Correlation of anterior segment optical coherence tomography and ultrasound biomicroscopy in congenital corneal opacity

PURPOSE

To investigate the correlation between swept-source anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) in congenital corneal opacity (CCO).

METHODS

All children with unilateral or bilateral congenital corneal opacities who underwent examination under anesthesia (EUA) and anterior segment optical coherence tomography (AS-OCT) imaging from January 1, 2022, to December 31, 2022, were included. Main outcome measures were corneal and anterior segment evaluation and correlation of UBM and AS-OCT findings.

RESULTS

A total of 22 eyes of 15 patients were imaged using both technologies. The age at first EUA ranged from 11 days to 4 years. Different phenotypes were classified based on the clinical examination, UBM, and AS-OCT findings. Fourteen eyes were diagnosed with Peters anomaly, congenital corneal staphyloma was observed in 4 eyes, 2 eyes had coloboma, 1 eye had peripheral sclerocornea, and 1 eye was diagnosed with congenital primary aphakia. AS-OCT and UBM findings were closely correlated in 18 of 22 eyes (82%) but AS-OCT failed to provide detailed information in 4 eyes (18%) where UBM revealed more details.

CONCLUSIONS

Although AS-OCT offers valuable preliminary data for initial assessment and counseling, it may not consistently provide precise assessments in all cases. Therefore, UBM should be considered for definitive evaluation.

The correlation of anterior segment structures in primary congenital glaucoma by ultrasound biomicroscopy with disease severity and surgical outcomes

PURPOSE

To evaluate the anterior segment structures using ultrasound biomicroscopy (UBM) in primary congenital glaucoma (PCG) and explore their correlation with disease severity and surgical outcomes.

METHODS

Clinical information of PCG patients who underwent UBM prior to their first glaucoma surgeries from September 2014 to March 2021 were reviewed. The study included 214 UBM images of 154 PCG eyes and 60 fellow unaffected eyes. Anterior segment characteristics were analyzed. UBM parameters, including the iris thickness (IT) at variant distances from the pupil edge and iris root, anterior chamber depth (ACD), and pupil diameter (PD), were compared between two groups and their relationship with clinical factors and surgical outcomes were analyzed in PCG eyes.

RESULTS

PCG eyes had unclear scleral spur, thin iris, wide anterior chamber angle, deep anterior chamber, rarefied ciliary body, elongated ciliary processes, and abnormal anterior iris insertion. ITs were thinner, ACD was deeper, and PD was larger in PCG eyes than fellow unaffected eyes (all P < 0.001). In PCG eyes, thinner ITs correlated with bilateral involvement and earlier age at presentation, and larger PD correlated with earlier age at presentation (P = 0.030) and higher intraocular pressure (P < 0.001). Thinner IT2 (P = 0.046) and larger PD (P = 0.049) were identified as risk factors for surgical failure.

CONCLUSION

UBM is a powerful technique to exam anterior segment structures in PCG. The anatomical features are associated with disease severity and surgical outcomes, providing essential clinical insights.

Ultrasound biomicroscopy in the management of complex cataract and intraocular lens: A review

Ultrasound biomicroscopy (UBM) is an invaluable investigation for imaging anterior segment structures. Although it is operator-dependent and time consuming, unlike optical-based imaging techniques, it is able to image structures posterior to the iris, such as the zonules, ciliary body and part of the pars plana. It is especially useful in advanced cataracts, traumatic cataracts, subluxed lenses, posterior polar cataracts, and congenital and developmental anomalies affecting the anterior segment. It provides diagnostic information in eyes with complex cataracts or intraocular lens (IOL)-related pathology, and aids in surgical planning in order to minimise complications. In this review, we describe the UBM features of various lenticular pathologies and demonstrate its application in the diagnosis and surgical management of lens and IOL-related pathologies.

Utilization of the Reinstein ICL Sizing Formula With Hand-held Ultrasound Biomicroscopy Measurements

PURPOSE

To evaluate the accuracy of the Reinstein formula with hand-held ultrasound biomicroscopy (UBM) measurements for sizing of the Implantable Collamer Lens (ICL).

METHODS

A total of 107 myopic eyes of 57 patients implanted with the ICL were included in the study. The size of the ICL was selected based on the manufacturer's recommendations. Agreement between the vault predicted by the Reinstein formula and the vault measured postoperatively was analyzed with Bland-Altman plots.

RESULTS

A total of 95% and 81% of patients had a postoperative vault ranging from 150 to 1,000 and 250 to 750 μm, respectively. The mean vault predicted by the Reinstein formula and the postoperative vault in the current study were 580 ± 181 and 547 ± 200 μm, respectively. The size recommendations of the Reinstein formula and the formula provided by the manufacturer, the Kojima formula, and the Dougherty formula overlapped in 50%, 57%, and 49% of eyes, respectively.

CONCLUSIONS

The results show that the Reinstein formula combined with a hand-held UBM provides reliable sizing predictions of the ICL. However, considering that robotic UBM measurements have demonstrated a narrower range of deviation in predicting vault depth in previous studies, a direct comparison study between robotic UBM and hand-held UBM measurements is necessary to fully assess the limitations of combining hand-held UBM with the Reinstein formula. [J Refract Surg. 2024;40(3):e142-e147.].

Acoustic resolution photoacoustic Doppler flowmetry for assessment of patient rectal cancer blood perfusion

Significance

Photoacoustic Doppler flowmetry offers quantitative blood perfusion information in addition to photoacoustic vascular contrast for rectal cancer assessment.

Aim

We aim to develop and validate a correlational Doppler flowmetry utilizing an acoustic resolution photoacoustic microscopy (AR-PAM) system for blood perfusion analysis.

Approach

To extract blood perfusion information, we implemented AR-PAM Doppler flowmetry consisting of signal filtering and conditioning, A-line correlation, and angle compensation. We developed flow phantoms and contrast agent to systemically investigate the flowmetry's efficacy in a series of phantom studies. The developed correlational Doppler flowmetry was applied to images collected during in vivo AR-PAM for post-treatment rectal cancer evaluation.

Results

The linearity and accuracy of the Doppler flow measurement system were validated in phantom studies. Imaging rectal cancer patients treated with chemoradiation demonstrated the feasibility of using correlational Doppler flowmetry to assess treatment response and distinguish residual cancer from cancer-free tumor bed tissue and normal rectal tissue.

Conclusions

A new correlational Doppler flowmetry was developed and validated through systematic phantom evaluations. The results of its application to in vivo patients suggest it could be a useful addition to photoacoustic endoscopy for post-treatment rectal cancer assessment.

Noninvasive imaging of rat-derived microglia and its reactivity to inflammatory molecules via acoustic impedance microscopy

PURPOSE

Microglia, the brain's immune cells, play important roles in neuronal differentiation, survival, and death. The function of microglia is deeply related to the morphologies; however, it is too complex to observe conventionally and identify the condition of living microglia using optical microscopes. Herein, we proposed a new method to observe living cultured microglia and their reactivity to inflammation via the acoustic impedance mode of a scanning acoustic microscope.

METHODS

Primary cultured microglia collected from rat pups exposed to acetamiprid, an insecticide, in utero were observed with both acoustic interface impedance mode (C-mode) and transparent three-dimensional impedance mode (B-mode).

RESULTS

We characterized microglia into four types based on the results obtained from acoustic impedance, cytoskeletal information, and laser confocal imaging. Biphasic acoustic observation using B-mode and C-mode gave us information regarding the dynamic morphologies of living microglia treated with adenosine triphosphate (ATP) (600 μmol/L), which reflects distress signals from inflamed neurons. Acetamiprid exposure induced microglia response even in the neonatal period. ATP stimulus altered the shape and thickness of microglia with a change in the bulk modulus of the cell. Three-dimensional alteration with ATP stimulus could be observed only after biphasic acoustic observation using B-mode and C-mode. This acoustic observation was consistent with confocal observation using anti-Iba-1 and P2Y12 immunocytochemistry.

