Effectiveness of external respiratory surrogates for in vivo liver motion estimation.
OBJECTIVE
Due to low frame rate of MRI and high radiation damage from fluoroscopy and CT, liver motion estimation using external respiratory surrogate signals seems to be a better approach to track liver motion in real-time for liver tumor treatments in radiotherapy and thermotherapy. This work proposes a liver motion estimation method based on external respiratory surrogate signals. Animal experiments are also conducted to investigate related issues, such as the sensor arrangement, multisensor fusion, and the effective time period.


METHODS
Liver motion and abdominal motion are both induced by respiration and are proved to be highly correlated. Contrary to the difficult direct measurement of the liver motion, the abdominal motion can be easily accessed. Based on this idea, our study is split into the model-fitting stage and the motion estimation stage. In the first stage, the correlation between the surrogates and the liver motion is studied and established via linear regression method. In the second stage, the liver motion is estimated by the surrogate signals with the correlation model. Animal experiments on cases of single surrogate signal, multisurrogate signals, and long-term surrogate signals are conducted and discussed to verify the practical use of this approach.


RESULTS
The results show that the best single sensor location is at the middle of the upper abdomen, while multisurrogate models are generally better than the single ones. The estimation error is reduced from 0.6 mm for the single surrogate models to 0.4 mm for the multisurrogate models. The long-term validity of the estimation models is quite satisfactory within the period of 10 min with the estimation error less than 1.4 mm.


CONCLUSIONS
External respiratory surrogate signals from the abdomen motion produces good performance for liver motion estimation in real-time. Multisurrogate signals enhance estimation accuracy, and the estimation model can maintain its accuracy for at least 10 min. This approach can be used in practical applications such as the liver tumor treatment in radiotherapy and thermotherapy.
Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan.
Kai-Hsiang
KH
Chang
Ming-Chih
MC
Ho
Chi-Chuan
CC
Yeh
Yu-Chien
YC
Chen
Feng-Li
FL
Lian
Win-Li
WL
Lin
Jia-Yush
JY
Yen
Yung-Yaw
YY
Chen
D000005:Abdomen / Q000473:pathology; D000818:Animals; D004867:Equipment Design; D005471:Fluoroscopy / Q000379:methods; D006801:Humans; D006979:Hyperthermia, Induced / Q000379:methods; D008099:Liver / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009038:Motion; D011878:Radiotherapy / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012044:Regression Analysis; D015203:Reproducibility of Results; D012119:Respiration; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods