision rate) or augmented baseplates (11.8% complication rate; 3.7% revision rate) for the management of glenoid bone loss and deformity (p=0.968; p=0.562). Furthermore, range of motion as well as patient-reported and functional outcome scores were similar between both techniques. However, infections (0.7% augmented baseplate; 1.9% bone grafting) and notching (4.7% augmented baseplate; 24.6% bone grafting) were found to be more common in the bone grafting group (p=0.012; p=0.018). CONCLUSIONS: Glenoid bone grafting and augmented baseplates have similar overall clinical outcomes, complication rates, and revision rates. However, there were some significant differences between groups with respect to notching and infections which deserve consideration and further exploration.

Oxygen sensors mediated HIF-1α accumulation and translocation: A pivotal mechanism of fine particles-exacerbated myocardial hypoxia injury.

Epidemiological studies have demonstrated a strong association of ambient fine particulate matter (PM2.5) exposure with the increasing mortality by ischemic heart disease (IHD), but the involved mechanisms remain poorly understood. Herein, we found that the chronic exposure of real ambient PM2.5 led to the upregulation of hypoxia-inducible factor-1 alpha (HIF-1α) protein in the myocardium of mice, accompanied by obvious myocardial injury and hypertrophy. Further data from the hypoxia-ischemia cellular model indicated that PM2.5-induced HIF-1α accumulation was responsible for the promotion of myocardial hypoxia injury. Moreover, the declined ATP level due to the HIF-1α-mediated energy metabolism remodeling from ß-oxidation to glycolysis had a critical role in the PM2.5-increased myocardial hypoxia injury. The in-depth analysis delineated that PM2.5 exposure decreased the binding of prolyl hydroxylase domain 2 (PHD2) and HIF-1α and subsequent ubiquitin protease levels, thereby leading to the accumulation of HIF-1α. Meanwhile, factor-inhibiting HIF1 (FIH1) expression was down-regulated by PM2.5, resulting in the enhanced translocation of HIF-1α to the nucleus. Overall, our study provides valuable insight into the regulatory role of oxygen sensor-mediated HIF-1α stabilization and translocation in PM-exacerbated myocardial hypoxia injury, we suggest this adds significantly to understanding the mechanisms of haze particles-caused burden of cardiovascular disease.

Imaging the Local Nonlinear Viscoelastic Properties of Soft Tissues: Initial Validation and Expected Benefits.

Imaging tissue mechanical properties has shown promise in noninvasive assessment of numerous pathologies. Researchers have successfully measured many linear tissue mechanical properties in laboratory and clinical settings. Currently, multiple complex mechanical effects such as frequency-dependence, anisotropy, and nonlinearity are being investigated separately. However, a concurrent assessment of these complex effects may enable more complete characterization of tissue biomechanics and offer improved diagnostic sensitivity. In this work, we report for the first time a method to map the frequency-dependent nonlinear parameters of soft tissues on a local scale. We recently developed a nonlinear elastography model that combines strain measurements from arbitrary tissue compression with radiation-force-based broadband shear wave speed (WS) measurements. Here, we extended this model to incorporate local measurements of frequency-dependent shear modulus. This combined approach provides a local frequency-dependent nonlinear parameter that can be obtained with arbitrary, clinically realizable tissue compression. Initial assessments using simulations and phantoms validate the accuracy of this approach. We also observed improved contrast in nonlinearity parameter at higher frequencies. Results from ex-vivo liver experiments show 32, 25, 34, and 38 dB higher contrast in elastograms than traditional linear elasticity, elastic nonlinearity, viscosity, and strain imaging methods, respectively. A lesion, artificially created by injection of glutaraldehyde into a liver specimen, showed a 59% increase in the frequency-dependent nonlinear parameter and a 17% increase in contrast ratio.

Spatial Coherence Adaptive Clutter Filtering in Color Flow Imaging-Part II: Phantom and In Vivo Experiments.