CONCLUSION

This study demonstrated the adequacy of using a scanning acoustic microscope in analyzing microglia's shape, motility, and response to inflammation.

Deep Learning-Based Model for Automatic Assessment of Anterior Angle Chamber in Ultrasound Biomicroscopy

OBJECTIVE

The goal of the work described here was to develop and assess a deep learning-based model that could automatically segment anterior chamber angle (ACA) tissues; classify iris curvature (I-Curv), iris root insertion (IRI), and angle closure (AC); automatically locate scleral spur; and measure ACA parameters in ultrasound biomicroscopy (UBM) images.

METHODS

A total of 11,006 UBM images were obtained from 1538 patients with primary angle-closure glaucoma who were admitted to the Eye Center of Renmin Hospital of Wuhan University (Wuhan, China) to develop an imaging database. The UNet++ network was used to segment ACA tissues automatically. In addition, two support vector machine (SVM) algorithms were developed to classify I-Curv and AC, and a logistic regression (LR) algorithm was developed to classify IRI. Meanwhile, an algorithm was developed to automatically locate the scleral spur and measure ACA parameters. An external data set of 1,658 images from Huangshi Aier Eye Hospital was used to evaluate the performance of the model under different conditions. An additional 439 images were collected to compare the performance of the model with experts.

RESULTS

The model achieved accuracies of 95.2%, 88.9% and 85.6% in classification of AC, I-Curv and IRI, respectively. Compared with ophthalmologists, the model achieved an accuracy of 0.765 in classifying AC, I-Curv and IRI, indicating that its high accuracy was as high as that of the ophthalmologists (p > 0.05). The average relative errors (AREs) of ACA parameters were smaller than 15% in the internal data sets. Intraclass correlation coefficients (ICCs) of all the angle-related parameters were greater than 0.911. ICC values of all iris thickness parameters were greater than 0.884. The accurate measurement of ACA parameters partly depended on accurate localization of the scleral spur (p < 0.001).

CONCLUSION

The model could effectively and accurately evaluate the ACA automatically based on fully automated analysis of UBM images, and it can potentially be a promising tool to assist ophthalmologists. The present study suggested that the deep learning model can be extensively applied to the evaluation of ACA and AC-related biometric risk factors, and it may broaden the application of UBM imaging in the clinical research of primary angle-closure glaucoma.

Observations of amyloid breakdown by proteases over time using scanning acoustic microscopy

Amyloid consists of insoluble beta-fibrillar proteins with stable structures. The Congo red staining method for histologically detecting amyloid is unsuitable for quantitatively assessing amyloid fibers. Scanning acoustic microscopy (SAM) detects the attenuation of sound (AOS) through sections. This study aimed to clarify whether AOS values reflected the amount of amyloid fibril degradation in tissues. Formalin-fixed paraffin-embedded unstained sections of various types of amyloidosis were digested with different endopeptidases. The AOS images after digestion were observed over time via SAM. The corresponding Congo red-stained images were followed to identify the amyloid. The amyloid and nonamyloid portions were statistically examined over time to determine the changes in the AOS values. Most of the amyloid areas showed significantly different AOS values from nonamyloid portions before digestion and significantly decreased after digestion; these findings corresponded with the disappearance and waning of the Congo red staining in the light microscopic images. Some nonamyloid areas with high AOS masked the reduction in AOS in the amyloid areas. The method used in this study may help detect the amyloid quantity and determine the appropriate treatment method for removing amyloid deposits from tissues.

Evaluation of ciliary body morphology and position of the implantable collamer lens in low-vault eyes using ultrasound biomicroscopy

PURPOSE

To investigate the ciliary body anatomy and position of the implantable collamer lens (ICL) in low-vault eyes and analyze factors related to insufficient vault.

SETTING

Zhongshan Ophthalmic Center, Guangzhou, China.

DESIGN

Retrospective case-control observational study.

METHODS

In this study, 73 eyes of 73 patients with an insufficient vault (<250 μm) were matched with 73 eyes with an ideal vault (250 to 750 μm). Ultrasound biomicroscopy was used to determine the ciliary body morphology and ICL position. The biometric parameters acquired by Scheimpflug tomography were compared. The correlation between the vault and these factors was analyzed, and the least absolute shrinkage and selection operator method was used to screen the risk factors for low vault.

RESULTS

The low-vault group had a steeper corneal curvature, thicker lens thickness (LT), higher crystalline lens rise, and shorter axial length (AL) (all P < .005). The ciliary process length (CPL) and maximum ciliary body thickness (CBTmax) were significantly smaller, and the trabecular-ciliary angle (TCA), iris-ciliary angle (ICA), and ciliary sulcus width (CSW) were significantly greater in the low-vault eyes (all P < .005). The low-vault group had more ICL haptics below the ciliary process, and TCA, ICA, CPL, CBTmax, CSW, and haptic position were related to the postoperative vault (all P < .05). CPL, AL, and LT were identified as predictors of a low vault.

CONCLUSIONS

Malposition of ICL haptics behind the ciliary process is a risk factor for low vault. A shorter CPL, thicker LT, and shorter AL are significant risk factors for the postoperative low vault.

Peering into the eye: A comprehensive look at ultrasound biomicroscopy (UBM) and its diagnostic value in anterior segment disorders

Background

Ultrasound biomicroscopy (UBM) is a noninvasive imaging modality that enables in-vivo visualization of the structures of the anterior segment of the eye. Unlike routine ophthalmic diagnostic ultrasound which uses frequencies of 5-10 MHz, UBM utilizes ultrasound frequencies in the range of 50-100 MHz. The high-frequency probes in UBM allows for higher resolution and better visualization of subsurface ocular structures, even in the presence of anatomic or pathological obscuration. UBM has qualitative as well as quantitative applications in various disorders affecting the anterior segment of the eye. Despite its huge importance, many clinicians lack in knowledge about the technique and its clinical usefulness. The current educational video aims to address this gap in knowledge by highlighting the technique and various clinical indications of UBM.

Purpose

The purpose of this video is to demonstrate the technique of UBM and showcase its quantitative and qualitative implications and importance through various clinical cases.

Synopsis

UBM is an imaging technique that assesses the depth of tissue structures by measuring the time delay of the returning ultrasound signal. This modality is capable of measuring the size of various structures within the eye, such as the cornea, iris, ciliary body, sclera, and the depth of the anterior and posterior chamber. To perform a UBM, a transducer is inserted into a specially designed eye cup filled with distilled water, creating a water bath environment. Axial and longitudinal scans can be performed in a similar fashion as in routine diagnostic B-scan ultrasound. Quantitative indications for UBM depicted in this video include measurements of corneal thickness, depth of the anterior chamber, and the width of the angle. The video also showcases how UBM can aid in the diagnosis and management of various anterior segment disorders like angle-closure glaucoma, plateau iris configuration, secondary glaucoma, and anterior uveitis with complicated cataract. Qualitative indications for UBM highlighted in this video include its role in intermediate uveitis, ocular hypotony, ocular surface tumors, cystic lesions of iris, and identifying the location and type of intraocular foreign bodies in the anterior segment based on the type of artifact seen. Additionally, the video shows the applications of UBM in scleral and episcleral pathologies.

Highlights

This video will educate clinicians about the technique of UBM and showcase a bouquet of UBM findings in various case scenarios, helping one to better understand the potential of this modality in clinical practice.

Video link

https://youtu.be/F626TMbJXoU.

The Agreement of the Nomogram Tool and Ultrasound Biomicroscopy Images in Calculating Ultrasound Cycloplasty Probe Model in Chinese Patients

PURPOSE

The aim of the study was to compare and explore the agreement between the nomogram tool and ultrasound biomicroscopy (UBM) images method to calculate the ultrasound cycloplasty (UCP) probe model in Chinese glaucoma patients.

