Medical & Biological Engineering & Computing

A stereo-photogrammetric method for three-dimensional reconstruction of points in low-dose digital X-ray images obtained using a scanner with similar imaging geometry to that of computed tomography scan projection radiography, was analysed. A calibration frame containing 25 radio-opaque markers with known three-dimensional locations was scanned, and the accuracy of reconstruction of the marker positions under varying control point configurations and separation angles was assessed. Errors of less than 1 mm were obtained when nine test points were reconstructed, with 16, 11 and 7 control points at a 90δ separation angle, and with 16 and 11 control points at 75° and 60° separation angles. The optimum reconstruction, with a resultant error of 0.68mm, was found to occur at a separation angle of 90°, with the largest number of control points (16) used to calculated the parameters of the transformation. Extrapolation in the scanning direction beyond the space defined by the control points gave errors of less than 2mm. This method should be suitable for three-dimensional point reconstruction in applications such as cephalometry, brachytherapy planning and assessment of spinal shape.

The imaging procedure shown in this paper has been developed for processing thermographic images, measuring the ocular surface temperature (OST) and visualizing the ocular thermal maps in a fast, reliable, and reproducible way. The strength of this new method is that the measured OSTs do not depend on the ocular geometry; hence, it is possible to compare the ocular profiles belonging to the same subject (right and left eye) as well as to different populations. In this paper, the developed procedure is applied on two subjects’ eyes: a healthy case and another affected by an ocular malignant lesion. However, the method has already been tested on a bigger group of subjects for clinical purpose. For demonstrating the potentiality of this method, both intra- and inter-examiner repeatability were investigated in terms of coefficients of repeatability (COR). All OST indices showed repeatability with small intra-examiner (%COR 0.06–0.80) and inter-examiner variability (%COR 0.03–0.94). Measured OSTs and thermal maps clearly showed the clinical condition of the eyes investigated. The subject with no ocular pathology had no significant difference (P value = 0.25) between the OSTs of the right and left eye. On the contrary, the eye affected by a malignant lesion was significantly warmer (P value < 0.0001) than the contralateral, where the lesion was located. This new procedure demonstrated its reliability; it is featured by simplicity, immediacy, modularity, and genericity. The latter point is extremely precious as thermography has been used, in the last decades, in different clinical applications.

To evaluate the possibility of respiratory-volume measurement using photoplethysmography (PPG), PPG signals from 16 normal volunteers are collected, and the respiratory-induced intensity variations (RIIV) are digitally extracted. The RIIV signals are studied while reepiratory volume is varied. Furthermore, respiratory rate, body posture and type of respiration are varied. A Fleisch pneumotachograph is used as the inspired volume reference. The RIIV and pneumotachography signals are compared, and a statisical analysis is performed (linear regression and t-tests). The key idea is that the amplitude of the RIIV signal is related to the respiratory volume. The conclusion from the measurements is that there exists a relationship between the amplitude of the RIIV signal and the respiratory volume (R=0.842, s=0.428, p<0.005). Absolute measurements of the respiratory volume are not possible from the RIIV signal with the present set-up. The RIIV signal also seems to be affected by respiratory rate and type. More knowledge about respiratory parameters and improved sensor and filter design are required to make absolute measurements of volumes possible.

In nonstationary flow the estimation of the mean flow with an indicator dilution technique can be described by applying a two-compartment model for the system between the injection site and detection site. The aim of this study was to investigate whether the two-compartment approach could be used in experimental situations as encountered in nonsteady blood flow during artificial ventilation. For this reason a two-compartment function was fitted to probability density functions associated with distributed models. The choice of the distributed functions was based on their superiority over other approaches with regard to the representation of the dispersion process of the indicator. Moreover, reference functions enable the practicability of fitting the two-compartment model as a function of the skewness of the curve to be studied. The first passage times (f.p.t.) distribution and the local density random walk (l.d.r.w.) distribution were used as reference functions. Good similarity between the two-compartment curves and the distributed curves was established for the skewness range found in the indicator dilution curves (i.d.c.s.) obtained at the right and left sides of the heart. The closer similarity to the l.d.r.w distribution could be explained theoretically. Moreover, it is concluded that in this skewness range the ratio of the slopes of the ascending and descending limbs at the inflection points of a curve gives an estimate of the time-constant ratio of the compartments of the compartment model.

Three automatic approaches to ventricular repolarisation duration measurement (R-Tapex, R-Tend threshold and R-Tend fitting methods) are compared on computer-generated and real ECG signals, in relation to their reliability in the presence of the most common electrocardiographic artefacts (i.e. additive broadband noise and additive and multiplicative periodical disturbances). Simulations permit the evaluation of the amount of R-T beat-to-beat variability induced by the artefacts. The R-Tend threshold method performs better than the R-Tend fitting one, and, hence, the latter should be used with caution when R-Tend variability is addressed. Whereas the R-Tapex method is more robust with regard to broadband noise than the R-Tend threshold one, the reverse situation is observed in the presence of periodical amplitude modulations. A high level of broadband noise does not prevent the detection of the central frequency of underlying R-T periodical changes. Comparison between the power spectra of the beat-to-beat R-T variability series obtained from three orthogonal ECG leads (X,Y,Z) is used to assess the amount of real and artefactual variability in 13 normal subjects at rest. The R-Tapex series displays rhythms at high frequency (HF) with a percentage power on the Z lead (57.1±4.9) greater than that on the X and Y leads (41.9±4.6 and 46.1±4.9, respectively), probably because of respiratory-related artefacts affecting the Z lead more remarkably. More uniform HF power distributions over X,Y,Z leads are observed in the R-Tend threshold series (31.8 ±3.8, 39.2±4.1 and 35.1±4.2, respectively), thus suggesting minor sensitivity of the R-Tend threshold measure to respiratory-related artefacts.

Apparatus is described for telementering electromyograph signals over a single frequency-modulated V.H.F. radio channel, also its use for measuring the periods of activity of leg muscles during normal walking on the flat. Results are given for eight male and six female subjects. Soleus contracts during the latter half of the support phase. Quadriceps contracts immediately prior to and during the first half of the support phase and again, in some subjects, as the opposite heel touches the ground. Hamstrings are active except during flexion of the knee during the swing phase. Flexors of the hip contract only at the end of hip flexion; some difference in timing between men and women was observed. The erector spinae on both sides contract twice per stride for a short period corresponding to heel contact of each limb. Inertial movements of the leg are stressed. Actions of the tibialis anterior, gluteus medius and maximus are also described.