Colon blood flow in the dog: effects of changes in arterial carbon dioxide tension.

A new method for measuring blood flow in the colon using a 133Xenon clearance technique has been developed in the greyhound. Values for 133Xe tissue blood partition coefficient for colon have been established. The mean basal colon blood flow in 35 animals was 39.8 cm3.min-1.100g-1 with a coefficient of variation for repeat measurements of 8.7%. Hypercapnia produced a significant rise in colon blood flow to a mean maximum level of 62.2 cm3.min-1.100g-1 and hypocapnia a significant fall to a mean level of 27.9 cm3.min-1.100g-1. For arterial carbon dioxide tension (PCO2) values between 2 and 12 kPa (15 and 90 mmHg) there was a straight line relationship between colon blood flow and arterial PCO2. When hypercapnia was prolonged for 75 min, the initial rise in colon blood flow was only partially sustained, while prolonged hypocapnia for a similar period resulted in sustained reduction in flow. Mean resting colon oxygen consumption in 35 animals was 1.17 cm3.min-1.100g-1 and this was not significantly affected by hypocapnia. Hypercapnia to arterial PCO2 levels between 8 and 14 kPa (60 and 105 mmHg), however, produced a significant rise in colon oxygen consumption. Since changes in colon blood flow during and after surgery may affect healing of colonic anastomoses, these results may be relevant when considering anaesthetic techniques for patients undergoing colon resection.

The placental transfer of propylthiouracil, methimazole and carbimazole.

The placental transfer of 35S-labelled methimazole (MMI), carbimazole and propylthiouracil (PTU) has been examined in the rat in late pregnancy and in patients undergoing therapeutic abortion. Although rapid equilibrium of fetal and maternal serum radioactivity (FS:MS ratio 1:1) occurred after iv administration of 35S-carbimazole or 35S-MMI in rats, a persistent fetal to maternal ratio of less than one was observed after 35S-PTU administration. Results from human studies after a single oral dose indicate that, as in the rat, the placenta appeared to be more permeable to 35S-MMI than to 35S-PTU as shown by the marked difference in fetal serum:maternal serum ratios and amounts accumulated in the fetus. Localization of radioactivity in the human fetal thyroid was also observed after administration of 35S-labelled MMI, carbimazole or PTU.

Theoretical of the measurement of choroidal blood flow using a radioactive inert gas clearance technique.

A mathematical model for the diffusion of krypton in ocular tissues and its removal by blood flow has been developed to explain the complex clearance pattern found experimentally in the rabbit--an animal which has predominantly a choroidal circulation. Comparison of theoretical and experimental results has shown that the initial slope of the clearance curve is a measure of choroidal blood flow for values of blood flow over 500 ml/100 g/min. The shape of the curve at later times has been shown to be attributable predominantly to the diffusion of krypton into other ocular tissues.

Monitoring of airborne contamination during the handling of technetium-99m and radioiodine.

Measurements have been made using an air sampler to measure airborne radioactivity produced during the routine handling of large activities of technetium-99m, iodine-125 and iodine-131. The results indicate that 99Tcm can be safely handled in environments without direct exhaust of the ventilated air but that 125I and 131I should always be handled in a ventilated environment such as a fume cupboard or a down-draught work-station of the total-exhaust type. Monitoring of thyroid uptake proves to be the most reliable means of monitoring airborne contamination by these radionuclides, but burdens and radiation doses for typical procedures are well within the maximum permissible limits of the Code of Practice for the Protection of Persons from Ionizing Radiation arising from Medical and Dental Use.

Rectilinear bone scanning: differentiation between metastases and degenerative spinal disease.

Criteria have been developed for radioisotope scanning of bone with an eight-colour-display rectilinear scanner, to differentiate metastases from degenerative spinal disease. If the area of increased uptake is two or more colours "hotter" than normal, this is probably due to metastases even if degenerative spinal disease coexists. The positivity of a scan due to degenerative spinal disease is a function of the degree of sclerosis adjacent to the intervertebral discs and apophyseal joints; it is not related to the degree of osteophyte formation.