METHODS

Retrospective analysis of Chinese glaucoma patients who visited Zhongshan Ophthalmic Center in Guangzhou from January to December 2019 and were eligible for UCP surgery. Visual acuity, intraocular pressure (IOP), ocular axial length (AL), and horizontal corneal diameter (white to white [WTW]) were measured. UBM images with clear ciliary body imaging and AL and WTW data were sent to trained personnel for probe model measurements. The data calculated by both methods were analyzed using unweighted and weighted κ statistics. The level of agreement refers to Landis and Koch's guideline for the strength of agreement indicated with weighted κ values.

RESULTS

1,061 eyes of 642 patients were involved, with a mean age of 61.66 ± 11.66 years. Their best-corrected visual acuity converted to logarithm of minimal-angle-of-resolution (logMAR) scores of -0.18-3.00 with a mean value of 0.69 ± 0.77. IOP was 22.0-60.0 mm Hg with a mean of 27.97 ± 5.66 mm Hg. The mean AL and WTW were 22.88 ± 1.33 (19.15-32.14) mm and 11.52 ± 0.49 (10.00-12.90) mm, respectively. The agreement between the two methods was fair (weighted κ = 0.299), matching in 62.86% of eyes (weighted κ = 0.299, κ = 0.264). The agreement in primary open angle glaucoma, acute primary angle-closure glaucoma, chronic primary angle-closure glaucoma, and secondary glaucoma patients was 60.85% (weighted κ = 0.336, κ = 0.301), 65.06% (weighted κ = 0.146, κ = 0.127), 62.26% (weighted κ = 0.204, κ = 0.184), and 57.97% (weighted κ = 0.332, κ = 0.280) of eyes, respectively.

CONCLUSION

The agreement between UBM images and the nomogram tool to calculate the UCP probe model of Chinese patients is at a fair level. The nomogram tool prefers to use larger probes. Improvements to the nomogram tool, such as including data from more ethnic groups and being able to calculate separately for different types of glaucoma, are needed to improve accuracy. The inclusion of parameters or images from more directions of the eye may help measure probe models more accurately for both the nomogram tool and the UBM image measurement.

Inter-device agreement between spectral domain optical coherence tomography, ultrasound biomicroscopy, and gonioscopy in evaluating the iridocorneal angle in normotensive dogs

BACKGROUND

There has not been a thoroughly reported study of the comparison between spectral domain-optical coherence tomography (SD-OCT) with both ultrasound biomicroscopy (UBM) and gonioscopy on the evaluation of the iridocorneal angle (ICA) in dogs.

OBJECTIVES

To investigate the diagnostic value of SD-OCT for the early detection of narrowing ICA by comparing and assessing inter-device agreement in anterior chamber angle (ACA) measurements obtained by SD-OCT and UBM, and ICA evaluations by gonioscopy.

METHODS

A total of 28 eyes from 28 client-owned dogs with normal intraocular pressure were included for examination. The ACA and angle opening distance (AOD) were measured from the SD-OCT and UBM images, and gonioscopy images were analyzed using the ICA grade and ZibWest angle index.

RESULTS

The mean ACA and AOD for SD-OCT were 28.31° ± 5.37° and 658.42 ± 219.90 µm, and for UBM, 28.34° ± 5.82° and 859.29 ± 221.80 µm, respectively. The mean difference in ACA between the average values of SD-OCT and UBM measurements was 0.03° with a 95% limit of agreement (LoA) span of 16.2°, indicating positive agreement; that in AOD was 200.85 µm with a 95% LoA span of 1,110.95 µm, indicating poor agreement. The Pearson correlation coefficient of the ACA of SD-OCT and ZibWest indices of gonioscopy was 0.624, indicating strong agreement; that of UBM and gonioscopy was 0.43, indicating moderate agreement.

CONCLUSIONS

SD-OCT is well tolerated by canine patients due to its non-contact method and might be an alternative option for early screening of ICA narrowing in clinical settings.

Ultrasound biomicroscopy of the equine iridocorneal angle

BACKGROUND

The iridocorneal angle (ICA) is the major pathway of aqueous humour outflow from the anterior chamber of the eye. Ultrasound biomicroscopy (UBM) has been utilised to characterise the morphology of this drainage pathway in numerous species. UBM may allow for early recognition of aqueous humour outflow obstructions in horses, allowing for earlier recognition of risk for glaucoma, a vision-threatening and painful disease. UBM morphology of the normal equine ICA has yet to be described.

OBJECTIVES

To determine the ultrasonographic morphology of the equine ICA by UBM in standing sedated horses.

STUDY DESIGN

In vivo experimental study.

METHODS

Thirty healthy adult horses underwent UBM of the ICA at four locations (superior, temporal, inferior, nasal) of each eye utilising standing sedation, topical anaesthesia and auriculopalpebral perineural anaesthesia. Anatomic structures were defined on ultrasound images through comparison to published histologic photomicrographs of the equine ICA.

RESULTS

Ultrasound imaging of the ICA at all four locations was easily performed in standing, sedated horses. High-resolution images of the ICA allowed for identification of the pectinate ligament, corneoscleral trabecular meshwork (TM), uveal TM and supraciliary TM.

MAIN LIMITATIONS

Pupil size was midrange in all eyes, but was not strictly controlled. Lighting conditions not controlled. Various breeds included.

CONCLUSION

In vivo UBM of the equine ICA is feasible and provides high-resolution images of the structures of the aqueous humour outflow pathway.

Super-Resolution Photoacoustic Microscopy via Modified Phase Compounding

Acoustic-resolution photoacoustic micro- scopy (AR-PAM) system can provide 3-D images of facial tissues. The lateral resolution of AR-PAM depends on the numerical aperture (NA) of the acoustic lens and the central frequency of the ultrasonic transducer. There is a trade-off between resolution enhancement and imaging depth. The acoustic beam is tight in the acoustic focal plane but expands in the out-of-focus regions, deteriorating the resolution. High-NA AR-PAM has depth-variant resolution. Synthetic aperture focusing technique (SAFT) based on a virtual detector (VD) concept can compensate for the beam shape and improve the lateral resolution via beamforming. Although, beamforming can enhance the resolution but the lateral resolution in the focal plane is still limited by acoustic diffraction. Structured-illumination can shift the spatial spectrum of an image to low frequencies hence high-frequency contents can be reserved to overcome the diffraction limit. Conventional structured-illumination via using a three-phase-shifting method can improve the resolution by two folds. Here, a modified phase-shifting method is used to generate the second harmonic of the fringes and double the spectral shift. In this idea, higher frequency information compared to the three-phase shifting method can fall into the band-limited system response. The modified phase-shifting method expands the spatial bandwidth and increases the lateral resolution by five folds. The mathematical relations and the theory are discussed in the context. Tungsten filament result shows resolution improvement from 44.6 [Formula: see text] to 11.3 [Formula: see text] by the modified structured illumination. In vivo and ex vivo experimental results validate the system performance.

Comparison of the Accuracy of Anterior Segment Optical Coherence Tomography and Ultrasound Biomicroscopy in Localizing Rectus Muscle Insertions

PURPOSE

To compare the accuracy of anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) in localizing rectus muscle insertions.

METHODS

The study was performed on 27 patients (39 rectus muscles) who required primary or secondary surgery. Using caliper function in the AS-OCT and UBM software, the distance from the insertion site to the anterior chamber angle was measured. The actual muscle insertion distance from limbus was considered as the measured distance plus 1 mm. The measurements by UBM and AS-OCT were compared with intraoperative measurements and with each other.

RESULTS

AS-OCT and UBM were performed on 13 medial rectus, 24 lateral rectus, and 2 superior rectus muscles. Ninety two percent of UBM measurements (36 muscles) were within 1 mm, one was within 1-1.5 mm, and 2 were within 1.5-2 mm of surgery measurements. Eighty five percent of AS-OCT measurements (33 muscles) were within 1 mm, 5 were within 1-1.5 mm, and one was within 1.5-2 mm of surgery measurements. In all cases, the mean absolute error of the UBM (0.54 ± 0.44) and AS-OCT (0.51 ± 0.36) showed no significant difference (p = .76).

