Eur. Radiol. (2001) 11: 1975±1985 DOI 10.1007/s003300100950
U. Joseph Schoepf Christoph R. Becker Nancy A. Obuchowski Georg-Friedemann Rust Bernd M. Ohnesorge Gerhard Kohl Stefan Schaller Michael T. Modic Maximilian F. Reiser
Received: 22 November 2000 Revised: 23 January 2001 Accepted: 20 March 2001 Published online: 10 July 2001 Springer-Verlag 2001 U. J.S. is the recipient of the Siemens Visiting Research Fellowship Grant of the ECR 2000 Research and Education Fund
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U. J. Schoepf ( ) ´ C. R. Becker ´ G.-F. Rust ´ M. F. Reiser Institute of Clinical Radiology, University of Munich, Klinikum Grosshadern, Marchioninistrasse 15, 81377 Munich, Germany E-mail:
[email protected]. uni-muenchen.de Phone: +49-89-70 95 36 20 Fax: +49-89-70 95 88 32 N. A. Obuchowski ´ M. T. Modic Division of Radiology, The Cleveland Clinic Foundation, Cleveland, OH, USA B. M. Ohnesorge ´ G. Kohl ´ S. Schaller Division of Computed Tomography, Siemens Medical Solutions, Forchheim, Germany
C O M P UT E R T OM OG R A P HY
Multi-slice computed tomography as a screening tool for colon cancer, lung cancer and coronary artery disease
Abstract Recent promising trials that use low-dose CT for the early detection of lung cancer have reinvigorated the interest in screening approaches. At the same time the development of fast image acquisition techniques, such as multislice CT, have sparked renewed interest in cardiac imaging within the radiological community. In addition to special cardiac capabilities, multislice CT has several other features such as high acquisition speed and low-dose requirements that may make this modality a universal radiological screening tool. Non-invasive disease detection is the radiologist's domain. In this paper we identify criteria for effective screening and apply these criteria to screening approaches with multislice CT when used for detection of three disease entities: colon cancer; lung cancer; and cardiovascular disease. Keywords Cancer screening ´ Screening ´ Lung cancer ´ Heart disease ´ Colon cancer ´ CT ´ Multislice CT ´ Multisection CT ´ Multidetector row CT
Introduction Screening per definition is the evaluation of an asymptomatic population at risk for the presence of a particular disease. Any measures of the accuracy of the screening test and of eventual patient outcome critically hinge on restricting the screening test to asymptomatic
individuals. A common but erroneous approach to assess the accuracy and effectiveness of screening is to apply a test to individuals who show first symptoms of their disease. For example, the effectiveness of lung cancer screening cannot accurately be measured in a population that includes individuals who seek medical attention for cough or other respiratory symptoms.
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The objective of screening must be to reduce morbidity and mortality from the targeted disease by detecting it at a pre-clinical and thus curable stage prior to manifestation. This must be achieved at a cost that does not outweigh the expected benefit in order for a screening test to be accepted and viable in today's socioeconomic environment. Whether a disease is amenable to screening depends on numerous factors among which the natural history of the disease and the effectiveness of the test are the most important. In order for a screening test to be effective, a number of criteria must be fulfilled. Obviously, any kind of screening program should be aimed at diseases with serious consequences, such as prolonged morbidity or death. An effective screening test results in early detection of the targeted disease, enables its successful treatment and truly delays death from the disease. Testing for a disease which usually does not progress to a clinical stage within the lifetime of a patient is not beneficial. Equally important is that effective treatment exists for the disease at the time of detection. If the disease has no known treatment or is usually detected at a time when it has already progressed to an incurable (e.g. metastasized) stage, screening for that disease cannot be effective. Secondly, the targeted disease should be of high prevalence in the screened population which is directly related to the cost-effectiveness of the screening program. Effectiveness can be increased by restricting the screening test to a population with special risk factors that are linked to the targeted disease; thus, a screening test aimed at the early detection of lung cancer is more effective in a population of heavy smokers than in the general population. Any screening test must be of reasonable accuracy in order to be cost-effective. The specificity of a screening test is reduced by a high prevalence of pseudo-disease in the screened population that mimics the target disease, such as post-inflammatory lung granulomas or benign colon polyps that will not progress to cancer. However, if a