BJR
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
First published online August 2, 2006
British Journal of Radiology (2007) 80, 107-112
© 2007 British Institute of Radiology
doi: 10.1259/bjr/87150291
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 HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Tsapaki, V
Right arrow Articles by Koulentianos, E D
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Tsapaki, V
Right arrow Articles by Koulentianos, E D

Full paper

Radiation doses to patients undergoing standard radiographic examinations: a comparison between two methods

V Tsapaki, MSc, PhD 1 I A Tsalafoutas, MSc, PhD 1 I Chinofoti, Tec 2 A Karageorgi, Tec 2 E Carinou, MSc, PhD 3 V Kamenopoulou, MSc, PhD 3 E N Yakoumakis, MSc, PhD 4 and E D Koulentianos, MD 2

1 Medical Physics Unit and 2 Radiology Department, General Hospital 'Konstantopoulio-Agia Olga', Athens, 3 Greek Atomic Energy Commission, Agia Paraskevi, Athens, and 4 Department of Medical Physics, Medical School, University of Athens, Athens, Greece

Correspondence: Dr Virginia Tsapaki, Medical Physics Unit, General Hospital 'Konstantopoulio-Agia Olga', 3-5 Agias Olgas Str., Nea Ionia 14233, Athens, Greece. E-mail: virginia{at}otenet.gr


   Abstract
Top
 Abstract
Introduction
 Methods and materials
 Results
 Discussion
 Conclusion
 References
 
The objective of the study was to derive a mathematical method for calculating the entrance surface dose (ESD) from exposure factors for all tube potentials used in clinical practice and to compare the calculated ESDs (ESDC) with those measured (ESDTLD) using thermoluminescent dosemeters (TLDs). The exposure parameters of 43 patients who underwent (a) posteroanterior (PA) and lateral (LAT) chest examination (13 patients), (b) supine abdomen (10 patients), (c) erectus abdomen (10 patients), or (d) urinary tract examination (10 patients) were recorded. Patient ESD was directly measured by TLDs and calculated from exposure factors. The differences between ESDC and ESDTLD were quite small and could be explained by the uncertainties involved in both methods, in all but the PA chest examination where the ESDC was about 50% larger than ESDTLD. However, in PA chest the ESDTLD was close to the minimum detectable dose of TLDs, questioning the accuracy of ESDTLD. Further investigation showed that using the high tube potential technique (130 kV) in the PA chest examination resulted in very short exposure times, in the region of 4 ms. In such short exposure times, the X-ray generator operation presented stability problems that led to loss of output linearity and consequently to false calculation of ESD. The calculation method offers a reliable and cheap alternative to the measurement of ESD by TLD, provided that the exposure times are not as short as in the PA chest examinations recorded in this study, so that the output linearity with tube current–time product (mAs) is maintained.


   Introduction
Top
 Abstract
 Introduction
Methods and materials
 Results
 Discussion
 Conclusion
 References
 
Diagnostic X-rays are used so extensively in medicine that they represent by far the largest man-made source of public exposure to ionizing radiation. Patient radiation dose from conventional radiographic procedures ranges from 0.1 mSv to 10 mSv, resulting in a collective dose to the population that can be significant [1]. Quality and safety have become hallmarks for efficient and successful medical intervention. A comprehensive quality and safety culture has been progressively developed throughout the European Union with regard to the medical use of ionizing radiation for diagnosis and treatment. The establishment of the Quality Criteria for Diagnostic Radiology Images started in 1984 when the first Directive on Radiation Protection of the Patient was adopted by the Member States of the European Union [2]. The two basic principles of radiation protection of the patient as recommended by the ICRP are justification of practice and optimization of protection [3, 4]. These principles are largely translated into legal framework by the Euratom Directive [5].

