The influence of patient size on the overall uncertainty in radiographic dose audit.

The aim of this work was to investigate the effect of patient and cohort size on the overall uncertainty associated with dose audit using radiography of the abdomen as the exemplar. Water equivalent diameterDwwas used as the surrogate for patient size and its distribution (σ(Dw)) was used to quantify the effect of sample size. The more precise the kerma area product calibration, the more patients are required in the cohort to have the same impact on the overall uncertainty. Patient sample sizes of 300-400 will result in expanded uncertainties approaching the theoretical limit of double the measurement uncertainty when audits are performed with instruments having measurement uncertainties equal to ±7%, ±10% or ±12.5%. By way of example, for a field instrument with a measurement uncertainty of ±10%, a minimum sample size of 350 is required to achieve a total expanded uncertainty of ±21%. In the case of instruments with associated measurement uncertainty of ±3.5%, patient sample sizes of 300-400 will result in expanded uncertainties of approximately ±10%. From review of the literature and comparison with the results obtained here, it is conjectured that for radiographic dose audits of all parts of the trunk the contribution to overall uncertainty due to patient and sample size could be predicted using an indicative value forσ(Dw) of 3.4 where local data is not available.

Validity and practical utility of accelerometry for the measurement of in-hand physical activity in horses.

BACKGROUND: Accelerometers are valid, practical and reliable tools for the measurement of habitual physical activity (PA). Quantification of PA in horses is desirable for use in research and clinical settings. The objective of this study was to evaluate a triaxial accelerometer for objective measurement of PA in the horse by assessment of their practical utility and validity. Horses were recruited to establish both the optimal site of accelerometer attachment and questionnaire designed to explore owner acceptance. Validity and cut-off values were obtained by assessing PA at various gaits. Validation study- 20 horses wore the accelerometer while being filmed for 10 min each of rest, walking and trotting and 5 mins of canter work. Practical utility study- five horses wore accelerometers on polls and withers for 18 h; compliance and relative data losses were quantified. RESULTS: Accelerometry output differed significantly between the four PA levels (P < 0•001) for both wither and poll placement. For withers placement, ROC analyses found optimal sensitivity and specificity at a cut-off of <47 counts per minute (cpm) for rest (sensitivity 99.5 %, specificity 100 %), 967-2424 cpm for trotting (sensitivity 96.7 %, specificity 100 %) and ≥2425 cpm for cantering (sensitivity 96.0 %, specificity 97.0 %). Attachment at the poll resulted in optimal sensitivity and specificity at a cut-off of <707 counts per minute (cpm) for rest (sensitivity 97.5 %, specificity 99.6 %), 1546-2609 cpm for trotting (sensitivity 90.33 %, specificity 79.25 %) and ≥2610 cpm for cantering (sensitivity 100 %, specificity 100 %) In terms of practical utility, accelerometry was well tolerated and owner acceptance high. CONCLUSION: Accelerometry data correlated well with varying levels of in-hand equine activity. The use of accelerometers is a valid method for objective measurement of controlled PA in the horse.

Developing a method and deriving an uncertainty budget for the internal calibration of dosemeters for radiographic equipment.

Any institution wishing to perform an internal cross calibration of its diagnostic dosemeters should first quantify the uncertainty associated with this to demonstrate that it remains appropriate for the measurements being undertaken.An uncertainty budget for internal cross calibration that covers a range of locally used dosemeters has been derived using the methodology of the International Atomic Energy Agency. The specific internal cross calibration protocol requirements necessary for this uncertainty budget to be valid are discussed.The final quantified uncertainty is 5.31%; this is dominated by the 5% uncertainty associated with the calibration of the reference instrument. The next largest contributions are from differences in temperature and pressure and dosemeter energy dependence.It has been demonstrated that with careful adherence to a well designed internal cross calibration protocol, dosemeters can be calibrated in-house against a calibrated reference dosemeter with very little increase in the associated calibration uncertainty.

CT chest abdomen pelvis doses in Scotland: has the DRL had its day?