CONCLUSION

AS-OCT and UBM can be used interchangeably to localize rectus muscle insertions and showed good agreement with intraoperative measurements.

Stiffness reduction and collagenase resistance of aging lungs measured using scanning acoustic microscopy

Lung tissue stiffness is altered with aging. Quantitatively evaluating lung function is difficult using a light microscope (LM) alone. Scanning acoustic microscope (SAM) calculates the speed-of-sound (SOS) using sections to obtain histological images by plotting SOS values on the screen. As SOS is positively correlated with stiffness, SAM has a superior characteristic of simultaneously evaluating tissue stiffness and structure. SOS images of healthy bronchioles, arterioles, and alveoli were compared among young, middle-aged, and old lung sections. Formalin-fixed, paraffin-embedded (FFPE) sections consistently exhibited relatively higher SOS values than fresh-frozen sections, indicating that FFPE became stiffer but retained the relative stiffness reflecting fresh samples. All lung components exhibited gradually declining SOS values with aging and were associated with structural alterations such as loss of smooth muscles, collagen, and elastic fibers. Moreover, reaction to collagenase digestion resulted in decreased SOS values. SOS values of all components were significantly reduced in young and middle-aged groups, whereas no significant reduction was observed in the old group. Protease damage in the absence of regeneration or loss of elastic components was present in old lungs, which exbited dilated bronchioles and alveoli. Aging lungs gradually lose stiffness with decreasing structural components without exposure to specific insults such as inflammation.

Time and frequency domain deconvolution for cross-sectional cultured cell observation using an acoustic impedance microscope

Herein, we propose a method to estimate the reflection coefficient of the ultrasonic wave transmitted onto an object and to display this with acoustic impedance distribution. The observation targets were glial cells, which have a rigid cytoskeleton and spread out well on a culture substrate. A reflection coefficient derived only from the cells was then obtained using a deconvolution process. In the conventional method, the deconvolution process that was performed only in the frequency domain would cause an error in the reconstructed signal, and it formed an artifact when the result was converted into the acoustic impedance image. To solve this problem, two types of deconvolution techniques were applied in either the full frequency or time-frequency domain. The results of both methods were then compared. Since the characteristic acoustic impedance is a physical property substantially equivalent to the bulk modulus, it can be considered that the internal elastic parameter is thus estimated. An analysis of the nucleus based on its position in the acoustic impedance image was then performed. The results indicated that the proposed time-frequency domain deconvolution method is able to maintain the structure of the cell, while the cell itself is free from unwanted artifacts. The nucleus was also estimated to be located toward the center of the cell, with lower acoustic impedance value than the cytoskeleton. The results of this study could contribute to establishing a method for monitoring the internal condition of cultured cells in regenerative medicine and drug discovery.

Ocular Phenotype of Peters-Plus Syndrome

PURPOSE

Peters-plus syndrome is a rare, autosomal recessive congenital disorder of glycosylation caused by mutations in the gene B3GLCT. A detailed description of the ocular findings is currently lacking in the scientific literature. We report a case series of Peters-plus syndrome with deep ocular phenotyping using anterior segment optical coherence tomography and ultrasound biomicroscopy. Where available, we describe the histology of host corneal buttons.

METHODS

A retrospective chart review of patients with Peters-plus syndrome was conducted under the care of the senior author between January 2000 and June 2019. Demographic and clinical data including ocular and systemic features, ophthalmic imaging, and molecular diagnostic reports were collected.

RESULTS

Four cases of Peters-plus syndrome were identified. Three patients were male and 1 was female. Five of the 8 eyes had an avascular paracentral ring opacity with relative central clearing. The paracentral opacity is due to iridocorneal adhesion and the relative central clearing associated with posterior stromal thinning. One eye had persistent fetal vasculature and microphthalmia, which has not previously been reported. One eye from each of 2 patients had a significantly different phenotype with a large vascularized central corneal opacity.

CONCLUSIONS

The most common ocular phenotype seen in Peters-plus syndrome is an avascular paracentral ring opacity with relative central clearing. A different phenotype with a large vascularized corneal opacity may also be observed.

Comparison of Ocular Morphological Parameters Related to Lens Position by Anterior Segment Optical Coherence Tomography and Ultrasound Biomicroscopy

OBJECTIVE

The objective is to compare parameters related to lens position measured using anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) in patients with senile cataract and perform a consistency analysis.

METHODS

This prospective study included 102 patients (102 eyes) scheduled for simple cataract surgery. Among the total patients, 44 were men, and 58 were women. AS-OCT (sitting) and UBM (lying) were used to measure the anterior chamber depth (ACD) in horizontal and vertical orientations and the iris-lens contact distance (ILCD) and iris-lens angle (ILA) in inferior, superior, nasal, and temporal quadrants. Paired-sample t-test was used to compare ACD, ILCD, and ILA measurements of the two methods, while Pearson's linear correlation and Bland-Altman analyses were used to analyze the correlation and consistency of the two results.

RESULTS

The horizontal (2.499 ± 0.464 mm) and vertical (2.531 ± 0.463 mm) ACD measured using AS-OCT and the horizontal (2.556 ± 0.467 mm) and vertical (2.563 ± 0.479 mm) ACD measured using UBM were significantly different (P < 0.001); moreover, the results showed good correlation and agreement. A significant difference was observed between the two methods in terms of ILCD measured in inferior, superior, nasal, and temporal quadrants (P < 0.001), and a significant correlation was found between measurements of both methods (P < 0.001). Approximately 3.92% (4/102), 0.98% (1/102), 3.92% (4/102), and 2.94% (3/102) of points were outside the 95% limits of agreement in the four quadrants, respectively, and the agreement of the results was good. ILA measured using both methods differed in inferior, superior, nasal, and temporal quadrants (P=0.003, 0.011, 0.001, 0.001, respectively), and the correlation was good (P < 0.001). The percentage of points outside the 95% limit was higher in inferior, superior, nasal, and temporal quadrants (4.90% (5/102), 5.88% (6/102), 5.88% (6/102), and 6.86% (7/102)) with poor agreement of the results.

CONCLUSIONS

The correlation between AS-OCT and UBM in terms of measuring lens position-related parameters was good, but the agreement was unstable. The differences in measurement position (sitting and supine) and/or measurement methods (optics and ultrasound) may lead to variability in results.

The role of imaging technologies for ocular surface tumors

PURPOSE OF REVIEW

This review will discuss the utility of high-resolution anterior segment optical coherence tomography (HR-OCT), in-vivo confocal microscopy (IVCM) and ultrasound biomicroscopy (UBM) in characterizing and diagnosing various ocular surface tumors, namely ocular surface squamous neoplasia (OSSN), conjunctival lymphoma and conjunctival melanoma. The strengths and limitations of each imaging modality will be discussed along with the characteristics findings of each lesion on each imaging platform.

RECENT FINDINGS

HR-OCT can consistently be utilized in the clinic setting to distinguish between epithelial ocular surface tumors such as OSSN as compared with subepithelial tumors such as conjunctival lymphoma and conjunctival melanoma given their distinctive findings. IVCM can be used as an adjunct to HR-OCT to obtain cellular and surface characteristics, whereas UBM can be used to assess tumor depth and thickness for larger and highly pigmented lesions as well as to detect intraocular invasion.

SUMMARY

HR-OCT, IVCM and UBM are all helpful imaging modalities to diagnose and characterize various ocular surface tumors and can serve as valuable adjuncts to monitor treatment response and assess for recurrence ocular surface tumors.