During recent years, patient dose has become a major issue and because of the increasing awareness and greater realisation of the effects of ionizing radiation, X-ray users are now more demanding of dose information and dose reduction [6]. The "European Guidelines on Quality Criteria for Diagnostic Radiographic Images" document defines the diagnostic requirements for normal, basic radiographs, specifying anatomical image criteria and important image details; it indicates criteria for the radiation dose to the patient and gives examples for good radiographic technique by which the diagnostic requirements and dose criteria can be achieved [7]. Two types of dosemeter are commonly used for estimating ESD to patients during radiographic examinations, namely thermoluminescent dosemeters (TLDs) and ionization chambers [8]. TLDs have the advantage of being physically small, enabling them to be stuck directly and unobtrusively on the patient's skin with very little interference in patient mobility or comfort. They will fully measure the radiation backscattered from the patient, an essential component of the entrance surface dose (ESD), and are unlikely to obscure useful diagnostic information. Ionization chambers, being more bulky and requiring connecting cables, are usually difficult to attach in sufficiently close contact to the patient's skin to ensure complete measurement of the backscattered radiation. They also severely restrict patient mobility and cast interfering shadows on radiographs. They are consequently not recommended for direct measurement of ESD. Ionization chambers can, however, be used to make measurements of the absorbed dose to air, in free air, on the axis of the X-ray beam without a patient or phantom present. Such measurements can be corrected using appropriate backscatter factors and the inverse square law to estimate the ESD. TLDs are recommended for direct measurement of ESD and are available in a variety of physical forms and in different materials. The National Radiological Protection Board (NRPB) recommends individual chips or pellets of lithium fluoride or lithium borate [8].

Certain studies are found in the literature that use indirect methods to estimate ESD based on free-in-air measurements of tube output and calculations using patient exposure factors [9–11]. Two of these studies [10, 11] compared the indirect method with the direct method of TLD and found good correlation of the results. However, the limitation of these studies was that output measurements were performed on either one tube potential [10] or specific tube potentials [9, 11]. In the case where the output was not measured in the tube potential utilized in the specific patient, it was derived from the value measured at the nearest possible potential, assuming that it was proportional to kVp2 [11].

The objectives of the current study were to derive a mathematical method for calculating the ESD from exposure factors for all tube potentials used in clinical practice and compare the calculated values with the ESDs determined using TLDs kindly provided and measured by the Greek Atomic Energy Commission (GAEC).


   Methods and materials
Top
 Abstract
 Introduction
 Methods and materials
Results
 Discussion
 Conclusion
 References
 
General
The study was carried out at the Konstantopoulio-Agia Olga General Hospital using a CGR MPG-50 generator and an overcouch tube (Buc, France). The unit was a three-phase radiograph machine, with automatic exposure chambers (AEC) fitted in both the table and the chest bucky. Both buckies were equipped with similarly focused antiscatter grids (ratio 12:1). The film–screen combination used was an Agfa CPG 400 speed class screen with an Agfa CPG-Plus orthochromatic film (Agfa-Gevaert, Belgium).

Quality assurance (QA) measurements were carried out with a PMX-III R/CT digital multimeter (RTI Electronics, Mölndal, Sweden) comprising a R25 solid state detector with a calibration traceable to a primary standard. According to the manufacturer specifications this instrument is accurate to within 3% for output measurements and has an energy dependence between 0.99 to 1.01 for tube potentials in the range of 50 kV to 140 kV. Tube and generator QA measurements were carried out in accordance with the IPEMB 32 (Part I) protocol [12] and AEC QA checks according to the IPEMB 32 (Part IV) protocol [13].

The results of the QA measurements showed that:

  1. The half-value layer (HVL) at 80 kVp was 2.9 mm Aluminium (Al).
  2. The nominal tube potential was accurate to within +2.5% across the range 50–140 kVp.
  3. The linearity of tube output at 80 kVp was accurate to within +5% across the range 2.5–80 mAs. (Tube output is defined as the absorbed dose to air per mAs at 75 cm).

ESD calculation method
A number of equations are found in the literature for describing the output variation with tube potential. Simpkin and Dixon [14] have used a third order polynomial for the output of a radiography tube and a second order polynomial for a Mo/Mo mammography tube. They noted, however, that a simple power relationship of the form O/P = a(kVp)b could also describe the output from the specific radiographic tube to within ±5%. The latter equation is consistent with the linear relationship between the logarithms of output and tube potential mentioned in the IPEMB report [12]. George et al [11] have used the same power low relationship setting however, with the b factor equal to two, following the commonly adopted concept of output variation with the square of tube potential.

