THE EFFECT OF THE LSO/YSO THE EFFECT OF THE LSO/YSO CONCENTRATIONS RATIO ON CONCENTRATIONS RATIO ON

THE IMAGING THE IMAGING CHARACTERISTICS UNDER CHARACTERISTICS UNDER

MAMMOGRAPHIC MAMMOGRAPHIC CONDITIONSCONDITIONS

Anastasios C. KonstantinidisAnastasios C. Konstantinidis11, Panayiotis F. Liaparinos, Panayiotis F. Liaparinos11, , George D. PatatoukasGeorge D. Patatoukas11, Ioannis , Ioannis

G. ValaisG. Valais1,21,2, Dimitrios N. Nikolopoulos, Dimitrios N. Nikolopoulos22, George S. , George S. PanayiotakisPanayiotakis11 and Ioannis S. Kandarakis and Ioannis S. Kandarakis22

11 Department of Medical Physics, Medical School, University of Patras, P.O. BOX 26500 Patras, Greece. Department of Medical Physics, Medical School, University of Patras, P.O. BOX 26500 Patras, Greece.2 2 Department of Medical Instruments Technology, Technological Educational Institution of Athens, Ag. Department of Medical Instruments Technology, Technological Educational Institution of Athens, Ag. Spyridonos, Aigaleo, P.O. Spyridonos, Aigaleo, P.O.

BOX 122 10 Athens, GreeceBOX 122 10 Athens, Greece

AIMAIM

To investigate the influence of the LSO/YSO To investigate the influence of the LSO/YSO concentrations ratio on:concentrations ratio on:– Signal to noise ratio -Signal to noise ratio - SNRSNR– Detection quantum efficiency - DQEDetection quantum efficiency - DQE

To investigate the effect of the anode material and To investigate the effect of the anode material and the x-ray energy on the SNR and DQE using the the x-ray energy on the SNR and DQE using the aforementioned detectors under mammographic aforementioned detectors under mammographic conditions.conditions.

INTRODUCTIONINTRODUCTION

Scintillators or phosphor screens are used as x-ray to Scintillators or phosphor screens are used as x-ray to light converters in radiation detectors of a large light converters in radiation detectors of a large variety of medical imaging applications: variety of medical imaging applications:

conventional and digital X-ray Radiography, conventional and digital X-ray Radiography, Mammography, X-ray Computed Tomography (CT), Mammography, X-ray Computed Tomography (CT), Positron Emission Tomography (PET) and Single Photon Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT)Emission Computed Tomography (SPECT)

Most radiation detectors consist of a scintillator Most radiation detectors consist of a scintillator coupled to an optical detector:coupled to an optical detector:

(photographic emulsion film, photocathode, photodiode, (photographic emulsion film, photocathode, photodiode, CCD etc.) CCD etc.)

INTRODUCTION IIINTRODUCTION II

In the present study, performances of LSO:Ce, In the present study, performances of LSO:Ce, YSO:Ce and LYSO:Ce, varying from 90/10 up to YSO:Ce and LYSO:Ce, varying from 90/10 up to 50/50 (fractions of LSO/YSO), were examined under 50/50 (fractions of LSO/YSO), were examined under Mammographic conditions (20-40 kVp). Mammographic conditions (20-40 kVp).

SNR and DQE were studied for the following SNR and DQE were studied for the following luminescent materials: LSO, YSO, 90/10 LYSO, luminescent materials: LSO, YSO, 90/10 LYSO, 80/20 LYSO, 70/30 LYSO, 60/40 LYSO and 50/50 80/20 LYSO, 70/30 LYSO, 60/40 LYSO and 50/50 LYSO. Phosphor coating weight was chosen to be LYSO. Phosphor coating weight was chosen to be equal to 30, 40 and 50 mg/cmequal to 30, 40 and 50 mg/cm22, typical for , typical for mammographic conditions. mammographic conditions.

