Diagnostics and Prognostics in IBD Dig Dis 2013;31:345–350 DOI: 10.1159/000354690
Update Imaging in Inflammatory Bowel Diseases Hans Herfarth Division of Gastroenterology and Hepatology, University of North Carolina, Chapel Hill, N.C., USA
Abstract Imaging is a central component of the diagnostic process in inflammatory bowel diseases. This review summarizes the recent progress of various most commonly used imaging modalities including computed tomography enterography, magnetic resonance enterography and capsule endoscopy. Advantages and disadvantages of each imaging protocol in suspected and established inflammatory bowel diseases are reviewed and brought into context in proposed diagnostic algorithms. © 2013 S. Karger AG, Basel
Introduction
Specific diagnostic algorithms should be followed for the diagnosis, staging and evaluation of possible complications in patients with inflammatory bowel diseases (IBD) [1, 2] (fig. 1, 2). Whereas the esophagus, stomach, duodenum, terminal ileum and colon are accessible by upper and lower gastrointestinal endoscopy, radiological evaluations including abdominal ultrasound (US) are generally used as first-line procedures for the assessment of the small bowel. Studies performed in the late 1980s demonstrated that scintigraphy using radioactively la© 2013 S. Karger AG, Basel 0257–2753/13/0314–0345$38.00/0 E-Mail [email protected] www.karger.com/ddi
beled technetium has comparable sensitivities and specificities for the detection of intestinal inflammation as computed tomography (CT), magnetic resonance imaging (MRI) and US [2, 3]. However, due to the inevitable exposure to radiation and the lack of visualization of the abdominal organs, this technique currently has no clinical value. Capsule endoscopy is used in specific clinical situations and in general a radiological evaluation of the small bowel is always recommended in patients with suspected or established IBD prior to capsule endoscopy to rule out small bowel stricturing disease. Interestingly, in many European countries the actual sequence of utilizing the various imaging techniques in the workup of suspected or established IBD is different compared to the USA. Whereas in the USA invariably a CT and occasionally a MRI is ordered as a first-line imaging modality, in countries where gastroenterologists are responsible for performing US examinations (e.g. Germany, Italy, Switzerland), an US examination of the abdomen is preferred as the first-line imaging method (fig. 3).
Imaging Modalities to Evaluate Patients Suspected Small Bowel Crohn’s Disease
Recently, both a meta-analysis and a systemic review concluded that for evaluation of suspected small bowel Crohn’s disease, the sensitivities and specificities of US, CT and MRI fall within the range of 80–90% [4, 5]. Small bowel follow-through examinations are equally as rigorous as Hans Herfarth, MD, PhD Department of Medicine, Division of Gastroenterology and Hepatology University of North Carolina, Bioinformatics Bldg, CB#7080 Chapel Hill, NC 27599 (USA) E-Mail hherf @ med.unc.edu
Downloaded by: UCSF Library & CKM 169.230.243.252 - 3/30/2015 3:38:00 PM
Key Words CT enterography · MR enterography · Computed tomography · Magnetic resonance imaging · Inflammatory bowel diseases · Crohn’s disease
CT and MRI in detecting location, extent and luminal complications of Crohn’s disease but extraintestinal complications such as abscesses, enlarged lymph nodes and other IBD- or non-IBD-related organ complications cannot be visualized [6, 7]. Studies comparing either CT or MRI with conventional enterography (oral application of contrast) or with conventional enteroclysis (nasojejunal tube placement and application of contrast) revealed additional pathological extraenteric abnormalities on CT or MRI in 11– 58% of the cases [8–14]. These extraintestinal findings can be of significant clinical importance, as shown in a retrospective single-center analysis comprising 710 patients with proven Crohn’s disease undergoing MRI. Of all patients, 12% were found to have extraintestinal findings with major clinical impact such as spondylitis or cancer [15].
Labs (CBC, CRP, LFTs, albumin) Stool studies (calprotectin in pediatric patients) Upper and lower GI endoscopy with duodenal + ileal/colonic biopsies, abdominal ultrasound* Ulcerative colitis
Normal
‘Staging’ Small bowel imaging (CT, MRI* or SBFT)
Findings suspicious of Crohn’s disease/ stricture: consider balloon enteroscopy
Small bowel imaging (CT, MRI* or SBFT) Normal, but still high suspicion of IBD Capsule endoscopy
* Depending on local availability
Fig. 1. Diagnostic algorithm in suspected IBD.
