These guidelines have been adopted by the British Nuclear Medicine Society.

The proposed technique provides a reproducible and sensitive index. It is hoped that its independence from the partial volume effect will improve consistency in quantitative measurements between centres with different imaging devices and analysis software.

SUMMARY Regional cerebral blood flow, blood volume, fractional oxygen extraction and oxygen consumption were measured by positron emission tomography in six patients with sickle cell disease to see how oxygen delivery to the brain is maintain**! in the presence of both anemia and a low oxygen affinity hemoglobin. Both regional cerebral Mood flow and blood volume were found to be markedly increased compared to values obtained from 14 normal subjects in the same age range. The mean fractional oxygen extraction was not significantly different in the two groups. Mean oxygen consumption in the two groups was also not significantly different but low values in individual patients with sickle cell disease and the presence of atrophy on the CT-scans of three of them were suggestive of some neuronal loss in patients without any history of nervous system involvement. In view of the known high values of cerebral blood flow and metabolism in childhood, it b suggested that when compounded by anemia and abnormal red cells, a hyperdrculatory state may make patients In this age-group particularly prone to ischemlc infarction.

Clinical research on the deposition of inhaled substances (e.g. inhaled medications, airborne contaminants, fumes) in the lungs necessitates anatomical models of the airways. Current conducting airway models lack three-dimensional (3D) reality as little information is available in the literature on the distribution of the airways in space. This is a limitation to the assessment or predictions of the particle deposition in relation to the subject's anatomy.Detailed information on the full topology and morphology of the airways is thus required to model the airway tree realistically. This paper presents the length, diameter, gravity, coronal and sagittal angles that together describe completely the airways in 3D space. The angle at which the airways branch out from their parent (branching angle) and the rotation angle between successive bifurcation planes are also included. These data are from the study of two sets of airways computed tomography (CT) images. One CT scan was performed on a human tracheobronchial tree cast and the other on a healthy male volunteer. The airways in the first nine generations of the cast and in the first six conducting generations of the volunteer were measured using a computer-based algorithm. The data contribute to the knowledge of the lung anatomy. In particular, the spatial structure of the airways is shown to be strongly defined by the central airways with clear angular lobar patterns. Such patterns tend to disappear with a mean gravity, coronal and sagittal angles of 90 ° in each generation higher than 13-15. The mean branching angle per generation appears independent of the lobe to which the airways belong. Non-planar geometry at bifurcation is observed with the mean ( ± SD) bifurcation plane rotation angle of 79 ± 41 ° ( n = 229). This angle appears constant over the generations studied. The data are useful for improving the 3D realism of the conducting airway structure modelling as well as for studying aerosol deposition, flow and biological significance of non-planar airway trees using analytical and computational flow dynamics modelling.

1. Simultaneous radioisotopic (99Tc‐DTPA) gastric emptying measurements and paracetamol pharmacokinetic studies were performed in eight healthy male volunteers with and without levodopa (125 mg orally). 2. In the absence of levodopa gamma camera imaging showed rapid mono or biexponential emptying in all subjects and the plasma concentration‐ time curves for paracetamol displayed a single major peak. 3. In the presence of levodopa the time to 90% emptying was prolonged from 32 +/‐ 24 min to 81 +/‐ 20 min (P less than 0.01). Gastric emptying was interrupted by a plateau phase in six subjects and this pattern of emptying was associated with double peaks in the plasma concentration‐ time curves of both levodopa and paracetamol. The time to the end of the plateau phase of emptying correlated with the time to the trough plasma concentrations of paracetamol and levodopa. 4. There was excellent agreement between the plasma concentration‐time curves of levodopa and paracetamol, i.e. time to initial peak, r = 0.946, P less than 0.001; time to trough concentration r = 0.943, P less than 0.01; time to second peak r = 0.974, P less than 0.001. 5. The results indicate that levodopa inhibits gastric emptying and thus influences its own absorption. Temporary inhibition of gastric emptying by levodopa (or a metabolite) is the cause of the multiple plasma peaks commonly observed following oral levodopa.