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Quality of computed tomography -- from image acquisition to dose, concept, myth and definition

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  • Save American Journal of Biomedical Engineer ing 2013, 3(6A): 15-21 DOI: 10.5923/s.ajbe.201310.03 Quality in Computorized Tomography – From Image Acquisition to Dose, Concepts, Myths and Definitions António Fernando Lagem Abrantes1, Luís Pedro Vieira Ribeiro2,*, Rui Pedro Pereira Almeida3, João Pe dro Pinhe iro4, Kevin Barros Azeve do5, Carlos Albe rto da Silva6 1PhD, M ember of the Research Center of Sociologic Studies of Lisbon´s Nova University (Cesnova), Professor and M ember of the Center for Health Studies (CES) of Algarve´s University Health School (ESSUAlg), Dir ector of the Radiology Department and professor at ESSUAlg, Algarve, Portugal 2PhD, M ember of the Research Center of Sports and Physical Activity (CIDAF) of Coimbra University, Professor and M ember of the Center for Health Studies (CES) of Algarve´s University Health School (ESSUAlg), Algarve, Portugal 3Post-graduate, M ember of the Center for Health Studies (CES), PhD Student at Beira Interior University, Professor and M ember of the Center for Health Studies (CES) of Algarve´s University Health School (ESSUAlg), Algarve, Portugal 4Post-graduate, M Sc student at the National Public Health School, Professor of the Radiology Department at Algarve´s University Health School ( ESSUAlg), Algarve, Portugal 5Post-graduate, M ember of the Center for Health Studies (CES), PhD Student at Cranfield University, Professor of the Radiology Department at Algarve´s University Health School (ESSUAlg), Algarve, Portugal 6PhD, M ember of the Research Center of Sociologic Studies of Lisbon´s Nova University (Cesnova), Professor and Director of the School of Social Sciences of Évora´s University Abstract W ith this review art icle, we intend to demonstrate the importance of Co mputerized To mography (CT) in healthcare quality and safety. The concept of safety in CT is wider than for general healthcare. Safe healthcare provided using CT must include d iagnostic image quality and reliab ility, as this is the only way to ensure diagnostic accuracy. The images must be acquired with the most adequate protocols available and with the lowest achievable radiation dose. In this article we will focus primarily on the concepts of dose, since this variable strongly affects the image quality and the consequent diagnostic accuracy. In methodological terms, 73 papers and 6 catalogues issued by the manufacturers of CT equip ment, that included the key words lo w dose, ultra-lo w dose and dose reduction were analysed. After rev iew of these articles we found that about 82% are chest exams, namely the lungs. The remaining were subdivided main ly by studies of the sinuses, heart and bone segments. After this review we selected the only 10 articles that present the keywords and simultaneously quantify the dose reduction. Given the lack of precision associated with these terms, introduced mainly by co mmercial catalogues of different equip ment brands, we intend to demonstrate that the concepts low dose and ultra-lo w dose are wrapped in unclear market ing strategies, without a strict and unambiguous definition of what is the effective dose. We propose that these concepts should be clearly defined and a precise indication of the effective dose reduction value should be compared to the default value (standard diagnostic dose) by exam region. Therefore, it is demonstrated that there is no concrete definition of what lo w dose or u ltra-low dose are. These slogans cannot be used until they are not holistically defined, as well as the correspondent dose reduction value. Keywords Dose, Lo w-Dose, Ult ra-Low-Dose, Co mputed Tomography, Image Quality 1. Introduction The preoccupation of healthcare institutions about quality, as led to a p rogressive imp lementation of management systems and procedures focused on achieving higher quality standards. A healthcare quality service is one that proves able to meet custo mer expectat ions [1]. In health care, quality intends to be a possible target of measurement and * Corresponding author: (Luís Pedro Vieira Ribeiro) Published online at Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved not just a defin ition of good. It is more of an ongoing effort to improve, than a degree of pre-defined excellence. In relation to healthcare services, there were major changes in recent years. The increasing demand, particularly in the case of CT, meant