screening test has high sensitivity but only moderate specificity, the initial screening test can be used to identify individuals that require further workup with more specific means which may be too invasive or too expensive to be used as a primary screening tool. If, for example, an asymptomatic individual has an elevated amount of coronary artery calcifications on a screening exam, the presence of cardiovascular disease can be verified or ruled out by cardiac catheter angiography. Finally, any diagnostic test that is applied to larger portions of the population must not cause morbidity or mortality in those screened for disease. It must be widely available to the general population in order to have significant impact to justify cost. Ideally, established screening tests should be covered by health in-
surance and, if they are not, must be cheap enough for a general population to afford. Approaches to screening are manifold: Different medical subspecialties use more or less sophisticated means for early disease detection, ranging from physical examination (prostate cancer) and endoscopic procedures (colorectal cancer) to laboratory (fecal occult blood) and genetic (breast cancer) tests. Non-invasive disease detection is the radiologist's domain. Surprisingly, until recently screening other than screening mammography has not played a major role in the field of radiology. Only recently has there been renewed interest in radiological approaches to screening, kindled mainly by new results of screening trials that use low-dose CT for the early detection of lung cancer [1]. At the same time renewed interest in cardiac imaging has been sparked within the radiological community, mainly by the advent of fast MR and CT imaging techniques that allow non-invasive assessment of cardiac morphology and function [2, 3, 4, 5, 6]. The most important development in the field of CT imaging after the introduction of spiral CT ([7] has been the advent of multislice technology [8]). While being an all-purpose imaging modality, multislice CT has unique features such as special cardiac capabilities, high acquisition speed, and low-dose requirements [9, 10]. Based on our year-long experience with multislice CT (Somatom VolumeZoom, Siemens, Forchheim, Germany) we believe that with this technology we may have a universal screening tool at hand. In this paper we apply the aforementioned criteria for effective screening to multislice CT when used for screening for three disease entities: colon cancer; lung cancer; and cardiovascular disease.
Colon cancer Colon cancer remains the second leading cause of cancer deaths in western societies [11, 12]. The incidence of the disease is markedly higher in individuals with a family history of colorectal neoplasia or with other well-established colorectal cancer risk factors [13]. Screening approaches in such high-risk groups thus may be most effective. The close association between precursor adenomatous colonic polyps and invasive colon cancer is now widely accepted [14]. The majority of invasive cancers are thought to arise from precursor polyps and timely removal of the latter seems to prevent the development of colorectal neoplasms by interrupting the adenoma±carcinoma sequence [15]; thus colonic polyps appear as worthy targets for screening endeavors in asymptomatic individuals and screening for colorectal cancer is increasingly recognized to result in a 25±50 % reduction in cancer mortality [13]. There is ample time for disease detec-
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Fig. 1 Virtual endoscopic rendering of a multislice CT data set of the colon. The high spatial resolution and acquisition speed of a 1-mm collimation multislice CT scan with 500-ms temporal resolution suppresses motion artifacts and allows for detailed visualization of colonic folds
tion since the natural history of the disease is a slow progression over a course of many years of adenomatous precursors (Figs. 1, 2) to invasive cancer (Fig. 3). The methods for early detection of colorectal neoplasms available to date include fecal occult blood testing, conventional colonoscopy and double-contrast barium enema. Occult blood testing by nature lacks accuracy [16] and does not permit inspection of the mucosal surface. Variable quality with impaired accuracy and patient discomfort are the main disadvantages of double-contrast barium enema examinations. Conventional colonoscopy is a costly procedure compared with the aforementioned examinations and carries a small but definite risk of colon perforation [17]. Compared with these more time-honored methods, ªvirtual colonoscopyº ± endoscopy-like rendered CT and MR data ± has the potential to be more accurate than fecal occult blood testing and double-contrast barium enema and to be safer than conventional colonoscopy [18]. Due to its rapid examination time and reduced invasiveness compared with conventional colonoscopy, virtual colonoscopy apparently also has the potential of being more acceptable as a screening procedure to a large segment of the population, although conventional bowel cleansing and distension is still required. Since the introduction of endoscopic rendering techniques based on cross-sectional imaging data [19] numerous approaches have been directed at using this technique for the detection of colorectal polyps and colon cancer [20, 21, 22, 23]. The ability to perform virtual endoscopic rendering of CT data has only been made feasi-
