Ephedrine activates brown adipose tissue in lean but not obese humans.

AIMS/HYPOTHESIS: Brown adipose tissue (BAT) activation increases energy consumption and may help in the treatment of obesity. Cold exposure is the main physiological stimulus for BAT thermogenesis and the sympathetic nervous system, which innervates BAT, is essential in this process. However, cold-induced BAT activation is impaired in obese humans. To explore the therapeutic potential of BAT, it is essential to determine whether pharmacological agents can activate BAT. METHODS: We aimed to determine whether BAT can be activated in lean and obese humans after acute administration of an orally bioavailable sympathomimetic. In a randomised, double-blinded, crossover trial, we administered 2.5 mg/kg of oral ephedrine to nine lean (BMI 22 ± 1 kg/m²) and nine obese (BMI 36 ± 1 kg/m²) young men. On a separate day, a placebo was administered to the same participants. BAT activity was assessed by measuring glucose uptake with [¹8F]fluorodeoxyglucose and positron emission tomography-computed tomography imaging. RESULTS: BAT activity was increased by ephedrine compared with placebo in the lean, but unchanged in the obese, participants. The change in BAT activity after ephedrine compared with placebo was negatively correlated with various indices of body fatness. CONCLUSIONS/INTERPRETATION: BAT can be activated via acute, oral administration of the sympathomimetic ephedrine in lean, but not in obese humans.

Radiation exposure and the justification of computed tomography scanning in an Australian hospital emergency department.

In an emergency department (ED), computed tomography (CT) is particularly beneficial in the investigation of high-speed trauma patients. With the advent of multidetector CT (MDCT) scanners, it is becoming faster and easier to conduct scans. In recent years, this has become evident with an increasing number of CT requests. Patients who have multiple CT scans during their hospital stay can receive radiation doses that have an increased theoretical risk of induction of cancer. It is essential that the clinical justification for each CT scan be considered on an individual basis and that due consideration is given to the radiation risk and possible diagnostic benefit. The current lack of a central State or Commonwealth data repository for medical images is a contributing factor to excessive radiation dosage to the population. The principles of justification and radiation risks are discussed in this study.

A prospective blinded evaluation of exercise thallium-201 SPET in patients with suspected chronic exertional compartment syndrome of the leg.

This study compared the quantitative and qualitative results of leg thallium-201 single-photon emission tomography (SPET) imaging in patients with and without raised intracompartmental pressure associated with exercise-related leg pain. The purpose of this study was to clarify the aetiology of chronic exertional compartment syndrome (CECS), and to investigate the diagnostic applications of 201Tl SPET in CECS. Thirty-four study participants underwent compartment pressure testing (CPT) between March and August 2000. There were 25 positive CPT results (patient group), and nine negative CPT results (control group). All 34 participants underwent scintigraphy. Quantitative and qualitative assessments were performed for the anterolateral and deep posterior compartments of the lower leg. There was no significant difference in either quantitative or qualitative assessments of perfusion between those compartments with and those without CECS. In contrast, a marked effect of exercise type upon compartment perfusion pattern was noted. Results of this study indicate that there is no compartment perfusion deficit in those patients with raised intracompartmental pressure associated with CECS, and suggest a non-ischaemic basis for the pain associated with CECS. They also suggest no role for exercise perfusion scintigraphy in the diagnosis of this syndrome.

The limited role of myocardial fluorine-18 fluorodeoxyglucose imaging in candidates for cardiac transplantation: a planar imaging study.

This study compares the incidence and extent of hibernating myocardium (defined by myocardial perfusion/metabolism mismatch) in 28 cardiac transplant candidates with ischaemic cardiomyopathy and in 16 other patients with coronary artery disease (CAD) undergoing viability assessment. It then reviews the impact of myocardial perfusion metabolism imaging on management decisions in the transplant candidates at 6 months after scintigraphy. Each patient underwent a planar myocardial thallium-201 and fluorine-18 fluorodeoxyglucose scan on a modified gamma camera. Perfusion/metabolism mismatch was sized semi-quantitatively and each patient was assigned a global mismatch score. Transplant candidates had a lower left ventricular ejection fraction (LVEF) (P < 0.0002) and extent of hibernation myocardium (lower global mismatch score: P = 0.005) than other CAD patients but the difference in respect of mismatch frequency (8/28 vs 9/16 patients) did not reach statistical significance. Transplant candidates with LVEF < 20% had a lower global mismatch score (P < 0.02) than those with an LVEF > or = 20%. Interestingly two of three other CAD patients with LVEF < 20% had a moderate mismatch. Follow-up studies revealed the lack of impact of metabolic imaging as none of the three transplant candidates who eventually underwent revascularisation had hibernating myocardium and transplantation was offered to one of only two candidates with more than one minor mismatch. Thus metabolic imaging in potential transplant candidates may be of limited value because of the very low extent of hibernating myocardium, particularly if LVEF is below 20% and where clinical decisions are often based on many other factors.

