BJR
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
British Journal of Radiology (2004) 77, 648-653
© 2004 British Institute of Radiology
doi: 10.1259/bjr/33291071
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Vassileva, J
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Vassileva, J

Full Paper

A phantom approach to find the optimal technical parameters for plain chest radiography

J Vassileva, PhD

Laboratory for Quality Control in Radiology, National Centre of Radiobiology and Radiation Protection, 132 Kliment Ohridski Blvd, Sofia 1756, Bulgaria


   Abstract
Top
 Abstract
Introduction
 Materials and method
 Results and discussion
 Conclusion
 References
 
A simple approach based on phantom measurements is proposed in this study to find the filtration, tube potential and antiscatter device that are optimal in respect of patient dose and image quality, at constant film–screen combination, film processing and viewing conditions. An original quasi-anthropomorphic chest phantom was exposed with 18 different beam qualities and three antiscatter devices. The entrance surface dose, organ doses and effective dose were estimated for each radiograph. The image quality was compared using two objective quality indexes, a contrast index and a scatter fraction, as well as two subjective indexes, a low contrast visualization index and a high contrast visualization index. It was found that for this X-ray unit, routinely using a 7:1 antiscatter grid, the optimal imaging technique is added filtration of 0.1 mm Cu+1 mm Al at a tube potential 100 kVp. Using a 25 cm air gap instead of the grid allows the tube potential to be increased to the upper limit of 120 kVp for this unit. The entrance surface dose of 0.075 mGy at 120 kVp with an air gap is less than half the value of the same quantity with a grid at 100 kVp and is significantly below the European reference level of 0.3 mGy. This phantom method, comprising both objective measurements and subjective estimation, is suitable for dose-image quality optimization in a clinical environment.


   Introduction
Top
 Abstract
 Introduction
Materials and method
 Results and discussion
 Conclusion
 References
 
A recognized method of reducing the patient dose in radiological practice is to increase X-ray beam filtration. Different materials, usually aluminium and copper, but also iron, erbium, yttrium, niobium, holmium and others, are in use to absorb the soft component in the spectrum which would otherwise be absorbed in the body and would increase the patient dose without contributing to image formation [1–5]. Another known method to reduce dose used in chest radiography is to apply high tube potential. In this hard-beam technique the dominant role of Compton scattering increases the contribution of scattered photons to image formation which leads to contrast degradation. This is the reason for the policy of implementing the use of antiscatter techniques [2, 6, 7]. Antiscatter grids are frequently used, the use of an air gap between patient and film cassette is less common. Air gaps of 15–30 cm at a focus to film distance of 250–350 cm have been used [6, 8–11].

The European guidelines [12] recommend using dedicated X-ray units for chest radiography with total filtration higher than 3 mm Al, a tube potential of 125 kVp and an antiscatter grid with grid ratio 10:1 (grid strip frequency 40 cm–1). Following the American College of Radiology Standards [13], tube potential should be in the range of 120–150 kVp and an antiscatter technique (grid or air gap) equivalent to at least a grid ratio 10:1 should be used.

In many practical situations however, chest radiography is performed with older X-ray units with limited technical resources, in particular with respect to the maximum tube potential and tube loading. In many radiological departments a soft-beam technique and moderate added filtration of 1–2 mm Al are still used. These technical limitations, combined with the use of low sensitivity film–screen combinations (FSCs), are the main reasons for patient doses exceeding the reference levels for chest radiography by up to 3–4 times in Bulgaria [14].

This work was undertaken to investigate the possibility of reducing the patient radiation exposure through an optimal choice of filtration, tube potential and antiscatter device, in parallel with a study of the image quality. Different approaches are used to achieve optimization. Both subjective and objective methods are applicable for real patients or for phantoms of varying complexity as well as theoretical studies based on Monte Carlo simulations [7, 9–11, 15–19]. Our study is aimed at further verification of a simple phantom method for dose-image quality optimization proposed earlier [20] and applying it to find the optimal technical parameters for a given X-ray unit, at a constant FSC, film processing and viewing conditions.


