ANALYSIS OF THE RADIOISOTOPE RENOGRAM

Abstract

Alterations of the I¹³¹ hippuran renogram curve were estimated in dogs in response to such specific procedures as changes of skin-crystal distance, displacement of the probe, changes of the dosis injected, changes of urine flow rate, ureteral obstruction, renal arterial stricture and suppression of tubular function.
Several experiments concerning blood attenuation curve of I¹³¹ hippuran, its site of secretion and its distribution in kidney were performed in dogs.
Assuming that renogram curve is composed of the counting rates in renal vascuature, extrarenal vasculature and urinary tract (including tubules) within the collimator view, the curve is shown theoretically by the formulae (8) and (9). In cases of prolonged renal circulation or presence of diffusion space in urinary tract, the formulae (10) (11) or (14) (15) are appropriate respectively.
Theoretical alterations of the curve in speciflc procedures as shown in Tab. 9 are in accord with the experimental results summarized in Tab. 8.
Renogram curve is considered to be composed of many variables as follows:
1. External variables:
special and instrumental states (ε), sort of radioactive nuclide (ε), time constant (τ), dosis injected (m), method of injection (m).
2. Somatic variables:
i) systemic variables: space of diffusion and total kidney function (p)
ii) renal variables: renal blood flow (F), renal extraction of labelled compound (E), renal circulation time (z₁, z₂), urine transit time (n), renal vascular capacity (Q₁, Q₂), urinary dead (diffusion) space (D)
iii) extrarenal variables: vascular capacity within collimator veiw except that in kidney (Q₃).
It is reasonable to presume that counting rate of the segment a would be determined chiefly by renal and extrarenal vascular capacities and it decreases in either renal parenchymal reduction or severe renal arterial stricture.
Slope of the segment b is predominantly influenced by tubular function, decrease of which accompanys diminution of the slope. Left and right ratio of the slopes or urinary tract counting rates obtained by subtraction of blood counting rate from the value of the segment b, would be approximately equal to the hippuran clearance ratio of left and right kidneys.
Inverse relationship is obtained between the peak time and the urine flow rate. It is presumed that the peak time indicates the urine transit time which is the time required for urine through tubular lumen and renal pelvis to flow away outside the collimator view. As ureteral obstruction prolongs the peak time, it is obvious that the urine transit time is influenced not only by urine flow rate but by urinary tract space.
An available indicator to evaluate the segment c is its attenuation constant which is equal to that of blood curve except when urinary tract has diffusion space caused by reduction of urine flow or urinary tract obstruction, in which case the constant becomes smaller than that of blood curve.
Based on these fundamental alterations of the parameters, vairous renogram patterns in diseases may be clearly interpreted.
However, quantitative evaluation of the curve is a difficult problem, because counting rate of the segment a and slope of the segment b are markedly influenced by external variables which are unable to be kept constant in all cases, and both the peak time and the attenuation constant of the segment c change within small ranges.
It may be concluded that qualitative or semi-quantitative information about hippuran clearance, urine transit time (urine flow rate) and urinary tract patency in separate kidneys may be obtained from the curve and as one of separate kidney function tests the renogram has clinical significance with its technical advantages.