Bases adjacent to mononucleotide repeats show an increased single nucleotide polymorphism frequency in the human genome.

Mononucleotide repeats (MNRs) are abundant in eukaryotic genomes and exhibit a high degree of length variability due to insertion and deletion events. However, the relationship between these repeats and mutation rates in surrounding sequences has not been systematically investigated. We have analyzed the frequency of single nucleotide polymorphisms (SNPs) at positions close to and within MNRs in the human genome. Overall, we find a 2- to 4-fold increase in the SNP frequency at positions immediately adjacent to the boundaries of MNRs, relative to that at more distant bases. This relationship exhibits a strong asymmetry between 3' and 5' ends of repeat tracts and is dependent upon the repeat motif, length and orientation of surrounding repeats. Our analysis suggests that the incorporation or exclusion of bases adjacent to the boundary of the repeat through substitutions, in which these nucleotides mutate towards or away from the base present within the repeat, respectively, may be another mechanism by which MNRs expand and contract in the human genome.

After-hours radiology.

After-hours radiological procedures are essential but expensive in any major teaching hospital. Using the criteria that radiological procedures performed after-hours should have a reasonable probability of influencing or changing patient management acutely, a study of the justification of after-hours radiological procedures was performed at the Princess Alexandra Hospital. Computer print-outs were used to select the patients based on the dates and times of the procedures. Their charts were then reviewed. The study found that most after-hours radiological procedures were justified. However, it also identified certain procedures that need not be performed or at least could be reduced after-hours. The procedures were: (i) computed tomography (CT) head--epilepsy, meningitis; (ii) CT abdomen--trauma (intubated)--unable to examine abdomen; (iii) CT spine--obvious unstable fractures; (iv) Ultrasound abdomen--biliary colic (afebrile); and (v) Ultrasound kidneys--renal failure (afebrile).

Radiation dose to the lens of the eye during computerised tomography examinations of the orbit, the pituitary fossa and the brain on a General Electric 9800 Quick C.T. scanner.

A phantom simulating the lens of the eye has been used during estimation of the radiation dose to the lens of the eye during C.T. scanning of the orbit, pituitary fossa and brain. Routine scanning will deliver a dose to the lens which is many times less than the threshold for cataracts. However the potential exists to use techniques which will increase the dose substantially. Repeat examinations of this sort could theoretically exceed the threshold dose required to induce cataracts in the lens.

Diaphyseal Paget's disease: an unusual finding in the tibia.

Paget's disease may present in the tibia without involvement of either end of the bone. Such unusual diaphyseal lesions are invariably lytic and, rarely, may be multifocal. They almost always involve the anterior cortex of the bone and usually have a characteristic 'V-shaped' margin at one or both ends. Expansion of the bone is common. This unusual appearance is frequently an early manifestation of the disease under the age of 40 years. Awareness of this appearance is important in order to prevent incorrect diagnosis and unnecessary biopsy or surgery.

Radiation doses to the lens of the eye during computerised tomography of the orbit; a comparison of four modern computerised tomography units.

A previous study has looked at the estimated radiation dose to the lens of the eye during CT scanning of the orbit, pituitary fossa and brain with a recently installed GE 9800 Quick CT using a phantom simulating the lens of the eye. In this study the same phantom was used to compare the estimated radiation dose delivered to the lens of the eye by three other newly installed CT units of different manufacture. There was significant variation between the doses measured from the four machines when operated with the parameters commonly used in clinical practice. However, in all cases scanning of the phantom using routine techniques delivered a dose to the simulated lens which was much lower than the threshold dose for cataracts. There is, never-the-less, a potential for delivery of much higher doses.

Corrosion of lead shielding in a radiology department.

Corrosion of lead sheet used for structural radiation protection in the Princess Alexandra Hospital radiology department has been identified. The corrosion is thought to have been caused by organic acid vapours released from oregon timber wall panelling. Non-destructive testing (NDT) and X-ray transmission measurements were used to define the extent and severity of damage, and subsequently to provide the data necessary for estimation of staff and public radiation doses. Although radiation dose limits have not been exceeded, corrective actions including structural modifications and staff information sessions have been undertaken.