Good vibrations

How and where the brain forms associations between sensation and action are crucial questions in the field of cognitive neuroscience. In this issue of Neuron, add to an already impressive body of work elucidating the neural mechanisms responsible for forming categorical decisions about vibrotactile stimuli that guide behavior. Here they show that single neurons in premotor cortex represent, remarkably, what appears to be the entire temporal evolution of the decision process-from representation of the sensory stimulus, to formation of the discrimination, to the choice of behavioral output.     

Cardiac imaging: the biological effects of diagnostic cardiac ultrasound

Diagnostic cardiac ultrasounds are an environment-friendly and non-ionising imaging technology. However, ultrasounds are not biologically inert, and their use might have profound clinical impact. This paper summarizes the known effects of cardiac ultrasound—compared to other major imaging techniques—to exposed patients and to clinically exposed physicians practising ultrasound imaging. Furthermore, this review also provides an overview of the evidences on the biological effects of diagnostic ultrasound—which suggest that ultrasound with frequency, intensity and duration fully in the diagnostic range have significant molecular, cellular and organ effects.

A better understanding of these effects may improve our understanding of the complex interactions between ultrasound and biological tissues and may open new avenues to therapeutic applications based on the ultrasound-modulated cell functions, such as membrane transduction, apoptosis, cell permeability and thrombolysis.     

Use of diagnostic ultrasound for assessing muscle size

The typical "gold standard" for assessing muscle size has been magnetic resonance imaging (MRI) and computerized tomography; however, these processes are very expensive and generally require a medical facility. The advent of B-mode diagnostic ultrasound (US) can perhaps offer a quick, cost-effective method to measure muscle size. The purpose of this study was to document the reliability of B-mode US for assessing muscle size in a variety of populations. Thirty-eight postmenopausal women (avg. age = 58.9 +/- 0.7 years) had both their right rectus femoris and biceps brachii imaged, 85 older men and women (avg. age = 65.0 +/- 0.4 yrs) had their right rectus femoris imaged, and 10 young men and women (avg. age = 26.1 +/- 2.4 yrs) had their right rectus femoris imaged by both US and MRI. The location used for imaging on the right rectus femoris was a point 15 cm above to the superior border of the patella following the midline of the anterior surface of the thigh, whereas the biceps brachii was measured at maximal girth following the midline of the anterior surface of the upper arm. All trials utilizing US (Fukuda Denshi, model 4500) and a 5 Mz transducer (FUT-L104) were obtained in duplicate on 2 separate days. The young subjects that also had their rectus femoris measured by MRI were imaged with a Picker 1.5 Tesla (The Edge), which used a fast spin sequence and 192 x 256 resolution to obtain 2 5-mm-thick slices separated by a 1-mm-thick space. All intraclass correlation coefficients for the various groups and muscles measured by US ranged from r = 0.72-0.99, whereas coefficients of variation (CVs) ranged between 3.5% and 6.7%. The intraclass correlation for the MRI images was r = 0.90 and the CV was 5.2%. In conclusion, it appears that diagnostic US can provide a reliable and cost-effective alternative method for assessing muscle.     

Reproductive performance in mares subjected to examination by diagnostic ultrasound

Mares were subjected to frequent examination by diagnostic ultrasound and data were compiled with respect to reproductive efficiency. The data were collected over a 3-yr period on 1032 light horse mares. The cummulative pregnancy rate at 35 d post-ovulation was 96.8% and the pregnancy rate per cycle was 76.0% as determined by ultrasound examination. The average number of cycles per conception was 1.43, with an average of 2.29 inseminations per cycle. The incidence of early embryonic death was 7.8%. Mares were subjected to an average of 5.04 scans during the follicular phase of the cycle. The average number of ultrasound examinations per mare (including pregnancy examinations) was 9.99. Although these data were obtained from an experiment that did not use both control and treated mares, there was no indication that preovulatory oocytes or embryos were damaged by routine ultrasound examination. Comparisons with existing data from commercial facilities are difficult to make concerning any improvement in reproductive efficiency resulting from the routine use of ultrasonography, but these data do suggest relative safety in equine reproductive management when ultrasound examinations are conscientiously used.     

Quantification of risk from fetal exposure to diagnostic ultrasound

Biomedical ultrasound may induce adverse effects in patients by either thermal or non-thermal means. Temperatures above normal can adversely affect biological systems, but effects also may be produced without significant heating. Thermally induced teratogenesis has been demonstrated in many animal species as well as in a few controlled studies in humans. Various maximum ‘safe’ temperature elevations have been proposed, although the suggested values range from 0.0 to 2.5° C. Factors relevant to thermal effects are considered, including the nature of the acoustic field in situ, the state of perfusion of the embryo/fetus, and the variation of sensitivity to thermal insult with gestational stage of development. Non-thermal mechanisms of action considered include acoustic cavitation, radiation force, and acoustic streaming. While cavitation can be quite destructive, it is extremely unlikely in the absence of stabilized gas bodies, and although the remaining mechanisms may occur in utero, they have not been shown to induce adverse effects. For example, pulsed, diagnostic ultrasound can increase fetal activity during exposure, apparently due to stimulation of auditory perception by radiation forces on the fetal head or auditory structures. In contrast, pulsed ultrasound also produces vascular damage near developing bone in the late-gestation mouse, but by a unknown mechanism and at levels above current US FDA output limits. It is concluded that: (1) thermal rather than nonthermal mechanisms are more likely to induce adverse effects in utero, and (2) while the probability of an adverse thermal event is usually small, under some conditions it can be disturbingly high.