Body surface area correction in single-sample methods of glomerular filtration rate estimation.

Single-sample methods of estimating glomerular filtration rate (GFR) are used routinely, in a number of institutions, to calculate values of total plasma clearance (TPC), which are then converted to GFR. Adjustment of the final estimate for body surface area (BSA) is not adequate to allow adult equations to be used in children and work has been undertaken to seek an age-independent technique. The aim of this study was to evaluate the ability of an alternative method of correcting for BSA, of scaling the plasma sample activity, to achieve an age-independent solution. The accuracy of the scaled TPC values was compared with a monoexponential analysis as the 'gold' standard. Data from 60 patients were analysed using 16 single-sample models. Patients were chosen so that 10 could be allocated to each of six categories involving three age groups (0-3 years, 4-17 years and 18+ years) and two classes of TPC (< 40 and > 40 ml.min-1). Adjustment of the plasma activity gave more accurate results than correction of the final estimate in 87% of the categories for 15 of the models. This improvement was particularly apparent in the case of adult equations applied to child data, which gave results similar to those obtained using child equations, indicating that they can be used with equal accuracy.

Interpretation of captopril transplant renography using a feed forward neural network.

UNLABELLED: Severe renal artery stenosis (RAS) is a relatively uncommon complication after renal transplantation but is a curable cause of hypertension, which demands reliable early diagnosis to reduce morbidity, mortality and graft loss. Captopril renography has been used for a number of years as a method of detecting RAS but controversy still exists as to the diagnostic accuracy of this test and as to the most appropriate interpretation criteria with which to establish a positive result. METHODS: This report presents the results of using artificial neural networks to impartially assess these interpretation criteria. Data comprised 31 99mTc-MAG3 captopril renography investigations undertaken on hypertensive renal transplant patients with a suspected diagnosis of RAS. Each renogram study was correlated with an arteriogram as the "gold standard". Training of the network was performed using the round-robin technique. RESULTS: An accuracy of 95% could be achieved by considering perfusion index, time-to-peak activity, accumulation index and excretion index for both pre- and post-challenge studies. This varied as the parameters were either included or excluded. CONCLUSION: Artificial neural network analysis is a useful technique to evaluate the most appropriate criteria for interpreting captopril transplant renography investigations.

Identification of a hypoperfused segment in bull's-eye myocardial perfusion images using a feed forward neural network.

Artificial neural networks are computer systems which can be trained to recognize similarities in patterns and which learn by example; one of the more straightforward types being the feed forward neural network (FFNN). We previously reported the use of FFNNs for classification of hypoperfusion patterns in bull's-eye representation of 201Tl single photon emission tomography myocardial perfusion studies and showed that, when such an image was divided into 24 segments, FFNNs could detect perfusion defects without direct comparison to a normal data base. This has been extended in this investigation to assess the ability of an FFNN, trained on data in which only a single segment was hypoperfused, to detect this abnormal segment when the hypoperfusion pattern of the other segments in the image varied. The results indicated that the network could reliably determine whether a segment was normally or under perfused, with accuracies of 99% and 100%, respectively, if all other segments were normally perfused. It could also reliably detect a normally perfused segment, even if other segments were hypoperfused, with accuracies of 95% and 98%. The network was less reliable, however, in detecting a hypoperfused segment when other segments were also hypoperfused, showing accuracies of only 74% and 88%.

A feed forward neural network for classification of bull's-eye myocardial perfusion images.

Identification of hypoperfused areas in myocardial perfusion single-photon emission tomography studies can be aided by bull's-eye representation of raw counts, lesion extent and lesion severity, the latter two being produced by comparison of the raw bull's-eye data with a normal data base. An artificial intelligence technique which is presently becoming widely popular and which is particularly suitable for pattern recognition is that of artificial neural network. We have studied the ability of feed forward neural networks to extract patterns from bull's-eye data by assessing their capability to predict lesion presence without direct comparison with a normal data base. Studies were undertaken on both simulation data and on real stress-rest data obtained from 410 male patients undergoing routine thallium-201 myocardial perfusion scintigraphy. The ability of trained neural networks to predict lesion presence was quantified by calculating the areas under receiver operating characteristic curves. Figures as high as 0.96 for non-preclassified patient data were obtained, corresponding to an accuracy of 92%. The results demonstrate that neural networks can accurately classify patterns from bull's-eye myocardial perfusion images and detect the presence of hypoperfused areas without the need for comparison with a normal data base. Preliminary work suggests that this technique could be used to study perfusion patterns in the myocardium and their correlation with clinical parameters.

