Assessing the variability in respiratory acoustic thoracic imaging (RATHI).
Multichannel analysis of lung sounds (LSs) has enabled the generation of a functional image for the temporal and spatial study of LS intensities in healthy and diseased subjects; this method is known as respiratory acoustic thoracic imaging (RATHI). This acoustic imaging technique has been applied to diverse pulmonary conditions, but it is important to contribute to the understanding of RATHI characteristics, such as acoustic spatial distribution, dependence on airflow and variability. The purpose of the current study is to assess the intra-subject and inter-subject RATHI variabilities in a cohort of 12 healthy male subjects (24.3±1.5 years) using diverse quantitative indices. The indices were obtained directly from the acoustic image and did not require scores from human raters, which helps to prevent inter-observer variability. To generate the acoustic image, LSs were acquired at 25 positions on the posterior thoracic surface by means of airborne sound sensors with a wide frequency band from 75 up to 1000 Hz under controlled airflow conditions at 1.0, 1.5 and 2.0 L/s. To assess intra-subject variability, the degree of similitude between inspiratory acoustic images was evaluated through quadratic mutual information based on the Cauchy-Schwartz inequality (I(CS)). The inter-subject variability was assessed by an image registration procedure between RATHIs and X-ray images to allow the computation of average and variance acoustic image in the same coordinate space. The results indicated that intra-subject RATHI similitude, reflected by I(CS-global), averaged 0.960±0.008, 0.958±0.008 and 0.960±0.007 for airflows of 1.0, 1.5, and 2L/s, respectively. As for the inter-subject variability, the variance image values for three airflow conditions indicated low image variability as they ranged from 0.01 to 0.04. In conclusion, the assessment of intra-subject and inter-subject variability by similitude indices indicated that the acoustic image pattern is repeatable along different respiratory cycles and across different subjects. Therefore, RATHI could be used to explore different aspects of spatial distribution and its association with regional pulmonary ventilation.
Electrical Engineering Department, Universidad Autonoma Metropolitana, Mexico City 09340, Mexico. Electronic address: schv@xanum.uam.mx.
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Charleston-Villalobos
Electrical Engineering Department, Universidad Autonoma Metropolitana, Mexico City 09340, Mexico.
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Torres-Jiménez
Department of Health Science, Universidad Autonoma Metropolitana, Mexico City 09340, Mexico.
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González-Camarena
National Institute of Respiratory Diseases, Mexico City 14080, Mexico.
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Chi-Lem
Electrical Engineering Department, Universidad Autonoma Metropolitana, Mexico City 09340, Mexico.
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Aljama-Corrales
D000328:Adult; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D013902:Radiography, Thoracic; D015203:Reproducibility of Results; D012135:Respiratory Sounds / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography / Q000295:instrumentation* / Q000379:methods*; D055815:Young Adult
Acoustic thoracic imaging; Breathing sounds; Inter-subject variability; Intra-subject variability; Mutual information