Fig. 2 A 5.8-mm polyp detected at multislice CT virtual colonoscopy. Ninety percent of all polyps in the colon are less than 10 mm in size. Small lesions were found to be a limitation of single-slice CT for virtual colon examinations. One-millimeter multislice CT acquisitions result in unprecedented z-axis resolution which markedly improves three-dimensional postprocessing and is likely to overcome the limitations of single-slice CT for the detection of small polyps
ble by the advent of the fast volume acquisition capabilities of fast spiral CT. Compared with conventional single-slice CT, there are specific advantages of using multislice CT for the purpose of virtual colonoscopy [24]. In our institution we perform virtual colonoscopy after standard bowel preparation, room air insufflation, and bowel relaxation in supine and prone patient position. We use the high acquisition speed of multislice CT to cover the entire abdomen with 1-mm collimation. Of all polyps in the colon, 90 % are less than 10 mm in size [25]. These small lesions were found to be a limitation of studies using single-slice CT data for virtual colon examinations [23]. The 1-mm slice thickness acquisitions that have become feasible with the advent of multislice CT scanning result in unprecedented z-axis resolution which markedly improves three-dimensional postprocessing and is likely to partially overcome the limitations of single-slice CT for the detection of small polyps (Figs. 1, 2). The high scan speed of multislice CT adds to patient acceptance of virtual colonoscopy and reduces motion artifacts that occur in the bowel despite of relaxation, thus allowing further increase of the diagnostic quality of virtual colonoscopy studies. Specific limitations of virtual colonoscopy remain despite the introduction of multislice CT. While advanced software systems and novel visualization techniques [26] facilitate and speed up the reconstruction of high-quality endoscopic renderings of the colon, per-
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Fig. 3 Invasive colon cancer causing malignant stenosis of the ascending colon. It takes several years for an adenomatous precursor lesion (Fig. 2) to evolve into invasive cancer. Colon cancer is therefore a worthy target for screening endeavors since there is ample time for early detection
forming virtual colonoscopy of sufficient diagnostic quality still involves a steep and long learning curve. This likely is the main reason why the use of virtual colonoscopy thus far has been limited to few specialized academic centers and has not been embraced as a general screening exam for the general public [27]. A solution to this latter limitation may be scan acquisition at peripheral sites, whereas postprocessing and reading is performed at dedicated specialized centers. Further limitations arise from the fact that approximately 35 % of the population aged 50 years and older are thought to harbor colonic polyps. Half of those lesions are of hyperplastic, nonneoplastic origin and are prone to increase the false-positive rate and thus reduce the effectiveness of screening using virtual colonoscopy. Moreover, insufficient cleansing results in fecal residues mimicking polyps and significantly increases the falsepositive rate of virtual colonoscopy. Fecal tagging which may obviate the need for bowel preparation prior to virtual colonoscopy with magnetic resonance imaging [28] cannot easily be applied for use with CT. Thus, conventional bowel cleansing and distension is still required prior to virtual colonoscopy with CT and reduces the acceptance rate of the virtual colonoscopy examination. Most importantly, however, conventional colonoscopy is required as a part of the screening algorithm in order to verify and remove polypous lesions. Addition of conventional colonoscopy, however, results
Fig. 4 Peripheral lung nodules in the right upper lobe of a patient (arrow) scanned with standard dose settings (120 kV, 120 mAs, left) and low-dose settings (120 kV, 10 mAs, right) on follow-up. A comparable assessment of the lesions is feasible with a fraction of the radiation dose. Effective dose of the 10-mAs examination is 0.27 mSv and thus only slightly higher than a biplanar chest radiograph
in increased cost compared with use of conventional colonoscopy alone [29] which will impede reimbursement schemes for colon cancer screening that include virtual colonoscopy techniques.
