Effects of Lung Ultrasound Technique and Pleural Line Depth on In Vitro and In Vivo Measurements of Pleural Line Thickness.

OBJECTIVE

The aim of the work described here was to determine the effects of imaging protocol, technique and pleural line depth on measured pleural line thickness (PLT).

METHODS

Sonograms were performed on a phantom and healthy volunteers. In vitro, pleural line depth, transducer type (5-1 MHz phased array vs. 13-6 MHz linear array), angle of the pleural line relative to the transducer and distance between the pleural line and focal length were explicitly modified. PLT was measured using electronic calipers. Regression equations described the effects of independent variables on PLT. Factors influencing PLT in vitro were tested in vivo.

RESULTS

In vitro (n = 250 sonograms), PLT was 3.8 (standard error: ±0.24) mm greater when using the phased array compared with the linear transducer (p < 0.001). For every additional centimeter of pleural line depth, PLT increased by 0.96 (±0.081) mm for the phased array (p < 0.001) and 0.26 (±0.019) mm for the linear transducer (p < 0.001). Neither pleural angle nor focal length altered PLT. In vivo (n = 160 sonograms), PLT was 2.56 (±0.06) mm greater when using the phased array (p < 0.001) compared with the linear transducer. PLT increased by 0.67 (±0.060) mm with the phased array (p < 0.001) and 0.25 mm (±0.019) with the linear transducer (p < 0.001) for every additional centimeter between the transducer and the pleura. Together the variables explained 93% of PLT variance in vivo (p < 0.001).

CONCLUSION

PLT measurements are affected by transducer type and pleural line depth. Future studies evaluating PLT as a disease marker should account for confounding by these variables.