MEDICAL IMAGING SCINTILATORS

SUMMARY

Scintillation is a well-known inherent process in luminescent materials (i.e scintillators) whereby a

characteristic light spectrum is emitted following the absorption of ionising radiation. A scintillation

detector is obtained when a scintillator is coupled to optical sensors, such as films, photocathodes,

photodiodes, active matrices of amorphous silicon photodiodes and thin film transistors (a-Si/TFTs),

charged coupled devices (CCDs) and complementary metal oxide semiconductors (CMOS) [1–7]. The

scintillation detectors have been widely used in many technological fields from high energy and

nuclear physics to industry and medical imaging [8]. Many medical imaging scintillation detectors have

been developed during the last few decades for application in conventional and digital imaging

detectors, as e.g. the X-ray radiography, the X-ray computed tomography, the single-photon emission

tomography (SPECT) and the positron emission tomography (PET) [7].

Objectives of the activities in the scintillator research include among others: (a) The evaluation of new

phosphors for use in detectors of medical imaging systems such as phosphor screens or radiographic

cassettes, image intensifiers, digital radiography detectors, portal imaging systems as well as the

phosphor layers incorporated in computed tomography and nuclear medicine detectors (b) The

evaluation of different optical photon detectors that are sensitive to the output of the scintillation light

and are used in conjunction with scintillators. (c) The simulation of (a) and (b) with Monte Carlo

methods based on: (c1) already developed software. (c2) Available Monte Carlo Platforms

(EGCnrcMP, MCNP, GEANT)

The anticipated results allow: (1) The selection of the best phosphor material for each one of the

aforementioned medical imaging applications and under various examination conditions (e.g.

exposure factors etc.) (2) The development of new innovative methods and techniques to be used in a

medical physics department for routine quality control and quality assurance measurements on

medical imaging systems. Selection of the most appropriate combination of scintillator and photon

detector with particular reference to the newer digital detector systems for diagnostic radiology taking

in1o account any affects of scintilla1or afterglow. (3) Proposal of new materials and constructions

according to the modelling with Monte-Carlo techniques

THEORETICAL METHODS

Absolute Luminescence Efficiency (AE)

The absolute luminescence efficiency, of a phosphor screen of thickness T, irradiated by X-ray

photons of energy E was theoretically evaluated [9] in terms of intrinsic physical properties, using the

following relation

AE=nQ ( E,T ) nC G l ( σ,β,ρ,T ) (1)

where, nQ ( E,T ) is the fraction of the incident X-ray energy which is deposited in the phosphor

material, nC, is the intrinsic X-ray to light conversion efficiency giving the fraction of deposited X-ray

energy transformed into light photon energy and G l ( σ,β,ρ,T ) is the light transmission efficiency,

expressing the fraction of the light produced that reaches the screen output. σ,β and ρ are optical

parameters related to light absorption, light scattering and light reflectivity in the phosphor material [9-

11]. Assuming one-dimensional radiation transfer, AE can be described by a one-dimensional model

for x-ray and light propagation in a phosphor screen as [9, 11]

AE=nC γtr μ (E )(1+ρ)e−μ( E )T

2( μ( E )2−σ2 )

( μ (E )−σ )(1−β )e−σT+ 2 (σ+μ (E ) β )e μ( E )T−( μ (E )+σ )( 1+β )eσT

(1+β )( ρ+β )eσT−(1−β )( ρ−β )e−σT

(2)

where μ(E ) is the X-ray energy absorption coefficient, γ is a conversion factor converting energy

fluence (W/m2) into exposure rate (mR/s) t r is the transparency of the phosphor screen substrate. If

the energy spectrum of X-rays, f (E ) , is to be taken into account, then AE can be calculated by

summing over this spectrum, up to the peak energy (kVp) of the X-ray spectrum:

AE kVp=∑E

f (E )AE

∑E

f ( E ) (3)

where kVp denotes the high voltage (kilovolt peak) applied to the x-ray tube. This voltage is equal to

the maximum energy of the x-ray spectrum.

Detective Quantum Efficiency

It has been shown that frequency depended DQE(u) can be written as [12,13]

DQE (u )=F ( dΦl

dF )2 MTF (u )2

NPS (0)NTF (u )2 (4)

where, u is the spatial frequency, F is the X-ray photon fluence incident on the screen surface, i.e.

