With the advantages of low cost, high imaging speed, non-intrusive and non-invasive, electrical capacitance tomography (ECT) becomes one of most maturely developed industrial tomography modalities. However, ECT had not been considered for medical applications before this work. This thesis is to explore medical applications of ECT, especially for root canal treatment (RCT) and revision total hip replacement (THR).A dental ECT system based on impedance analyser has been designed for RCT for two purposes: (1) to visualise the tooth surface in real time and (2) to determine the position of an endodontic file. To adapt the limited space in oral cavity, a miniature two–plate dental ECT sensor with either 2×2 or 2×3 array has been designed and fabricated. The sensor has a similar performance to the conventional ECT sensor and can provide good image quality. By registering and fusing with the radiograph based on a Major-axis method, a real-time image with high resolution can be obtained. A piecewise linear function has been used to locate the axial position of the apex of an endodontic file. The results show that high accuracy can be achieved near the ‘End Point’ as it is one of the reference points, determined by the sudden change in capacitance when a grounded metallic file touches the root apex (conductive media or solution).For revision THR, a conventional 8-electrode single plane sensor has been used, generating real-time 3D images of a metallic rod using a model based method. By this method, the 3D image reconstruction is simplified to estimate the cross-sectional and axial potions of the rod in the sensing area and to draw an image of the rod with prior knowledge. A high accuracy can be achieved with the maximum absolute error of 0.13 cm in estimating cross-sectional position using a weighted mean method and 0.4 cm in estimating axial position by the linear function based on the relative change in capacitance between file and electrodes. A preliminary experiment has been carried out to generate an electrical impedance tomography (EIT) image of a metallic object in conductive solution with high permittivity. Using the impedance analyser based system, the EIT image can be obtained with a conventional ECT sensor and the result is promising, providing the possibility of obtained a real-time EIT 3D image of a milling/drilling tool during revision THR.