Acoustic impedance measurement of tissue mimicking materials by using scanning acoustic microscopy

Tissue-mimicking materials (TMMs) play a key role in the quality assurance of ultrasound diagnostic equipment and should have acoustic properties similar to human tissues. We propose a method to quantify the acoustic properties of TMM samples through the use of an 80 MHz Scanning Acoustic Microscopy (SAM), which provides micrometer resolution and fast data recording. We produced breast TMM samples in varying compositions that resulted in acoustic impedance values in the range of 1.373 ± 0.031 and 1.707 ± 0.036 MRayl. Additionally, liver TMM and blood mimicking fluid (BMF) samples were prepared that had acoustic impedance values of 1.693 ± 0.085 MRayl and 1.624 ± 0.006 MRayl, respectively. The characterization of the TMMs by SAM may provide reproducible and uniform acoustic reference data for tissue substitutes in a single-run microscopy experiment.

Optical resolution photoacoustic computed microscopy

Optical resolution photoacoustic microscopy (ORPAM) has demonstrated both high resolution and rich contrast imaging of optical chromophores in biologic tissues. To date, sensitivity remains a major challenge for ORPAM, which limits the capability of resolving biologic microvascular networks. In this study, we propose and evaluate a new ORPAM modality termed as optical resolution photoacoustic computed microscopy (ORPACM), through the combination of a two-dimensional laser-scanning system with a medical ultrasonographic platform. Apart from conventional ORPAMs, we record multiple photoacoustic (PA) signals using a 128-element ultrasonic transducer array for each pulse excitation. Then, we apply a reconstruction algorithm to recover one depth-resolved PA signal referred to as an A-line, which reveals more detailed information compared with conventional single-element transducer-based ORPAMs. In addition, we carried out both in vitro and in vivo experiments as well as quantitative analyses to show the advanced features of ORPACM.

High Resolution Multimodal Photoacoustic Microscopy and Optical Coherence Tomography Visualization of Choroidal Vascular Occlusion

Photoacoustic microscopy is a novel, non-ionizing, non-invasive imaging technology that evaluates tissue absorption of short-pulsed light through the sound waves emitted by the tissue and has numerous biomedical applications. In this study, a custom-built multimodal imaging system, including photoacoustic microscopy (PAM) and optical coherence tomography (OCT), has been developed to evaluate choroidal vascular occlusion (CVO). CVO was performed on three living rabbits using laser photocoagulation. Longitudinal imaging of CVO was obtained using multiple imaging tools such as color fundus photography, fluorescein angiography, indocyanine green angiography (ICGA), OCT, and PAM. PAM images were acquired at different wavelengths, ranging from 532 to 700 nm. The results demonstrate that the CVO was clearly observed on PAM in both two dimensions (2D) and 3D with high resolution longitudinally over 28 days. In addition, the location and margin of the CVO were distinguished from the surrounding choroidal vasculature after the injection of ICG contrast agent. PAM imaging was achieved using a laser energy of approximately 80 nJ, which is about half of the American National Standards Institute safety limit. The proposed imaging technique may provide a potential tool for the evaluation of different chorioretinal vascular disease pathogeneses and other biological studies.

In Vivo Confocal Imaging of Fluorescently Labeled Microbubbles: Implications for Ultrasound Localization Microscopy

We report the time kinetics of fluorescently labeled microbubbles (MBs) in capillary-level microvasculature as measured via confocal microscopy and compare these results to ultrasound localization microscopy (ULM). The observed 19.4 ± 4.2 MBs per confocal field-of-view ( [Formula: see text]) are in excellent agreement with the expected count of 19.1 MBs per frame. The estimated time to fully perfuse this capillary network was 193 s, which corroborates the values reported in the literature. We then modeled the capillary network as an empirically determined discrete-time Markov chain with adjustable MB transition probabilities though individual capillaries. The Monte Carlo random walk simulations found perfusion times ranging from 24.5 s for unbiased Markov chains up to 182 s for heterogeneous flow distributions. This pilot study confirms a probability-derived explanation for the long acquisition times required for super-resolution ULM.

Ultrasound localization microscopy of renal tumor xenografts in chicken embryo is correlated to hypoxia

Ultrasound localization microscopy (ULM) permits the reconstruction of super-resolved microvascular images at clinically relevant penetration depths, which can be potentially leveraged to provide non-invasive quantitative measures of tissue hemodynamics and hypoxic status. We demonstrate that ULM microbubble data processing methods, applied to images acquired with a Verasonics Vantage 256 system, can provide a non-invasive imaging surrogate biomarker of tissue oxygenation status. This technique was applied to evaluate the microvascular structure, vascular perfusion, and hypoxia of a renal cell carcinoma xenograft model grown in the chorioallantoic membrane of chicken embryos. Histological microvascular density was significantly correlated to ULM measures of intervessel distance (R = -0.92, CI95 = [-0.99,-0.42], p = 0.01). The Distance Metric, a measure of vascular tortuosity, was found to be significantly correlated to hypoxyprobe quantifications (R = 0.86, CI95 = [0.17, 0.99], p = 0.03). ULM, by providing non-invasive in vivo microvascular structural information, has the potential to be a crucial clinical imaging modality for the diagnosis and therapy monitoring of solid tumors.

Disease-related and age-related changes of anterior chamber angle structures in patients with primary congenital glaucoma: An in vivo high-frequency ultrasound biomicroscopy-based study

OBJECTIVES

To provide in vivo measurements of anterior chamber angle structures and their relationship with age as evaluated by high-frequency ultrasound biomicroscopy (UBM) in patients with primary congenital glaucoma (PCG).

METHODS

High-frequency UBM was done for 51 PCG eyes from 40 patients (aged from 3 to 96 months) and 11 unaffected contralateral eyes. Parameters, including the proportion of observable abnormal tissue membrane and Schlemm's canal, the largest cross-sectional area (CSA) of Schlemm's canal (SC), SC meridional diameter, trabecular-iris angle (TIA), trabecular meshwork (TM) thickness, iris thickness, ciliary process length, and corneal limbus thickness were compared between the two groups and their relationship with age was explored in PCG eyes.

RESULTS

Abnormal tissue membrane was detected in 27.5% of PCG eyes and none in unaffected eyes. SC was observed in 73.1% of PGC eyes compared to 100% in unaffected eyes (P<0.001). The largest CSA of SC, SC meridional diameter, iris thickness, and corneal limbus thickness were all significantly smaller in PCG eyes compared to unaffected eyes (all P<0.05). TIA and ciliary process length in unaffected eyes were smaller than PCG eyes (both P<0.05). The largest CSA of SC, TM thickness, iris thickness, and ciliary process length were all significantly correlated to age in PCG eyes (P<0.05).

CONCLUSIONS

The anatomical information evaluated by high-frequency UBM may provide glaucoma specialists a useful tool to aid in understanding the dysgenesis and changes with age of anterior chamber angle in PCG.

Enhancement of Acoustic Microscopy Lateral Resolution: A Comparison Between Deep Learning and Two Deconvolution Methods

Scanning acoustic microscopy (SAM) provides high-resolution images of biological tissues. Since higher transducer frequencies limit penetration depth, image resolution enhancement techniques could help in maintaining sufficient lateral resolution without sacrificing penetration depth. Compared with existing SAM research, this work introduces two novelties. First, deep learning (DL) is used to improve lateral resolution of 180-MHz SAM images, comparing it with two deconvolution-based approaches. Second, 316-MHz images are used as ground truth in order to quantitatively evaluate image resolution enhancement. The samples used were mouse and rat brain sections. The results demonstrate that DL can closely approximate ground truth (NRMSE = 0.056 and PSNR = 28.4 dB) even with a relatively limited training set (four images, each smaller than 1 mm ×1 mm). This study suggests the high potential of using DL as a single image superresolution method in SAM.

Accuracy of the Ultrasound Biomicroscopy Bag/Balloon Technique in Locating Horizontal Extraocular Muscle Insertions Before and After Strabismus Surgery

PURPOSE

To investigate the accuracy of high frequency ultrasound biomicroscopy using the bag/balloon technique to locate recti muscle insertions before and after strabismus surgery.

