Effects of an electric field on white sharks: in situ testing of an electric deterrent.

Elasmobranchs can detect minute electromagnetic fields, <1 nV cm(-1), using their ampullae of Lorenzini. Behavioural responses to electric fields have been investigated in various species, sometimes with the aim to develop shark deterrents to improve human safety. The present study tested the effects of the Shark Shield Freedom7™ electric deterrent on (1) the behaviour of 18 white sharks (Carcharodon carcharias) near a static bait, and (2) the rates of attacks on a towed seal decoy. In the first experiment, 116 trials using a static bait were performed at the Neptune Islands, South Australia. The proportion of baits taken during static bait trials was not affected by the electric field. The electric field, however, increased the time it took them to consume the bait, the number of interactions per approach, and decreased the proportion of interactions within two metres of the field source. The effect of the electric field was not uniform across all sharks. In the second experiment, 189 tows using a seal decoy were conducted near Seal Island, South Africa. No breaches and only two surface interactions were observed during the tows when the electric field was activated, compared with 16 breaches and 27 surface interactions without the electric field. The present study suggests that the behavioural response of white sharks and the level of risk reduction resulting from the electric field is contextually specific, and depends on the motivational state of sharks.

Quantitation of regional ejection fractions using gated tomographic imaging with 99mTc-sestamibi.

BACKGROUND: Gated single photon emission CT (SPECT) sestamibi imaging allows the simultaneous assessment of myocardial perfusion and left ventricular function. OBJECTIVE: The purpose of this study was to evaluate a technique for quantitative regional wall motion assessment using gated SPECT (99m)Tc-sestamibi imaging. PATIENTS AND INTERVENTIONS: Fourteen subjects without cardiac pathology and 25 patients who had experienced myocardial infarction (MI) were studied. After tomographic reconstruction of gated short-axis slices, the identification of endocardial borders was made using a standard edge-detection program in systole and diastole in each of five selected slices. Regional ejection fraction (EF) and myocardial perfusion were determined for five regions within each slice. Ten patients underwent echocardiographic regional wall-motion analysis, the results of which were compared to corresponding regional EF results. RESULTS: High interobserver reproducibility in the assessment of regional EFs was found, with r values ranging from 0.94 to 0.98. In patients with anterior and inferior MIs, the regional EFs were abnormal in the anterior and septal regions, and the inferior and lateral regions, respectively. The regional EFs correlated significantly with regional perfusion in the anterior walls (r = 0.71; p = 0.0001), the lateral walls (r = 0.66; p = 0.0001), and inferior walls (r = 0.54; p = 0.0004). There was a significant association between the regional EFs and the echocardiographic regional wall motion assessment at the base (p < 0.0001), mid-ventricle (p = 0.0004), and apex (p = 0.0003). CONCLUSIONS: Gated SPECT images obtained (99m)Tc-sestamibi can provide reproducible quantitative, segmental regional EFs for multiple left ventricular slices that are significantly associated with subjective regional wall motion assessment by echocardiography.