- Email: [email protected]
Reducing Patient Radiation Dose With Image Noise Reduction Technology in Transcatheter Aortic Valve Procedures
Reducing Patient Radiation Dose With Image Noise Reduction Technology in Transcatheter Aortic Valve Procedures Michael Lauterbach, MD, PhD*, and Karl Eugen Hauptmann, MD X-ray radiation exposure is of great concern for patients undergoing structural heart interventions. In addition, a larger group of medical staff is required and exposed to radiation compared with percutaneous coronary interventions. This study aimed at quantifying radiation dose reduction with implementation of specific image noise reduction technology (NRT) in transcatheter aortic valve implantation (TAVI) procedures. We retrospectively analyzed 104 consecutive patients with TAVI procedures, 52 patients before and 52 after optimization of x-ray radiation chain, and implementation of NRT. Patients with 1-step TAVI and complex coronary intervention, or complex TAVI procedures, were excluded. Before the procedure, all patients received a multislice computed tomography scan, which was used to size aortic annulus, select the optimal implantation plane, valve type and size, and guide valve implantation using a software tool. Air kerma and kermaearea product were compared in both groups to determine patient radiation dose reduction. Baseline parameters, co-morbidity, or procedural data were comparable between groups. Mean kermaearea product was significantly lower (p <0.001) in the NRT group compared with the standard group (60 – 39 vs 203 – 106 Gy 3 cm2, p <0.001), which corresponds to a reduction of 70%. Mean air kerma was reduced by 64% (494 – 360 vs 1,355 – 657 mGy, p <0.001). In conclusion, using optimized x-ray chain combined with specific image noise reduction technology has the potential to significantly reduce by 2/3 radiation dose in standard TAVI procedures without worsening image quality or prolonging procedure time. Ó 2016 Elsevier Inc. All rights reserved. (Am J Cardiol 2016;117:834e838) Unlike percutaneous coronary interventions, exposure to radiation in transcatheter aortic valve implantation (TAVI) procedures involves not only patient and operator but also additional personnel taking care of the patient. Furthermore, some of the additional personnel, such as anesthetist, cardiac surgeon, echocardiographer, and nurses, might work in a zone around the x-ray radiation source and cannot be fully protected against radiation exposure by (lead) shielding.1 Current, mandatory, measures to reduce radiation exposure include using state of the art personal protection devices and using radiation in a dose as low as reasonably achievable (the ALARA principle).2,3 However, it would be even better to have a technology that uses less radiation while maintaining or improving image quality. The ClarityIQ imaging technology (Philips Healthcare, Best, The Netherlands) implements an x-ray image acquisition chain optimization with image noise reduction technology (NRT) and helps to reduce radiation exposure while maintaining image quality.4e6 The aim of our study was to research to what extent the implementation of this new technology would reduce Third Medical Clinic, Department of Cardiology, Krankenhaus der Barmherzigen Brüder Trier (a teaching affiliate of the University Medical Center of the Johannes Gutenberg-University Mainz), Trier, Germany. Manuscript received October 23, 2015; revised manuscript received and accepted December 3, 2015. See page 838 for disclosure information. *Corresponding author: Tel: (þ49) 651-208-1774; fax: (þ49) 651-2082876. E-mail address: [email protected] (M. Lauterbach). 0002-9149/15/$ - see front matter Ó 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.amjcard.2015.12.016
radiation exposure under the highly standardized setting of TAVI procedures. Methods We retrospectively analyzed 104 consecutive patients, 52 before and 52 patients after implementation of NRT to our x-ray system. Patients with 1-stage complex percutaneous coronary intervention (bifurcations, >1 vessel involved) and TAVI procedure and patients with complex TAVI procedures (>1 valve) were excluded. Patients who required covered stent implantation into the femoral artery because of insufficient closure of the puncture site despite the use of a closure device were not excluded, although placement of these stents prolonged procedure time and mandated more radiation. Only radiation exposure data from the TAVI procedure itself including 1-stage coronary interventions and femoral artery stenting for closure of TAVI access site were collected for this study. Badge dosimetry from operators was not reported because badges were not exclusively worn during TAVI procedures. Fluoroscopy time, procedure time, air kerma, and kermaearea product (KAP) were recorded. Air kerma represents the energy extracted from an x-ray beam per unit mass of air in a small irradiated air volume.2 KAP is calculated by integration of air kerma across the entire x-ray beam emitted from the x-ray tube. KAP, previously called doseearea product, is a surrogate for the amount of radiation energy delivered to the patient.2 Basic demographic data, transthoracic and transesophageal echocardiography data, information about www.ajconline.org
Valvular Heart Disease/Noise Reduction Technology in TAVI Procedures
