Serial noninvasive photoacoustic imaging of neovascularization in tumor angiogenesis.

We present photoacoustic images of tumor neovascularization obtained over a 10-day period after subcutaneous inoculation of pancreatic tumor cells in a rat. The images were obtained from ultrasound generated by absorption in hemoglobin of short laser pulses at a wavelength of 1064 nm. The ultrasound signals were measured in reflection mode using a single scanning piezodetector, and images were reconstructed with a weighted delay-and-sum algorithm. Three-dimensional data visualize the development and quantify the extent of individual blood vessels around the growing tumor, blood concentration changes inside the tumor and growth in depth of the neovascularized region.

Monitoring cerebral perfusion using near-infrared spectroscopy and laser Doppler flowmetry.

This paper describes the simultaneous use of two, noninvasive, near-infrared techniques near-infrared spectroscopy (NIRS) and a continuous wave NIR laser Doppler flow system (LDF) to measure changes in the blood oxygenation, blood concentration and blood flow velocity in the brain. A piglet was used as animal model. A controlled change in the arterial CO2 pressure (PaCO2) was applied for achieving changes in the listed cerebrovascular parameters. The time courses of blood concentration parameters (NIRS) and RMS blood flow velocity (LDF) were found to correspond closely with those of carotid blood flow and arterial carbon dioxide pressure (PaCO2). This result shows the additional value of LDF when combined with NIRS, preferably in one instrument. Development of pulsed LDF for regional blood flow measurement is indicated.

Instrument-independent flux units for laser Doppler perfusion monitoring assessed in a multi-device study on the renal cortex.

To investigate the feasibility of instrument-independent perfusion units for laser Doppler flowmetry, a comparison was performed of two commercial fiberoptic laser Doppler perfusion monitors measuring the same flux situation for two different types of probes. In vivo measurements were performed on the cortex of pig's kidney, with an ultrasonic arterial flow meter as reference. The flow was mainly varied by internal arterial constriction using a balloon catheter. For each probe, instruments are compared in terms of the ratio of laser Doppler flux and arterial flow. For a given probe, the flux-to-flow ratios of the two instruments show a linear mutual relationship for a wide variety of arterial flows and laser Doppler fluxes. In vitro measurements were performed on an aqueous suspension of polystyrene microspheres. For the probe with interfiber distance 500 microm the ratio of the in vivo fluxes appears to agree within 16% to the value found in vitro, while for the 250-microm probe a difference of 28% was found. For a wide range of fluxes, the in vivo flux values of one instrument can be translated into flux values for the other instrument, in spite of the instrumental differences. This enables the user to render experimental results independent of the specific instrument, thus facilitating multi-center studies.

Photoacoustic imaging of brain perfusion on albino rats by using evans blue as contrast agent.

The visualization of the brain vascular system could be of great importance for studying its functionality and for diagnosing possible disorders. In this paper we report the use of photoacoustics for imaging brain perfusion on Albino rats in vivo and post mortem. The measurements on the animals were direct on the skin surface. The blood perfusion on skull cartilage was imaged and 2D slices were constructed by using a beamforming algorithm. From the images representation the Interactive Data Language (IDL, Research System Inc.) was used. We also investigated the possibility of using the Evans Blue dye as a substitute of blood for imaging brain structures in vitro. The breakdown of the dye under pulsed laser irradiation was studied and the energy under which this effect occurs was calculated for the wavelength of 532 nm.