Optical coherence tomography (OCT) is a promising noninvasive imaging modality in vivo for label-free three-dimensional tissue imaging in vivo.¹ In recent years, methods for calculating attenuation coefficients from OCT signals to identify various tissue types and obtain their pathological status information have begun to attract the attention of scholars. This idea first came from ultrasonic imaging.² When the ultrasound or infrared light penetrate the tissue, the intensity decays exponentially, and therefore the attenuation coefficient reflects the acoustic/optical characteristics of different tissues or the same type of tissues under different physiological conditions. According to some basic research, due to the lack of oxygen and energy, cerebral ischemia is accompanied by changes in cellular morphology, which optical attenuation coefficient (OAC) is sensitive to. Consequently, OAC increases during cerebral ischemia.³ Observations of ischemia tissue by transmission electron microscopy suggest that the increase in OAC is due to deformation or enlargement of mitochondria and dendrites expansion.⁴ Through quantitative measurement of OAC, cerebral tissue damaged by ischemia can be effectively labeled and evaluated. This method provides additional information and increases the potential of OCT in exploring cerebral infarction.

The size and shape of the foveal avascular zone (FAZ) have a strong positive correlation with several vision-threatening retinovascular diseases. The identification, segmentation and analysis of FAZ are of great significance to clinical diagnosis and treatment. We presented an adaptive watershed algorithm to automatically extract FAZ from retinal optical coherence tomography angiography (OCTA) images. For the traditional watershed algorithm, “over-segmentation” is the most common problem. FAZ is often incorrectly divided into multiple regions by redundant “dams”. This paper analyzed the relationship between the “dams” length and the maximum inscribed circle radius of FAZ, and proposed an adaptive watershed algorithm to solve the problem of “over-segmentation”. Here, 132 healthy retinal images and 50 diabetic retinopathy (DR) images were used to verify the accuracy and stability of the algorithm. Three ophthalmologists were invited to make quantitative and qualitative evaluations on the segmentation results of this algorithm. The quantitative evaluation results show that the correlation coefficients between the automatic and manual segmentation results are 0.945 (in healthy subjects) and 0.927 (in DR patients), respectively. For qualitative evaluation, the percentages of “perfect segmentation” (score of 3) and “good segmentation” (score of 2) are 99.4% (in healthy subjects) and 98.7% (in DR patients), respectively. This work promotes the application of watershed algorithm in FAZ segmentation, making it a useful tool for analyzing and diagnosing eye diseases.

Ischemic cerebrovascular disease (ICVD) is characterized by high morbidity, high disability, high recurrence rate, and high mortality.¹ Cerebral edema is a severe complication of ICVD.² Recent studies have shown that cerebral edema can independently impair cerebral metabolism and may cause compression of microcirculation, which can lead to additional ischemic damage.³

