State-of-the art of acousto-optic sensing and imaging of turbid media

Acousto-optic (AO) is an emerging hybrid technique for measuring optical contrast in turbid media using coherent light and ultrasound (US). A turbid object is illuminated with a coherent light source leading to speckle formation in the remitted light. With the use of US, a small volume is selected,which is commonly referred to as the “tagging” volume. This volume acts as a source of modulated light, where modulation might involve phase and intensity change. The tagging volume is created by focusing ultrasound for good lateral resolution; the axial resolution is accomplished by making either the US frequency, amplitude, or phase time-dependent. Typical resolutions are in the order of 1 mm. We will concentrate on the progress in the field since 2003. Different schemes will be discussed to detect the modulated photons based on speckle detection, heterodyne detection, photorefractive crystal (PRC) assisted detection, and spectral hole burning (SHB) as well as Fabry-Perot interferometers. The SHB and Fabry-Perot interferometer techniques are insensitive to speckle decorrelation and therefore suitable for in vivo imaging. However, heterodyne and PRC methods also have potential for in vivo measurements. Besides measuring optical properties such as scattering and absorption, AO can be applied in fluorescence and elastography applications

Tandem-pulsed acousto-optics: an analytical framework of modulated high-contrast speckle patterns

Recently we presented acousto-optic (AO) probing of scattering media using addition or subtraction of speckle patterns due to tandem nanosecond pulses. Here we present a theoretical framework for ideal (polarized, noise-free) speckle patterns with unity contrast that links ultrasound-induced optical phase modulation, the fraction of light that is tagged by ultrasound, speckle contrast, mean square difference of speckle patterns and the contrast of the summation of speckle patterns acquired at different ultrasound phases. We derive the important relations from basic assumptions and definitions, and then validate them with simulations. For ultrasound-generated phase modulation angles below 0.7 rad (assuming uniform modulation), we are now able to relate speckle pattern statistics to the acousto-optic phase modulation. Hence our theory allows quantifying speckle observations in terms of ultrasonically tagged fractions of light for near-unity-contrast speckle pattern

Solving the speckle decorrelation challenge in acousto-optic sensing using tandem nanosecond pulses within the ultrasound period

We present a novel acousto-optic (AO) method, based on a nanosecond laser system, which will enable us to obtain AO signals in liquid turbid media. By diverting part of the light in a delay line, we inject tandem pulses with 27 ns separation. The change of the speckle pattern, caused by the ultrasound phase shift, reduces the speckle contrast of the integrated speckle pattern captured in a single camera frame. With these tandem pulses, we were able to perform AO on a 2 cm liquid turbid medium in transmission mode. We show the raw signal and a spatial AO scan of a homogenous water-intralipid sample. This approach is potentially capable of AO probing in vivo, since the acquisition time (of approximately 40 ns) is four orders of magnitude less than the typical time scales of speckle decorrelation found in vivo. The method may eventually enable us to obtain fluence compensated photoacoustic signals generated by the same lase

Towards acousto-optic tissue imaging with nanosecond laser pulses

We present a way to generate acousto-optical signals in timovssue-like media with nanosecond laser pulses. Our method is based on recording and analyzing speckle patterns formed by interaction of nanosecond laser pulses with tissue, without and with simultaneous application of ultrasound. Stroboscopic application allows visualizing the temporal behavior of speckles while the ultrasound is propagating through the medium. We investigate two ways of quantifying the acousto-optic effect, viz. adding and subtracting speckle patterns obtained at various ultrasound phases. Both methods are compared with the existing speckle contrast method using a 2D scan and are found to perform similarly. Our method gives outlook on overcoming the speckle decorrelation problem in acousto-optics, and therefore brings in-vivo acousto-optic measurements one step closer. Furthermore it enables combining acousto-optics and photoacoustics in one setup with a single laser

Platelet Membrane and Calcium Control Abnormalities in Essential Hypertension

The mechanisms whereby intracellular calcium concentration is controlled are briefly reviewed. With the current knowledge of both calcium homeostasis and the function and properties of cellular Ca2+-target proteins / signal transduction systems, a dysfunction of cellular calcium metabolism is considered in relation to the pathogenesis of hypertension. Although the enhanced peripheral vascular resistance characteristic of hypertension is ultimately a function of Ca2+ availability for smooth muscle cell contraction, the platelet possesses many parallel biochemical and physiologic properties. Therefore, we have utilized the platelet as the cell model for investigating the role of Ca2+ in hypertension disorders. An overview of Ca2+-linked platelet processes altered in essential hypertension is presented, and an attempt is made to integrate these multiple aberrations in a fundamental membrane lesion. Am J Hypertens 1:42-46, 198

T-cadherin upregulation correlates with cell-cycle progression and promotes proliferation of vascular cells

