Biomedical subjects

N G Holmer

Publications and source records attributed to N G Holmer.

At least 19 recordsLinked to original sources

PubMed2001

Validity and reliability of triaxial accelerometers for inclinometry in posture analysis.

There is a need for objective and quantitative methods for measuring posture and movement, so that, for instance, exposure-response relationships for work-related musculoskeletal disorders can be established. Inclinometry data have been obtained from triaxial accelerometers based on uniaxial solid-state accelerometers used in conjunction with a computer program to perform co-ordinate transformations. The transducer can be mounted in an arbitrary orientation on a body segment, since if two reference positions are recorded, the co-ordinate system of the transducer can be transformed to that of the body segment. The angular error of the system is small (1.3 degrees), the reproducibility is high (0.2 degrees), and the inherent angular noise is small (0.04 degrees) and independent of the orientation of the device. Under quasi-static conditions, the angular velocities can be derived from the inclinometry data. The angular and the angular-velocity errors can be approximated using the relative deviation of the acceleration magnitude from gravitation. For applications involving a high degree of movement, the accelerometer data are still valid, although they cannot be interpreted as inclination. Used in combination with the computer program, the transducer can be used to measure posture and movement under static and quasi-static conditions, which occur in most areas of occupational work. It is shown that spherical co-ordinates can be used to present the inclinometry data.

Acceleration↗

PubMed1997

An experimental high energy therapeutic ultrasound equipment: design and characterisation.

High energy ultrasound equipment for well controlled experimental work on extracorporeal shockwave lithotripsy (ESWL) and hyperthermia has been built. The design of two sets of equipment with operating frequencies of 0.5 and 1.6 MHz, respectively, is described and characterised in terms of measured generated pressure fields. The treatment heads consist of six or seven focused ultrasound transducers. The transducers have a diameter of 50 mm each and are mounted in a hemispherical Plexiglass fixture with a geometrical focus 100 mm from the transducer surfaces. Measurements were performed in a water bath in several planes perpendicular to the central axis of the ultrasound beam, using a miniature hydrophone which was positioned with a computer controlled stepping motor system. Resulting diagram plots show well defined pressure foci, located at the geometrical foci of the transducer units.

Equipment Design↗

PubMed1994

Evaluation of the image quality of ink-jet printed paper copies of digital chest radiographs as compared with film: a receiver operating characteristic study.

Paper copies of digital radiographs printed with the continuous ink-jet technique have proved to be of a high enough quality for demonstration purposes. We present a study on the image quality of ink-jet printed paper copies of digital chest radiographs, based on receiver operating characteristic (ROC) analysis. Eighty-three digital radiographs of a chest phantom with simulated tumors in the mediastinum and right lung, derived from a computed radiography (CR) system were presented in two series of hard copies as ink-jet printed paper copies and as laser recorded film. The images, with a matrix of 1,760 x 2,140 pixels, were printed with a spatial resolution of 10 pixels/mm in the CR film recorder as well as in the ink-jet printer. On film, every image was recorded in two versions, one optimized for the mediastinum and one for the lungs. On paper, only one image was printed; this constituted an effort to optimize both the mediastinum and the lungs. The ink-jet printed images, printed on a matt coated paper, were viewed as on-sight images with reflected light. The examinations were reviewed by six radiologists, and ROC curves were constructed. No significant difference was found between the performance of film and that of ink-jet paper prints. Because the cost for a paper copy is only a tenth of that of film, remarkable cost reductions can be achieved by using the ink jet technique instead. Our results show that further quality studies of ink-jet printed images are worthwhile.

Copying Processes↗

PubMed1994

A current injecting device for electrical impedance tomography.

Electrical impedance tomography (EIT) has to be improved in order to become an accepted diagnostic technique in clinical use. The aim of this study is to improve the hardware of this technique and preferably upgrade the current injecting device. Instead of using a constant current generator the idea is to implement a voltage source and measure current accurately, in order to improve the resolution in the image. The performance of such a device is analysed, particularly concerning theoretical and practical limitations. The amplitude and phase accuracy, noise and settling time are measured and presented in diagrams. The results show that improvements are possible to achieve and that such a device will improve the stability of an EIT system and the image quality.