coronary artery disease from preprocedural coronary angiograms, and contrast computed tomography (CT) scans were extracted from patient records. Body surface area was calculated using the Dubois formula.7 At our center, a contrast multislice CT scan is routinely made in preparation for TAVI procedures as previously described.8,9 The CT scan is used to plan access route (transfemoral, subclavian, transapical) and to determine vessel size, calcification, and its distribution in main vessels. Furthermore, the CT scan is routinely imported into the HeartNavigator tool (Philips Healthcare, DA Best, The Netherlands, and Andover, Massachusetts). This tool, which was cleared by the US Food and Drug Administration in December 2011, allows for accurate sizing of the aortic annulus, for choosing an optimal implantation plane and for virtual implantation of transcatheter valves of various valve types and sizes. Furthermore, the HeartNavigator combines CT data sets and real-time fluoroscopy imaging and helps to save both, radiation and contrast agent, by providing an overlay projection of the aortic root outline, aortic annulus, and coronary ostia onto the fluoroscopy screen during the procedure. The TAVI program at our center started early in 2010. From the year thereafter, 150 to 180 procedures were carried out annually. All TAVI procedures within this study were carried out by the same operators, who had repeatedly completed full radiation safety training as required by German law. TAVI operators had an experience of >500 successful procedures before beginning of this study. All TAVI procedures were carried out following a standardized local TAVI protocol in all patients with no protocol changes during the study period. During the procedure, 7.5 fps were used for valve implantation and femoral artery stenting and 15 fps for coronary stent procedures. Before implementation of specific NRT, the x-ray system used was a standard monoplane AlluraXper FD20 (Philips Healthcare, Best, The Netherlands). This is referred to as “standard” x-ray system throughout the manuscript. The AlluraXper FD20 was updated with NRT (ClarityIQ; Philips Healthcare) in November 2013. According to information provided by the manufacturer, the Philips Allura Clarity system with ClarityIQ technology consists of a novel x-ray imaging technology that combines noise reduction algorithms with state-of-the-art hardware to enable real-time image processing and to reduce patient entrance dose significantly. This is realized by optimization of the full image-processing chain including grid switch, pulse width, focus spot size, beam filtering, detector, and image processing engine, for every anatomic area and clinical task individually.4e6 Furthermore, the image quality could be improved using a smaller focal spot sizes and enabling shorter pulses. The implementation of a motion compensation algorithm enables alignment of moving objects before averaging and allows to average more consecutive images as compared with traditional temporal noise reduction filters and to reduce radiation dose requirement per frame. Furthermore, a spatial noise reduction algorithm has been developed that takes into account the random nature of noise to distinguish between useful clinical information and noise in a single image. If a pixel is determined as noise, it is averaged with surrounding pixels. Because of the high computational
835
power of the ClarityIQ technology, a larger neighborhood of pixels can be used for averaging compared with traditional spatial noise filters even when working with 30 fps and therefore increasing the likelihood of maintaining the relevant clinical information in the image.4,5 The final step in the ClarityIQ image processing is the image enhancement process that reduces so-called “low-frequency areas” to better compensate overexposed and underexposed image regions and, at the same time, enhance high-frequency edges and contours to sharpen contrast. For the fluoroscopy modes I, II, and III, the maximum patient entrance dose for fluoroscopy was reduced by 50%, 50%, and 10%, respectively. This is the same relative reduction over the entire patient thickness range. For the cine exposures, operators can choose from 3 cine acquisition settings, 50%, 75%, and no patient dose reduction compared with standard, and switch settings anytime during the procedure. As a consequence of the ClarityIQ Image processing, it was possible to increase the additional copper filtration from 0.1 to 0.4 mm independent from patient body mass index. Lower energy photons do not contribute to image quality as they cannot penetrate the patient’s body but add needless, and harmful, radiation dose to the patient. Additional copper filtration reduces these photons and hence patient radiation dose.10,11 To assess image quality, cine sequences from all procedures were shown to interventional cardiologists unaware of the imaging technology used. The interventionalists were asked to assign to the 2 groups all the cine sequences in a blinded fashion. Data in tables are presented as means standard deviation where indicated. Statistical analysis was performed with Sigma Stat (SPSS Science Inc., Chicago, Illinois). The Student t test was used to detect statistical significant differences between groups. For nonparametric values, a ranksum test was applied. Statistical significance was accepted at p <0.05. Results After implementation of the NRT, patient radiation dose could be reduced by at least 2/3 in our patients who underwent TAVI (Figure 1). We did not find a significant loss in imaging quality. Interventional cardiologists shown cine sequences of the procedures, and being unaware of the imaging technology used, identified correctly on average only 50 7% of sequences with NRT and 51 6% of sequences with standard technology. Baseline characteristics of standard and NRT group are summarized in Table 1. Both groups did not differ significantly in age, gender, body weight, body mass index, and body surface area. Creatinine concentration was greater, and hence, GFRepi lower, in the NRT group compared with the standard group, although this did not reach statistical significance. Frailty, New York Heart Association class, and the commonly used risk scores EuroSCORE 2 and Society for Thoracic Surgeons score show a high risk for cardiac surgery in both groups. Patients in the NRT group tended to be sicker; however, there was no statistical significant difference between scores of both groups. When looking at cardiovascular risk factors and relevant co-morbidity, more
836
The American Journal of Cardiology (www.ajconline.org) Table 2 Cardiovascular risk factors, co-morbidity Standard (n¼52) NRT (n¼52) Diabetes Hypertension Coronary artery disease Previous coronary artery bypass grafting Previous valve surgery Atrial fibrillation Chronic obstructive pulmonary disease Prior chest radiation Neurologic dysfunction
24 50 29 5 1 22 15 1 16
(46%) (96%) (55%) (10%) (2%) (42%) (29%) (2%) (31%)
25 51 26 9 2 25 11 6 15
(48%) (98%) (50%) (17%) (4%) (48%) (21%) (12%) (29%)
NRT ¼ noise reduction technology.
