Laser speckle imaging complements other blood flow measurement techniques, such as laser Doppler flowmetry and magnetic resonance imaging and allows to measure local blood flow distribution with a relatively high spatial-temporal resolution and does so without the need for emission scanning. Laser speckle imaging instrumentation can also be made radically low-cost, allowing for wide educational or mobile applications. Speckle is an interference pattern produced by coherent (laser) light scattering on a rough surface. The intensity of speckle patterns fluctuates if the illuminated object contains individual moving scatterers such as blood cells. These fluctuations blur the speckles, leading to a reduction of the local speckle contrast, with the contrast value inversely proportional to the flow speed. These principles form the basis of laser speckle flowmetry.

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Current projects

The evaluation of coherence between many nephrons

In collaboration with Niels-Henrik Holstein-Rathlou and Donald Marsh

Full-field laser speckle microscopy provides real-time imaging of superficial blood flow rate. Here we apply continuous wavelet transform to time series of speckle-estimated blood flow from each pixel of the images to map synchronous patterns in instantaneous frequency and phase on the surface of rat kidneys. The regulatory mechanism in the renal microcirculation generates oscillations in arterial blood flow at several characteristic frequencies. Our approach to laser speckle image processing allows detection of frequency and phase entrainments, visualization of their patterns, and estimation of the extent of synchronization in renal cortex dynamics.

Kidney speckle We are able to observe substantial areas of locally synchronized tubuloglomerulus oscillations on the surface of the rat kidney.

The evaluation of changes in blood flow in retinal vascular networks

In collaboration with Jens Christian Brings Jacobsen

Laser speckle contrast imaging (LSCI) offers a cost effective means to image blood flow in vivo. Our study demonstrates the feasibility of performing LSCI via an endoscope to generate images of blood flow in the rat retina. Because rodents are common animal models for human retinal diseases, this approach may prove useful information about retinal disease pathophysiology at hypertension and diabetes.

Speckle contrast imaging of relative blood flow in the rat retina. The brighter areas indicate greater blood velocity.

The evaluation of blood flow in brain vascular networks

In collaboration with Martin Lauritzen

We build a high resolution laser full-field speckle-imaging set-up for monitoring of changes in blood microcirculation in the brain cortex of rats under the conditions of developing stroke and administration of vasodilating and vasoconstrictive agents. The studies aim to optimize conditions of speckle-image formation and to detect minor flow changes.

Brain Speckle Speckle contrast imaging of relative blood flow in the rat brain. The blood flow in vessels of different diameter are clearly depictured.