Computationally Efficient Forward Operator for Photoacoustic Tomography Based on Coordinate Transformations

IEEE Photoacoustic tomography (PAT) is an imaging modality that utilizes the photoacoustic effect. In PAT, a photoacoustic image is computed from measured data by modeling ultrasound propagation in the imaged domain and solving an inverse problem utilizing a discrete forward operator. However, in realistic measurement geometries with several ultrasound transducers and relatively large imaging volume, an explicit formation and use of the forward operator can be computationally prohibitively expensive. In this work, we propose a transformation based approach for efficient modeling of photoacoustic signals and reconstruction of photoacoustic images. In the approach, the forward operator is constructed for a reference ultrasound transducer and expanded into a general measurement geometry using transformations that map the formulated forward operator in local coordinates to the global coordinates of the measurement geometry. The inverse problem is solved using a Bayesian framework. The approach is evaluated with numerical simulations and experimental data. The results show that the proposed approach produces accurate three-dimensional photoacoustic images with a significantly reduced computational cost both in memory requirements and in time. In the studied cases, depending on the computational factors such as discretization, over 30-fold reduction in memory consumption and was achieved without a reduction in image quality compared to a conventional approach

Characterization of ultrasound fields using a potential optical flow based synthetic schlieren tomography

Synthetic schlieren tomography is an optical imaging method for characterization of ultrasound fields based on observing bending of light due to acousto-optic effect. In this work, potential optical flow based pressure estimation method is introduced

Cooper-pair resonances and subgap Coulomb blockade in a superconducting single-electron transistor

We have fabricated and measured superconducting single-electron transistors with Al leads and Nb islands. At bias voltages below the gap of Nb we observe clear signatures of resonant tunneling of Cooper pairs, and of Coulomb blockade of the subgap currents due to linewidth broadening of the energy levels in the superconducting density of states of Nb. The experimental results are in good agreement with numerical simulations.Comment: 4 pages, 3 figure

Epigenetic and transcriptional analysis supports human regulatory T cell commitment at the CD4+CD8+thymocyte stage

The natural CD25 + FOXP3 + regulatory T cell (Treg) population is generated as a distinct lineage in the thymus, but the details of Treg development in humans remain unclear, and the timing of Treg commitment is also contested. Here we have analyzed the emergence of CD25 + cells at the CD4 + CD8 + double positive (DP) stage in the human thymus. We show that these cells share T cell receptor repertoire with CD25 + CD4 single-positive thymocytes, believed to be committed Tregs. They already have a fully demethylated FOXP3 enhancer region and thus display stable expression of FOXP3 and the associated Treg phenotype. Transcriptome analysis also grouped the DP CD25 + and CD4 CD25 + thymocytes apart from the CD25 - subsets. Together with earlier studies, our data are consistent with human Treg commitment already at the DP thymocyte stage. We suggest that the most important antigens and signals necessary for human Treg differentiation may be found in the thymic cortex.Peer reviewe

Profiling water vapor mixing ratios in Finland by means of a Raman lidar, a satellite and a model

We present tropospheric water vapor profiles measured with a Raman lidar during three field campaigns held in Finland. Co-located radio soundings are available throughout the period for the calibration of the lidar signals. We investigate the possibility of calibrating the lidar water vapor profiles in the absence of co-existing on-site soundings using water vapor profiles from the combined Advanced InfraRed Sounder (AIRS) and the Advanced Microwave Sounding Unit (AMSU) satellite product; the Aire Limitee Adaptation dynamique Developpement INternational and High Resolution Limited Area Model (ALADIN/HIRLAM) numerical weather prediction (NWP) system, and the nearest radio sounding station located 100 km away from the lidar site (only for the permanent location of the lidar). The uncertainties of the calibration factor derived from the soundings, the satellite and the model data are <2.8, 7.4 and 3.9 %, respectively. We also include water vapor mixing ratio intercomparisons between the radio soundings and the various instruments/model for the period of the campaigns. A good agreement is observed for all comparisons with relative errors that do not exceed 50% up to 8 km altitude in most cases. A 4-year seasonal analysis of vertical water vapor is also presented for the Kuopio site in Finland. During winter months, the air in Kuopio is dry (1.15 +/- 0.40 g kg(-1)); during summer it is wet (5.54 +/- 1.02 g kg(-1)); and at other times, the air is in an intermediate state. These are averaged values over the lowest 2 km in the atmosphere. Above that height a quick decrease in water vapor mixing ratios is observed, except during summer months where favorable atmospheric conditions enable higher mixing ratio values at higher altitudes. Lastly, the seasonal change in disagreement between the lidar and the model has been studied. The analysis showed that, on average, the model underestimates water vapor mixing ratios at high altitudes during spring and summer.Peer reviewe