Figure 1. (Top) Kinetic energy released in mass (air kerma) in mGy; (Bottom) kermaearea product in Gy cm2; box and whisker plot: box shows first, second, and third percentiles. Whiskers show tenth and ninetieth percentiles. All outliers are plotted. *Statistical significant difference. Table 1 Baseline characteristics Variable
In the study period, more CoreValve (Medtronic CV, Luxembourg Sarl, Luxembourg) were used in both groups compared with SapienXT (Edwards Lifesciences Corporation, Irvine, California) valves (Table 3). In the NRT group, some of the SapienXT were replaced for Lotus valve systems, which might account for the insignificant prolongation of procedure time in the NRT group (Figure 2). Both groups had comparable valve sizes. The preferred access was transfemoral over subclavian and transapical access in both groups. Fluoroscopy time did not differ between standard and NRT group (Figure 2). Mean air kerma was reduced by 64% from 1,355 657 mGy in the standard group to 494 360 mGy in the NRT group (Figure 1, p <0.001). Mean KAP was significantly lower in the NRT group with 60 39 Gy cm2 compared with the standard group with 203 106 Gy cm2 (Figure 1, p <0.001). This corresponds to a mean reduction of total patient radiation dose of 70%. Discussion
Standard (n¼52)
NRT (n¼52)
Mean stdDev
Mean stdDev
80 5 27 (52%) 75 17 165 7 27 5 1.82 0.20 1.24 0.46 54 19 5.8 0.8 3.1 0.6 13.5 7.5 8.2 4.3
80 7 28 (54%) 76 17 168 9 27 5 1.84 0.21 1.42 1.0 50 19 6.1 0.7 3.2 0.5 14.1 8.8 10.7 7.0
34 10
39 14
Age (years) Females body weight (kg) Heigth (cm) Body mass index (kg/m2) Body surface area (m2) Creatinine concentration (mg/dl) GFRepi Clinical frailty scale NYHA functional class Euroscore 2 Society of Thoracic Surgeons’ risk model - mortality (%) Society of Thoracic Surgeons‘ risk model e morbidity & mortality (%) NRT ¼ noise reduction technology.
patients in the NRT group had previous CABG and previous therapeutic chest radiation for cancer as compared with the standard group (Table 2).
Noise reduction technology significantly reduced radiation exposure in TAVI procedures as compared with standard x-ray chain technology. We chose to research dose reduction using image noise reduction technology in the setting of TAVI procedures because patient radiation exposure is usually greater compared with percutaneous coronary intervention (PCI), and a larger group of medical personnel is exposed to radiation compared with PCI.1 In transapical procedures, there are data showing that less radiation is required compared with transfemoral procedures.12 However, cardiac surgeon and surgical assistant are in close proximity to the radiation source and receive considerable doses of radiation annually.1 Hence, it is of utmost importance not only to optimize shielding from radiation, which can only be done to a certain extent, but also to minimize patient entrance dose, in addition to applying the ALARA principle.2,3 A further reason to research radiation dose reduction in TAVI procedures is the high level of standardization of the procedure, which allows for easier comparison. Standardization can be achieved by accurate planning of the procedure, standardized procedural steps, and reduced interoperator variability in TAVI procedures as compared with coronary interventions. To enhance standardization, we routinely use the HeartNavigator tool, which requires being
Valvular Heart Disease/Noise Reduction Technology in TAVI Procedures Table 3 Procedural data
Valve type Sapien XT Corevalve DirectFlow Lotus Valve System Valve size, mm, mean StdDev Access route transfemoral transaxillaris transapical Coronary stenting þ TAVI Femoral artery stenting, covered stent
Standard (n¼52)
NRT (n¼52)
21 (40%) 30 (58%) 1 (2%) 0 (0%) 28 3
16 (31%) 30 (57%) 1 (2%) 5 (10%) 28 2
41 6 5 7 15
41 7 4 3 16
(79%) (12%) (10%) (14%) (37%*)
(79%) (14%) (8%) (6%) (39%*)
NRT ¼ noise reduction technology. * Percentage of patients with femoral stenting of patients with transfemoral access.
Figure 2. (Top) Procedure time in minutes; (Bottom) total fluoroscopy time in minutes; box and whisker plot: box shows first, second, and third percentiles. Whiskers show tenth and ninetieth percentiles. All outliers are plotted.
