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Biomedical subjects

C Kollmann

Publications and source records attributed to C Kollmann.

13 recordsLinked to original sources
PubMed2005

[Ultrasound contrast agents--physical basics].

The concept of ultrasound contrast agents (UCA) is based on the inherent physical and acoustical properties of gas-filled microbubbles within an ultrasonic (US) field. Depending on the magnitude of the incident US wave different scattering behavior occurs. While it is linear for low acoustic pressures, increasing it leads to the occurrence of nonlinear effects, such as emission of harmonics. High pressure results in destruction of the bubbles producing a highly nonlinear echo signal. Using these specific acoustic signatures opens new perspectives for the development of bubble-specific imaging techniques such as harmonic or intermittent imaging. This review deals with the physical properties of the gas-filled microbubbles, their behavior within an ultrasonic field, and the use of the bubbles' acoustic signatures for contrast-specific imaging. Novel applications such as tissue-specific microbubbles, targeted imaging, and therapeutic applications using the bubbles as vehicles for drug or gene delivery are discussed as well as acoustically induced bioeffects and considerations for the safe use of UCA from an acoustic standpoint.

Contrast Media↗
PubMed2001

[A testing device for quality assurance of 3D-ultrasound equipment].

A test object for 3D-ultrasound (US) imaging equipment was constructed, that could be used for various purposes: For training of the correct technical setup procedures and practical handling of a 3D-US equipment, as well as for various quality assurance procedures. The size and volume of these structures were known precisely (+/- 0.1 mm resp. +/- 0.06 mL, respectively; smallest volume: 0.1 mL). The stability of the structures was in agreement with guideline IEC 854 and allowed to quantify exactly the imaging and measurement errors of size and volume measurements performed with commercial 3D-equipment. The test object is well suited to validate measured volume data, as well as to perform procedures of technical quality assurance in a reproducible manner.

Guidelines as Topic↗
PubMed2001

In vitro measurement accuracy of three-dimensional ultrasound.

OBJECTIVES: We sought to validate distance and volume measurements in three-dimensional (3-D) ultrasound images. BACKGROUND: Even with the latest equipment, it is not known how accurate 3-D echocardiographic measurements are. METHODS: Six models were imaged in ethanol solution and two within a tissue phantom using a mechanical rotation device rotating in 1 degrees intervals and a real-time 3-D scanner. Distance and volume measurements (n = 60) were performed in two-dimensional (2-D) and 3-D images using TomTec and InViVo software. RESULTS: Distance measurements had a mean total error between 1.12% and 2.31% for Acuson (2.5 MHZ, 3 MHZ, and 4 MHZ) and Hewlett Parkard (HP) fusion frequencies h and m, HP fusion harmonic B in the axial, and between 3.5% and 4.9% in the lateral dimension. HP Harmonic A and B, Volumetrics (2.5 MHZ), and HP fusion Harmonic A exhibited significantly higher differences to reality with a mean difference between 5.1% and 8.9% in the axial and between 6.2% and 7.9% in the lateral direction. Axial 2-D measurements were not different from real dimensions except Volumetrics model 1. In the lateral axis, all imaging modalities were different from reality except the fusion harmonic modus B. Using the HP fusion frequency h and HP fusion Harmonic B-mode, volume measurements in 3-D images significantly underestimated reality, while Acuson's fundamental frequency 3.5 MHZ was not different from real volumes. CONCLUSION: Three-dimensional visualization using different ultrasound settings results in different accuracy.

Echocardiography, Three-Dimensional↗
PubMed2000

Strong in vitro synergy between the fusion inhibitor T-20 and the CXCR4 blocker AMD-3100.