Capsule Endoscopy for Suspected Small Bowel Crohn’s Disease
Unexplained clinical symptoms (bleeding, diarrhea, pain, obstructive symptoms) despite presumably adequate therapy Abdominal ultrasound*, Upper and lower GI endoscopy, small bowel imaging (MR*, CT) Pathologies explaining symptoms
Normal
Adaption medical therapy Endoscopic therapy of strictures Surgery
Patency capsule+ Capsule endoscopy Normal
Strictures Inflammation
Adaption medical therapy for IBS/IBD
* Depending on local availability
Fig. 2. Diagnostic algorithm in established Crohn’s disease and
Capsule endoscopy
Fourth line
MRI or CT
Third line
Ultrasound
Second line
First line
Europe Enteroscopy
(single or double balloon, spiral technique)
Capsule endoscopy
Third line
CT or MRI
Second line
First line
USA
Color version available online
unexplained clinical symptoms.
Enteroscopy
(single or double balloon, spiral technique)
Fig. 3. Comparison of diagnostic imaging approach in Europe and
the USA.
346
Dig Dis 2013;31:345–350 DOI: 10.1159/000354690
For the initial evaluation of small bowel involvement in patients with IBD, one has to keep in mind that either CT or MRI might not visualize superficial ulcers in the small bowel. Capsule endoscopy has been proven to be superior to both modalities in patients with suspected Crohn’s disease [16–18]. However, due to the risk of concurrent strictures even in clinically asymptomatic patients, a radiological evaluation of the small intestine is always recommended before performing capsule endoscopy [19]. Using an ‘imaging-first approach’ with conventional enteroclysis and MR enterography, it has been demonstrated that only about 10% of all patients with negative upper endoscopy and ileocolonoscopy might obtain a diagnostic benefit with capsule endoscopy after negative radiological imaging [20]. The main difficulties of identifying Crohn’s disease utilizing capsule endoscopy in patients with otherwise negative previous workup are (a) the lack of histological verification of the findings, which can be only achieved with a balloon enteroscopy, and (b) the lack of validated ‘diagnostic criteria’. The limitations of the characterization of capsule endoscopy findings were illustrated by a recent study [21]. A total of 102 patients with suspicion of Crohn’s disease underwent capsule endoscopy following normal or equivocal findings on colonoscopy and radiological small bowel imaging. After 12 months of follow-up, only 13% of patients, who were found to have small bowel ulcerations had been diagnosed with Crohn’s disease by subsequent endoscopic or radiographic re-evaluations. The overall sensitivity of capsule endoscopy, using the presence of any small Herfarth
Downloaded by: UCSF Library & CKM 169.230.243.252 - 3/30/2015 3:38:00 PM
Crohn’s disease
Table 1. Published prospective and retrospective studies comparing CT and MRI in the evaluation of patients with IBD
Reference (first author)
Study design
Patients, n
Result
Papadia, 2013 [48]
prospective
186
No difference between CT and MRI in detection of internal fistulas
Jensen, 2011 [49]
prospective
50
Sensitivities for small bowel inflammation and stenosis similar between CT and MRI
Gee, 2011 [50]
prospective
21
Sensitivities for small bowel inflammation and stenosis similar between CT and MRI
Fiorino, 2011 [51]
prospective
44
No significant difference in sensitivity except small advantage for MRI in detection of fistulae
Schreyer, 2010 [52]
retrospective
53
No difference in sensitivity to detect small bowel inflammation, but CT scans better in visualization of lymph nodes and colonic inflammation
33
Similar sensitivity to detect small bowel disease, but MRI with inferior image quality
Lee, 2009 [6]
prospective
30
No significant difference in sensitivity to detect small bowel inflammation
Schmidt, 2003 [54]
prospective
55 (not all IBD)
CT better than MRI in detecting small bowel inflammation and better inter-observer agreement
Low, 2000 [55]
prospective
26
MRI superior in detection of mild inflammation, (MRI scans were compared to images obtained by a helical CT scanner)
bowel ulcers as criterion for the diagnosis of Crohn’s disease (within 12 months of capsule endoscopy) was 85%, the specificity was 73%, the positive predictive value was 31%, and the negative predictive value was 97%. The positive predictive value increased to 50% if >3 ulcers were used as a criterion for Crohn’s disease on the initial capsule study. Given the high negative predictive value of a normal capsule endoscopy study, the real value is the exclusion of the diagnosis of Crohn’s disease in patients with suspected small bowel inflammation and otherwise negative previous workup.