fed with multislice contrast CT scan data sets of the heart. Although the CT scan itself requires contrast agent and radiation, even when using ultralow-contrast multislice CT scan,13 the software tool helps to save contrast agent and radiation during the TAVI procedure.8 In every
837
patient, we use the tool to size the aortic annulus, choose an optimal implantation plane, and carry out virtual implantations of available TAVI types in different sizes. In our experience, with the tool, we save more on procedure time than we spend time with the tool, preparing the procedure. We do 1-stage TAVI procedures and PCI, albeit knowing that this might increase radiation exposure. There are conflicting reports as to whether this approach is safe for the patient, independent of additional radiation exposure.14,15 We did not experience any difficulties with the 1-stage approach but try to avoid combining complex PCI and TAVI procedures. In our study, more patients in the standard group had PCI compared with the NRT group. In preparation of TAVI at our center, all patients underwent coronary angiography with which 1-stage PCI and TAVI was planned. This allowed us to minimize radiation exposure while performing PCI with TAVI. The insignificantly longer fluoroscopy time in the standard group might be explained with the greater number of patients with PCI in the standard group. However, although quantification of the exact radiation dose added with stenting in our patients is difficult, the additive effect of PCI to the total radiation dose is probably minimal. Adding a new valve type (Lotus valve system, Boston Scientific) to the portfolio usually prolongs procedure time and radiation exposure, until a plateau of the learning curve has been reached. However, although we added this valve system and had prolonged mean procedure time in the NRT group, radiation exposure remained significantly lower compared with the standard group. All TAVI procedures within this study were carried out by the same operators. TAVI procedures at our center started in 2010. The annual TAVI volume is 150 to 180 procedures, and our TAVI operators have had an experience of >500 procedures before patient entry into this study. This does not eliminate but partially overcome the potential confounding influence of a learning curve of the operators with the consecutive recruitment of study groups. It would have been better to compare using NRT in a randomized fashion; however, the implementation of NRT requires a complete revision of hardware and software of the x-ray chain and cannot be easily removed. In addition to the potential bias of the operators being aware that a new technology was implemented, the study is further limited by its retrospective character. One further limitation of the study is that although the dosimetry chamber of the x-ray system was not changed with the implementation of NRT, tolerance for 100 mGy of air kerma and >2.5 Gy cm2 of KAP is 35% according to information provided by the manufacturer. Hence, although this tolerance is common among -ray system of different manufacturers, comparability of absolute values of patient radiation dose from different x-ray systems is impaired. To our knowledge, this is the first study showing a significant reduction of patient radiation dose with the use of specific NRT in TAVI procedures. The same radiationsaving technology has proven to effectively reduce radiation exposure in the field of neuroangiography and interventional neuroradiology4,5 and in pediatric and adult patients treated for congenital heart disease.16,17
838
The American Journal of Cardiology (www.ajconline.org)
Acknowledgment: The authors thank Dr. Peter Belei, Advanced Clinical ApplicationseIGT Systems, Philips GmbH, Germany, for help with technical information about the AlluraXper ClarityIQ system and valuable comments. Disclosures The authors have no conflicts of interest to report. 1. Drews T, Pasic M, Juran R, Unbehaun A, Dreysse S, Kukucka M, Mladenow A, Hetzer R, Buz S. Safety considerations during transapical aortic valve implantation. Interact Cardiovasc Thorac Surg 2014;18: 574e579. 2. Stecker MS, Balter S, Towbin RB, Miller DL, Vañó E, Bartal G, Angle JF, Chao CP, Cohen AM, Dixon RG, Gross K, Hartnell GG, Schueler B, Statler JD, de Baère T, Cardella JF; SIR Safety and Health Committee; CIRSE Standards of Practice Committee. Guidelines for patient radiation dose management. J Vasc Interv Radiol 2009;20:S263eS273. 3. Chambers CE, Fetterly KA, Holzer R, Lin P-JP, Blankenship JC, Balter S, Laskey WK. Radiation safety program for the cardiac catheterization laboratory. Catheter Cardiovasc Interv 2011;77:546e556. 4. Söderman M, Holmin S, Andersson T, Palmgren C, Babic D, Hoornaert B. Image noise reduction algorithm for digital subtraction angiography: clinical results. Radiology 2013;269:553e560. 5. Söderman M, Mauti M, Boon S, Omar A, Marteinsdóttir M, Andersson T, Holmin S, Hoornaert B. Radiation dose in neuroangiography using image noise reduction technology: a population study based on 614 patients. Neuroradiology 2013;55:1365e1372. 6. van Strijen MJ, Grünhagen T, Mauti M, Zähringer M, Gaines PA, Robinson GJ, Railton NJ, van Overhagen H, Habraken J, van Leersum M. Evaluation of a noise reduction imaging technology in iliac digital subtraction angiography: noninferior clinical image quality with lower patient and scatter dose. J Vasc Interv Radiol 2015;26:642e650; e1. 7. Dubois D, Dubois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med 1916;17: 863e871.
