Legislation requires the reporting to regulatory authorities of incidents in which patients have been exposed to ionizing radiation to an extent "much greater than that intended". The authorities have published guidance on what is considered to meet this requirement. However, there is still some confusion regarding, particularly, the necessity to report some unintended doses. It is believed that there is a disproportionate amount of resource spent investigating some unintended exposures because all such exposures will have an effective overexposure factor of infinity, irrespective of the magnitude of the dose and the associated risk. This paper proposes changing the definitions of "overexposure" and "unintended exposure" and the adoption of a reporting process based upon risk assessment. All records and data would be collected and, if required, reported, but investigation of individual incidents would take place only for incidents carrying a greater risk than 1 in 10 000.

To image microstructures within tissue in detail using conventional light microscopy it is necessary to process the tissue and obtain thin (≈5 μm) physical sections by using destructive physical sectioning techniques. This article describes a microscopy technique, using near-infra-red light (700-1500 nm) as the source, which is able to image thin sections of thick-tissue specimens nondestructively. Images of contiguous two-dimensional thin sections obtained serially can be combined to generate a three-dimensional image of the structures being imaged.

Organ motion can cause artefacts in abdominal imaging particularly with magnetic resonance imaging (MRI), and may often limit the diagnostic quality of an image. If spatial resolution and image quality are to improve in MRI and other imaging techniques, a more detailed understanding of organ motion is required. Despite the importance of organ motion little quantitative information is available to date. This study was the continuation of work instigated to investigate and quantify respiratory movements of upper abdominal organs for a group of healthy volunteers in order to provide the design criteria for a motion test object for use in MRI. A previous phase of the project allowed construction of a test object but refinements were needed to represent respiratory motion more closely as a consequence of the data presented in this paper. Improvements in the scanning technique and the recording procedure have revealed that, contrary to our initial findings, motion of the diaphragm and liver is predominantly in the superior-inferior (SI) direction with an average displacement (+/- SD) (quiet respiration) of 12 +/- 7 mm (range 7-28 mm) and 10 +/- 8 mm (range 5-17 mm), respectively. For some volunteers, motion of the kidneys can be complex, especially during deep inspiration. New data have been provided by this phase of the motion study on the displacement, velocity and acceleration of abdominal organs as a function of time. These data show that MRI motion artefact reduction techniques which assume that either organ displacement, velocity or acceleration are constant are only applicable during certain phases of the respiratory cycle.

Magnetic resonance angiography is a relatively new method used to image vascular structure. However, a limitation manifested through signal loss due to non-stable flow makes this technique unreliable for directly visualizing occlusions and estimating the degree of stenosis. In this study, a quantitative approach is developed to understand further the situations where signal loss occurs and a phase mapping technique is used quantitatively to study acceleration in test objects designed to generate flow disturbance. In regions of acceleration the correlation coefficient between magnetic resonance imaging velocity and the inverse of area was r > 0.999 (p < 0.001). The range of acceleration calculated was 6514-63053 mm s-2 and at maximum acceleration the measured velocity had a systematic error of 4.0(+/-2.0)% and coefficient of variation of 3.1%. Test objects were devised and utilized for demonstrating non-stable flow and jet formation with comparison being made to predictions from fluid dynamics theory.

Uncemented prosthetic joint implants used in orthopaedic surgery are usually coated with a porous surface to encourage bone ingrowth. Better contact between the endosteal bone and the porous surface improves ingrowth, and such contact may be increased if the joint further subsides into position in the first weeks following implantation. An image processing technique has been developed as part of a study undertaken to determine the effect of early subsidence on endosteal contact. The method provides a measure of the degree of contact between the surfaces from transverse x-ray CT images, but is suitable for application to any image with a similar intensity distribution.

A device and technique to study the effects of respiratory motion on the quality of magnetic resonance images is proposed. The construction of the device enables a variety of test objects to be mounted and used in the evaluation of imaging parameters that may be affected by motion. The equipment is constructed of cast acrylic and the movement is actuated and controlled pneumatically thus ensuring that there are no interactions with the magnetic field and radiofrequency detection system to cause further image artefacts. Separate studies have been performed, using ultrasound, to assess the degree and rate of movement of organs owing to respiration in order to derive the motion parameters for the apparatus. Preliminary results indicate that the technique produces motion induced artefacts simulating those which are the result of the effects of respiration.