Is planar thallium-201/fluorine-18 fluorodeoxyglucose imaging a reasonable clinical alternative to positron emission tomographic myocardial viability scanning?

This comparative study was performed to determine whether a conventional planar gamma camera optimised for 511-keV imaging can reliably assess myocardial viability using the fluorine-18 fluorodeoxyglucose (FDG) metabolic tracer previously developed for positron emission tomography (PET). Twenty-seven patients with severe ischaemic cardiomyopathy (mean left ventricular ejection fraction: 20% +/- 9%) having clinically indicated nitrogen-13 ammonia/FDG PET myocardial viability studies consented to resting, four-view, planar myocardial thallium-201 perfusion and FDG metabolism imaging. The resultant PET and planar perfusion/metabolism images (PPI) were independently assessed for FDG defect size and perfusion/metabolism mismatch, using a four-point scale, in each of four vascular regions: apex, circumflex, left anterior and posterior descending coronary artery territories. Of 108 regions, 106 were evaluable (two not assessed by PET). There was complete agreement in 70% of coronary vascular territories, giving an unweighted kappa score of 0.56. Moreover, in 94% of segments agreement was within one grade. Interestingly, six of the seven differences of more than one grade occurred in the circumflex coronary territory, which was also the only region for which planar positron imaging underestimated FDG defect size. Three of four moderate areas of perfusion/metabolism mismatch seen with PET were also seen on PPI. PPI showed three small regions of mismatch not seen on PET, whilst the reverse occurred with one other small region of mismatch. Thus, for this PET protocol, PPI provides very similar information on the extent of regional FDG uptake and occurrence of mismatch.(ABSTRACT TRUNCATED AT 250 WORDS)

Planar cardiac F-18 fluorodeoxyglucose imaging with a conventional gamma camera.

OBJECTIVE: To examine the potential of an adapted gamma camera to image cardiac uptake of the positron emitting glucose analogue fluorine-18 fluorodeoxyglucose (FDG). DESIGN: Postprandial studies were performed in 19 patients (mean age, 56 +/- 9 years) with coronary disease and resting cardiac dysfunction who had undergone a routine clinical 7 min/view planar thallium-201 (Tl-201) stress reinjection or rest redistribution study. A glucose/insulin protocol was used and, an hour after FDG injection, 15-minute static planar myocardial images were acquired in the four views used for Tl-201 scanning. RESULTS: The diagnostic quality of FDG images was at least as good as that of their Tl-201 counterparts, with less liver background in all but one FDG study. In the left anterior oblique 45 degrees view uncorrected global myocardial FDG and stress Tl-201 counts were similar, but the FDG study had significantly higher peak myocardial to background ratios. CONCLUSION: Assessing regional cardiac FDG uptake and myocardial perfusion seems feasible with conventional gamma camera technology, providing a widely available and cost effective means of detecting hibernating myocardium. Similar equipment may appreciably reduce the need for positron emission tomography in a range of clinical conditions.

Measurements of computed tomography radiation scatter.

This paper describes the measurement of scattered radiation from a computed tomography (CT) scanner in a clinical situation and compares the results with those obtained from a CT performance phantom and with data obtained from CT manufacturers. The results are presented as iso-dose contours. There are significant differences between the data obtained and that supplied by manufacturers, both in the shape of the iso-dose contours and in the nominal values. The observed scatter in a clinical situation (for an abdominal scan) varied between 3% and 430% of the manufacturers' stated values, with a marked reduction in scatter noted at the head and feet of the patient. These differences appear to be due to the fact that manufacturers use CT phantoms to obtain scatter data and these phantoms do not provide the same scatter absorption geometry as patients. CT scatter was observed to increase as scan field size and slice thickness increased, whilst there was little change in scatter with changes in gantry tilt and table slew. Using the iso-dose contours, the orientation of the CT scanner can be optimised with regard to the location and shielding requirements of doors and windows. Additionally, the positioning of staff who must remain in the room during scanning can be optimised to minimise their exposure. The data presented here allows for realistic radiation protection assessments to be made.

Radiolytic breakdown of sodium iodide (131I) in sodium iodide (131I) capsules.

Sodium iodide (131I) capsules are widely used for both diagnosis and therapy. The radiochemical purity of both diagnostic and therapeutic capsules in use in Australia was studied by gel chromatography, high voltage electrophoresis and paper chromatography. It was found that in two of the three bands of therapeutic capsules examined, significant quantities of a labelled high molecular weight component was produced with the result that these capsules failed to meet British Pharmacopoeia, BP, and United States Pharmacopoeia, USP, requirements for radiochemical purity well before their quoted expiry time. The nature of the impurity has not been identified but it is thought to be either iodinated gelatin or an iodinated capsule component.