Diuretic renal scan: is it always reliable?

99mTc-MAG3 diuresis renography in differentiating renal obstruction: Using statistical parameters as new quantifiable indices

OBJECTIVE

The aim of this study was to research, develop and assess the feasibility of using basic statistical parameters derived from renogram, "mean count value (MeanCV) and "median count value (MedianCV)", as novel indices in the diagnosis of renal obstruction through diuresis renography.

SUBJECTS AND METHODS

First, we re-digitalized and normalized 132 renograms from 74 patients in order to derive the MeanCV and MedianCV. To improve the performance of the parameters, we extrapolated renograms by a two-compartmental modeling. After that, the cutoff points for diagnosis using each modified parameter were set and the sensitivity and specificity were calculated in order to determine the best variants of MeanCV and MedianCV that could differentiate renal obstruction status into 3 distinct classes - i) unobstructed, ii) slightly obstructed, and iii) heavily obstructed.

RESULTS

The modified MeanCV and MedianCV derived from extended renograms predicted the severity of the renal obstruction. The most appropriate variants of MeanCV and MedianCV were found to be the MeanCV₅₀ and the MedianCV₆₀. The cutoff points of MeanCV₅₀ in separating unobstructed and obstructed classes as well as slightly and heavily obstructed classes were 0.50 and 0.72, respectively. The cutoff points of MedianCV₆₀ in separating unobstructed and obstructed classes as well as slightly and heavily obstructed classes were 0.35 and 0.69, respectively. Notably, MeanCV₅₀ and MedianCV₆₀ were not significantly influenced by either age or gender.

CONCLUSIONS

The MeanCV₅₀ and the MedianCV₆₀ derived from a renogram could be incorporated with other quantifiable parameters to form a system that could provide a highly accurate diagnosis of renal obstructions.

Quantitative means for differentiating renal obstruction by analysing renography by compartmental modelling of renal fluid flow rate

OBJECTIVE

The aim of this study was to investigate the accuracy of using a newly developed index, the ratio of urine outflow to renal pelvis volume U/V2 (1/s), in evaluating renal obstruction and determining the severity of obstruction.

PATIENTS AND METHODS

A total of 42 patients' renograms (80 kidneys) were studied. Compartmental modelling was used to model the behaviour of tracers flowing through the kidney. The derived model led to the formation of the normalized urine flow rate U/V2. An analysis was carried to test the accuracy of the developed index by comparing the developed model and the clinical evaluation of renograms. The Support Vector Machine algorithm was implemented to predict the renal obstruction status.

RESULTS

From the comparison performed between the index and the clinical evaluation from certified experts, it was shown that a higher value of index U/V2 indicated a normal kidney, whereas a lower value indicated an obstructed kidney. The classifier developed could provide a 100% accurate diagnosis of differentiated unobstructed kidneys (42/42) and obstructed kidney (18/18). For further classification of obstructed kidneys, the system grouped the samples into slightly obstructed cases with an accuracy of 100% (9/9) and heavily obstructed cases with an accuracy of 89% (8/9).

CONCLUSION

The use of the single parameter U/V2 could produce the diagnosis of renal obstruction with a high level of accuracy. This method has the potential to be used as a benchmark to distinguish the severity level of the renal obstruction.

The true clinical significance of renography in nephro-urology

Isotopic renography is a non-invasive technique used routinely by the clinician to provide information about kidney structure and function. Whilst there is no doubt of its value in the accurate measurement of glomerular filtration rate and in the detection of parenchymal abnormalities, its role in the diagnosis of renovascular disease (especially in patients with renal insufficiency), the exclusion of obstruction and the evaluation of the patient with either acute renal failure or renal transplant dysfunction remains unproven. In part, this reflects a failure to standardise protocols and rigorously evaluate diagnostic techniques. Recent developments in ultrasound, computerised X-ray tomography and nuclear magnetic resonance now present the clinician with rival techniques and emphasise the need for the clinical development of isotopic renography.

Imaging for ureteropelvic junction obstruction in adults

The three goals of imaging for ureteropelvic junction (UPJ) obstruction are to determine the presence and degree of renal obstruction, to assess renal function, and to determine the cause of the problem. The diagnostic techniques are intravenous urography, which is unreliable; ultrasonography, with the addition of pulsed Doppler technology; diuretic scintigraphy; and pressure-flow studies (Whitaker test), which is the only direct clinical test of renal outflow resistance. Voiding cystography, retrograde ureteropyelography, and CT have utility in some patients. In determining the cause of obstruction, the patient often is evaluated for crossing vessels using angiography, endoluminal ultrasonography, or spiral CT. It is not possible to formulate a single algorithm for radiographic evaluation of suspected UPJ obstruction, but in the average adult patient, urography and diuretic scintigraphy are sufficient.