Equipment standards for cardiology

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Equipment standards for cardiology

  1. 1. Equipment Standards for Interventional Cardiology Author: A. Dowling, A. Gallagher, C. Walsh, T. Kenny, J. Malone Lead partner: Houghton Institute, St. James’s Hospital, Dublin, Ireland Introduction: Interventional radiology (IR) has seen rapid growth in the field of cardiology over the past decade and often represents an alternative to more hazardous surgery [1-6]. Interventional cardiac procedures are currently the most common group of interventional procedures performed in Europe [1]. Such procedures are complex and may involve prolonged irradiations, which may subject patients and operators to higher levels of risk than those, which normally prevail [1-5]. This has prompted many international bodies to issue special advice and initiate research in this area [3]. Currently interventional cardiology contributes over 10% to annual collective dose in the UK in spite of contributing to a total annual examination frequency of 0.68% [7]. The EU Medical Exposures Directive 97/43/Euratom and consequent national legislation identifies interventional radiology as an area of special concern [8,9]. Advances in imaging technology have facilitated the development of increasingly complex radiological equipment for interventional cardiology [2,4]. The development of the technology is industry and end user driven and is developing at a rate that is ahead of supporting research, equipment standards and the regulatory framework [1]. Consequently, there is a need for definitive equipment requirements and standardisation in the design, manufacture, acceptance and maintenance of this equipment. Part of the work of the EU DIMOND III research programme is to develop material for standards in this area [1]. Methods: It is a requirement of the Medical Exposures Directive, that acceptance testing be carried out on radiological equipment before its first use for clinical purposes and performance testing performed on a regular basis thereafter [8]. A Commissioning / Quality Assurance survey of 12 interventional cardiac systems was carried out by the Department of Medical Physics and Bioengineering, St. James’s Hospital, Dublin. The survey aims to assess the requirements for equipment standards to address the imbalance between the advancing technology and existing standards. The systems are listed in Table 1 and consisted of 15 Image Intensifier-TV chains in total (3 Bi-plane systems). Published results for the GE Innova 2000 flat panel system are included for comparison purposes [10]. Six of the imaging chains were new, 6 were approx. 5 years old and the remaining 3 were greater than 10 years old. All systems had a nominal detector diameter of 23cm with the 1
  2. 2. exception of the GE Advantx (36cm) and GE Innova (20cm x 20cm). Testing was performed in line with current international and national guidelines and standards [11-29]. Testing included assessing the performance of the X-ray tube and generator, measuring dose levels in fluoroscopy and digital acquisition modes and a subjective assessment of image quality using the Leeds test objects [11-29]. Dose levels were measured under Automatic Exposure Control (AEC) in fluoroscopy and digital acquisition modes by measuring the detector and patient entrance dose rates / dose per exposure, using published methodology [11-29]. Electrical, mechanical and general radiation safety were also assessed. No. Manufacturer System 1 Philips Integris Allura (Bi-plane) 1 Philips Integris 2 Philips DCI 4 Siemens Coroscop 1 Siemens Axiom Artis 2 Siemens Bicor (Bi-plane) 1 GE Advantx 1 GE Innova 2000 Table 1. Systems included in Commissioning / QA Survey Results: Dose Levels: The majority of the systems tested had a wide range of user selectable dose options available including a range of pulsed fluoroscopy modes, digital acquisition frame rates, AEC