In this study, the output values measured across the range 50–140 kVp were fitted by all four relationships mentioned above and the results are given in Table 1Go. It is obvious that the third and second order polynomials provide the best fit with the smallest mean and maximum errors compared with the other two equations.


View this table:
[in this window]
[in a new window]

  		Table 1. The results of the four different fitting equations tested for describing the output(O/P)

 
As verified by applying the same fitting procedures to nine additional X-ray tubes in our hospital, the second order polynomial presents similar accuracy with the third order polynomial and it is expected that the majority of X-ray tubes will reproduce the output with an accuracy better than ±5%. On the other hand, the power law, especially the kVp2 relationship, were not always as accurate, as shown in Table 1Go. It is instructive that for an identical radiographic unit with a more heavily filtered X-ray beam (HVL = 3.8 mm Al at 80 kVp), the power law gave a mean and maximum error of 3% and 8%, respectively, whereas the respective values for the a(kVp)2 relationship were 9.5% and 40%. For that tube, third and second order polynomial fitting gave mean and maximum error of less than 1% and 2.2%, respectively.

Taking all of the above into account, it was decided that the output of the X-ray tube will be described by the second order polynomial given by the following equation, with fitting parameters a = 0.0099, b = 1.1594 and c = -44.75.


Formula 001

It should be clarified that whichever of the four aforementioned equations is chosen for describing the output, the fitting parameters will be different for each radiographic unit and should be updated after routine QA tests and following a major service.

Having established the output variation with tube potential, the ESD can then be calculated using the following equation:


Formula 002

where f is the dose absorbed to tissue/dose absorbed to air (usually assumed to be unity); BSF is the backscatter factor dependent on beam quality and field size [8, 15]; FDD is the focus–detector distance; and FSD is the focus–skin distance.

ESD measurement procedure
Validation of the calculation method previously described was undertaken using TLDs (Harshaw TLD-100 rods: Harshaw-Bicron, Solon, OH [LiF:Mg,Ti, 3x3x9 mm]) provided by the GAEC. TLD calibrations were carried out in the GAEC Secondary Standard Dosimetry Laboratory using ISO Narrow 4037 reference quality beams. The TLDs were read using a Harshaw 4500 TLD reader and annealed in a PTW oven (PTW Company, Freiburg, Germany). The TLD energy response was ±18% across the range 50–150 kVp, the uncertainty of measurement was estimated to be less than ±10% and the minimum detectable dose 30 µGy.

The five most frequently performed diagnostic radiographic examinations were included in the study; posteroanterior (PA), chest and lateral (LAT) chest, anteroposterior (AP) abdomen (erect and supine) and AP urinary tract. 43 patients took part in the study; 13 patients had both PA and LAT chest radiographs, 10 patients had AP abdomen erect radiographs, 10 patients had AP abdomen supine radiographs and 10 patients had AP urinary tract radiographs. The minimum number of patients for each examination was 10, based on the requirements given by the European Commission guidelines (EG) [7]. For each radiographic projection, the mean patient weight was within the range of 70 kg ±5. For each radiograph, the tube potential, milliampere settings, FSD, FFD, cassette size, patient weight and age were recorded. The image quality of all radiographic examinations included in the sample was satisfactory according to the radiologists of the department and fulfilled all image criteria set by the European guidelines [7].


   Results
Top
 Abstract
 Introduction
 Methods and materials
 Results
Discussion
 Conclusion
 References
 
Table 2Go presents the mean values and standard deviation of clinical and technical data, as well as the calculated ESD (ESDC) and measured ESD (ESDTLD), for PA chest, LAT chest, erect and supine AP abdomen and AP urinary tract examinations. As shown in Table 2, the mean ESDTLD ranged from approximately 120 µGy (PA chest) to 1.61 mGy (AP abdomen supine). The ESDC values were slightly higher than ESDTLD in all but the AP abdomen erectus examination. The deviation of the mean ESDC from the mean ESDTLD values were: PA chest: 50%; LAT chest: 9%; AP erectus abdomen: 6%; AP supine abdomen: 13%; and AP urinary tract: 6%.


