Consensus report on quality control of quantitative measurements of renal function obtained from the renogram: International Consensus Committee from the Scientific Committee of Radionuclides in Nephrourology.

Among all the physiological indices that can be quantified using renography, measurement of renal function is the most basic. These measurements are used to make critical clinical management decisions and, as such, their reliability needs to be quality assured. This article seeks to address each aspect of the renography procedure, with particular emphasis on the effect on measurement of relative renal function. Estimation of individual kidney function is mentioned, but only briefly. A consensus approach was adopted, overseen, and directed by a chairman appointed by the Scientific Committee of the International Radionuclides in Nephro-Urology Group. The chairman selected the panel of experts from eight different countries based on their practical experience in the field. Where evidence exists to support the various recommendations it is given. Otherwise, the stated guidance represents the considered opinion of a body of experts, based on long experience and unpublished data. Some necessary compromises were made to account for the fact that renography is seldom performed solely with the purpose of measuring relative renal function. The technicalities of renography have always been a source of debate in nuclear medicine, which is reflected by the fact that a consensus could simply not be reached on a small number of issues. The structure of the report ensures that these are clearly indicated. This should serve to highlight gaps in our current knowledge, thus helping to direct future research. It is envisaged that the recommendations will be revised on a 2-year cycle to ensure that they remain up to date. An "open" process will be used to encourage participation and ownership. It is hoped that promotion of these guidelines, suitably complemented by audit processes, will raise standards in the practice of gamma camera renography.

Transport dynamics of the hepato-biliary system: a mathematical model allied to Tc 99m IDA scintigraphy.

A generalised mathematical model of hepatic biliary tracer flows is formulated in terms of physiologically identifiable transport parameters. From a particular solution derived from this, the system response to intravenous administration of Tc99m IDA biliary tracer is predicted. Minimisation procedures applied to this solution combined with experimental scintigraphic observations yield estimates for the physiological parameters pertaining to a number of patient studies. Some hepatic conditions where quantitative indicators may contribute to clinical diagnosis are discussed.

Measurement of renal functional reserve of the single kidney in man.

The renal functional reserve capacity (RFRC) and response of the single kidney to a low protein diet (LPD) were investigated. Effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) were measured using a single injection of I125 Hippuran and Cr51 EDTA during a dopamine infusion (3 micrograms/kg/min) and after 2 weeks on a LPD (0.6 g/kg/day). Dopamine increased ERPF but the associated rise in GFR was not significant. There was a significant decrease in both ERPF and GFR on LPD. The change in GFR during dopamine infusion, but not during LPD, correlated inversely with baseline GFR. Dopamine and LPD had no effect on heart rate or blood pressure and LPD did not alter urinary sodium excretion. These results suggest that the single kidney lacks functional reserve capacity and that protein restriction may be useful in preserving long term function.

Quality assurance in renography: a review.

Despite the fact that renography is practised by most nuclear medicine departments, some doubt remains about its clinical utility in certain settings. Unfortunately, lack of standardization has made it difficult to judge whether some reports of poor diagnostic accuracy are due to a fundamental limitation of the test, or simply to sub-optimal implementation. Some important work may therefore have been overlooked. Technical factors, to do with data acquisition and processing, are the most obvious reasons for variability of results between centres, but patient selection can also have a profound effect on diagnostic accuracy in situations where disease prevalence is low (e.g. renovascular hypertension). Belatedly, these issues are being addressed by the nuclear medicine community and this review summarizes the efforts that have been made to date. Published guidelines need to be reinforced by an audit process if real improvements in quality and consistency are to be realized.

Estimating plasma volume from red cell volume.

Following the withdrawal of the only licensed supply of 125I-HSA in 1997, most UK centres now simply estimate plasma volume from a knowledge of the red cell volume and venous haematocrit. We compared measured and estimated plasma volume in 107 consecutive patients who had had red cell and plasma volume measured independently in the conventional way. In only 40% of cases was the estimated value accurate to within +/- 5%, and discrepancies of more than +/- 10% were seen in 35%. As there appears to be no simple way of predicting those patients for whom an estimation is inappropriate, it is recommended that plasma volume is measured independently in all patients, using a reputable source of unlicensed 125I-HSA.

Measurement of the extravascular concentration of renal agents following intravenous bolus injection.