that radiology departments had to invest effectively in their quality and not focus only on the quality of image acquisition and interpretation. This "holistic department quality" gives greater relevance to the mood and atmosphere perceived by the patient, than to the processes within the department. This concept of quality can be perverse when analyzed by the actual competit ive perspective, especially focused in increasing profits through increasing the number of exams, the volu me size of the 16 António Fernando Lagem Abrantes et al.: Quality in Computorized Tomography – From Image Acquisition to Dose, Concepts, Myths and Definitions acquisition or the reduction of collimat ion, since these are the factors that most influence negatively the dose in CT. When we discuss radiology, especially CT, we are referring to a diagnostic tool that is responsible for much of the artificial irradiat ion of populations. CT corresponds to about 25% o f the annual average exposure in the U.S. (2006) and 50% of the exposure in terms of med ical exams[2]. For this reason, CT is subject to strict monitoring of rad iological protection, existing leg islation to limit and reduce dose levels resulting fro m CT examinat ions[3]. Surveillance and safety measures, as well as the diagnostic reference levels (DRL´s), relate to amounts of radiation by examination or procedure. However, the introduction of concepts such as ultra-low-dose and low-dose are abstract and turn out to be purely qualitative, serving above all, in most cases, as market ing strategies. Such concepts do not effectively materialize the quantitative aspects of rad iological exposure, fundamental to account for irradiat ion and absorbed dose. After reviewing 73 articles that address the concepts of reduction in dose, low dose and ultra-low dose, only 4 of them (Ne roladaki et a l[4], Bacher et al[5], Schuncke et a l[6] and Bulla et al[7], although differing between them, point in fact an effective value of dose reduction. In this context and according to the available literature, some questions remain unanswered as we move forward. So what are we talking about when we refer to procedures, tests and equipment using ultra low-dose or low-dose? A CT equip ment built under the concept of low-dose; uses this feature on all procedures or just part of them? What is the difference between low-dose and ultra-low dose? What measurable values (CTDI vol and DLP) are we talking about? 2. Methods The present study is a literature review. The research criteria established were the use of peer review papers and catalogues of CT equipment, published since January 2000. The research was guided by the following terms: Dose Reduction, Low Dose and Ultra Lo w Dose. After analysing the 73 docu ments defined above, we selected the ones that mention exp licitly, in absolute or percentage value, the level of dose reduction associated to the equipment, reconstruction algorithms or protocols used in the exam. 3. Computerised Tomography – Image Quality, Acquisition and Dose In a way, radiology strongly reflects the technical, economic develop ment and train ing policies of a country. These in turn are determined by the political environ ment, socio-economic status and level of urban and rural development of each country[8]. However, countries with more and better CT equip ment have higher average levels of exposure, due to the greater number of examinations performed[9]. Presently, ionizing radiat ion fro m CT is the largest source of medical exposure per capita in industrialized countries (Fig. 1)[10; 11]. Figure 1. Distribution and development of annual per capita dose in mSv to the population from 1980 to 2006 in the USA as an example for the development in industrialized countries According to the Organizat ion for Economic Co-operation and Development (OECD), the average number of CT equipment in 23 countries of the European Union was 20.4 per million people in 2010. In Portugal this figure was 27, 4. In the Portuguese case, 15.6 CT equip ment are installed outside hospitals (i.e. private pract ice clin ics)[8]. The relative contribution of CT to dose resulting from medical examinations has increased proportionally. In 1994 in Germany, a study showed that although CT scans accounted for only 5% of all radiological examinations performed, its contribution to the total dose was approximately 35 to 40%[3]. In 1999, in the U.S., CT scans corresponded to 11.1%, with a contribution of 67% to the total dose[9]. In another study conducted in 2006 in the U.S. population, the annual average exposure