THEORYTHEORY

NameName:Cerium doped Lutetium :Cerium doped Lutetium OxyorthosilicateOxyorthosilicate – LuLu22SiOSiO55:Ce (LSO:Ce):Ce (LSO:Ce)– high density (7.4 g/cm3)high density (7.4 g/cm3)– high effective atomic number (Zhigh effective atomic number (Zeffeff=66)=66)– fast response (40ns) fast response (40ns) – relatively high light yield (26000 ph/MeV)relatively high light yield (26000 ph/MeV)– it is non-hydroscopicit is non-hydroscopic

!!Large crystals show inhomogeanity in light !!Large crystals show inhomogeanity in light production and decay time and their energy production and decay time and their energy resolution is poorer than expectedresolution is poorer than expected

THEORY IITHEORY II

LuLu22YY22SiOSiO55:Ce (LYSO:Ce):Ce (LYSO:Ce)

Cerium doped Lutetium Yttrium OxyorthosilicateCerium doped Lutetium Yttrium Oxyorthosilicate

Product of LSO:CeProduct of LSO:Ce mixture with YSO:Cemixture with YSO:Ce– YSO:Ce =Cerium doped Yttrium OxyorthosilicateYSO:Ce =Cerium doped Yttrium Oxyorthosilicate

LYSO:Ce has better performance and advantages LYSO:Ce has better performance and advantages compared with LSO:Ce. Yttrium is a low cost compared with LSO:Ce. Yttrium is a low cost material and it exhibits high intrinsic efficiency due material and it exhibits high intrinsic efficiency due to its K-absorption edge at 17.04 keVto its K-absorption edge at 17.04 keV . .

THEORY IIITHEORY III

Input signal to noise ratioInput signal to noise ratio

– For photon fluenceFor photon fluence

– For energy fluenceFor energy fluence

0

0

0

0

20

0

2

2

( )

( )

( )

E

in E

d

SNR E

dE

0

0

0

0

20

0

2

2

( )

( )

( )

E

in E

d

SNR E

dE

THEORY IVTHEORY IVAbsorbed signal to noise ratioAbsorbed signal to noise ratio

– For photon fluenceFor photon fluence

– where where ΦΦabsabs((ΕΕ)=)=ΦΦ00((ΕΕ))ηηqq(E)(E)..

– where where ΨΨabsabs((ΕΕ)=)=ΨΨ00((ΕΕ))ηηεε(E)(E)

– For energy fluenceFor energy fluence

0

0

0

2

0

2

2

( )

( )

( )

E

abs

abs E

abs

d

SNR E

dE

0

0

0

2

0

2

2

( )

( )

( )

E

abs

abs E

abs

d

SNR E

dE

( ( ) / ),( )μ E ρ Wtot t

qη E 1 e

( μ ( Ε ) / ρ ) Wtot ,en tot ,t

tot ,tε

μ ( Ε )η ( Ε ) (1 e )

μ ( Ε )

THEORY VTHEORY V

Detection quantum efficiency Detection quantum efficiency

That describes the degradation of the SNR That describes the degradation of the SNR from the input to absorption within the from the input to absorption within the scintillator mass.scintillator mass.

2abs abs inDQE ( E ) ( SNR / SNR )

RESULTSRESULTS

Molybdenum, Rhodium Molybdenum, Rhodium and Tungsten anode x-and Tungsten anode x-ray spectra, filtered by ray spectra, filtered by inherent and additional inherent and additional 30 mm of Lucite, for 30 mm of Lucite, for 28kVp tube voltage.28kVp tube voltage.

0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

10 12 14 16 18 20 22 24 26 28 30

Energy (keV)

Phot

on F

luen

ce (P

hoto

ns/m

m^2

)

Mo Anode

Rh Anode

W Anode

RESULTS IIRESULTS II

Variation of input SNRVariation of input SNR22 with x-ray tube voltage with x-ray tube voltage for Mo anode with for Mo anode with constant air Kermaconstant air Kerma in in the range from 20 up to the range from 20 up to 40 kVp.40 kVp.

1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1.E+12

18 22 26 30 34 38 42

Tube Voltage (kVp)

Input

SNR^

2 SNR_Inp_unf_Φο

SNR_Inp_flt_Φο

SNR_Inp_unf_Ψο

SNR_Inp_flt_Ψο

RESULTS IIIRESULTS III

Variation of DQEVariation of DQEabsabs with x-ray tube voltage with x-ray tube voltage for Rh anode, filtered by for Rh anode, filtered by an additional 30 mm of an additional 30 mm of Lucite, Lucite, for all for all scintillators of same scintillators of same coating thickness (40 coating thickness (40 mg/cmmg/cm22) using ) using ΦΦabsabs(E) (E) . .

DQEDQEabsabs were found to were found to decrease with increasing decrease with increasing tube voltage, because of tube voltage, because of the behaviour of the behaviour of μμtot,t/tot,t/ρρ . .

