Cathodoluminescent Efficiency

Alig, R. Casanova; Bloom, S.

doi:10.1149/1.2133497

Cited by 58 publications

(41 citation statements)

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“…where E is the absorbed X-ray energy, E λ is the energy of the optical photons and n C is the intrinsic conversion efficiency of the phosphor expressing the fraction of the absorbed X-ray energy converted to light [12][13][14].…”

Section: Methodsmentioning

confidence: 99%

“…The average energy required to create an electron-hole pair of energy E g (fundamental electronic band gap of the host material) equals βE g . β is a constant that characterize the excess energy above E g that should be absorbed, in order for an electron-hole pair to be created [12,[14][15][16]. Therefore the total number of electronholes created equals E/βE g .…”

Section: Methodsmentioning

confidence: 99%

“…Therefore the total number of electronholes created equals E/βE g . The theoretical value of β is 1.5 [15], but in several cases its value has been experimentally determined to be higher [12,14,16].…”

Section: Methodsmentioning

confidence: 99%

“…A fraction, R, of the created electron-holes, will reach the luminescent center and subsequently a fraction q will be absorbed in the activator [12,14,17]. From the absorbed electron-hole pairs only a fraction β will actually contribute to optical photon creation.…”

Section: Methodsmentioning

confidence: 99%

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Effect of intrinsic-gain fluctuations on quantum noise of phosphor materials used in medical X-ray imaging

Kalivas

Costaridou

Kandarakis

et al. 1999

Applied Physics A: Materials Science & Processing

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The quality of a medical image depends, among other parameters, on quantum noise. Quantum noise is affected by the fluctuations in the number of optical quanta produced within the phosphor, per absorbed X-ray (i.e. phosphor intrinsic-gain fluctuations). This effect is considered by means of a factor, called in this study intrinsic-gain noise factor, IGNF(E). In existing theoretical models of quantum noise, the corresponding factor is taken to be equal to one. In this paper, an expression that accounts for the coefficient of variation of the phosphor intrinsic gain is introduced. This expression takes into account the process of electron-hole pair conversion to optical photons and the frequency distribution function of the emitted optical photon energy. Subsequently IGNF(E) is expressed in terms of this coefficient of variation. IGNF(E) has been calculated for several phosphors and for various energies. For all medical X-ray energies studied, phosphors that exhibit a high relative fluctuation of emitted optical photon energy, IGNF(E) exceeds by 2% to over 17% the corresponding factor of the existing theoretical models of quantum noise. PACS: 78.65; 42.80Phosphors doped with various activators (Eu, Tb, Ag, etc.) are widely used in medical imaging as X-ray-to-light converters in conjunction with optical detectors (films, photodiodes, etc.) [1][2][3]. The quality of a medical image depends, among other parameters, on quantum noise. Quantum noise is affected by the number of optical quanta, produced within the phosphor, per absorbed X-ray of energy E (i.e. phosphor intrinsic gain) [4,5]. Phosphor intrinsic gain is subject to statistical fluctuations. Thus for equal X-ray energy absorption, unequal number of optical quanta are produced [4][5][6][7]. Quantum noise is proportional to the variation of the intrinsic phosphor gain, which reflects the statistical fluctuations in the production of optical quanta produced by the activator material within the phosphor. Experimental methods have reported to determine the fluctuation of the optical quanta emitted by the phosphor per absorbed X-ray [8-10]. However, to the best of our knowledge, no experimental method has been introduced, to measure the fluctuation of intrinsic phosphor gain. In addition, the contribution to quantum noise, called in this study intrinsic-gain noise factor (IGNF(E)), in existing theoretical models, of the fluctuation of phosphor intrinsic gain, is unity, as the gain procedure is assumed to follow Poisson distribution [2,[4][5][6]11].In this paper, an alternative expression of phosphor intrinsic-gain fluctuation is presented, which can contribute to quantum-noise modeling. This expression takes into account the process of electron-hole pair conversion to optical photons and the frequency distribution function of the emitted optical photon energy. IGNF(E) incorporating the above expression has been calculated for several phosphor materials and for various energies, based on X-ray conversion efficiency and optical emission spectral data. Method and mate...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Effect of intrinsic-gain fluctuations on quantum noise of phosphor materials used in medical X-ray imaging

Kalivas

Costaridou

Kandarakis

et al. 1999

Applied Physics A: Materials Science & Processing

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“…The intrinsic X-ray to light conversion efficiency for La 2 O 2 S:Tb (0.18) and for Gd 2 O 2 S:Tb (0.20) were obtained from previous studies [19]. In these studies data obtained under cathode ray excitation [31] were initially used. It is accepted that intrinsic conversion efficiencies under X-ray or cathode ray excitation do [4], since they depend on intrinsic phosphor properties and on temperature.…”

Section: Theoretical Calculationsmentioning

confidence: 99%

Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb–La2O2S:Tb mixtures for X-ray imaging