Lung cancer Lung cancer is the most common malignant disease in males in western societies and affects more than 60 individuals per 100,000 inhabitants each year. Related to changing smoking habits, the percentage of affected women is rapidly increasing. Lung cancer is now the most common cause of cancer-related death in both men and women and kills more people than colon, prostate, and breast cancer combined. The association with cigarette smoking is well established. Lung cancer is usually detected late in the course of the disease, when the cure rate is a mere 12 % with only a slightly higher 5-year survival rate. However, when stage-I cancer is resected, 5-year survival increases to 70 %. In the absence of resection, survival is only 12 % [30, 31]. The characteristics of lung cancer should in theory make the disease amenable to screening: Major criteria for the effectiveness of a screening program are fulfilled. The prevalence of the disease within the target population is high and can be further increased by stringent selection of inclusion criteria such as a smoking history. In a population of heavy smokers [1] the detection rates of lung cancer may be ten times higher
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Fig. 5 Radiation exposure with multislice CT lung cancer screening protocols. A 1-mm collimation multislice CT acquisition with 10, 20, 30, and 40 mAs and 120 kV is compared with a conventional chest radiograph in two planes (CXR) and a 10-mm collimation monoslice CT acquisition with 40 mA (see [1]). Despite the 1-mm slice, the radiation exposure of a multislice CT acquisition with 10 mAs is only marginally higher than CXR and is considerably lower than that of a monoslice screening protocol
than in an unselected population [32]. Early detection and treatment seemingly result in a dramatic increase in survival [1]. Earlier lung cancer trials based on radiography and sputum cytology that had yielded unfavorable results [33] were flawed in their study designs as recognized by the investigators themselves [34, 35]. More recent trials that take advantage of the higher sensitivity of CT [1, 32, 36] seem to clearly demonstrate the usefulness of CT lung cancer screening for detecting the disease at a curable stage. Multislice CT may take the advantages of CT for the early detection of lung cancer to yet another level. The main benefits of this technology for screening purposes are low-dose requirements and high spatial resolution. At our institution we currently use a protocol that comprises acquisition of the entire chest within one 20- to 25-s breath-hold by use of a 1-mm collimation at 120 kV and 10±40 mAs adapted to the body type of the screened individual. At a tube current of 10 mAs (Fig. 4) this results in an effective radiation dose of 0.27 mSv which is approximately equivalent to two conventional chest radiographs (Fig. 5). Low-dose requirements are of paramount importance for any diagnostic tool that is to be applied to a large number of a priori healthy, asymptomatic individuals. For routine reading of screening chest studies the 1-mm acquisition can be fused into 5- to 10-mm axial multiplanar reconstructions (MPRs) or maximal intensity projections (MIPs) to limit the number of individual axial slices for
reading and to restore low image noise (Fig. 6a). However, owing to the thin-slice acquisition, 1-mm reading can be performed for detecting localized calcifications or fat if a scrutinized analysis of a lung nodule is required (Fig. 6b). This is all the more important in the light of ongoing low-dose CT screening trials that, depending on the geographic location, show a prevalence of lung nodules in more than 50 % of the screened individuals. Especially in areas where microorganisms, such as histoplasma capsulatum are endemic, the high prevalence of pseudo-lesions due to granulomatous disease that may mimic incipient peripheral lung cancer is a specific limitation of screening approaches aimed at the detection of small lung nodules. If lung nodules are found, the diagnostic algorithm at many institutions that perform screening require recalling the screened individual in order to perform a thin-section spiral acquisition of the nodule for further characterization and volumetry. If a low-dose 1-mm multislice CT acquisition is employed as the initial screening test, this step can be abandoned with a very beneficial impact on work flow and cost-effectiveness of the