OBJECTIVE: This article reports on a pilot study designed to collect dose data representative of current CT chest abdomen pelvis (CAP) practice in Scotland, make any immediately obvious interventions and to identify if the current UK diagnostic reference level (DRL) of 940 mGy cm is still appropriate. The aims are to identify if a Scotland-wide picture archiving and communication system (PACS)-based dose audit of a number of CT examinations is likely to have value in terms of optimization of patient doses and to comment on the significance of the results in terms of future optimization strategies. METHODS: Dose audit of CT CAP examinations at 32 different scanner sites across Scotland using accepted data collection and analysis methods. The minimum sample size was 30. RESULTS: RESULTS indicate that CT CAP doses are lower than those previously reported (median, 800 mGy cm, 75th percentile 840 mGy cm) but follow a distribution that is not in keeping with the concept of DRLs as presently understood or implemented. CONCLUSION: There is value in a PACS-based dose audit project to provide serial snapshots of patient doses as optimization efforts take place and to revise current knowledge about CT doses. In our opinion, the results call into question whether DRLs or the concept of "achievable dose" are suitable for devising optimization strategies once a certain degree of optimization has taken place. ADVANCES IN KNOWLEDGE: The results reported here suggest that it may be time to take a different approach to optimization, concentrating on tools that are more refined than the DRL, which may have become more of a compliance tool than an aid to optimization.

An assessment of lead eyewear in interventional radiology.

The International Commission on Radiological Protection (ICRP) has recently issued a proposal to reduce the occupational eye dose limit from 150 to 20 mSv. A series of experiments has been performed to determine the level of protection from scattered radiation afforded to the interventional radiology operator by protective lead glasses, taking into account variation in operator position and angle of head rotation. The lenses of the glasses have a lead equivalence of 0.75 mm lead with 0.5 mm lead present in the side shields. Our results have led us to propose the use of a general dose reduction factor of 5 when using eyewear with this lead equivalence and construction. We have also concluded that the forehead of the wearer provides the most robust position to site a dosemeter that will be used to estimate the dose to both eyes as part of a personal monitoring regime. We have confirmed that backscatter from the head itself is the limiting factor for the dose reduction potential of lead eyewear.

Derivation of factors for estimating the scatter of diagnostic x-rays from walls and ceiling slabs.

Computed tomography (CT) scanning rooms and interventional x-ray facilities with heavy workloads may require the installation of shielding to protect against radiation scattered from walls or ceiling slabs. This is particularly important for the protection of those operating x-ray equipment from within control cubicles who may be exposed to radiation scattered from the ceiling over the top of the protective barrier and round the side if a cubicle door is not included. Data available on the magnitude of this tertiary scatter from concrete slabs are limited. Moreover, there is no way in which tertiary scatter levels can be estimated easily for specific facilities. There is a need for a suitable method for quantification of tertiary scatter because of the increases in workloads of complex x-ray facilities. In this study diagnostic x-ray air kerma levels scattered from concrete and brick walls have been measured to verify scatter factors. The results have been used in a simulation of tertiary scatter for x-ray facilities involving summation of scatter contributions from elements across concrete ceiling slabs. The majority of the ceiling scatter air kerma to which staff behind a barrier will be exposed arises from the area between the patient/x-ray tube and the staff. The level depends primarily on the heights of the ceiling and protective barrier. A method has been developed to allow tertiary scatter levels to be calculated using a simple equation based on a standard arrangement for rooms with different ceiling and barrier heights. Coefficients have been derived for a CT facility and an interventional suite to predict tertiary scatter levels from the workload, so that consideration can be given to the protection options available.

Proposals for revised factors in intra-oral radiography shielding calculations.

The current value for weighted average primary plus scatter kerma at 1 m for intra-oral radiography shielding assessment is based on scatter radiation measurements made with the trunk of a RANDO phantom and an assessment of primary transmission that is unverified. Measurements of primary transmission and scatter radiation during intra-oral radiography were made at 30° intervals through a full 360° rotation using two anthropomorphic head phantoms and similar equipment at three different sites. The results suggest that a scatter factor of 5 µGy (Gy cm(2))(-1) and a primary transmission of 0.03% of the entrance surface dose are more appropriate and, therefore, we recommend that the weighted average primary plus scatter kerma used for shielding calculations can be reduced from 1 to 0.5 µGy per exposure at 1 m. This factor will adequately account for exposures made at 60 and 70 kV using a range of intra-oral units.

The characterization and transmission of scattered radiation resulting from x-ray beams filtered with zero to 0.99 mm copper.

