Towards task-based assessment of CT performance: System and object MTF across different reconstruction algorithms Samuel Richard a) Carl E. Ravin Advanced Imaging Laboratories, Department of Radiology, Duke University, Durham, North Carolina 27705 Daniela B. Husarik Duke University Medical Center, Department of Radiology, Duke University, Durham, North Carolina 27705 Girijesh Yadava GE Healthcare, Waukesha, Wisconsin 53188 Simon N. Murphy Carl E. Ravin Advanced Imaging Laboratories, Department of Radiology, Duke University, Durham, North Carolina 27705 Ehsan Samei Carl E. Ravin Advanced Imaging Laboratories, Department of Radiology, Duke University, Durham, North Carolina 27705 (Received 21 July 2011; revised 15 May 2012; accepted for publication 16 May 2012; published 11 June 2012) Purpose: To investigate a measurement method for evaluating the resolution properties of CT imag- ing systems across reconstruction algorithms, dose, and contrast. Methods: An algorithm was developed to extract the task-based modulation transfer function (MTF) from disk images generated from the rod inserts in the ACR phantom (model 464 Gammex, WI). These inserts are conventionally employed for HU accuracy assessment. The edge of the disk objects was analyzed to determine the edge-spread function, which was differentiated to yield the line-spread function and Fourier-transformed to generate the object-specific MTF for task-based assessment, de- noted MTF Task . The proposed MTF measurement method was validated against the conventional wire technique and further applied to measure the MTF of CT images reconstructed with an adaptive statis- tical iterative algorithm (ASIR) and a model-based iterative (MBIR) algorithm. Results were further compared to the standard filtered back projection (FBP) algorithm. Measurements were performed and compared across different doses and contrast levels to ascertain the MTF Task dependencies on those factors. Results: For the FBP reconstructed images, the MTF Task measured with the inserts were the same as the MTF measured from the wire-based method. For the ASIR and MBIR data, the MTF Task using the high contrast insert was similar to the wire-based MTF and equal or superior to that of FBP. However, results for the MTF Task measured using the low-contrast inserts, the MTF Task for ASIR and MBIR data was lower than for the FBP, which was constant throughout all measurements. Similarly, as a function of mA, the MTF Task for ASIR and MBIR varied as a function of noise—with MTF Task being proportional to mA. Overall greater variability of MTF Task across dose and contrast was observed for MBIR than for ASIR. Conclusions: This approach provides a method for assessing the task-based MTF of a CT system using conventional and iterative reconstructions. Results demonstrated that the object-specific MTF can vary as a function of dose and contrast. The analysis highlighted the paradigm shift for iterative reconstructions when compared to FBP, where iterative reconstructions generally offer superior noise performance but with varying resolution as a function of dose and contrast. The MTF Task generated by this method is expected to provide a more comprehensive assessment of image resolution across different reconstruction algorithms and imaging tasks. © 2012 American Association of Physicists in Medicine.[http://dx.doi.org/10.1118/1.4725171] Key words: MTF, NPS, NEQ, detectability index, CT, iterative reconstruction, statistical reconstruc- tion, quality assurance, image quality assessment I. INTRODUCTION The evaluation of spatial resolution of imaging systems has played a central role in imaging performance evaluation. 1 The advent of more complex imaging systems has posed an increasing challenge in our ability to assess their perfor- mance, including spatial resolution. For example, iterative and statistical reconstructions can exhibit nonlinear signal characteristics, which can affect system resolution properties 4115 Med. Phys. 39 (7), July 2012 © 2012 Am. Assoc. Phys. Med. 4115 0094-2405/2012/39(7)/4115/8/$30.00