Velocity measurements in major blood vessels were obtained in studies of volunteers using magnetic resonance imaging (MRI) and compared with Doppler ultrasound (US). The vessels studied were the abdominal aorta, superior mesenteric artery, common carotid artery, superficial femoral artery and middle cerebral artery. Using a paired t-test, no significant difference was found between velocity values estimated by MRI and US (p > 0.08). The relative advantages of each technique in radiological practice are discussed.

Light transport in three-dimensional plane-parallel tissue slabs has been modelled by Monte Carlo analogue simulation. The model design has allowed the study of transmission properties that are pertinent to imaging systems for the detection of breast cancer. An important aspect of the investigations is that they make use of data obtained from quantitative measurements of light scattering and absorption in normal and pathological breast tissues. It is shown that an imaging technique which used a raster scanning laser and detector arrangement and plane-parallel compression of the breast could have considerable advantages in terms of improved transmittance, spatial unsharpness and contrast. Time-of-flight gating of images is also found to be beneficial provided that the light intensities after temporal filtering remain adequate.

A study was undertaken to examine the accuracy and precision of the measurement of flow by magnetic resonance imaging (MRI) with consideration to the equipment and patient related parameters that might be encountered in vivo. For this purpose, test objects were devised consisting of PVC tubing, in which the internal diameter simulated the size of the arteries in the body. The design of the test objects ensured that steady laminar flow was obtained in the sections being imaged. The calibration study suggests that, using MRI, flow can be measured in vitro with systematic error of better than 7.0 +/- 5.0% and random error of better than 7.5%. In general, flow measurements obtained from MRI were found to correlate well with the known flows. However, the results indicated that there are prerequisite conditions for the validity of the measurements, such as the selection of appropriate flow pulse sequences and velocity limits. Measurements taken at vertically 40 mm away from the isocentre of the magnetic field were significantly different (p less than 0.01) from that at the isocentre.

SUMMARY The Dinantian of north-west Devon is represented by a poorly exposed thin pelagic succession. New sedimentological and palaeontological data permit the recognition of five formations: Pilton Shales (partly Devonian), Landkey, Tawstock (three members), Hearson and Rubble Hills. The last four are newly named and defined, and form part of the Codden Hill (Chert) Group. The two different stratigraphic successions previously proposed are shown to be based on incomplete sequences and erroneous age assessments. Instead, a fairly uniform stratigraphy is recognised. The local variations that do occur can be explained by either tectonic excision of strata (for which there is independent evidence) or basin floor morphology. Redeposited pelagic carbonates suggest a submarine rise existed nearby through much of the Dinantian. Limestone turbidites of shallow-water debris also point to topographic highs in the region.

Expensive diagnostic imaging technologies need to be assessed. Assessment is most difficult with new technologies. Rapid technical change creates pressure for widespread provision because of apparently self-evident advantages. For the health care provider, technology assessment is of central importance. Timing is crucial; economic and clinical studies have to be carried out simultaneously; and studies must be broadly based. Assessment should be carried out only on properly selected technologies. Apart from picture archiving and communication systems, existing expensive diagnostic imaging technologies are now so mature that assessment is concerned mainly with costs and benefits. To be provided, a technology needs to be effective, economic, appropriate and needed. The history of computed tomography illustrates technology assessment from innovation to routine application. Technology assessment also provides essential guidance for equipment selection. Different regulations and controls, explicit or implicit, exist in different countries. There are special requirements for technology assessment in each country according to overall health requirements and policies. The main contemporary challenges are the correct selection of equipment for assessment, and the development of predictive methods of assessment.