0.E+00

2.E-01

4.E-01

6.E-01

8.E-01

20 24 28 32 36 40

Tube Voltage (kVp)

DQE A

bsor

bed

LSO

YSO

90/10 LYSO

80/20 LYSO

70/30 LYSO

60/40 LYSO

50/50 LYSO

RESULTS IVRESULTS IV

Variation of DQEVariation of DQEabsabs

with x-ray tube voltage with x-ray tube voltage for Rh anode, filtered by for Rh anode, filtered by an additional 30 mm of an additional 30 mm of Lucite, Lucite, for all for all scintillators of same scintillators of same coating thickness (40 coating thickness (40 mg/cmmg/cm22)) using using ΨΨabsabs(E)(E)..

0.E+00

1.E-01

2.E-01

3.E-01

4.E-01

5.E-01

6.E-01

7.E-01

20 24 28 32 36 40Tube Voltage (kVp)

DQE A

bsor

bed LSO

YSO90/10 LYSO80/20 LYSO 70/30 LYSO60/40 LYSO50/50 LYSO

RESULTS VRESULTS V

Variation of DQEVariation of DQEabsabs with x- with x-

ray tube voltage for Mo, Rh ray tube voltage for Mo, Rh and W anodesand W anodes using using

ΦΦabsabs(E). (E).

Mo anode spectra exhibited Mo anode spectra exhibited the highest DQEthe highest DQEabsabs, while , while

the W anode spectra the W anode spectra exhibited the lowest values exhibited the lowest values of DQEof DQEabsabs. It was found that . It was found that

Rh anode produced highest Rh anode produced highest amount of x-ray photons amount of x-ray photons than the Mo anode.than the Mo anode.

0.E+00

2.E-01

4.E-01

6.E-01

8.E-01

20 24 28 32 36 40

Tube Voltage (kVp)

DQE A

bsor

bed

90/10 LYSO_Mo

90/10 LYSO_Rh

90/10 LYSO_W

RESULTS VIRESULTS VI

Variation of DQEVariation of DQEabsabs

with x-ray tube voltage with x-ray tube voltage for Mo, Rh and W for Mo, Rh and W anodesanodes using using ΨΨabsabs(E).(E).

Mo anode spectra Mo anode spectra exhibited the highest exhibited the highest DQEDQEabsabs, especially in , especially in

medium energies, due to medium energies, due to the lower mean energy the lower mean energy than Rh anode spectra.than Rh anode spectra.

0.E+00

1.E-01

2.E-01

3.E-01

4.E-01

5.E-01

6.E-01

7.E-01

20 24 28 32 36 40

Tube Voltage (kVp)

DQE A

bsor

bed

90/10 LYSO_Mo

90/10 LYSO_Rh

90/10 LYSO_W

CONCLUSIONS ICONCLUSIONS I

When the When the absorbed x-rayabsorbed x-ray photon fluencephoton fluence ((ΦΦabsabs(E)) was used, (E)) was used, YSO exhibited highest YSO exhibited highest

SNRSNR22 and DQE of absorbed x-rays and DQE of absorbed x-rays in the in the energy range from 24 up to 40 kVpenergy range from 24 up to 40 kVp while while LSO had the lowest values.LSO had the lowest values.

When the When the absorbed x-ray energy fluenceabsorbed x-ray energy fluence ((ΨΨabsabs(E)) was used, (E)) was used, LSO had superior SNRLSO had superior SNR22

and DQE of absorbed x-raysand DQE of absorbed x-rays to other to other materials, while YSO was found with the materials, while YSO was found with the lowest valueslowest values..

CONCLUSIONS IICONCLUSIONS II

In the first case calculations were made considering In the first case calculations were made considering that the produced K characteristic x-ray radiation that the produced K characteristic x-ray radiation totally escapes from the scintillator, while in the totally escapes from the scintillator, while in the second case the K characteristic is totally absorbed by second case the K characteristic is totally absorbed by the scintillatorthe scintillator It seems that the first point of view is an It seems that the first point of view is an overestimation and the second is an underestimation. overestimation and the second is an underestimation. The reality lies somewhere in between.The reality lies somewhere in between.

In both cases of In both cases of ΦΦabsabs(E) and (E) and ΨΨabsabs(E), it was observed (E), it was observed that the Mo anode spectra exhibited the highest that the Mo anode spectra exhibited the highest DQEDQEabsabs, while the W anode spectra exhibited the , while the W anode spectra exhibited the lowest values.lowest values.

