A Monte Carlo study of the influence of focal spot size,intensity distribution,breast thickness and magnification on spatial resolution of an a-Se digital mammography system using the generalized MTF |
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| Affiliation: | 1. Catholic University of Portugal, Faculty of Engineering, 2635-631 Rio de Mouro, Portugal;2. Radiation Protection Section, Medical Physics Department, Colchester Hospital University NHS Foundation Trust, Colchester CO3 3NB, UK;3. Biomedical Research Foundation, Academy of Athens, 115 27 Athens, Greece;1. Department of Radiology, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania;2. Department of Medical Imaging, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, Illinois;3. Department of Radiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois;4. Department of Radiology, Texas Children’s Hospital, Houston, Texas;5. Department of Pediatric Radiology, Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania;6. Department of Radiology, Monroe Carell Jr. Children’s Hospital at Vanderbilt, Nashville, Tennessee;1. Arizona Oncology Services Foundation, Scottsdale, Arizona;2. Barrow Neurological Institute, St. Joseph''s Hospital and Medical Center, Phoenix, Arizona;3. Radiation Therapy Oncology Group Statistical Center, Philadelphia, Pennsylvania;4. University of Florida College of Medicine, Gainesville, Florida;5. University of Wisconsin Hospital, Madison, Wisconsin;7. University of Washington Medical Center, Seattle, Washington;11. Emory University, Atlanta, Georgia;1. St Michael''s Hospital, University of Toronto, Toronto, and Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada;2. Institute for Clinical Evaluative Science, Toronto, Ontario, Canada;3. Departments of Medicine, Health Policy Management and Evaluation, and Obstetrics and Gynecology, St Michael''s Hospital, University of Toronto, Toronto, Ontario, Canada;1. Dutch Reference Centre for Screening (LRCB), Radboud University Medical Centre, The Netherlands;2. Department of Medical Physics, Elisabeth TweeSteden ziekenhuis, The Netherlands;3. Radboud Institute for Health Sciences (RIHS), Radboud University Medical Centre, The Netherlands;4. National Co-ordinating Centre for the Physics of Mammography (NCCPM), Royal Surrey County Hospital, United Kingdom;5. Department of Physics, University of Surrey, United Kingdom;6. Department of Radiology, Leiden University Medical Centre (LUMC), The Netherlands;1. Medical Physics Unit, IRCCS Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori (IRST), Meldola, FC, Italy;2. Nuclear Medicine Unit, IRCCS IRST, Meldola, FC, Italy;3. Nuclear Medicine Unit, Pierantoni-Morgagni Hospital, Forlì, FC, Italy;4. Medical Physics Unit, Bufalini Hospital, Cesena, FC, Italy;5. Laboratory of Medical Physics and Expert Systems, Regina Elena National Cancer Institute, IFO, Rome, Italy |
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| Abstract: | In this study the generalized Modulation Transfer Function (GMTF) and the geometric sharpness (Sgeo) were used (i) to study the effects of various focal spot sizes (0.04 mm–0.3 mm), x-ray intensity distributions (Gaussian and double Gaussian), breast thicknesses (2–7 cm) and magnifications M (1.0–2.0) on the spatial resolution of an a-Se digital mammography system, (ii) to identify suitable focal spots for magnification mammography and (iii) derive optimum magnifications. For the calculation of GMTF the required components were: focal spot MTF, obtained from theory, detector MTF, scatter MTF and scatter fraction obtained from Monte Carlo simulations. The results showed that focal spots with sizes up to 0.18 mm are suitable for magnification mammography offering a GMTF which is >50% and >20% at the respective object frequencies of 6.5 mm−1 and 9 mm−1. Focal spots with sizes < 0.16 mm and Gaussian. intensity distribution, or sizes ≤ 0.1 mm and double Gaussian, offer a system resolution which improves or does not deteriorate with magnification for most object frequencies. For larger focal spots, i.e. 0.16–0.18 mm for a Gaussian and 0.12–0.18 mm for a double Gaussian. intensity distribution, optimum magnifications exist which depend on the object frequency and breast thickness. System resolution (in terms of Sgeo) is maximized at M = 1.8–2.0 (all breast thicknesses) for Gaussian intensity distribution, and at M = 1.4–1.6 (breast thicknesses ≤ 4 cm) and M = 1.6–1.8 (thicker breasts) for double Gaussian. |
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| Keywords: | Generalized MTF Digital mammography Magnification Monte Carlo |
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