G. Fichtinger, A. Martel, and T. Peters (Eds.): MICCAI 2011, Part I, LNCS 6891, pp. 428–435, 2011. © Springer-Verlag Berlin Heidelberg 2011 Motion Tracking and Strain Map Computation for Quasi-Static Magnetic Resonance Elastography Y.B. Fu 1,* , C.K. Chui 1 , C.L. Teo 1 , and E. Kobayashi 2 1 Department of Mechanical Engineering, National University of Singapore, Singapore 2 Department of Precision Engineering, The University of Tokyo, Tokyo, Japan g0800248@nus.edu.sg Abstract. This paper presents a new imaging method for quasi-static magnetic resonance elastography (MRE). Tagged magnetic resonance (MR) imaging of human lower leg was acquired with probe indentation using a MR-compatible actuation system. Indentation force was recorded for soft tissue elasticity reconstruction. Motion tracking and strain map of human lower leg are calculated using a harmonic phase (HARP)-based method. Simulated tagged MR images were constructed and analyzed to validate the HARP-based method. Our results show that the proposed imaging method can be used to generate accurate motion distribution and strain maps of the targeted soft tissue. Keywords: MR tagging, HARP, motion tracking, strain, soft tissue indentation. 1 Introduction Elasticity is an important property for characterization of biological soft tissues. Local changes in mechanical properties of soft tissues may indicate the presence of tumors and other diseases [1]. In order to quantitatively study the soft tissue mechanical properties, Magnetic Resonance Elastography (MRE) has been developed in recent years. MRE can be categorized into dynamic MRE [2-4] and static or quasi-static MRE [5,6]. However, there are less literature about the quasi-static MRE due to the difficulty of motion tracking and strain calculation of soft tissue. Various techniques, such as Ultrasound, Computed Tomography (CT), and Magnetic Resonance Imaging (MRI) have been used to image the spatial deformation of soft tissue. Tagged MRI is widely used for the quantification of motion and deformation of cardiac tissue due to its easy access and good performance. However, the applicability of Tagged MRI on other parts of human body has not been investigated. In this paper, we extended the use of tagged MRI technique to other biological soft tissue by building a MR compatible actuating device synchronized with simulated electrocardiogram (ECG) signal. Large indentation tests on human lower leg were conducted using this imaging method. Template Matching [7-10], Active Geometry [11-13], Optical Flow [14-17] and Harmonic Phase (HARP) [18] are the main methods for tagged MR images processing. Template matching methods calculate the displacement by tracking the * Corresponding author.