Comparison between thermoelastic and ablative induced elastic waves in soft media using ultra-fast line-field low coherent holography

Laser induced elastic waves in soft media have great potential to characterize tissue biomechanical properties. The instantaneous increase in local temperature caused by absorption of laser energy leads to a mechanical perturbation in the sample, which can then propagate as a pressure (or an elastic) wave. The generation of the elastic wave can be via thermoelastic or ablative processes depending on the absorption coefficient of the sample and incident laser fluence. It is critical to differentiate between these regimes because only the thermoelastic regime is useful for nondestructive analysis of tissues. To investigate the transition point between these two different regimes, we induced elastic waves in tissue mimicking agar phantoms mixed with different concentrations of graphite powder. The elastic waves were excited by a 532nm pulsed laser with a pulse duration of 6 ns. The fluence of the pulsed laser was tuned from 0.08 J/cm2 to 3.19 J/cm2 , and the elastic wave was captured by ultra-fast line-field low coherent holography system capable of single-shot elastic wave imaging with nanometer-scale displacement sensitivity. Different concentrations of graphite powder enabled excitation in sample with controlled and variable attenuation coefficient, enabling measurement of the transition between the thermoelastic and ablative regimes. The results show that the transition from thermoelastic to ablative generated waves was 0.75 J/cm2 and 1.84 J/cm2 for phantoms with optical attenuation coefficients of 6.64±0.32 mm-1 and 26.19±1.70 mm-1, respectively. Our results show promise for all optical biomechanical characterization of tissues

Assessing the effects of storage medium on the biomechanical properties of porcine lens with optical coherence elastography

There has been a large amount of research focused on studying the biomechanical properties of the lens ex vivo. However, the storage medium of the lenses may affect the biomechanical evaluation during ex vivo measurements, which has been demonstrated with other tissues such as the cornea. In this work, we utilized a focused micro air-pulse and phase-sensitive optical coherence elastography to quantify the changes in lenticular biomechanical properties when incubated in different media, temperatures, and pHs for up to 24 hours. The results show that the lenses became stiffer when incubated at lower temperatures and higher pHs. Meanwhile, lenses incubated in M-199 were more mechanically stable than lenses incubated in PBS and DMEM

Biomechanical properties of murine embryos using optical coherence tomography and brilloiun microscopy

A combination of optical coherence tomograph

Quantifying changes in lenticular stiffness with optical coherence elastography

Maintaining a normal intraocular pressure (IOP) is important for visual health. Elevated IOPs have been implicated in many diseases, such as glaucoma and uveitis. The effects of an elevated IOP on the delicate tissues of the optic nerve head and retina are well-studied, but there is a lack of information about the effects of high IOPs on the stiffness of the crystalline lens. Changes in lenticular biomechanical properties have been implicated in diseases such as presbyopia and cataract, therefore, measuring lenticular biomechanical properties is crucial to understanding the etiology and progression of the leading causes of vision impairment. Additionally, there has been even less research focused on the effects of storage media on lenticular stiffness. Previous studies have been focused on the “gold standard” of mechanical testing on excised lenses. However, mechanical testing is invasive and destructive, and removal of the lens from the eyeglobe does not allow for properly replicating the lens environment in the eye-globe. Thus, there is a need for noninvasive measurement techniques capable of performing in situ and in vivo elastographic measurements of the lens. Here, we artificially controlled the IOP of whole porcine eye-globes (N=3). Acoustic radiation force induced low amplitude displacements (<10 µm) at the apex of the lenses, which then propagated as an elastic wave. The elastic wave propagation was detected by a phase-sensitive optical coherence elastography (PhS-OCE) system. The results show that the stiffness of the lenses increased when IOP increased from 10 mmHg IOP to 40 mmHg. Additional OCE measurements were made on excised lenses stored in various media (PBS, DMEM, and M-199) at different pHs (4-7) and at different temperatures (4°C, 22°C, and 37°C). The results show that the stiffness of the lenses increased slightly when incubated at 4°C or 22°C, but decreased when the lenses were incubated at 37°C, while lenses incubated in M-199 showed more stability in their stiffness than lenses incubated in PBS and DMEM. Moreover, the lenses stored in M-199 at a pH of 7 showed a decrease in stiffness over 24 hours, while the more acidic M-199 media caused an increase in lenticular stiffness

Quantifying lens elastic properties with optical coherence elastography as a function of intraocular pressure

Normal intraocular pressure (IOP) is crucial for proper maintaining of eye-globe geometry, ocular tissue health, and visual acuity. An elevated IOP is associated with diseases such as glaucoma and uveitis. While the effects of an elevated IOP on the delicate tissues of the optic nerve head and retina are well-studied, the changes in lenticular biomechanical properties as a function of IOP are not as clear. Moreover, changes in lenticular biomechanical properties have been implicated in conditions and diseases such as presbyopia and cataract. However, measuring the biomechanical properties of the lens as it sits inside the eye-globe is a challenge, but it is necessary to correctly understand the interplay between lenticular biomechanical properties and IOP. In this work, we utilized optical coherence elastography (OCE) to measure the biomechanical properties of the porcine lens in situ

