Introduction I

The effect of energy weighting on the SNR under the influence of non ideal detectors in mammographic applications G. Patatoukasa, A. Gaitanisa,b, N. Kalivasc, P. Liaparinosa,b, A. Konstantinidisb, I. Kandarakisb,*, D. Cavourasb, G. Panayiotakisa a Department of Medical Physics, Medical School, University of Patras, 26500 Patras, Greece bDepartment of Medical Instruments Technology, Technological Educational Institute of Athens, Aigaleo, 12210, Athens Greece cGreek Atomic Energy Commission, 15310 Ag. Paraskevi, P.O box 60092, Greece 3rd ITBS, Milos 25-25 September 2005

Introduction I • The purpose of this work was to investigate the effect of the energy weighting technique on the signal to noise ratio (SNR) response of X-ray imaging detectors. • An algorithm was produced to describe the variation of the weighting factor, and SNR, with respect to the anode material (Mo or W), at a particular energy range (25 to 40 keV), typical for mammography. • A simulated Computed Tomography Breast Imaging (CTBI) system was modeled and studied for various parameters such as breast software phantoms, scintillation materials and reconstruction filters, for the further investigation of this method. 3rd ITBS, Milos 25-25 September 2005

Introduction II • The idea of signal enhancement with the use of an energy-dependent function that operates upon the detector’s output signal has already been considered as a promising technique. • In previous studies, Monte Carlo simulations have shown that energy weighting can result in SNR enhancement by a factor of 1.9. In addition, such a SNR enhancement is more obvious when using Molybdenum anode rather that Tungsten anode . Furthermore, it has been reported that DQE results for weighted signals were similar for microcalcification regions and tumours. • In previous works all noise sources have been assumed to be zero except for quantum fluctuations. 3rd ITBS, Milos 25-25 September 2005

Materials and Methods I • 1-D Imaging geometry • Weighting factor • Signal and Noise

Materials and Methods II • SNR • SNRweighted • SNR ratio 3rd ITBS, Milos 25-25 September 2005

Materials and Methods III • 1-D simulation • Two different anode materials were considered; Molybdenum and Tungsten. • For each anode the X-ray tube voltage ranged from 25 to 40 kVp. • The phantom consisted of two regions. A 4.5 cm breast tissue equivalent region (region 1) and tumor/microcalcification region of varying thickness (region 2). • The scintillator embodied to this process was Gd2O2S:Tb with a coating thickness of 31.7 mg/cm2. 3rd ITBS, Milos 25-25 September 2005

Materials and Methods IV • CTBI simulation • A Mo/Mo X-ray tube produced a poly-energetic parallel beam with tube voltages ranging from 20 to 40 kV. • A scintillator based energy weighted detector array obtained 2D images. • Image reconstruction was performed using the Filtered Back-Projection (FBP) algorithm and five different reconstruction filters: Shepp-Logan, Ram-Lak, Cosine, Hamming and the Hanning. 3rd ITBS, Milos 25-25 September 2005

1-D simulation results • SNR ratio variation with respect to microcalcification thickness (0.02-0.2 cm) at 30 keVusing Mo and W anodes • SNR ratio variation with respect to tumour thickness (0.1-1.4 cm) at 30 keV using Mo and W anodes

CTBI simulation results I • CTBI results show that the SNR increases with the energy weighted technique for carcinomas and calcifications 3rd ITBS, Milos 25-25 September 2005

CTBI simulation results II A B C Transverse images of a software breast phantom with a set of objects and base material with 50% adipose and 50% glandular (left) with linear attenuation coefficients for 4 keV. A: Glandular objects, B: Carcinomas (middle row, 1, 2, 2.5, 4 and 8 mm) and C: Calcifications (bottom row, 1.5, 2, 2.5 and 3 mm).

Reconstructed breast computed tomography images with non-energy weighted (left) and energy weighted (right) technique for x-ray spectrum of 20 kV. 3rd ITBS, Milos 25-25 September 2005

Conclusions • SNR enhancement is achievable with this method. • The SNR ratio of the weighted signal to the output signal can reach values up to 30 depending on the lesion thickness. • We can confirm that larger enhancement is achieved when using Molybdenum than Tungsten spectra • Microcalcifications can lead to bigger SNR ratios than tumour regions. • The CTBI simulation showed that SNR increases with the energy weighted technique for carcinomas and calcifications, verifying the previous results. 3rd ITBS, Milos 25-25 September 2005

Acknowledgement • ‘This work was financially supported by the TEI of Athens research program ‘ATHINA 2004’. • References • R.N. Cahn, B.Cederstrőm, M. Danielsson, A. Hall, M. Lundqvist, D. Nygren, Med. Phys., 26 (1999) 2680. • J. Griesh, D. Niederlőhner, G. Anton, Nucl.Instr. and Meth. A, 531 (2004) 68. • C.W.E Van Eijk, Phys. Med. Biol. 47 (2002), R85. • http://www.med.siemens.com/med/rv/spektrum/mamIn.asp • J. M. Boone, T.R Fewell, R.J. Jennings, Med. Phys., 24 (12)(1997) 1863. • G. W. Ludwig, J. Electrochem. Soc., 118 (1971) 1152. • R. K. Swank, Appl. Opt.,12 (1973) 1865. • J.Beutel, B. A. Apple, R. Shaw, Phys. Med. Biol.,38 (1993) 1181. • I.Kandarakis, D. Cavouras, G.S. Panayiotakis, C.D Nomicos, Phys. Med. Biol. 42 (1997) 1351. • I. Kandarakis, D. Cavouras, C.D. Nomicos, G.S Panayiotakis Nucl.Instr. And Meth. B 179 (2001) 215. • Gaitanis, A., Kandarakis I., et. al, European Congress of Radiology 2005, Vienna, 4-8 March 2005, Book of abstracts, pp. 541. • Gaitanis A., Kandarakis I., et. al., Proceedings of 14th International Conference of Medical Physics, Nuremberg, 14-17th September 2005. • B. Chen, R. Ning, (2002), Med. Phys. 29 (5), pp. 755-770. 3rd ITBS, Milos 25-25 September 2005

Introduction I

Introduction I

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I. Introduction

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I. INTRODUCTION