screening program. For determining the dignity and for follow-up of suspicious lesions we currently adopt the recommendations as outlined in the ELCAP study design [1]. However, we foresee that an adaptation of our diagnostic algorithms will be necessary to increase the efficacy of screening in Europe. A major concern with lung cancer screening is overdiagnosis [37] resulting in unnecessary surgical procedures to remove benign lung nodules found at imaging. This has been recognized to significantly increase the morbidity and mortality in cohorts undergoing screening programs [38]; thus, invasive procedures for lesions that will not grow into invasive cancer must be avoided at all cost in order to maintain the effectiveness and acceptance of screening programs. As demonstrated by the ELCAP study, follow-up of lesions found at low-dose CT with size-dependent algorithms for diagnostic work-up are an effective tool to avoid overdiag-
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a Fig. 6 a Screening examination of a 65-year-old male smoker. A 10-mm lung nodule is seen in the right lower lobe on the low-dose scan. The scan was acquired with 1-mm collimation, 120 kV, and 10 mAs. The dose equivalent is 0.27 mSv. Fusion of the acquisition in a 10-mm slice restores acceptable image noise. b For further characterization of the lung nodule a 1-mm reconstruction is performed from the same raw-data set. One-millimeter sections through the lung nodule reveal small popcorn-like calcifications, suggesting a benign hamartomatous lesion. The ability to characterize a lesion by means of 1-mm slices reconstructed from the same raw-data set obviates the need for a high-resolution followup study of the lesion, which would require recalling the patient. Since a considerable percentage of our screening population has lung nodules, this allows for improved work-flow and patient management
nosis and unnecessary invasive procedures. In the initial ELCAP cohort not a single patient underwent lung resection for benign lesions, when the recommendations of the study design were followed [1]. A prerequisite for reliable assessment of lesion size are automated tools for lung nodule volumetry, which enable accurate measurement of lesions upon detection and on follow-up in order to determine growth as the most important indicator of malignancy (Fig. 7). If 1-mm low-dose multislice CT is used as the initial screening exam, accurate volumetry can be performed from a full field of view study without rescanning the screened individual (Fig. 7). Also, the substantial number of individual images generated by low-dose high-resolution multislice CT screening necessitates the development of automated tools for the sensitive detection of small lung lesions (Fig. 8). Approaches for automated detection also benefit from the increased conspicuity of lung lesions on thinner slices with less volume averaging facilitating computer-aided diagnosis. If lung cancer is detected, accurate staging of the disease is of paramount importance to determine the optimal therapeutic regimen for the individual patient. The high spatial resolution of a 1-mm multislice CT data set allows intuitive visualization of the tumor in its ana-
tomic relationship to pulmonary vessels (Fig. 9) and the chest wall (Fig. 10) which facilitates surgical planning; thus, the technical requirements of lung cancer screening are ideally met by multislice CT. General limitations are related to our current uncertainty about the real benefit of screening for lung cancer in terms of decreased mortality, delay of death, and socioeconomic effects. Doubts have been raised that early detection of small lung nodules influences lung cancer survival [39]; however, larger studies clearly seem to demonstrate the beneficial impact of early cancer detection and removal at a curable stage [40]. Furthermore, no randomized trials are available to date that compare morbidity and mortality in highrisk groups with and without screening. Conclusive results of randomized controlled trials are not to be expected any earlier than in 5±8 years time. Until then we should exploit the information provided to us by cohort studies in order to answer the most immediate questions posed to us in the context of screening. Our main focus for the upcoming years should be the benefit, which we can provide by averting a dire fate from the individual at risk by the early detection of a devastating disease.