Amyloid $\beta$ ($\mathrm{A}\beta$) peptides are naturally occurring cleavage products of the amyloid precursor protein via sequential proteolytic processes called $\beta$- and $\gamma$-secretase.¹ A primary neuropathological hallmark of Alzheimer’s disease (AD) involves extracellular $\mathrm{A}\beta$ deposition to form senile plaques, leading to neuronal death and cognitive degeneration.² Therefore, $\mathrm{A}\beta$ deposit elimination has been a major focus of $\mathrm{A}\beta$-based AD therapeutics over the past decades. Currently, there are more than one hundred agents in clinical trials for AD therapeutics.³ Although, Aducanumab, an anti-$\mathrm{A}\beta$ human monoclonal antibody, was approved by the U.S. Food and Drug Administration in 2021 for early AD.⁴ The efficacy of this drug remains highly controversial.^5,6 In addition, amyloid-related imaging abnormalities (ARIA) often co-occur during anti-$\mathrm{A}\beta$ immunotherapy (also seen with Aducanumab).^7,8 The high incidence of ARIA makes it a major adverse effect of $\mathrm{A}\beta$-targeted immunotherapies, which hinders the drug to reach the primary clinical endpoints.^{9 – 11} ARIA can be detected by magnetic resonance imaging (MRI) as hyperintensities on fluid-attenuated inversion recovery but is mostly asymptomatic.^7,12 It is suggested that the phenomena might be due to the breakdown of the $\mathrm{A}\beta$ plaque, liberating abundant amount of soluble $\mathrm{A}\beta$ peptides that overwhelm the capacity of $\mathrm{A}\beta$ clearance through perivascular cerebrospinal fluid (CSF) bulk flow system.^{13 – 17} This leads to greater $\mathrm{A}\beta$ deposition in the vessel wall and causes a self-reinforcing cycle, thereby exacerbating the development of cerebral amyloid angiopathy (CAA), a common feature of AD that has been reported to affect 80% to 90% of AD cases.^{9,13,14,18,19} Besides, under pathological conditions of mild cognitive impairment and AD, the balance between $\mathrm{A}\beta$ production and clearance is disrupted so the decline of the clearance system, rather than the $\mathrm{A}\beta$ overproduction, contributes to $\mathrm{A}\beta$ deposition.^20,21 Perivascular drainage is a major route of amyloid clearance from brain²² and a key contributor is the glymphatic system, which involves CSF entering the brain along paravascular spaces surrounding penetrating arteries and exchanging with interstitial fluid, which then exit the brain alongside veins.^{23 – 25} It has been reported that ventricular CSF clearance of $\mathrm{A}\beta$ is negatively related with the magnitude of brain $\mathrm{A}\beta$ deposition.²⁶ Consequently, efficient $\mathrm{A}\beta$ clearance via the glymphatic transport system is crucial for maintaining brain health and efficacious AD therapeutics; therefore, it is necessary to monitor the clearance dysfunction. Although ARIA occurs during anti-$\mathrm{A}\beta$ treatment, it does not correlate with the speed of $\mathrm{A}\beta$ elimination and might not have adequate sensitivity.²⁷ Pathological modification to the cerebral vascular architecture represents one of the earliest events in the AD pathological cascade and are evident earlier than the classical hallmark of the disease, $\mathrm{A}\beta$ deposition, and the onset of cognitive impairment.^{28 – 30} While the significance of vascular dysfunction is widely appreciated, its pathological changes caused by the $\mathrm{A}\beta$ clearance deficit through glymphatic transport are not clear. This raises the urgent need to characterize and quantitively evaluate vascular modifications after $\mathrm{A}\beta$ overload in CSF in preclinical settings. This may help us unravel the direct vascular consequences of $\mathrm{A}\beta$ clearance dysfunction and may also guide better treatment adjustments in patients receiving $\mathrm{A}\beta$-targeted immunotherapy.

A blockage of the middle cerebral artery (MCA) on the cortical branch will seriously affect the blood supply of the cerebral cortex. Real-time monitoring of MCA hemodynamic parameters is critical for therapy and rehabilitation. Optical coherence tomography (OCT) is a powerful imaging modality that can produce not only structural images but also functional information on the tissue. We use OCT to detect hemodynamic changes after MCA branch occlusion. We injected a selected dose of endothelin-1 (ET-1) at a depth of 1 mm near the MCA and let the blood vessels follow a process first of occlusion and then of slow reperfusion as realistically as possible to simulate local cerebral ischemia. During this period, we used optical microangiography and Doppler OCT to obtain multiple hemodynamic MCA parameters. The change trend of these parameters from before to after ET-1 injection clearly reflects the dynamic regularity of the MCA. These results show the mechanism of the cerebral ischemia-reperfusion process after a transient middle cerebral artery occlusion and confirm that OCT can be used to monitor hemodynamic parameters.

We introduce a method to extract the photoacoustic (PA) signal from a contrast reduction of the interference spectrum acquired by spectral domain optical coherence tomography (SDOCT). This all-optical detection is achieved in a noncontact manner directly on the water surface covered on the sample by using its specular reflection. During SDOCT exposure, the phase of the interference spectrum keeps shaking according to the water surface vibration induced by PA excitation. This results in an interference contrast reduction which is quantified by a fast Fourier transform (FFT) for PA imaging. A tungsten filament, asparagus fern leaf, and mouse auricle are imaged to demonstrate the method.