METHODS

This was a prospective masked study. The distance from the limbus to horizontal recti muscle insertions was measured by caliper intraoperatively and ultrasound biomicroscopy preoperatively and during follow-up. Accuracy was defined as the difference between ultrasound biomicroscopy and caliper measurements.

RESULTS

Thirty-nine muscles (19 medial rectus and 20 lateral rectus) of 22 patients were included. The mean age of the patients was 34.7 ± 15.5 years (range: 18 to 78 years). Follow-up measurements were available for 25 muscles: 12 muscles were recessed and 13 were resected/advanced. Twelve of the included muscles underwent prior surgery. There was a strong correlation between preoperative mean ultrasound biomicroscopy and caliper measurements (P < .001, r_p = 0.872) without significant difference between the accuracy of identification of medial rectus and lateral rectus muscles (P = .116 and .377, respectively). On average, postoperative ultrasound biomicroscopy measurements of recessed muscles were 1.15 mm greater than caliper measurements at the end of surgery (P = .003), whereas the mean difference in the resected muscles was not statistically significant (-0.07 mm, P > .999). Overall, in 16 of 25 muscles (64%), the differences between the postoperative measurements and the end of surgery measurements were less than 1 mm. There was no correlation between the accuracy and the time of ultrasound biomicroscopy after surgery (P = .516).

CONCLUSIONS

The ultrasound biomicroscopy bag/balloon technique is an accurate and reliable method of locating recti muscle insertions before and after strabismus surgery. Ultrasound biomicroscopy may assist strabismologists in planning repeated operations. [J Pediatr Ophthalmol Strabismus. 2020;57(1):12-20.].

Mechanical Weakness of Thoracic Aorta Related to Aging or Dissection Predicted by Speed of Sound with Collagenase

Scanning acoustic microscopy reveals information on histology and speed of sound (SOS) through tissues. Slower SOS corresponds to lower stiffness. The aim of the present study was to investigate whether SOS values reflect the degree of degeneration with aging or dissection and whether enzymatic digestion susceptibility is distinct. The SOSs of media other than the atheromatous areas of normal and surgical dissections were measured and compared using medial degeneration grade (MDG) scores. To evaluate the damage rate, SOS was assessed after collagenase digestion. SOS scores negatively correlated with aging and MDG scores. Dissected aortas had higher SOS and MDG scores without age correlation. Collagenase digestion was present in all aortas, but older aortas were more injured than younger aortas. Dissected aortas were more vulnerable to collagenase. Older and dissected aortas expressed specific extracellular matrix components to compensate for mechanical weakness. The present method can evaluate mechanical weakness corresponding to histology to investigate the cause of rupture.

Acoustic Histology with Specific Dyes and Antibodies

The present study aims to identify specific staining methods for acoustic histology. We compared attenuation-of-sound (AOS) images from scanning acoustic microscopy (SAM) with light microscopy (LM) images. Ethanol-fixed tissue or cytology samples and formalin-fixed surgical or autopsy specimens were examined. Nuclei, collagen, elastic fibers and polysaccharides and various antigens, including cell surface, cytoplasmic, nuclear and stromal substances, were observed. Samples with various fixation methods were used. Hematoxylin staining had significantly higher AOS values in accordance with staining duration. Specific staining for collagen, elastic fibers and polysaccharides increased the AOS values of the specific substance. Using diaminobenzidine tetrahydrochloride in NiCl₂ solution as a substrate for horseradish peroxidase increased the AOS values to those suitable for acoustic immunostaining. Collagenase digestion after collagen staining decreased AOS values, reflecting collagen density and distribution. Staining with specific dyes or acoustic immunostaining enabled the histologic localization of specific substances by SAM, similar to LM.

Scanning Acoustic Microscopy (SAM): A Robust Method for Defect Detection during the Manufacturing Process of Ultrasound Probes for Medical Imaging

The main aim of this paper is to provide the feasibility of non-destructive testing (NDT) method, such as scanning acoustic microscopy (SAM), for damage detection in ultrasound (US) probes for medical imaging during the manufacturing process. In a highly competitive and demanding electronics and biomedical market, reliable non-destructive methods for quality control and failure analysis of electronic components within multi-layered structures are strongly required. Any robust non-destructive method should be capable of dealing with the complexity of miniaturized assemblies, such as the acoustic stack of ultrasonic transducers. In this work, the application of SAM in an industrial scenario was studied for 24 samples of a phased array probe, in order to investigate potential internal integrity, to detect damages, and to assess the compliance of high-demanding quality requirements. Delamination, non-homogeneous layers with micron-thickness, and entrapped air bubbles (blisters) in the bulk of US probe acoustic stacks were detected and studied. Analysis of 2D images and defects visualization by means of ultrasound-based NDT method were compared with electroacoustic characterization (also following as pulse-echo test) of the US probe through an ad-hoc measurement system. SAM becomes very useful for defect detection in multilayered structures with a thickness of some microns by assuring low time-consuming (a limit for other NDT techniques) and quantitative analyses based on measurements. The study provides a tangible contribution and identifies an advantage for manufacturers of ultrasound probes that are oriented toward continuous improvement devoted to the process capability, product quality, and in-process inspection.

Three-dimensional acoustic impedance mapping of cultured biological cells

The acoustic microscope is a powerful tool for the observation of biological matters. Non-invasive in-situ observation can be performed without any staining process. Acoustic microscopy is contrasted by elastic parameters like sound speed and acoustic impedance. We have proposed an acoustic microscope that can acquire three-dimensional acoustic impedance profile. The technique was applied to cell-size observation. Glial cells were cultured on a 70 μm-thick polypropylene film substrate. A highly focused ultrasound beam was transmitted from the rear side of the substrate, and the reflection was received by the same transducer. An acoustic pulse, its spectrum spreading briefly 100 through 450 MHz, was transmitted. By analyzing the internal reflections in the cell, the distribution of characteristic acoustic impedance along the beam direction was determined. Three-dimensional acoustic impedance mapping was realized by scanning the transducer, exhibiting the intra-cellular structure including nucleus and cytoskeleton.

Real-time OCT guidance and multimodal imaging monitoring of subretinal injection induced choroidal neovascularization in rabbit eyes

Choroidal neovascularization (CNV) is a major cause of vision loss that consists of abnormal growth of new blood vessels from the choroidal vasculature. High resolution in vivo imaging of animal models is essential to better elucidate and conduct research on CNV. This study evaluates a novel multimodal imaging platform combining optical coherence tomography (OCT) and photoacoustic microscopy (PAM). Using real-time OCT guidance subretinal injection to induce and multimodality imaging system to monitor CNV over time in rabbit eyes. The significance of our work lies in providing the optimal setting and conditions to make use of the OCT image guided system to improve the consistency and reproducibility of experimental results in subretinal injection induced CNV model in rabbits. For the first time, this study successfully demonstrated the dual-modality PAM-OCT system, without using exogenous contrast agents, can detect and visualize CNV in the rabbit eye with high resolution. This is promising system for diagnosing and monitoring CNV.

Contribution of the Visante® OCT and B-scan ultrasound in the diagnosis and follow up of a topiramate-induced bilateral ciliochoroidal effusion syndrome

A 45 year-old man with bilateral acute angle-closure and myopia after starting treatment with topiramate, secondary to alcohol and heroin dependence. Using Visante® OCT (Optical Coherence Tomography) and B-scan Ultrasound he was diagnosed with bilateral ciliochoroidal effusion as the pathophysiological mechanism. Topiramate was stopped and ocular hypotensive therapy with a topical cycloplegic and corticosteroids were started, resolving ciliochoroidal effusion syndrome. Visante® OCT and B-scan Ultrasound are useful tools for the diagnosis and follow-up of patients with acute angle-closure and myopia due to topiramate. As a result of broad spectrum of indications for topiramate, physicians and ophthalmologists should be aware of the possible ophthalmological manifestations attributable to this drug.

