The validity and reliability of the exposure index as a metric for estimating the radiation dose to the patient.

INTRODUCTION: With the introduction of digital radiography, the feedback between image quality and over-exposure has been partly lost which in some cases has led to a steady increase in dose. Over the years the introduction of exposure index (EI) has been used to resolve this phenomenon referred to as 'dose creep'. Even though EI is often vendor specific it is always a related of the radiation exposure to the detector. Due to the nature of this relationship EI can also be used as a patient dose indicator, however this is not widely investigated in literature. METHODS: A total of 420 dose-area-product (DAP) and EI measurements were taken whilst varying kVp, mAs and body habitus on two different anthropomorphic phantoms (pelvis and chest). Using linear regression, the correlation between EI and DAP were examined. Additionally, two separate region of interest (ROI) placements/per phantom where examined in order to research any effect on EI. RESULTS: When dividing the data into subsets, a strong correlation between EI and DAP was shown with all R-squared values > 0.987. Comparison between the ROI placements showed a significant difference between EIs for both placements. CONCLUSION: This research shows a clear relationship between EI and radiation dose which is dependent on a wide variety of factors such as ROI placement, body habitus. In addition, pathology and manufacturer specific EI's are likely to be of influence as well. IMPLICATIONS FOR PRACTICE: The combination of DAP and EI might be used as a patient dose indicator. However, the influencing factors as mentioned in the conclusion should be considered and examined before implementation.

Responses to tuberculin in the guinea-pig eye as a model of cell mediated immune responses in the external eye.

The clinical and histological findings in an animal model of ocular cell mediated immune responses are described. These were evoked in sensitised guinea-pigs by dropping tuberculin into the conjunctival sac or injecting it under the palpebral conjunctiva. When tuberculin was dropped into the conjunctival sac, higher doses were required to evoke a strong response than when it was injected subconjunctivally. When high doses of antigen were used for challenge, a mild response was observed in unchallenged contralateral eyes. The cellular response at low doses of tuberculin consisted predominantly of mononuclear cells. At higher doses the cellular infiltrate was more pronounced, and polymorphonuclear cells tended to predominate 24 hours after challenge, while at 48 hours mononuclear cells predominated.

Pharmacologic inhibition of immediate hypersensitivity in the guinea pig conjunctiva.

The release of histamine and other mediators from an immediate hypersensitivity reaction is energy dependent and cyclic AMP dependent. Drugs which inhibit the active secretion of mediators, or which may change cyclic AMP are effective in inhibiting mediator release. We used a model of Type I (immediate) hypersensitivity in the conjunctiva of guinea pigs sensitized to normal rabbit serum to test the efficacy of 2-deoxy-D-glucose or a combination of isoproterenol and diethylcarbamazine in inhibiting conjunctival hypersensitivity. After topical challenge with rabbit serum, edema was evaluated in five areas of the guinea pig conjunctiva. Controls were compared to conjunctiva pretreated with 2-deoxy-D-glucose or isoproterenol and diethylcarbamazine. Pretreatment with 2-deoxy-D-glucose or a combination of isoproterenol and diethylcarbamazine was found to inhibit the immediate hypersensitivity reaction.

Unusual features in the conjunctiva and cornea of the normal guinea-pig: clinical and histological studies.