Black Mesoporous Silicon as a Contrast Agent for LED-Based 3D Photoacoustic Tomography

Mesoporous silicon (PSi) nanoparticles have been widely studied in different biomedical imaging modalities due to their several beneficial material properties. However, they have not been found to be suitable for photoacoustic imaging due to their poor photothermal conversion performance. In the present study, biodegradable black mesoporous silicon (BPSi) nanoparticles with strong light absorbance were developed as superior image contrast agents for photoacoustic tomography (PAT), which was realized with a light-emitting diode (LED) instead of the commonly used laser. LED-based PAT offers the advantages of low cost, compactness, good mobility, and easy operation as compared to the traditional laser-based PAT modality. Nevertheless, the poor imaging sensitivity of the LED-PAT systems has been the main barrier to prevent their wide biomedical application because the LED light has low optical energy. The present study demonstrated that the imaging sensitivity of the LED-PAT system was significantly enhanced with the PEGylated BPSi (PEG–BPSi) nanoparticles. The PEG–BPSi nanoparticles were clearly detectable with a low concentration of 0.05 mg/mL in vitro and with an LED radiation energy of 5.2 μJ. The required concentration of the PEG–BPSi nanoparticles was 10 times lesser than that of the reference gold nanoparticles to reach the corresponding level of the imaging contrast. The ex vivo studies demonstrated that the submillimeter BPSi nanoparticle-based absorbers were distinguishable in chicken breast tissues. The strong contrast provided by the BPSi particles indicated that these particles can be utilized as novel contrast agents in PAT, especially in LED-based systems with low light intensity

Lapsen osallisuuden tukeminen päiväkodin arjessa

Tiivistelmä. Tutkielmassamme avaamme osallisuuden käsitettä teorioiden, niiden tulkintojen sekä osallisuutta haastavien tekijöiden kautta. Olemme myös koonneet yhteen osallisuutta tukevia keinoja. Tutkimme näitä seuraavien tutkimuskysymysten kautta: miten osallisuutta on määritelty varhaiskasvatuksessa ja mitkä tekijät haastavat osallisuutta sekä miten lapsen osallisuutta voidaan tukea päiväkodin arjessa. Osallisuus tarkoittaa lapsen mahdollisuuksia vaikuttaa häntä koskeviin päätöksiin. Lapsen tulee myös olla tietoinen siitä, että hänen mielipiteensä vaikuttavat päätöksiin. Lasten osallisuutta voidaan tukea monella tavalla. Varhaiskasvatuksen opettaja on avainasemassa mahdollistamassa lapsen osallisuutta. Osallisuutta tuetaan kuuntelemalla lasta ja keskustelemalla hänen kanssaan, kodin ja päiväkodin välisellä yhteistyöllä, joustavilla rutiineilla ja pienryhmätoiminnalla päiväkodissa, lasten mielenkiinnonkohteiden huomioimisella sekä toiminnan havainnoinnilla ja sen mahdollistamisella. Tutkielmamme aihe on ajankohtainen ja aiheen valintaan ovat vaikuttaneet myös omat kokemuksemme. Lasten osallisuus varhaiskasvatuksessa on noussut ajankohtaiseksi aiheeksi varhaiskasvatuslain (540/2018) päivityksen myötä. Olemme myös havainneet itse päiväkodissa työskennellessämme, että varhaiskasvatuksen opettajien ajatukset lasten osallisuudesta ovat hyvin erilaisia. Tämän vuoksi, päädyimme tutkimaan lasten osallisuutta päiväkodin arjessa. Kandidaatin tutkielmamme on toteutettu integroivana kirjallisuuskatsauksena. Integroiva kirjallisuuskatsaus mahdollistaa laajan aineiston käytön sekä aineistojen yhdistelemisen ja uuden tiedon luomisen. Laaja aineisto mahdollistaa tutkielmamme luotettavuutta ja yleistettävyyttä. Olemme valinneet tutkielmaamme kattavasti erilaisia tutkimuksia, joiden pohjalta olemme muodostaneet monipuolisen käsityksen lapsen osallisuuden haasteista sekä sen tukemisesta. Tutkielmamme tavoitteena on tuoda konkreettisia esimerkkejä varhaiskasvatuksen opettajille siitä, miten lasten osallisuutta voidaan päiväkodin arjessa tukea