Electric Impedance↗

PubMed1992

Demonstration of digital radiographs by means of ink jet-printed paper copies: pilot study.

Different digital medical images have been printed on paper with a continuous ink jet printer, and the quality has been evaluated. The emphasis has been on digital chest radiographs from a computed radiography system. The ink jet printing technique is described as well as the handling of the image data from image source to printer. Different versions of paper prints and viewing conditions were compared to find the optimum alternative. The evaluation has been performed to maximize the quality of the paper images to make them conform with the corresponding film prints and monitor images as much as possible. The continuous ink jet technique offers high-quality prints on paper at a considerably lower cost per copy compared with the cost of a film print. With a future switch-over from diagnosing of digital images on film to diagnosing them on monitors, hard copies for demonstration purposes will occasionally be needed. This need can be filled by ink jet-printed paper copies.

Copying Processes↗

PubMed1991

On the mechanism of kidney stone disintegration by acoustic shock waves.

In the present study we have, by theoretical and experimental investigations, especially concentrated on the importance of acoustic streaming, transient cavitation and microstreaming in the fluid close to the stone. Artificial stones, round stones 20 mm in diameter made of Plaster of Paris or rectangular flat stones, 25 x 25 x 15 mm, were suspended in a water bath at the focus of an EDAP LT01 lithotripter. "Unprotected" stones were disintegrated while stones surrounded by a layer of silicone showed no or very small disintegration. For successful destruction of the calculus, it seems to be essential that the stones are surrounded by a liquid, i.e., water.

Humans↗

PubMed1991

Analysis and classification of secondary sounds from the disintegration of kidney stones with acoustic shock waves.

Secondary sound emission, partly in the audible frequency range, from shock wave disintegration of kidney stones has been recorded during the treatment of two patients. A skilled operator can determine by listening if the stone is hit by the shock-wave or not. Spectral analysis of these recordings show differences between the sounds which can be used to evaluate the fragmenting effect on the stone. Results are presented of a preliminary discriminating method based on parameters in an autoregressive signal model.

Humans↗

PubMed1991

A measurement system for continuous wave ultrasound fields.

A measurement system for evaluating ultrasound fields is presented. The system utilizes a PVDF hydrophone and a mechanical scanning device. For continuous wave (CW) ultrasound, a high sensitivity is achieved by using a narrow band technique. The high sensitivity is demonstrated in a recording of the beam profile from an air transducer. Recordings from fetal Doppler equipment shows that, due to interference between the multiple transmitters, a high spatial resolution is needed in the field measurements in order to obtain correct values for peak intensities.

Female↗

PubMed1991

Registration of surface structures using airborne focused ultrasound.

A low-cost measuring system, based on a personal computer combined with standard equipment for complex measurements and signal processing, has been assembled. Such a system increases the possibilities for small hospitals and clinics to finance advanced measuring equipment. A description of equipment developed for airborne ultrasound together with a personal computer-based system for fast data acquisition and processing is given. Two air-adapted ultrasound transducers with high lateral resolution have been developed. Furthermore, a few results for fast and accurate estimation of signal arrival time are presented. The theoretical estimation models developed are applied to skin surface profile registrations.

Humans↗

PubMed1991

The use of ink jets in ultrasound registrations.

The continuous ink jet method developed by Professor Hellmuth Hertz, Lund Institute of Technology, Sweden, is today used in printers that print digitally stored high-quality images rapidly and at low cost. The development started in the late 1950s when there was a need for a direct registration method for ultrasound echocardiograms. The development steps are described from the early ultrasound registrations to the true halftone printing of digital images today. Images from ultrasonic color Doppler examinations have been printed by an ink jet printer at our laboratory. The color capabilities of the printer are further illustrated by the printing of pseudo-colored gray-scale images and an image where color is used to highlight differences between two gray-scale images. The results show that the printer based on continuous ink jets is an interesting alternative to the existing hard-copy devices for medical images.

Echocardiography, Doppler↗

PubMed1991