High frequency ultrasound tissue characterization and acoustic microscopy of intracellular changes.

The objective of this work is to investigate changes in the acoustic properties of cells when exposed to chemotherapy for monitoring treatment response. High frequency ultrasound spectroscopy (10-60 MHz) and scanning acoustic microscopy (0.9 GHz) were performed on HeLa cells (Ackermann et al. 1954, Masters 2002) that were exposed to the chemotherapeutic agent cisplatin. Ultrasonic radio-frequency data were acquired from pellets containing HeLa cells after exposure to cisplatin to induce apoptosis. Scanning acoustic and laser fluorescence microscopy images were recorded from single HeLa cells exposed to the same drug. Data acquisition in both cases was performed at several time points throughout the chemotherapeutic treatment for up to 27 h. In the high frequency ultrasound investigation, normalized power spectra were calculated within a region-of-interest. A 20 MHz transducer (f-number 2.35) and a 40 MHz transducer (f-number 3) were used for the data collection in the high frequency ultrasound experiments. The backscatter coefficients, integrated backscatter coefficients, mid-band fit and spectral slope were computed as a function of treatment time to monitor acoustical property changes during apoptosis. Acoustic attenuation was measured using the spectral substitution technique at all time points. Spectral parameter changes were detected after 12 h of exposure and coincided with the initiation of cell damage as assessed by optical microscopy. Integrated backscatter coefficients increased by over 100% between 0 h and 24 h of treatment, with small changes in the associated attenuation ( approximately 0.1 dB/[MHz cm]). Acoustic microscopy was performed at 0.9 GHz frequency. The cell structure was imaged using staining in laser fluorescence microscopy. All cells showed excellent correspondence between the locations of apoptotic nuclear condensation observed in optical imaging and changes in attenuation contrast in acoustic microscopy images. The time after drug exposure at which such changes occurred in the optical images were coincident with the time of changes detected in the acoustic microscopy images and the high frequency ultrasound experiments.

In-vivo observation of cells with a combined high-resolution multiphoton-acoustic scanning microscope.

We present a combined multiphoton-acoustic microscope giving collocated access to the local morphological as well as mechanical properties of living cells. Both methods relay on intrinsic contrast mechanisms and dispense with the need of staining. In the acoustic part of the microscope, a gigahertz ultrasound wave is generated by an acoustic lens and the reflected sound energy is detected by the identical lens in a confocal setup. The achieved lateral resolution is in the range of 1 mum. Contrast in the images arises mainly from the local absorption of sound in the cells related to viscose damping. Additionally, acoustic microscopy can access the sound speed as well as the acoustic impedance of the cell membrane and the cell shape, as it is an intrinsic volume scanning technique. The multiphoton image formation bases on the detection of autofluorescence due to endogenous fluorophores. The nonlinearity of two-photon absorption provides submicron lateral and axial resolution without the need of confocal optical detection. In addition, in the near-IR cell damages are drastically reduced in comparison with direct excitation in the visible or UV. The presented setup was aligned with a dedicated procedure to ensure identical image areas. Combined multiphoton/acoustic images of living myoblast cells are discussed focusing on the reliability of the method.

Imaging of focal contacts of chicken heart muscle cells by high-frequency acoustic microscopy.

A study of the adhesion of embryonic chicken heart muscle cells was conducted with a newly developed time-resolved acoustic microscope, which operates in the GHz-frequency range. The interpretation of the acoustical images of the heart muscle cells was done in combination with the fluorescence optical microscopy. A comparison between the acoustical images of chicken heart muscle cells and optical images of the same cells after staining showed that the actin fibers end inside the dark streaks in the acoustical images and thus represent the focal contacts (FCs). For cell biology applications, this demonstrates (a) the use of SAM as a tool for studying the dynamics of the FCs of living cells without any chemical staining and (b) that the combination of acoustic and optical microscopes allows interpretation of the acoustical images by using the wide variety of techniques available in optical microscopy.

Mechanical properties of single cells by high-frequency time-resolved acoustic microscopy.