dose was 6 mSv per capita, where natural sources contributed with 3 mSv and medical examinations with the remaining 3 mSv (1.5 mSv fro m CT exams )[2]. The issues of radiological protection and the contribution of CT equip ment for the irrad iation of populations for diagnostic purposes is well known, so our theoretical approach will focus on the quality of care provided to the patient, so we can p lace the image quality in CT (h ighly influenced by dose) within and highly influential factor while other more general concept, the quality of the CT scan. In healthcare, due to a climate of uncertainty, it is difficult to define quality. Actually, there are several definit ions of quality in healthcare. For examp le, the Jo int Co mmission on Accreditation of Healthcare Organizations (JCA HO) defines it as "the way health services, with the current level of knowledge, increase the possibility of obtaining the desired results and reduce the possibility of obtaining unwanted results "[14]. Quality can also be defined as "the production of health and satisfaction for a population with the limitations of the existing technology, the resources American Journal of Biomedical Engineer ing 2013, 3(6A): 15-21 17 available and the characteristics of users"[15]. The issue of resources available, raised by the above definition of quality in healthcare, in a technological area such as CT, whose evolution has been dizzying, especially in the last ten years, opens a large range of co mb inations and binomial hypothesis of patient/equipment that is very difficult to control and monitor. The issues of diagnostic quality, co mbined with the absorbed dose are, among others, highly dependent on the equipment used. Despite all the effort that the industry has done to develop new technology to reduce dose in CT, the DRL´s by anatomic region examined, in parallel, do not accompany this decrease. This is due to the large variab ility of equip ment that is operating in each country. Thus, DRL´s have not followed the technological evolution of the equipment, since the period of its use may be less extensive, depending on the laws of each country. Growing concerns about radiation dose is leading manufacturers of CT equipment to develop tools to reduce radiation dose. In the latest generation of CT equip ment such tools include automatic tube current modulat ion, automat ic selection of the tube voltage and iterative reconstruction (16). It is worthy to note the effort and demand for all brands of equip ment in the reduction of patient dose (Table 2). In addit ion to Filtered back project ion (FBP) developed and used since the 1970´s, new image reconstruction algorithms have been marketed since 2008, such as adaptive statistical iterative reconstruction (ASIR), iterative reconstruction in image space (IRIS), adaptive iterative dose reduction (AIDR), the fourth version of its iterative method, wh ich was called iDose4 and model-based iterative reconstruction (MBIR), comme rcia l na me of VEO[4], they all focus on the reduction of dose (Table 1). Table 1. Examples of iterative reconstruction algorithms available in the Unit ed Stat es from major manufact urers Vendor Acronym Siemens IRIS Siemens SAFIRE Name Image Reconstruction Iterative Recon st ruct io n Sinogram Affirmed Iterative Reconstruction GE Philips Toshiba ASiR iDose ADIR Adaptive Statistical Iterative Reconstruction iDose Adaptive Iterative Dose Reduction Toshiba ADIR 3D Table 2. Main articles reviewed by thematic approaches Author Thematic approaches Year Frédéric A. Miéville, François Gudinchet, François O. Bochud, Francis R Verdun[4] Francis Brunelle, Iterative reconstruction methods in 2012 Angeliki Neroladaki, Diomidis Botsikas, Sana Boudabbous, Christoph D. Becker, Xavier Montet[5] Computed tomography of the chest with model-based iterative reconstruction using a radiation exposure similar to chest X-ray examination 2012 Bulla, S., Blanke, P., Hassepass, F., Krauss, T., Winterer, J. T., Breunig, C., Pache, G.[7] Reducing the radiation dose for low-dose CT of the paranasal sinuses using iterative reconstruction: feasibility and image quality 2012 Siva P. Raman, Pamela T. Johnson, Swati Deshmukh, Mahadevappa Mahesh, Katharine L. Grant, Elliot K. Dose Reduction Applications 2013 Fishman,[16] Lui, D., Cameron, A., Modhafar, A., Cho, D. S., & Wong, A.[18] Lui, D., Cameron, A., Modhafar, A., Cho, D. S., & Wong, A. 2013 Lois Romans[25] CT Image Quality 2013 Rodrigues, S. I., Abrantes, A. F., Ribeiro, L. P., Almeida, R. P. P .