Ultrasonic tissue characterization of prostate biopsy tissues by ultrasound speed microscope

Acoustic characterization of contrast-to-tissue ratio and axial resolution for dual-frequency contrast-specific acoustic angiography imaging

Recently, dual-frequency transducers have enabled high-spatial-resolution and high-contrast imaging of vasculature with minimal tissue artifacts by transmitting at a low frequency and receiving broadband superharmonic echoes scattered by microbubble contrast agents. In this work, we examine the imaging parameters for optimizing contrast-to-tissue ratio (CTR) for dual-frequency imaging and the relationship with spatial resolution. Confocal piston transducers are used in a water bath setup to measure the SNR, CTR, and axial resolution for ultrasound imaging of nonlinear scattering of microbubble contrast agents when transmitting at a lower frequency (1.5 to 8 MHz) and receiving at a higher frequency (7.5 to 25 MHz). Parameters varied include the frequency and peak negative pressure of transmitted waves, center frequency of the receiving transducer, microbubble concentration, and microbubble size. CTR is maximized at the lowest transmission frequencies but would be acceptable for imaging in the 1.5 to 3.5 MHz range. At these frequencies, CTR is optimized when a receiving transducer with a center frequency of 10 MHz is used, with the maximum CTR of 25.5 dB occurring when transmitting at 1.5 MHz with a peak negative pressure of 1600 kPa and receiving with a center frequency of 10 MHz. Axial resolution is influenced more heavily by the receiving center frequency, with a weak decrease in measured pulse lengths associated with increasing transmit frequency. A microbubble population containing predominately 4-μm-diameter bubbles yielded the greatest CTR, followed by 1- and then 2-μm bubbles. Varying concentration showed little effect over the tested parameters. CTR dependence on transmit frequency and peak pressure were confirmed through in vivo imaging in two rodents. These findings may lead to improved imaging of vascular remodeling in superficial or luminal cancers such as those of the breast, prostate, and colon.

Ultrasound biomicroscopy (UBM) and scanning acoustic microscopy (SAM) for the assessment of hernia mesh integration: a comparison to standard histology in an experimental model

BACKGROUND

Mesh integration is a key parameter for reliable and safe hernia repair. So far, its assessment is based on histology obtained from rare second-look operations or experimental research. Therefore, non-invasive high-resolution imaging techniques would be of great value. Ultrasound biomicroscopy (UBM) and scanning acoustic microscopy (SAM) have shown potential in the imaging of hard and soft tissues. This experimental study compared the detection of mesh integration, foreign body reaction and scar formation in UBM/SAM with standard histology.

MATERIALS AND METHODS

Ten titanized polypropylene meshes were implanted in rats in a model of onlay repair. 17 days postoperative animals were killed and samples were paraffin embedded for histology (H&E, Cresyl violet) or processed for postmortem UBM/SAM. The observation period was uneventful and meshes appeared well integrated.

RESULTS

Relocation of neighboring cross-sectional levels could easily be achieved with the 40-MHz UBM and granulation tissue could be distinguished from adjacent muscle tissue layers. The spatial resolution of approximately 8 μm of the 200-MHz UBM system images was comparable to standard histology (2.5-5× magnification) and allowed a clear identification of mesh fibers and different tissue types, e.g., scar, fat, granulation, and muscle tissues, as well as vessels, abscedations, and foreign body giant cell clusters.

CONCLUSION

This pilot study demonstrates the potential of high-frequency ultrasound to assess hernia mesh integration non-invasively. Although the methods lack cell-specific information, tissue integration could reliably be assessed. The possibility of conducting UBM in vivo advocates this method as a guidance tool for the indication of second-look operations and subsequent elaborate histological analyses.

Echogenicity in transrectal ultrasound is determined by sound speed of prostate tissue components

Typically, conventional transrectal ultrasound (TRUS) imaging of the cancer tissue is hypoechoic in echo texture. However, TRUS does not reliably distinguish between cancerous and non-cancerous tissue in the prostate. In the present study, sound speed of prostate needle biopsy specimens were measured by ultrasound speed microscope (USM) to construct a database for interpreting clinical TRUS images. Biopsy specimens were formalin-fixed and sectioned approximately 5 µm in thickness. They were mounted on glass slides without cover slips. The ultrasonic transducer with the central frequency of 120 MHz was mechanically scanned over the specimen to measure sound speed distribution. Echo intensity of TRUS images were qualitatively classified into three categories; hyperechoic, iso-echoic and hypoechoic areas. Sound speed was 1596.9 ± 28.2 m/s in hyperechoic, 1571.2 ± 35.8 m/s in iso-echoic and 1562.6 ± 35.1 m/s in hypoechoic area, respectively. However, echo intensity showed no significant relationship to malignancy of prostatic tissue. Echo intensity of TRUS is significantly affected with tissue components and USM findings would provide important information for interpretation of TRUS images.