The specification of shielding for fluoroscopic facilities in the UK is based on the determination of scatter incident on a barrier using a simple formula linking kerma area product and scatter kerma. Over the last few years there has been a move to incorporate additional copper filtration in equipment used for high dose fluoroscopic and interventional examinations, and the existing formula does not take this into account. The spectral and transmission characteristics of the scattered radiation resulting from a primary x-ray beam filtered with additional copper are not known. In this study, the relationship between primary and scattered radiation in these beams has been investigated as have their transmission characteristics. The scatter kerma area product from filtered beams is shown to be greater than that from conventional x-rays and a simple numerical correction linking the two has been derived. The implications for shielding calculations have been assessed and the impact of the correction on calculated barrier thickness has been shown to be relatively small. The broad beam transmission characteristics of the radiation scattered from the filtered beams have been simulated using Monte Carlo methods and found to be adequately described by the standard transmission equation using conventional coefficients.

Establishment of scatter factors for use in shielding calculations and risk assessment for computed tomography facilities.

The specification of shielding for CT facilities in the UK and many other countries has been based on isodose scatter curves supplied by the manufacturers combined with the scanner's mAs workload. Shielding calculations for radiography and fluoroscopy are linked to a dose measurement of radiation incident on the patient called the kerma-area product (KAP), and a related quantity, the dose-length product (DLP), is now employed for assessment of CT patient doses. In this study the link between scatter air kerma and DLP has been investigated for CT scanners from different manufacturers. Scatter air kerma values have been measured and scatter factors established that can be used to estimate air kerma levels within CT scanning rooms. Factors recommended to derive the scatter air kerma at 1 m from the isocentre are 0.36 µGy (mGy cm)(-1) for the body and 0.14 µGy (mGy cm)(-1) for head scans. The CT scanner gantries only transmit 10% of the scatter air kerma level and this can also be taken into account when designing protection. The factors can be used to predict scatter air kerma levels within a scanner room that might be used in risk assessments relating to personnel whose presence may be required during CT fluoroscopy procedures.

Equine piroplasmosis treatment protocols: specific effect on orocaecal transit time as measured by the lactose 13C-ureide breath test.

REASONS FOR PERFORMING STUDY: Imidocarb dipropionate is the drug of choice for equine piroplasmosis but its administration causes severe colic and diarrhoea. An imidocarb protocol that reduces these effects is needed. OBJECTIVES: 1) Quantification of the effects of imidocarb dipropionate on equine orocaecal transit time (OCTT), with and without atropine or glycopyrrolate premedication and 2) investigation of an improved pretreatment regimen for imidocarb administration. HYPOTHESIS: Treatment with imidocarb dipropionate will result in colic and reduced OCTT as demonstrated by the lactose 13C-ureide breath test which will be ameliorated by premedication with either atropine or glycopyrrolate. METHODS: The effects of 3 drug therapies on OCTT were compared in 6 healthy horses in a randomised double-blind study vs. a saline control: 1) imidocarb dipropionate 2.4 mg/kg bwt administered intramuscularly (i.m.) with saline administered intravenously (i.v.; imidocarb/saline); 2) imidocarb dipropionate 2.4 mg/kg bwt administered i.m. with atropine 0.035 mg/kg bwt administered i.v. (imidocarb/atropine) and 3) imidocarb dipropionate 2.4 mg/kg bwt administered i.m. with glycopyrrolate 0.0025 mg/kg bwt administered i.v. (imidocarb/glycopyrrolate). The lactose 13C-ureide breath test was used to measure OCTT in each case and significance of treatment effect determined by a linear model analysis of variance. RESULTS: Imidocarb/atropine treatment caused an increase in OCTT (P < 0.05) whereas imidocarb/saline produced a nonsignificant decrease in OCTT. Imidocarb/saline caused colic and diarrhoea in 4 of 6 horses, which were not seen in any of the horses treated with imidocarb/atropine or imidocarb/glycopyrrolate or administered the saline control. Intestinal borborygmi were increased in imidocarb/saline and decreased in imidocarb/atropine treated horses, respectively. CONCLUSIONS: Imidocarb/saline treatment induced colic signs and a potential reduction in OCTT while imidocarb/atropine treatment increased OCTT significantly when compared with imidocarb/saline. Both atropine and glycopyrrolate premedication ameliorated the clinical gastrointestinal effects of imidocarb but atropine produced significant inhibition of gastric and/or small intestinal motility not detected with glycopyrrolate. Premedication with glycopyrrolate is recommended when using imidocarb for treatment of equine piroplasmosis.

In vitro validation of the lactose 13C-ureide breath test for equine orocaecal transit time measurement.