Cardiovascular disease Coronary artery disease is the leading cause of mortality in western societies and affects 5±10 % of the male population. Each year more than 300 individuals per 100,000 inhabitants sustain a myocardial infarction (MI), often as the first symptom of their cardiovascular disease. In more than 35 % of cases the patient dies from MI. The risk factors linked to coronary artery disease are well defined and comprise hypercholesterinemia, cigarette smoking, hypertension, hereditary factors, diabetes, and many more. The morbidity caused by coronary artery disease is a tremendous burden to any health care system. Accordingly, great efforts are directed to
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Fig. 7 a A soft tissue nodule (arrow) in the right upper lobe of the lung of a screened individual is visualized using the LungCare (Siemens, Forchheim, Germany) software platform (left). For volumetry, the lung nodule is automatically segmented from surrounding lung tissues and attached vessels (right). Using LungCare software, segmentation and volumetry of suspicious lung nodules can be accurately performed based on full field of view low-dose multislice CT studies. b After segmentation, the volume of the lung nodule is automatically determined and surface-shaded 3D rendering is performed for visualizing the shape of the nodule. Documented growth of a nodule on follow-up is the most important sign of malignancy; thus, accurate lung nodule volumetry is of paramount importance in identifying malignant lesions and in avoiding unnecessary invasive work-up of benign pseudo-lesions
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the early identification of individuals with cardiovascular risk factors and increased risk for future cardiovascular events. Detection of coronary calcifications (Fig. 11) reveals preclinical forms of atherosclerosis before symptoms may be present and before the disease can be diagnosed by other non-invasive tests [41].
A scoring method aimed at estimating the amount of coronary artery calcification using CT scanning has been developed by Agatston et al. to determine the likelihood of coronary artery disease in patients with and without clinical symptoms [42]. In later studies this scoring method was embraced as a generally applied
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Fig. 8 Prototype tool for computerized automated detection of lung nodules. A soft tissue nodule is identified in the right lung of a screened smoker. Approaches for automated detection benefit from the increased conspicuity of lung lesions on thinner slices with less volume averaging facilitating computer-aided diagnosis
quantification method to address a variety of different clinical questions. Recent studies show that prospectively EKG-triggered single-slice CT can be used for a reliable assessment of the coronary artery calcium load [3] and for a general improvement of thoracic image quality [43]. With single-slice CT (Somatom Plus 4, Siemens, Forchheim, Germany) partial scan views in 750-ms rotation allow for 500-ms exposure time. This relatively long exposure time limits the reproducibility of coronary calcium quantification with single-slice CT to some degree and causes blurring artifacts of thoracic structures [44]. Multislice CT holds promise to overcome the limited reproducibility of single-slice CT due to its shorter exposure and investigation time which is achieved by simultaneous acquisition of four slices with one scan. Simultaneous acquisition of multiple slices results in fewer slice gaps or overlaps caused by EKG misregistration. Moreover, partial-volume effects are reduced and signal-to-noise ratio is improved. We found that multislice CT enables for reliable lesion detection in obese patients and superior delineation of small plaques against background image noise [45, 46, 47]. Going one step further, it would be desirable to scan the entire heart with a single scan. Indeed, this can be achieved using multislice CT spiral scanning with retrospective EKG gating instead of single-slice scanning with prospective EKG triggering [45, 46, 48]. With ret-
Fig. 9 Solitary pulmonary nodule in a 48-year-old male smoker. Volume rendering of a 1-mm multislice CT data set allows visualization of the lesion in its spatial relationship to surrounding pulmonary vessels, the visceral pleura, and the mediastinum
rospectively EKG-gated multislice CT acquisition time is reduced to 16 s (500-ms rotation time). Also, common problems of prospective EKG triggering in patients with arrhythmia are overcome by retrospective EKG analysis and slice reconstruction. We employ multislice CT with prospective EKG triggering in patients with regular sinus rhythm to avoid redundant radiation exposure which is inherent to continuous spiral scanning. In patients with arrhythmia, however, retrospective EKG gating is the method of choice for coronary screening. A more direct and sophisticated method to screen for significant luminal obstruction of coronary arteries is CT angiography (Fig. 12). For this application motionfree images are mandatory. With an acquisition time of 250 ms, high image quality is achieved in patients with a heart rate of up to 74 beats per minute. Using biphasic image reconstruction with image data acquired during two consecutive heart cycles, the acquisition time can now be reduced to 125 ms with some heart rates. Retrospective EKG gating is superior to prospective triggering to time the data acquisition in the optimal phase of the EKG between the T and the P wave. In this phase, motion artifacts are substantially reduced, even in the right coronary artery. High z-axis resolution is achieved by using spiral scanning with four times 1-mm collimation and 3-mm/s table feed (500-ms revolution). With these parameters the slice thickness is smaller than the vessel diameter of the distal parts of the coronary artery tree. Initial experiences comparing multislice CT and
