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Charles E Willis, M.S., Ph.D., FAAPM

Present Title & Affiliation

Primary Appointment

Associate Professor, Department of Imaging Physics, Division of Diagnostic Imaging, University of Texas MD Anderson Cancer Center, Houston, TX

Dual/Joint/Adjunct Appointment

Regular Faculty Member, GSBS University of Texas Graduate School of Biomedical Sciences, Houston, TX
Adjunct Associate Professor, Baylor College of Medicine, Houston, TX

Research Interests

The objective of my research is to optimize the clinical use of computed radiography (CR) and direct digital radiography (DR) for diagnostic radiology. These technologies allow digital acquisition of ordinary radiological examinations in sufficient quality and quantity to enable an all-digital radiology department. Because clinical practice with CR and DR has been relatively limited, there remain a number of questions concerning their use, including appropriate technical factors, optimal digital image processing, quality control tests and quality assurance indicators.   This work also includes evaluation of whether phantoms properly test the performance of CR and DR systems. I am also interested in the study of CR and DR artifacts that appear in clinical images, and the correlation of these artifacts with errors in operation, performance, and configuration of CR and DR systems.

Optimizing radiographic techniques for CR and DR examinations. Based on an empirical model of x-ray generator output and tabulated values of attenuation and scatter, I developed a radiographic technique guide for CR examinations in a pediatric ICU setting. This model was successfully extended to adult bedside CR exams, and served as the basis for pediatric DR techniques here. Based on a more rigorous model, we have been exploring the effects of pre-filtration on the contrast-to-noise ratio and patient dose for adult and pediatric chest CR exams using CDRH LucAl phantoms. The typical body habitus of the U.S. population has changed since classic data were reported in 1948, and because optimal radiographic technique factors were derived from these dimensions, both require revision. Our work involved use of anthropometric design software, study of radiographic positioning, and understanding of the principles of x-ray production and attenuation in tissue. As part of my efforts to determine the optimal exposure conditions for digital radiography systems, I have been interested in acquiring actual x-ray spectra under a variety of conditions. The effects of scatter on the x-ray spectrum are particularly difficult to model. I acquired a solid state CdTe x-ray detector and spectrometry system, and designed and fabricated a special test fixture to address the problem of alignment of the spectrometer with the central axis of the beam.

Establishing practical quality metrics for CR and DR. Standards for testing advanced projection radiographic imaging modalities are absent or only recently under development. Quality assurance (QA) and quality control (QC) methods developed for conventional screen-film technology require significant modification for application to filmless imaging. Dual-energy subtraction chest radiography is a relatively new examination enabled by digital radiography for differentiating between calcified and non-calcified anatomy. Although many of these dual-energy systems are in clinical use in our hospital and elsewhere, criteria for assessing their baseline performance have not been established. The ultimate purpose of my research is to translate my findings into improvements in the quality of clinical imaging practice. For example, one of my patient care activities involves collection and assessment of test data for CR and DR imaging modalities. I am studying longitudinal data to determine performance parameters that indicate when service intervention is needed.

Evaluating phantoms for CR and DR. We have been acquiring a collection of phantoms including CDRH LucAl Adult Chest, Abdomen, and Pediatric Chest, the ACR RF phantom, the Fuji CR QC phantom, the Agfa CR QA phantoms, the Nuclear Associates CR phantom, the Leeds TO-16 object, and the UAB phantom. We are beginning to examine the role of these objects in acceptance testing and routine quality control with CR and DR. We would especially like to be able to compare performance results between the LucAl adult objects and the ACR RF object.

