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Alzheimer’s disease (AD) is the most common form of dementia, which is one of the main death leading causes with around 46 million people affected worldwide. Alzheimer’s disease is characterized by the accumulation of extracellular deposits of proteins in the brain, known as amyloid-beta (Aß) plaques. Currently, in-vivo detection of Aß pathology is solely possible by two invasive techniques: the analysis of cerebral fluid or PET imaging. Raman spectroscopy may be an alternative way of in-vivo diagnosis of Aß deposits as it is sensitive to concentrations of bio-molecules. It is an established and common non-destructive technique, which in addition allows for minimal sample preparation. Recent publications on transgenic mouse and human AD brain tissue suggest that Raman spectroscopy is an adequate technique to identify and localize Aß plaques1,2. However, publications on human tissue lack the proof of plaque existence at the same location, imaged with Raman spectroscopy. The present study is designed to confirm ultimately a match between Raman spectra and possible amyloid-beta plaque locations. This is achieved by superimposing the autofluorescence image, the Raman imaging map and the stained fluorescence image of the same tissue section. Additionally, obtained data will be compared to previous studies of post mortem human AD brain tissue that was formalin fixed and paraffin embedded.

Extracellular vesicles (EVs) are nanoparticles secreted from cells into bodily fluids. EVs are potential biomarkers for diseases such as thrombosis or cancer. However, the small size and low refractive index of EVs complicates their detection. A flow cytometer is suited for EV characterisation, but typically lacks scatter sensitivity on one or both scatter detectors for derivation of both particle size and refractive index. Here, we aim to improve the FACSCanto (Becton Dickinson) forward scatter detector for the detection of 100 nm EVs, which requires an improvement in SNR of 107-fold based on Mie theory. This was achieved through replacement of the 20 mW laser by an 200 mW laser, replacement of the photodiode detector with a photomultiplier tube and a confocalized optical geometry. Using a prototype optical setup, we obtained an improvement in SNR which was 1,11·104 – fold better than the standard design. However, the optics was suboptimal and far from diffraction-limited. Zemax simulations led to a nearly diffraction limited optical design which is expected to yield another 200-fold improvement. Taken together these changes will improve the SNR 2.2·106-fold and thus improve the detection limit of the FACSCanto to 130 nm EVs.

Photoacoustic imaging is a relatively new medical imaging modality. In principle it can be used to image the optical absorption distribution of an object by measurements of optically induced acoustic signals. Recently we have developed a modified photoacoustic measurement system which can be used to simultaneously image the ultrasound propagation parameters as well. By proper placement of a passive element we obtain isolated measurements of the object's ultrasound propagation parameters, independent of the optical absorption inside the object. This passive element acts as a photoacoustic source and measurements are obtained by allowing the generated ultrasound signal to propagate through the object. Images of the ultrasound propagation parameters, being the attenuation and speed of sound, can then be reconstructed by inversion of a measurement model. This measurement model relates the projections non-linearly to the unknown images, due to ray refraction effects. After estimating the speed of sound and attenuation distribution, the optical absorption distribution is reconstructed. In this reconstruction problem we take into account the previously estimated speed of sound distribution. So far, the reconstruction algorithms have been tested using computer simulations. The method has been compared with existing algorithms and good results have been obtained.

Recently, various groups have developed wide field laser Doppler perfusion imaging systems based on high speed camera's. The limiting factor for the frame rate and measurement duration in whole field laser Doppler perfusion imaging is the speed of transfer and analysis of data. We present an algorithm for calculating perfusion estimations with much lower demands for data storage and computational effort than the conventional FFT-based method. Our algorithm works in the time domain and estimates perfusion through simple time differentiations and multiplications of speckle image values. The algorithm is partly based on mathematical reasoning, and partly on a hypothesis that cannot be proven with rigorous mathematics. We will compare our algorithm with the frequency-domain counterpart for phantom studies involving static and dynamic media, and in vivo experiments on human skin. It is found that both algorithms, applied on the same dataset, approximately give the same perfusion estimations. The random differences are similar to the random variations found in tissue perfusion. Systematic differences between the algorithms smaller than 15% are found. The algorithm is currently twice as fast as the FFT-counterpart. Another advantage is that our algorithm can be included in a moving average scheme, where a new perfusion value can be determined based on the previous value and a small number of new raw speckle images.

