Local hyperthermia induced by focussed and overlapping ultrasonic fields—An in vivo demonstration

Axial temperature distributions were measured in living and post mortem porcine tissues during sonication with plane, focussed and overlapping ultrasonic fields. With the focussed field it was always possible to induce the temperature maxima at depths up to 50 mm, although the actual temperatures achieved varied from animal to animal. The plane 0.75 MHz transducer produced a maximum temperature close to the skin surface. With 7 overlapping plane fields a relatively uniform temperature distribution was produced in a large tissue volume. The blood perfusion in tissue has a significant effect not only on the magnitude of the temperature increase, but also on the temperature distribution.     

Characterisation of in vivo placental ultrasonic images using digital techniques-a preliminary report

Computer analysis of the digitized ultrasonic waveform from in vivo placentae (14–40) weeks gestation has been used to quantify the B-scan appearance. The amplitude distribution of echo peaks detected from the video waveform is described by two parameters, coefficient of variation and skew. Both indices correlate with B-scan appearance (p<0.001) for a group of 22 patients. The results of 92 scans suggest that the texture index value reflects the degree of calcification and fibrin deposition in the tissue. The texture indices of second trimester placentae (14–18 weeks gestation, n = 20) correlate with the development of hypertension later in pregnancy (p<0.05).     

Computer based pattern recognition of carotid artery Doppler signals for disease classification: prospective validation

A computer based pattern recognition method has been developed to classify the percent diameter reduction in nonoccluded internal carotid arteries. Using a combined B-mode/pulsed Doppler unit, the system utilizes spectral waveforms obtained from the low common and proximal internal carotid artery locations. The ECG-R wave is used as a time reference to synchronize the averaging of Doppler spectra from 20 heart cycles. An averaged waveform is generated and represents the spectral data from which features are extracted for analysis. A stepwise selection algorithm identifies a feature subset for partitioning the entire range of disease into two states, less than and greater than a decision point. Three such partitions are made, leading to the following categories: Normal, 1-20, 21-50 and 51-99% dia. reduction. A classifier was trained, tested prospectively against unknown data and the results compared to angiography. Of the 170 vessels tested, 141 (82%) were classified in the same category by angiography and the computer system. Agreement for each category was 93% (27/29) for the normals, 81.5% (44/54) for the 1-20% lesions, 78% (29/37) for the 21-50% lesions and 82% (41/50) for the 51-99% lesions. The computer method and angiography differed by more than one category in only one of the 170 tests. The level of agreement corrected for chance (Kappa +/- SE(K] was 0.769 +/- 0.039. Future efforts will be directed toward dividing classification of disease further (especially in the 51-99% category), developing a dedicated microprocessor for on-line analysis of the signals and using the system for prospective epidemiological studies of various populations.     

Variability and reproducibility of arterial Doppler waveforms

The variability and reproducibility of arterial Doppler waveforms are influenced by factors such as operator experience, physiological changes in the patient, and the type of Doppler processing system. Some aspects of these were studied using Laplace transform analysis of waveforms from the femoral and posterior tibial arteries of normal subjects and arteriopaths.Five consecutive waveforms were obtained from the femoral and posterior tibial arteries of normal subjects during about 1 hr of supine rest. Group 1 (n = 20) was studied 9 months before Group 2 (n = 11), early in the operator's experience of waveform recording. Variability (root mean square) of femoral and posterior Laplace 6 decreased from 16.9 to 12.5%, and 23.3 to 17.9% respectively (P < 0.05 in each case). In arteriopaths (n = 8) there was a trend to more variable results at femoral level (only significant in the case of Laplace ω₀ - P < 0.05), while posterior tibial results tended to be less variable. Normal subjects examined in the longer term (n = 4), with a mean interval of 28 days between recordings, did not show significantly greater variability than those examined over 1 hr.There was no significant difference in variability of results in normal subjects (n = 30) using instantaneous average Doppler processing compared with maximum frequency processing, except in the case of posterior tibial Laplace ω₀ (maximum frequency more variable - P < 0.05).     

