Affiliations: Department of Radiation Oncology, University of
Oklahoma Health Sciences Center, Oklahoma City, OK, USA | Department of Electrical and Computer Engineering,
Penn State University, Behrend College, Erie, PA, USA
Note: [] Corresponding author: Imad Ali, Department of Radiation
Oncology, Stephenson Oklahoma Cancer Center, University of Oklahoma Health
Sciences Center, 800 N.E. 10th Street, OKCC L100, Oklahoma City, OK 73104, USA.
Tel.: +1 405 271 8290; Fax: +1 405 271 8297; E-mail: iali@ouhsc.edu
Abstract: PURPOSE: To investigate variations in mobile target length induced
by sinusoidal motion in helical (HCT) and axial CT (ACT) imaging. A
mathematical model was derived that predicts the measured broadening of the
apparent lengths of mobile targets and its dependence on motion parameters,
target size, and imaging couch speed in CT images. MATERIALS AND METHODS: Three mobile targets of differing lengths and
sizes were constructed of tissue-equivalent gel material and embedded into
artificial lung phantom. Respiratory motion was mimicked with a mobile phantom
that moves in one-dimension along the superior-inferior direction with
sinusoidal motion patterns. A mathematical model was derived to predict
quantitatively the variations of apparent lengths for mobile targets and its
dependence on phantom and imaging couch motion parameters in HCT and ACT. The
model predictions were verified by length measurements of the mobile phantom
targets that were imaged with the different motion patterns using CT imaging.
RESULTS: The measured lengths of mobile targets enlarged or shrunk
depending on the phantom motion parameters that include phantom speed,
amplitude, frequency, phase and speed of the imaging couch. The target length
variations were significant where some targets doubled lengths or shrunk to
less than half of their actual length. The apparent lengths of mobile targets
decreased if the target was moving in the same direction as the imaging couch
motion and increased if the mobile target was moving opposed to imaging couch
in both HCT and ACT. The model predicts well the variations in the mobile
target apparent lengths and their dependence on the motion parameters. CONCLUSION: The measured and model variations of apparent lengths of
mobile targets are considerable and may affect the accuracy of tumor volumes
obtained from HCT and ACT. This mathematical model provides a method to
quantitatively assess the length variations of mobile targets and their
dependence on motion parameters of the phantom and imaging system which may
have potential applications in the fields of diagnostic imaging and
radiotherapy.
