PII: S0301-5629(01)00429-X ● Original Contribution A FREEHAND ELASTOGRAPHIC IMAGING APPROACH FOR CLINICAL BREAST IMAGING: SYSTEM DEVELOPMENT AND PERFORMANCE EVALUATION MARVIN M. DOYLEY,JEFFERY C. BAMBER,FRANK FUECHSEL and NIGEL L. BUSH Institute of Cancer Research, Sutton Surrey, UK (Received 2 February 2001; in final form 28 June 2001) Abstract—A prototype freehand elastographic imaging system has been developed for clinical breast imaging. The system consists of a fast data acquisition system, which is able to capture sequences of intermediate frequency echo frames at full frame rate from a commercial ultrasound scanner whilst the breast is deformed using hand-induced transducer motion. Two-dimensional echo tracking was used in combination with global distortion compensation and multi-compression averaging to minimise decorrelation noise incurred when stress is applied using hand-induced transducer motion. Experiments were conducted on gelatine phantoms to evaluate the quality of elastograms produced using the prototype system relative to those produced using mechanically induced transducer motion. The strain sensitivity and contrast-to-noise ratio of freehand elastograms compared favourably with elastograms produced using mechanically induced transducer motion. However, better dynamic range and signal-to-noise ratio was achieved when elastograms were created using mechanically induced transducer motion. Despite the loss in performance incurred when stress is applied using hand-induced transducer motion, it was concluded that the prototype system performed sufficiently well to warrant clinical evaluation. (E-mail: marvin.m.doyley@Dartmouth.edu) © 2001 World Federation for Ultrasound in Medi- cine & Biology. Key Words: Breast imaging, Freehand elastography, Hand-induced transducer motion, Tissue elasticity, Tumour detection. INTRODUCTION Elastography is a new imaging technique that depicts tissue stiffness by imaging internal tissue strain induced using an externally applied stress (O’Donnell et al. 1991; Ophir et al. 1991). This imaging technique has been utilised in various medical imaging applications, includ- ing the breast (Ce ´spedes and Ophir 1993; Garra et al. 1997), the prostate (Lorenez et al. 1999; Pesavento et al. 2000), and the intra-coronary artery (Ce ´spedes et al. 1997; de Korte et al. 1997, 2000). However, more wide- spread clinical utilisation of breast elastography is cur- rently limited by the specialised methods and equipment that are used to apply stress, which prevents the entire organ from being examined. Sonoelasticity imaging (Lerner et al. 1990; Parker et al. 1990) is an alternative elasticity imaging approach, which is generally more flexible compared to elastogra- phy and has the advantage of being able to produce real-time elasticity images. Unfortunately, sonoelasticity images are generally very difficult to interpret because of the complicated modal patterns that are produced. Con- sequently, we have developed a novel technique known as freehand elasticity imaging (Bamber and Bush 1995; Bamber et al. 1988) for clinical breast imaging. Our goal is to improve the clinical usefulness of breast elastogra- phy by producing images of internal tissue strain induced during manual palpation (i.e., to apply stress to the breast using hand-induced transducer motion). Unfortunately, the use of hand-induced transducer motion as the source of tissue displacement poses several problems in elas- tography. First, difficulty in avoiding out-off-plane trans- ducer motion during palpation will reduce contrast res- olution and may even result in failure to estimate internal tissue strain. Second, registration errors (i.e., misalign- ment of the pre- and postdeformed echo frames) are likely to be incurred during palpation, which will reduce the fidelity (i.e., accuracy and precision) of the estimated tissue strains. Finally, the magnitude of internal tissue Address correspondence to: Dr Marvin M Doyley, Thayer School of Engineering, Dartmouth College, 800 Cummings Hall, Hanover, NH 03755, USA. E-mail: marvin.m.doyley@dartmouth.edu Ultrasound in Med. & Biol., Vol. 27, No. 10, pp. 1347–1357, 2001 Copyright © 2001 World Federation for Ultrasound in Medicine & Biology Printed in the USA. All rights reserved 0301-5629/01/$–see front matter 1347