Optical experiments are described for measuring the attenuation characteristics of breast tissues at visible and near-infrared wavelengths. Total attenuation coefficients post mortem were measured directly in thin tissue sections. They are usually within the range from 10 to 30 mm-1, are rather higher in fat than in fibroglandular specimens and decrease with increasing wavelength. The scattering phase function is strongly forward-peaked with the mean cosine of scattering in the range from 0.85 to 0.97 and appearing more forward-peaked in fat than in fibroglandular tissue. The reduced scattering coefficient is of the order of 1 mm-1 in all tissues. Absorption coefficients were measured indirectly in optically thick sections. They are typically between 0.1 and 0.5 mm-1 at wavelengths around 580 nm and an order of magnitude lower at 850 nm. At 580 nm and shorter wavelengths the absorption in carcinoma is significantly higher than in adjacent uninvolved tissue. Significant differences were observed in the first-order derivatives of the transmission spectra of carcinoma and surrounding tissues at certain infrared wavelengths. Transmission spectra measured in vivo across the wavelength range from 500 to 860 nm have a similar form to the spectra of excised samples. Linear absorption coefficients are generally of the same order of magnitude as those found in vitro although they are lower at green wavelengths.

Radioiodinated monoclonal antibodies (MCA) were administered by the lumbar route into the cerebrospinal fluid (CSF) of four patients with malignant leptomeningeal disease. Evidence suggesting uptake of131I-MCA by tumour sites was seen in scintigrams. Dosimetry calculations were carried out, assuming that a proportion of the administered radionuclide was bound as a thin layer on the CSF surfaces of the meninges. The percentage injected dose and the clearance curves for the head and four spinal segments were obtained by scintigraphy after administration of tracer amounts of131I-MCA (7–18 MBq). Although radioisotope levels in the central nervous system (CNS) fell, as determined by both external scintillation counting and direct CSF sampling, a marked difference in the measurements developed with respect to time. The ratio of these two measurements reached a maximum of 49:1, 7 days after monoclonal antibody administration. Patients subsequently received therapeutic amounts (870–1600 MBq) of131I-MCAs, resulting in clinical remissions and prolonged survival. The mean absorbed radiation dose was estimated as 3.9 cGy·MBq−1 to the thoraco-lumbar region of the spine and 0.51 cGy·MBq−1 to the outer surface of the brain. The maximal dose delivered to the surface of the CNS in the region of the spine and brain was 5800 and 600 cGy, respectively.

PULMONARY UPTAKE OF MDP Radionuclide bone scanning is now a standard technique in the staging of many malignancies. Probably the most frequent application is in screening patients with known primary malignancy and potential bone metastases. In primary malignant bone tumours, bone scanning is also useful with images often showing the lesion to be more extensive than was suspected from radiographs (McKillop et al., 1974). Bone forming metastases in the lungs can sometimes be detected before they become visible on the chest radiograph (McKillop et al. 1974, Robinson 1979, Ghaed et al. 1981). Although radionuclide imaging of bone is very sensitive, it is of low specificity and a variety of other pathologies can also be shown. It is occasionally difficult when looking at the thorax on the bone

Two-dimensional images obtained using ultrasound have been digitized from videotape recordings and stored within a maximum of 240 digital memory planes to form a three-dimensional data set using a commercially available image processing unit. This data set has been manipulated to produce images in planes perpendicular to the original scan set. The reformatted images represent not only the scans that could have been obtained by rotating the scan head but also demonstrate planes that are not accessible by conventional scanning. The system has been evaluated with a tissue-equivalent phantom to determine the geometric accuracy of the reformatting process. Clinical material has also been used to evaluate the practical value of such a technique and to highlight difficulties that may be encountered in its routine use.

A review of the current state of transillumination imaging for the detection and diagnosis of breast cancer and the difficulties that impede more widespread acceptance of the methods is presented. An outline is given of the physical models that may be used to describe the propagation and scattering of light in a tissue matrix and how these models might be valuable in identifying imaging improvements. Some of the proposals for future imaging arrangements are described and the preliminary work on a system for light transmission computed tomography is presented.

Digital subtraction angiography (DSA) allows the degree of arterial patency or stenosis to be rapidly quantified. We have assessed the accuracy with which a single-plane DSA system is able to quantify area patency by densitometric and geometric methods. Arterial phantoms were designed to test for systematic error; intra-arterial DSA images of critical lesions of the carotid bifurcation and the lower abdominal and peripheral vessels were used to determine intra- and interobserver reproducibility. The densitometric method, which was more accurate than the geometric method, had a mean systematic error of up to 4% and a mean intra-observer variability of about 15% (coefficient of variation). We have identified the principal sources of inaccuracy and ways in which it may be reduced.