8. Lauterbach M, Sontag B, Hauptmann KE. Transcatheter aortic valve implantation in the hybrid catheterisation laboratory—navigating into the future. Interv Cardiol 2012;7:53e58. 9. Lauterbach M, Hauptmann KE. Treating severe aortic valve regurgitation with TAVI. Exp Clin Cardiol 2014;20:5494e5499. 10. Fetterly KA. Investigation of the practical aspects of an additional 0.1 mm copper x-ray spectral filter for cine acquisition mode imaging in a clinical care setting. Health Phys 2010;99:624e630. 11. Bacher K, Bogaert E, Lapere R, De Wolf D, Thierens H. Patientspecific dose and radiation risk estimation in pediatric cardiac catheterization. Circulation 2005;111:83e89. 12. Hartrumpf M, Erb M, Zytowski M, Kuehnel R-U, Aigner S, Butter C, Albes J. Radiation exposure and contrast volume differ between transapical and transfemoral aortic valve implantation with the Edwards SAPIEN aortic valve. Thorac Cardiovasc Surg 2015;63: 479e486. 13. Spagnolo P, Giglio M, Di Marco D, Latib A, Besana F, Chieffo A, Montorfano M, Sironi S, Alfieri O, Colombo A. Feasibility of ultra-low contrast 64-slice computed tomography angiography before transcatheter aortic valve implantation: a real-world experience. Eur Heart J Cardiovasc Imaging 2016;17:24e33. 14. Penkalla A, Pasic M, Drews T, Buz S, Dreysse S, Kukucka M, Mladenow A, Hetzer R, Unbehaun A. Transcatheter aortic valve implantation combined with elective coronary artery stenting: a simultaneous approach†. Eur J Cardiothorac Surg 2015;47:1083e1089. 15. Griese DP, Reents W, Tóth A, Kerber S, Diegeler A, Babin-Ebell J. Concomitant coronary intervention is associated with poorer early and late clinical outcomes in selected elderly patients receiving transcatheter aortic valve implantation. Eur J Cardiothorac Surg 2014;46: e1e7. 16. Haas NA, Happel CM, Mauti M, Sahyoun C, Kececioglu D, Laser KT. Substantial radiation reduction in pediatric and adult congenital heart disease interventions with a novel X-ray imaging technology. Int J Cardiol 2015;6:101e109. 17. Schernthaner RE, Duran R, Chapiro J, Wang Z, Geschwind JF, Lin M. A new angiographic imaging platform reduces radiation exposure for patients with liver cancer treated with transarterial chemoembolization. Eur Radiol 2015;25:3255e3262.
radiation exposure under the highly standardized setting of TAVI procedures. Methods We retrospectively analyzed 104 consecutive patients, 52 before and 52 patients after implementation of NRT to our x-ray system. Patients with 1-stage complex percutaneous coronary intervention (bifurcations, >1 vessel involved) and TAVI procedure and patients with complex TAVI procedures (>1 valve) were excluded. Patients who required covered stent implantation into the femoral artery because of insufficient closure of the puncture site despite the use of a closure device were not excluded, although placement of these stents prolonged procedure time and mandated more radiation. Only radiation exposure data from the TAVI procedure itself including 1-stage coronary interventions and femoral artery stenting for closure of TAVI access site were collected for this study. Badge dosimetry from operators was not reported because badges were not exclusively worn during TAVI procedures. Fluoroscopy time, procedure time, air kerma, and kermaearea product (KAP) were recorded. Air kerma represents the energy extracted from an x-ray beam per unit mass of air in a small irradiated air volume.2 KAP is calculated by integration of air kerma across the entire x-ray beam emitted from the x-ray tube. KAP, previously called doseearea product, is a surrogate for the amount of radiation energy delivered to the patient.2 Basic demographic data, transthoracic and transesophageal echocardiography data, information about www.ajconline.org
Valvular Heart Disease/Noise Reduction Technology in TAVI Procedures
coronary artery disease from preprocedural coronary angiograms, and contrast computed tomography (CT) scans were extracted from patient records. Body surface area was calculated using the Dubois formula.7 At our center, a contrast multislice CT scan is routinely made in preparation for TAVI procedures as previously described.8,9 The CT scan is used to plan access route (transfemoral, subclavian, transapical) and to determine vessel size, calcification, and its distribution in main vessels. Furthermore, the CT scan is routinely imported into the HeartNavigator tool (Philips Healthcare, DA Best, The Netherlands, and Andover, Massachusetts). This tool, which was cleared by the US Food and Drug Administration in December 2011, allows for accurate sizing of the aortic annulus, for choosing an optimal implantation plane and for virtual implantation of transcatheter valves of various valve types and sizes. Furthermore, the HeartNavigator combines CT data sets and real-time fluoroscopy imaging and helps to save both, radiation and contrast agent, by providing an overlay projection of the aortic root outline, aortic annulus, and coronary ostia onto the fluoroscopy screen during the procedure. The TAVI program at our center started early in 2010. From the year thereafter, 150 to 180 procedures were carried out annually. All TAVI procedures within this study were carried out by the same operators, who had repeatedly completed full radiation safety training as required by German law. TAVI operators had an experience of >500 successful procedures before beginning of this study. All TAVI procedures were carried out following a standardized local TAVI protocol in all patients with no protocol changes during the study period. During the procedure, 7.5 fps were used for valve implantation and femoral artery stenting and 15 fps for coronary stent procedures. Before implementation of specific NRT, the x-ray system used was a standard monoplane AlluraXper FD20 (Philips Healthcare, Best, The Netherlands). This is referred to as “standard” x-ray system throughout the manuscript. The AlluraXper FD20 was updated with NRT (ClarityIQ; Philips Healthcare) in November 2013. According to information provided by the manufacturer, the Philips Allura Clarity system with ClarityIQ technology consists of a novel x-ray imaging technology that combines noise reduction algorithms with state-of-the-art hardware to enable real-time image processing and to reduce patient entrance dose significantly. This is realized by optimization of the full image-processing chain including grid switch, pulse width, focus spot size, beam filtering, detector, and image processing engine, for every anatomic area and clinical task individually.4e6 Furthermore, the image quality could be improved using a smaller focal spot sizes and enabling shorter pulses. The implementation of a motion compensation algorithm enables alignment of moving objects before averaging and allows to average more consecutive images as compared with traditional temporal noise reduction filters and to reduce radiation dose requirement per frame. Furthermore, a spatial noise reduction algorithm has been developed that takes into account the random nature of noise to distinguish between useful clinical information and noise in a single image. If a pixel is determined as noise, it is averaged with surrounding pixels. Because of the high computational