Education & Training

Degree-Granting Education

1984 University of Houston, Houston, TX, PHD, Biophysical Sciences
1980 Louisiana State University, Baton Rouge, LA, MS, Nuclear Engineering
1975 Louisiana State University, Baton Rouge, LA, BS, General Studies (Sciences)

Board Certifications

6/1997 American Board of Radiology (ABR)

Honors and Awards

2010 Fellow, American Association of Physicists in Medicine
2007 Certificate of Recognition, Excellence in Research Mentorship, Bioengineering Summer Clinical Research Internship Program, University of Texas M. D. Anderson Cancer Center/University of Texas at Austin/Rice University
2005 Certificate of Appreciation for Contributions Educating Radiation Control Staff, Texas Department of State Health Services
2005 Certificate of Appreciation for Excellence in Reviewing Manuscripts in Pediatric Radiology, The Society for Pediatric Radiology
2005 Certificate of Appreciation, Physics Case of the Day Education Exhibit, Chicago, IL, 91st Scientific Assembly and Annual Meeting of the Radiological Society of North America, Chicago, IL
2004 Certificate of Appreciation, Physics Case of the Day Exhibit, Chicago, IL, 90th Radiological Society of North America, 90th Scientific Assembly and Annual Meeting
2002 Certificate of Appreciation, Physics Case of the Day Exhibit, Chicago, IL, Radiological Society of North America, 88th Scientific Assembly and Annual Meeting
1981 The Lyndon B. Johnson Space Center Group Achievement Award, NASA
1978 Phi Kappa Phi Honor Fraternity

Professional Memberships

American Association of Physicists in Medicine
Member, Work Group on Periodic Review of Medical Physics Residency Training, 2010-present