curves and spectral filtration settings. The options available in the fluoroscopy mode on one typical cardiac system are presented in figure 1. This system has two fluoroscopy modes, ‘low/normal’ and ‘high’, three field sizes and the fluoroscopy pulse rate is selectable from 3.12 to 25 pulses per second. The Image Intensifier/detector entrance dose rate is thus user selectable from 0.06 to 2.19 µGy/sec on a single spectral filtration setting. The pulsed fluoroscopy mode most frequently used on the equipment tested was 12.5 or 15 pulses per second (pps). Image Intensifier Entrance Dose Rates 2.5 2 High uGy/sec Full Field 1.5 Mag 1 1 Low Mag 2 0.5 0 3.12 6.25 12.5 25 3.12 6.25 12.5 25 1 3.12 6.232 12.5 3 25 4 3.12 5 6.25 6 12.5 7 25 8 0.06 – 2.19 0.06 – 2.19 µGy/sec Pulses/sec Figure 1: Fluoroscopy Detector Entrance Dose Rates on a typical cardiac system 2
  3. 3. The measured detector entrance dose rates for the systems tested, on the 12.5/15pps setting, are presented in figure 2. The systems are grouped according to manufacturer. From figure 2 it is evident that the detector entrance dose rates ranged from 0.2 – 0.7 µGy/sec across the systems. It is also evident that the detector entrance dose rates are manufacturer dependent. The results from one equipment manufacturer were consistently found to be approximately double, or more, that of another manufacturer for both the old and new systems. In figure 2, systems 4 and 5 have no pulsed fluoroscopy option and system 11 was configured incorrectly at commissioning in that the 12.5pps option was incorrectly operating at 25pps. Detector Entrance Dose Rates - Grouped By Manufacturer 0.8 0.6 µGy/sec 0.4 X 0.2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 * ** ** System * ** * * : Continuous Fluoro only Figure 2: Fluoroscopy Detector Entrance Dose Rates – 12.5/15pps Detector entrance dose rates in the continuous fluoroscopy mode (25/30pps) (normal and high fluoroscopy modes) are presented in figure 3. The detector entrance dose rates range from 0.3 – 1.3 µGy/sec. It is also evident in the continuous fluoroscopy mode that the detector entrance dose rates for one manufacturer are consistently notably higher than those for another manufacturer and that the dose rates on one manufacturers ‘normal’ setting are equivalent to, and in some cases higher than, the dose rates on another manufacturers ‘high’ setting. Detector Entrance Dose Rates Grouped by Manufacturer 1.4 1.2 µGy/sec 1 0.8 Cont 0.6 High 0.4 0.2 0 11 13 15 1 3 9 5 7 System Figure 3: Fluoroscopy Detector Entrance Dose Rates – 25/30pps The majority of systems operated with a detector entrance dose rate of 0.4 – 0.6 µGy/sec, in the continuous fluoroscopy mode (25/30 pps) as presented in figure 4. 3
  4. 4. 12 No of Systems 10 8 6 4 2 0 µGy/sec 0.0-0.2 0.2-0.4 0.4-0.6 0.6-0.8 0.8-1.0 1.0-1.2 1.2-1.4 1 2 3 4 5 6 7 Figure 4: Fluoroscopy Detector Entrance Dose Rates – 25/30pps Patient entrance dose rates, measured using the methodology published by Martin et al [17], are presented in figures 5, 6 and 7. Current guidelines are presented beneath the figures. Patient Entrance Dose Rates Grouped by Manufacturer 25 20 mGy/min 15 X 10 5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 * * System * * Martin: Low < 15 mGy/min; Normal 15-30 mGy/min; High 31 – 45 mGy/min IPEM: 50 mGy/min; IAEA: 25 mGy/min, WHO: 17 mGy/min Figure 5: Fluoroscopy Patient Entrance Dose Rates – 12.5 / 15 pps Patient Entrance Dose Rates - Grouped by Manufacturer 70 60 50 mGy/min 40 Cont 30 High 20 10 0 15 11 13 1 3 5 7 9 Systems Martin: Low < 15 mGy/min; Normal 15-30 mGy/min; High 31 – 45 mGy/min IPEM: 50 mGy/min; High > 1.5 x; IAEA: 25 mGy/min; W HO: 17 mGy/min; RSNA High: 20-43 Figure 6: Fluoroscopy Patient Entrance Dose Rates – 25 / 30 pps 4