835
power of the ClarityIQ technology, a larger neighborhood of pixels can be used for averaging compared with traditional spatial noise filters even when working with 30 fps and therefore increasing the likelihood of maintaining the relevant clinical information in the image.4,5 The final step in the ClarityIQ image processing is the image enhancement process that reduces so-called “low-frequency areas” to better compensate overexposed and underexposed image regions and, at the same time, enhance high-frequency edges and contours to sharpen contrast. For the fluoroscopy modes I, II, and III, the maximum patient entrance dose for fluoroscopy was reduced by 50%, 50%, and 10%, respectively. This is the same relative reduction over the entire patient thickness range. For the cine exposures, operators can choose from 3 cine acquisition settings, 50%, 75%, and no patient dose reduction compared with standard, and switch settings anytime during the procedure. As a consequence of the ClarityIQ Image processing, it was possible to increase the additional copper filtration from 0.1 to 0.4 mm independent from patient body mass index. Lower energy photons do not contribute to image quality as they cannot penetrate the patient’s body but add needless, and harmful, radiation dose to the patient. Additional copper filtration reduces these photons and hence patient radiation dose.10,11 To assess image quality, cine sequences from all procedures were shown to interventional cardiologists unaware of the imaging technology used. The interventionalists were asked to assign to the 2 groups all the cine sequences in a blinded fashion. Data in tables are presented as means standard deviation where indicated. Statistical analysis was performed with Sigma Stat (SPSS Science Inc., Chicago, Illinois). The Student t test was used to detect statistical significant differences between groups. For nonparametric values, a ranksum test was applied. Statistical significance was accepted at p <0.05. Results After implementation of the NRT, patient radiation dose could be reduced by at least 2/3 in our patients who underwent TAVI (Figure 1). We did not find a significant loss in imaging quality. Interventional cardiologists shown cine sequences of the procedures, and being unaware of the imaging technology used, identified correctly on average only 50 7% of sequences with NRT and 51 6% of sequences with standard technology. Baseline characteristics of standard and NRT group are summarized in Table 1. Both groups did not differ significantly in age, gender, body weight, body mass index, and body surface area. Creatinine concentration was greater, and hence, GFRepi lower, in the NRT group compared with the standard group, although this did not reach statistical significance. Frailty, New York Heart Association class, and the commonly used risk scores EuroSCORE 2 and Society for Thoracic Surgeons score show a high risk for cardiac surgery in both groups. Patients in the NRT group tended to be sicker; however, there was no statistical significant difference between scores of both groups. When looking at cardiovascular risk factors and relevant co-morbidity, more
836
The American Journal of Cardiology (www.ajconline.org) Table 2 Cardiovascular risk factors, co-morbidity Standard (n¼52) NRT (n¼52) Diabetes Hypertension Coronary artery disease Previous coronary artery bypass grafting Previous valve surgery Atrial fibrillation Chronic obstructive pulmonary disease Prior chest radiation Neurologic dysfunction
24 50 29 5 1 22 15 1 16
(46%) (96%) (55%) (10%) (2%) (42%) (29%) (2%) (31%)
25 51 26 9 2 25 11 6 15
(48%) (98%) (50%) (17%) (4%) (48%) (21%) (12%) (29%)
NRT ¼ noise reduction technology.
Figure 1. (Top) Kinetic energy released in mass (air kerma) in mGy; (Bottom) kermaearea product in Gy cm2; box and whisker plot: box shows first, second, and third percentiles. Whiskers show tenth and ninetieth percentiles. All outliers are plotted. *Statistical significant difference. Table 1 Baseline characteristics Variable
In the study period, more CoreValve (Medtronic CV, Luxembourg Sarl, Luxembourg) were used in both groups compared with SapienXT (Edwards Lifesciences Corporation, Irvine, California) valves (Table 3). In the NRT group, some of the SapienXT were replaced for Lotus valve systems, which might account for the insignificant prolongation of procedure time in the NRT group (Figure 2). Both groups had comparable valve sizes. The preferred access was transfemoral over subclavian and transapical access in both groups. Fluoroscopy time did not differ between standard and NRT group (Figure 2). Mean air kerma was reduced by 64% from 1,355 657 mGy in the standard group to 494 360 mGy in the NRT group (Figure 1, p <0.001). Mean KAP was significantly lower in the NRT group with 60 39 Gy cm2 compared with the standard group with 203 106 Gy cm2 (Figure 1, p <0.001). This corresponds to a mean reduction of total patient radiation dose of 70%. Discussion
Standard (n¼52)
NRT (n¼52)
Mean stdDev
Mean stdDev
80 5 27 (52%) 75 17 165 7 27 5 1.82 0.20 1.24 0.46 54 19 5.8 0.8 3.1 0.6 13.5 7.5 8.2 4.3
80 7 28 (54%) 76 17 168 9 27 5 1.84 0.21 1.42 1.0 50 19 6.1 0.7 3.2 0.5 14.1 8.8 10.7 7.0
34 10
39 14
Age (years) Females body weight (kg) Heigth (cm) Body mass index (kg/m2) Body surface area (m2) Creatinine concentration (mg/dl) GFRepi Clinical frailty scale NYHA functional class Euroscore 2 Society of Thoracic Surgeons’ risk model - mortality (%) Society of Thoracic Surgeons‘ risk model e morbidity & mortality (%) NRT ¼ noise reduction technology.
