When laser light illuminates a diffuse object, it produces a random interference effect known as a speckle pattern. If there is movement in the object, the speckles fluctuate in intensity. These fluctuations can provide information about the movement. A simple way of accessing this information is to image the speckle pattern with an exposure time longer than the shortest speckle fluctuation time scale—the fluctuations cause a blurring of the speckle, leading to a reduction in the local speckle contrast. Thus, velocity distributions are coded as speckle contrast variations. The same information can be obtained by using the Doppler effect, but producing a two-dimensional Doppler map requires either scanning of the laser beam or imaging with a high-speed camera: laser speckle contrast imaging (LSCI) avoids the need to scan and can be performed with a normal CCD- or CMOS-camera. LSCI is used primarily to map flow systems, especially blood flow. The development of LSCI is reviewed and its limitations and problems are investigated.

Perfusion is an indicator for tissue viability, and several laser-based optical imaging modalities to assess this have been developed. Medical users want a noncontact, fast, simple, and cheap modality.¹ Laser speckle contrast imaging (LSCI) is a fast, full-field, cheap, and relatively simple imaging method that can give 2-D perfusion maps of large surfaces.² LSCI is based on the principle that the backscattered light from a tissue that is illuminated with coherent laser light forms a random interference pattern at the detector, the so-called speckle pattern. Movement of particles inside the tissue causes fluctuations in this speckle pattern resulting in blurring of speckle images when obtained with an exposure time equal to or longer than the speckle fluctuation time scale. This blurring can be related to blood flow if the fluctuations are caused by the movement of red blood cells (RBCs). Starting out as a slow analogue research tool, LSCI systems can now image blood flow in (near) real-time as a result of the rapid increase in cheap computing power. This empowers the translation of LSCI into clinical practice where it is well suited for the assessment of perfusion in a wide range of tissues. LSCI has been applied to image burn wounds, retinal perfusion, cerebral blood flow (CBF), skin microvasculature, liver, esophagus, and the large intestine. Despite the vast amount of research on LSCI, few applications are commonly applied in clinical practice. This review serves as an introductory overview of current clinical applications of LSCI for medical specialists.

Ultrasound and photoacoustics can be utilized as complementary imaging techniques to improve clinical diagnoses. Photoacoustics provides optical contrast and functional information while ultrasound provides structural and anatomical information. As of yet, photoacoustic imaging uses large and expensive systems, which limits their clinical application and makes the combination costly and impracticable. In this work we present and evaluate a compact and ergonomically designed handheld probe, connected to a portable ultrasound system for inexpensive, real-time dual-modality ultrasound/photoacoustic imaging. The probe integrates an ultrasound transducer array and a highly efficient diode stack laser emitting 130 ns pulses at 805 nm wavelength and a pulse energy of 0.56 mJ, with a high pulse repetition frequency of up to 10 kHz. The diodes are driven by a customized laser driver, which can be triggered externally with a high temporal stability necessary to synchronize the ultrasound detection and laser pulsing. The emitted beam is collimated with cylindrical micro-lenses and shaped using a diffractive optical element, delivering a homogenized rectangular light intensity distribution. The system performance was tested in vitro and in vivo by imaging a human finger joint.

A real-time photoacoustic imaging system is designed and built. This system is based on a commercially available ultrasound imaging system. It can achieve a frame rate of $8frames∕sec$. Vasculature in the hand of a human volunteer is imaged, and the resulting photoacoustic image is combined with the ultrasound image. The real-time photo acoustic imaging system with a hybrid ultrasound probe is demonstrated by imaging the branching of subcutaneous blood vessels in the hand.

Room for improvement in the current practice of breast cancer screening and diagnosis, and the fact that breast cancer is an enormous burden on society, have been the stimuli for relentless efforts on two fronts. On the one, the current state of the art in detection and diagnosis, using x-rays, ultrasound, and magnetic resonance, is being pushed forward. On the second front, there is a quest for new modalities that can address the limitations and drawbacks of the current technologies.

We introduce a needle probe based on photoacoustics (PA) to extend the scope of optical needle methods in guiding biopsies. Pulsed light is coupled to an optical fiber in a needle to be inserted in tissue, and PA signals are detected using an ultrasound imager used for needle guidance. This PA needle samples large volumes and possesses an imaging component so that sites forward and off-axis of the fiber are surveyed. This allows navigation of those regions for optical characterization and direct biopsy in a subsequent step. The concept is explored on simple phantoms and biological specimens.