Conventional color flow processing is associated with a high degree of operator dependence, often requiring the careful tuning of clutter filters and priority encoding to optimize the display and accuracy of color flow images. In a companion paper, we introduced a novel framework to adapt color flow processing based on local measurements of backscatter spatial coherence. Through simulation studies, the adaptive selection of clutter filters using coherence image quality characterization was demonstrated as a means to dynamically suppress weakly-coherent clutter while preserving coherent flow signal in order to reduce velocity estimation bias. In this study, we extend previous work to evaluate the application of coherence-adaptive clutter filtering (CACF) on experimental data acquired from both phantom and in vivo liver and fetal vessels. In phantom experiments with clutter-generating tissue, CACF was shown to increase the dynamic range of velocity estimates and decrease bias and artifact from flash and thermal noise relative to conventional color flow processing. Under in vivo conditions, such properties allowed for the direct visualization of vessels that would have otherwise required fine-tuning of filter cutoff and priority thresholds with conventional processing. These advantages are presented alongside various failure modes identified in CACF as well as discussions of solutions to mitigate such limitations.

Spatial Coherence Adaptive Clutter Filtering in Color Flow Imaging-Part I: Simulation Studies.

The appropriate selection of a clutter filter is critical for ensuring the accuracy of velocity estimates in ultrasound color flow imaging. Given the complex spatio-temporal dynamics of flow signal and clutter, however, the manual selection of filters can be a significant challenge, increasing the risk for bias and variance introduced by the removal of flow signal and/or poor clutter suppression. We propose a novel framework to adaptively select clutter filter settings based on color flow image quality feedback derived from the spatial coherence of ultrasonic backscatter. This framework seeks to relax assumptions of clutter magnitude and velocity that are traditionally required in existing adaptive filtering methods to generalize clutter filtering to a wider range of clinically-relevant color flow imaging conditions. In this study, the relationship between color flow velocity estimation error and the spatial coherence of clutter filtered channel signals was investigated in Field II simulations for a wide range of flow and clutter conditions. This relationship was leveraged in a basic implementation of coherence-adaptive clutter filtering (CACF) designed to dynamically adapt clutter filters at each imaging pixel and frame based on local measurements of spatial coherence. In simulation studies with known scatterer and clutter motion, CACF was demonstrated to reduce velocity estimation bias while maintaining variance on par with conventional filtering.

Characterization of ASES score pain and functional improvement after anatomic total shoulder arthroplasty: a patient-centered perspective.

BACKGROUND: Interpretation of anchor-based clinical differences in the context of pain and functional change remains undefined. The purpose of this study was to characterize American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) scores for patients after anatomic total shoulder arthroplasty with minimum 1 year of follow-up in terms of pain and change in each functional element on the ASES. METHODS: We performed a retrospective study of a prospective institutional patient database of primary anatomic total shoulder arthroplasties from 2017-2020 with baseline and 1-year postoperative ASES scores. Three clinical outcome groups were established using an anchor-based global rating of change assessment: minimal clinically important difference (MCID), moderate clinical benefit (MCB), and substantial clinical benefit (SCB). Pain and functional outcomes in each group where then characterized and compared. RESULTS: A total of 67 patients were analyzed in terms of demographics and clinical outcomes. Two-thirds (65%) of patients achieved the SCB, 24% achieved the MCB, and 10% achieved the MCID. Washing, reaching for a shelf, and throwing were the most common functional deficits experienced preoperatively and accounted for the largest improvement in function postoperatively. Patients in the MCID group had higher preoperative visual analog scale (VAS) pain scores (7.1 ± 3.0) than the MCB (5.8 ± 2.5) or SCB (5.8 ± 2.2) groups (P = .0612). The MCID group had the least amount of preoperative functional deficits when compared to the MCB and SCB groups (P = .041). Postoperative VAS pain scores improved by 5.1 in the SCB, 3.6 in the MCB, and 3.7 in the MCID groups. Functional change in each element of the ASES improved by 1.4/4 in the SCB, followed by 0.9/4 in the MCB group and 0.05/4 in the MCID group (P < .001). CONCLUSION: The MCID group had higher preoperative pain scores and the least amount of preoperative functional deficits when compared to the MCB and SCB groups. The MCID was realized through pain improvement only, whereas the MCB and SCB consisted of meaningful improvements in pain and function.