Rotational imaging optical coherence tomography for full-body mouse embryonic imaging

Optical coherence tomography (OCT) has been widely used to study mammalian embryonic development with the advantages of high spatial and temporal resolutions and without the need for any contrast enhancement probes. However, the limited imaging depth of traditional OCT might prohibit visualization of the full embryonic body. To overcome this limitation, we have developed a new methodology to enhance the imaging range of OCT in embryonic day (E) 9.5 and 10.5 mouse embryos using rotational imaging. Rotational imaging OCT (RI-OCT) enables full-body imaging of mouse embryos by performing multiangle imaging. A series of postprocessing procedures was performed on each cross-section image, resulting in the final composited image. The results demonstrate that RI-OCT is able to improve the visualization of internal mouse embryo structures as compared to conventional OCT

Applanation optical coherence elastography: noncontact measurement of intraocular pressure, corneal biomechanical properties, and corneal geometry with a single instrument

Current clinical tools provide critical information about ocular health such as intraocular pressure (IOP). However, they lack the ability to quantify tissue material properties, which are potent markers for ocular tissue health and integrity. We describe a single instrument to measure the eye-globe IOP, quantify corneal biomechanical properties, and measure corneal geometry with a technique termed applanation optical coherence elastography (Appl-OCE). An ultrafast OCT system enabled visualization of corneal dynamics during noncontact applanation tonometry and direct measurement of micro air-pulse induced elastic wave propagation. Our preliminary results show that the proposed Appl-OCE system can be used to quantify IOP, corneal biomechanical properties, and corneal geometry, which builds a solid foundation for a unique device that can provide a more complete picture of ocular health

Ultra-high speed OCT allows measurement of intraocular pressure, corneal geometry, and corneal stiffness using a single instrument

Screening for ocular diseases, such as glaucoma and keratoconus, includes measuring the eye-globe intraocular pressure (IOP) and corneal biomechanical properties. However, currently available clinical tools cannot quantify corneal tissue material parameters, which can provide critical information for detecting diseases and evaluating therapeutic outcomes. Here, we demonstrate measurement of eye-globe IOP, corneal elasticity, and corneal geometry of in situ porcine corneas with a technique termed applanation optical coherence elastography (Appl-OCE) with single instrument. We utilize an ultrafast phase-sensitive optical coherence tomography system comprised of a 4X buffered Fourier domain mode-locked swept source laser with an Ascan rate of ~1.5 MHz and a 7.3 kHz resonant scanner. The IOP was measured by imaging the response of in situ porcine corneas to a large force air-puff. As with other noncontact tonometers, the time when the cornea was applanated during the inwards and outwards motion was correlated to a measure air-pressure temporal profile. The IOP was also measured with a commercially available rebound tonometer for comparison. The stiffness of the corneas was assessed by directly imaging and analyzing the propagation of a focused micro air-pulse induced elastic wave, and the corneal geometry was obtained from the OCT structural image. Our results show that corneal thickness decreased as IOP increased, and that corneal stiffness increased with IOP. Moreover, the IOP measurements made by Appl-OCE were more closely correlated with the artificially set IOP than the rebound tonometer, demonstrating the capabilities of Appl-OCE to measure corneal stiffness, eye-globe IOP, and corneal geometry with a single instrument

In utero optical coherence tomography reveals changes in murine embryonic brain vasculature after prenatal cannabinoid exposure

Prenatal substance abuse is a major public health concern. Much research has been focused on alcohol and other drug use, but there is a lack of information about prenatal cannabinoid use. Nevertheless, marijuana use during pregnancy increases the risk of a stillbirth by approximately 2.3X. Synthetic cannabinoids (SCB) are a group of heterogeneous compounds which were developed to understand the endogenous cannabinoid system and as potential therapeutics. SCBs are legally available for purchase in several places, and the use of natural and synthetic cannabinoids is high among women of reproductive age. Combined with the prevalence of unplanned pregnancies, the high use of cannabinoids may lead to an increase in prenatal exposure to cannabinoids. Early studies have shown morphological and behavioral anomalies similar to fetal alcohol syndrome. Even though the mechanisms of Δ9 -tetrahydrocannabinol (Δ9 -THC), the major psychoactive component of marijuana, and SCB are similar, there are several important differences. Subsequently, some SCBs have a 40 to 600 fold higher potency than Δ9 -THC. However, there is paucity of research focused on the prenatal effects of SCBs. This study uses correlation mapping optical coherence tomography (cm-OCT) to evaluate acute changes in the murine fetal brain vasculature in utero after exposure to CP-55,940, a well-characterized and commonly used reference compound in cannabinoid research. Our results showed a rapid decrease in parameters quantifying vasculature, i.e., vessel area density, and vessel length fraction, as compared to the sham group, demonstrating a dramatic and rapid effect of cannabinoids on fetal brain vasculature. Our work shows the need for further research on the effects of cannabinoids on fetal development