[2 6] Dosimetry in abdominal imaging by 6-slice computed 2012 Chance S. Dumaine, David A. Leswick, Derek A. Fladeland, Changing Radiation Dose From Diagnostic Computed Hyun J. Lim, Lori J. Toews[27] Tomography 2012 Tiddens, H. a W. M., Stick, S. M., & Davis, S.[28] Multi-modality monitoring of cystic fibrosis lung disease: The role of chest computed tomography 2013 Sui-T oWong, Gwendolin Yiu, Yiu-Man Poon, Ming-Keung Yuen & Dawson Fong[29] Reducing radiation exposure from computedtomography 2012 18 António Fernando Lagem Abrantes et al.: Quality in Computorized Tomography – From Image Acquisition to Dose, Concepts, Myths and Definitions In summary, we intend to improve the diagnostic capacity with the lowest possible dose. Recent clinical data have shown that the algorith m IRIS using three iterat ions provide a similar picture quality than normal CT of the chest with a dose reduction of about 35% when compared with filtered back projection (FBP)[5]. In a study of the chest performed with a Ultra-Low Dose protocol, resulted in an exposure of 0.16 ± 0.006 mSv, values next dose of a PA and Lateral Chest X-Ray (CXR)[5], wh ich is reported between 0, 05 and 0.24 mSv in the literature[6-17]. Th is corresponds to a dose reduction of 98.6% in co mparison with the standard diagnostic CT dose and 94% in co mparison with the low-dose CT. Regarding the study of the sinuses, by reducing the current output / time at 20%, 40% and 60% were obtained dose reductions of up to 60% co mpared to the initial protocol. The best image quality, according to the researchers, was verified with a dose reduction of 20%[7]. The image quality produced by these protocols is subjective because there are few studies on the subject. As we know, low-dose CT reduces radiation exposure, but decreases the signal to noise ratio and consequently the diagnostic capabilit ies[18]. However, the results regarding the quality of the image look pro mising. In this study, we found that the use of MBIR provides even greater noise reduction, compared with only ASIR. The noise reduction of 12%, 28% and 79% was achieved by ASIR-40-80 and ASIR M BIR, respectively, which is in agreement with the results published recently by other researchers[19]. As a result, the Iterative reconstruction techniques lead to a significant increase in image quality, reducing its noise, even in cases where the contrast-to-noise ratio is very low. As a result, CT scans can be performed with a significantly lo wer dose, remain ing however the diagnostic image quality[16]. In the past two years, several studies have exa mined the effects on patient dose and image noise of various iterative reconstruction methods. All showed significant reductions in radiation dose (up to 40% -50% in so me cases)[20, 21, 22]. A study which was analysed in the algorithm SAFIRE body scans (abdomen), showed a dose reduction by 50% wh ile preserving image quality[22]. With doses of radiation constant, SAFIRE (Sinogram Affirmed Iterative Reconstruction) can reduce image noise by 35% and improve the noise contrast in 50%[23]. When we move away fro m marketing strategies, the concepts of low dose and ultra-low dose become nonspecific and undefined. Fro m the healthcare point of view, especially CT, along with the traditional concepts of quality in healthcare, we have to add image quality and patient safety[24]. Image quality is not a clear issue nor is it consistent among specialists, raising questions as: to which extent CT image provides information for establishing a diagnosis? When an image is no longer suitable for diagnostic? When analysing image quality in CT, we are interested in the same level of consistency and to what extent it actually rigorously corresponds to the patient. Many factors influence a CT image (the representation of an object in dig itized form). To assess what concerns us, if the image represents the actual anatomy, we mainly consider two main features: the detectability of resolution or low contrast resolution and detail that is, the high contrast resolution. The high contrast resolution is the level of detail that is visible in the picture. For examp le, two thin lines are very close to an object, will they be identified on the image as two separate lines? The low contrast resolution is the system's ability to distinguish objects with similar densities. For example, consider an object (i.e. s mall tu mor) which has almost the same density as the tissue around it. Will this object be detectable on the image?