Comparative study of linear and curvilinear ultrasound probes to assess quadriceps rectus femoris muscle mass in healthy subjects and in patients with chronic respiratory disease

Abstract

Introduction: Ultrasound measurements of rectus femoris cross-sectional area (RFCSA) are clinically useful measurements in chronic obstructive pulmonary disease (COPD) and critically ill patients. Technical considerations as to the type of probe used, which affects image resolution, have limited widespread clinical application. We hypothesised that measurement of RFCSA would be similar with linear and curvilinear probes.

Methods: Four studies were performed to compare the use of the curvilinear probe in measuring RFCSA. Study 1 investigated agreement of RFCSA measurements using linear and curvilinear probes in healthy subjects, and in patients with chronic respiratory disease. Study 2 investigated the intra-rater and inter-rater agreement using the curvilinear probe. Study 3 investigated the agreement of RFCSA measured from whole and spliced images using the linear probe. Study 4 investigated the applicability of ultrasound in measuring RFCSA during the acute and recovery phases of an exacerbation of COPD.

Results: Study 1 showed demonstrated no difference in the measurement of RFCSA using the curvilinear and linear probes (308±104 mm(2) vs 320±117 mm(2), p=0.80; intraclass correlation coefficient (ICC)>0.97). Study 2 demonstrated high intra-rater and inter-rater reliability of RFCSA measurement with ICC>0.95 for both. Study 3 showed that the spliced image from the linear probe was similar to the whole image RFCSA (308±103.5 vs 263±147 mm(2), p=0.34; ICC>0.98). Study 4 confirmed the clinical acceptability of using the curvilinear probe during an exacerbation of COPD. There were relationships observed between admission RFCSA and body mass index (r=+0.65, p=0.018), and between RFCSA at admission and physical activity levels at 4 weeks post-hospital discharge (r=+0.75, p=0.006).

Conclusions: These studies have demonstrated that clinicians can employ whole and spliced images from the linear probe or use images from the curvilinear probe, to measure RFCSA. This will extend the clinical applicability of ultrasound in the measurement of muscle mass in all patient groups.

Keywords: COPD Exacerbations; Imaging/CT MRI etc; Respiratory Muscles.

Figure 1

A representative example of imaging splicing.

Figure 2

Rectus femoris cross-sectional area (RF_CSA) image acquired using (A) linear ultrasound probe at two-third distance (same subject) and (B) curvilinear ultrasound probe at two-third distance (same subject).

Figure 3

(A) Bland-Altman plot of linear probe and curvilinear probe rectus femoris cross-sectional area (RF_CSA) measurements at two-third distance from anterior superior iliac spine and patella. (B) Bland-Altman plot of linear probe and curvilinear probe RF_CSA measurements at three-fifth distance from anterior superior iliac spine and patella. (C) Bland-Altman plot of two independent operator measurements of RF_CSA using a curvilinear probe at three-fifth distance from anterior superior iliac spine and patella. (D) Bland-Altman plot of whole and spliced RF_CSA measurements using linear probe at two-third distance from anterior superior iliac spine and patella. (E) Bland-Altman plot of whole and spliced RF_CSA measurements using linear probe at three-fifth distance from anterior superior iliac spine and patella.

Figure 4

(A) Correlation between rectus femoris cross-sectional area (RF_CSA) at admission and body mass index. (B) Correlation between RF_CSA at admission and activity at 4-week follow-up.