∑E

f ( E ) in equation 3, and Φl is the optical photon fluence. MTF denotes the modulation transfer

function, which describes the efficiency of signal transfer as a function of spatial frequency. MTF

indicates spatial resolution deterioration from the input to the output of an imaging system. NPS

denotes the noise power spectrum, which expresses the noise variations in terms of spatial frequency

and indicates image detectability and NTF is the corresponding noise transfer function.

Calculation of MTF, NPS and Φl

Lets assume an X-ray fluence distribution, f(E), incident on the surface of a phosphor screen of

thickness T. A fraction, q(t,E), of the absorbed X-ray photons, (e.g. a fraction of the product

f ( E ) n Q ( E,T ) ), will deposit an amount of energy in a thin layer dt at depth t . This energy will

then produce optical photons. The fraction q(t,E) may be calculated by the following expression [10,

12,13]

q ( t,E )=f ( E )e−μ (E ) t μ(E )dt

f (E )nQ(E,T ) (5)

The number of optical photons produced inside a phosphor screen depends upon the intrinsic

quantum gain, mo(E), of the phosphor. The latter is equal to the fraction of absorbed x-ray photon

energy converted into light within the scintillator’s mass, divided by the mean energy of the emitted

optical photons E λ [12,13]:

mo ( E )=nCEE λ

(6)

The number of emitted optical photons, created at depth t and transmitted through the rest of the

screen thickness (T-t), may be expressed in the spatial frequency domain by a function M(u,E,t), given

by the following product [9, 12, 13]

M ( u,E,t )=f ( E ) nQ ( E,T ) q ( t,E )m o ( E )G l ( σ,β,ρ,u,t ) (7)

where, G l ( σ,β,ρ,u,t ) expresses the Fourier transform of the light burst distribution of the optical

quanta originating from depth between t and t+dt end escaping to the output per x-ray absorbed.

G l ( σ,β,ρ,u,t ) can be written [9, 12, 13] as the product of the number of the optical photons

originating from a depth between t and t+dt end escaping to the output, denoted as G l ( σ,β,ρ,t ) ,

multiplied by the modulation transfer function of a thin layer positioned at depth between t and t+dt.

That is G l ( σ,β,ρ,u,t )=G l ( σ,β,ρ,t ) MTF ( u,t ) . Since at zero spatial frequency MTF=1, G l ( σ,β,ρ,t )

can be estimated as G l ( σ,β,ρ,u= 0, t ) [12, 13]. G l ( σ,β,ρ,u,t ) can be calculated as [8, 11, 12]

G l ( σ,β,ρ,u,t )=σρ [ (bβ+σ ) ebt+ (bβ−σ ) e−bt

(bβ+σ )(bβ+σρ )ebT−(bβ−σ )(bβ−σρ )e−bT (8)

where, b2=σ 2+ 4π 2( u

d)2

, d is the density of the phosphor material. Equation (8) is valid under the

assumptions that: (i) there are no discontinuities (in the sense of gross non-uniformities) in the

properties of the screen, (ii) the probability of light absorption is small compared with the probability of

scattering and (iii) solutions are sought for points far from the source [12, 13].

The MTF of the phosphor screen can be derived by summing equation (6) over the total screen

thickness T and over the X-ray spectral distribution f (E ) , and by normalising to zero spatial

frequency, that is

MTF ( u )=∑E∑T

f ( E )nQ(E,T )q( t,E )mo (E )G l (σ,β,ρ,u,t )

∑E∑T

f (E )nQ (E,T )q( t,E )mo (E )Gl (σ,β,ρ, 0,t ) (9)

The NPS(u,E,t) of a phosphor screen may be defined as the spatial frequency distribution of the

variance in the emitted optical photons over the screen area. The NPS associated with the emitted

optical photons generated at depth t and escaping to the output may be written as follows [9, 12, 13]

NPS (u,E,t )=f (E )nQ (E,T )q( t,E ) [mo (E )Gl (σ,β,ρ,u,t )]2 (10)

The total screen NPS(u) can be obtained by summing over the screen thickness and the X-ray

spectral distribution, as follows

NPS (u )=∑E∑T

f ( E )nQ ( E,T )q ( t,E ) [mo ( E )G l ( σ,β,ρ,u,t ) ]2 (11)

Similar to MTF, a noise transfer function can be defined as [12, 13]:

NTF 2(u )=∑E∑T

f (E )nQ(E,T )q( t,E ) [mo (E )Gl (σ,β,ρ,u,t )]2

∑E∑T

f (E )nQ (E,T )q( t,E ) [mo (E )Gl (σ,β,ρ, 0,t ) ]2(12)

Finally Φl can be calculated as:

Φ l=∑E∑T

f ( E )nQ ( E,T )q ( t,E )m o( E )G l ( σ,β,ρ,0, t ) (3)

EXPERIMENTAL METHODS

Phosphor materials are commercially supplied ίn powder form. Phosphor screens of various coating

thickness will be prepared in the laboratory employing sedimentation techniques on a variety of

substrates and with different optical coupling media between the scintillator and the substrate.