Selected Publications

Peer-Reviewed Original Research Articles

1. Willis CE, Vinogradskiy YY, Lofton BK, White RA. Gain and offset calibration reduces variation in exposure-dependent SNR among systems with identical digital flat panel detectors. Med Phys 38(7):4422-4429, 7/2011. PMID: 21859043.
2. Don S, Goske MJ, John S, Whiting B, Willis CE. Image Gently pediatric digital radiography summit: executive summary. Pediatr Radiol 41(5):562-565, 5/2011. e-Pub 1/2011. PMID: 21253718.
3. Jones AK, Polman R, Willis CE, Shepard SJ. One Year's Results from a Server-Based System for Performing Reject Analysis and Exposure Analysis in Computed Radiography. J Digit Imaging 24(2):243-255, 4/2011. PMCID: PMC3056967.
4. Shepard SJ, Wang J, Flynn M, Gingold E, Goldman L, Krugh K, Leong DL, Mah E, Ogden K, Peck D, Samei E. Willis CE. Erratum: An exposure indicator for digital radiography: AAPM Task Group 116 (Executive Summary) Med Phys (2009) 36 (2898-2914). Med Phys 37(1):405, 2010.
5. Willis CE. Optimizing Digital Radiography of Children. Eur J Radiol 72(2):266-273, 11/2009. e-Pub 4/2009. PMID: 19345030.
6. Shepard SJ, Wang J, Flynn M, Gingold E, Goldman L, Krugh K, Leong DL, Mah E, Ogden K, Peck D, Samei E, Wang J, Willis CE. "An exposure indicator for digital radiography: AAPM Task Group 116 (Executive Summary)". Med Phys 36(7):2898-2914, 7/2009. PMID: 19673189.
7. Shah C, Jones AK, Willis CE. Consequences of Modern Anthropometric Dimensions for Radiographic Techniques and Patient Radiation Exposures. Med Phys 35(8):3616-3625, 8/2008. PMID: 18777922.
8. Liu HL, Liu RR, Reeve DM, Shepard SJ, Willis CE. Measurement of CT radiation profile width using CR imaging plates. Med Phys 32(9):2881-7, 9/2005. PMID: 16266102.
9. Samei E, Badano A, Chakraborty D, Compton K, Cornelius C, Corrigan K, Flynn MJ, Hemminger B, Hangiandreou N, Johnson J, Moxley-Stevens DM, Pavlicek W, Roehrig H, Rutz L, Shepard J, Uzenoff RA, Wang J, Willis CE, AAPM TG18. Assessment of display performance for medical imaging systems: executive summary of AAPM TG18 report. Med Phys 32(4):1205-25, 4/2005. PMID: 15895604.
10. Willis, CE, Slovis, TL. The ALARA Concept in pediatric CR and DR: dose reduction in pediatric radiographic exams A white paper conference. Executive Summary. Radiology 234:343-344, 4/2005.
11. Willis CE, Slovis TL. The ALARA concept in pediatric CR and DR: dose reduction in pediatric radiographic exams--a white paper conference. AJR Am J Roentgenol 184(2):373-4, 2/2005. PMID: 15671348.
12. Willis CE, Slovis TL. The ALARA Concept in Radiographic Dose Reduction. Radiol Technol 76(2):150-2, Nov-Dec, 11/2004. PMID: 15587617.
13. Willis CE. Discussion. Pediatr Radiol 34(Suppl 3):S234-241, 10/2004.
14. Willis CE. Introduction. Pediatr Radiol 34(Suppl 3):S165-S166, 10/2004.
15. Willis CE. Strategies for dose reduction in ordinary radiographic examinations using CR and DR. Pediatr Radiol 34 Suppl 3:S196-200, 10/2004. PMID: 15558261.
16. Willis CE, Slovis TL. The ALARA concept in pediatric CR and DR: dose reduction in pediatric radiographic exams--a white paper conference executive summary. Pediatr Radiol 34 Suppl 3:S162-164, 10/2004. PMID: 15558256.
17. Willis, CE, Thompson SK, Shepard SJ. Artifacts and Misadventures in Digital Radiography. Applied Radiology 33(1):11-20, 1/2004.
18. Samei E, Seibert JA, Willis CE, Flynn MJ, Mah E, Junck KL. Performance evaluation of computed radiography systems. Med Phys 28(3):361-71, 3/2001. PMID: 11318318.
19. Roehrig H, Willis CE, Damento MA. Characterization of monochrome CRT display systems in the field. J Digit Imaging 12(4):152-65, 11/1999. PMID: 10587910.
20. Cawthon MA, Goeringer F, Telepak RJ, Burton BS, Pupa SH, Willis CE, Hansen MF. Preliminary assessment of computed tomography and satellite teleradiology from Operation Desert Storm. Invest Radiol 26(10):854-7, 10/1991. PMID: 1960024.
21. Willis CE, Bencomo JA. Logistic representation of the sensitometric response of screen-film systems: empirical validation. Med Phys 17(4):676-80, Jul-Aug, 7/1990. PMID: 2215413.
22. Willis CE. Diagnostic Radiologic Imaging for the Health Maintenance Facility. Research and Technology Annual Report 1987. NASA Technical Memorandum #100 463:22, 12/1988.
23. Willis CE, Willis DG, Holmquist GP. An equation for DNA electrophoretic mobility in agarose gels. Appl Theor Electrophor 1(1):11-8, 1988. PMID: 3154955.
24. Bencomo, JA, LeDuc T, McGraw FJ, Fallone BG, Willis CE. Logit analysis of screen/film modulation transfer function data. J Imag Sci 30:270-273, 4/1986.
25. Willis, CE, Holmquist GP. Quantitative measurements of fluorescently-stained DNA in gels from photographic images. Electrophoresis 6:259-267, 12/1985.
26. Long BH, Willis CE, Prestayko AW, Crooke ST. Effect of anthracycline analogues on the appearance of newly synthesized total RNA and messenger RNA in the cytoplasm of erythroleukemia cells. Mol Pharmacol 22(1):152-7, 7/1982. PMID: 6956804.
Other Articles
1. Willis, CE, Oro JA, Gray HB, Jr. Photographic quantification of fluorescently-stained DNA in gels through analog modification of spectrophotometer output. Biomedical Engineering II: 2nd Southern Bio-Engineering Conference:381-384, 1983.

Last updated: 7/24/2013