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H Ermert

Publications and source records attributed to H Ermert.

At least 37 records · Page 2Linked to original sources
PubMed2001

Freehand ultrasound elastography of breast lesions: clinical results.

We developed a freehand method for ultrasound elastography, which can be applied during a routine sonographic examination with off-line calculation of strain images (elastograms). Forty-eight patients with 53 breast lesions were examined and, after biopsy or operation, histologic reports were available for all lesions. The correlation coefficient of time delay estimates was used as a quality criterion for the subsequent calculation of elastograms. Beyond the qualitative evaluation of elastograms, we suggested a semiquantitative approach. For that purpose, the elastogram of each lesion was normalized to an overall strain of 1% (i.e., the average strain in the image was set to 1%). After normalization, we determined mean strain values inside and outside of each lesion, respectively. Defining solid lesions as benign and malignant lesions except for fibrous mastopathy, we found significant difference in strain between solid lesions and their surrounding tissue. However, that result must not be misunderstood to suggest that it was possible to distinguish benign from malignant lesions in general. Still, we address the potential of ultrasound elastography to improve the detection and localization of breast lesions as well as their differential diagnosis. Besides, we developed a freehand applicator for further studies, which guarantees a homogeneous axial compression regardless of the experience of the examiner.

Adult↗
PubMed2001

Synthetic aperture-based beam compression for intravascular ultrasound imaging.

In this paper, intravascular ultrasound (IVUS) images acquired with a 64-element array transducer using a multistatic acquisition scheme are presented. The images are reconstructed from a collection of pulse-echo measurements using a synthetic aperture array imaging technique. The main limitations of IVUS imaging are a poor lateral resolution and elevated grating lobes caused by the imaging geometry. We propose a Synthetic Aperture Focusing Technique (SAFT), which uses a limited number of A-scan signals. The focusing process, which is performed in the Fourier domain, requires far less computation time than conventional delay-and-sum methods. Two different reconstruction kernel functions have been derived and are compared for the processing of experimental data.

Computer Simulation↗
PubMed2000

Segmentation of 3D intravascular ultrasonic images based on a random field model.

Segmentation of intravascular ultrasound images provides important information about the degree of vessel obstruction as well as about the shape and size of plaques. To address the problems of inter- and intra-observer variances associated with conventional manual tracing, a fully automated segmentation was developed. The algorithm is based on the optimisation of a maximum a posteriori estimator, implementing the Rayleigh distribution of speckle and a priori information about the contours. Within 3D image sets, additional information by the blood flow resulting in a decorrelation of the pixels within the luminal boundary is used to initialise the segmentation. To accelerate the estimation, dynamic programming was used. The segmentation algorithm was realised as a Windows 95 application on a Pentium II/233 MHz and delivered reliable and reproducible results independent of the catheter position and the total image brightness (except overflow). In contrast, contours drawn by two physicians for an evaluation of 29 clinical cases showed large intra- and inter-observer variances. In vivo images were acquired with a 20 MHz transducer array (EndoSonics InVision). Comparison with the contours drawn by the physicians and histology demonstrates the potential of the segmentation algorithm.

Algorithms↗
PubMed2000

[Ultrasound elastography of the prostate. A new technique for tumor detection].

AIM: Prostate tumours are often of harder consistency than the surrounding tissue. During digital rectal examination, this fact can be used not only to detect hypertrophy but also localized hardenings. The examination by digital palpation is inaccurate and, even in combination with PSA-value and a transrectal ultrasonic examination, the result is often not reliable. Ultrasound elastography enables us to measure and visualize the elastic properties of a tissue region and is a useful supplement to the examination by digital palpation. Ultrasound elastography is able to measure and visualize the elastic properties of a tissue region, therefore it is a useful supplement to commonly used diagnostic procedures. METHOD: We have developed a new system for elastographic prostate diagnosis which can be used during the transrectal ultrasonic examination. During the examination a sequence of ultrasonic images is acquired while the organ is slightly compressed by the ultrasound probe. Using numerical analysis of image pairs for the acquired sequence we calculate the tissue strain which represents the spatial elasticity distribution of a specific cross-section of the organ. This enables us to distinguish hard areas in the tissue. Image artifacts resulting from lateral motion components, i.e., orthogonal to the direction of the applied force, are compensated for by a special approach. RESULTS: We present results obtained from a typical elastography phantom and also the first in vivo images from patients who were undergoing radical prostatectomy. Our images prove that ultrasound elastography has the potential to detect malignant tissue areas, which are inconspicuous in the B-mode image. Our findings are confirmed by the corresponding histological specimens.

