What question did this study set out to answer?

To assess the feasibility of ultrasound/photoacoustic imaging for evaluating dyspnea severity by examining intercostal muscle oxygenation and morphology in COPD patients.

March 3, 2026Open Access

Assessing Dyspnea Severity in Chronic Obstructive Pulmonary Disease using Intercostal Muscle Ultrasound/Photoacoustic Multimodal Imaging

Key Points

To assess the feasibility of ultrasound/photoacoustic imaging for evaluating dyspnea severity by examining intercostal muscle oxygenation and morphology in COPD patients.
Conducted a retrospective analysis of patients who underwent ultrasound/photoacoustic imaging.
Stratified participants into non-COPD controls and two COPD severity groups based on mMRC scores.
Utilized gray-scale ultrasound to measure intercostal muscle thickness and photoacoustic imaging to quantify oxygen saturation.
Employed receiver operating characteristic analysis to determine diagnostic performance of the measurements.
Intercostal muscle thickness and oxygen saturation decreased with higher dyspnea severity.
SO₂ achieved an AUC of 0.960 for distinguishing non-COPD from COPD patients compared to 0.926 for muscle thickness.
Combination of thickness and SO₂ gave higher diagnostic AUC values across all groups, indicating better assessment capability.

Abstract

This study investigated the feasibility of ultrasound/photoacoustic imaging (US/PAI) for assessing dyspnea severity in patients with chronic obstructive pulmonary disease (COPD) by concurrently evaluating intercostal muscle oxygenation and morphology. In this retrospective study, participants who underwent US/PAI examination between January 2024 and September 2024 were stratified into three groups: Group 1 (non-COPD controls), Group 2 (COPD with modified Medical Research Council mMRC ≤1‌), and Group 3 (COPD with mMRC >1). US/PAI was performed on the right intercostal muscles. Gray-scale ultrasound measured muscle thickness, while PAI quantified oxygen saturation (SO₂). Diagnostic performance of thickness, SO₂, and combined diagnosis was evaluated using receiver operating characteristic (ROC) analysis and area under the curve (AUC). In total, 103 participants were included: 20, 32, and 51 in Groups 1, 2, and 3, respectively. Intercostal muscle thickness measured by B-mode ultrasound decreased with severity (Group 1: 4.1±0.5 mm; Group 2: 3.0±0.8 mm; Group 3: 2.8±0.8 mm), paralleled by a decline in SO₂ obtained from PAI (78.2±0.8%, 68.8±6.0%, 63.2±7.2%). Between non-COPD and all COPD patients, SO₂ (cut-off 71.2%) achieved an AUC of 0.960, versus 0.926 for thickness (cut-off 3.5 mm). For Group 1 vs. Group 2, the respective AUCs were 0.939 (SO₂ cut-off 71.3%) and 0.890 (thickness cut-off 3.6 mm). For Group 2 vs. Group 3, AUCs were 0.761 (SO₂ cut-off 64.4%) and 0.608 (thickness cut-off 3.1 mm). Critically, the combination of thickness and SO₂ consistently yielded a higher diagnostic AUC than thickness alone across all group The oxygenation and mass of intercostal muscles, measured by US/PAI, are negatively correlated with the dyspnea severity of COPD. • We innovatively used PAI to assess intercostal muscle morphology and function in COPD • This study is the first to assess intercostal SO₂ using photoacoustic imaging (PAI) • PAI provides a objective tool for assessing dyspnea severity in patients with COPD • There is a negative correlation between intercostal muscle SO₂ and dyspnea severity in patients with COPD

Assessing Dyspnea Severity in Chronic Obstructive Pulmonary Disease using Intercostal Muscle Ultrasound/Photoacoustic Multimodal Imaging

Key Points

Abstract

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