   Materials and method
Top
 Abstract
 Introduction
 Materials and method
Results and discussion
 Conclusion
 References
 
X-ray unit
The study was performed with an X-ray unit type TUR D800-3 (VEB Hermann Mattern, Dresden, Germany) frequently used in Bulgaria. This system comprises a 12-pulse generator and a DRX 124/30/60 oDw tube with 16° target angle. Following the methods recommended by IPEM [21] the actual tube potential, measured with digital kVp-meter (type 07-473; Victoreen Inc., Florida, USA), was found to be within ±5% of the nominal value for the working kilovoltage range between 40 kV and 120 kV, with better than 1% precision. The constancy of the output is better than 5% at 80 kV and deviations from the mean output value for different tube currents and exposure times are less than 10%. A FSC with speed class 400 was used with Quanta fast detail screens (Sterling Diagnostic Imaging, Bad Homburg, Germany) combined with blue Agfa CP-BU New films (Agfa-Gevaert AG, Morstel, Belgium). Films were processed with an automatic processor Optimax (Protec Medizintechnik, Oberstenfeld, Germany) with Agfa chemistry at developer temperature 32°C and processing time 90 s chosen according to the manufacturer's specifications. Quality control of film processing was performed using a light sensitometer (type 07-417; Nuclear Associates, Carle Place, USA). Optical density (OD) was measured with a densitometer (PTW DensiX, PTW Freiburg, Germany) with measuring aperture 7 mm2 and accuracy ±0.02 OD at optical densities OD≤1 and ±1.5% at OD>1.

Chest radiography was performed on a vertical chest stand equipped with a moving grid with a grid ratio of 7:1 and a grid strip frequency 28 mm–1, at 150 cm focus to film distance. A soft-beam technique with 70–80 kVp was routine for this unit with an automatic selection of the tube current–exposure time product (mAs).

Anthropomorphic LucAl chest phantom
For the purpose of dose–image quality optimization a chest phantom, realistically simulating the average patient's thorax is needed. Because of a lack of the expensive anthropomorphic phantoms, a simple geometrical quasi-anthropomorphic phantom was constructed. The design of this phantom and the method for phantom-image evaluation are described in detail elsewhere [20]. The standard geometrical LucAl chest phantom, reliably approximating a standard sized patient for PA chest projection, was modified by adding an "anthropomorphic" insert and image quality test plate (IQT plate). Different test objects are arranged on the plate and used to evaluate image quality in three important anatomical areas: lung, cardiac and subdiaphragmal (Figure 1Go). The objects are set in two groups, according to the method of estimation of image quality parameters. On the left side of the IQT plate objects for subjective estimation of image quality are arranged. The size and structure of these objects were selected on the basis of the clinical requirements for chest radiography [12]. In the lung and the cardiac areas of the phantom objects simulating small tumour masses (N1, N2, N3, M), pulmonary infiltrates (I1, I2), small vessels (V1, V2), fibroses (G1, G2, F1, F2) are arranged. Objects for determining the low contrast visualization (L1, L2) and the high contrast resolution capability of the imaging system (W1, W2, P1, P2, H) are also positioned over the "lung" and "heart". On the right side of the IQT plate 20 areas for optical density measurements needed to evaluate objective image quality indices in important anatomical regions of the thorax are arranged. To measure the scatter fraction, lead stoppers are placed in the lung, cardiac and subdiaphragmal regions. A narrow strip in the lower end of the plate (S) is preserved from the exposure for sensitometry before film processing. The central area of the IQT plate (D) is left free of test objects as the dosimetric detector is fixed in this position on the entrance surface of the phantom.



View larger version (39K):
[in this window]
[in a new window]
  		Figure 1. Cross-sectional view of the anthropomorphic LucAl chest phantom with 20 objects for objective estimation of image quality (in the right side) and objects for subjective estimation of image quality (in the left side) as described in the text.

 
Phantom method
Standard chest radiography was simulated with the anthropomorphic LucAl chest phantom. The phantom was exposed in three series, changing a) tube potential, b) added filtration and c) antiscatter device as described below. Automatic exposure control (AEC) settings were adjusted to give an optical density of 1.8 OD in the lung fields. This value was found using the same phantom method, to be optimal for the imaging system, including FSC, viewing box and viewing conditions [20]. For each exposure the incident air kerma on the phantom surface was measured with a diode detector (H/DN-2X) and dosemeter WD10 (Wellhofer Dosimetrie GmbH, Schwarzenbruck, Germany) and the entrance surface dose (ESD) was then calculated applying appropriate backscatter factors [22]. The organ doses, Dt, and effective dose, E, were calculated by Monte Carlo methods using the computer code PCXMC 1.4 (STUK, Helsinki, Finland) [23]. The Cristy mathematical phantom with standard body mass and height was selected and 50 000 photon histories were traced in the simulations. This allowed the statistical error in doses for all organs of interest to be below 5%. For small organs outside the beam, like ovaries and testes, the error was in the range 50–60%. The effective dose, E, was calculated using tissue weighting factors from ICRP Publication 60 [24]. Only one radiographic cassette was used for each exposure. All exposed films were processed with the same processor in 1 day. The constancy of the film processing was controlled by means of light sensitometry. Evaluation of all the images was done with unchanged viewing conditions. Image quality for each radiograph of the phantom was evaluated using two objective indexes: contrast index {Delta}C and scatter fraction Ps, and two subjectively estimated indexes: a low contrast visualization index Plow, and a high contrast visualization index Phigh. The methods of calculation were described in our previous paper [20].