In this paper, we describe a new, high-frequency, time-resolved scanning acoustic microscope developed for studying dynamical processes in biological cells. The new acoustic microscope operates in a time-resolved mode. The center frequency is 0.86 GHz, and the pulse duration is 5 ns. With such a short pulse, layers thicker than 3 microm can be resolved. For a cell thicker than 3 microm, the front echo and the echo from the substrate can be distinguished in the signal. Positions of the first and second pulses are used to determine the local impedance of the cell modeled as a thin liquid layer that has spatial variations in its elastic properties. The low signal-to-noise ratio in the acoustical images is increased for image generation by averaging the detected radio frequency signal over 10 measurements at each scanning point. In conducting quantitative measurements of the acoustic parameters of cells, the signal can be averaged over 2000 measurements. This approach enables us to measure acoustical properties of a single HeLa cell in vivo and to derive elastic parameters of subcellular structures. The value of the sound velocity inside the cell (1534.5 +/- 33.6 m/s) appears to be only slightly higher than that of the cell medium (1501 m/s).

Enhanced drug targeting by attachment of an anti alphav integrin antibody to doxorubicin loaded human serum albumin nanoparticles.

Specific transport of anti-cancer drugs into tumor cells may result in increased therapeutic efficacy and decreased adverse events. Expression of alphavbeta3 integrin is enhanced in various types of cancer and monoclonal antibodies (mAbs) directed against alphavbeta3 integrins hold promise for anti-cancer therapy. DI17E6 is a monoclonal antibody directed against alphav integrins that inhibits growth of melanomas in vitro and in vivo and inhibits angiogenesis due to interference with alphavbeta3 integrins. Here, DI17E6 was covalently coupled to human serum albumin nanoparticles. Resulting nanoparticles specifically targeted alphavbeta3 integrin positive melanoma cells. Moreover, doxorubicin loaded DI17E6 nanoparticles showed increased cytotoxic activity in alphavbeta3-positive melanoma cells than the free drug. Therefore, DI17E6-coupled human serum albumin nanoparticles represent a potential delivery system for targeted drug transport into alphavbeta3-positive cells.

High frequency optoacoustic microscopy.

Photoacoustic imaging--also called optoacoustic imaging--is a new hybrid modality of high tissue contrast which is based on the varying optical properties of tissue. The acoustic signal generated by pulsed laser absorption reports tissue-specific information with high spatial resolution. To increase the intrinsic contrast in tissue, absorbing particles are of great interest for optical imaging because of their considerable capacity to absorb and scatter light at visible and near-infrared wavelengths. The aim of the work presented here is to establish a scalable photoacoustic technology for volume imaging of biological samples down to diffraction limited microscopy. For this purpose a versatile photoacoustic microscopy platform has been developed with unmatched spatial resolution consisting of a microchip laser and a measurement cell with different transducers attached allowing generation and detection of laser-induced ultrasound signals in a frequency range up to 400 MHz. The performance of a versatile photoacoustic microscopy platform was evaluated via 2D optoacoustic images of light absorbing microparticles (5 microm Fe(3)0(4) and 1 micromblack toner particles) embedded in a polystyrene matrix. High frequency signals in the frequency range of 400 MHz generated by a single 1 microm particle could be recorded with a high signal to noise ratio (SNR) of 34 dB.

Subunits alpha, beta and gamma of the epithelial Na+ channel (ENaC) are functionally related to the hypertonicity-induced cation channel (HICC) in rat hepatocytes.

Specific small interfering RNA (siRNA) constructs were used to test for the functional relation of subunits alpha, beta, and gamma of the epithelial Na(+) channel (ENaC) to the hypertonicity-induced cation channel (HICC) in confluent rat hepatocytes. In current-clamp recordings, hypertonic stress (300 --> 400 mosM) increased membrane conductance from 75.4 +/- 9.4 to 91.1 +/- 11.2 pS (p < 0.001). The effect was completely blocked by 100 microM amiloride and reduced to 46, 30, and 45% of the control value by anti-alpha-, anti-beta-, and anti-gamma-rENaC siRNA, respectively. Scanning acoustic microscopy revealed an initial shrinkage of cells from 6.98 +/- 0.45 to 6.03 +/- 0.43 pl within 2 min. This passive response was then followed by a regulatory volume increase (RVI) by 0.42 +/- 0.05 pl (p < 0.001). With anti-alpha-, anti-beta-, and anti-gamma-rENaC siRNA, the volume response was reduced to 31, 31, and 36% of the reference level, respectively. It is concluded that all three subunits of the ENaC are functionally related to RVI and HICC activation in rat hepatocytes.