Study for quantitative evaluation of photoaging with photoacoustic microscopy.

Skin aging caused by ultraviolet light exposure is one of the serious problems from the viewpoint of beauty and healthcare. This is because ultraviolet light can cause age spot, wrinkles, at the worst case, skin cancer and so on. To evaluate skin aging, various modalities are being used, such as histopathological diagnosis, optical coherence tomography, ultrasound examination (B-mode imaging). However, they have disadvantages in terms of invasiveness, penetration depth and tissue specificity, respectively. To overcome these defects, photoacoustic imaging (PAI), a novel modality was used in this work. This modality can sense differences of tissue characteristics non-invasively. In this experiment, human skin tissues in various generations (i.e. various degrees of photoaging) were measured by using acoustic resolution photoacoustic microscopy (AR-PAM). To verify the feasibility of quantitative skin aging evaluation with PA technique, signals from sectioned human skin (cheek and buttock; female from 28 to 95 years old) were measured with PA microscopy. The effects of photoaging progress on the signal intensity were investigated. The results demonstrated that the PA signal from the dermis significantly increases with aging progress (p < 0.05). These analyses demonstrate the feasibility of quantitative skin aging evaluation with a PAI system.

A first case of meningitis/encephalitis associated with SARS-Coronavirus-2.

Novel coronavirus (SARS-Coronavirus-2:SARS-CoV-2) which emerged in Wuhan, China, has spread to multiple countries rapidly. We report the first case of meningitis associated with SARS-CoV-2 who was brought in by ambulance due to a convulsion accompanied by unconsciousness. He had never been to any foreign countries. He felt generalized fatigue and fever (day 1). He saw doctors nearby twice (day 2 and 5) and was prescribed Laninamivir and antipyretic agents, His family visited his home and found that he was unconsciousness and lying on the floor in his vomit. He was immediately transported to this hospital by ambulance (day 9). Under emergency transport, he had transient generalized seizures that lasted about a minute. He had obvious neck stiffness. The specific SARS-CoV-2 RNA was not detected in the nasopharyngeal swab but was detected in a CSF. Anti- HSV 1 and varicella-zoster IgM antibodies were not detected in serum samples. A brain MRI showed hyperintensity along the wall of right lateral ventricle and hyperintense signal changes in the right mesial temporal lobe and hippocampus, suggesting the possibility of SARS-CoV-2 meningitis. This case warns the physicians of patients who have CNS symptoms.

Ring-array photoacoustic tomography for imaging human finger vasculature.

For early diagnosis of rheumatoid arthritis (RA), it is important to visualize its potential marker, vascularization in the synovial membrane of the finger joints. Photoacoustic (PA) imaging, which can image blood vessels at high contrast and resolution, is expected to be a potential modality for earlier diagnosis of RA. In previous studies of PA finger imaging, different acoustic schemes, such as linear-shaped arrays, have been utilized, but these have limited detection views, rendering inaccurate reconstruction, and most of them require rotational detection. We are developing a PA system for finger vascular imaging using a ring-shaped array ultrasound (US) transducer. By designing the ring-array sensor based on simulations, using phantom experiments, it was demonstrated that we have created a system that can image small objects around 0.1 to 0.5 mm in diameter. The full width at half maximum of the slice direction of the system was within 2 mm and corresponded to that of the simulation. Moreover, we could clearly visualize healthy index finger vasculature and the location of the distal interphalangeal and proximal interphalangeal joints by PA and US echo images. In the future, this system could be used as a method for visualizing the three-dimensional vascularization of RA patients' fingers.

Coded excitation using periodic and unipolar M-sequences for photoacoustic imaging and flow measurement.

Photoacoustic imaging is an emerging imaging technology combining optical imaging with ultrasound. Imaging of the optical absorption coefficient and flow measurement provides additional functional information compared to ultrasound. The issue with photoacoustic imaging is its low signal-to-noise ratio (SNR) due to scattering or attenuation; this is especially problematic when high pulse repetition frequency (PRF) lasers are used. In previous research, coded excitation utilizing several pseudorandom sequences has been considered as a solution for the problem. However, previously proposed temporal coding procedures using Golay codes or M-sequences are so complex that it was necessary to send a sequence twice to realize a bipolar sequence. Here, we propose a periodic and unipolar sequence (PUM), which is a periodic sequence derived from an m-sequence. The PUM can enhance signals without causing coding artifacts for single wavelength excitation. In addition, it is possible to increase the temporal resolution since the decoding start point can be set to any code in periodic irradiation, while only the first code of a sequence was available for conventional aperiodic irradiation. The SNR improvement and the increase in temporal resolution were experimentally validated through imaging evaluation and flow measurement.

Sonographic and pathologic image analysis of pure mucinous carcinoma of the breast.

The aims of this study were to elucidate sonographic and histologic features of pure mucinous carcinoma (P-MC) of the breast using quantitative analysis and to evaluate the relationship between quantitative analysis and visual qualitative assessment. Eleven P-MCs (nine patients) were evaluated qualitatively and quantitatively. Three experts assessed these sonographic images using the Breast Imaging Reporting and Data System (BI-RADS) lexicon. For assessment of internal echoes and posterior echoes, quantitative measures were determined using ImageJ software. Histologic thin sections were stained for classification into separate parts of the tumor (stroma, mucin and cancer cells) and were digitized. Internal echoes were isoechoic in 7 of 11 (63.6%) tumors and hypoechoic in 4 of 11 (36.4%); all P-MCs were "enhanced" in qualitative evaluation. As internal echoes increased, the proportion of stroma increased and that of mucin decreased. The high level of internal echoes is correlated with reflection and back-scattering, which are caused mainly by the interface between mucin and stroma.

Model-based reconstruction integrated with fluence compensation for photoacoustic tomography.

Photoacoustic (PA) tomography (PAT) is a rapidly developing imaging modality that can provide high contrast and spatial-resolution images of light-absorption distribution in tissue. However, reconstruction of the absorption distribution is affected by nonuniform light fluence. This paper introduces a reconstruction method for reducing amplification of noise and artifacts in low-fluence regions. In this method, fluence compensation is integrated into model-based reconstruction, and the absorption distribution is iteratively updated. At each iteration, we calculate the residual between detected PA signals and the signals computed by a forward model using the initial pressure, which is the product of estimated voxel value and light fluence. By minimizing the residual, the reconstructed values converge to the true absorption distribution. In addition, we developed a matrix compression method for reducing memory requirements and accelerating reconstruction speed. The results of simulation and phantom experiments indicate that the proposed method provides a better contrast-to-noise ratio (CNR) in low-fluence regions. We expect that the capability of increasing imaging depth will broaden the clinical applications of PAT.