Reverberation Clutter Suppression Using 2-D Spatial Coherence Analysis.

Diffuse reverberation clutter often significantly degrades the visibility of abdominal structures. Reverberation clutter acts as a temporally stationary haze that originates from the multiple scattering within the subcutaneous layers and has a narrow spatial correlation length. We recently presented an adaptive beamforming technique, Lag-one Spatial Coherence Adaptive Normalization (LoSCAN), which can recover the contrast suppressed by incoherent noise. LoSCAN successfully suppressed reverberation clutter in numerous clinical examples. However, reverberation clutter is a 3-D phenomenon and can often exhibit a finite partial correlation between receive channels. Due to a strict noise-incoherence assumption, LoSCAN does not eliminate correlated reverberation clutter. This work presents a 2-D matrix array-based LoSCAN method and evaluates matrix-LoSCAN-based strategies to suppress partially correlated reverberation clutter. We validated the proposed matrix LoSCAN method using Field II simulations of a 64×64 symmetric 2-D array. We show that a subaperture beamforming (SAB) method tuned to the direction of noise correlation is an effective method to enhance LoSCAN's performance. We evaluated the efficacy of the proposed methods using fundamental and harmonic channel data acquired from the liver of two healthy volunteers using a 64×16 custom 2-D array. Compared to azimuthal LoSCAN, the proposed approach increased the contrast by up to 5.5 dB and the generalized contrast-to-noise ratio (gCNR) by up to 0.07. We also present analytic models to understand the impact of partially correlated reverberation clutter on LoSCAN images and explain the proposed methods' mechanism of image quality improvement.

Improving Minimum Variance Beamforming with Sub-Aperture Processing for Photoacoustic Imaging.

Minimum variance (MV) beamforming improves resolution and reduces sidelobes when compared to delay-and-sum (DAS) beamforming for photoacoustic imaging (PAI). However, some level of sidelobe signal and incoherent clutter persist degrading MV PAI quality. Here, an adaptive beamforming algorithm (PSAPMV) combining MV formulation and sub-aperture processing is proposed. In PSAPMV, the received channel data are split into two complementary nonoverlapping sub-apertures and beamformed using MV. A weighting matrix based on similarity between sub-aperture beamformed images was derived and multiplied with the full aperture MV image resulting in suppression of sidelobe and incoherent clutter in the PA image. Numerical simulation experiments with point targets, diffuse inclusions and microvasculature networks are used to validate PSAPMV. Quantitative evaluation was done in terms of main-lobe-to-side-lobe ratio, full width at half maximum (FWHM), contrast ratio (CR) and generalized contrast-to-noise ratio (gCNR). PSAPMV demonstrated improved beamforming performance both qualitatively and quantitatively. PSAPMV had higher resolution (FWHM =0.19 mm) than MV (0.21 mm) and DAS (0.22mm) in point target simulations, better target detectability (gCNR =0.99) than MV (0.89) and DAS (0.84) for diffuse inclusions and improved contrast (CR in microvasculature simulation, DAS = 15.38, MV = 22.42, PSAPMV = 51.74 dB).

Subaperture Processing-Based Adaptive Beamforming for Photoacoustic Imaging.