[25]. We are in the field of healthcare safety. So what is safety in TC? Is this concept only related to radiation protection and dose reduction? Clearly not! Safety in TC, as in other imaging methods that use radiation, must be broader than the generalist definit ions of Patient Safety[24]. We need to ensure that the level of noise that we accept for a particular study is balanced. On one hand we need guarantees that we do not lose any detail in the image that would allow us to establish the diagnostic, and secondly, to respect scrupulously the ALARP principle (as low as reasonably practicable). We must also combine the issues of noise with the radioprotective capacity of dose modulation software, as it reduces dose according to the pattern of noise for a certain image or anatomical region. Typ ically, this noise level is defined by the type of exam. The results obtained in a study published in 2012 for abdominal exams performed on a 6 slice CT, showed that the radiation dose received in these tests also depends on some of the patient´s characteristics, being important to adjust the acquisition parameters to patient’s dimensions. An effective method is the use of automatic exposure control (A EC) wh ich allows reducing, or varying, the tube current according to the size of the patient. In the case of children, this method is not sufficient and there should be special attention due to their increased radiosensitivity, using paediatric protocols and taking into account all the precautions and princip les of radiation protection. In some types of CT scans, it is possible to make the image acquisition with lower dose to the patient, which leads to increased image noise. Th is increase in noise is acceptable as long as images continue to enable an efficient clinical d iagnosis.[26]. 4. Discussion After rev iewing the literature, we found no description that quantifies dose reduction with the concepts low dose and ultra-low dose. It is necessary to establish a clear and unambiguous quantitative defin ition of these concepts. We know only that each contains a reduced level of dose administered to the patient for the same (or similar) CT Scan. With the exception of four art icles[5, 6, 7, and 17], there is no quantitative mention of how much dose reduction each concept provides in relation to the previous protocols used. All major manufacturers of CT p rovide meaningful tools to reduce the radiation dose. Not many users take advantage of the capabilit ies of their equip ment to reduce the dose, due American Journal of Biomedical Engineer ing 2013, 3(6A): 15-21 19 to lack of familiarity and knowledge of how such tools work[16]. We also know that each tool can be used individually, but when combined, have a synergistic effect in reducing the radiation dose[16]. In addition to all the tools available, we cannot forget what has been observed between 2006 and 2008: a decrease in dose on chest CT, always using the same equipment. As noted above, this dose reduction occurred without any change in equip ment, which emphasizes the importance of acquisition protocols, combined with techniques for dose management in CT[27]. Certain ly the increased routine of teams trying to achieve the universal goals of dose reduction inherent in all the d iagnostic techniques that use ionizing radiation, are responsible for the fact noted earlier. As regards the concepts and ultra-low dose low-dose recently introduced, remains only a qualitative reference for dose level, because they are devoid of any quantitative reference standard. It is clear that there is no concrete definit ion of what is and what matches each. The concept is an ultra-low dose supposed evolution of the low dose, although, with the exception of an article[5], which we cannot quantify the value of reduced dose of ultra-low dose compared to lo w dose. As shown, the scientific literature, these two designations used without reference is made (in the percentage or absolute value) as the equivalent each. Regarding the concepts of qualitative dose measurement, low dose and ultralow dose are devoid of any quantitative standard reference that allows us to determine where one begins and the other ends, much less which concept manufacturer´s market ing campaigns will follow. As we have seen, there is a starting point, a DRL, which is much connoted with the FBP algorith m used in CT since the 1970´s. This algorith m has been the reference from which we intend to establish buzzwords that characterize dose reduction, but often we cannot quantify it. Established standard diagnostic dose references, when we speak about low-dose, what is the percentage decrease of radiation dose? And for ultralow-dose what