View this table:
[in this window]
[in a new window]

  		Table 2. Mean values of patient weight, exposure parameters and entrance surface dose(ESD) (calculated and measured)

 
Scatter diagrams of PA and LAT chest are presented in Figure 1Go. Regarding the PA chest scatter diagram, it is obvious that ESDTLD values are slightly above the minimum detectable dose of the TLD used which, as reported by a number of authors [16–19], is in the range of 50 µGy to 100 µGy. It must be stressed that the TLD threshold dose not only depends strongly on the annealing and measurement protocols used and the equipment available, but also on the particular batch of TLDs used for the ESD measurements. Therefore, at these low dose levels common in PA chest examinations, more investigation should be done using other types of TLDs such as calcium fluoride (CaF) dosemeters that are much more sensitive (but also more expensive) than LiF TLDs.


Figure 1
View larger version (14K):
[in this window]
[in a new window]

  		Figure 1. Plot of measured entrance surface dose(ESDTLD) and calculated ESD (ESDC) doses for posteroanterior (PA) and lateral (LAT) chest radiographs.

 
The correlation between ESDC and ESDTLD in all radiographic procedures included in the study were: PA chest: R2 = 0.719; LAT chest: R2 = 0.970; AP abdomen erectus: R2 = 0.935; AP supine abdomen: R2 = 0.990; and AP urinary tract: R2 = 0.940. Thus for all examinations studied, the correlation between calculated and measured doses was very high, especially for doses above 0.2 mGy.

Table 3Go presents the comparison of technical parameters (tube potential and FFD) and ESDC with the corresponding recommendations of the EG [7]. The only examination for which no recommendations were found in these guidelines was the abdomen radiograph. All remaining procedures fall within the EG suggestions, with the mean ESDC in all radiographic examinations being substantially lower than European Guidelines dose reference levels (EG DRL). More specifically, mean ESDC for PA chest is 1.7 times lower than the EG DRL, for LAT chest mean ESDC is 3.0 times lower and for urinary tract 7.2 times lower than the EG DRL. Mean ESDC values found in this work were also lower than the DRLs recently proposed by NRPB [20] given in the same table. It is evident that the low dose levels in Konstantopoulio-Agia Olga General Hospital can probably be attributed to the technical parameters used (for example, the high tube potential in chest examinations) and the use of a high speed class screen–film combination.


View this table:
[in this window]
[in a new window]

  		Table 3. Comparison of tube potential, FFD and ESDC with corresponding values recommended in the European Commission guidelines (EG) [7] and the National Radiation Protection Board [20]

 

   Discussion
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
Conclusion
 References
 
Regarding the comparison of the calculation technique and the direct TLD measurement of ESD, it should be noted that the uncertainty of the TLD method was ±10%. On the other hand, the calculation method presents certain inaccuracies arising mainly from the errors in the fitting of measured output values with Equation (1), the linearity of output with mAs, the determination of FSD and the selection of the BSF value. The fitted output values for the tube potentials used in this study agree to within ±3% of the measured values, while for a radiographic unit complying with the QC standards the variation of output with mAs should be less than ±10% [12]. The error in the FSD should be less than ±1 cm when a measuring tape is available. The BSF does not dramatically change with tube potential and field size, and for the majority of the radiographic examinations it ranges from about 1.25 to 1.45 [8, 15]. Therefore, the error when selecting a BSF value from the literature according to the tube potential and the cassette used should never exceed 5%. Thus, the ESDC should be within ±10–15% from the actual ESD values, provided that the output measurements have been made with a calibrated dosemeter.