High-speed simultaneous multiscale photoacoustic microscopy

Photoacoustic microscopy (PAM) is a fast-growing biomedical imaging technique that provides high-resolution in vivo imaging beyond the optical diffusion limit. Depending on the scalable lateral resolution and achievable penetration depth, PAM can be classified into optical resolution PAM (OR-PAM) and acoustic resolution PAM (AR-PAM). The use of a microelectromechanical systems (MEMS) scanner has improved OR-PAM imaging speed significantly and is highly beneficial in the development of miniaturized handheld devices. The shallow penetration depth of OR-PAM limits the use of such devices for a wide range of clinical applications. We report the use of a high-speed MEMS scanner for both OR-PAM and AR-PAM. A high-speed, wide-area scanning integrated OR-AR-PAM system combining MEMS scanner and raster mechanical movement was developed. A lateral resolution of 5  μm and penetration depth ∼0.9-mm in vivo was achieved using OR-PAM at 586 nm, whereas a lateral resolution of 84  μm and penetration depth of ∼2-mm in vivo was achieved using AR-PAM at 532 nm.

Frequency-domain differential photoacoustic radar: theory and validation for ultrasensitive atherosclerotic plaque imaging

Lipid composition of atherosclerotic plaques is considered to be highly related to plaque vulnerability. Therefore, a specific diagnostic or imaging modality that can sensitively evaluate plaques' necrotic core is desirable in atherosclerosis imaging. In this regard, intravascular photoacoustic (IVPA) imaging is an emerging plaque detection technique that provides lipid-specific chemical information from an arterial wall with great optical contrast and long acoustic penetration depth. While, in the near-infrared window, a 1210-nm optical source is usually chosen for IVPA applications since lipids exhibit a strong absorption peak at that wavelength, the sensitivity problem arises in the conventional single-ended systems as other arterial tissues also show some degree of absorption near that spectral region, thereby generating undesirably interfering photoacoustic (PA) signals. A theory of the high-frequency frequency-domain differential photoacoustic radar (DPAR) modality is introduced as a unique detection technique for accurate and molecularly specific evaluation of vulnerable plaques. By assuming two low-power continuous-wave optical sources at ∼1210 and ∼970  nm in a differential manner, DPAR theory and the corresponding simulation/experiment studies suggest an imaging modality that is only sensitive and specific to the spectroscopically defined imaging target, cholesterol.

Determining sodium diffusion through acoustic impedance measurements using 80 MHz Scanning Acoustic Microscopy: Agarose phantom verification

The purpose of this study is to explore the feasibility of time-dependent acoustic impedance measurement by Scanning Acoustic Microscopy (SAM) for analyzing the sodium diffusion. The purpose is motivated by the fact that sodium monitoring is challenging and still in the area of exploratory analysis despite its biological importance. To our knowledge, this is the first study in which sodium diffusion has been investigated by time-dependent acoustic impedance measurements provided by SAM. We first tested the idea in an agarose phantom as a proof-of-concept. Accordingly, we designed the agarose phantom which initially contains a well of sodium chloride (NaCl) solution moving radially into the phantom. By using NaCl diffusion in the phantom, we obtained two-dimensional (2D) acoustic impedance (Z) maps over time through SAM operating with 80 MHz ultrasonic transducer having a lateral resolution of 20 μm. A linear correlation between the changes in the concentration profile of the phantom and its acoustic impedance was introduced. Analysis of experimental data proved that spatially changing acoustic impedance could be ascribed to the diffusion process and produced a diffusion coefficient in the order of 10^-5 cm²/s which matches well with the literature. Our results showed that SAM could monitor the time-dependent alterations in acoustic impedance resulting from the diffusion of sodium inside the agarose phantom. With this study, SAM shows a promise as a monitoring tool not only to obtain static images but also to perform dynamic investigations of sodium ions with the advantages of providing images in micrometer resolution with a scanning time no longer than 2 min for an image area of 4.8 mm × 4.8 mm.

A Novel 2-D Synthetic Aperture Focusing Technique for Acoustic-Resolution Photoacoustic Microscopy

Acoustic-resolution photoacoustic microscopy (AR-PAM) is a promising technology for vascular or tumor-targeted molecular imaging. Unique advantages of AR-PM are its non-invasive, non-ionizing real-time, and deeper imaging depth. AR-PAM typically uses an ultrasound transducer with a high acoustic numerical aperture (NA) to enable deeper imaging depth. While high NA achieves good lateral resolution in the focal plane but significantly degrades the lateral resolution in the out-of-focus region. Synthetic aperture focusing technique (SAFT) has been introduced to overcome this out-of-focus degradation by synthesizing the correlated signals. Several 2-D SAFTs have been also reported to improve degraded resolution in all directions. However, the resolution enhancement of the previously reported 2-D SAFTs are suboptimal and are not equivalent to the 1-D SAFT performance under an ideal condition with the sample orientation perpendicular to the synthetic aperture direction. In this paper, we present a new 2-D SAFT called 2-D directional SAFT that improves the lateral resolution significantly and we compare our results against 1-D SAFT under ideal condition. We applied this algorithm to phantom and in vivo images to show the improvement in image quality. We also implement this algorithm in a graphical processing unit to achieve high performance to show the practicality of implementing this new algorithm in a system.

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.

BMD-based assessment of local porosity in human femoral cortical bone

Cortical pores are determinants of the elastic properties and of the ultimate strength of bone tissue. An increase of the overall cortical porosity (Ct.Po) as well as the local coalescence of large pores cause an impairment of the mechanical competence of bone. Therefore, Ct.Po represents a relevant target for identifying patients with high fracture risk. However, given their small size, the in vivo imaging of cortical pores remains challenging. The advent of modern high-resolution peripheral quantitative computed tomography (HR-pQCT) triggered new methods for the clinical assessment of Ct.Po at the peripheral skeleton, either by pore segmentation or by exploiting local bone mineral density (BMD). In this work, we compared BMD-based Ct.Po estimates with high-resolution reference values measured by scanning acoustic microscopy. A calibration rule to estimate local Ct.Po from BMD as assessed by HR-pQCT was derived experimentally. Within areas of interest smaller than 0.5 mm², our model was able to estimate the local Ct.Po with an error of 3.4%. The incorporation of the BMD inhomogeneity and of one parameter from the BMD distribution of the entire scan volume led to a relative reduction of the estimate error of 30%, if compared to an estimate based on the average BMD. When applied to the assessment of Ct.Po within entire cortical bone cross-sections, the proposed BMD-based method had better accuracy than measurements performed with a conventional threshold-based approach.

Stomach wall structure and vessels imaging by acoustic resolution photoacoustic microscopy

AIM

To image stomach wall blood vessels and tissue, layer-by-layer.

METHODS

We built up the acoustic resolution photoacoustic microscopy (AR-PAM) system for imaging layered tissues, such as the stomach wall. A tunable dye laser system was coupled to a fiber bundle. The fibers of the bundle were placed in nine directions with an incident angle of 45° around a high-frequency ultrasound transducer attached to the acoustic lens. This structure formed a dark field on the tissue surface under the acoustic lens and the nine light beams from the fibers to be combined near the focal point of the acoustic lens. The sample piece was cut from a part of the porcine stomach into a petri dish. In order to realize photoacoustic depth imaging of tumor, we designed a tumor model based on indocyanine green (ICG) dye. The ICG solution (concentration of 129 μM/mL) was mixed into molten gel, and then a gel mixture of ICG (concentration of 12.9 μM/mL) was injected into the stomach submucosa. The injection quantity was controlled by 0.1 mL to make a small tumor model.

RESULTS

An acoustic resolution photoacoustic microscopy based on fiber illumination was established and an axial resolution of 25 μm and a lateral resolution of 50 μm in its focal zone range of 500 μm has been accomplished. We tuned the laser wavelength to 600 nm. The photoacoustic probe was driven to do B-scan imaging in tissue thickness of 200 μm. The photoacoustic micro-image of mucosa and submucosa of the tissue have been obtained and compared with a pathological photograph of the tissue stained by hematoxylin-eosin staining. We have observed more detailed internal structure of the tissue. We also utilized this photoacoustic microscopy to image blood vessels inside the submucosa. High contrast imaging of the submucosa tumor model was obtained using ICG dye.

