The use of a LUP has been validated in measuring RFcsa in healthy subjects and COPD patients. A technical concern of this method in obese patients is that although the standard LUP has sufficient resolution it may have an insufficient width window and penetration to measure RFcsa. In contrast, the CUP has sufficient penetration, but insufficient resolution. We hypothesised there would be no difference between RFcsa measured with the LUP and CUP and that the “spliced” RFcsa using the LUP has the same value as the whole RFcsa.Method
Subjects had RFcsa measured at 2/3 of the distance from the anterior superior iliac spine to superior border of the patella. Image acquisition was made using real time B-mode ultrasonography using a 6 MHz linear probe and 2–5 MHz curvilinear probe. Whole and matching “spliced” RFcsa images were acquired in a subgroup. RFcsa measurements were calculated offline using the Image J® programme.Results
27 subjects (5 COPD patients; 22 healthy subjects) were scanned. Of these, 14 had whole RFcsa images visualised with the LUP. These were compared with RFcsa images obtained using the CUP (Abstract P132 figure 1). There was no difference between the LUP and CUP RFcsa measurements (mean LUP RFcsa 344 (112) mm2 vs mean CUP RFcsa 364 (110) mm2; p=ns; intraclass correlation coefficient r=0.95). In addition there was no significant differences between mean “spliced” and whole images (335 (110) mm2 vs 344 (112) mm2; p=ns). Three measurements were acquired with each probe with the mean CV of 2.4% and 2.78% for the CUP and LUP, respectively. For the spliced images, the mean CV was 2.5%.Conclusion
These data demonstrate that both linear and curvilinear probes can be used to acquire accurate RFcsa measurements. Furthermore, “splicing” the images from the LUP, when a CUP is not available is a justified method to assess RFcsa. This method should be considered for RFcsa image acquisition in obese patients.