patients in the NRT group had previous CABG and previous therapeutic chest radiation for cancer as compared with the standard group (Table 2).
Noise reduction technology significantly reduced radiation exposure in TAVI procedures as compared with standard x-ray chain technology. We chose to research dose reduction using image noise reduction technology in the setting of TAVI procedures because patient radiation exposure is usually greater compared with percutaneous coronary intervention (PCI), and a larger group of medical personnel is exposed to radiation compared with PCI.1 In transapical procedures, there are data showing that less radiation is required compared with transfemoral procedures.12 However, cardiac surgeon and surgical assistant are in close proximity to the radiation source and receive considerable doses of radiation annually.1 Hence, it is of utmost importance not only to optimize shielding from radiation, which can only be done to a certain extent, but also to minimize patient entrance dose, in addition to applying the ALARA principle.2,3 A further reason to research radiation dose reduction in TAVI procedures is the high level of standardization of the procedure, which allows for easier comparison. Standardization can be achieved by accurate planning of the procedure, standardized procedural steps, and reduced interoperator variability in TAVI procedures as compared with coronary interventions. To enhance standardization, we routinely use the HeartNavigator tool, which requires being
Valvular Heart Disease/Noise Reduction Technology in TAVI Procedures Table 3 Procedural data
Valve type Sapien XT Corevalve DirectFlow Lotus Valve System Valve size, mm, mean StdDev Access route transfemoral transaxillaris transapical Coronary stenting þ TAVI Femoral artery stenting, covered stent
Standard (n¼52)
NRT (n¼52)
21 (40%) 30 (58%) 1 (2%) 0 (0%) 28 3
16 (31%) 30 (57%) 1 (2%) 5 (10%) 28 2
41 6 5 7 15
41 7 4 3 16
(79%) (12%) (10%) (14%) (37%*)
(79%) (14%) (8%) (6%) (39%*)
NRT ¼ noise reduction technology. * Percentage of patients with femoral stenting of patients with transfemoral access.
Figure 2. (Top) Procedure time in minutes; (Bottom) total fluoroscopy time in minutes; box and whisker plot: box shows first, second, and third percentiles. Whiskers show tenth and ninetieth percentiles. All outliers are plotted.
fed with multislice contrast CT scan data sets of the heart. Although the CT scan itself requires contrast agent and radiation, even when using ultralow-contrast multislice CT scan,13 the software tool helps to save contrast agent and radiation during the TAVI procedure.8 In every
837
patient, we use the tool to size the aortic annulus, choose an optimal implantation plane, and carry out virtual implantations of available TAVI types in different sizes. In our experience, with the tool, we save more on procedure time than we spend time with the tool, preparing the procedure. We do 1-stage TAVI procedures and PCI, albeit knowing that this might increase radiation exposure. There are conflicting reports as to whether this approach is safe for the patient, independent of additional radiation exposure.14,15 We did not experience any difficulties with the 1-stage approach but try to avoid combining complex PCI and TAVI procedures. In our study, more patients in the standard group had PCI compared with the NRT group. In preparation of TAVI at our center, all patients underwent coronary angiography with which 1-stage PCI and TAVI was planned. This allowed us to minimize radiation exposure while performing PCI with TAVI. The insignificantly longer fluoroscopy time in the standard group might be explained with the greater number of patients with PCI in the standard group. However, although quantification of the exact radiation dose added with stenting in our patients is difficult, the additive effect of PCI to the total radiation dose is probably minimal. Adding a new valve type (Lotus valve system, Boston Scientific) to the portfolio usually prolongs procedure time and radiation exposure, until a plateau of the learning curve has been reached. However, although we added this valve system and had prolonged mean procedure time in the NRT group, radiation exposure remained significantly lower compared with the standard group. All TAVI procedures within this study were carried out by the same operators. TAVI procedures at our center started in 2010. The annual TAVI volume is 150 to 180 procedures, and our TAVI operators have had an experience of >500 procedures before patient entry into this study. This does not eliminate but partially overcome the potential confounding influence of a learning curve of the operators with the consecutive recruitment of study groups. It would have been better to compare using NRT in a randomized fashion; however, the implementation of NRT requires a complete revision of hardware and software of the x-ray chain and cannot be easily removed. In addition to the potential bias of the operators being aware that a new technology was implemented, the study is further