Search for the optimal beam quality
The first series of six films was acquired with unchanged exposure geometry at a film–focus distance of 150 cm with added filtration of 1 mm Al, varying the tube potential between 70 kVp and 120 kVp in 10 kVp steps. Two other series of films were acquired with the same kilovoltage steps but with 0.1 mm Cu and 0.2 mm Cu, respectively, added to the 1 mm Al filter. These 18 X-ray spectra were theoretically generated using a dedicated software program based on the Birch and Marshall catalogue [25]. Input data are the target angle and material, peak value and ripple of the applied tube potential and total beam filtration. The output data are photon energy distribution, radiation output at 75 cm from the focus, first half value layer (HVL) and mean photon energy in the spectrum. The theoretical simulation shows that the spectra chosen cover a wide range of beam qualities between HVL 2.5 mm Al and 7.8 mm Al. More heavily filtered beams were not examined in this work The choice of the optimal spectrum was made on the basis of a complex analysis of the changes in dose, tube loading and image quality indexes.

Search for the optimal antiscatter device
The changes in exposure parameters, tube loading, ESD, organ doses and effective dose as well as the changes in image quality parameters were investigated by exposing the "anthropomorphic" chest phantom at unchanged beam quality with three antiscatter devices: the antiscatter grid used routinely with grid ratio 7:1 and two air gaps 16 cm and 25 cm wide, respectively. A special device hanging on the chest stand was designed for phantom positioning to control the distances between exit surface of the phantom and film. The tube was moved to 210 cm or 300 cm to keep the magnification of the thorax image unchanged.

Clinical comparison of the routine and the recommended optimal methods
The optimal parameters identified in the phantom study were then applied to a clinical study of 10 adult patients. Each patient gave consent to being exposed to both routine and recommended optimal techniques. The films were scored independently by five radiologists using the European anatomical criteria for good images [12] and for each film an individual quality factor was calculated. Comparison between the two groups of films was done with averaged quality factors Qi for each of the six criteria for the radiographic technique. The ESD for each patient was found by an indirect method using the tube output data and exposure factors. The organ doses and effective dose were calculated using the PCXMC computer program [23]. The patient's body mass and height were used for the mathematical phantom adjustment and 50 000 photon histories were traced in the Monte Carlo simulation.


   Results and discussion
Top
 Abstract
 Introduction
 Materials and method
 Results and discussion
Conclusion
 References
 
Phantom dose and image quality as a function of beam quality
The results for phantom dose changes when varying the added filtration and tube potential are summarized in Table 1Go. The values of ESD, organ doses Dt for some critical organs and effective dose E are presented as a function of HVL. For constant OD in the lung area ESD decreases fourfold from 0.470 mGy at 70 kVp and 1 mm Al (HVL=2.5 mm Al) to 0.118 mGy at 120 kVp and 0.2 mm added Cu (HVL=7.8 mm Al). The dose to the lungs is reduced by a factor of two, with 40% reduction for active bone marrow and about 17% reduction for breast and stomach. We observed an increase in dose to the ovaries with tube potential and filtration from zero at 70 kVp to 0.42 µSv at 120 kVp. This was also noted by Fung and Gilboy with thermoluminescent dosemeter (TLD) measurements and is, possibly, due to the increase of scatter reaching those organs, which are outside the primary beam [26]. The increase in dose to the ovaries is very small in absolute terms. The effective dose E, as an indicator of radiation risk, is lowered with beam hardening by about 40%, from 46.2 µSv (at 70 kVp and Al filter) to 26.1 µSv (at 120 kVp and added 0.2 mm Cu filter). One reason for the dose decrease is that the added 0.2 Cu effectively absorbs the soft component of the spectrum. The ESD reduction is mainly due to the kVp increase and to a lesser extent because of filtration. The ESD values at 120 kVp – 0.170 mGy for 1 mm Al filter, 0.132 mGy for 0.1 mm Cu+1 mm Al and 0.118 mGy for 0.2 mm Cu+1 mm Al are – much lower than the European reference dose level of 0.3 mGy [12] whereas the low kV technique gives a higher value of 0.470 mGy.