  5. 5. The patient entrance dose rates in the pulsed fluoroscopy mode (12.5/15pps) ranged from 2.5 – 21.5 mGy/min and in the continuous mode (25/30pps) ranged from 5 – 42 mGy/min. On the high fluoroscopy setting a maximum patient entrance dose rate in excess of 60 mGy/min was measured for an old system. As with the detector entrance dose rates, patient entrance dose rates were found to be manufacturer dependent. Measured patient entrance dose rates for one manufacturer were found to be consistently double, or more, those measured for another manufacturer, for both old and new systems. As with the detector entrance dose rates, patient entrance dose rates on one manufacturers ‘normal’ setting were equivalent to or higher than another manufacturers ‘high’ setting. For the majority of systems tested, the patient entrance dose rate was 10 – 20 mGy/min. A breakdown is presented in figure 7. 8 No of Systems 6 4 2 0 0 – 10 10 – 20 mGy/min 20 – 30 30 – 40 40 – 50 1 2 3 4 5 Figure 7: Fluoroscopy Patient Entrance Dose Rates – 25/30 pps. Patient entrance dose rates were also measured using the IEC protocol [24]. Using the IEC protocol, the measured entrance dose rate is typically higher that that measured using the Martin BJR protocol [17] as the phantom is positioned closer to the X-ray tube. A comparison of results from one cardiac system, using the two protocols [17,24] is presented in figure 8. 160 140 120 100 IEC 80 Martin, BJR 60 40 20 0 Low FF High FF Low M1 High M1 Low M2 High M2 1 2 3 4 5 6 Figure 8: Fluoroscopy Patient Entrance Dose Rates – comparison of IEC [24] and Martin, BJR [17] protocols. Detector entrance dose per exposure measurements in the digital acquisition mode are presented in figure 9. 5
  6. 6. Detector Entrance Dose / Exposure Grouped by Manufacturer 0.25 µGy/exposure 0.2 0.15 0.1 0.05 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 System Figure 9: Digital Acquisition Mode – Detector Entrance Dose / Exposure The detector entrance dose per exposure ranged from 0.06 – 0.2 µGy/exposure on the systems tested. As in fluoroscopy mode, the detector entrance dose per exposure in the digital acquisition mode was found to be consistently higher for one manufacturer over another, for old and new systems. For the majority of systems, the detector entrance dose per exposure was in the range 0.1 – 0.15 µGy/exposure, figure 10. 7 No. of Systems 6 5 4 3 2 1 0 0.05 - 0.1 0.1 – 0.15 µGy/exp 0.15 – 0.2 0.2 – 0.25 1 2 3 4 Figure 10: Digital Acquisition Mode – Detector Entrance Dose / exposure. Patient entrance dose per exposure measurements in the digital acquisition mode are presented in figure 11. This ranged from 0.03 – 0.12 mGy/exposure, with the majority of systems operating in the range 0.1 – 0.2 mGy/exposure, figure 12. 6
  7. 7. Patient Entrance Dose / Exposure Grouped by Manufacturer 0.14 0.12 mGy/exposure 0.1 0.08 0.06 0.04 0.02 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 System Figure 11: Digital Acquisition Mode, Patient Entrance Dose per exposure. 4.5 4 No. of Systems 3.5 3 2.5 2 1.5 1 0.5 0 0.02 – 0.04 0.04 – 0.08 mGy/exp 0.08 – 0.1 0.1 – 0.12 1 2 3 4 Figure 12: Digital Acquisition Mode, Patient Entrance Dose per exposure. Image Quality: Image Quality was assessed using the Leeds test objects and published protocols [12-16]. Threshold Contrast results are presented in figure 13. As with figures 2-12, these results are grouped by manufacturer. All of the systems had a measured threshold contrast of less than 4%, but 66% of new systems had a threshold contrast of greater than 2.7% which is the maximum threshold contrast expected for new systems of this type [12-16]. In general, an improvement in image quality was not apparent for the systems operating at higher dose levels. 7
  8. 8. Fluoroscopy - Low Contrast / Noise N3 4 % Threshold Contrast 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Systems 6 (40%) < 2.7% Figure 13: Fluoroscopy Mode – Threshold Contrast Limiting spatial resolution results are presented in figure 14. Fifteen out of the 16 systems has a measured spatial resolution of greater than 1.25 lp/mm which is expected for systems if this type [12-16]. One old system had a resolution lower than 1.25 lp/mm. Fluoroscopy - Spatial Resolution 3 2 Lp / mm 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 System 15 > 1.25 lp/mm Figure 14: Fluoroscopy Mode – Limiting Spatial Resolution 8