Attachment and entry of HIV-1 into CD4 cells involve a series of events in which different viral envelope proteins interact with specific cell receptors, culminating in fusion of viral and cell membranes. AMD-3100 is a small molecule inhibitor of HIV-1 attachment to the CXCR4 chemokine receptor, and T-20 is a synthetic peptide corresponding to a region of HIV-1 gp41 that blocks fusion to cell membranes. To evaluate the interaction between agents acting at two different steps of the entry process, we conducted in vitro studies of the combination of T-20 and AMD-3100 against an X4 HIV-1 isolate. Single drugs or multiply diluted fixed ratio combinations of drugs were added to peripheral blood mononuclear cells infected with a clinical isolate, 14aPre. Drug interactions were evaluated using the median-effect principle and the combination index technique. The 50% inhibitory concentration (IC50) for T-20 was 0.10 microg/ml and for AMD-3100 was 0.19 microg/ml. Synergy was observed between T-20 and AMD-3100 and this increased with higher inhibitory concentrations, with combination indices ranging from 0.62 at IC50 to 0.02 at IC95. Whether these synergistic interactions translate into clinical benefit will need to be addressed in the context of clinical trials.

Anti-HIV Agents↗
PubMed1999

Amplitude-coded color doppler: clinical applications.

Amplitude-coded color Doppler sonography (ACD) has become an useful adjunct to gray-scale US and conventional color Doppler sonography (CD) for the assessment of vascular diseases and pathologic conditions that might affect or alter tissue vascularization or perfusion. Basically, all US units that generate conventional color Doppler information through autocorrelation technique are capable of displaying ACD. This technique is also referred to as power Doppler, amplitude-mode color Doppler US, color Doppler energy (CDE), or US angiography. Amplitude-coded color Doppler sonography has already emerged as a valuable adjunct to conventional CD, particularly for evaluating flow in parts of the body where CD signal is weak because of slow flow, small blood vessels, or both.

Blood Flow Velocity↗
PubMed1999

[A test object for quality control of the instrument for doppler (duplex) ultrasonography, based on the Draft IEC 61685 Standard].

PURPOSE: The authors, forming part of a multicenter project funded by the European Community, summarize the validation of a tissue-mimicking flow Doppler test object and of procedures for testing medical diagnostic Doppler equipment. The results of the project are expected to contribute to a future international IEC Standard concerning flow Doppler test objects (Draft IEC 61685 Standard) and for the European Medical Device Directive (MD 93/42/EEC). METHODS: Within this project a test protocol was developed that includes a set of different procedures, suitable for checking Spectral and Colour Doppler systems. The performance parameters for describing the image quality as well as the accuracy and the correct functioning of a system are in accordance with the definitions made in the Draft IEC 61685 Standard. RESULTS: A survey of the design and materials used for this Doppler test object will be presented with a special emphasis on the suitability of the procedures for routine measurement of performance parameters in hospitals. CONCLUSION: The test object satisfies the requirements of the Draft IEC 61685 Standard. The test procedures in combination with this test object can be used for checking different transducer models with nominal frequencies between 2.5-10.0 MHz.

Blood↗
PubMed1998

Amplitude-coded colour Doppler sonography: physical principles and technique.

The purpose of this review is to help in understanding the principles of a new ultrasound Doppler technique called amplitude-coded colour Doppler (power) mode. All pertinent information available in the literature on the physical principles of this technique has been revised in order to give a detailed survey. The main components and the key characteristics of this mode are discussed together with illustrative examples. In addition, work-in-progress developments and other future aspects of US imaging in combination with this technique are discussed.

Algorithms↗
PubMed1998

Development of an example flow test object and comparison of five of these test objects, constructed in various laboratories.

Doppler test objects are used to characterise Doppler systems, both stand-alone systems and the Doppler part of so-called duplex scanners. The aim of the project partially presented here is the development and validation of an example of a Doppler test object fulfilling the requirements of the IEC 1685. The project has been carried out by nine partners of five European countries and has been funded by the European Commission. The flow Doppler test object is composed of: tissue mimicking material (TMM), blood mimicking fluid (BMF), tube (embedded in the TMM and carrying the BMF), tank flow system, including a pump and a flow meter. In the normative part of the IEC 1685, requirements are given for the values of acoustical parameters of TMM and BMF such as sound velocity, attenuation and backscattering. For BMF, requirements are given also for values of density and viscosity. In an informative (but not compulsory) annex, a description is given of a flow test object meeting these requirements as an example. 'example test object' developed during the project is composed of TMM based on agar and including SiC- and Al2O3-powders, BMF based on nylon particles suspended in water and glycerine, and a tube of c-flex, a silicon copolymer. Two tube sizes are used: 4.0 mm ID and 8.0 mm ID. During the project, very precise recipes have been developed for the composition and preparation of both TMM and BMF. Based on these recipes and a description of the construction in a design five flow test objects have been constructed in the laboratories of five participants. The test objects have been compared by measurements of the physical parameters and by Doppler measurements of the five test objects with the Doppler system. The measurements have been carried out by five observers. Inter-test object and inter-observer variabilities are determined, yielding information about usefulness of the parameters.

