Non-stationary theory of blood-borne tracers.

Although cardiac mechanical activity causes periodic fluctuations of the regional volumes and flows through the cardiac chambers and great vessels, hitherto, the developed theory of blood-borne tracers has rested upon stationarity of flow, volume and distribution of transit time. Allowing for an arbitrary indicator injection, a more general theory is presented that accounts for periodic changes in the transport laws, flows and volumes of the system. When indicator particles are not thoroughly mixed with the entering blood, the intracycle changes violate most of the stationary equations.

Deconvolving out indicator smearing in the right ventricle facilitates left-to-right shunt quantitation.

A simple algorithm is developed to enhance the resolution of components of multimodal pulmonary radiohistograms. Based on the assessed right ventricular ejection fraction (RVEF), it deconvolves out the effect of indicator smearing in the right ventricle on the heart rate samples of the pulmonary radiohistogram, ck. The output is the ideal curve, c'k = ck/RVEF--(1-RVEF).

Theoretical considerations on the validity of the Stewart-Hamilton principle in measuring cycle-averaged flows via histogram of indicator in the pulsating compartment.

It has been heuristically shown that the Stewart-Hamilton principle, adapted to external counting observables of system indicator histogram, A(t), its cycle-averaged equilibrium count rate, A(equ), and indicator volume of distribution in the body, V(body), is F/V(body) = A(equ)/integral of o infinity A(t)dt, where F is the cycle-averaged cardiac output. Since the method lacks the theoretical plausibility, it remained unclear whether it is an approximation and what conditions warrant its usability. This paper presents an exact derivation of the above equation.

Q-T interval as predictor of serum calcium level.

To assess whether measurement of the electrocardiograhic (ECG) Q-T interval is a useful predictor of total serum calcium concentration, 15 uraemic patients were studied (10 female, five male; age range, 25-60 years). Resting ECGs were interpreted by three independent observers without knowledge of the patients' identity or serum calcium. Three variants of measurement of the Q-T interval were analysed, of which Q-aTc, the interval from the beginning of the Q-wave to the apex of the T-wave, was the most consistent (coefficient of variation, 2.

High resolution pulmonary computed tomography scans quantified by analysis of density distribution: application to asbestosis.

A new method for quantitative evaluation for high resolution computed tomography (HRCT) of the lungs was developed by assessment of the distribution of radiological densities within the lung slices. To enable effective reduction of data and improve the sensitivity of detection of abnormalities, the density distributions were analysed by curve fitting through the gamma variate model. The output of two variables proved most representative: the most frequent density (Hoansfield units; HU) and width of distribution (HU).