The importance of the perfusion index in the evaluation of captopril renography for transplant renal artery stenosis.

Severe renal artery stenosis (RAS) is a relatively uncommon complication following renal transplantation but is a curable cause of hypertension which demands reliable early diagnosis to reduce morbidity, mortality and graft loss. Captopril renography has been used for a number of years as a method of detecting RAS mainly in native kidneys, with only a few studies concerning the transplant situation. Controversy still exists as to the diagnostic accuracy of this test and as to the most appropriate interpretation criteria with which to establish a positive result. This paper reports the evaluation of 26 captopril renography investigations on hypertensive renal transplant patients with a suspected diagnosis of RAS. Each renogram study was correlated with an arteriogram as the 'gold standard' which was undertaken within 28 days of the renography. A sensitivity of 92%, a specificity of 86% and an accuracy of 88% were achieved by including a consideration of the change in perfusion to the kidney between pre- and post-challenge studies. It is concluded that captopril renography is a useful screening test for the detection of transplant renal artery stenosis (TRAS).

Inter-beat changes in left ventricular function with cardiomyoplasty as measured using MUGA scanning.

Dynamic cardiomyoplasty is a new surgical technique that uses electrically stimulated skeletal muscle to partially replace or reinforce the heart muscle in the treatment of advanced heart failure. Clinical experience with cardiomyoplasty is limited, which has precluded definitive conclusions about its value. We have studied the effect of cardiomyoplasty on the heart muscle when the skeletal muscle was being stimulated to coincide with alternate natural beats. The left ventricular function was assessed using radionuclide angiography during the beat immediately following skeletal muscle stimulation and during the beat immediately before stimulation. When the supported beat is compared with the unsupported beat, the results demonstrate that cardiomyoplasty improves the global and regional ejection fraction. The regurgitation index remains unchanged. The systolic peak emptying rate improves but the diastolic peak filling rate worsens. This latter finding provides additional information regarding the diastolic function of the heart following cardiomyoplasty, which is presently not well understood.

The renal transplant perfusion index: reduction in the error and variability.

For 15 years, perfusion indices derived from scintigraphic studies have proved useful in the serial evaluation of renal transplants and they have recently been confirmed as being more sensitive than Doppler ultrasound as an indicator of vascular rejection and cyclosporin toxicity. In the calculation of these indices, correction for administered activity is often accomplished using activity measurements made over a convenient artery which, therefore, has a critical influence on the value of the index obtained. In this communication, a theoretical assessment is made of the error and variability introduced into the calculation of the perfusion index, because of inadequate spatial sampling of activity in these narrow arteries and the consequential inconsistencies in the measurement of the arterial tracer activity. Using numerical simulation, it is shown that the errors in repeat studies on the same patient may be as high as 39% and between patients as high as 53%. These figures can be reduced to below 18% and 21%, respectively, by constructing a region of interest (ROI) to extend over as much of the arterial width as possible rather than relying only on the maximum pixel count. Further reduction to below 12% and 10% is possible by utilising a 128 x 128 acquisition matrix instead of 64 x 64 and drawing the ROI over the aorta instead of the iliac artery.

Case report: investigation of chyluria.

We present a case of chyluria in which the demonstration of abnormal lymphaticourinary communication was established by conventional lymphangiography. Radiocolloid lymphoscintigraphy failed to demonstrate the site of leakage, probably due to technical factors which are discussed.

Silicon measurement in a lung phantom by neutron inelastic scattering.

A study was made to assess the feasibility of determining the silicon level in human lungs in vivo by measuring the gamma rays arising from the neutron inelastic scattering reaction 28Si(n, n' gamma)28Si. Neutron energies in the range 5--8 MeV represent the best compromise between the conflicting requirements of high energy for good detection statistics and low energy to minimize the dose to the subject. The sensitivity of measurement was enhanced by pulsing the neutron beam and counting only during the period of bombardment. This effectively reduced the background counts emanating from thermal neutron reactions in the phantom and from the fast neutron reaction 31P(n, alpha)28 A1. In measurements with an anthropomorphic phantom, no interference peaks from other prompt inelastic scattering reactions were observed. With one Ge(Li) detector of 19% relative efficiency, a detection limit of 0.6 g of silicon per 10 mSv was obtained. On this basis, it is estimated that six Ge(Li) detector of 25% efficiency each would be capable of measuring 0.15 g of silicon in the lungs, the average level found in nonoccupationally exposed adults.U