should we expect in relat ion to the standard diagnostic dose, or in relation to the lo w-dose concept? In fact, we found in the literature, several references that enable us to conclude that we have presently on the market, algorith ms that reduce the dosage from about 35% (IRIS using three iterations) to 98.6% (ultralow dose CT). We also found that the reduction of dose related to the concept of low-dose is about 94%, co mpared with standard diagnostic dose. Thus we see that the ULD has an absolute value close to 40% to 50% reduction for the LD concept [14 ,15, 16]. According to several researchers, this pattern appears constant for chest studies. There are also studies that measure the image quality for this anatomical reg ion, by using technical expert boards or Delphi panels[15, 16]. The chest (lung) therefore seems to be the p rime test spot for dose reduction. As we analyse other anatomica l regions, we found a large d ispersion and discrepancy. In summary, accord ing to the previously defined quality standard of care in CT, we can focus on the issues of dose reduction, and proceed to the goal of providing safe care; we must assume that image quality and any assumptions generically associated with health care quality are comp lied. Thus, in order to provide safer healthcare and make wise choices in CT, we need to delimit the concepts of low dose and ultra-low dose. There are no studies that define the concepts assertive low dose and ultra-low dose, similar to what happened at the beginning of the XXI century with the concept of pitch, it is necessary to normalize defin itively which corresponds, under penalty of being an expression trivialized. It is important that the responsible authorities and departments for rad iation issues define among which ranges of percentage of the standard diagnostic dose we can call dose reduction as LD and ULD. This concept should be established by the type of examination. 5. Conclusions The main results of this literature review point to the ine xistence of lite rature that clarifies all the concepts related to Dose Reduction, Low Dose and Ult ra Low Dose. These terms were introduced by CT equipment manufacturers and are used when it is intended to refer dose reduction. Although, these terms rarely discriminate, in absolute or percentage values, the effective dose radiation reduction achieved by the several techniques and technologies used. The dose reduction concept, due to his non-specificity and qualitative connotation, must be understood as any technique, technology or software that reduces the radiation level, when compared to a similar exam with the same diagnostic goals. Th is concept is fairly explained in the literature. However, it is unclear in the majority of the documents analysed, what should be the reference to use when it is intended to quantify the dose reduction level. Some literature is obscure when expressing that the reference pattern is the filtered back p rojection reconstruction algorith m. The reference pattern to be used when quantifying the radiation dose variation must be indicated unequivocally and universally. We also propose, based on the reduction of effective dose per examinat ion type, an interval scale for the classification of new technologies (CT equipment), averaged over the dose values obtained after analysis of the levels of all types of examinations that the equipment can perform. This way we would know the rea l value of dose reduction (considering the maximu m permissible standard deviation) for each of the concepts associated with dose reduction. Finally, it is intended that the findings of this article serve as a point of reflection on the determination of concepts extremely important and sensitive computerized tomography, starting from studies that have consolidated and universally quantify their use, under penalty of being t riv ialized 20 António Fernando Lagem Abrantes et al.: Quality in Computorized Tomography – From Image Acquisition to Dose, Concepts, Myths and Definitions foreseeable future. ACKNOWLEDGEMENTS I would like to thank all rad iology professional who work with CT, as well as all those who have contributed to the development of this diagnostic tool with increasing quality and safety. [11] UNSCEAR. Sources and eff ects of ionizing r adiation. United Nations Scientific Committee on the Effects of Atomic Radiation 2000 Report to the General Assembly, with Scientific Annexes. volume I: Sources. UN Sales Publication E.00.IX.3. New York, USA: United Nations, 2000. 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