It has previously been shown that an iterative constrained least-squares (CLSR) technique using a noise-based constraint may be superior to other methods of renogram deconvolution analysis. To test this hypothesis on real data, renography was performed on 70 patients with established diagnoses of normal, insufficient or acutely obstructed kidneys. Standard renography parameters were obtained from the time activity curves which were then deconvolved using three techniques. One kidney per patient was chosen at random for analysis resulting in a total of 43 normal and 27 diseased kidneys. The ability of each of the analytical techniques to discriminate between normal and diseased kidneys was assessed using logistic regression. CLSR proved to be robust and provide the best discrimination of the deconvolution techniques. However, the best overall discrimination was provided by a model based on the renography parameters excretion ratio, rate of uptake and time to peak activity which correctly classified 86% of the kidneys. It is possible that the renogram parameters could be used to produce notional probabilities of renal dysfunction which the physician could use as an aid in the interpretation of gamma-camera renography.
The present study aimed at comparing two renal function tests using 99mTc-DTPA (diethylene triamine penta acetic acid) and 131I-labeled hippuran (o-hippuric acid). A mixture of 80 MBq 99mTc-DTPA and 7.4 MBq 131I-hippuran in a total volume of 1.5 ml or less was injected into an arm-vein. Both radiopharmaceuticals have identical initial distributions in the blood pool when injected in this manner. Seventy-two patients were studied with the present dual radionuclide technique. The following parameters were derived from the renogram: area under curve, uptake ratio, Tmax, decrease ratio, excretion ratio, and rate of decrease. The parameters for 99mTc-DTPA and 131I-hippuran were compared for various kidney groups. Generally the renographic parameters were well correlated. Apart from the systematic differences due to different modes of renal excretion, the curve patterns virtually agreed. The differences that were observed between the two tracers lacked clinical significance.
Before deconvolution can be used in renography, it is necessary to decide whether the renal function is sufficiently good to allow it. To see if this decision can be circumvented, an iterative constrained least-squares restoration (CLSR) method was implemented in which the point of termination of the iteration occurs when a residual vector has a value less than an estimate of the noise in the original renogram curve. The technique was compared with the matrix algorithm and with direct FFT division. The comparison was achieved by deconvolving simulated renogram data with differing transit time spectra and statistics. As expected, the FFT technique produced results of little value whereas the CLSR and matrix methods produced values of mean transit time (MTT) that differed slightly from the expected results. Analysis indicated that the matrix approach was superior when the percentage noise component was less than 6% and vice versa. No technique produced useful transit time spectra. As the CLSR technique produced better results than the matrix method in simulations with relatively long MTTs and high noise, it seems reasonable to suggest that it might be used for renogram deconvolution without the need for previous inspection of the curves.
Seventy patients were studied with a dual radionuclide technique. The conventional renograms and the blood curve were subjected to deconvolution analysis using the matrix algorithm method, and the following curve data calculated from the retention functions: absolute and relative amplitudes, minimum time of the retention function, maximum time of the retention function and mean transit time. The findings with the two radiopharmaceuticals 99mTc-DTPA and 131l-Hippuran were compared under normal and pathological conditions. The correlations between the data with 99mTc-DTPA and those with 131l-Hippuran were highly significant (p <0.01). So was the correlation between the absolute amplitude of the retention curve and the rate of uptake based on the corresponding renogram (p <0.01). Due to the difference in the renal handling of the two tracers, longer maximum times were obtained with 99mTc-DTPA. The mean transit times were also longer with 99mTc-DTPA, except in kidneys with parenchymal insufficiency. The highest amplitudes were found in normal kidneys, while the lowest values were observed in parenchymal insufficiency. In the group with acute ureteral obstruction, the mean transit times tended to be increased. The maximum times were even more increased. With both tracers it is possible to distinguish between the three groups of renal conditions studied here: Normal, parenchymal insufficiency, and acute ureteral obstruction.
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