Clinical and histological studies of the outer eyes of newborn and adult female guinea-pigs were carried out together with histological studies of fetal eyes. Fine superficial corneal vessels, extending from the limbus, were seen in most newborn and adult eyes and were also present in histological preparations of fetal eyes. These vessels were therefore considered to be features of the normal guinea-pig eye. Masses of tissue composed of lymphoid cells, which were often organised into germinal centres, were found in the fornices of newborn and adult eyes. Smaller accumulations of lymphoid cells were found in fetal eyes, and this lymphoid tissue was therefore also considered to be a normal feature of the guinea-pig eye. In adult eyes mild but short-lived oedema or hyperaemia of the palpebral conjunctiva was quite common. There were no differences in the amounts of conjunctival cellular infiltration in these eyes c found in fetal eyes, and this lymphoid tissue was therefore also considered to be a normal feature of the guinea-pig eye. In adult eyes mild but short-lived oedema or hyperaemia of the palpebral conjunctiva was quite common. There were no differences in the amounts of conjunctival cellular infiltration in these eyes c found in fetal eyes, and this lymphoid tissue was therefore also considered to be a normal feature of the guinea-pig eye. In adult eyes mild but short-lived oedema or hyperaemia of the palpebral conjunctiva was quite common. There were no differences in the amounts of conjunctival cellular infiltration in these eyes compared with normal eyes, and these inflammatory changes were therefore not considered to be significant.

Chlamydial urethral infection in Teheran. A study of male patients attending an STD clinic.

The prevalence of chlamydial infection of the urethra was studied in 172 consecutive male patients attending a sexually transmitted disease clinic in Teheran. Chlamydia trachomatis was isolated in 8.8% of the patients with a valid culture result. Of the five isolates serotyped, two were serotype E and three were serotypes G, H, and K. Type-specific antibodies against C trachomatis serotypes D to K were found in 16% of patients, and IgM, indicating current infection, was detected in 12%. Type-specific antibodies against serotypes A to C (trachoma agent) were detected in 5.4%. The low chlamydial isolation rate may have been due to the inclusion of a large number of patients with a mild or trivial urethritis or a history of previous treatment with antichlamydial drugs. The results indicate that in Iran where trachoma is still endemic, chlamydial infection of the urethra does occur in the urban population and is caused by serotypes D to K.

Immediate hypersensitivity in the guinea pig conjunctiva. III. long-term persistence of the hypersensitive state and characterization of antibodies.

The ocular immediate hypersensitivity reaction in guinea pigs to topically applied normal rabbit serum can be evoked as long as 4 years after sensitization. The reaction was as severe and tended to persist for longer than that evoked 6 months after sensitization. Passive cutaneous anaphylaxis tests showed that very high titres of homocytotropic antibodies were present and that both IgE- and IgG1-like antibodies were involved. Sensitization with one set of injections instead of two was not consistently successful and the response on challenge was mild to moderate. Pretreatment of eyes with Isoptocarpine before antigenic challenge had no effect on the response. The addition of bacterial lipopolysaccharide to the first set of sensitizing injections produced hypersensitivity in animals which were otherwise refractory to sensitization.

Antichlamydial antibody in tears and sera, and serotypes of Chlamydia trachomatis isolated from schoolchildren in Southern Tunisia.

A predominance of TRIC serotype A has been isolated from schoolchildren in a population in Southern Tunisia with severe hyperendemic trachoma. The serotyping results correspond precisely with the serological findings in patients' tears and sera. Geometric mean titres of serum or tear antibody in defined populations or areas can thus give a useful indication of the prevalent serotypes. Collection of tear fluids on sponges is a more practical method than collection by filter paper strips and gives higher levels of antibody. The presence of antibody to Chlamydia trachomatis in tears correlates well with the presence of infectious agent in the eye and with the intensity of conjunctival inflammatory disease. The measurement of antichlamydial tear antibody can thus provide a meaningful index of the prevalence and intensity of active trachoma in a population. The role these antibodies may play in resistance to re-infection is not yet clear.

Immediate hypersensitivity in the guinea pig conjunctiva. II. Effect of treatment with antihistamines, steroids and disodium cromoglycate.

The effects of antihistamines, steroids and disodium cromoglycate on an immediate hypersensitivity reaction in the guinea pig eye are described in terms of clinical observations, histological examinations of sections of eyes and cytological studies of material from the conjunctival surface. The use of brushes to sample the cells on the conjunctival surface is described. The effect of repeated daily challenges on the reaction is also reported.