The extravascular concentration (Ce) of some renal agents, in relation to the simultaneous plasma concentration (Ci), was calculated as a function of time after intravenous injection. Four agents were studied: 51Cr-ethylenediamine tetraacetate (EDTA) (n = 11), 125I-hippuran (n = 11), 99Tcm-dimercaptosuccinic acid (DMSA) (n = 11) and 99Tcm-mercaptoacetyl triglycine MAG3 (n = 20). Plasma clearance curves were constructed from data acquired from multiple blood sampling and fitted with two exponentials. The extravascular content of tracer at any time is equal to the injected dose remaining after subtraction of the intravascular tracer content and the total amount of tracer cleared from plasma. Mean Ce/Ci at equilibrium (defined as the time, > 120 min, when Ce/Ci reaches its maximum value) was 1.087 (S.D. 0.019) for EDTA, 1.73 (0.48) for hippuran, 0.37 (0.2) for DMSA and 0.64 (0.3) for MAG3. Corresponding clearance (F) values were 68 (13), 415 (149), 15.6 (9.5) and 214 (52) ml min-1 1.73 m-2. Ce/Ci correlated with F and was also related to protein binding in plasma. Extrapolation of the regressions of Ce/Ci on F to F = 0 at several time points after injection gives a curve of Ce/Ci (at F = 0) against time which represents the rate of equilibration of the tracer throughout its distribution volume that would be seen with zero clearance, and therefore allows measurement of the in vivo protein binding of the tracer in plasma. Protein binding was zero for EDTA, 30% for hippuran, 86% for DMSA and 88% for MAG3.(ABSTRACT TRUNCATED AT 250 WORDS)

User requirements for information systems in nuclear medicine.

In the field of COST cooperation (COST = European Cooperation in the Field of Scientific and Technical Research) a project B2 for Quality Assurance in Nuclear Medicine Software has been established. In a memorandum of understanding setting up this project, user requirements were to be defined for the hardware and software used for data acquisition, processing and presentation. A subgroup of the management committee of COST B2 were interested in the Advanced Informatics in Medicine, AIM, task T-734 'Quality Assurance of Medical Software', and the AIM Project 'A 1034', coordinated by Dr K. Britton, was initiated. The initial drafts of this document were written in Helsinki during 1988-1990, and submitted for comment by the members of the management committee of COST B2. These comments were integrated in the text and this document was finalized by the UK group so as to make it available for international discussion. It is anticipated that, after appropriate international discussion, these User Requirements for Information Systems in Nuclear Medicine will be adopted by the management committee of COST B2 as a COST document. Towards these ends, a working group chaired by Dr Britton, including the British and Finnish teams and Ulrich Noelpp from Switzerland, was appointed by the management committee of COST B2 in April 1990. While writing it we have had the pleasure of working with referees from different European hospitals in many countries. We are happy to thank all of them for their valuable contributions.

UK audit of single photon emission computed tomography reconstruction software using software generated phantoms.

The purpose of this study was to undertake an audit of the quantitative characteristics of single photon emission computed tomography software using projection data from an analytically generated software phantom and a measured line source. The phantom consisted of three structures. A uniformly filled cylinder, a series of cylindrical rods of various diameters in a background activity with a rod to background ratio of 2:1 and lastly, a set of three concentric rings of activity in the ratio 1:0:1. The phantom contained no added statistical noise. No attenuation was imposed on the data. The phantom was generated analytically and projections were distributed at six different count densities. A single set of projections from a thin line source was also distributed. These data were distributed to centres throughout the UK. Centres were asked to reconstruct the data using a 'ramp only' reconstruction with no additional smoothing function applied. Data were requested for mean and standard deviation in the uniform cylinder, the maximum counts for each cylindrical rod and the mean counts in regions placed within the concentric rings. For the measured line source, centres were asked to measure the full width at half maximum and peak pixel counts for a profile through the reconstructed line. Results from 115 systems were obtained from 100 centres throughout the UK. These provided data from 12 software providers, 11 of these being commercial companies. Data were compared with the known input values and histograms of the distribution of results obtained. Significant differences in quantitative parameters were noted for the different input count densities as well as between suppliers and revisions of software from single suppliers.

UK audit of relative renal function measurement using DMSA scintigraphy.

A variety of software is used to determine quantitative parameters from radionuclide imaging procedures. Knowledge of the variability of parameter values found in different hospitals is an important aspect of clinical audit of these techniques. This study investigated the variation in relative renal function measurement from static DMSA scintigraphy in the UK. Ten studies representing a range of ages and relative function values were distributed in digital form to 100 hospitals with the assistance of the gamma camera computer suppliers and regional audit coordinators. The studies were analysed at each participating hospital and details of the different techniques and computer systems used were documented. The median value of relative percentage function was assessed for each of the studies. Methods varied in terms of the view used for analysis (54% geometric mean, 46% posterior), the type of background subtraction (single region 32%, separate regions 60%, none 8%) and the definition of the renal regions of interest (73% manual, 27% semi-automatic). Eighty-eight percent of results were within two percentage points of the study median and 98% within five percentage points. There were statistically significant differences observed in the results arising from the view used for the analysis and the background subtraction protocol. The results indicate that relative renal function assessment from static DMSA scintigraphy in the UK is essentially a reliable procedure, although improvements could be made by standardizing the technique used.

