Biomedical subjects

R J Simeoni

Publications and source records attributed to R J Simeoni.

5 recordsLinked to original sources

PubMed2003

Bicoherence analysis of quadriceps electromyogram during isometric knee extension.

Bicoherence analysis is applied to electromyogram (EMG) data for the vastus lateralis quadriceps muscle of 18 adult male subjects for isometric knee extension exercise. Bicoherence spectra display ridge-like features that are indicative of deterministic chaotic behaviour and similar to those reported for normal electrocardiogram and electroencephalogram bicoherence spectra. No other obvious features are visually identified within bicoherence spectra in response to the stimulus of isometric tension. Histograms that show the occurrence of constituent EMG frequencies associated with the strongest bicoherence display subtle fluctuations. Validation tests that include the analysis of white noise data show these fluctuations to most likely be a consequence of the normal time evolution of a deterministic chaotic process. The finding suggests that second-order phase coupling is not pronounced between any particular bands of constituent EMG frequencies for the vastus lateralis EMG generation process during the specified isometric task. Previous studies into bicoherence analysis of EMG data are not apparent in the literature for comparison. Since nonlinear processes are known, through mechanomyogram bicoherence analysis, to be significant within active muscle fibre twitch summation patterns, the finding does not exclude the potential for bicoherence analysis to complement standard EMG frequency analysis techniques in the area of sports rehabilitation and medicine. Further investigation is required to establish whether this potential exists. An introduction to bicoherence analysis theory is also presented.

Adult↗

PubMed2003

Quadriceps muscles vastus medialis obliques, rectus femoris and vastus lateralis compared via electromyogram bicoherence analysis.

Bicoherence analysis is applied to electromyogram (EMG) data for vastus medialis obliques (VM), rectus femoris (RF) and vastus lateralis (VL) quadriceps muscles of 18 adult male subjects for isometric knee extension exercise. Mean average bicoherence for VM, RF and VL is 30.9 +/- 5.8, 26.0 +/- 1.2 and 25.4 +/- 1.4% respectively and repeated measures ANOVA differentiates the muscles on the basis of average bicoherence (F = 16.2 (1, 17), p = 0.0009, VM cf. VL and F = 15.4 (1, 17), p = 0.0011, VM cf. RF). Prominent regions representative of strong second-order phase coupling between constituent EMG frequencies are identified within VM and RF bicoherence spectra. No such prominent regions are identified for VL which is thought to be less activated than VM during the specified task. Hence, the degree of second-order phase coupling may increase as the level of muscle activation increases. The subject group consists of young (24.0 +/- 0.9 years) and elderly (68.9 +/- 0.9 years) subgroups that cannot be differentiated by standard indices (median and spectral edge frequency) to within p < 0.05 using the Mann-Whitney test. Average bicoherence differentiates the subgroups for RF (T = 9 (8,10), p < 0.005) but not for VM or VL. The application of a bicoherence threshold that takes harmonic amplitude into account graphically differentiates the subgroups for all muscle types. The findings suggest that nonlinear processes play a role within the EMG generation process and support a mechanomyogram bicoherence analysis study that shows nonlinear processes occur within active muscle fibre twitch summation patterns. A potential exists for bicoherence analysis to complement standard EMG frequency analysis techniques.

Adult↗

PubMed1993

Scatter radiation in mammography.

Current information pertinent to scatter radiation for mammographic x-ray spectra is limited. Data presented by the National Council on Radiation Protection and Measurements (NCRP), the current shielding authority, are restricted to 50 kVp tungsten target spectra and contain several incompatibilities with the modern mammographic situation. The ratio of scattered to incident exposure was measured for two molybdenum target spectra (36 kVp, 30 microns molybdenum filtration and 49 kVp, 50 microns aluminium filtration). The maximum scatter ratio occurred at 150 degrees to the primary beam direction for both spectra; the values were (1.73 +/- 0.09) x 10(3) and (2.6 +/- 0.1) x 10(3) respectively for a field area of 400 cm2, a scattering distance of 1 m and a primary beam exposure distance of 1 m from the x-ray source. The results obtained differ significantly from NCRP based data presently used for mammographic shielding calculations. The consequences of these differences are discussed.

Female↗

PubMed1993

A device for measuring compression force in mammography.

Compression in mammography is an accepted technique for improving image quality and reducing dose, but excessive compression can cause pain and other undesirable effects. Therefore, maximum compression force should be measured in a quality assurance programme. A compression force meter, based on a load cell design, has been constructed and used to make compression force measurements on three GE Senographe 600T mammography machines. These measurements show that the conversion from pneumatic pressure (as indicated on the machine) to applied compression force is given by Compression Force (N) = (79.0 +/- 0.9) x Pneumatic Pressure (bars) + (12.2 +/- 4.0). Using this equation and pneumatic pressure settings on nine GE Senographe 600T units in our quality assurance programme, the maximum compression force in clinical use ranges from 102 to 150 N with a mean of 126 N. This is lower than guidelines used in the United States and the United Kingdom.

Female↗

PubMed1992

A calibration comparison of mammographic kVp meters.

Modern screen-film mammography employs a molybdenum target and molybdenum filtration to obtain both high image contrast and low patient dose. Typical x-ray emission spectra are therefore dominated by molybdenum's characteristic radiation. The form of such spectra makes the accurate measurement of mammographic kVp difficult. Non-invasive digital kVp meters provide the simplest method of measuring mammographic kVp routinely, with a typical uncertainty of greater than +/- 1 kVp. With the expansion of breast screening, more stringent demands have been placed on these meters and recent calls for accuracies of better than +/- 1 kVp have been made. The responses of six popular mammographic kVp meters were compared in the range 22 to 32 kVp. Agreement between four of these meters above 24 kVp was within 1.8 kVp. The responses of the two remaining meters differed from the other meters by up to 5 kVp over the range. The results have highlighted the need for regular calibration checks on mammographic kVp meters and the provision of a national standard to which these calibrations can be traceable. Such a standard is currently not available in Australia.

Calibration↗