Plasmon resonant nanoparticles such as gold nanoshells and gold nanorods can be tuned to possess sharp interaction peaks in the near-infrared wavelength regions. These have great importance as contrast agents in photoacoustic imaging and as photothermal agents for therapeutic applications due to their high absorptions. While the optical properties of the particles are can be described using Mie theory and/or numerical methods such as the Discrete Dipole Approximation, discriminating between their optical absorption and scattering in experiments is not easy. In this paper we discuss for the first time a novel method based on a two-fiber spectrometer that allows measurement of the scattering and absorption coefficients of gold nanoparticles in solution. This technique, called Differential Path length Spectroscopy, has been developed earlier for measurement in highly diffusive media such as tissue. We demonstrate this concept on gold nanospheres and nanoshells of various sizes. We believe that this will develop into a fast and reliable method able to work on small samples (

A real-time photoacoustic imaging system was designed and built. This system is based on a commercially available ultrasound imaging system. It can achieve a frame rate of 8 frames/sec. This system has been characterized in phantom experiments. In addition, vasculature in the hand of a human volunteer was imaged

Rod shaped gold nanoparticles are synthesized using cetyltriammonium bromide (CTAB) as a major component of growth solutions. This surfactant is toxic to cells, but is at the moment unavoidable when monodisperse and high yield nanorods are to be synthesized. CTAB is found coating side walls of the nanoparticles and plays a role in maintaining colloidal stability. It may be displaced using thiolated PEG which is non-toxic to cells. Here we report on systematic studies of cell viability of such PEGylated nanorods on an SKBR3 cell-line using the MTS assay. These PEGylated particles are characterized using electron microscopy, optical spectroscopy and zeta potential measurements. It is expected that such treatment will be crucial in making nanorods compatible for in vivo biomedical applications

We present a 'hybrid' imaging system, which can image both optical absorption properties and acoustic transmission properties of an object in a two-dimensional slice using a computed tomography photoacoustic imager. The ultrasound transmission measurement method uses a strong absorber of light which is placed in the path of the light illuminating the sample. This acts as a source of ultrasound, whose interaction with the sample can be measured at the far-end of the sample using the same ultrasound detector used for photoacoustics. Such measurements are made at various angles around the sample in a computerized tomography approach. The ultrasound transients at the multi-element detector at all projections are analyzed for both times-of-arrival and amplitude. Using a fan-beam projection reconstruction algorithm we obtain hybrid images of optical absorption, speed-of-sound and acoustic attenuation. We validate the method on an appropriate phantom

Photoacoustic imaging is an upcoming medical imaging modality with the potential of imaging both optical and acoustic properties of objects. We present a measurement system and outline reconstruction methods to image both speed of sound and acoustic attenuation distributions of an object using only pulsed light excitation. These acoustic properties can be used in a subsequent step to improve the image quality of the optical absorption distribution. A passive element, which is a high absorbing material with a small cross-section such as a carbon fiber, is introduced between the light beam and the object. This passive element acts as a photoacoustic source and measurements are obtained by allowing the generated acoustic signal to propagate through the object. From these measurements we can extract measures of line integrals over the acoustic property distribution for both the speed of sound and the acoustic attenuation. Reconstruction of the acoustic property distributions then comes down to the inversion of a linear system relating the obtained projection measurements to the acoustic property distributions. We show the results of applying our approach on phantom objects. Satisfactory results are obtained for both the reconstruction of speed of sound and the acoustic attenuation.

Gold nanoparticles exhibit intense and narrow optical extinction bands due to the phenomenon of plasmon resonance making them useful as contrast agents for light-based imaging techniques. Localized heating results from the absorbed light energy, which shows potential for these particles in photothermal therapy as well. The bioconjugation of gold nanoparticles to appropriate antibodies targeted to tumors in vivo, could make highly selective detection and therapy of tumors possible. We have synthesised gold nanorods based on seed mediated protocols using two methods. The first method is based on using a mono-surfactant silver assisted method which produces gold nanorods having plasmon peaks between 670-850 nm within the "optical imaging and therapeutic window". These nanorods have aspect ratios between 2.3 - 3.7. A second method is a silver assisted bi-surfactant method which produce nanorods with peaks in the range of 850-1100 nm having aspect ratios between 5 - 11. Typical concentrations of these particles in aqueous dispersions are in the range of 1x1010 - 1x1011 particles per mL. We have bioconjugated these gold nanorods with anti-HER2/neu mouse monoclonal antibodies (MAb). Since the as-prepared CTAB-stabilized nanorods were found to be toxic to SKBR3 cells, we decided to coat the gold nanorods with polyethylene glycol (PEG). Characterization and size estimation of the nanoparticles were performed using electron microscopies, optical spectroscopy and confocal microscopy. We present these results and implications for use of these nanoparticles for in vivo biomedical applications.

Background and Objective: To optimize laser therapy of port-wine stains (PWSs), information about the vasculature as well as lesion depth is valuable. In this study we investigated the use of photoacoustic imaging (PAI) to obtain this information. - Study Design/Materials and Methods: PAI uses pulsed light to generate ultrasound upon absorption of short light pulses by blood. In this study we used PAI to image vasculature in PWSs in three human volunteers. Two-dimensional imaging (scan direction vs. depth) was carried out by scanning a double-ring photoacoustic sensor over the tissue surface. - Results: In the photoacoustic images we observed an increased photoacoustic signal intensity at the locations of the PWS that is associated with increased vascularization. From the obtained images we measured the thickness of the vascular layer and estimated lesion depth. In some cases single vessels could be observed at the position of the PWS whereas in other cases the PWS appeared as a region with large photoacoustic signal intensity. - Conclusions: PAI has the potential to reveal information about the lesion depth as well as thickness of the vascular layer. Laser Surg. Med. 40:178-182, 2008.