Planar pulmonary scintigraphy is currently the standard investigation for the diagnosis of pulmonary embolism. There are a number of problems with the technique, particularly in patients with an intermediate scan report under the PIOPED criteria. The technique is also under threat from the increasing use of spiral CT angiography. A putative improvement may be gained by use of tomography. The incremental value of tomography over planar studies was therefore evaluated in a virtual model of pulmonary scintigraphy. A model of the segmental anatomy of the lungs was developed from computed tomography, cadaveric human lungs and available anatomical texts. Counts were generated within the phantom by Monte Carlo simulation of photon emission. Eighteen single segmental lesions were interspersed with 47 subsegmental defects and displayed on an Icon reporting station. These were presented in the transaxial, sagittal and coronal planes to four experienced reporters to obtain assessment of defect size. Planar studies of the same defects were displayed to the same observers in the standard eight views with a normal study for comparison. With planar studies, the accuracy of estimation of defect size was 51% compared with 97% using tomographic studies. Defects in the medial basal segment of the right lower lobe were not identified in planar studies but were easily seen by all observers in the tomographic study. It is concluded that there is marked improvement in the accuracy of determination of defect size for tomographic studies over the planar equivalents. This is especially important in the lung bases, the most common reported site of pulmonary emboli. Tomography permits visualisation of defects in the medial basal segment of the right lung, which are not seen in planar studies.

The model provides the opportunity to address several issues germane to scintigraphy and important for diagnosing pulmonary embolic disease. In particular, the model allows the manipulation of three-dimensional data sets to explore issues of importance to tomographic lung scanning.

No abstract

No abstract

fetal immune system and the prevalence of postnatal autoimmune disease. Size development of fetal thymus and adrenal glands has been implicated with fetal stress response and prematurity. Our aim was to assess intra-observer variability, reproducibility and operator learning curve for thymus and adrenal gland size measurements. Methods: Within the PRINCE study, thymus and adrenal gland size were measured at gestational age (GA) 24, 28 and 36 weeks. For the fetal thymus, transverse diameter and perimeter were measured. For the adrenal gland, length, width and depth of both the complete organ and the medulla were measured in a 3D volume. Each individual parameter was measured in triplicate volumes by an experienced operator. For learning curve, the first 10 measurements were compared with the second and the last 10. Results: We observed a significant learning curve for both organs leading to successful and reproducible measurements of the thymus in more than 95% of subjects in the last 10 subjects. Thymus transverse diameter was more reproducible (standard deviation of about 2 mm) and less variable than perimeter independent of GA. The adrenal gland length and width and the medulla could be successfully measured in more than 90% independent of GA in the last 10 subjects. However adrenal gland depth measurement remained variable and GA dependent. Conclusions: To investigate for subtle changes in size, the fetal thymus should be measured by the transverse diameter and the adrenal gland by length and width or medulla/cortex ratio. Taking this and the learning curve into consideration, accurate measurements of thymus and adrenal gland are feasible in the setting of a large prospective trial. OP08.10Comprehensive ultrasound evaluation of short-term fetal effects of dexamethasone and betamethasone