Jaap Lubbers

Validation of a New Blood-Mimicking Fluid for Use in Doppler Flow Test Objects

A blood-mimicking fluid (BMF) suitable for use in Doppler flow test objects is described and characterised. The BMF consists of 5 microns diameter nylon scattering particles suspended in a fluid base of water, glycerol, dextran and surfactant. The acoustical properties of various BMF preparations were measured under uniform flow to study the effects of particle size, particle concentration, surfactant concentration, flow rate and stability. The physical properties, (density, viscosity and particle size), and acoustical properties (velocity, backscatter and attenuation) of the BMF are within draft International Electrotechnical Commission requirements.

A simple and accurate formula for the sound velocity in water

The sound velocity in test objects and phantoms is often measured by performing a differential measurement with pure water. To promote standardization, a simple formula for the sound velocity in water is derived that renders true values within 0.20 m s(-1) over the temperature range 15-35 C. The formula is given by c = 1404.3 + 4.7 T - 0.04 T2, with sound velocity c in m s(-1) and temperature T in C.

An ultrasonic detector for microgasemboli in a bloodflow line

Abstract A detector for small gas bubbles in the blood-flow line from a heart-lung machine was constructed and tested. The way in which a passing bubble forms a signal is analyzed. The relation between signal size and bubble size is established experimentally and confirmed by theoretical calculations. It is shown that solid and soft (tissuelike) particles give much smaller signals than gaseous particles. The influence of the measuring frequency on the detectability of particles is derived from theory and shown experimentally.

Skeletal muscle perfusion measured by positron emission tomography during exercise

Abstract The applicability of H215O-positron emission tomographic (PET) imaging for the assessment of skeletal muscle perfusion during exercise was investigated in five healthy subjects performing intermittent isometric contractions on a calf ergometer. The workload of the left calf muscles was kept constant in all exercises, while that of the right calf muscles was varied. During exercise H215O distribution in the calf muscles was measured by PET. Radioactivity measured in the left calf muscles was used as a reference for the radioactivity measured in the right calf muscles. In all studies, muscles were delineated by uptake of radioactivity. Four subjects demonstrated high radioactivity in the gastrocnemius medialis muscle, in one subject high radioactivity was distributed over the triceps surae muscles. The observed muscles demonstrated also local foci of radioactivity indicating regionally enhanced tissue perfusion. The right-left ratio of radioactivity in the active muscles increased as a function of the load. We conclude that inter- and intramuscle perfusion differences can be measured during exercise by H215O-PET imaging.

Time to threshold (TT), a safety parameter for heating by diagnostic ultrasound

Activities in the standardisation of medical ultrasonic imaging and monitoring devices have been undertaken to ensure the safe application and to provide the user with tools to perform risk-to-benefit analysis. Internationally, agreement has not been reached to implement a system based on a physical quantity such as temperature rise. Therefore, recently, the IEC Standard 60601-2-37 has adopted the thermal index (TI) as a safety parameter. TI indicates conditions that are more likely than others to produce thermal effects. The models used to calculate TI are based on the equilibrium temperature rise for a stationary transducer. Ultrasound (US) is often applied during a short time at one place. To characterise the situation before equilibrium is reached, this study proposes a new parameter: TT (time to threshold). TT indicates the time after which a threshold temperature rise is exceeded. TT is calculated for some tissue models to illustrate the meaning of TT. TT indicates how long one piece of tissue can be insonated safely, provided the safe threshold is known. Using TT, higher intensities can be applied safely during a limited time. This paper illustrates the effects of short insonation times and the influence of the beam diameter. Questions that are critical to the introduction of TT as a safety parameter are discussed.

Increased release of gentamicin from acrylic bone cements under influence of low-frequency ultrasound

The release profile of antibiotics from antibiotic-loaded bone cement, used to prevent infections in total joint arthroplasty, is neither ideal nor complete. Ultrasound has been used to allow drugs to cross otherwise impermeable barriers. The aim of this study was to establish a possible effect of ultrasound on antibiotic release from bone cements. Samples were made of three commercially available gentamicin-loaded bone cements. Part of the samples was allowed to release gentamicin for 3 weeks before insonation. An insonation device produced an ultrasound field with a time average acoustic intensity of 167 mW/cm2 at a frequency of 46.5 kHz. The samples were exposed to the ultrasound field or not exposed to it as a control. The amount of gentamicin released was measured by fluorescence polarization immunoassay. There was a limited increase of gentamicin release with application of ultrasound in fresh samples but not in the samples that had been allowed to release gentamicin. For fresh samples, a linear regression model showed that this ultrasound effect was statistically significant. The mechanism behind these observations is not clear, but it is suggested that microstreaming or localized temperature rises may be involved.

