Shining a light on automated diaphragm function quantification
Towards an ultrasound-based, reproducible measuring tool
S.Y. van Loosbroek (TU Delft - Mechanical Engineering)
D. van Westerloo – Graduation committee member (Leiden University Medical Center)
J.E. Lopez Matta – Mentor (Leiden University Medical Center)
H. Pham – Graduation committee member
R. Dekker – Graduation committee member (TU Delft - Electronic Components, Technology and Materials)
A. Schoe – Graduation committee member (Leiden University Medical Center)
C. Elzo Kraemer – Mentor
J. Haartsen – Mentor
J.M. Visser – Mentor
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Abstract
Background: The diaphragm is poorly monitored in the Intensive care unit (ICU), despite its evident importance in respiration. Ultrasound (US) is frequently employed to evaluate diaphragm thickness (DT) and diaphragm thickening factor (DTF) but requires expertise and only covers a small diaphragm area. Therefore, advanced US (post-)processing techniques are being investigated for diaphragm applications, including speckle tracking methods.
Objective: The primary aim of this pilot study was to develop an algorithm enabling DT quantification. Second, both an existing Fourier-based (FBST) and intensity-based speckle tracking (IBST) algorithm were modified to determine their feasibility in diaphragm strain quantification.
Results: Minimal (DTmin, mm) and maximal DT (DTmax, mm), and DTF (%) values were 1.9 ± 0.4, 2.3 ± 0.5, and 22.6 ± 10.9 in the MV patient group, and 2.2 ± 0.4, 3.7 ± 1.5 and 66.5 ± 45.0 in the volunteer group (all p > 0.05). Correlation of DT algorithm variables and manual expert grading were allsignificant, with a good correlation in DTmax (ICC 0.9, r or ρ 0.7, p < 0.001) and a moderate correlation in DTmin and DTF (ICC 0.7, r or ρ 0.7, p < 0.001 and p = 0.001, respectively). Inter- and intra-rater reproducibility of manual DT assessment was poor (ICC < 0.4 and r or ρ < 0.2). GLS (%) and GLSR (%/s) values were -32.0 ± 19.8 and -6.6 ± 3.8 in the patient group and -40.3 ± 17.3 and -10.4 ± 6.8 in the volunteer group, respectively (all p > 0.05). IBST scores were 26.2 ± 17.6 in the patient group and 68.1 ± 32.5 in the volunteer group (p = 0.009). IBST score values showed a good correlation with DTF (r or ρ 0.7, p = 0.003), and a moderate, negative correlation with DTmin (r or ρ -0.5, p = 0.043). No significant correlations were seen between the remaining manual expert DT assessment and algorithm-derived FBST and IBST variables.Conclusion: DT quantification using the algorithm developed during this study correlated to conventional US expert assessment. Poor reproducibility of current diaphragm function quantification supports the need for such an automated assessment. The clinical value of diaphragm strain assessment using the modified FBST and IBST algorithms remains unclear. Further research involving a widely defined gold standard technique in diaphragm function quantification is warranted.