Finn Pedersen

Speckle reduction in optical coherence tomography images of human skin by a spatial diversity method

A range of compounding techniques have been suggested for dealing with the signal degrading speckle noise in optical coherence tomography (OCT). Recent implementations of angular compounding have shown great promise, but some of the implementations require substantial modifications of the OCT system. Here, we consider a method that in principle can be fitted to most OCT systems without major modifications. Specifically, we address a spatial diversity technique for suppressing speckle noise in OCT images of human skin. The method is a variant of changing the position of the sample relative to the measuring probe. Instead of physically moving the sample, which is often not feasible for in vivo imaging, the position of the focal plane of the probe beam is shifted. If the numerical aperture is sufficiently high this spatial diversity scheme incorporates a variant of angular compounding. We have tested the scheme with a mobile fiber-based time-domain real-time OCT system. Essential enhancement was obtained in image contrast when performing in vivo imaging of normal skin and lesions. Resulting images show improved delineation of structure in correspondence with the observed improvements in contrast-to-noise ratios.

Field programmable gate-array-based real-time optical Doppler tomography system for in vivo imaging of cardiac dynamics in the chick embryo

We demonstrate a field programmable gate- array-based real-time optical Doppler tomography system. A complex-valued bandpass filter is used for the first time in optical coherence tomography signal processing to create the analytic signal. This method simplifies the filter design, and allows efficient and compact implementation by combin- ing the conversion to an analytic signal with a pulse shaping function without the need for extra resources as compared to the Hilbert transform method. The conversion of the analytic signal to amplitude and phase is done by use of the coordi- nate rotation digital computer CORDIC algorithm, which is an efficient algorithm that maps well to the field program- mable gate array. Flow phantom experiments, and the use of this system for in vivo imaging of cardiac dynamics in the chick embryo, are presented. We demonstrate the visualiza- tion of blood flow in the early embryonic heart as well as in the aorta, small peripheric vitelline vessels, and coronary ar- teries of fully formed chick hearts.

Development of a compact bio-optofluidic cell sorter

We develop an active cell sorter that utilizes machine vision for cell identification. Particles are identified based on visual features such as shape, size and color using image processing. The sorter shares features from our previously developed BioPhotonics Workstation. Hence, it benefits from the extended axial manipulation range provided by the low numerical aperture geometry. Detected particles are catapulted axially by several hundred microns, allowing them to be moved from one laminar flow region to another. As the sorting motion is transverse to the viewing plane, multiple particles can be catapulted at the same time, therefore enabling parallel sorting. The sorter is developed with a minimal footprint such that it can operate as a table top device, an advantage over flow cytometry or FACS systems.

Optical coherence tomography in clinical examination of non-pigmented skin malignancies

Optical coherence tomography (OCT) images of basal cell carcinomas (BCCs) have been acquired using a compact handheld probe with an integrated video camera allowing the OCT images to be correlated to a skin surface image. In general the healthy tissue of the skin has an obvious stratified structure, whereas the cancerous tissue shows a more homogenous structure. Thus it was demonstrated that it is possible to distinguish BCCs from healthy tissue by means of OCT. Furthermore different histological types of BCC were identified. Comparison of OCT images taken prior to and immediately after photodynamic therapy clearly shows the tissue response to the treatment, and indicates local oedema in the treated area.

Optical Doppler tomography based on a field programmable gate array

Abstract We report the design of and results obtained by using a field programmable gate array (FPGA) to digitally process optical Doppler tomography signals. The processor fits into the analog signal path in an existing optical coherence tomography setup. We demonstrate both Doppler frequency and envelope extraction using the Hilbert transform, all in a single FPGA. An FPGA implementation has certain advantages over general purpose digital signal processor (DSP) due to the fact that the processing elements operate in parallel as opposed to the DSP, which is primarily a sequential processor.

Optical coherence tomography in clinical examinations of nonpigmented skin malignancies

Optical coherence tomography (OCT) images of basal cell carcinomas (BCCs) have been acquired using a compact handheld proble with an integrated video camera allowing the OCT images to be correlated to a skin surface image. In general the healthy tissue of the skin has an obvious stratified structure, whereas the cancerous tissue shows a more homogeneous structure. Thus it was demonstrated that it is possible to distinguish BCCs from healthy tissue by means of OCT. Furthermore different histological types of BCC were identified. Comparison of OCT images taken prior to and immediately after photodynamic theory clearly shows the tissue response to the treatment, and indicates local oedema in the treated area.

Optical Doppler tomography for monitoring vascularization during photodynamic therapy of skin cancer lesions

We investigate vascular changes during Photodynamic therapy (PDT) of skin tumors using optical Doppler tomography (ODT). The effect of vascular shut down on tumor destruction is currently not known, and to optimize treatment it is relevant to investigate this issue further. Optical Doppler tomography is capable of measuring blood flow in biological tissue down to 1-2 mm with sub-mm/s velocity sensitivity and micrometer spatial resolution making it suitable for blood flow measurements in the skin. We demonstrate the ability of detecting blood flow in the human skin using non-interstitial ODT to preserve the non-invasiveness. In general a very limited blood flow activity was observed in normal skin and around skin tumors making monitoring of changes difficult. We suggest solutions to a number of practical issues such as sampling errors and natural fluctuations in flow activity for future work.

Optical Doppler coherence tomography based on a field-programmable gate array

We report the design of and results obtained by using a Field Programmable Gate Array (FPGA) to digitally process Optical Doppler Tomography signals. The processor fits into the analog signal path in an existing OCT setup. We demonstrate both Doppler frequency and envelope extraction using the Hilbert transform, all in a single FPGA. An FPGA implementation has certain advantages over a general purpose Digital Signal Processor (DSP) due to the fact that the processing elements operate in parallel as opposed to the DSP, which is primarily a sequential processor. In this paper, we demonstrate that the use of a FPGA enables sampling rates exceeding DSP-based solutions. In addition, this implementation has the important feature that calculation of the phase in addition to the amplitude of the interference fringe pattern only requires few additional resources. The proposed implementation of Doppler frequency extraction in a single FPGA is feasible for real-time Doppler OCT applications requiring high signal sampling rates.