Utility of high-frequency ultrasonography in the diagnosis of benign and malignant skin tumors.

Various benign and malignant tumors may arise from the skin. These may be of epidermal, dermal, subcutaneous or appendageal origin. Skin biopsy is the gold standard for diagnosis of skin tumors. There is paucity of published data on the role of imaging modalities in diagnosis of skin tumors. High-frequency ultrasonography (7-50 MHz) is a potential non-invasive, objective modality which can be utilized in the diagnosis and localization of skin tumors. It provides valuable information about the tumor characteristics such as size, shape, depth, consistency and vascularity before invasive skin biopsy or surgery is planned. Sentinel lymph nodes in malignant melanoma can be well visualized and studied by this technique. It is also a good modality to detect local recurrence of tumors during post-operative follow up, especially those with a high likelihood of local recurrence or lesions excised with inadequate margins. High-frequency ultrasonography is additive to clinical diagnosis and can be considered a useful non-invasive method to plan the management of various skin tumors and is of prognostic value in some cases.

Improved optoacoustic microscopy through three-dimensional spatial impulse response synthetic aperture focusing technique.

Synthetic aperture focusing technique (SAFT) is effective in restoring lateral resolution of ultrasonic images for scans with focusing-related distortions. Although successfully applied in pulse-echo ultrasonics, the physical nature of an optoacoustic modality requires a modified algorithm to return accurate results. The SIR-SAFT method reported here uses the spatial impulse response (SIR) of the transducer to weight the contributions to the SAFT and is tailored to provide significant resolution and signal gains for out-of-focus sources in scanning optoacoustic microscopy systems. Furthermore, the SIR-SAFT is implemented in full three dimensions, applicable to signals both far of and at the focus of the ultrasonic detector. The method has been further shown to outperform conventional SAFT algorithms for both simulated and experimental optoacoustic data.

In vivo optically encoded photoacoustic flowgraphy.

We present an optically encoded photoacoustic (PA) flow imaging method based on optical-resolution PA microscopy. An intensity-modulated continuous-wave laser photothermally encodes the flowing medium, and a pulsed laser generates PA waves to image the encoded heat pattern. Flow speeds can be calculated by cross correlation. The method was validated in phantoms at flow speeds ranging from 0.23 to 11 mm/s. Venous blood flow speed in a mouse ear was also measured.

The grave necessity to make eye bank specular microscopy mandatory in all eye banks in the subcontinent to improve utilization of scarce donor corneas.

CONTEXT: Donor tissue scarcity, Eye Bank Specular Microscopy as yet not made mandatory and tissue utilization often based on clinical judgment only. AIMS: Prospectively analyze alteration in clinical grading of donor corneas and hence utilization, based on Eye Bank Specular Microscopy (EBSM) and to infer if EBSM should be mandatory in all eye banks. MATERIALS AND METHODS: 200 consecutive otherwise 'suitable for surgery' donor eyes were graded clinically. On quantitative and qualitative analysis of endothelial cells by EBSM, final grading was adjusted. Impact on subsequent utilization for various surgeries was analyzed with regard to Age of Donor, Death to Enucleation Time, Death to Preservation Time and Lens Status of Donor Eye. RESULTS: 76 eyes (38%) (P < 0.05) had significant change in grading. 12/59 (20.30%) tissues from donors <=40 years showed Cell Density (CD) between 1801-2500. 19/76 (25%) tissues from donor >60 years showed CD >= 2500. From donor >=81 years, 2/13 (15.3%) eyes showed CD between 2501-3000 and 1 (7.6%) eye showed CD > 3000. Owing to better grading after EBSM, 13/14 (92.85%) tissues with DTET >6 hours and 5/5 (100%) tissues with DTPT > 16 hours were transplanted. Out of 45 (22.5%) pseudo-phakic tissues, 21 (46.67%) tissues were used for Therapeutic/Tectonic Penetrating Keratoplasty (PKP) while 24 (53.33%) tissues were used for Optical PKP. CONCLUSIONS: EBSM significantly alters final grading of tissues and its subsequent utilization. Acquiring huge importance in areas where adequate supply of corneas is lacking, EBSM becomes an indispensable tool for optimizing availability of qualified tissues for surgery. EBSM should be made a mandatory analysis.

In vivo photoacoustic microscopy with 7.6-µm axial resolution using a commercial 125-MHz ultrasonic transducer.

Photoacoustic microscopy has achieved submicron lateral resolution, but its axial resolution is much lower. Here an axial resolution of 7.6 µm, the highest axial resolution validated by experimental data, has been achieved by using a commercial 125 MHz ultrasonic transducer for signal detection followed by the Wiener deconvolution for signal processing. Limited by the working distance, the high-frequency ultrasonic transducer can penetrate 1.2 mm into biological tissue from the ultrasound detection side. At this depth, the signal-to-noise ratio decreases by 11 dB, and the axial resolution degrades by 36%. The new system was demonstrated in imaging melanoma cells ex vivo and mouse ears in vivo.