View this table:
[in this window]
[in a new window]
  		Table 1. Entrance surface dose (ESD), organ doses, Dt, and effective dose, E, as a function of added filtration and tube potential for posteroanterior chest radiography for constant optical density in the lung area of 1.8 OD

 
Another advantage of the high kV technique is a shorter exposure time, decreasing from 20 ms at 70 kV to 10 ms at 120 kV, which results in reduced movement unsharpness. This is in accordance with a recommendation given by European guidelines [12] and by other authors [18, 27]. Our study showed that for constant geometrical conditions, the same antiscatter grid and FSC, the heavily filtered beam at maximum possible tube potential would have advantages in respect of patient dose. These conclusions correlate well with the results of Shrimpton et al [2] and Huda and Gkanatsios [28]. Increasing the tube potential and adding extra filtration reduces the tube loading from 13 mAs to 1.6 mAs for the same OD of about 1.8 in the lung field. Added copper filter however increases the tube loading at constant tube potential by about 23% and 54% for 0.1 mm Cu and 0.2 mm Cu, respectively. The selection of filtration should be determined by image quality factors.

Our phantom study did not find any significant changes in the subjective image quality indexes with beam quality. This result suggests that all films should meet clinical requirements. The objective phantom image evaluation shows that when the tube potential and the filtration are increased whilst keeping the film OD over the lungs constant, the OD in the cardiac and subdiaphragmal areas increases. The changes in the contrast index {Delta}C in the lung and cardiac areas with increasing the tube potential for two added filters are presented in Figure 2Go. The contrast index in the lung area decreases (Figure 2aGo) but {Delta}C for denser mediastinal areas goes up with increasing HVL of the beam (Figure 2bGo). Above 100 kVp, however, when using a heavily filtered beam this trend is reversed. This is caused by an increase in the scatter fraction Ps with increasing HVL above 5.5–6.0 mm Al (Figure 3Go).



View larger version (10K):
[in this window]
[in a new window]
  		Figure 2. Variation of the contrast index {Delta}C with tube potential for added filters of 1 mm Al and 0.2 mm Cu+1 mm Al at constant optical density 1.8 OD in the lung field for: (a) lung area; (b) cardiac area.

 


View larger version (13K):
[in this window]
[in a new window]
  		Figure 3. Variations of scatter fraction Ps in the cardiac and the subdiaphragmal areas with half value layer (HVL) at constant optical density 1.8 OD in the lung field.

 
A thorough analysis of the data leads to the conclusion that the optimum dose and image quality for chest radiography with the X-ray unit under investigation could be attained adding 0.1 mm Cu to the routine 1 mm Al filter and increasing the tube potential to 100 kVp. Using more filtration is not justified because of the increase in tube loading and some deterioration in image quality. Applying a tube potential above 100 kVp requires a more effective antiscatter device.

Search for the optimal antiscatter device
We investigated the possibility of increasing the tube kilovoltage to the upper limit of 120 kVp with a suitable antiscatter device with greater selectivity than the standard 7:1 ratio grid. The results from the phantom study with three antiscatter devices, standard grid and air gaps of 16 and 25 cm width are presented in Table 2Go, including ESD, E, and the objective image quality indexes in the lung and the cardiac areas–scatter fraction Ps and contrast index {Delta}C. All data are obtained using the "anthropomorphic" chest phantom with unchanged beam quality at 120 kVp and added filter of 1 mm Al+0.1 mm Cu. The parameters used at 100 kVp for optimal beam quality when using the standard grid are also presented in the table for comparison.


