Nils-Gunnar Holmer

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°), the reproducibility is high (0.2°), and the inherent angular noise is small (0.04°) 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.

A Comparison Between Different Ultrasonic Display Techniques, Radiography and Invasive Control For Different Disorders Of The Paranasal Sinuses

Three pieces of simplified ultrasound equipment adapted for investigation of the paranasal sinuses have been tested in a clinical investigation of 148 sinuses in comparison with radiography and invasive control. An oscilloscope (OSC), one single row of light emitting diodes (LED) and a gas discharge (GD) display were used as display units. No statistically significant difference was found between the different displays or radiography in their screening capacity. It was found that the OSC-display was significantly more reliable than the other displays and radiography in separating different pathological conditions.

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.

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 phatom with simulated tumors in the mediastinum and right lund, 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 1,760×2,140 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 exdaminations 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.

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.

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 jetprinted paper copies.

Digital Preshaping of Ultrasonic Signals: Equipment and Applications

This p aper describes an a rrangement that uses AD and DA conversion and a computer in order to preshape a transmitted ultrasonic wave. Normally the ultrasonic transducer is excited by a very short e lectrical pulse. Using a DAC, the ultrasonic transducer can be excited by any desired waveform e g the digitally determined inverse filter, chirp signals etc. The desired excitation waveform is stored in a high speed memory. It is shifted out via the DAC to an amplifier and thence to the transducer. The ADC, which is triggered by the DAC equipment, converts one sample per sweep into 12 bits. Therefore, actual sample rate is low. But the virtual sample rate limited by the sample and hold circuit can reach 15 MHz. The ADC and DAC are connected to a microcomputer system that determines the desired excitation waveform. Various waveforms can be stored and it is then possible to change the excitation waveforms interactively during clinical examinations.

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.

Isolation Amplifier Energized by Ultrasound

A power supply energized by ultrasound has been developed and investigated. The supply can be used in medical applications where a high isolation from earth is essential, for example in the protection of a patient from the hazards of electric shock caused by medical instrumentation. The ultrasound energy is generated by a transmitting piezoelectric crystal (transducer) and sent to a receiving transducer via a glass rod 20 mm long. At the receiving transducer the acoustic energy is converted back to electric energy. The power transmission has been measured at different resonances of the glass rod-transducer combination. The radial mode resonance of the transducer seems to give the largest power transfer and the highest efficiency.

An Electrometer Amplifier with Low Input Capacitance and Large Input Dynamic Range

An electrometer amplifier has been designed for biological research with the following data: input resistance larger than 10 12 ; input current 10 -12 A; low input capacitance; and an input dynamic range from 0 to ± 7 v. The input stage consists of JFET.