Is the depth correction using the geometric mean really necessary in a 99Tcm-DMSA scan in the paediatric population?

Abstract

Determination of the left to right dimercaptosuccinic acid (DMSA) uptake ratio is theoretically one of the easiest quantitative procedures in nuclear medicine. The quantification can be performed on the posterior view, with or without the lateral view for correction of kidney depth. The geometric mean can also be determined using both the anterior and the posterior views. The aim of this study was to evaluate the occurrence of remarkable differences in the results from quantification of the relative renal function using the geometric mean and those obtained using the posterior counts only. Moreover, we evaluated to what extent the patient age influenced these differences. We reviewed 328 99Tcm-DMSA scans. The difference between the relative renal function obtained using the posterior view and that obtained using the geometric mean was calculated and analysed statistically. For the purpose of evaluating the value of performing the geometric mean calculation in patients of different ages, patients were divided into four age groups (group I, < or =2 years; group II, 3-9 years; group III, 10-18 years; group IV, >18 years). Using the Student's t test, no statistical differences were found in the relative renal function obtained by the two methods (posterior projection and geometric mean) in groups I (t = 0.01, P = 0.992) and II (t = 1.43, P = 0.155), which consisted of patients younger than 10 years (77% of the patients). In groups III and IV statistical differences were found (t = 2.27, P = 0.028 and t = 2.170, P = 0.038), respectively. We conclude that for children under 10 years it is unnecessary to perform depth correction using the geometric mean except in rare cases of major malformations and position anomalies.

Split renal function in patients with suspected renal artery stenosis: a comparison between gamma camera renography and two methods of measurement with computed tomography

“…First, renography is less reliable when one or both of the kidneys has a low uptake, due to the lower signal-noise ratio (7). A difference in depth of the kidneys is also known to affect the outcome owing to the soft-tissue attenuation (9,12). Second, the presence of renal artery stenosis in most of the subjects and the pharmacological conditions could have effects not readily accounted for.…”

Comparison of planar DMSA scan with an evaluation based on SPECT imaging in the split renal function assessment

“…The most accurate assessment of split renal function has always been at the forefront in many papers [14][15][16][17], in the interest of both nuclear medicine physicians and nephrologists and urologists. 99m Tc-DMSA as a very good cortical imaging agent is preferentially taken up by the proximal renal tubule and first part of Henle´s loop.…”

“…The quantification of the split renal function can be performed by different mathematical analysis, most often from planar images with compensation for kidney depth based on the geometric mean, which can be determined using anterior and posterior views [15]. In context of quantitative 99m Tc-DMSA imaging, it has been reported that the kidney depth compensation is unnecessary when calculating differential renal function for normally located kidneys in the pediatric population [16].…”

“…The geometric mean correction is less important in children than in adults, since children have a smaller renal depth. Hervas et al [15] conclude that for children less than 10 years it is unnecessary to perform depth correction using the geometric mean except in cases of major malformations and position anomalies.…”

“…Based on the facts provided by the phantom study and also because the percentage points differences within the patient study were mostly under the threshold of any clinical impact (less than or equal to 5 pp) [15], it is possible to keep practice of planar imaging without any risk of mistake. Also the simplicity and shorter acquisition speak for it.…”