BLOOD-FLOW IN THE CALF DURING AND AFTER EXERCISE - MEASUREMENTS WITH DOPPLER ULTRASOUND AND VENOUS OCCLUSION PLETHYSMOGRAPHY IN HEALTHY-SUBJECTS AND IN PATIENTS WITH ARTERIAL OCCLUSIVE DISEASE

From the Laboratory of Medical Physics, University of Groningen, and the Department of Cardiology, University Hospital of Groningen, The Netherlands. Obviously, the measurement of the blood flow in the calf at rest does not give information about the functional reserve capacity of the arterial system to and in the lower leg. More information can be obtained by measuring the peak flow after 5-minute arterial occlusion.1-8 However, it was found that in

Application of a new blood-mimicking fluid in a flow Doppler test object.

OBJECTIVE To construct and apply a flow Doppler test object and its flow rig. METHODS In this flow rig, particular attention was given to use of a long inlet length and to ensure the absence of disturbing particles. The latter was obtained by proper degassing, use of a filter and application of a fungicide. Two blood-mimicking fluids were used, with a viscosity of 4 and 8 mPa s respectively. RESULTS Predictable Poiseuille flow profiles were obtained. The velocity range could be extended by increasing the viscosity of the blood-mimicking fluid. Predictable axial velocities up to 2.5 m/s were obtained in an 8-mm tube and 5 m/s in a 4-mm tube. CONCLUSION Well-defined flow conditions that can be applied to investigate clinical ultrasound Doppler systems in a number of situations have been obtained.

In vitro measurements of aerodynamic characteristics of an improved tracheostoma valve for laryngectomees

Abstract Tracheostoma valves are often required in the rehabilitation process of speech after total laryngectomy. Patients are thus able to speak without using their hands to close the tracheostoma. The improved Groningen tracheostoma valve consists of a “cough” valve with an integrated (“speech”) valve, which closes for phonation. The cough valve opens as the result of pressure produced by the lungs during a cough. The speech valve closes by the airflow produced by the lungs, thus directing air from the lungs into the esophagus at a deliberately chosen moment. An experimental setup with a computer-based acquisition program was developed to measure the pressure at which the cough valve opened and the flow at which the speech valve closed. In addition, the airflow resistance coefficient of the tracheostoma valve was defined and measured with an open speech valve. Both dry air from a cylinder and humid expired air were used. Results showed a pressure range of 1–7 kPa to open the cough valve and a flow range of 1.2–2.7 l/s to close the speech valve. These values were readily attained during speech, while the flow range occurred above values reached in quiet breathing. The device appeared to function well in physiological ranges and was optimally adjustable to an individual setting. No significant differences were measured between air from a cylinder and humid expired air. Findings showed that methods used to obtain results could be employed as a reference method for comparing aerodynamic characteristics of tracheostoma valves.

A continuous wave doppler velocimeter for monitoring blood flow in the popliteal artery, compared with venous occlusion plethysmography of the calf

A transcutaneous Doppler velocimeter has been used for monitoring changes in blood flow in the popliteal artery during and after exercise of the calf muscles on a calf-ergometer. The instrument and the positioning of the probe are described. The validity of the Doppler measurements has been assessed by comparing results after exercise and after 5 min arterial occlusion with venous occlusion plethysmography. For 10 healthy volunteers calibration lines were found which are curved. This can be ascribed partly to alinearity of the Doppler instrument and partly to changes of the diameter of the popliteal artery. Displacement of the probe with respect to the artery, which influences the measured velocity signal, can be detected and to a certain extent corrected by taking into account the intensity of the Doppler signal. The largest deviation of a data point from the corresponding calibration line varies for the ten subjects between 90 and 170 Hz in the high flow range (mean Doppler frequency around 1000 Hz) and between 20 and 60 Hz in the low flow range (mean Doppler frequency below 200 Hz).