REFERENCESREFERENCES[1] Melcher, C. L., Schweitzer, J.S. (1992) ‘‘Cerium-doped Lutetium Oxyorthosilicate: A Fast, Efficient New Scintillator’’, IEEE [1] Melcher, C. L., Schweitzer, J.S. (1992) ‘‘Cerium-doped Lutetium Oxyorthosilicate: A Fast, Efficient New Scintillator’’, IEEE Trans. on Nucl. Sci., Vol. 39, pp. 502.Trans. on Nucl. Sci., Vol. 39, pp. 502.[2] Ren, G., Qin, L., Lu, S., Li, H. [2] Ren, G., Qin, L., Lu, S., Li, H. (2004), ‘‘Scintillation characteristics of lutetium oxyorthosilicate (2004), ‘‘Scintillation characteristics of lutetium oxyorthosilicate

(Lu2SiO5:Ce) crystals doped with cerium ions’’, Nucl. Instr. Meth. Phys. Res. A, Vol. 531, pp. 560-565.(Lu2SiO5:Ce) crystals doped with cerium ions’’, Nucl. Instr. Meth. Phys. Res. A, Vol. 531, pp. 560-565.[3]Valais, I., Kandarakis, I., Nikolopoulos, D., Konstantinidis, A., Sianoudis, I., Cavouras, D., Dimitropoulos, D., Nomicos, C., [3]Valais, I., Kandarakis, I., Nikolopoulos, D., Konstantinidis, A., Sianoudis, I., Cavouras, D., Dimitropoulos, D., Nomicos, C., Panayiotakis, G. (2005) ‘‘Evaluation of light emission efficiency of LYSO: Ce scintillator under x-ray excitation for possible Panayiotakis, G. (2005) ‘‘Evaluation of light emission efficiency of LYSO: Ce scintillator under x-ray excitation for possible applications in medical imaging’’, Nucl. Instr. Meth. Phys. Res. A, (Article in Press).applications in medical imaging’’, Nucl. Instr. Meth. Phys. Res. A, (Article in Press).[4]Swank, R.K. (1973), ‘‘Calculation of Modulation Transfer Functions of X-ray Fluorescent Screens’’, Appl. Opt., Vol. 12, [4]Swank, R.K. (1973), ‘‘Calculation of Modulation Transfer Functions of X-ray Fluorescent Screens’’, Appl. Opt., Vol. 12, pp.1865-1870.pp.1865-1870.[5]Swank, R.K. (1974), ‘‘Absorption and noise in x-ray phosphors’’, J. Appl. Phys., Vol. 45, pp. 4109-4203.[5]Swank, R.K. (1974), ‘‘Absorption and noise in x-ray phosphors’’, J. Appl. Phys., Vol. 45, pp. 4109-4203.[6]Nishikawa, R.M., Yaffe, M.J. (1985), ‘‘Signal-to-noise properties of mammographic film-screen systems’’, Med. Phys., Vol. [6]Nishikawa, R.M., Yaffe, M.J. (1985), ‘‘Signal-to-noise properties of mammographic film-screen systems’’, Med. Phys., Vol. 12, pp. 32-39.12, pp. 32-39.[7]Dick, C. E., Motz, J. W. (1981), ‘‘Image information transfer properties of x-ray fluorescent screens’’, Med. Phys., Vol. 8, pp. 337-[7]Dick, C. E., Motz, J. W. (1981), ‘‘Image information transfer properties of x-ray fluorescent screens’’, Med. Phys., Vol. 8, pp. 337-346.346.[8]Ginsburg, A., Dick, C. E. (1993), ‘‘Image information transfer properties of x-ray intensifying screens in the energy range from 17 to [8]Ginsburg, A., Dick, C. E. (1993), ‘‘Image information transfer properties of x-ray intensifying screens in the energy range from 17 to 320 keV’’, Med. Phys., Vol. 20, pp. 1013-1021. 320 keV’’, Med. Phys., Vol. 20, pp. 1013-1021. [9]Cavouras, D., Kandarakis, I., Nikolopoulos, D., Kalatzis, I., Episkopakis, A., Linardatos, D., Roussou, M., Nirgianaki, E., Margetis, [9]Cavouras, D., Kandarakis, I., Nikolopoulos, D., Kalatzis, I., Episkopakis, A., Linardatos, D., Roussou, M., Nirgianaki, E., Margetis, D., Valais, I., Kalivas, N., Sianoudis, I., Kourkoutas, K., Dimitropoulos, N., Louizi, A., Nomicos, C., Panayiotakis, G. (2005), ‘‘Light D., Valais, I., Kalivas, N., Sianoudis, I., Kourkoutas, K., Dimitropoulos, N., Louizi, A., Nomicos, C., Panayiotakis, G. (2005), ‘‘Light emission efficiency and imaging performance of Y3Al5O12: Ce (YAG: Ce) powder scintillator under diagnostic radiology conditions’’, emission