The evaluation of the phosphor screen performance will be accomplished by determining the following

image quality parameters: 1.The x-ray luminescence efficiency (XLE) of a phosphor screen. XLE

expresses the emitted light fluence per unit of incident x-ray fluence and is of importance when the

final image brightness with respect to the patient radiation dose is considered. 2.The spectral

compatibility (SC) of the phosphor light emission spectrum with the spectral sensitivity of films.

photocathodes, photodiodes or other type of light photon detectors used in medical imaging. SC is

very important for estimating how well a new phosphor's light will be detected by existing films,

photodiodes etc. 3.The modulation transfer function (MTF) MΤF describes the image contrast and

spatial resolution of an imaging system. 4.The noise power spectrum (NPS) or Wiener spectrum

describing the noise contained ίn the final image.5.The detective quantum efficiency (DQE) describing

the efficiency of an imaging system to transfer the input signal to noise ratio to its output. 6.The

measurement of the MTF, NPS and DQE when the scintillator screens are bonded to different photon

detector systems used in medicine. In particular the newer devices such as CCDs and am-Si.7.The

measurement of the temporal response of some of the scintilla1ors and the effects of screen

preparation upon this process. 8.The Monte Carlo description of 1-8 and the development of

scintillator - geometry targeted Monte Carlo codes

The aforementioned parameters are determined under different exposure conditions used in variοus x-

ray imaging techniques such as mammography, general radiography and fluoroscopy, computed

tomography etc.

REFERENCES

1. S. Hejazi, D.P. Tauernicht, Med. Phys. 24 (1997) 287-297.

2. T. Yu, J.M. Sabol, J.A. Seibert, J.M. Boone, Med. Phys. 24 (1997) 279-285.

3. H.J. Besch, Nucl. Instrum. Meth. A. 419 (1998) 202-216.

4. T.T. Farman, A.G. Farman, J. Digit. Imaging 11 (1998) 169-171.

5. J.H. Siewerdsen, L.E. Antonuk, Y. el-Mohri, J. Yorkston,W. Huang, V.E. Scarpine, R.A. Street,

Med. Phys. 24 (1997) 51-70.

6. E. Hell, W. Knupfer, D. Mattern, Nucl. Instrum. Meth. A. 454 (2000) 40-48.

7. C.W.E. van Eijk, Phys. Med. Biol. 47 (2002) R85-R106.

8. The Crystal Clear Project, Development of detectors, based on inorganic scintillators, for basic

research and applications, 1999.

9. I. Kandarakis, D. Cavouras, et al.: Phys. Med. Biol. 42, 1351 (1997)

10. N. Kalivas, L. Costaridou et al.: Nucl. Instr. and Meth A, 490, 614 (2002)

11. I. Kandarakis, D. Cavouras, et. al.: Radiat. Meas. 33, 217 (2001)

12. R.M. Nishikawa and M.J. Yaffe Med. Phys. 16, 773 (1989)

13. R.M. Nishikawa and M.J. Yaffe: Med. Phys. 17, 894 (1990)

14. I. Kandarakis, D. Cavouras, et al.: Rad. Meas. 39, 263 (2005)

15. I. Kandarakis, D. Cavouras, et.al. Nucl. Instrum. Meth. Phys. Res. B 179, 215 (2001)

16. I. Kandarakis, D. Cavouras, et.al : Appl. Phys. B 72, 877 (2001)

17. http://www.healthcare.siemens.0com/med/rv/spektrum/radIN.asp

RELATED PEER-REVIEWED JOURNAL PUBLICATIONS

1. LIAPARINOS P, KANDARAKIS I, CAVOURAS D, NIKOLOPOULOS, D, VALAIS I. Simulating

the emission efficiency and resolution properties of fluorescent screens by Monte Carlo

methods, Nuclear Science Symposium Conference Record IEEE CNF 2004; 2:874 – 878

2. VALAIS I, KANDARAKIS I, NIKOLOPOULOS D, SIANOUDIS I, DIMITROPOULOS N,

CAVOURAS D, NOMICOS C, PANAYIOTAKIS G. Luminescence efficiency of (Gd2SiO5:Ce)

scintillator under x-ray excitation,, Nuclear Science Symposium Conference Record IEEE CNF

2004; 5:2737 – 2741

3. KANDARAKIS I, CAVOURAS D, NIKOLOPOULOS D., ANASTASIOU A, DIMITROPOULOS

N , KALIVAS N, VENTOURAS E, KALATZIS I, NOMICOS C, PANAYIOTAKIS G. Evaluation of

ZnS:Cu phosphor as x-ray to light converter under mammographic conditions, Radiat. Meas.

