Interobserver Variability in Interpretation of Planar and SPECT Tc-99m-DMSA Renal Scintigraphy in Children

Abstract

Objective: This study objective was to evaluate interobserver agreement between individual pairs of three nuclear medicine physicians in interpretation of renal cortical scintigraphy in children with respect to the mode of acquisition (planar vs. SPECT), diagnoses and kidney site (left vs. right).

Materials and methods: Thirty children were imaged in planar and SPECT mode per protocol upon the injection of Tc-99m DMSA dose adjusted to their body weight. Patients were classified according to diagnoses into four groups. Three nuclear medicine physicians interpreted the findings blindly and independently. Renal defects were interpreted as focal and diffuse, per three renal segments. For the raters we calculated simple percentage agreement, the Cohen kappa statistic with 95% confidence intervals, and the overall kappa defining the levels of reliability as almost perfect or perfect, substantial, moderate, fair and slight agreement.

Results: Interobserver agreement in planar interpretation was 77,2% (kappa=0.59; 95% confidence interval, 0.41 to 0.75) and SPECT 72,9% (kappa= 0,57; 95% confidence interval, 0,41 to 0,72). In planar interpretation, all individual pairs had moderate agreements except one that had a substantial agreement. In SPECT, all the pairs had moderate agreements except one that had an almost perfect agreement. Overall agreement per kidney site was on planar 73,4% for the left (kappa=0,54, moderate agreement), and 81,1% for the right kidney (kappa 0,63, substantial agreement). On SPECT, there was 72,2% agreement for the left (kappa=0,59, mode rate agreement), and 73,7% for the right kidney (kappa=0,54, moderate agreement). Overall agreement per diagnoses ranged from 70-88,9% on planar (kappa= -0,04 to 0,79), and 50-100% on SPECT (kappa=-0,02-1,000) indicating agreements from slight to substantial.

Discussion: Our results suggest acceptable levels of interobserver agreement in all individual pairs of raters with respect to the mode of acquisition (planar vs. SPECT), diagnoses and kidney site (left vs. right). For the mode of acquisition, we would recommend hybrid imaging SPECT/CT method to be used whenever possible in the detection of renal cortical defects on Tc-99m-DMSA scintigraphy.

Keywords: Interobserver variability; SPECT; Tc-99m-DMSA; cortical scintigraphy; planar.

Figure 1

A 12-year-old girl with urinary tract infection. Ultrasound revealed chronic inflammatory changes in both kidneys without signs of dilatation of the collecting systems. Tc-99m-DMSA planar imaging revealed normal right kidney. Left kidney showed diffusely reduced uptake of radiotracer, particularly in the poles. The findings were consistent with the inflammatory changes.

Figure 2

Tc-99m-DMSA SPECT images of the same patient performed consequently to planar imaging, depicted in detail the inflammatory changes in the left kidney. Affection of the lower pole with disappearance of the renal contour was prominent.