Elasticity↗
PubMed2000

New real-time strain imaging concepts using diagnostic ultrasound.

Two real-time strain imaging concepts and systems are presented. Both systems are based on a conventional ultrasound scanner that is connected to a PC with an A/D converter card for real-time data acquisition of rf data. Differential strain between successively acquired rf frames are estimated using phase root seeking. The first concept uses a special real-time implementation of manual elastography. In the second concept, denoted 'vibrography', the static compression is replaced by low-frequency axial vibration of the probe, still operating in quasistatic acquisition mode. The properties of both concepts are discussed with regard to noise and motion artefacts, and it is shown, using simulations and phantom experiments, that both imaging concepts yield the same kind of strain images. Vibrography has the advantage that no manual compression has to be applied, total compression can be very low and some motion artefacts are better suppressed.

Algorithms↗
PubMed2000

Contrast agent specific imaging modes for the ultrasonic assessment of parenchymal cerebral echo contrast enhancement.

Previous work has demonstrated that cerebral echo contrast enhancement can be assessed by means of transcranial ultrasound using transient response second harmonic imaging (HI). The current study was designed to explore possible advantages of two new contrast agent specific imaging modes, contrast burst imaging (CBI) and time variance imaging (TVI), that are based on the detection of destruction or splitting of microbubbles caused by ultrasound in comparison with contrast harmonic imaging (CHI), which is a broadband phase-inversion-based implementation of HI. Nine healthy individuals with adequate acoustic temporal bone windows were included in the study. Contrast harmonic imaging, CBI, and TVI examinations were performed in an axial diencephalic plane of section after an intravenous bolus injection of 4 g galactose-based microbubble suspension in a concentration of 400 mg/mL. Using time-intensity curves, peak intensities and times-to peak-intensity (TPIs) were calculated off-line in anterior and posterior parts of the thalamus, in the region of the lentiform nucleus, and in the white matter. The potential of the different techniques to visualize cerebral contrast enhancement in different brain areas was compared. All techniques produced accurate cerebral contrast enhancement in the majority of investigated brain areas. Contrast harmonic imaging visualized signal increase in 28 of 36 regions of interest (ROIs). In comparison, TVI and CBI examinations were successful in 32 and 35 investigations, respectively. In CHI examinations, contrast enhancement was most difficult to visualize in posterior parts of the thalamus (6 of 9) and the lentiform nucleus (6 of 9). In TVI examinations, anterior parts of the thalamus showed signal increase in only 6 of 9 examinations. For all investigated imaging modes, PIs and TPIs in different ROIs did not differ significantly, except that TVI demonstrated significantly higher PIs in the lentiform nucleus as compared with the thalamus and the white matter (P < 0.05). The current study demonstrates for the first time that CBI and TVI represent new ultrasonic tools that allow noninvasive assessment of focal cerebral contrast enhancement and that CBI and TVI improve diagnostic sensitivity as compared with CHI.

Adult↗
PubMed2000

Axial strain imaging using a local estimation of the scaling factor from RF ultrasound signals.

The main signal-processing techniques used in elastography compute strains as the displacement derivative. They perform well for very low deformations, but suffer rapidly from decorrelation noise. Aiming to increase the range of accurate strain measurements, we developed an adaptive method based on the estimation of strains as local scaling factors. Its adaptability makes this method appropriate for computing scaling factors resulting from larger strains or a wide spread of strain variations. First, segments corresponding to the same part of tissue are adaptively selected in the rest and stressed state echo signals. Then, local scaling factors are estimated by iteratively varying their values until reaching the zero of the phase of the complex cross-correlation function. Results from simulation and from experimental data are presented. They show how this adaptive method can track various local deformations and its accuracy for strain up to 7%.

Algorithms↗
PubMed1999

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.

Adult↗
PubMed1999

[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.

Administration, Topical↗
PubMed1998

[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.

Adult↗
PubMed1997

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.

Artifacts↗
PubMed1997

[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.

Blood↗