Assessment of micro-dose biplanar radiography in lower limb measurements in children.

Objectives: To evaluate in children microdose protocol compared with low dose for lower limb alignment (LLA) measurements on biplanar radiography.

Methods: Children 6 years or older were included. Height, weight and hip width were measured prior to imaging. Hip width allowed classifying children into morphotype M1 (width <25 cm), M2 (25-35 cm) or M3 (>35 cm) corresponding to predefined acquisition parameters (kV, mA, tube speed). Micro- and low-dose protocols were used alternately, with simultaneous acquisition of frontal and lateral radiographs. LLA measurements were performed by two independent observers (n = 526). In 15 children per morphotype, a third observer performed measurements twice (n = 180). Intraclass correlation coefficients and the dose (delivered, absorbed) were calculated.

Results: 100 girls and 160 boys (mean age = 11.7 years) were investigated: 74 M1 (mean BMI, 15.7kg/m), 149 M2 (19.8 kg/m) and 40 M3 (30.2 kg/m). With microdose, inter- and intra-observer agreement was >0.90 for lengths whatever the morphotype, 0.75-0.90 (M1) and >0.90 (M2, M3) for valgus/varus and flexion/hyperextension deviations. Dose reduction reached a factor of 8.5 and 5.4 for the delivered and absorbed dose respectively.

Conclusions: Microdose could be used for LLA measurements in children and permits a significant dose reduction.

Key Points: • Lower limb lengths of children can be evaluated with microdose biplanar radiography. • Valgus/varus deviations also can be evaluated with microdose biplanar radiography. • Microdose biplanar radiography significantly reduces delivered and absorbed dose in children.