REASONS FOR PERFORMING STUDY: Validation of a reliable, noninvasive clinical test for quantification of equine orocaecal transit time (OCTT) is required. This would facilitate an evidence-based approach to investigation and treatment of equine small intestinal disorders. OBJECTIVES: 1) Comparison of the lactose (13) C-ureide breath test (LUBT) with the hydrogen breath test (H(2) BT) for OCTT measurement. 2) Identification of the characteristics of gastrointestinal microbial glycosylureide hydrolase activity in vitro. 3) Production of an optimised protocol for the LUBT for in vivo measurement of equine OCTT. HYPOTHESIS: Significant lactose (13) C-ureide ((13) C-LU) hydrolase activity is restricted to the large bowel. The rate of expiratory (13) CO(2) production after ingestion of the isotope will provide an indirect quantifiable measure of orocaecal transit rate. Requisite bacterial activity may be enhanced by a primer dose of unlabelled substrate as shown in Man. METHODS: Combined LUBT and H(2) BT were performed in 8 healthy individuals. Analysis of sequential end expiratory breath samples was used to calculate OCTT and results compared. Digestion of (13) C-LU was investigated in vitro using fresh faecal material or intestinal aliquots collected post mortem. Isotopic fermentation rate was measured by rate of appearance of (13) CO(2) . RESULTS: Peaks in expiratory (13) CO(2) occurred in all individuals after ingestion of the labelled test meal, whereas H(2) expiration was variable. Both faecal and intestinal microbial digestion of (13) C-LU were maximised by prior exposure to (12) C-LU. Induced bacterial glucoseureide hydrolase activity was significantly greater in the caecum than in the small intestine (n = 10, P<0.05). CONCLUSIONS: Significant (13) C-LU digestion is restricted to the equine large intestine under normal conditions, and is enhanced by prior exposure to (12) C-LU, making (13) C-LU a suitable noninvasive marker of equine OCTT. The LUBT is more reliable than the H(2) BT for measurement of equine OCTT.

Application of the lactose 13C-ureide breath test for measurement of equine orocaecal transit time.

REASONS FOR PERFORMING STUDY: Application of the lactose (13) C-ureide breath test (LUBT) for measurement of equine orocaecal transit time (OCTT) has not been reported previously. The ability to assess OCTT noninvasively, and to investigate its relationship to gastric emptying rate and small intestinal transit, would be of both clinical and research value. OBJECTIVES: 1) Assessment of the LUBT in healthy horses, with comparison of induced versus noninduced test protocols. 2) Application of a new dual stable isotope breath test (lactose (13) C-ureide and (13) C-octanoic acid) for gastrointestinal transit measurement. HYPOTHESIS: The LUBT will allow quantification of equine OCTT, and test efficacy will be enhanced by prior administration of lactose (12) C-ureide as shown in vitro. The dual tracer breath test will permit simultaneous measurement of gastric emptying, OCTT and small bowel transit times. METHODS: Induced and noninduced LUBTs were performed in 3 healthy mature horses in randomised order using a standard test meal and protocol. Combined LUBT and (13) C-octanoic acid breath tests ((13) C-OABT) were performed in 4 individuals on 4 occasions at weekly intervals. Expiratory isotopic recovery was modelled to allow generation of gastric emptying data, small bowel transit times and caecal transit parameters. RESULTS: The induction protocol for the LUBT increased the rate and magnitude of expiratory (13) CO(2) significantly. Mean ± s.d. values for OCTT, caecal lag phase (t(lag) ) and caecal t(1/2) using the induced LUBT were 3.24 ± 0.65 h, 5.62 ± 1.22 h and 6.31 ± 1.21 h, respectively. Dual stable isotope tests resulted in the production of 2 discrete peaks in expiratory (13) CO(2) in 15/16 tests from which gastric t(1/2), OCTT and small bowel transit (SBT) parameters could be calculated. CONCLUSIONS: The induced LUBT provides a reliable noninvasive measure of equine OCTT and can be paired with the (13) C-OABT to provide further information about small intestinal motility.

The radiobiology/radiation protection interface in healthcare.