  9. 9. Threshold Contrast Detail Detectability curves in the digital acquisition mode are plotted in figure 15. These curves are plotted against the published results of a system in good adjustment [29]. 100 Threshold Detection Index Threshold Detection Index, H (A) T 10 1 1 10 1/2 Square Root Detail Area, A Figure 15: Digital Acquisition Mode – Threshold Contrast Detail Detectability 9
  10. 10. Discussion: From the results presented, it is evident that many interventional cardiac systems offer a wide range of selectable dose rates to the operator. On many systems, the selected mode is not prominently displayed to the operator although the difference in dose delivered from one mode to another may be quite substantial. More recently, an audible alarm has been fitted to some systems to alert the operator when the high fluoroscopy mode is in operation. It is also evident from the results for new and old systems that dose levels are manufacturer dependent. Dose rates were found to be consistently higher for one manufacturer than for another manufacturer (100% more or greater), in both the fluoroscopy and digital acquisition modes. Justification for this in terms of image quality was not evident for the standard range of quality assurance tests [11-29]. Dose levels classified as ‘high’ by one manufacturer were found to be equivalent to those classified as ‘normal’ by another manufacturer. Various faults were found on the systems during acceptance testing. On one system, the ‘normal’ fluoroscopy mode of operation was configured to 12.5pps but configured to 25pps on the equivalent system in the room next door. The default configurations were not consistent across the systems tested with 20% of the systems automatically defaulting to the high mode of operation. Four of the systems tested had no pulsed fluoroscopy option available. Of these, three systems were old systems but the other system was a newly purchased system and although the option had been purchased, there had been a failure to install it. On the vast majority of systems tested, there was no indication of the spectral filter is use. In general, the spectral filters were found to operate under automatic control, without the operator’s knowledge, and on one new system, the filter became jammed out of the beam during commissioning testing. Several issues relating to DAP meters were identified and in general it was found that the DAP meters were not calibrated to the radiology systems in question and account was not taken of the attenuation of X-ray table nor the spectral filtration. On one old system, the irradiated field size was found to be substantially greater than the imaged field size, ranging from 60% to 320% greater depending on the field size selected. In general, it was found that there was a requirement for a more meaningful display to the operator of radiation risk or injury to the patient. In terms of image quality, all systems were found to have a measured threshold contrast of < 4% although 66% of the systems commissioned had a measured threshold contrast of > 2.7% which was higher than would have been expected for new systems of this type. The spatial resolution, visible on the diagnostic monitor, was as expected on all systems with the exception of one old system. No improvement in image quality was detected, using published methodology [12-16], for the systems operating at higher dose levels. The imaged field size was found to be less than 85% of the detector nominal diameter in more than 90% of systems tested. This may be the result of a magnification effect due to the positioning of crash barriers at the detectors. 66% of systems commissioned demonstrated electrical safety faults. 10