Thus, the slight differences found between ESDC and ESDTLD, for all examination types except PA chest, can be explained by the uncertainties of the measurements using either method. For PA chest, further investigation was required to test whether the measurement or the calculation method provided the most reliable ESD values. For this reason, the following experiment was executed: PA chest clinical conditions were simulated using a 1 mm Cu plate placed on the centre of the X-ray field, so as to cover the central chamber of AEC and produce similar mAs values with PA chest. In order to measure ESD the dosemeter was placed beside the phantom, so as not to block the AEC chamber. A series of exposures was performed with the central AEC chamber activated and the corresponding milliampere, milliseconds settings and ESD were recorded along with the optical density (OD) of the film. In all these exposures, the exposure times selected by the AEC system were lower than 4 ms; that is, comparable with the generator "switching time". In such short exposure times the stability of the generator is questionable and the mAs value indicated may not be accurate, while it is also probable that the pre-set tube potential value cannot be obtained. Indeed, it was found that the mean ESD was smaller than the theoretically predicted value by approximately 40% while the optical density of the film was 1.4 OD.

The experiment was repeated by manually setting the tube current and the exposure time (values selected were always higher than 10 ms) so that similar values of mAs were applied, as before. This time, the ESD measured by the dosemeter was in agreement with the theoretical value calculated using Equation (1) and the optical density of the film was 2.7. The almost-double OD of the film eliminated the possibility that the reduced output measured with the dosemeter was due to false dosemeter indication in such short exposure times.

With these additional measurements, it was evident that below a certain exposure time (for this specific unit it seemed to be approximately 10 ms), the output was no longer consistent with the corresponding output values of longer exposure times even if the milliampere settings were equal. Thus the loss of linearity observed was not a matter of low milliampere settings, but of very short exposure times – a fact that had not been initially accounted for in the routine quality control. While in the QA tests a very good output linearity has been observed for a large range of milliampere settings, it was now evident that this linearity was not maintained at the very short exposure times observed in the PA chest examination. Since reproducibility problems of both the generator and the AEC measuring chamber may also appear in such short exposure times, it would be preferable to slightly lower the tube potential selection so that the exposure time in clinical conditions will be higher than the value below which the stability of the generator is not assured. In some generators there is also the alternative option of pre-selecting a low tube current value, of around 100 mA, so as to ensure that the exposure times under AEC operation will be longer than 10 ms.

Taking into account the output reduction observed for short exposure times, it may be considered that the ESDTLD values are more reliable than was initially thought. Still, since the output reduction increases with decreasing exposure times, it was not possible for us to verify the TLD accuracy. This, however, could be achieved using Plexiglas® plates to reproduce the clinically observed milliampere settings along with a calibrated dosemeter capable of fully recording the backscattered radiation.


   Conclusion
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
 Conclusion
References
 
Patient radiation dose is a very important parameter which controls the quality of the X-ray services within the hospital. Dose monitoring helps to ensure that the best possible protection of the patient is maintained at all times and provides an immediate indication of incorrect use of technical parameters or equipment malfunction. However, it is not always easy to measure the dose for a number of reasons, such as a lack of the appropriate dosimetry system recommended by international bodies and the recent literature. This study demonstrated that using the results from the quality control procedure to estimate the ESD could be an alternative reliable and cheap method for patient dose monitoring in the everyday routine of a diagnostic radiology department, provided that the X-ray system works within international quality control standards and clinical exposure times are longer than the minimum required for the X-ray generator to retain the linearity of output within ±10%.

More detailed investigation should be carried out in very small ESD values (around 100 µSv) for the following reasons: (1) this dose region is close to the minimum detectable dose level of commonly used TLD; (2) this dose level is observed in the PA chest examination, which is the most frequent X-ray examination in all diagnostic radiological departments; and (3) it is highly probable that X-ray systems are not reliable for very short exposure times (smaller than 10 ms) when a high tube potential technique is used (as recommended in the EG).

Received for publication November 30, 2005. Revision received June 8, 2006. Accepted for publication June 27, 2006.


