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.

Thermotherapy: feasibility study using a single focussed ultrasound transducer.

Feasibility studies on tissue lesioning using high intensity focussed ultrasound (HIFU) thermotherapy were carried out. A single strongly focussed transducer was used. The transducer has a diameter of 50 mm, a centre resonance frequency of 1 MHz and a focal distance of 50mm. Experiments were carried out both in vitro on pig muscle samples and in vivo on a pig (exposures on the thigh and on the liver). Different types of burst pulse signals were used, the best results were obtained with 1-2 s burst pulses, with a repetition period of 10s. The risk for skin damage increases for longer burst pulses. Lesions at the focus were obtained both in the experiments in vitro as well as in vivo. The size and the shape of the lesions in vivo resemble those obtained in vitro. The results of the experiments show that tissue lesions can be obtained at deep locations (4.5 cm in the tissue) with the transducer. The lesions were well discriminated from the surrounding tissue and were ellipsoid- or drop-shaped. The lesion size can be controlled by the choice of time parameters of the burst pulse signal, power and treatment time. Temperatures of about 80 degrees C were measured in the tissue at the ultrasound focus in vitro. These results show that elevated temperatures can be induced rapidly at the focus, thus reducing the effect of heat dissipation through blood perfusion.

Teleradiology in southern Sweden--a tool for reorganization of health care and for education.

The county organization, including health care, is reorganized in the province of Scania in southern Sweden. As part of the restructuring of health care, a program for digitalization of the departments of diagnostic imaging, as well as for teleradiology, has been set up. Standards for network, radiology information systems, and workstations have been settled, and teleradiology links both for on-call consultations and for on-line consultations day-time have been implemented, mainly running at 10 Mb/s. Further digitalization and implementation of teleradiology is planned for the nearest years. Parallel to this, a video conference system including several disciplines, hospitals and health care levels in the whole of southern Sweden has been implemented. The links are now also used for education, both in the province and internationally.

Measurements of the thermal focus of an experimental focused ultrasound thermotherapy system.

The thermal focus of an experimental thermotherapy equipment based on high energy focused ultrasound has been investigated. The in-house built equipment has a treatment head of seven separate focused transducers arranged in a semispherical fixture with a common focus at 100 mm from the transducer surfaces. Each transducer has a diameter of 50 mm and operates at 0.5 MHz. The ultrasound field of this seven-transducer arrangement, as well as of a single transducer of the same type as the ones in the arrangement, has been investigated in terms of temperature distribution evolved by absorption in castor oil. The results of the single transducer measurements show an ellipsoid-shaped focus displaced from the geometrical focus towards the transducer, whereas the measurements of the treatment head show a thermal focus which practically coincides with the geometrical one. Differences in location and shape of the thermal focuses depend on differences in the focusing action and the absorption in the media. Pilot investigations on tissue lesioning in vitro on pig muscle samples and in vivo on pig thigh were also carried out. Well discriminated local lesions with ellipsoid shape were obtained in the experiments in vitro and in vivo. Temperatures of up to 80 degrees C were measured in tissue at the focus in vitro. The results show that the equipment is well suited for thermotherapy applications.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The pulsed ultrasound method adapted for examination of paranasal sinuses.

Three different ultrasonic display systems for examination of paranasal sinuses (oscilloscope; light emitting diodes; gas discharge display) have been evaluated in model experiments, on healthy subjects and in clinical materials. With the three different ultrasonic display systems air could be separated from other types of sinusal contents in model experiments. The detectable amount of saline solution in normal sinuses was 1-5 ml with all display units. The different display units showed the same screening capacity as radiography. The oscilloscope display system was significantly more efficient than the other display systems in separating different pathological conditions. Also regarding radiography the oscilloscope display was significantly more efficient in detecting secretion, but no difference was found in the capacity of predicting intrasinusal cysts. Thus, the oscilloscope display seems to be the most useful for both clinical and scientific purposes.