  11. 11. Conclusions: The results of this study are consistent with findings from previous commissioning surveys [30]. Problems were identified with all radiological systems commissioned, with approximately 70% of systems demonstrating significant problems. This emphasises the importance of commissioning radiological equipment and interventional cardiac equipment in particular given the associated levels of risk [1-5]. It also demonstrates the importance of including electrical safety testing in a commissioning programme. The findings of this study, particularly in the area of dose and image quality, demonstrate the need for definitive equipment requirements and standardisation in the design, manufacture, acceptance and maintenance of equipment for interventional cardiology. The existing interventional standard IEC60601-2-43, 2000, deals with requirements for the safety of X-ray equipment for interventional procedures [24]. Dedicated interventional equipment for cardiology poses its own unique requirements over and above those of IR equipment in general and warrants consideration to ensure that the particular requirements are well considered and properly reflected in the equipment manufactured. Proposals for updates to international equipment standards have been prepared in order to address the current imbalance between the advancing technology in the area of interventional cardiology and existing standards. Contact has been made with the International Electrotechnical Commission (IEC), the body with responsibility for standards in this area and a formal proposal has been submitted. The proposed additions are most notably in the areas of Dose and Image Quality, for both Image Intensifier and flat panel technology, which are not addressed by the existing standards. It is essential that research keeps pace with developments in digital imaging technology if Quality Assurance efforts are to be properly guided and sufficiently comprehensive, and if equipment related standards are to remain relevant in this rapidly changing environment. This study was partly funded by the European Commissions 5th Framework Programme, Nuclear fission and Radiation Protection Contract, DIMOND III (FIGM-CT-2000-00061). References : [1] EU DIMOND III project proposal, Measures for Optimising Radiological Information Content and Dose in Digital Imaging and Interventional Radiology, 1999. [2] Radiological Society of North America, Categorical Course in Diagnostic Radiology Physics: Cardiac Catheterisation Imaging, 1998. [3] ICRP 85, Avoidance of Radiation Injuries from Medical Interventional Procedures, Vol 30, 2, 2000 [4] Balter S., Interventional fluoroscopy, physics, technology and safety, Wiley-Liss, 2001. [5] Neofotistou V, Vano E, Padovani R, Kotre J, Dowling A et al, Preliminary reference levels in interventional cardiology, European Radiology, Springer-Verlag 2003, 10.1007/s00330-003-1831-x [6] Timmis A, Nathan A, Essentials of Cardiology. Blackwell Scientific Publications, 1993. [7] NRPB, Radiation Exposure to the UK population from Medical and Dental X-ray Examinations, NRPB-W4, D. Hart and B. Wall, 2002. 11
  12. 12. [8] Council Directive 97/43/Euratom on health protection of individuals against the dangers of ionising radiation in relation to medical exposure, 1997. [9] Statutory Instruments SI 478 of 2002, European Communities (Medical Ionising Radiation Protection) Regulations, 2002, Stationery Office, Dublin. [10] Medical Devices Agency, Cardiovascular Imaging Systems, update report, GE Medical Systems Innova 2000, Evaluation Report MDA 01144, 2001. [11] Cardiac Catheterisation Equipment Performance AAPM Report No. 70, 2001. [12] British Institute of Radiology (BIR), Assurance of Quality in the Diagnostic Imaging Department (2nd Edition) (2001). [13] Institute of Physics and Engineering in Medicine (IPEM), Recommended Standards for the Routine Performance