   References
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
 Conclusion
 References
 

  1. United Nations Scientific Committee on the Effects of Atomic Radiation. 2000 report to the General Assembly, Annex D: medical radiation exposures. New York, NY: United Nations, 2000
  2. Council Directive 84/466, Euratom O.J. No. L 265/1
  3. International Commission on Radiological Protection. Radiological Protection and Safety in Medicine. ICRP Publication 73. Annals of the ICRP 26 (2). Oxford, UK: Pergamon Press, 1996
  4. International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Annals of the ICRP 21(1-3). Oxford, UK: Pergamon Press, 1991
  5. Council Directive 97/43, Euratom 30 June 1997 on health protection of individuals against the dangers of ionizing radiation in relation to medical exposure. Official Journal No. L 180, 1997
  6. Rehani M. Protection of patients in general radiography. Proceedings of the International Conference on Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy in Malaga. International Atomic Energy Agency, Vienna, 2001
  7. European Guidelines on quality criteria for diagnostic radiographic images. European Commission, EUR 16260 EN, 1996
  8. Dosimetry Working Party of the Institute of Physical Sciences in Medicine. National Protocol for Patient Dose Measurements in Diagnostic Radiology. Chilton, UK: National Radiation Protection Board (NRPB), 1992
  9. Olivera C, Srpko M, Dusko K. First results on patient dose measurements from conventional diagnostic radiology procedures in Serbia and Montenegro. Radiat Prot Dosim 2005;113:330–5.[Abstract/Free Full Text]
  10. Armpilia C, Fife I, Croasdale P. Radiation dose quantities and risk in neonates in a special care baby unit. Br J Radiol 2002;75:590–5.[Abstract/Free Full Text]
  11. George J, Eatough J, Moutford P, Koller C, Oxtoby J, Frain G. Patient dose optimization in plain radiography based on standard exposure factors. Br J Radiol 2004;77:858–63.[Abstract/Free Full Text]
  12. Institution of Physics and Engineering in Medicine and Biology. Measurement of the performance characteristics of diagnostic X-ray systems used in medicine. Part I: X-ray tubes and generators (Second edition). IPEMB report 32. York, UK: IPEMB, 1995
  13. Institution of Physics and Engineering in Medicine and Biology. Measurement of the performance characteristics of diagnostic X-ray systems used in medicine. Part IV: Automatic Exposure Chambers (Second edition). IPEMB report 32. York, UK: IPEMB, 1995
  14. Simpkin DJ, Dixon RL. Secondary shielding barriers for diagnostic X-ray facilities: scatter and leakage revisited. Health Phys 1998;74:350–65.[Medline]
  15. IPSM. Patient dosimetry techniques in diagnostic radiology. IPSM report No. 53. York UK: IPSM, 1988
  16. Burke K, Sutton D. Optimization and deconvolution of lithium fluoride TLD-100 in diagnostic radiology. Br J Radiol 1997;70:261–71.[Abstract]
  17. Casal OP, Gil J, Llorka N, Martinez JM. Experimental comparison of automatic TLD readout systems. Radiat Prot Dosim 1990;30:23–31.[Abstract]
  18. Broadhead DA, Faulkner K, Rawlings DJ, Chapple CL. Automated thermoluminescent dosimetry for simple radiographic procedures. J Radiol Prot 1997;17:17–24.[CrossRef]
  19. Nordic guidance levels for patient dose in diagnostic radiology. N-5, Norwegian Radiation Protection Authority. Østerås, Norway: NRPA, 1996
  20. Hart D, Hillier MC, Wall BF. Doses to patients from medical X-ray examinations in the UK-2000 Review. National Radiation Protection Board (NRPB)-W14. Chilton, UK: NRPB, 2002



This article has been cited by other articles:


Home page
 Am. J. Roentgenol.Home page
W. E. Muhogora, N. A. Ahmed, A. Almosabihi, J. S. Alsuwaidi, A. Beganovic, O. Ciraj-Bjelac, F. K. Kabuya, A. Krisanachinda, M. Milakovic, G. Mukwada, et al.
Patient Doses in Radiographic Examinations in 12 Countries in Asia, Africa, and Eastern Europe: Initial Results from IAEA Projects
Am. J. Roentgenol., June 1, 2008; 190(6): 1453 - 1461.
[Abstract] [Full Text] [PDF]

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 HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Tsapaki, V
Right arrow Articles by Koulentianos, E D
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Tsapaki, V
Right arrow Articles by Koulentianos, E D

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