Dr. Tong Xu

Associate Professor, Medical Physics
Physics Department - Carleton University
3318 HP
(613) 520 - 2600 Ext. 8794
txuatphysics [dot] carleton [dot] ca

Research Summary

Real-time motion tracking for medical procedures

Real-time motion tracking of a target (patient body, organ, tumour, endoscope, catheter etc.) has very wide applications in medical care. For example, during external beam radiation therapy on pulmonary and abdominal tumours, delivering accurate radiation therapy is limited by the motion of the tumour as the patient breathes. The solution is to track the tumours location during radiotherapy, then compensate for the motion through respiratory gating or even adjust the beam to follow the tumour in real-time. We proposed to use implanted positron emission markers for real-time tumor tracking (PeTrack). By implanting positron emission markers into the tumor, and using pairs of position-sensitive detectors to detect the resulting annihilation gamma rays, the position of the tumor can be tracked in real-time with high accuracy. We are also applying this technique to image guided surgery. By integrating the PeTrack with surgical x-ray c-arm, we will be able to provide real-time feed-back of the position of the surgical instruments without constant x-ray imaging, thus reduce the radiation dose to patient and surgeons.

Dynamic Dual-energy x-ray imaging (dDEXI)

While x-ray fluoroscopy can be used to observe internal organ motion, automatic and accurate evaluation of the motion is usually hindered by the interference between bone and soft tissue signals. For example, during breathing, the regional lung density variation can be observed on the x-ray images, which may be used to diagnosis emphysema and chronic obstructive pulmonary diseases. However, due to the overlapping rib signal in the image, the accuracy of these analyses is questionable. Dual-Energy x-ray imaging can overcome this issue by separating bone and soft-tissue images, taking advantage of their different attenuation coefficients as a function of x-ray energy. We have developed the dDEXI technique that acquires two image sequences simultaneously, thus, it is free of motion artifacts. We also propose using dDEXI for lung tumour motion assessment. The oncologist can use this information to determine whether motion management is required during radiotherapy. dDEXI can be a faster, cheaper, low dose alternative to current motion assessment methods, such as MRI or 4D CT.


  1. T. Xu, J.T. Wong, S. Molloi.,Method and apparatus for real-time tumor tracking by detecting annihilation gamma rays from low activity position isotope fiducial markers, U.S. Patent # 8447387. 2013

  2. C. Mennessier, B. Spencer, R. Clackdoyle, and T. Xu. Distortion correction, geometric calibration, and volume reconstruction for an isocentric c-arm x-ray system. In Conference Proceedings of the 2011 IEEE Nuclear Science Symposium and Medical Imaging Conference, 2011. p2943-2947

  3. M Chamberland, R Wassenaar, B Spencer, and T Xu. "Performance evaluation of real-time motion tracking using positron emission fiducial markers", Medical Physics 38 (2), 810-819 (2011).

  4. T. Xu, JL Ducote, JT Wong, and S Molloi.Dynamic dual-energy chest radiography: a potential tool for lung tissue motion monitoring and kinetic studyPhys. Med. Biol. 56 (2011) 115

  5. Churchill NW, Chamberland M, Xu T. Algorithm and simulation for real-time positron emission based tumor tracking using a linear fiducial marker. Med Phys. 2009 May;36(5):1576-86.

  6. T. Xu, J.T. Wong, P.M. Shikhaliev, J.L. Ducote, M.S. Al-Ghazi, and S. Molloi, "Real-time tumor tracking using implanted positron emission markers: concept and simulation study", Med Phys, 33, 2598-609 (2006).

  7. T. Xu, J.L. Ducote, J.T. Wong, and S. Molloi, "Feasibility of real time dual-energy imaging based on a flat panel detector for coronary artery calcium quantification", Med Phys, 33, 1612-22(2006).

  8. J.T. Wong, J.L. Ducote, T. Xu, M.T. Hassanein, and S. Molloi, "Automated technique for angiographic determination of coronary blood flow and lumen volume", Acad Radiol, 13, 186-94,(2006).

  9. P.M. Shikhaliev, T. Xu, J.L. Ducote, B. Easwaramoorthy, J. Mukherjee, and S. Molloi, "Positron autoradiography for intravascular imaging: feasibility evaluation", Phys Med Biol,51, 963-79,(2006).

  10. J.L. Ducote, T. Xu, and S. Molloi, "Optimization of a flat-panel based real time dual-energy system for cardiac imaging". Med Phys, 33, 1562-8,(2006).P.M. Shikhaliev, J.L. Ducote, T. Xu, and S. Molloi, Q"uantum  efficiency of the MCP detector: Monte Carlo calculation", IEEE Transactions  on Nuclear Science, 52, 1257-1262,(2005).

  11. P.M. Shikhaliev, T. Xu, and S. Molloi, "Photon counting computed  tomography: Concept and initial results", Medical Physics 32, 427-436,(2005).

  12. T. Xu, P.M. Shikhaliev, G.R. Berenji, J. Tehranzadeh, F. Saremi, and S. Molloi, "Area beam equalization: optimization and performance of an automated prototype system for chest radiography", Acad. Radiol., 11, 377-89(2004).

  13. T. Xu, M.S. Al-Ghazi, and S. Molloi, "Treatment planning considerations of reshapeable automatic intensity modulator for intensity modulated radiation therapy", Med Phys 31, 2344-55(2004).

  14. J.T. Wong, T. Xu, A. Husain, H. Le, and S. Molloi, "Effect of area x-ray beam equalization on image quality and dose in digital mammography", Phys Med Biol 49, 3539-57 (2004).