3D Ultrasound Elastography for Early Detection of Lesions. Evaluation on a Pressure Ulcer Mimicking Phantom. Jean-François Deprez, Guy Cloutier, Cedric Schmitt, Claudine Gehin, André Dittmar, Olivier Basset, Elisabeth Brusseau To cite this version: Jean-François Deprez, Guy Cloutier, Cedric Schmitt, Claudine Gehin, André Dittmar, et al.. 3D Ultrasound Elastography for Early Detection of Lesions. Evaluation on a Pressure Ulcer Mim- icking Phantom.. Conference proceedings : .. Annual International Conference of the IEEE En- gineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, Institute of Electrical and Electronics Engineers (IEEE), 2007, 1, pp.79-82. 10.1109/IEMBS.2007.4352227. inserm-00192829 HAL Id: inserm-00192829 https://www.hal.inserm.fr/inserm-00192829 Submitted on 29 Nov 2007 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. HAL author manuscript Conf Proc IEEE Eng Med Biol Soc 2007;1:79-82 3D Ultrasound Elastography for Early Detection of Lesions. Evaluation on a Pressure Ulcer Mimicking Phantom. Jean-François Deprez, Guy Cloutier, Cédric Schmitt, HAL author manuscript inserm-00192829, version 1 Claudine Gehin, André Dittmar, Olivier Basset and Elisabeth Brusseau Abstract— A pressure ulcer is a damaged tissue area induced of bedsores affect these two locations. by an unrelieved pressure compressing the tissue during a Above a threshold, compression results in local occlusions prolonged period of immobility. The lack of information and of blood capillaries. This shortage of blood supply, called studies on the development of this pathology makes its ischemia, prevents the natural exchanges of oxygen and prevention difficult. However, it is both acknowledged that nutrients between the blood and body cells to occur. These lesions initiate in the deep muscular tissues before they expand to the skin, and that lesions are harder than healthy tissues. ischemic conditions may lead to cell death and severe tissue Elastography is therefore an interesting tool for an early damages. Besides, skin and muscle have different detection of the pathology. A 3D strain estimation algorithm is metabolisms: skin metabolism is anaerobic, while muscle presented and evaluated on a PVA-cryogel phantom, has an aerobic metabolism, requiring much more oxygen [1]. mimicking a pressure ulcer at an early stage. Muscles are therefore more vulnerable to ischemia than the skin and surrounding fat tissues. Thus, lesions first initiate in I. INTRODUCTION the deep muscle tissue before expanding to the skin, making ressure ulcers, also known as bedsores, are lesions of the difficult their early detection. This explains why the sore is P skin and underlying tissues, caused by a high and already at a severe stage when it appears on the skin surface. prolonged pressure at the body interface. This pathology In the literature, few studies are available on pressure concerns any people with weakened sensitivity or limited ulcer mechanical properties. The main reference in this area mobility. But it mostly strikes elders and spinal cord injury is given by Gefen et al. [2], who showed that tissues patients. This disease is painful, handicapping and becomes damaged by pressure ulcer are harder than healthy tissues. a growing issue, as life expectancy increases in western By applying a prolonged compression on rat muscle tissues countries. Yet, it has been neglected till now, and there is in vivo, they observed a significant increase of tissue elastic still little consensus about the pathological process that modulus with time and pressure level. triggers the formation of bedsores. Because of this process of hardening of damaged areas It is now acknowledged that pressure ulcers appear after a and the deep origin of the ulcer, ultrasound elastography prolonged period of immobility, during which the body seems especially appropriate for the early detection of interface lying on a support (either a bed or a wheelchair) pressure ulcer formation. undergoes a high and unrelieved pressure. During a short Elastography is a promising technique, which aim is to time, biological soft tissues can tolerate relatively high provide information about the mechanical properties of soft pressures. However, a weaker but continuous pressure can biological tissues, by investigating their deformation under result in severe injuries and a pressure ulcer can therefore an external load. Pre- and post-compression ultrasonic (US) appear anywhere in the body as soon as it is subjected