The current knowledge of radiation effects is reviewed and implications for its application in healthcare considered. The 21st L H Gray conference gathered leading experts in radiobiology, radiation epidemiology, radiation effect modelling, and the application of radiation in medicine to provide an overview of the subject. The latest radiobiology research in non-targeted effects such as genomic instability and the bystander effect challenge the old models, but the implications for health effects on humans are uncertain. Adaptive responses to external stresses, of which radiation is one, have been demonstrated in cells and animal models, but it is not known how these might modify human dose-effect relationships. Epidemiological evidence from the Japanese A-bomb survivors provides strong evidence that there is a linear relationship between the excess risk of cancer and organ dose that extends from about 50 mSv up to 2.5 Sv, and results from pooled data for multiple epidemiological studies indicate that risks extend down to doses of 20 mSv. Thus linear extrapolation of the A-bomb dose-effect data provides an appropriate basis for radiological protection standards at the present time. Risks from higher dose diagnostic procedures fall within the range in which health effects can be demonstrated. There is therefore reason for concern about the rise in the number of computed tomography (CT) scans performed in many countries, and in particular the use of CT for screening of asymptomatic individuals. New radiotherapy techniques allow high dose radiation fields to be conformed more effectively to target volumes, and reduce doses to critical organs, but they tend to give a higher and more uniform dose to the whole body which may increase the risk of second cancer. It is important that radiation protection practitioners keep abreast of developments in understanding of radiation effects and advise the medical community about the implications of fundamental research when planning medical applications for the future.

21st L H Gray Conference: the radiobiology/radiation protection interface.

The 21st L H Gray Conference, organised by the L H Gray Trust with the Society for Radiological Protection, brought together international experts in radiobiology, epidemiology and risk assessment, and scientists involved in diagnostic and therapeutic radiation exposure. The meeting - held in Edinburgh, Scotland, on 4-6 June 2008 - aimed to raise awareness, educate and share knowledge of important issues in radiation protection. A distinguished group of speakers discussed topics that included (i) non-targeted effects of radiation, (ii) exposure to high natural background radiation, (iii) non-cancer effects in Japanese bomb survivors, (iv) lessons learnt from Chernobyl, (v) radiation in the workplace, (vi) biokinetic modelling, (vii) uncertainties in risk estimation, (viii) issues in diagnostic medical exposures, (ix) lessons leant from the polonium-210 incidence and (x) how the radiobiology/radiation oncology community is needed to help society prepare for potential future acts of radiation terrorism. The conference highlighted the importance, relevance and topicality of radiobiology today.

Current and future uses of breath analysis as a diagnostic tool.

The analysis of exhaled breath is a potentially useful method for application in veterinary diagnostics. Breath samples can be easily collected from animals by means of a face mask or collection chamber with minimal disturbance to the animal. After the administration of a 13C-labelled compound the recovery of 13C in breath can be used to investigate gastrointestinal and digestive functions. Exhaled hydrogen can be used to assess orocaecal transit time and malabsorption, and exhaled nitric oxide, carbon monoxide and pentane can be used to assess oxidative stress and inflammation. The analysis of compounds dissolved in the aqueous phase of breath (the exhaled breath condensate) can be used to assess airway inflammation. This review summarises the current status of breath analysis in veterinary medicine, and analyses its potential for assessing animal health and disease.

A review of methods for assessment of the rate of gastric emptying in the dog and cat: 1898-2002.

Gastric emptying is the process by which food is delivered to the small intestine at a rate and in a form that optimizes intestinal absorption of nutrients. The rate of gastric emptying is subject to alteration by physiological, pharmacological, and pathological conditions. Gastric emptying of solids is of greater clinical significance because disordered gastric emptying rarely is detectable in the liquid phase. Imaging techniques have the disadvantage of requiring restraint of the animal and access to expensive equipment. Radiographic methods require administration of test meals that are not similar to food. Scintigraphy is the gold standard method for assessment of gastric emptying but requires administration of a radioisotope. Magnetic resonance imaging has not yet been applied for assessment of gastric emptying in small animals. Ultrasonography is a potentially useful, but subjective, method for assessment of gastric emptying in dogs. Gastric tracer methods require insertion of gastric or intestinal cannulae and are rarely applied outside of the research laboratory. The paracetamol absorption test has been applied for assessment of liquid phase gastric emptying in the dog, but requires IV cannulation. The gastric emptying breath test is a noninvasive method for assessment of gastric emptying that has been applied in dogs and cats. This method can be carried out away from the veterinary hospital, but the effects of physiological and pathological abnormalities on the test are not known. Advances in technology will facilitate the development of reliable methods for assessment of gastric emptying in small animals.

Validation of the 13C-octanoic acid breath test for measurement of equine gastric emptying rate of solids using radioscintigraphy.