2005; 39:263-275

4. KANDARAKIS I, CAVOURAS D, SIANOUDIS I, NIKOLOPOULOS D, EPISKOPAKIS A,

LINARDATOS D, MARGETIS D, NIRGIANNAKI E, ROUSSOU M, MELISSAROPOULOS P,

KALIVAS N, KALATZIS I, KOURKOUTAS K, DIMITROPOULOS N, LOUIZI A, NOMICOS C,

PANAYIOTAKIS G. On the response of Y3Al5O12: Ce (YAG: Ce) powder scintillating screens to

medical imaging x-rays Nucl.Instr.Meth. Α 2005; 538: 615-630

5. CAVOURAS D, KANDARAKIS I, NIKOLOPOULOS D, KALATZIS I, EPISKOPAKIS A,

LINARDATOS D, ROUSSOU M, NIRGIANAKI E, MARGETIS D, VALAIS I, KALIVAS N,

KOURKOUTAS K, SIANOUDIS I, DIMITROPOULOS N, LOUIZI A, NOMICOS C,

PANAYIOTAKIS G. Light emission efficiency and imaging performance of Y2Al5O12: Ce

(YAG:Ce) powder scintillator under diagnostic radiology conditions, Appl. Phys. (B) 2005;

80:923-933

6. VALAIS I, KANDARAKIS I, NIKOLOPOULOS D, SIANOUDIS I, DIMITROPOULOS N,

CAVOURAS D, NOMICOS C, PANAYIOTAKIS G. Luminescence efficiency of Gd2SiO5:Ce

scintillator under x-ray excitation, IEEE Trans.Nucl.Sci 2005; (5):1830-1835

7. KANDARAKIS I, CAVOURAS D, NIKOLOPOULOS D, LIAPARINOS P, EPISKOPAKIS A,

KOURKOUTAS K, KALIVAS N, DIMITROPOULOS N, SIANOUDIS I, NOMICOS C,

PANAYIOTAKIS G. Modelling Angular distribution of light emission in granular scintillators used

in X-ray imaging detectors, Recent Advances in Multidisciplinary Applied Physics, Elsevier

2005; ISBN: 0-08-044648-5

8. VALAIS I, CONSTANTINIDIS A, SALEMIS G, NIKOLOPOULOS D, DIMITROPOULOS N,

CAVOURAS D, PANAYIOTAKIS G, KANDARAKIS I. Evaluation of cerium doped Yttrium

Aluminum Oxide (YAG andYAP) powder scintillating screens for use in x-ray imaging. Biomed.

Tech. 2005; 50(1):11-12

9. VALAIS I, KANDARAKIS I, NIKOLOPOULOS D, LOUDOS G, GIOKARIS N, KARAGIANNIS C,

EPISKOPAKIS A, DIMITROPOULOS N, PANAYIOTAKIS G. Experimental determination of

luminescence emission properties of CsI:Tl, LuYSiO5:Ce (LYSO:Ce) and Gd2SiO5:Ce

(GSO:Ce) single crystal scintillators for use in non projection X-ray imaging. Biomed. Tech.

2005; 50(1) 1112-1113

10.NIKOLOPOULOS D, KANDARAKIS I, VALAIS I, GAITANIS A, CAVOURAS D, PANAYIOTAKIS

G, LOUIZI A. X-ray absorption and x-ray fluorescence of medical imaging scintillating screens

via application of Monte Carlo methods. Biomed. Tech. 2005; 50(1):1124-1125

11. TSANTILAS X, LOUIZI A, VALAIS I, NIKOLOPOULOS D, SAKELLIOS N, KARAKATSANIS N,

LOUDOS G, NIKITA K, MALAMITSI J, KANDARAKIS I. Simulation of commercial PET

scanners with GATE Monte Carlo simulation package. Biomed. Tech. 2005; 50(1):1124-1125

12.CAVOURAS D, NIKOLOPOULOS D, EPISKOPAKIS A, KALIVAS N, SIANOUDIS I,

DIMITROPOULOS N, NOMICOS C, PANAYIOTAKIS G. KANDARAKIS I. A theoretical model

evaluating the angular distribution of luminescence emission in x-ray scintillating screens, Appl.