CONCLUSION

This AR-PAM is able to image layer-by-layer construction and some blood vessels under mucosa in the stomach wall without any contrast agents.

A rotary scanning method to evaluate grooves and porosity for nerve guide conduits based on ultrasound microscopy

Grooved nerve guide conduits (NGCs) have been effective in the clinical treatment of peripheral nerve injury. They are generally fabricated from a micro-structured spinneret using a spinning process, which easily can cause a variety of pores and morphological deviation. The topography of internal grooves as well as the porosity can greatly influence the therapeutic effect. Traditional optical or scanning electron microscopy (SEM) methods can be used to image the grooves; however, these methods are destructive and require slicing NGCs to prepare specimens suitable for imaging. Moreover, lengthy experiments and large batches of NGCs are required to ensure reliable results from both in vitro experiments and clinical studies. In this paper, a non-destructive method for evaluating the grooves and porosity of NGCs is proposed using ultrasonic imaging combined with rotary scanning and an image analysis algorithm. Two ultrasonic methods were used: a 25-MHz point-focus ultrasonic transducer applied to observe axial cross sections of the conduits and a 100-MHz point-focus ultrasonic transducer to detect large pores caused by defects. Furthermore, a theoretical algorithm for detecting the local porosity of a conduit based on density is proposed. Herein, the proposed acoustic method and traditional optical methods are evaluated and compared. A parameter representing the specific surface area of the internal grooves is introduced and computed for both the optical and acoustic methods, and the relative errors of the computed parameter values for three different NGCs were 7.0%, 7.9%, and 15.3%. The detected location and shape of pores were consistent between the acoustic and optical methods, and greater porosity was observed in the middle of the conduit wall. In this paper, the results of the acoustic and optical methods are presented and the errors relating to the acoustic factors, device characteristics, and image processing method are further analyzed.

Combination of virtual point detector concept and fluence compensation in acoustic resolution photoacoustic microscopy

We propose a hybrid approach to image enhancement in acoustic resolution photoacoustic microscopy. The developed technique is based on compensation for nonuniform spatial sensitivity of the optoacoustic (OA) system in both optical and acoustic domains. Spatial distribution of optical fluence is derived from full three-dimensional Monte Carlo simulations accounting for conical geometry of tissue laser illumination at the wavelength of 532 nm. Approximate nonuniform spatial response of acoustic detector with numerical aperture of 0.6 is derived from the two-dimensional k-Wave modeling. Application of the developed technique allows to improve the spatial resolution and to balance in-depth signal-level distribution in OA images of phantom and in-vivo objects.

Acute ocular pain during magnetic resonance imaging due to retained intraocular metallic foreign body: the role of ultrasonography and ultrasound biomicroscopy in diagnosis and management of this condition

PURPOSE

To report the case of a 65-year-old metalworker with no known history of ocular trauma, who suffered from intense ocular pain during magnetic resonance imaging (MRI) of the brain, due to a retained intraocular metallic foreign body (IOFB).

CASE REPORT

Meticulous ophthalmological examination was inconclusive. An IOFB was confirmed with X-ray scan, whereas its exact localization was enabled by means of ultrasonography and ultrasound biomicroscopy (UBM).

CONCLUSIONS

Despite appropriate screening protocols, MRI-related ocular complications might occur in the presence of a hidden metallic IOFB. Clinical detection of ocular foreign bodies can sometimes be challenging. Ultrasonography and UBM are valuable adjuncts for the accurate localization, especially of small or hidden particles.

Subdiffraction-limited second harmonic photoacoustic microscopy based on nonlinear thermal diffusion

We have developed a second harmonic photoacoustic microscopy (SH-PAM) for subdiffraction-limited imaging based on nonlinear thermal diffusion. When a sine-modulated Gaussian temperature field is introduced by a laser beam, the temperature dependence of the thermal diffusivity induces a nonlinear photoacoustic (PA) effect and thus results in the production of second harmonic PA signals. We demonstrate through both simulation and experiment that the second harmonic PA images can be reconstructed with a lateral resolution exceeding that of conventional optical resolution PA microscopy. The feasibility of SH-PAM was verified on phantom samples. Amphioxus zygotes and germinated pollens have been studied by SH-PAM to demonstrate its biomedical imaging capability. This method expands the scope of conventional PA imaging and opens up new possibilities for super-resolution imaging, prefiguring great potential for biological imaging and material inspection.

In Vivo Imaging of Microvasculature during Anesthesia with High-Resolution Photoacoustic Microscopy

Anesthesia monitoring is extremely important in improving the quality of anesthesia and ensuring the safety of patients in operation. Photoacoustic microscopy (PAM) is proposed to in vivo image the skin microvasculature of 10 nude mice undergoing general anesthesia by using the isoflurane gas with a concentration of 3%. Benefiting from strong optical absorption of hemoglobin, PAM has good contrast and high resolution in mapping of microvasculature. A series of high quality images can clearly reveal the subtle changes of capillaries in morphology over time. Two indices, vessel intensity and vessel density, are extracted from these images to measure the microvasculature quantitatively. The imaging results show that the vessel intensity and density are increased over time. After 65 min, the vessel intensity increased 42.7 ± 8.6% and the density increased 28.6 ± 12.2%. These indices extracted from photoacoustic images accurately reflect the greater blood perfusion undergoing general anesthesia. Additionally, abnormal reductions of vessel intensity and density are also observed as overtime anesthesia. This preclinical study suggests that PAM holds potential to monitor anesthesia by imaging the skin microvasculature.

Anterior Segment Imaging for Angle Closure

PURPOSE

To summarize the role of anterior segment imaging (AS-imaging) in angle closure diagnosis and management, and the possible advantages over the current standard of gonioscopy.

DESIGN

Literature review and perspective.

METHODS

Review of the pertinent publications with interpretation and perspective in relation to the use of AS-imaging in angle closure assessment focusing on anterior segment optical coherence tomography and ultrasound biomicroscopy.

RESULTS

Several limitations have been encountered with the reference standard of gonioscopy for angle assessment. AS-imaging has been shown to have performance in angle closure detection compared to gonioscopy. Also, imaging has greater reproducibility and serves as better documentation for long-term follow-up than conventional gonioscopy. The qualitative and quantitative information obtained from AS-imaging enables better understanding of the underlying mechanisms of angle closure and provides useful parameters for risk assessment and possible prediction of the response to laser and surgical intervention. The latest technologies-including 3-dimensional imaging-have allowed for the assessment of the angle that simulates the gonioscopic view. These advantages suggest that AS-imaging has a potential to be a reference standard for the diagnosis and monitoring of angle closure disease in the future.

CONCLUSIONS

Although gonioscopy remains the primary method of angle assessment, AS-imaging has an increasing role in angle closure screening and management. The test should be integrated into clinical practice as an adjunctive tool for angle assessment. It is arguable that AS-imaging should be considered first-line screening for patients at risk for angle closure.

Ultracompact high-resolution photoacoustic microscopy

Optical resolution photoacoustic microscopy (ORPAM), benefiting from rich optical contrast, scalable acoustic resolution, and deep penetration depth, is of great importance for the fields of biology and medicine. However, limited by the size and performance of reported optical/acoustic scanners, existing portable/handheld ORPAMs are bulky and heavy, and suffer from low imaging quality/speed. Here, we present an ultracompact ORPAM probe, which is miniature and light, and has high imaging quality. The probe only weighs 20 grams and has an outer size of 22  mm×30  mm×13  mm, a high lateral resolution of 3.8 μm, and an effective imaging domain of 2  mm×2  mm. To show its advantages over existing ORPAMs, we apply this probe to image vasculatures of internal organs in a rat abdominal cavity and inspect the entire human oral cavity.