limited by its retrospective character. One further limitation of the study is that although the dosimetry chamber of the x-ray system was not changed with the implementation of NRT, tolerance for 100 mGy of air kerma and >2.5 Gy cm2 of KAP is 35% according to information provided by the manufacturer. Hence, although this tolerance is common among -ray system of different manufacturers, comparability of absolute values of patient radiation dose from different x-ray systems is impaired. To our knowledge, this is the first study showing a significant reduction of patient radiation dose with the use of specific NRT in TAVI procedures. The same radiationsaving technology has proven to effectively reduce radiation exposure in the field of neuroangiography and interventional neuroradiology4,5 and in pediatric and adult patients treated for congenital heart disease.16,17
838
The American Journal of Cardiology (www.ajconline.org)
Acknowledgment: The authors thank Dr. Peter Belei, Advanced Clinical ApplicationseIGT Systems, Philips GmbH, Germany, for help with technical information about the AlluraXper ClarityIQ system and valuable comments. Disclosures The authors have no conflicts of interest to report. 1. Drews T, Pasic M, Juran R, Unbehaun A, Dreysse S, Kukucka M, Mladenow A, Hetzer R, Buz S. Safety considerations during transapical aortic valve implantation. Interact Cardiovasc Thorac Surg 2014;18: 574e579. 2. Stecker MS, Balter S, Towbin RB, Miller DL, Vañó E, Bartal G, Angle JF, Chao CP, Cohen AM, Dixon RG, Gross K, Hartnell GG, Schueler B, Statler JD, de Baère T, Cardella JF; SIR Safety and Health Committee; CIRSE Standards of Practice Committee. Guidelines for patient radiation dose management. J Vasc Interv Radiol 2009;20:S263eS273. 3. Chambers CE, Fetterly KA, Holzer R, Lin P-JP, Blankenship JC, Balter S, Laskey WK. Radiation safety program for the cardiac catheterization laboratory. Catheter Cardiovasc Interv 2011;77:546e556. 4. Söderman M, Holmin S, Andersson T, Palmgren C, Babic D, Hoornaert B. Image noise reduction algorithm for digital subtraction angiography: clinical results. Radiology 2013;269:553e560. 5. Söderman M, Mauti M, Boon S, Omar A, Marteinsdóttir M, Andersson T, Holmin S, Hoornaert B. Radiation dose in neuroangiography using image noise reduction technology: a population study based on 614 patients. Neuroradiology 2013;55:1365e1372. 6. van Strijen MJ, Grünhagen T, Mauti M, Zähringer M, Gaines PA, Robinson GJ, Railton NJ, van Overhagen H, Habraken J, van Leersum M. Evaluation of a noise reduction imaging technology in iliac digital subtraction angiography: noninferior clinical image quality with lower patient and scatter dose. J Vasc Interv Radiol 2015;26:642e650; e1. 7. Dubois D, Dubois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med 1916;17: 863e871.
8. Lauterbach M, Sontag B, Hauptmann KE. Transcatheter aortic valve implantation in the hybrid catheterisation laboratory—navigating into the future. Interv Cardiol 2012;7:53e58. 9. Lauterbach M, Hauptmann KE. Treating severe aortic valve regurgitation with TAVI. Exp Clin Cardiol 2014;20:5494e5499. 10. Fetterly KA. Investigation of the practical aspects of an additional 0.1 mm copper x-ray spectral filter for cine acquisition mode imaging in a clinical care setting. Health Phys 2010;99:624e630. 11. Bacher K, Bogaert E, Lapere R, De Wolf D, Thierens H. Patientspecific dose and radiation risk estimation in pediatric cardiac catheterization. Circulation 2005;111:83e89. 12. Hartrumpf M, Erb M, Zytowski M, Kuehnel R-U, Aigner S, Butter C, Albes J. Radiation exposure and contrast volume differ between transapical and transfemoral aortic valve implantation with the Edwards SAPIEN aortic valve. Thorac Cardiovasc Surg 2015;63: 479e486. 13. Spagnolo P, Giglio M, Di Marco D, Latib A, Besana F, Chieffo A, Montorfano M, Sironi S, Alfieri O, Colombo A. Feasibility of ultra-low contrast 64-slice computed tomography angiography before transcatheter aortic valve implantation: a real-world experience. Eur Heart J Cardiovasc Imaging 2016;17:24e33. 14. Penkalla A, Pasic M, Drews T, Buz S, Dreysse S, Kukucka M, Mladenow A, Hetzer R, Unbehaun A. Transcatheter aortic valve implantation combined with elective coronary artery stenting: a simultaneous approach†. Eur J Cardiothorac Surg 2015;47:1083e1089. 15. Griese DP, Reents W, Tóth A, Kerber S, Diegeler A, Babin-Ebell J. Concomitant coronary intervention is associated with poorer early and late clinical outcomes in selected elderly patients receiving transcatheter aortic valve implantation. Eur J Cardiothorac Surg 2014;46: e1e7. 16. Haas NA, Happel CM, Mauti M, Sahyoun C, Kececioglu D, Laser KT. Substantial radiation reduction in pediatric and adult congenital heart disease interventions with a novel X-ray imaging technology. Int J Cardiol 2015;6:101e109. 17. Schernthaner RE, Duran R, Chapiro J, Wang Z, Geschwind JF, Lin M. A new angiographic imaging platform reduces radiation exposure for patients with liver cancer treated with transarterial chemoembolization. Eur Radiol 2015;25:3255e3262.