View this table:
[in this window]
[in a new window]
  		Table 2. Entrance surface dose (ESD), effective dose (E), scatter fraction (Ps) and contrast index ({Delta}C) for chest radiography with three antiscatter devices

 
The results show that at 120 kVp the 16 cm air gap is less effective than the grid for removing scatter, while the 25 cm air gap is more effective. The scatter fraction Ps=0.23 with a 25 cm air gap is the same as that at 100 kVp with the grid but the contrast in the lung and heart areas is higher with the air gap. Although the focus to film distance is increased, obtaining the optimal OD in the lung fields with a 25 cm air gap requires less than half the ESD of that with a grid. The ESD value 0.075 mGy with an air gap is significantly lower than the European reference level. The effective dose is also reduced from 32.5 µSv to 14.4 µSv.

Clinical comparison of the routine and the recommended optimal methods
As a result of the phantom investigations presented above, an optimal method for chest radiography with the X-ray unit could be recommended. This method was compared with the routine one in a clinical study. The results are presented in Table 3Go including the technical parameters for both methods, averaged patient data and mean values of ESD and E. The averaged quality factors from subjective scoring of film are summarized in Table 4Go.


View this table:
[in this window]
[in a new window]
  		Table 3. Results from the clinical comparison between the routine and recommended optimal techniques for chest radiography with X-ray unit TUR D800-3

 

View this table:
[in this window]
[in a new window]
  		Table 4. Image quality factors (Qi) obtained by subjective scoring of films exposed by the routine and the recommended method for chest radiography

 
The clinical study confirms the conclusions that the optimized technique has advantages with respect to the patient dose. The image quality comparison shows that the radiolucency of the mediastinal areas is increased, improving the visualization of the pleural shadow, trachea and main bronchi. The increased radiolucency of the ribs, heart and diaphragm improves the reproduction of the lung parenchyma as well as of the pathological objects in the lungs. There is debate among radiologists whether or not this increased radiolucency is an advantage. In the opinion of some radiologists, decreased anatomical structure noise helps the interpretation of the interstitial changes and excludes false-positive findings, as is also demonstrated by Stieve [27] and Vyborny [18]. In contrast, some radiologists prefer low kV technique images. This confirms the opinion of many authors that the diagnostic process is strongly subject dependent [15, 17, 18, 27]. Radiologists' preferences depend on education, training and practical experience. A move towards high kV techniques requires standardization of the procedures, wider discussion and more clinical trials.


   Conclusion
Top
 Abstract
 Introduction
 Materials and method
 Results and discussion
 Conclusion
References
 
Our main aim was to use a phantom study to find the optimal technical parameters for a given X-ray unit for chest radiography. The modified LucAl chest phantom was used to evaluate the influence of different technical parameters on image quality and patient dose.

An important conclusion is that there is potential for optimization in all X-ray units, even in older units with some technical limitations. It was demonstrated that some changes in technical parameters made after careful optimization enable use of the recommended high kV technique for chest radiography with reduction in patient dose and improved image quality.


   Acknowledgments
 
The author is grateful to the staff of the Radiology Department of the Regional Hospital in Shumen for making the radiological equipment available. The radiologists of the Department are acknowledged for the film scoring and discussion.

Received for publication March 18, 2003. Revision received November 24, 2003. Accepted for publication December 23, 2003.


   References
Top
 Abstract
 Introduction
 Materials and method
 Results and discussion
 Conclusion
 References
 

