Acoustic Imaging of the Human Chest* Martin Kompis, MD, PhD; Hans Pasterkamp, MD; and George R. Wodicka, PhD Study objectives: A novel method for acoustic imaging of the human respiratory system is proposed and evaluated. Design: The proposed imaging system uses simultaneous multisensor recordings of thoracic sounds from the chest wall, and digital, computer-based postprocessing. Computer simulations and recordings from a life-size gelatin model of the human thorax are used to evaluate the system in vitro. Spatial representations of thoracic sounds from 8-microphone and 16-microphone recordings from five subjects (four healthy male adults and one child with lung consolidation) are used to evaluate the system in vivo. Results: Results of the in vitro studies show that sound sources can be imaged to within 2 cm, and that the proposed algorithm is reasonably robust with respect to changes in the assumed sound speed within the imaged volume. The images from recordings from the healthy volunteers show distinct patterns for inspiratory breath sounds, expiratory breath sounds, and heart sounds that are consistent with the assumed origin of the respective sounds. Specifically, the images support the concept that inspiratory sounds are produced predominantly in the periphery of the lung while expiratory sounds are generated more centrally. Acoustic images from the subject with lung consolidation differ substantially from the images of the healthy subjects, and localize the abnormality. Conclusions: Acoustic imaging offers new perspectives to explore the acoustic properties of the respiratory system and thereby reveal structural and functional properties for diagnostic purposes. (CHEST 2001; 120:1309 –1321) Key words: acoustics; heart sounds; image processing, computer-assisted; respiratory sounds; respiratory system; thorax S everal imaging methods for the human lung are available and widely used. Conventional radiog- raphy, CT, MRI, and methods provided by nuclear medicine are well established. Other methods, such as electrical impedance tomography, are still under development. 1 Methods using acoustic signals, most notably ultrasound, have not been successfully de- veloped, primarily because acoustic damping of the lung parenchyma is prohibitively high at high fre- quencies. 2 The absence of acoustic imaging methods may be somewhat surprising, since alterations in the struc- ture and function of thoracic organs that occur in disease often give rise to measurable changes in lung sound production and transmission. Acoustic assess- ment by stethoscope has been known for almost 2 centuries 3 and is a widely used clinical method to assess these changes. In the last decade, the avail- ability of computer technology has prompted many research efforts in the area of respiratory sounds and provided knowledge beyond what has been known based on classical auscultation. 4 Thoracic sounds are known to contain spatial information that can be accurately accessed using simultaneous multimicrophone recordings but not by successive auscultation at different locations of the thoracic surface. 5,6 The use of this additional spatial information may lead to acoustic imaging methods beyond the relatively simple mapping of sounds on the thoracic surface, which has been proposed both for lung 7,8 and heart sounds. 9 In this study, a novel acoustic imaging method for the human respiratory system that exploits this addi- tional spatial information is proposed and evalu- ated. The attractiveness of such a technique stems from its noninvasive nature and its relation to both the anatomy and physiology of the respiratory system. *From the School of Electrical and Computer Engineering, Department of Biomedical Engineering (Drs. Kompis and Wod- icka), Purdue University, West Lafayette, IN; the Department of Pediatrics and Child Health (Dr. Pasterkamp), University of Manitoba, Winnipeg, Canada; and the University Clinic of ENT, Head and Neck Surgery (Dr. Kompis), Inselspital, Berne, Swit- zerland. This work has been supported by the Swiss and the US National Science Foundations, the Ciba-Geigy-Jubila ¨ ums-Foundation, and the Children’s Hospital of Winnipeg Foundation. Manuscript received October 20, 2000; revision accepted March 8, 2001. Correspondence to: Martin Kompis, MD, PhD, University Clinic of ENT, Head and Neck Surgery, Inselspital, 3010 Berne, Swit- zerland; e-mail: martin.kompis@insel.ch CHEST / 120 / 4 / OCTOBER, 2001 1309 Downloaded From: http://journal.publications.chestnet.org/ on 06/04/2013