Objective function to obtain multiple representative waveforms for a novel helical CT scan protocol.
OBJECTIVE
To develop objective functions for selecting multiple representative respiratory waveforms. A specific application considered is to reduce the number of swiping scans in a novel helical CT scan protocol to harvest efficiency and dose reduction benefit.


METHODS
The authors consider a general class of potential objective functions consisting of weighted norms on pointwise profile differentials. The authors utilize the Lagrangian approach and derive proper conditions on the formulation based on first and second order optimality conditions. The derived objective functions are applied to clinically acquired respiratory trajectories for swipe subset selection to verify the validity and generality of the proposed rationale. An end-to-end 4DCT reconstruction comparison is performed using a swipe subset of data corresponding to 3 out of the full 25 waveforms to assess the consequence in image quality and dose.


RESULTS
Their results show that maximizing the proposed objective function with the suggested parameters yields maximal spread of trajectories among the selected subset. 4DCT Reconstruction using the chosen subset of data indicates the potential for further dose reduction by about 5 to 10 folds without significant sacrifice in image quality. Experimental results also support further generalization to include slice prioritization.


CONCLUSIONS
The authors have derived a formulation that is both simple and general as a metric to quantify the spread of a set of respiratory trajectories, which can be used for subset selection with potential computation and dose reduction benefit when applied to a newly developed helical 4DCT scan protocol.
Department of Radiation Oncology, David Geffen Medical School, University of California, Los Angeles, California 90095.
Dan
D
Ruan
Department of Radiation Oncology, David Geffen Medical School, University of California, Los Angeles, California 90095.
David
D
Thomas
Department of Radiation Oncology, David Geffen Medical School, University of California, Los Angeles, California 90095.
Daniel A
DA
Low
D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D012119:Respiration; D036542:Tomography, Spiral Computed / Q000379:methods*