High speed perfusion imaging based on laser speckle fluctuations

Noninvasive methods to visualize blood flow in tissue are important in the clinical environment. Most methods use dynamic speckles to measure the level of perfusion. The most well-known techniques based on these speckle patterns are laser Doppler perfusion imaging (LDPI) and laser speckle contrast analysis (LASCA). For LASCA measurements an inexpensive camera which can achieve a frame-rate of 200 Hz is sufficient, whereas for LDPI, only a state-of-the-art high-speed camera which can achieve a frame-rate of about 25 kHz is suitable.\ud \ud A review of laser speckle contrast techniques so far, and a comparison of these techniques on the hand of a volunteer is given in chapter 2. In chapter 3 the Twente Optical Perfusion Camera (TOPCam), an imaging system based on high-speed CMOS technology is presented. The TOPCam was used to evaluate the capability and efficacy of the TOPCam to measure perfusion differences in burn wounds. In chapter 4 these first clinical results of the TOPCam in the setting of a burn centre are presented. In chapter 5, a Time Domain (TD) algorithm is presented for determining the first order spectral moment. This algorithm involves multiplications of an image with the difference between two subsequent images. The issue of the relation between the competing methods of laser Doppler perfusion imaging and laser speckle contrast methods is addressed in chapter 6. A theory is developed which expresses the contrast in time integrated dynamic speckle patterns in terms of the power spectral density of their local temporal intensity fluctuations

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

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