to a radio-frequency (RF) signals are first acquired. Then, significant pressure. Nevertheless, thin layered tissues in changes within the signals induced by the stress are analyzed regard to a bony prominence are privileged regions, as a to compute a map of local strains. high stress is focused on a small volume. This pattern is met Since static elastography has appeared in the early 90s [3], for sacrum or heels. These are privileged regions and 80 % mainly 1D methods were developed. A few 2D methods have also been worked out [4]-[10]. These techniques are Manuscript received April 2, 2007. This work was supported in part by a adapted to current clinical equipment since ultrasound grant of the Region Rhône-Alpes, France. scanners essentially provides 2D data. However they may J.F. Deprez, O. Basset and E. Brusseau are with the laboratory lead to noisy elastograms if significant out-of plane motion CREATIS (Application & Research Center for Image and Signal occurs, since it represents a source of decorrelation between Processing), INSA-Lyon, Université de Lyon, CNRS UMR 5220 & INSERM U630 (corresponding author mail: 7 avenue Jean Capelle, pre- and post-compression signals. To overcome this Villeurbanne, 69621 France; phone: 33 4 72 43 62 54; fax: 33 4 72 43 85 decorrelation problem, and with the development of 2D 26; e-mail: [email protected] ). transducer arrays, we use in this study a 3D estimator, which G. Cloutier and C. Schmitt are with the Laboratory of Biorheology and Medical Ultrasonics of the University of Montreal Hospital, Canada (e- computes the axial strain while considering lateral and mail: [email protected] , [email protected] ). azimuthal motions. This strain estimation model is further C. Gehin and A. Dittmar are with the Biomedical Microsensors Department of Institut des Nanotechnologies de Lyon of INSA (National Institute of Applied Sciences), France (e-mail: [email protected] and [email protected] ). This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. scatterers due to the compression and enables to work on US probe corresponding tissue regions, and therefore equivalent US y (lateral) data in both volumes. To cover the whole US volume V1, the l) ha Healthy ut pre-compression region of study R1 is regularly moved by im tissues az constant steps of ∆ , ∆ , and ∆ in the axial, lateral and ( (1 cycle) ax lat azim z azimuthal directions, respectively. An adaptive displacement x (axial) Ulcer is considered for R2: its axial displacement results from the HAL author manuscript inserm-00192829, version 1 (2 cycles) accumulation of axial deformations of the regions located Bone between the probe and the region of interest, and the lateral m and azimuthal displacements are directly linked to those 30 mm 30 m 0 1 1 estimated over adjacent regions. uR1 and uR2, the positions of 60 mm R1 in V1 and R2 in V2, respectively, are then given by: G G G Fig. 1. Phantom scheme. = ∆ + ∆ + ∆ uR (m,n,q) m. ax .i n. lat . j q. azim .k 1 (1) m −1 G n−1 G q −1 G u (m,n,q) = ( 1 ).∆ .i + τ . j + ν .k detailed in the following section. Pressure ulcer early R 2 ∑ α ax ∑ k ∑ k k detection is then investigated with the proposed method. k =0 k =0 k =0 where αk is the axial scaling factor at position uR1(m,n,q), τk the lateral displacement and vk the azimuthal displacement, estimated on step k. The axial time-delay (parameter d) is II. METHOD directly linked to the axial coordinate of uR2. Hence, with The proposed 3D strain estimator is based on an adaptive such an initialization for the location of R2 in V2, the and iterative constrained optimization process. For each parameter d is already determined, and the three parameters elementary RF region R1 selected in the pre-compression α, τ and ν remain to be estimated, the two latter being of volume V1, its deformed version R2 is searched in the post- small magnitude. compression volume V2 and the corresponding local strain is then estimated. In the axial direction (see directions in fig. 1), R2 is considered as a time-delayed (parameter d) and B. Joint estimation of the parameters α, τ and ν scaled (parameter α) replica of R1. Because lateral and A joint estimation of the parameters α, τ and ν is then azimuthal resolutions are much coarser than the axial performed. The region of interest R2 is searched within V2, as resolution, R2 is only considered to be a shifted version of R1 an axially scaled, laterally and azimuthally shifted replica of in these directions (parameters τ and ν).