efficiency and imaging performance of Y3Al5O12: Ce (YAG: Ce) powder scintillator under diagnostic radiology conditions’’, Applied Physics B, Vol. 00, pp. 1-11. Applied Physics B, Vol. 00, pp. 1-11. [10]Konstantinidis, A., Episkopakis, A., Pyrovolakis, I., Valais, I., Patatoukas, G., Nikolopoulos, D., Panayiotakis, G., Kandarakis I. [10]Konstantinidis, A., Episkopakis, A., Pyrovolakis, I., Valais, I., Patatoukas, G., Nikolopoulos, D., Panayiotakis, G., Kandarakis I. (2005), ‘‘Modelling the Signal to Noise Ratio in energy integrating radiation detectors’’, 1st International Conference on Experiments / (2005), ‘‘Modelling the Signal to Noise Ratio in energy integrating radiation detectors’’, 1st International Conference on Experiments / Process / System Modelling / Simulation / Optimization (EpsMsO), Athens Greece, 6-9 July, CD-ROM Proceedings.Process / System Modelling / Simulation / Optimization (EpsMsO), Athens Greece, 6-9 July, CD-ROM Proceedings.[11]Hubbell, J.H., Seltzer, S.M. (1995), [11]Hubbell, J.H., Seltzer, S.M. (1995), Tables of X-ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients 1 KeV Tables of X-ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients 1 KeV to 20 MeV for Elements Z=1 to 92 and 48 Additional Substances of Dosimetric Interestto 20 MeV for Elements Z=1 to 92 and 48 Additional Substances of Dosimetric Interest , NISTIR 5632, Gaithersburg., NISTIR 5632, Gaithersburg.[12]NIST: X-Ray Mass Attenuation Coefficients, http:// physics.nist.gov/PhysRefData/XrayMassCoef/cover.html [12]NIST: X-Ray Mass Attenuation Coefficients, http:// physics.nist.gov/PhysRefData/XrayMassCoef/cover.html [13]Siemens - Vacuum Technology Division - Simulation of X-ray spectra, http:// [13]Siemens - Vacuum Technology Division - Simulation of X-ray spectra, http:// www.healthcare.siemens.com/med/rv/spektrum/radIn.aspwww.healthcare.siemens.com/med/rv/spektrum/radIn.asp[14]Boone, J.M. (2000), [14]Boone, J.M. (2000), X-ray production, interaction, and detection in diagnostic imagingX-ray production, interaction, and detection in diagnostic imaging in: in: Handbook of Medical Imaging, Vol. 1, Handbook of Medical Imaging, Vol. 1, Physics and Psychophysics,Physics and Psychophysics, edited by Beutel J., Kundel H.L., Van Metter R.L., SPIE, Bellingham. edited by Beutel J., Kundel H.L., Van Metter R.L., SPIE, Bellingham.[15]Boone, J.M., Seibert., J.A. (1997), ‘‘An accurate method for computer-generating tungsten anode x-ray spectra from 30 to 140 kV’’, [15]Boone, J.M., Seibert., J.A. (1997), ‘‘An accurate method for computer-generating tungsten anode x-ray spectra from 30 to 140 kV’’, Med. Phys., Vol. 24, pp. 1661-1670.Med. Phys., Vol. 24, pp. 1661-1670.[16]Kandarakis, I., Cavouras, D., Sianoudis, I., Nikolopoulos, D., Episkopakis, A., Linardatos, D., Margetis, D., Nirgianaki, E., Roussou, [16]Kandarakis, I., Cavouras, D., Sianoudis, I., Nikolopoulos, D., Episkopakis, A., Linardatos, D., Margetis, D., Nirgianaki, E., Roussou, M., Melissaropoulos, P., Kalivas, N., Kalatzis, I., Kourkoutas, K., Dimitropoulos, N., Louizi, A., Nomicos, K., Panayiotakis, G. (2005), M., Melissaropoulos, P., Kalivas, N., Kalatzis, I., Kourkoutas, K., Dimitropoulos, N., Louizi, A., Nomicos, K., Panayiotakis, G. (2005), ‘‘On the response of Y3Al5O12:Ce (YAG:CE) powder scintillating screens to medical imaging X-rays’’, Nucl. Instr. Meth. Phys. Meth. ‘‘On the response of Y3Al5O12:Ce (YAG:CE) powder scintillating screens to medical imaging X-rays’’, Nucl. Instr. Meth. Phys. Meth. A, Vol. 538, pp. 615-630.A, Vol. 538, pp. 615-630.