Rad. Isotop. 2006; 64: 508–519

13.NIKOLOPOULOS D, VALAIS I, KANDARAKIS I, CAVOURAS D, LINARDATOS D,

SIANNOUDIS I, LOUIZI A, DIMITROPOULOS N, VATTIS D., EPISKOPAKIS A, NOMICOS C,

PANAYIOTAKIS G. Evaluation of GSO:Ce scintillator in the x-ray energy range from 40 to 140

kV for possible applications in medical X-ray imaging. Nucl.Instr.Method.(A) 2006; 560(2): 577-

583

14.NIKOLOPOULOS D, KANDARAKIS I, CAVOURAS D, LOUIZI A, NOMICOS C. Investigation of

radiation absorption and x-ray fluorescence of medical imaging scintillators by Monte Carlo

Methods, Nucl.Instr.Method.(A) 2006; 565:821-832

15. PATATOUKAS G, GAITANIS A, KALIVAS N, LIAPARINOS P, NIKOLOPOULOS D,

KONSTANTINIDIS A, KANDARAKIS I, CAVOURAS D, PANAYIOTAKIS G, The effect of

energy weigthing on the SNR under the influence of non ideal detectors in mammographic

applications, Nucl.Instr.Method.(A) 2006; 569:260-263

16.KALIVAS Ν, VALAIS Ι, NIKOLOPOULOS D, SALEMIS G, KARAGIANNIS C,

KONSTANTINIDIS A, MICHAIL C, LOUDOS G, SAKELIOS N, KARAKATSANIS N, NIKITA K,

GAYSHAN V. L., GEKTIN A. V., SIANOUDIS I, GIOKARIS N, NOMICOS C,

DIMITROPOULOS N, CAVOURAS D, PANAYIOTAKIS G, KANDARAKIS I, Imaging properties

of cerium doped Yttrium Aluminum Oxide (YAP: Ce) powder scintillating screens under x-ray

excitation, Nucl.Instr.Method.(A) 2006; 569:210-214

17.NIKOLOPOULOS D, KANDARAKIS I, TSANTILAS X, VALAIS I, CAVOURAS D, LOUIZI A,

Comparative study of the radiation detection efficiency of LSO, LuAP, GSO and YAP

scintillators for use in positron emission imaging (PET) via Monte-Carlo Methods,

Nucl.Instr.Method.(A) 2006; 569:350-354

18.VALAIS I, KANDARAKIS I, NIKOLOPOULOS D, KONSTANTINIDIS A, SIANNOUDIS I,

CAVOURAS D, DIMITROPOULOS N, NOMICOS C, PANAYIOTAKIS G, Evaluation of light

emmission efficiency of LYSO:Ce scintillator under x-ray excitation for possible applications in

medical imaging. Nucl.Instr.Method.(A) 2006; 569:201-204

19.N. KARAKATSANIS, N. SAKELLIOS, N.X. TSANTILAS, N. DIKAIOS, C. TSOUMPAS, D.

LAZARO, G. LOUDOS, C.R. SCHMIDTLEIN, K. LOUIZI, J. VALAIS, D. NIKOLOPOULOS, J.

MALAMITSI, J. KANDARAKIS, K. NIKITA, Comparative evaluation of two commercial PET

scanners, ECAT EXACT HR+ and Biograph 2, using GATE, Nucl.Instr.Method (A) 2006; 569:

368-372

20.GONIAS P, BERTSEKAS N, KARAKATSANIS N, SAATSAKIS G, GAITANIS A,

NIKOLOPOULOS D, LOUDOS G, PAPASPYROU L, SAKELLIOS N, TSANTILAS X,

DASKALAKIS A, LIAPARINOS P, NIKITA K, LOUIZI A, CAVOURAS D, KANDARAKIS I,

PANAYIOTAKIS GS, Validation of a GATE model for the simulation of the Siemens PET

Biograph™ 6 scanner Nucl.Instr.Method.(A) 2007; 571(1-2):263-266

21.VALAIS I, KANDARAKIS I, NIKOLOPOULOS D, MICHAIL C, DAVID E, SIANOUDIS I,

LOUDOS G, CAVOURAS D, DIMITROPOULOS N, NOMICOS C, PANAYIOTAKIS G,

Luminescence properties of (Lu,Y)2SiO5:Ce and Gd2SiO5:Ce single crystal scintillators under x-

ray excitation, for use in medical imaging systems, IEEE Trans.Nucl.Sci. 2007; 54 (1) 11-18

