Modeling and incorporating cardiac-induced lung tissue motion in a breathing motion model.
OBJECTIVE
The purpose of this work is to develop a cardiac-induced lung motion model to be integrated into an existing breathing motion model.


METHODS
The authors' proposed cardiac-induced lung motion model represents the lung tissue's specific response to the subject's cardiac cycle. The model is mathematically defined as a product of a converging polynomial function h of the cardiac phase (c) and the maximum displacement y(X0) of each voxel (X0) among all the cardiac phases. The function h(c) was estimated from cardiac-gated MR imaging of ten healthy volunteers using an Akaike Information Criteria optimization algorithm. For each volunteer, a total of 24 short-axis and 18 radial planar views were acquired on a 1.5 T MR scanner during a series of 12-15 s breath-hold maneuvers. Each view contained 30 temporal frames of equal time-duration beginning with the end-diastolic cardiac phase. The frames in each of the planar views were resampled to create a set of three-dimensional (3D) anatomical volumes representing thoracic anatomy at different cardiac phases. A 3D multiresolution optical flow deformable image registration algorithm was used to quantify the difference in tissue position between the end-diastolic cardiac phase and the remaining cardiac phases. To account for image noise, voxel displacements whose maximum values were less than 0.3 mm, were excluded. In addition, the blood vessels were segmented and excluded in order to eliminate registration artifacts caused by blood-flow.


RESULTS
The average cardiac-induced lung motions for displacements greater than 0.3 mm were found to be 0.86 ± 0.74 and 0.97 ± 0.93 mm in the left and right lungs, respectively. The average model residual error for the ten healthy volunteers was found to be 0.29 ± 0.08 mm in the left lung and 0.38 ± 0.14 mm in the right lung for tissue displacements greater than 0.3 mm. The relative error decreased with increasing cardiac-induced lung tissue motion. While the relative error was > 60% for submillimeter cardiac-induced lung tissue motion, the relative error decreased to < 5% for cardiac-induced lung tissue motion that exceeded 10 mm in displacement.


CONCLUSIONS
The authors' studies implied that modeling and including cardiac-induced lung motion would improve breathing motion model accuracy for tissues with cardiac-induced motion greater than 0.3 mm.
Department of Radiation Oncology, University of California, Los Angeles, California 90095 and Biomedical Physics IDP, University of California, Los Angeles, California 90095.
Benjamin M
BM
White
Department of Radiation Oncology, University of California, Los Angeles, California 90095 and Biomedical Physics IDP, University of California, Los Angeles, California 90095.
Anand
A
Santhanam
Department of Radiation Oncology, University of California, Los Angeles, California 90095 and Biomedical Physics IDP, University of California, Los Angeles, California 90095.
David
D
Thomas
Department of Radiation Oncology, University of California, Los Angeles, California 90095.
Yugang
Y
Min
Department of Radiation Oncology, University of California, Los Angeles, California 90095 and Biomedical Physics IDP, University of California, Los Angeles, California 90095.
James M
JM
Lamb
Department of Radiation Oncology, University of California, Los Angeles, California 90095 and Biomedical Physics IDP, University of California, Los Angeles, California 90095.
Jack
J
Neylon
Department of Radiation Oncology, University of California, Los Angeles, California 90095 and Biomedical Physics IDP, University of California, Los Angeles, California 90095.
Shyam
S
Jani
Department of Radiation Oncology, University of California, Los Angeles, California 90095.
Sergio
S
Gaudio
Biomedical Engineering IDP, University of California, Los Angeles, California 90095 and Department of Radiological Sciences, University of California, Los Angeles, California 90095.
Subashini
S
Srinivasan
Biomedical Physics IDP, University of California, Los Angeles, California 90095; Biomedical Engineering IDP, University of California, Los Angeles, California 90095; and Department of Radiological Sciences, University of California, Los Angeles, California 90095.
Daniel
D
Ennis
Department of Radiation Oncology, University of California, Los Angeles, California 90095 and Biomedical Physics IDP, University of California, Los Angeles, California 90095.
Daniel A
DA
Low
D016477:Artifacts; D006321:Heart / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D009068:Movement; D012119:Respiration