Sonography of the skin at 100 MHz enables in vivo visualization of stratum corneum and viable epidermis in palmar skin and psoriatic plaques

A main drawback of 20-25 MHz ultrasound units for skin imaging is their limited resolution. We used a transducer with a center frequency of 95 MHz and a resolution of 8.5 microm axially and 27 microm laterally - an almost 10-fold increase compared with 20 MHz. By means of a new scanning technology we reached a depth of field of 3.2 mm. We examined normal palmar skin, normal glabrous skin on the abdomen, the upper back, the calf and the dorsal forearm, and 35 lesions of psoriasis vulgaris. From 11 psoriatic plaques biopsies were taken for correlation with the sonograms. In normal palmar skin, the horny layer is represented as an echopoor band below the skin entry echo, traversed by echorich coils, which correspond to eccrine sweat gland ducts. The thickness of this band significantly increases after occlusive application of petrolatum. Its lower border is defined by an echorich line, representing the stratum corneum/stratum Malpighii-interface. Underneath, a second echopoor band is visible, which corresponds to the viable epidermis plus the papillary dermis, bordered by the scattered echo reflexes of the reticular dermis. This band is also visible in glabrous skin; however, the stratum corneum cannot be detected. In psoriatic lesions, the thickened horny layer appears echorich; after application of petrolatum, its echodensity decreases. Below, the acanthotic epidermis plus the dermis with the inflammatory infiltrate are represented as an echopoor band. There is an excellent correlation between the sonometric thickness of this band and the histometric thickness of the acanthosis plus the infiltrated dermis. Our results show that 100 MHz sonography is a valuable tool for in vivo examination of the upper skin layers.

[100 MHz sonography in the visualization of the palmar stratum corneum after application of various creams and ointments]

To visualise the effects of different topically applied substances on the stratum corneum in vivo by means of sonography, it is necessary to have an ultrasound unit with a much higher resolution than provided for by the 20 MHz scanners currently used in dermatology. We developed a workstation with a highly focussed transducer with a large bandwidth, providing a resolution of 9 microns axially and 27 microns laterally. Using this ultrasound unit, we investigated the effects of different creams and ointments in 10 persons on the palmar side of the distal finger segments (vaseline, a water-in-oil-emulsion, an oil-in-water-emulsion, 10% urea in an oil-in-water-emulsion and water). Sonograms were taken after an occlusion period of 0, 30, 60, 120, 180 and 240 min. In 100 MHz sonograms of palmar skin, the stratum corneum is represented as an echo-poor band below the echo-rich entry echo--the correlate of the interface between the coupling water and the horny layer. The echo-poor band is traversed by echo-rich coils, representing eccrine sweat gland ducts. It is separated by an echo-rich line from the viable epidermis, which is echo-poor as well. The topically applied substances differ in the time course of the swelling of the stratum corneum. After longer application all externals cause a significant thickening of the stratum corneum (p < 0.005) and a reduction of the echogenicity of the skin entry echo due to altered impedance. 100 MHz sonography is well suited to visualise and quantify the effects of externals on the stratum corneum in vivo.

A time-efficient and accurate strain estimation concept for ultrasonic elastography using iterative phase zero estimation

In ultrasonic elastography, the exact estimation of temporal displacements between two signals is the key to estimating strain. An algorithm was previously proposed that estimates these displacements using phase differences of the corresponding base-band signals. A major advantage of these algorithms compared with correlation techniques is the computational efficiency. In this paper, an extension of the algorithm is presented that iteratively takes into account the time shifts of the signals to overcome the problems of aliasing and accuracy in the estimation of the phase shift. Thus, it can be proven that the algorithm is equivalent to the search of the maximum of the correlation function. Furthermore, a robust logarithmic compression is proposed that only compresses the envelope of the signal. This compression does not introduce systematic errors and significantly reduces decorrelation noise. The resulting algorithm is a computationally simple and very fast alternative to conventional correlation techniques, and the accuracy of strain images is improved.

Tissue-characterization of the prostate using radio frequency ultrasonic signals

In this paper, we will present a complete method and system for the detection of prostatic carcinoma, providing color-coded images of the estimated probability of malignancy by processing radio-frequency ultrasonic echo signals. For this, a hardware setup based on a conventional diagnostic sonograph was realized. The image-processing software works on ultrasound images automatically segmented into regions of about 3x3.5 mm. System-dependent effects, as well as tissue attenuation, were measured and compensated for. Tissue-characterisation parameters, which have been used successfully by other authors, were calculated for each segment. To demonstrate the methods of selection of relevant parameters and comparison of different classifiers, a first clinical study using data of 33 patients with local prostatic carcinoma was performed. For these patients, location and extent of the carcinoma were known from histological findings after radical prostatectomy. Classifiers investigated during the study were: the linear and quadratic Bayes classifier, a nearest neighbor classifier, and several classifiers based on Kohonen-maps. The best classifier was used to calculate color-coded result images. Applying a threshold of 50% to the estimated probability of malignancy, produced the encouraging results of 82 and 88% for sensitivity and specificity, respectively.

A new system for the acquisition of ultrasonic multicompression strain images of the human prostate in vivo

We describe a novel recording system for the acquisition of multicompression strain images of the human prostate in vivo. The force at the tip of an ultrasonic transrectal probe is measured continuously, and ultrasonic RF-images are acquired consecutively at specified levels of compression. The acquired image sequence is processed by conventional cross-correlation techniques to obtain time shift estimates and corresponding strain images. We present phantom measurements as well as in vivo results and discuss the advantages and restrictions of the proposed system.

[100 MHz ultrasound of psoriasis vulgaris plaque]

PURPOSE

20 MHz sonography of inflammatory diseases has concentrated on the evaluation of the echo-poor area in the upper dermis. With regard to higher resolution, this study focuses on the alterations of the epidermis and upper dermis skin using 100 MHz sonography.

METHOD

70 fully developed psoriasis vulgaris plaques of 20 patients were examined using our 100 MHz ultrasound equipment after application of salicylic acid in petrolatum for 24 h. After informing the patient about the aims of the study, a small knife biopsy was taken from 11 plaques.

RESULTS

All psoriasis plaques exhibited, in comparison with normal skin, a significant widening of the skin entry echo (p < 0.001). Focally, this echo-rich line broke up into two thinner lines. Correlating histology exhibited in these areas an orthohyperkeratosis and focal parakeratosis. The upper dermis showed an echo-poor, band-shaped area which corresponded histologically to an acanthosis, elongation of rete ridges, and widening of the stratum papillare. The mean grey level of the echo-poor area and of the dermis beneath was significantly lower (p < 0.001) than the normal adjacent dermis. The thickness of the echo-poor area correlated with the thickness of the sum of the acanthosis and the inflammatory infiltrate in the histological sections (r = 0.94).

CONCLUSION

Using 100 MHz sonography changes of the skin entry echo and the upper dermis can be visualized and quantified.

[Models for describing ultrasound scattering in blood]

The acoustic scattering properties of blood, which are of fundamental importance for the diagnostic utilization of ultrasonic signals backscattered by blood in Doppler-based procedures, have now been investigated using three different scattering models: the particle model, the continuum model and the hybrid model. The analysis shows the limitations of the approaches so far described in the literature, and also permits a modification of the hybrid model to produce an appreciably more accurate description of the true scattering properties of the blood. This is verified by a comparison of theoretical and experimental results obtained for a large range of haematocrits.

Linear synthetic aperture modes for ultrasonic pulse-echo imaging

A unified approach is developed to characterize and compare the most widely used two-dimensional ultrasound pulse-echo imaging procedures. The methods of monostatic, bistatic and multistatic time-domain holography are theoretically investigated with regard to line spread functions, resolution capabilities, and the effects of multiple scattering and object inhomogeneities. Analytical derivations and computer simulations show the superiority of monostatic holography in applications such as nondestructive testing, where in most cases the assumptions generally made in the calculation of the inverse scattering formulae are justified. However, if higher order scattering and/or the spatial variations of the sound speed play a significant role, then multistatic imaging is more advantageous. A modification of this latter mode, with fixed focus on transmission, is commonly used in medical imaging B-scan systems, but implementation of the full algorithm would offer improved resolving power and reduced side lobe levels throughout the image plane.

In vivo study of online liver tissue classification based on envelope power spectrum analysis

An ultrasonic imaging and signal analysis system, combining a 3.5 MHz linear array B-scanner and an array processor, has been realized for a clinical liver tissue classification study. Based on the complete unprocessed rf data set of a real time B-image, local envelope power spectra averaged over interactively defined regions are computed. These spectra are partially corrected for several tissue type independent effects that affect comparability. A library containing the in vivo data of 65 patients with known liver tissue states in three groups (normal, cirrhotic, fat) was built up. An algorithm based on numerical optimization of parametrized spectrum characteristics combined with a k-nearest-neighbors classifier, applied to the library, leads to correct classification rates of 85.8 to 87.5 percent in discriminating pathological from normal tissue states. The method can be used for k-weighted color coded tissue type imaging with acceptable spatial resolution.

Psoriasis vulgaris in 50 MHz B-scan ultrasound--characteristic features of stratum corneum, epidermis and dermis

One hundred and forty fully developed, non-treated plaques of psoriasis vulgaris from the arms and legs of 22 patients were examined using 50 MHz B-scan ultrasound and compared with the images from adjacent, clinically normal skin. To visualize the dermis, high pre-amplification (digitization range 200 mV) was used, determined according to A-scan images. For evaluation of epidermal phenomena, low pre-amplification (digitization range 380 mV) was chosen in order to avoid overmodulation of the skin entry echo. In 10 patients, sonographic images were compared with histological sections from the exact same planes at the same magnification. At low pre-amplification, the skin entry echo is displayed as a markedly widened, frequently interrupted band composed of spots varying in thickness, height and echo density. Within these spots, several lamellae can be observed, represented as fine, echo-rich lines stacked one upon another. These phenomena correspond histologically to focal hyperparakeratosis, scaling and cracking of the stratum corneum. Due to the low amplification of the echo-signal the dermis is not visible. High pre-amplification allows evaluation of dermal changes. Below the entry echo there is an echopoor band (EPB) corresponding to the sum of acanthosis and infiltrate in the upper dermis. Underneath the EPB the dermis is represented as a zone with scattered internal echoes which are less intense than in normal skin. Dorsal shadows are typically present. They are artifacts emanating from epidermal regions with marked hyperkeratosis and disappear when the sonographic characteristics of the epidermis are changed, for instance by application of ointments prior to sonographic examination.(ABSTRACT TRUNCATED AT 250 WORDS)