REASONS FOR PERFORMING STUDY: Disordered gastric motility may be a significant factor in the pathogenesis of many equine conditions. Although tests for liquid phase emptying rate have been validated in the horse, there are no effective tests for solid phase emptying measurement that can be performed routinely in the field. OBJECTIVES: The objective of this study was the assessment of a novel stable isotope technique, the 13C-octane acid breath test (13C-OABT), for the measurement of gastric emptying of solid ingesta, by direct comparison with the optimum method of gastric scintigraphy. METHODS: To facilitate dual measurement of gastric emptying, a test meal was used containing baked egg yolk labelled with both 13C-octanoic acid and 99mtechnetium sulphur colloid. Simultaneous, serial lateral gastric scintigraphs and expiratory breath samples were obtained in 12 healthy horses after voluntary ingestion of the test meal. Analysis of breath 13CO2:12CO2 ratio was performed by continuous flow isotope ratio mass spectrometry. Power regression was used to determine the gastric emptying coefficient, the gastric half-emptying time (t 1/2) and duration of the lag phase (tlag). RESULTS: Significant correlations (P < 0.001) were found between the 2 techniques for measurement of both t 1/2 and tlag. In addition, scintigraphic left t 1/2 was correlated significantly to breath test gastric emptying coefficient (P < 0.001). CONCLUSIONS: It was concluded that the 13C-octanoic acid breath test is a reliable diagnostic procedure to measure gastric emptying rate of solids in the horse. POTENTIAL RELEVANCE: Being safe, noninvasive and easy to perform, this test has potential value as both sensitive diagnostic modality and humane research tool for motility studies.

Quantitative detection of atropine-delayed gastric emptying in the horse by the 13C-octanoic acid breath test.

The 13C-octanoic acid breath test has been correlated significantly to radioscintigraphy for measurement of gastric emptying indices in healthy horses. The objective of this study was to investigate the validity of the test for measurement of equine delayed gastric emptying, prior to its potential clinical application for this purpose. A model of atropine-induced gastroparesis was used. Gastric emptying rate was measured twice in 8 horses using concurrent radioscintigraphy and/or breath test after treatment i.v. with either atropine (0.035 mg/kg bwt) or saline in randomised order. Analysis of both data sets demonstrated that the atropine treatment had caused a significant delay in gastric emptying rate. Paired breath test data showed an atropine-induced delay in gastric half-emptying time (t 1/2), with no overlap in the 99% CI range (P < 0.001). Significant correlations were found between scintigraphy and 13C-octanoic acid breath test for calculation of both t 1/2 (P < 0.01) and lag phase duration (P < 0.05) in the atropine-delayed emptying results. The mean (s.d.) bias in breath test t 1/2 when compared with scintigraphy was 1.78 (0.58) h. The results demonstrated that the 13C-octanoic acid breath test was an effective diagnostic modality for the measurement of equine delayed gastric emptying. The technique offers advantages to existing methods for clinical investigation, as it is noninvasive, not radioactive, quantitative and requires minimal equipment or training to perform.

The effects of xylazine, detomidine, acepromazine and butorphanol on equine solid phase gastric emptying rate.

The aim of this study was to measure the effects of specific commonly used sedative protocols on equine solid phase gastric emptying rate, using the 13C-octanoic acid breath test (13C-OABT). The gastric emptying of a standard 13C-labelled test meal was measured once weekly in 8 mature horses over two 4 week treatment periods. Each horse acted as its own control. In treatment Period 1, saline (2 ml i.v.), xylazine (0.5 mg/kg i.v.), detomidine (0.01 mg/kg i.v.) or detomidine/butorphanol combination (0.01/0.02 mg/kg i.v.) was administered in randomised order after ingestion of the test meal. During treatment Period 2, test meal consumption was followed by saline, xylazine (1.0 mg/kg i.v.), or detomidine (0.03 mg/kg i.v.) administration, or preceded by acepromazine (0.05 mg/kg i.m.) in randomised order. The 13C:12C ratio of sequential expiratory breath samples was determined by isotope ratio mass spectrometry, and used to measure the gastric half-emptying time, t 1/2, and duration of the lag phase, t lag, for each of the 64 tests. In treatment Period 1, detomidine/butorphanol prolonged both t 1/2 and t lag with respect to xylazine 0.5 mg/kg and the saline control (P < 0.05). In Period 2, detomidine 0.03 mg/kg delayed each parameter with respect to saline, acepromazine and xylazine 1.0 mg/kg (P < 0.001). Xylazine 1.0 mg/kg also lengthened t lag relative to the saline control (P = 0.0004), but did not cause a significant change in t 1/2. Comparison of treatment periods showed that the inhibitory effect of detomidine on gastric emptying rate was dose related (P<0.05). These findings may have clinical significance for case selection when these agents are used for purposes of sedation and/or analgesia.