Delay-and-sum (DAS) beamformers, when applied to photoacoustic (PA) image reconstruction, produce strong sidelobes due to the absence of transmit focusing. Consequently, DAS PA images are often severely degraded by strong off-axis clutter. For preclinical in vivo cardiac PA imaging, the presence of these noise artifacts hampers the detectability and interpretation of PA signals from the myocardial wall, crucial for studying blood-dominated cardiac pathological information and to complement functional information derived from ultrasound imaging. In this article, we present PA subaperture processing (PSAP), an adaptive beamforming method, to mitigate these image degrading effects. In PSAP, a pair of DAS reconstructed images is formed by splitting the received channel data into two complementary nonoverlapping subapertures. Then, a weighting matrix is derived by analyzing the correlation between subaperture beamformed images and multiplied with the full-aperture DAS PA image to reduce sidelobes and incoherent clutter. We validated PSAP using numerical simulation studies using point target, diffuse inclusion and microvasculature imaging, and in vivo feasibility studies on five healthy murine models. Qualitative and quantitative analysis demonstrate improvements in PAI image quality with PSAP compared to DAS and coherence factor weighted DAS (DAS CF ). PSAP demonstrated improved target detectability with a higher generalized contrast-to-noise (gCNR) ratio in vasculature simulations where PSAP produces 19.61% and 19.53% higher gCNRs than DAS and DAS CF , respectively. Furthermore, PSAP provided higher image contrast quantified using contrast ratio (CR) (e.g., PSAP produces 89.26% and 11.90% higher CR than DAS and DAS CF in vasculature simulations) and improved clutter suppression.

H-scan, Shear Wave and Bioluminescent Assessment of the Progression of Pancreatic Cancer Metastases in the Liver.

The non-invasive quantification of tumor burden and the response to therapies remain an important objective for imaging modalities. To characterize the performance of two newly optimized ultrasound-based analyses, we applied shear wave and H-scan scattering analyses to repeated trans-abdominal ultrasound scans of a murine model of metastatic pancreatic cancer. In addition, bioluminescence measurements were obtained as an alternative reference. The tumor metastases grow aggressively and result in death at approximately 4 wk if untreated, but longer for those treated with chemotherapy. We found that our three imaging methods (shear wave speed, H-scan, bioluminescence) trended toward increasing output measures with time during tumor growth, and these measures were delayed for the group receiving chemotherapy. The relative sensitivity of H-scan tracked closely with bioluminescence measurements, particularly in the early to mid-stages of tumor growth. The correlation between H-scan and bioluminescence was found to be strong, with a Spearman's rank correlation coefficient greater than 0.7 across the entire series. These preliminary results suggest that non-invasive ultrasound imaging analyses are capable of tracking the response of tumor models to therapeutic agents.

Shear Induced Non-Linear Elasticity Imaging: Elastography for Compound Deformations.

The goal of non-linear ultrasound elastography is to characterize tissue mechanical properties under finite deformations. Existing methods produce high contrast non-linear elastograms under conditions of pure uni-axial compression, but exhibit bias errors of 10-50% when the applied deformation deviates from the uni-axial condition. Since freehand transducer motion generally does not produce pure uniaxial compression, a motion-agnostic non-linearity estimator is desirable for clinical translation. Here we derive an expression for measurement of the Non-Linear Shear Modulus (NLSM) of tissue subject to combined shear and axial deformations. This method gives consistent nonlinear elasticity estimates irrespective of the type of applied deformation, with a reduced bias in NLSM values to 6-13%. The method combines quasi-static strain imaging with Single-Track Location-Shear Wave Elastography (STL-SWEI) to generate local estimates of axial strain, shear strain, and Shear Wave Speed (SWS). These local values were registered and non-linear elastograms reconstructed with a novel nonlinear shear modulus estimation scheme for general deformations. Results on tissue mimicking phantoms were validated with mechanical measurements and multiphysics simulations for all deformation types with an error in NLSM of 6-13%. Quantitative performance metrics with the new compound-motion tracking strategy reveal a 10-15 dB improvement in Signal-to-Noise Ratio (SNR) for simple shear versus pure compressive deformation for NLSM elastograms of homogeneous phantoms. Similarly, the Contrast-to-Noise Ratio (CNR) of NLSM elastograms of inclusion phantoms improved by 25-30% for simple shear over pure uni-axial compression. Our results show that high fidelity NLSM estimates may be obtained at ~30% lower strain under conditions of shear deformation as opposed axial compression. The reduction in strain required could reduce sonographer effort and improve scan safety.