UK audit and analysis of quantitative parameters obtained from gamma camera renography.

The purpose of this study was to perform an audit of quantitative values obtained from gamma camera renography in the UK. Ten patient image sequences representing normal and pathological renal function were obtained from archived studies and distributed to hospitals in the UK. Hospitals were asked to measure five parameters: relative function, renogram time-to-peak (left and right), and whole kidney mean transit time (left and right). Details of methodology, software used and operator experience were requested. This allowed the influence of operational factors on variations in reported values to be examined. A total of 180 responses from 81 hospitals were received. Values reported for the parameters, together with other details supplied, were entered into Excel and SPSS for statistical analysis. Histograms representing the distribution of values were produced for each parameter. The largest variations were found for mean transit time and occasionally for time-to-peak. The effect of factors was assessed using nonparametric statistical tests applied independently to each renogram. For all the parameters, the hospital, UK region, supplier, computer and software version influenced variations in the reported values. Algorithm and site of background region were influencing factors for relative function, the background subtraction method influenced time-to-peak, and curve smoothing influenced mean transit time.

Appropriate corrections to glomerular filtration rate and volume of distribution based on the bolus injection and single-compartment technique.

The bolus injection, single-compartment technique for measuring GFR overestimates the true value. Nevertheless, assuming that for a given indicator the area under the first exponential of the plasma clearance curve is constant from subject to subject, the observed (uncorrected) value can be corrected by multiplication with a 'sliding' factor, the value of which is a nonlinear function of GFR. Several second-order polynomials, based on pre-determined relationships between simultaneously determined two-compartment and one-compartment GFR, have been described for correcting GFR (GFR correction). It is, however, theoretically more rational to use a factor which depends on the rate constant, alpha2, of the terminal exponential of the clearance curve. We have therefore determined a set of linear equations from retrospectively analysed multiple-sample inulin, 99mTc-DTPA and 51Cr-EDTA clearance curves to enable correction of GFR using alpha2. A set of linear equations is also developed to correct the volume of distribution (Vd) of the indicator (close to extracellular fluid volume for these indicators), which is also overestimated by the one-compartment technique. At low levels of GFR, alpha2-corrected GFR is similar to uncorrected GFR for all three indicators. As GFR increases, however, uncorrected GFR progressively overestimates (alpha2-corrected GFR. The overestimation is greater for inulin than for 99mTc-DTPA or 51Cr-EDTA. In the one-compartment approximation, Vd is overestimated more than GFR, and again the greatest overestimation is seen with inulin. In a prospective study of 129 patients undergoing routine measurement of GFR with 51Cr-EDTA, alpha2 correction using a factor based on retrospective EDTA data gave values of GFR which were higher than values obtained from GFR correction using a previously published polynomial (also based on EDTA clearances) by 15% in children and 12.5% in adults when uncorrected GFR was 150 ml/min/1.73 m2. Moreover, the ratio of uncorrected GFR to GFR-corrected GFR was higher in children than adults. We conclude that alpha2 is a more rational variable with which to correct two-sample or three-sample GFR than GFR itself, that the correction formulae are not interchangeable between inulin on the one hand and EDTA and DTPA on the other, and that the relative magnitudes of the corrections given by alpha2 correction versus GFR correction are different for children and adults.

Technetium labelled red blood cell scintigraphy in the diagnosis of intestinal haemorrhage.

99m-Technetium labelled red blood cell scintigraphy was used in the investigation of 15 adult patients with suspected small or large bowel bleeding requiring at least five units of blood (mean 14.3 units) and one neonate with rectal bleeding. Scintigraphy was found to be an accurate method of detecting the site of haemorrhage and was superior to angiography. This technique may be of particular value in patients with profuse colonic haemorrhage when the view at colonoscopy is poor.

Quality assurance of medical software.

Quality assurance is a topical issue within the software industry, and various methodological solutions aimed at improving software quality have been proposed. Medical software is generally deemed safety-critical and, as such, should be subject to control procedures exceeding those applicable to general-purpose software. The user/purchaser of medical equipment has an important part to play in the drive for higher-quality medical software, and ways in which the user can influence commercial suppliers are outlined. The implications of existing and planned legislation are also discussed.