Michaela Weigel1, Sabrina V Vollmar, Willi A Kalender. 1. Institute of Medical Physics, University Erlangen-Nürnberg, Henkestr. 91, 91052 Erlangen, Germany. michaela.weigel@imp.uni-erlangen.de
Abstract
PURPOSE: The authors investigated the choice of spectra for the optimization of the dose-weighted contrast-to-noise ratio (CNRD) for a dedicated breast CT scanner. The objective is to provide the desired image quality level at minimal dose values. The CNRD was investigated as a function of energy or tube voltage and filtrations for various breast sizes and contrasts. METHODS: The authors performed simulations of the pendant female breast as cylinders consisting of a homogeneous mixture of adipose and glandular tissue with diameters from 6 to 18 cm. The contrasts of adipose tissue, calcium hydroxyapatite, and iodine contrast agent relative to glandular tissue were analyzed using inserts of 9 mm in diameter. Simulations were conducted for monochromatic and polychromatic radiation with a 3 mm Al or a 0.3 mm Cu filter. Simulations and measurements on an experimental micro-CT scanner were performed for validation purposes with a 6 cm water-equivalent cylinder, with inserts representing a pure density difference of 10%, calcium hydroxyapatite, and iodine contrast agent. A breast tissue sample embedded in paraffin was investigated to confirm the simulation results. RESULTS: Optimal tube voltages were found to be in the range of 30-55 kV for breast CT imaging. For example, with 3 mm Al or 0.3 mm Cu filtration, optimal tube voltages were about 53 and 48 kV, respectively, for the contrast iodine/glandular tissue for all diameters. With 3 mm Al filtration, optimal tube voltages increased from 30 to 37 kV and from 30 to 47 kV for the contrast calcium hydroxyapatite/glandular tissue and adipose/glandular tissue, respectively. Tube power requirements were estimated and the change in tube current relative to 80 kV was found to be between 4 and 14 and between 11 and 214 with 3 mm Al filtration or 0.3 mm Cu filtration, respectively. These numbers show that realizing the low optimal tube voltages may not be feasible in most cases due to power requirements. CONCLUSIONS: Depending on the filtration, the authors assume that a compromise solution has to be found between the highest potential dose reduction and a solution working with available x-ray sources. In view of the tube power constraints, the authors recommend aiming for tube voltages in the range of 50 kV and higher.
PURPOSE: The authors investigated the choice of spectra for the optimization of the dose-weighted contrast-to-noise ratio (CNRD) for a dedicated breast CT scanner. The objective is to provide the desired image quality level at minimal dose values. The CNRD was investigated as a function of energy or tube voltage and filtrations for various breast sizes and contrasts. METHODS: The authors performed simulations of the pendant female breast as cylinders consisting of a homogeneous mixture of adipose and glandular tissue with diameters from 6 to 18 cm. The contrasts of adipose tissue, calcium hydroxyapatite, and iodine contrast agent relative to glandular tissue were analyzed using inserts of 9 mm in diameter. Simulations were conducted for monochromatic and polychromatic radiation with a 3 mm Al or a 0.3 mm Cu filter. Simulations and measurements on an experimental micro-CT scanner were performed for validation purposes with a 6 cm water-equivalent cylinder, with inserts representing a pure density difference of 10%, calcium hydroxyapatite, and iodine contrast agent. A breast tissue sample embedded in paraffin was investigated to confirm the simulation results. RESULTS: Optimal tube voltages were found to be in the range of 30-55 kV for breast CT imaging. For example, with 3 mm Al or 0.3 mm Cu filtration, optimal tube voltages were about 53 and 48 kV, respectively, for the contrast iodine/glandular tissue for all diameters. With 3 mm Al filtration, optimal tube voltages increased from 30 to 37 kV and from 30 to 47 kV for the contrast calcium hydroxyapatite/glandular tissue and adipose/glandular tissue, respectively. Tube power requirements were estimated and the change in tube current relative to 80 kV was found to be between 4 and 14 and between 11 and 214 with 3 mm Al filtration or 0.3 mm Cu filtration, respectively. These numbers show that realizing the low optimal tube voltages may not be feasible in most cases due to power requirements. CONCLUSIONS: Depending on the filtration, the authors assume that a compromise solution has to be found between the highest potential dose reduction and a solution working with available x-ray sources. In view of the tube power constraints, the authors recommend aiming for tube voltages in the range of 50 kV and higher.
Authors: Willi A Kalender; Marcel Beister; John M Boone; Daniel Kolditz; Sabrina V Vollmar; Michaela C C Weigel Journal: Eur Radiol Date: 2011-06-09 Impact factor: 5.315
Authors: Willi A Kalender; Daniel Kolditz; Christian Steiding; Veikko Ruth; Ferdinand Lück; Ann-Christin Rößler; Evelyn Wenkel Journal: Eur Radiol Date: 2016-06-15 Impact factor: 5.315