Objective: In vascular tissue, T-cadherin (T-cad) levels correlate with the progression of atherosclerosis, restenosis and tumour neovascularization. This study investigates whether T-cad influences proliferation of vascular cells. Methods and Results: Cultures of human umbilical vein endothelial cells (HUVEC) and rat and human aortic smooth muscle cells (rSMC, hSMC) were used. T-cad was overexpressed in HUVEC and hSMC using an adenoviral expression system. In cultures released from G1/G0 synchrony parallel immunoblot analysis of T-cad and cell cycle phase specific markers (p27Kip1, cyclin D1, E2F1, PCNA, cyclin B) showed increased T-cad protein levels subsequent to entry into early S-phase with sustained elevation through S-and M-phases. T-cad was increased in G2/M-phase (colchicine) synchronized cultures. In FACS-sorted cell populations, expression of T-cad in S-and G2/M-phase was higher than G1/G0-phase. Compared with empty-and LacZ-vector infected controls, HUVEC and hSMC overexpressing T-cad exhibited increased proliferation as assessed in enumeration and DNA synthesis assays. Additionally, following release from G1/G0 synchrony, HUVEC and hSMC overexpressing T-cad enter S-phase more rapidly. Flow cytometry after BrdU/propidium labelling confirmed increased cell cycle progression in T-cad overexpressing cells. Conclusion: In vascular cells, T-cad is dynamically regulated during the cell cycle and its expression functions in the promotion of proliferation. T-cad may facilitate progression of proliferative vascular disorders such as atherosclerosis, restenosis and tumour angiogenesi

Polarisation of T-cadherin to the leading edge of migrating vascular cells in vitro: a function in vascular cell motility?

Both histological and in vitro studies indicate a relationship between T-cadherin levels and acquisition of a modulated, migratory phenotype by vascular cells. This study further examines a role for T-cadherin in relation to cell migration and adhesion. Fluorescence microscopic examination of T-cadherin localisation in confluent cultures of human umbilical vein endothelial cells (HUVEC), human aortic smooth muscle cells and the human carcinoma cell line ECV-304 revealed global distribution over the entire cell body, and with only slight enrichment at cell borders. This contrasts with restricted cell-cell junction localisation of classical cadherin (for example, VE-cadherin in HUVEC). In wounded cultures, T-cadherin polarised to the leading edge of cells migrating into the wound area, again contrasting with classical VE-cadherin, which was undetectable in this region. Confocal microscopy demonstrated that potential signalling functions of T-cadherin at the leading edge are unrelated to physical interactions with caveolin. Adherence of HUVEC onto a monolayer of T-cadherin-transfected L929 cells is significantly reduced compared with adhesion onto control (T-cadherin-negative) L929. Thus T-cadherin is not required for maintenance of intercellular adhesion, but may rather function as a signalling molecule involved in cell-cell recognition and sensing of the environment in processes where cell detachment occur

Passive element enriched photoacoustic computed tomography (PER PACT) for simultaneous imaging of acoustic propagation properties and light absorption\ud

We present a ‘hybrid’ imaging approach which can image both light absorption properties and acoustic transmission properties of an object in a two-dimensional slice using a computed tomography (CT) photoacoustic imager. The ultrasound transmission measurement method uses a strong optical absorber of small cross-section placed in the path of the light illuminating the sample. This absorber, which we call a passive element acts as a source of ultrasound. The interaction of ultrasound with the sample can be measured in transmission, using the same ultrasound detector used for photoacoustics. Such measurements are made at various angles around the sample in a CT approach. Images of the ultrasound propagation parameters, attenuation and speed of sound, can be reconstructed by inversion of a measurement model. We validate the method on specially designed phantoms and biological specimens. The obtained images are quantitative in terms of the shape, size, location, and acoustic properties of the examined heterogeneitie

Angiotensin-Induced Growth Related Metabolism Is Activated in Cultured Smooth Muscle Cells From Spontaneously Hypertensive Rats and Wistar-Kyoto Rats

Smooth muscle cells from spontaneously hypertensive rats (SHR) proliferate in culture faster than those isolated from sex- and age-matched Wistar- Kyoto (WKY) animals. There was no difference in the kinetics of S6 kinase activation in the two cultures, but later metabolic events associated with proliferation were stimulated earlier in SHR cells than in WKY, eg, activation of ornithine decarboxylase. Both cell types elaborated an extensive extracellular matrix in culture composed of a different blend of connective tissue macromolecules. Matrix material from SHR cells was more stimulatory to growth of WKY cultures than their own matrices. Angiotensin stimulated the growth and synthesis of extra-cellular matrix material in SHR more than in WKY derived vascular smooth muscle cell cul-tures. Am J Hypertens 1991;4:183-18