Quantitative assessment of the radiation hazards and risks in sentinel node procedures.

Sentinel node localization using an injected radiopharmaceutical and a gamma probe is performed in many hospitals. Employers have a duty to give appropriate training to staff who may not have been previously formally trained to work with unsealed radioactive sources. A study was performed to assess hazards and risks at all stages of the localization procedure. Whole body doses and finger doses of imaging, surgery and pathology staff were determined. The activity remaining in the tumour specimen, excised nodes and disposable waste from the operating theatre was measured. Any radioactive contamination of the operating theatre and equipment was also ascertained. All results were then assessed in light of current UK radiation protection legislation for the protection of staff and members of the public. Results showed that radiation doses are low and no additional procedures are required for protection of staff, provided the usual procedures for biohazards are in place. However, an information sheet has been prepared for the reassurance of staff, and theatre swabs may need to be stored temporarily before disposal. Injecting and imaging on the day before surgery is preferred, compared with injecting and imaging before surgery on the same day, since this gives lower radiation doses to staff, lower activity in excised specimens and waste, and provides a higher count rate giving better image quality.

Variability of ejection fraction results using commercial cardiac phantoms.

Variable ejection fraction results were obtained using two commercial phantoms with three different computer systems. The reasons for the results and their implications are discussed.

Improved accuracy of ejection fraction measurements using a commercial cardiac phantom.

Variable ejection fraction results were obtained with a cardiac phantom using different computer systems. The problems was traced to the phantom design. A modification produced more reliable results consistent with expected values.

Attenuation characteristics of MagnaDense high-density concrete at 6, 10 and 15 mv for use in radiotherapy bunker design.

The attenuation characteristics of MagnaDense high-density concrete are measured using the x-ray beams from two Varian linear accelerators at nominal 6, 10, and 15 megavolt energies. The tenth value layers for the primary beam are evaluated under broad- and narrow-beam conditions. The attenuation of secondary radiation is also investigated. Measured data are compared with existing data used in radiotherapy bunker design, derived from the scaling of published tenth value layers for ordinary concrete according to physical density. Instantaneous dose rates around an existing bunker with MagnaDense concrete walls and a conventional concrete roof are predicted using the various different data and compared to actual dose-rate measurements. Primary beam tenth value layer values derived from the broad-beam measurements are found to represent the attenuation properties of the MagnaDense more accurately than those produced by density-based scaling or from narrow-beam measurements.

Quality assurance and harmonisation of nuclear medicine investigations in Europe.

A survey of all member societies of the European Association of Nuclear Medicine has shown that a satisfactory degree of harmonisation exists for the quality assurance of the preparation and handling of radiopharmaceuticals and the performance of nuclear medicine instrumentation. However, variations were found in acquisition protocols, data analysis and the interpretation and presentation of clinical results. Harmonisation of these areas of a nuclear medicine investigation would help ensure the overall quality. A European initiative is proposed to collect and collate procedures in these areas in order to produce a reference framework of good practice for the acquisition, analysis and interpretation of nuclear medicine investigations. This would involve collaboration between national societies and exchange of information with and support from European organisations, taking into account relevant international activities. The reference framework should be compatible with quality management guidelines.

The value of the 14C breath test in the assessment of fat absorption.

The absorption of oral 14C-glyceryl tripalmitate was tested in 77 subjects by hourly interval sampling of breath 14CO2 for up to 6 h. A highly significant correlation was obtained between maximum breath 14CO2 activity and faecal fat excretion. The test was very effective in differentiating between patients with and without steatorrhoea. Repetition of this examination with oral 14C-palmitic acid demonstrated normal absorption in pancreatic steatorrhoea but impaired absorption in intestinal steatorrhoea, thus enabling these conditions to be distinguished. The 14C breath tests are most useful as simple and inexpensive outpatient screening tests for steatorrhoea.