Photoacoustic and high-frequency power Doppler ultrasound biomicroscopy: a comparative study.

Both photoacoustic imaging and power Doppler ultrasound are capable of producing images of the vasculature of living subjects, however, the contrast mechanisms of the two modalities are very different. We present a quantitative and objective comparison of the two methods using phantom data, highlighting relative merits and shortcomings. An imaging system for combined photoacoustic and high-frequency power Doppler ultrasound microscopy is presented. This system uses a swept-scan 25-MHz ultrasound transducer with confocal dark-field laser illumination optics. A pulse-sequencer enables ultrasonic and laser pulses to be interlaced so that photoacoustic and power Doppler ultrasound images can be coregistered. Experiments are performed on flow phantoms with various combinations of vessel size, flow velocity, and optical wavelength. For the task of blood volume detection, power Doppler is seen to be advantageous for large vessels and high flow speeds. For small vessels with low flow speeds, photoacoustic imaging is seen to be more effective than power Doppler at the detection of blood as quantified by receiver operating characteristic analysis. A combination of the two modes could provide improved estimates of fractional blood volume in comparison with either mode used alone.

Optical resolution photoacoustic microscopy using novel high-repetition-rate passively Q-switched microchip and fiber lasers.

Optical-resolution photoacoustic microscopy (OR-PAM) is a novel imaging technology for visualizing optically absorbing superficial structures in vivo with lateral spatial resolution determined by optical focusing rather than acoustic detection. Since scanning of the illumination spot is required, OR-PAM imaging speed is limited by both scanning speed and laser pulse repetition rate. Unfortunately, lasers with high repetition rates and suitable pulse durations and energies are not widely available and can be cost-prohibitive and bulky. We are developing compact, passively Q-switched fiber and microchip laser sources for this application. The properties of these lasers are discussed, and pulse repetition rates up to 100 kHz are demonstrated. OR-PAM imaging was conducted using a previously developed photoacoustic probe, which enabled flexible scanning of the focused output of the lasers. Phantom studies demonstrate the ability to image with lateral spatial resolution of 7±2 µm with the microchip laser system and 15±5 µm with the fiber laser system. We believe that the high pulse repetition rates and the potentially compact and fiber-coupled nature of these lasers will prove important for clinical imaging applications where real-time imaging performance is essential.

Repeatability, reproducibility, and agreement of central anterior chamber depth measurements in pseudophakic and phakic eyes: optical coherence tomography versus ultrasound biomicroscopy.

PURPOSE: To evaluate the intraexaminer repeatability, interexaminer reproducibility, and agreement of central anterior chamber depth (ACD) measurements obtained by anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) in pseudophakic eyes and phakic eyes. SETTING: Eye Hospital, Wenzhou Medical College, Wenzhou, Zhejiang, China. METHODS: In this prospective study, the central ACD in right pseudophakic eyes and right phakic eyes was measured with the Visante AS-OCT system and the OTI-Scan HF 35-50 UBM system. Intraexaminer repeatability and interexaminer reproducibility were evaluated in a subgroup of eyes from each group. The repeatability and reproducibility of the measurements were evaluated using intraclass correlation coefficients (ICCs) and the Bland-Altman method. RESULTS: The mean ACD in the 70 pseudophakic eyes was 3.91 mm +/- 0.29 (SD) by AS-OCT and 3.76 +/- 0.33 mm by UBM and in the 70 phakic eyes, 2.97 +/- 0.31 mm and 2.90 +/- 0.32 mm, respectively. The 95% limits of agreement between the 2 methods were -0.32 to 0.62 mm in pseudophakic eyes and -0.11 to 0.25 mm in phakic eyes. The ICC for the repeatability and reproducibility of AS-OCT and UBM measurements was high (range 0.985 to 0.996). CONCLUSIONS: Both AS-OCT and UBM ACD measurements showed good repeatability and reproducibility. However, the agreement was better in phakic eyes than in pseudophakic eyes. Thus, the measurements should not be used interchangeably in pseudophakic eyes.

Ultrasonic tissue characterization of photodamaged skin by scanning acoustic microscopy.

The aim of this study was to ultrasonically characterize photodamaged skin of the elderly at the microscopic level using scanning acoustic microscopy which showed two-dimentional distribution of sound speed in the skin section. We confirmed that the expression level of the elastin gene was increased in the preauricular skin (photodamaged area), compared with postauricular skin (photo-protected area). The expression level of the procollagen gene was also increased in the preauricular skin compared with postauricular skin. The preauricular skin showed higher sound speed in the papillary dermis (Grenz zone). The site of progressive solar elastosis showed a somewhat sound speed velocity than that of the Grenz zone. Immunohistochemical staining showed conserved deposition of collagen in the Grenz zone even in the more photodamaged preauricular skin. These results suggest that fibrosis in the Grenz zone compensates tissue strength with the progress of solar elastosis. The sound speed analysis of skin will provide important information on heterogeneous mechanical changes in the skin during the process of photoaging.