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b a Fig. 10 a Screening exam (120 kV, 10 mAs) of a 56-year-old female smoker reveals a T2 adenocarcinoma of the right upper lobe. b Contrast-enhanced staging examination of the same patient. Volume rendering demonstrates the exact localization in the right upper lobe and aids planning the surgical approach
catheter angiography indicate the potential of this noninvasive modality to rule out coronary artery disease. Especially in the population of young smokers significant coronary artery disease without calcified components may be present that by nature cannot be visu-
Fig. 11 Non-contrast-enhanced multislice CT coronary artery screening examination in an asymptomatic individual reveals severe calcifications in the left descending coronary artery (LAD) and in the left circumflex artery (CX). The calcium score is calculated using the HeartView software platform (Siemens, Forchheim, Germany) which allows applying different scoring systems (Agatston score, Volume score, Mass score) to multislice CT data for accurately determining the coronary calcium load
alized by means of a non-contrast scan. In these patients multislice CT angiography with intravenous contrast enhancement enables detection of non-calcified atherosclerotic plaques. In many cases these plaques cause high-grade vessel obstruction as subsequently confirmed by conventional angiography [46]. The high spatial resolution of contrast-enhanced multislice CT now allows assessing the composure (fat, fibrous tissue, calcium, thrombus) of the lesions that may or may not
Fig. 12 Contrast-enhanced multislice CT coronary angiography demonstrates a complex atherosclerotic lesion in the left main coronary artery. The lesion has both calcified and non-calcified (white arrow) components. The non-calcified component causes a significant luminal narrowing of the vessel, whereas no stenosis is visible at the site of the calcification; thus, only the high-resolution contrast-enhanced multislice CT scan is able to non-invasively demonstrate the full extent of the disease
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cause stenosis seen on conventional angiography [45]. Thus, the advent of multislice CT has brought about a new quality of coronary arterial imaging by providing a means of non-invasively characterizing the nature and prognosis of vessel wall lesions in a way unprecedented by non-invasive (magnetic resonance) or invasive (coronary angiography, intravascular ultrasound) techniques (Fig. 12). Eventually this modality may prove to be a much better screening tool for defining individuals at risk of sustaining a hard cardiac event than detection and quantification of coronary calcifications had been able to provide. Thus, the technical prerequisites for an accurate, non-invasive detection of coronary arterial calcification and stenosis are fulfilled by multislice CT; however, the true potential of multislice CT screening for coronary artery disease needs to be evaluated more clearly with large prospective cohort studies.
Conclusion With the advent of multislice CT we are in the possession of a versatile and powerful screening tool that fulfills the technical prerequisites for accurate disease detection at an early and potentially curable stage. This is true for all three applications discussed herein. It is now
warranted to look into each application, whether this increased technical prowess can be used in beneficial ways to achieve a real reduction in morbidity and mortality in populations at risk. It is equally warranted to determine the cost-effectiveness of the proposed screening investigations in order to keep screening programs viable in today's socioeconomic environments and to extend their benefits not only to the few well off and worried but also to the general population. These measures must be taken before applications such as cardiac, colon, and lung cancer screening become a business opportunity for the general medical community since it would mean an excessive waste of resources if these procedures prove to be unsuited for the intended purpose. It is our responsibility to raise the quality standards of screening examinations. Only by consequent scientific evaluation and maintaining high-quality standards will we be able to prevent entrepreneurs who are not able or committed to providing quality care from prematurely rushing screening exams onto the market. There is a unique opportunity at hand for radiologists to become pivotal in helping people to identify disease before symptoms occur. We should embrace this opportunity in a meaningful and irreproachable manner.
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