  1. Nikoloff E, Atherton J. Patient x-ray exposure reduction using increased beam filtration. Med Phys 1987;14:454.
  2. Shrimpton P, Jones D, Wall B. The influence of tube filtration and potential on patient dose during x-ray examinations. Phys Med Biol 1988;33:1205–12.[CrossRef][Medline]
  3. Behrman R, Yasuda G. Effective dose in diagnostic radiology as a function of x-ray beam filtration for a constant film density. Med Phys 1998;25:780–90.[CrossRef][Medline]
  4. Cranage R, Phil D, Howard J, Welsh D. Dose reduction by the use of erbium filtration in a general radiographic room. Br J Radiol 1992;65:232–7.[Abstract/Free Full Text]
  5. Thierens H, Kunnen M, Van der Plaetsen A, Segaert O. Evaluation of the use of a niobium filter for patient dose reduction in chest radiography. Br J Radiol 1991;64:334–40.[Abstract/Free Full Text]
  6. Kelsey C. Techniques for chest radiography. In: Haus AG, editor. The physics of medical imaging: recording system measurements and techniques. Medical Physics Monograph No.3. AAPM, 1979:442–58.
  7. Sandborg M, Dance D, Alm Carlsson G, Persliden J. Monte Carlo study of grid performance in diagnostic radiology: factors which affect the selection of tube potential and grid ratio. Br J Radiol 1993;66:1164–76.[Abstract/Free Full Text]
  8. Butler P, Conway B, Suleiman O, Koustenis G, Showalter C. Chest radiography: a survey of techniques and exposure levels currently used. Radiology 1985;156:533–6.[Abstract/Free Full Text]
  9. Leitz W, Mansson L, Hedberg-Vikstrom B, Kheddache S. In search of optimum chest radiography techniques. Br J Radiol 1993;66:314–21.[Abstract/Free Full Text]
  10. Manninen H, Terho E, Wiljasalo M, Wiljasalo S, Soimakallio S. An evaluation of different imaging chains in clinical chest radiography. Br J Radiol 1984;57:991–5.[Abstract/Free Full Text]
  11. Niklason L, Sorenson J, Nelson J. Scattered radiation in chest radiography. Med Phys 1981;8:677–81.[CrossRef][Medline]
  12. European Commission. European guidelines on quality criteria for diagnostic radiographic images, EUR 16260. Luxembourg: European Commission, 1996.
  13. American College of Radiology. Standards for performance of adult chest radiography. Reston, VA: American College of Radiology, 1990.
  14. Vassileva J. An indirect method of assaying radiation exposure of patients in conventional diagnostic radiology. Roentgenologia Radiologia 2000;39:293–9 [In Bulgarian].
  15. International Commission on Radiological Units and Measurements. ICRU Report 54: Medical imaging - the assessment of image quality. ICRU, 1996.
  16. Sandborg M, McVey G, Dance D, Alm Carlsson G. Schemes for the optimization of chest radiography using a computer model of the patient and X-ray imaging system. Med Phys 2001;28:2007–19.[CrossRef][Medline]
  17. Vucich J. The role of anatomic criteria in the evaluation of radiographic images. In: Haus AG, editor. The physics of medical imaging: recording system measurements and techniques. Medical Physics Monograph No.3. AAPM, 1979:573–87.
  18. Vyborny C. Image quality: the radiologist's perspective. In: Specification, acceptance testing and quality control of diagnostic X-ray imaging equipment. Medical Physics Monograph No.20, AAPM, 1994:145–52.
  19. Warren-Forward H, Millar J. Optimization of radiographic technique for chest radiography. Br J Radiol 1995;68:1221–9.[Abstract/Free Full Text]
  20. Vassileva J. A phantom for dose-image quality optimization in chest radiography. Br J Radiol 2002;75:837–42.[Abstract/Free Full Text]
  21. The Institute of Physics and Engineering in Medicine. Recommended Standards for the Routine Performance Testing of Diagnostic X-Ray Imaging Systems, Report No.77. York: IPEM, CoR, NRPB, 1998.
  22. Jones D, Wall B. Organ doses from medical X-ray examinations calculated using Monte Carlo techniques. NRPB-R186, London: HMSO, 1985.
  23. Tapiovaara M, Lakkisyo M, Servomaa A. PCXMC - a PC-based Monte Carlo program for calculating patient doses in medical X-ray examinations. STUK-A139: Helsinki 1997.
  24. International Commission on Radiological Protection (ICRP). 1990 Recommendations of the ICRP 60, Ann ICRP, 21 Nos 1-3. Oxford: Pergamon Press, 1991.
  25. Cranley K, Gilmore BJ, Fogarty G, Desponds L. Electronic version prepared by D Sutton. Catalogue of diagnostic X-ray spectra and other data, The Institute of Physics and Engineering in Medicine Report No.78. 1997.
  26. Fung K, Gilboy W. The effect of beam tube potential variation on gonad dose to patients during chest radiography investigated using high sensitivity LIF:Mg,Cu,P thermoluminescent dosemeters. Br J Radiol 2001;74:358–67.[Abstract/Free Full Text]
  27. Stieve F-E. Radiological requirements for the specification of image quality criteria. In: Moores BM, Wall BF, Eriskat H, Schibilla H, editors. Optimization of image quality and patient expoure in diagnostic radiology, BIR Report 20. London, UK: BIR, 1989:221–38.
  28. Huda W, Gkanatsios A. Effective dose and energy imparted in diagnostic radiology. Med Phys 1997;24:1311–6.[CrossRef][Medline]




This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Vassileva, J
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Vassileva, J

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
BJR DMFR IMAGING  ALL BIR JOURNALS