Dr. Robert M. Lemor Profile

Dr. Robert M. Lemor

at Ctr de Recherche Public Henri Tudor

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Proceedings Article | 25 February 2010 Paper

Gigahertz optoacoustic imaging for cellular imaging

Min Rui, Sankar Narashimhan, Wolfgang Bost, Frank Stracke, Eike Weiss, Robert Lemor, Michael Kolios

Proceedings Volume 7564, 756411 (2010) https://doi.org/10.1117/12.841479

KEYWORDS: Signal detection, Photoacoustic spectroscopy, Transducers, Ultrasonography, Blood, Particles, Signal to noise ratio, Pulsed laser operation, Acoustics, Microscopy

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Photoacoustic imaging exploits contrast mechanisms that depend on optical and thermomechanical properties of optical absorbers. The photoacoustic signal bandwidth is dictated by the absorber size and the laser pulse width. In this work we demonstrate that photoacoustic signals can be detected from micron and sub-micron particles. We anticipate applications to include cellular imaging with nanometer sized contrast agents such as gold nanoshells, nanorods, and nanocages. An existing acoustic microscopy system was used (the SASAM 1000, kibero GmbH). This platform is developed on an Olympus IX81 optical microscope with a rotating column that has an optical condenser for transmission optical microscopy and an acoustic module for the acoustic microscopy. The adapted optoacoustic module consists of a Qswitched Nd:YAG solid-state-laser (Teem Photonics, France) generating sub-nanosecond pulses. Scans were acquired of microparticles (1 μm black Toner particles) and cells. The confocal arrangement allowed high signal to noise ratio photoacoustic signals (>30 dB) to be detected at approximately 400 MHz. The particles of various sizes produced signals of different frequency content. In imaging mode, the full width half maximum (FWHM) was measured to be 3.6 μm for the 400 MHz transducer which is in general agreement theory for a 0.3 NA objective (4.3μm). Moreover, images are generated from single melanoma cells, generated by the endogenous contrast from the intracellular melanin.

Proceedings Article | 13 February 2007 Paper

Imaging living cells with a combined high-resolution multi-photon-acoustic microscope

Selma Schenkl, Eike Weiss, Martin Stark, Frank Stracke, Iris Riemann, Robert Lemor, Karsten König

Proceedings Volume 6437, 64372A (2007) https://doi.org/10.1117/12.702391

KEYWORDS: Acoustics, Microscopes, Ultrasonography, Luminescence, Microscopy, Sapphire, Imaging systems, Absorption, Image resolution, In vivo imaging

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With increasing demand for in-vivo observation of living cells, microscope techniques that do not need staining become more and more important. In this talk we present a combined multi-photon-acoustic microscope with the possibility to measure synchronously properties addressed by ultrasound and two-photon fluorescence. Ultrasound probes the local mechanical properties of a cell, while the high resolution image of the two-photon fluorescence delivers insight in cell morphology and activity. In the acoustic part of the microscope an ultrasound wave, with a frequency of GHz, is focused by an acoustic sapphire lens and detected by a piezo electric transducer assembled to the lens. The achieved lateral resolution is in the range of 1&mgr;m. Contrast in the images arises mainly from the local absorption of sound in the cells, related to properties, such as mass density, stiffness and viscose damping. Additionally acoustic microscopy can access the cell shape and the state of the cell membrane as it is a intrinsic volume scanning technique.The optical part bases on the emission of fluorescent biomolecules naturally present in cells (e.g. NAD(P)H, protophorphyrin IX, lipofuscin, melanin). The nonlinear effect of two-photon absorption provides a high lateral and axial resolution without the need of confocal detection. In addition, in the near-IR cell damages are drastically reduced in comparison to direct excitation in the visible or UV. Both methods can be considered as minimal invasive, as they relay on intrinsic contrast mechanisms and dispense with the need of staining. First results on living cells are presented and discussed.

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