Standardizing evaluation of pQCT image quality in the presence of subject movement: qualitative versus quantitative assessment

Abstract

Peripheral quantitative computed tomography (pQCT) is an essential tool for assessing bone parameters of the limbs, but subject movement and its impact on image quality remains a challenge to manage. The current approach to determine image viability is by visual inspection, but pQCT lacks a quantitative evaluation. Therefore, the aims of this study were to (1) examine the reliability of a qualitative visual inspection scale and (2) establish a quantitative motion assessment methodology. Scans were performed on 506 healthy girls (9-13 years) at diaphyseal regions of the femur and tibia. Scans were rated for movement independently by three technicians using a linear, nominal scale. Quantitatively, a ratio of movement to limb size (%Move) provided a measure of movement artifact. A repeat-scan subsample (n = 46) was examined to determine %Move's impact on bone parameters. Agreement between measurers was strong (intraclass correlation coefficient = 0.732 for tibia, 0.812 for femur), but greater variability was observed in scans rated 3 or 4, the delineation between repeat and no repeat. The quantitative approach found ≥95% of subjects had %Move <25 %. Comparison of initial and repeat scans by groups above and below 25% initial movement showed significant differences in the >25 % grouping. A pQCT visual inspection scale can be a reliable metric of image quality, but technicians may periodically mischaracterize subject motion. The presented quantitative methodology yields more consistent movement assessment and could unify procedure across laboratories. Data suggest a delineation of 25% movement for determining whether a diaphyseal scan is viable or requires repeat.

Figure 1

Visual inspection rating scale for femur (upper row) and tibia (lower row). Each score reflects the level of movement: 1 – none, very minimal; 2 – minimal; 3 – moderate; 4 – severe; 5 – extreme.

Figure 2

Analyses for quantitative assessment of movement. Analysis #1 is used find all bone area plus any positive movement. Analysis #2 finds only the bone. The difference in area between these two analyses will measure the movement in the scan.

Figure 3

Error plots (95% confidence interval bars) illustrating the distribution of the movement rating score for each rater within the average movement rating.

Figure 4

Relationship between the quantitative movement percentage and the technicians’ average movement rating. Vertical and horizontal reference lines represent 95% confidence intervals for respective variables.