High-resolution quantitative acoustic microscopy of cutaneous carcinoma and melanoma: Comparison with histology.

BACKGROUND: The increased incidence rate of skin cancers during the last decades is alarming. One of the significant difficulties in the histopathology of skin cancers is appearance variability due to the heterogeneity of diseases or tissue preparation and staining process. This study aims to investigate whether the high-resolution acoustic microscopy has the potential for identifying and quantitatively classifying skin cancers. MATERIAL/METHODS: Unstained standard formalin-fixed skin tissue samples were used for ultrasonic examination. The high-frequency acoustic microscope equipped with the 320 MHz transducer was utilized to visualize skin structure. Fourier transform was performed to calculate the sound speed and attenuation in the tissue. RESULTS: The acoustic images demonstrate good concordance with the traditional histology images. All histological features in the tumour were easily identifiable on acoustic images. Each skin cancer type has its combination of ultrasonic properties significantly different from the healthy skin. CONCLUSIONS: High-resolution acoustic imaging strengthened with quantitative analysis shows a potential to work as an auxiliary imaging modality assisting pathologists to lean to the particular decision in doubtful cases. The method can also assist surgeon to ensure the complete resection of a tumour.

Ultrasonic imaging of foreign inclusions and blood vessels through thick skull bones.

We report a new progress in the development of a portable ultrasonic transcranial imaging system, which is expected to significantly improve the clinical utility of transcranial diagnostic ultrasound. When conventional ultrasonic phased array and Doppler techniques are applied through thick skull bones, the ultrasound field is attenuated, deflected, and defocused, leading to image distortion. To address these deficiencies, the ultrasonic transcranial imaging system implements two alternative ultrasonic methods. The first method improves detection of small foreign objects, such as bone fragments, pieces of shrapnel, or bullets, lodged in the brain tissue. Using adaptive beamforming, the method compensates for phase aberration induced by the skull and refocuses the distorted ultrasonic field at the desired location. The second method visualizes the blood flow through intact human skull using ultrasonic speckle reflections from the blood cells, platelets, or contrast agents. By analyzing these random temporal changes, it is possible to obtain 2D or 3D blood flow images, despite the adverse influence of the skull. Both methods were implemented on an advanced open platform phased array controller driving linear and matrix array probes. They were tested on realistic skull bone and head phantoms with foreign inclusions and blood vessel models.

New data on histology and physico-mechanical properties of human tooth tissue obtained with acoustic microscopy.

Quantitative evaluation of human tooth structural elements, revealed in acoustic images, has been carried out. It has been shown that tissue elements with different acoustic impedances differed in acoustic images by intensity of grey color, and also feature with different longitudinal sound velocities (C(L)). In the layer of mantle dentin, C(L) is 7% to 8% lower than in bulk dentin, and in the layer of dentin around the pulp chamber, C(L) is 15% lower. In carious enamel and dentin, C(L) decreases up to 7% to 17%. In pathologic teeth, dentin areas with higher density can be revealed; they feature higher C(L); in transparent dentin C(L) can be 15% to 20% higher than in bulk dentin. Results of the present study show that acoustic images reflect internal biomechanical properties of tooth tissue microstructure that can be evaluated quantitatively by means of longitudinal sound velocity determination.

Fine mapping of tissue properties on excised samples of melanoma and skin without the need for histological staining.

This paper develops a novel two-frequency approach for noninvasive evaluation of cancerous tissue with optimum depth and resolution. Frequencies of about 50 MHz are used in thickly sliced tissue to detect differences of the relative attenuation (C-scan mode scanning) with relatively limited resolution. Thus, suspect zones can be identified according to a quantitative criterion. These suspect zones are then selected for preparation of thin, transversal slices from within the original thick slices. Very-high-resolution (1-µm) visualization of cells is obtained at around 600 MHz on these transversal sections and adjacent sections are prepared for histological study in parallel. The technique's feasibility and potential are demonstrated on both normal and cancerous (melanoma) skin tissue. Isotropy of the specimens is experimentally verified to ensure that conditions were coherent for use of a 5-layer, angular spectrum model made to simulate longitudinal velocity, allowing estimation of longitudinal velocity from semiquantitative V(z) data.

Acoustic imaging of thick biological tissue.

Up to now, biomedical imaging with ultrasound for observing a cellular tissue structure has been limited to very thinly sliced tissue at very high ultrasonic frequencies, i.e., 1 GHz. In this paper, we present the results of a systematic study to use a 150 to 200 MHz frequency range for thickly sliced biological tissue. A mechanical scanning reflection acoustic microscope (SAM) was used for obtaining horizontal cross-sectional images (C-scans) showing cellular structures. In the study, sectioned specimens of human breast cancer and tissues from the small intestine were prepared and examined. Some accessories for biomedical application were integrated into our SAM (Sonix HS-1000 and Olympus UH-3), which operated in pulse-wave and tone-burst wave modes, respectively. We found that the frequency 100 to 200 MHz provides optimal balance between resolution and penetration depth for examining the thickly sliced specimens. The images obtained with the lens focused at different depths revealed cellular structures whose morphology was very similar to that seen in the thinly sectioned specimens with optical and scanning acoustic microscopy. The SAM operation in the pulse-echo mode permits the imaging of tissue structure at the surface, and it also opens up the potential for attenuation imaging representing reflection from the substrate behind the thick specimen. We present such images of breast cancer proving the method's applicability to overall tumor detection. SAM with a high-frequency tone-burst ultrasonic wave reveals details of tissue structure, and both methods may serve as additional diagnostic tools in a hospital environment.