Effects of ultrasound on Drosophila—II. The heating mechanism

An exposure of the eggs of Drosophila melanogaster to a traveling wave of 1 MHz ultrasound at 5 W/cm² for 30 sec has been found to kill approximately 70% of the population. To determine whether heating could be responsible for this effect, the sensitivity of the eggs to heat alone was tested. Temperature increments attributable to ultrasound were estimated by treating the eggs as heat sources in a thermally conducting medium. The absorption coefficient of the eggs was found to be very large but estimated to be less than 5 nepers/cm. The corresponding maximum temperature increments were calculated to be less than 3°C. This value is far too low to account for the observed effects on the basis of heating.     

Unusual intrauterine objects: potential pitfalls in ultrasonographic identification.

Three cases of echogenic objects in the uterine cavity are reported. These objects had ultrasonographic characteristics of contraceptive intrauterine devices (IUDs) and, in the absence of patients' medical histories, would almost certainly have been wrongly identified as such. The authors demonstrate that noncontraceptive intrauterine objects can mimic IUDs.     

Methods for ultrasonic imaging of the heart

Ultrasound imaging of the heart is divided into one-dimensional methods currently in use, preliminary techniques which have been developed for two-dimensional static and motion imaging, those techniques currently under development for two-dimensional motion imaging, and goals which appear achievable and which would appear to lead to an ultimate cardiac diagnostic system. The primary current one-dimensional display of cardiac ultrasound data is range as a function of time. This provides dynamic information about cardiac structures lying within a relatively narrow ultrasonic beam but fails to show the coordinated motion of entire structures under study and depicts movements which occur across the beam as intermittently appearing echo complexes. Preliminary approaches employing mechanical assemblies which contain either moving transducers or rotating reflectors have been used to show feasibility of motion imaging. Systems currently under development for two-dimensional motion imaging of the heart use mechanical or electronic beam scanning or multielement arrays for real-time presentations or use ECG-based sampling and computer processing for image construction and data processing. Achievable goals for future development include the simultaneous imaging of solid structures of the heart as well as quantitative display of blood flow data in a motion format and in three dimensions with specific indications of tissue and flow macrostructure.     

Sonoluminescence, in water and in human blood plasma, generated using ultrasonic therapy equipment

Sonoluminescence in a liquid indicates both cavitation and free radical formation. This experimental study showed that it can be generated in both water and blood plasma using ultrasound at therapeutic intensities (less than 2W cm⁻², spatial average) and frequencies (0.75 and 1.5 MHz). Pulsing the ultrasound raised the intensity threshold for sonoluminescence. Recordings of acoustic emission from the liquid (for 0.75 MHz continuous insonation) showed that sonoluminescence was accompanied by the emission of ‘broad-band’ noise. The applicability of these results to tissue insonation, and the implications for ultrasound therapy, are discussed.     

Cell death thresholds in Elodea for 0.45–10 MHz ultrasound compared to gas-body resonance theory

Leaves of the aquatic plant Elodea were sonicated continuously for 100 sec at ten frequencies in the range 0.45–10 MHz. Cell death thresholds were determined for three cell populations in the leaves for each frequency. The intensity thresholds were strongly dependent on frequency, and the minimum threshold for each population generally occurred near the expected resonance frequency of the gas bodies associated with each population. The thresholds were as low as 75 mW/cm² at 0.65 MHz and 180 mW/cm² at 5 MHz.     

In vitro measurements of sound velocity in human fetal brain tissue

Sound velocity measurements were performed on 23 fresh fetal brain samples obtained at gestations between 17 and 41 weeks duration. Determinations were made at 0, 8, 16, 24, 30 and 37°C.

In 14 samples the water content was also calculated. An increase in sound velocity through fetal brain tissue with advancing gestational age, together with an increase in sound velocity associated with increasing temperature of the sample from 0 to 37°C, was found. Sound velocity was higher through fetal brain tissue from pregnancies terminated using intra-amniotic urea when compared with spontaneous abortions of the same gestational age. A significant positive correlation was found between sound velocity and the percentage content of solids in the brain.