Twente Optical Perfusion Camera: system overview and performance for video rate laser Doppler perfusion imaging

We present the Twente Optical Perfusion Camera (TOPCam), a novel laser Doppler Perfusion Imager based on CMOS technology. The tissue under investigation is illuminated and the resulting dynamic speckle pattern is recorded with a high speed CMOS camera. Based on an overall analysis of the signal-to-noise ratio of CMOS cameras, we have selected the camera which best fits our requirements. We applied a pixel-by-pixel noise correction to minimize the influence of noise in the perfusion images. We can achieve a frame rate of 0.2 fps for a perfusion image of 128×128 pixels (imaged tissue area of 7×7 cm2) if the data is analyzed online. If the analysis of the data is performed offline, we can achieve a frame rate of 26 fps for a duration of 3.9 seconds. By reducing the imaging size to 128×16 pixels, this frame rate can be achieved for up to half a minute. We show the fast imaging capabilities of the system in order of increasing perfusion frame rate. First the increase of skin perfusion after application of capsicum cream, and the perfusion during an occlusion-reperfusion procedure at the fastest frame rate allowed with online analysis is shown. With the highest frame rate allowed with offline analysis, the skin perfusion revealing the heart beat and the perfusion during an occlusion-reperfusion procedure is presented. Hence we have achieved video rate laser Doppler perfusion imaging

Photoacoustic guided ultrasound wavefront shaping for targeted acousto-optic imaging

To overcome speed of sound aberrations that negatively impact the acoustic focus in acousto-optic imaging, received photoacoustic signals are used to guide the formation of ultrasound wavefronts to compensate for acoustic inhomogeneities. Photoacoustic point sources composed of gold and superparamagnetic iron oxide nanoparticles are used to generate acoustic waves that acoustically probe the medium as they propagate to the detector. By utilizing cross-correlation techniques with the received photoacoustic signal, transmitted ultrasound wavefronts compensate for the aberration, allowing for optimized and configurable ultrasound transmission to targeted locations. It is demonstrated that utilizing a portable commercially available ultrasound system using customized software, photoacoustic guided ultrasound wavefront shaping for targeted acousto-optic imaging is robust in the presence of large, highly attenuating acoustic aberration

Time domain algorithm for accelerated determination of the first order moment of photo current fluctuations in high speed laser Doppler perfusion imaging

Advances in optical array sensor technology allow for the real time acquisition of dynamic laser speckle patterns generated by tissue perfusion, which, in principle, allows for real time laser Doppler perfusion imaging (LDPI). Exploitation of these developments is enhanced with the introduction of faster algorithms to transform photo currents into perfusion estimates using the first moment of the power spectrum. A time domain (TD) algorithm is presented for determining the first-order spectral moment. Experiments are performed to compare this algorithm with the widely used Fast Fourier Transform (FFT). This study shows that the TD-algorithm is twice as fast as the FFT-algorithm without loss of accuracy. Compared to FFT, the TD-algorithm is efficient in terms of processor time, memory usage and data transport

Review of laser speckle contrast techniques for visualizing tissue perfusion

When a diffuse object is illuminated with coherent laser light, the backscattered light will form an interference pattern on the detector. This pattern of bright and dark areas is called a speckle pattern. When there is movement in the object, the speckle pattern will change over time. Laser speckle contrast techniques use this change in speckle pattern to visualize tissue perfusion. We present and review the contribution of laser speckle contrast techniques to the field of perfusion visualization and discuss the development of the techniques

Towards quantitative photoacoustic tomography by acoustooptically measured light fluence

We present a method of measuring fluence using ultrasonic tagging of light in tomographic manner. Proof of concept experiments show that the combined photoacoustics and acousto optics in tomographic settings enable fluence compensated images