Kandarakis

Cavouras

2001

Eur Radiol

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The purpose of this work was to investigate and compare the imaging performance of Gd2O2S:Tb and La2O2S:Tb phosphors as well as of Gd2O2S:Tb and La2O2S:Tb mixtures for use in X-ray imaging detectors (intensifying screens). Phosphors were supplied in powder form and were used to prepare test screens. Three types of screens were prepared: Gd2O2S:Tb; (Gd50La50)O2S:Tb; and La2O2S:Tb. Screens were excited by X-rays with tube voltages from 40 to 120 kV and their efficiency (light intensity or light energy flux over exposure) was measured with a photomultiplier and a dosimeter. The light spectrum was also measured with a monochromator. From these measurements, the number of emitted photons per incident X-ray (NEP) and the zero frequency detective quantum efficiency (DQE(0)) of the screens were determined. Additionally, modulation transfer function (MTF) was measured by the square wave response function (SWRF) method. A theoretical model calculating NEP and DQE was also developed to fit experimental data and predict the performance of Gd2O2S:Tb-La2O2S:Tb mixtures by weight from 10-90% to 90-10%. Gd2O2S:Tb screens exhibited highest NEP, DQE, and MTF at tube voltages higher than 55 kV and lower than 45 kV, whereas La2O2S:Tb screens had better NEP, DQE, and MTF within the 45- to 55-kV range. Maximum NEP values were higher than 700 at 100-120 kV while maximum DQE(0) was 0.314 at 80 kV. Gd2O2S:Tb screens are more efficient for high X-ray tube voltage applications (e.g., abdominal imaging, chest radiography, lumbar spine radiography, CT) and for very low voltage applications (e.g., mammography). La2O2S:Tb screens are useful for medium-range X-ray voltages (e.g., pediatric radiography).

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Hormones, Adrenal‐Cortical

Avery

Woolfrey

2000

Kirk-Othmer Encyclopedia of Chemical Technology

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Adrenal‐cortical hormones, following the introduction of cortisone and hydrocortisone nearly a half‐century ago, have continued to be the drug of choice in treatment of afflictions ranging from skin rash to severe acute inflammatory disorders and are now included in many other therapeutic regimes. The adrenal cortex releases both mineralocorticoids and glucocorticoids; the latter influence carbohydrate and protein metabolism, and the former regulate sodium reabsorption in the kidney. Moreover, corticosteroids and their metabolites were early noted to possess powerful antiinflammatory and immunomodulatory properties, leading to a massive increase in research in the area of steroid synthesis and physiology, imparting great impetus to the development of synthetic steroids. These exhibited activities far greater than those of the natural hormones, thereby opening the way to development of many more active antiinflammatory agents. Corticosteroids are commonly used as topicals for the suppression of symptoms, including inflammation. Though they are rarely considered curative, many diseases respond well symptomatically to treatment with them, eg, liver disease, acute spinal cord injury, organ transplants, GI diseases, and dermatologic diseases, among others. Mineralocorticoid therapy is less common. Progesterone is the key intermediate in both mineralocorticoid and glucocorticoid biosynthesis. Cortisol and aldosterone are results of oxidations of progesterone. The major metabolic transformations of the adrenal cortical hormones generally follow the metabolism of cortisol. The effects of adrenal‐cortical steroids are thought to result from their interaction with intracellular receptors; these are the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). The primary structure of the GR has been identified as a 795 residue protein; a significant amount of 3‐D structure elucidation of the GR has been made. The process by which adrenocortical steroids impart their action is based on the action of the steroid on a receptor (GR or MR). The use of glucocorticoids leads to antiinflammatory effects by first controlling gene expression, which subsequently leads to the synthesis and/or suppression of inflammation regulatory proteins. Microorganisms are available which transform progesterone and cortisone into steroids. These steroids surpass their parent hormones in antirheumatic and antillergic activity and produce lower levels of side effects. When tested in patients with rheumatoid arthritis, fludrocortisone acetate proved to be 10 times more potent than hydrocortisone acetate. Triamcinolone possesses high glucocorticoid and antiinflammatory activity and is almost entirely devoid of salt‐retaining activity. 2α‐Methyl‐9α‐fluorocortisol has been reported to show enhanced glucocorticoid activity and greatly enhanced mineralocorticoid activity, surpassing aldosterone in sodium‐retaining and potassium‐excreting potency. Hyperaldosteronism is accompanied by elevation of blood pressure and can be treated with an aldosterone antagonist, eg, spironolactone. Antagonists of glucocorticoid and mineralocorticoid activity have found increased use in the treatment of hypertension. The most clinically useful GR antagonist is RU‐486.

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Cathodoluminescent Efficiency

Abstract: not Available.

Cited by 58 publications

References 0 publications

Effect of intrinsic-gain fluctuations on quantum noise of phosphor materials used in medical X-ray imaging

Effect of intrinsic-gain fluctuations on quantum noise of phosphor materials used in medical X-ray imaging

Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb–La2O2S:Tb mixtures for X-ray imaging

Hormones, Adrenal‐Cortical

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