Testing of Diagnostic X-ray Imaging Systems, Report No. 77 (1997). [14] Institute of Physics and Engineering in Medicine (IPEM), Measurement of the Performance Characteristics of Diagnostic X-ray Systems used in Medicine, Report No. 32, Second Edition. Part 1: X-ray Tubes and Generators. (1996). [15] IPEM, Measurement of the Performance Characteristics of Diagnostic X-ray Systems used in Medicine, Part II, X-ray Image Intensifier Television Systems, Report no. 32, 2nd Edition 1996. [16] MDA Evaluation Report, The Testing of X-ray Image Intensifier Television Systems: 1998, MDA/98/68. [17] Martin CJ, Sutton, Workman A, Shaw A, Temperton D, Protocol for measurement of patient entrance surface dose rates for fluoroscopic equipment, The British Journal of Radiology, 71, (1998), 1283 – 1287. [18] Institute of Physical Sciences in Medicine (IPSM), Data for Estimating X-ray Tube Total Filtration, Report No. 64. [19] European Commission (EC), Radiation Protection 91, Criteria for Acceptability of Radiological (including radiotherapy) and Nuclear Medicine Installations (Luxembourg: Office for Official Publications of the European Communities) (1997). [20] National Radiological Protection Board (NRPB), National Protocol for Patient Dose Measurements in Diagnostic Radiology, Institute of Physical Sciences in Medicine, (1992). [21] AAPM, Quality Control in Diagnostic Radiology, Report of task group no 12, Diagnostic X-ray Imaging Committee, AAPM report no 74, 2002. [22] NCRP, Quality Assurance for Diagnostic Imaging, report no 99, 1997. [23] IEC 61223-3-1 Evaluation and routine testing in medical imaging departments: Acceptance tests – imaging performance of X-ray equipment for radiographic and radioscopic systems. [24] IEC 60601-2-43 International Standard, Medical Electrical Equipment, Part 2-43 Particular requirements for the safety of X-ray equipment for interventional procedures, 2000. 25 70 60 Patient Entrance DoseDose Rates GroupedManufacturer Patient Entrance Rates - Grouped by Equipment, Part 1: [25] International Electrotechnical Commission (IEC), Medical Electrical by Manufacturer 2050 4 General requirements for safety, 60601-1 (1988). Cont 1540 330 [26] Medical Devices Agency, KCARE, Comparative- Specification of Single Noise N3 Fluoroscopy Low Contrast / Plane Cardiac High 10 20 Systems, Evaluation Report MDA 01034, 2001. 2 0.25 510 [27] International Standard IEC-60580, Medical Electrical Equipment - Dose Area Product Detector Entrance Dose / Exposure Grouped by Manufacturer Lp / mm mGy/min 3 Detector Entrance Dose Rates Grouped by Manufacturer Fluoroscopy - Spatial Resolution mGy/min 1 0 0.2 0 Meters, (IEC 60580:2000(E)). % Threshold Contrast 2 1.4Institute of Physics and 12 13 14 15 16in Medicine (IPEM), Medical and Dental Guidance 1 3 5 7 9 11 13 15 0.15 1 0 2 [28] 4 5 6 7 8 9 10 11 Engineering 3 0.1 1 2 3 4 A Good Practise Guide on 14 15 16 Notes, 5 6 7 8 9 10 11 12 13 all aspects of Ionising Radiation Protection in the Clinical X 1.2 µGy/exposure 1 Environment, (2002). µGy/sec 0.05 0 0 1 [29] Medical Devices Agency, Cardiovascular Imaging Systems, A comparative report, 1 Evaluation Report 8MDA 01143, 13 14 15 16 2 3 4 5 6 7 9 10 11 12 2001. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0.8 Dowling A, Kenny T, Malone J, A Critical Overview of Acceptance Testing using various [30] Measured Indices, Radiation Protection Dosimetry, p53 – 59, Vol 94, 1-2, 2001. 0.6 0.4 0.2 * * 12 Systems System µGy/sec 0 11 13 15 Martin: Low < < 15 mGy/min; Normal 15-30 mGy/min; High 31 – 45 mGy Martin: Low 15 mGy/min; Normal 15-30 mGy/min; High 31 – 45Cont mGy/m 1 3 9 5 7 IPEM: 50 mGy/min; High mGy/min; IAEA: 25 System WHO: 17 mGy/min;> 1.25 IPEM: 50 > 1.5 x; IAEA: 25 System Grouped by Manufacturer Systems WHO: 17 mGy/minRSNA mGy/min; mGy/min, System Detector Entrance Dose Rates 15 (40%) 6 Figure 0.2 High3. System 1 5 3 1.4 1.2 0.8 0.6 0.4 1 0

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