Acoustics↗
PubMed1998

Systematic distortions in magnetic position digitizers.

Medical devices equipped with position sensors enable applications like image guided surgical interventions, reconstruction of three-dimensional 3D ultrasound (US) images, and virtual or augmented reality systems. The acquisition of three-dimensional position data in real time is one of the key technologies in this field. The systematic distortions induced by various metals, surgical tools, and US scan probes in different commercial electromagnetic tracking systems were assessed in the presented work. A precise nonmetallic six degree-of-freedom measurement rack was built that allowed a quantitative comparison of different electromagnetic trackers. Also, their performance in the presence of large metallic structures was quantified in a phantom study on an acrylic skull model in an operating room (OR). The trackers used were alternating current (ac) and direct current (dc) based systems. The ac trackers were, on average, distorted by 0.7 mm and 0.5 degree by metallic objects positioned at a distance greater than 120 mm between the geometrical center of the sample and the sensor. In the OR environment, the ac system exhibits mean errors of 3.2 +/- 2.4 mm and 2.9 degrees +/- 1.9 degrees. The dc trackers are more sensitive to distortions caused by ferromagnetic materials (averaged value: 1.6 mm and 0.5 degree beyond a distance of 120 mm). The dc tracker shows no distortions from other conductive materials but was less accurate in the OR environment (typical error: 6.4 +/- 2.5 mm and 4.9 degrees +/- 2.0 degrees). At distances smaller than approximately 100 mm between sample and sensor error increases quickly. It is also apparent from our measurements that the influence of US scan probes is governed by their shielding material. The results show that surgical instruments not containing conductive material are to be preferred when using an ac tracker. Nonferromagnetic instruments should be used with dc trackers. Static distortions caused by the OR environment have to be compensated by precise calibration methods.

Acrylates↗
PubMed1995

[Results of a study of quality control of diagnostic ultrasound equipment].

AIMS: In this paper results of a quality control programme for B-mode ultrasound equipment used in clinical routine are presented. Over a period of 18 months 5 modern scanners with altogether 19 scanheads were periodically controlled. METHODS: The methods used for measuring the various performance parameters of an ultrasound equipment followed closely standard methods. All measurements were carried out with commercially available tissue-mimicking phantoms, and documented in a uniform protocol. RESULTS: Based on the results it was found that 11 of the scanheads did not operate correctly; 2 additional ones were severely defective. Only 6 scanheads were without loss of image quality or function. For the 13 malfunctioning scanheads adjustments, repair or even an exchange was necessary. CONCLUSION: The study demonstrates that quality control performed periodically is necessary to ensure optimal image quality and safe operation of the equipment.

Equipment Failure↗
PubMed1990

[Effects of various alfentanil doses on blood pressure, heart rate and plasma catecholamine level in endotracheal intubation].

METHOD: In 56 patients undergoing arthroscopy of the knee blood pressure (BP), heart rate (HR) and plasma catecholamines were measured during induction of anaesthesia. To a standard treatment including etomidate (K), either 1 (A1), 2 (A2) or 3 (A3) mg alfentanil were added. The control-group included 8 patients, the other groups consisted of 16 patients. Blood pressure and heart rate were measured the day before anaesthesia (T1), at the arrival in the operation theatre (T2), 1 minute after the induction (T3) and 1 minute after intubation (T4). Catecholamines were analysed at T2 and T4. - RESULTS: At T1 and T2 no significant differences were measured. The control-group had a significant rise of BP, HR and adrenalin at T4. In group A1 (1 mg alfentanil) BP and catocholamines remained at the same levels, HR rose significantly. In group A2 all parameters did not change. The group A3, BP dropped significantly, whereas the other parameters remained stable.- DISCUSSION: 2 mg Alfentanil given 1 minute before endotracheal intubation depress the sympathoadrenergic reactions but do not impair the circulation.

Adolescent↗