22.VALAIS I, NIKOLOPOULOS D, KALIVAS N, GAITANIS AN LOUDOS G, KANDARAKIS I,

SIANOUDIS I, GIOKARIS D, CAVOURAS D, DIMITROPOULOS N, NOMICOS

C,PANAYIOTAKIS G, A systematic study of the performance of the CsI:Tl single-crystal

scintillator under x-ray excitation, Nucl.Instr.Method.(A) 2007; 571(1-2): 343-345

23.EFTHIMIOU N, KALIVAS N, PATATOUKAS G, KONSTANTINIDIS A, VALAIS I,

NIKOLOPOULOS D, GAITANIS A, DAVID S, MICHAIL C, LOUDOS G, CAVOURAS D,

KOURKOUTAS K, PANAYIOTAKIS G, KANDARAKIS I, Investigation of the effect of the

scintillator material on the overall X-ray detection system performance by application of

analytical models, Nucl.Instr.Method.(A) 2007; 571:270-273

24.NIKOLOPOULOS D, LINARDATOS D, VALAIS I, MICHAIL C, DAVID S, GONIAS P,

BERTSEKAS N, CAVOURAS D, LOUIZI A, KANDARAKIS I, MONTE Carlo Validation in the

Diagnostic Radiology Range, Nucl.Instr.Method.(A) 2007; 571: 267-269.

25.DAVID S, MICHAIL C, VALAIS I, NIKOLOPOULOS D, LIAPARINOS P, KALIVAS N,

KALATZIS I, EFTHIMIOU N, TOUTOUNTZIS A, LOUDOS G, SIANOUDIS I, CAVOURAS D,

DIMITROPOULOS N, NOMICOS C, KANDARAKIS I, PANAYIOTAKIS G, Efficiency of Lu2SiO5:

Ce (LSO) powder phosphor as X-ray to light converter under mammographic imaging

conditions, Nucl.Instr.Method.(A) 2007; 571(1-2) 346-349

26.VALAIS I, DAVID S, MICHAIL C, NIKOLOPOULOS D, KALIVAS N, TOUTOUNTZIS A,

SIANOUDIS I, CAVOURAS D, DIMITROPOULOS N, NOMICOS C, KANDARAKIS I,

PANAYIOTAKIS G, Comparative study of luminescence properties of LuYAP:Ce and LYSO:Ce

single-crystal scintillators for use in medical imaging, Nucl.Instr.Method.(A) 2007; 580(1):614-

616.

27.MICHAIL C, PANAYIOTAKIS G, DAVID S, LIAPARINOS P, VALAIS I, NIKOLOPOULOS D,

KALIVAS N, KANDARAKIS I Evaluation of the imaging performance of LSO powder scintillator

for use in X-ray mammography, Nucl.Instr.Method.(A) 2007;580(1):558-561

28.KALIVAS Ν, VALAIS Ι, NIKOLOPOULOS D, KONSTANTINIDIS A, GAITANIS A, CAVOURAS

D, NOMICOS C.D, PANAYIOTAKIS G, KANDARAKIS I, Light Emission efficiency and imaging

properties of YAP:Ce granular phosphor screens, App Phys (Α) 2007; 89(2):443-449

29.DAVID S, MICHAIL C, VALAIS Ι, NIKOLOPOULOS D, KALIVAS N, KALATZIS I, KARATOPIS

A, CAVOURAS D, LOUDOS G, PANAYIOTAKIS G.S, KANDARAKIS I, Luminescence

efficiency of Lu2SiO5:Ce (LSO) powder scintillator for X-ray medical radiography applications,

Nuclear Science Symposium Conference Record IEEE CNF 2007; 2: 1178-1182.

30.VALAIS Ι, DAVID S, MICHAIL C, NIKOLOPOULOS D, CAVOURAS D, SIANOUDIS A,

KOURKOUTAS C.D, KANDARAKIS I, PANAYIOTAKIS G.S, Investigation of luminescence

emission properties of (Lu,Y)2SiO5:Ce (LYSO:Ce) and (Lu,Y)AlO3:Ce (LuYAP:Ce) single

crystal scintillators under x-ray exposure for use in medical imaging, Nuclear Science

Symposium Conference Record IEEE CNF 2007; 2: 1187-1191.