Imaging Modalities in Established Crohn’s Disease
There seems to be no significant difference with regard to the clinical diagnostic value (sensitivity, specificity and accuracy) between US, CT and MRI for the evaluation of the extent of inflammation, stricturing or penetrating disease or extraintestinal complications [5, 22]. Comparing only CT and MRI, more recent studies have indisputably established that both imaging modalities have similar sensitivities for detection of intestinal inflammation and extraintestinal complications of IBD (table 1). Most of the Update Imaging in IBD
differences found in the tabulated studies might be explained by the technical capabilities of the imaging systems at the time of the study (e.g. single versus multidetector spiral CT, different image processing in MRI) and the experience of the reader with either CT or MRI. Capsule endoscopy can be performed in patients with established Crohn’s disease in cases in which imaging results from CT or MRI or other radiological methods are not conclusive enough to explain the symptoms (e.g. continuing diarrhea despite negative upper and lower gastrointestinal endoscopy and negative CT enterography). A retrospective single-center analysis including 128 capsule endoscopies in patients with IBD reported a change in medication in 62% of the patients in the 3 months after the capsule endoscopy, with 40% initiating a new IBD medication [23].
Advantages and Disadvantages of Imaging Modalities
Before choosing a particular imaging technique, one should be aware of its advantages and disadvantages (table 2). The major disadvantage of CT scans is the expoDig Dis 2013;31:345–350 DOI: 10.1159/000354690
347
Downloaded by: UCSF Library & CKM 169.230.243.252 - 3/30/2015 3:38:00 PM
Siddiki, 2009 [53]
Table 2. Advantages and disadvantages of different imaging modalities for evaluation of small bowel involvement
on patients with IBD Advantages of individual techniques MRI, CT, US: visualization of extraluminal pathologies US: cheap and fast, feasible technique for intervention (abscess drainage) MRI, US: no radiation Small bowel follow-through: information about small bowel motility (adhesions) Disadvantages of individual techniques MRI, CT: no information about small bowel motility (except for MRI if locally MRI fluoroscopy is available) US: operator-dependent, no standardized documentation, quantification of inflammation often difficult MRI: long acquisition time, higher costs compared to CT, limited availability
Perspectives in Imaging of IBD Patients
Radiation Exposure with CT Undoubtedly, the primary advantage of MRI is the lack of radiation exposure. Given the need for repeat imaging due to the chronic nature of IBD, MRI lacks the long-term risk of radiation-induced cancers, whereas the lasting risk of multiple CT scans is broadly acknowledged [24, 25]. Radiation is an important concern, particularly in pediatric patients, in young or pregnant women and in patients with IBD who require frequent repeated imaging examinations. No estimates are currently available for the future risk for cancer in relation to previous abdominal CT scans [26]. The latest epidemiological study in the UK conducted in children receiving head CTs estimated the lifetime risk for leukemia as 1:10,000 and a lifetime risk for brain cancer as 1:2,000 [27]. Estimates for the USA suggest that radiation exposure from CT examinations may be responsible for 0.5–2% of all cancers [28, 29]. Similar estimates for other countries revealed a cumulative cancer risk of 0.6% in the United Kingdom, 1.5% in 348
Dig Dis 2013;31:345–350 DOI: 10.1159/000354690
Germany and 3.2% in Japan [30]. It is important to note that these estimates are derived proposing a linear dose effect (‘linear no-threshold dose-effect model’), which postulates the possibility of carcinogenesis even with an exposure to low-dose radiation. Opponents to this model argue that extrapolating the cancer risk from high-dose exposure (>100 mSv) to lower doses may result in overestimation of the overall cancer risk. More recently, studies have demonstrated that by using multidetector CT scans and specific algorithms for image processing, a substantial radiation dose reduction without compromising diagnostic information can be achieved [31–33]. Lee et al. [34] determined that the effective dose of a standard CT enterography of 4.7 ± 1.1 mSv could be reduced to 2.4 ± 0.5 mSv. However, there were some drawbacks in image quality between normal and reduced dose CT scans. Without a doubt, further technical evolution of CT scanners and imaging software will solve issues of poor image quality by low-dose radiation approaches [35]. Hence, despite the presence of, albeit low, overall cancer risk due to cumulative radiation exposure, the lower costs of CT compared to MRI will be a compelling consideration in the choice of imaging at least in the USA. A Markov analysis taking into account cumulative radiation-induced cancers with yearly or every 2-year CT scans versus MRI examinations revealed that CT would be more cost-effective than MRI if CT is performed with radiation doses
Update Imaging in Inflammatory Bowel Diseases Hans Herfarth Division of Gastroenterology and Hepatology, University of North Carolina, Chapel Hill, N.C., USA
Abstract Imaging is a central component of the diagnostic process in inflammatory bowel diseases. This review summarizes the recent progress of various most commonly used imaging modalities including computed tomography enterography, magnetic resonance enterography and capsule endoscopy. Advantages and disadvantages of each imaging protocol in suspected and established inflammatory bowel diseases are reviewed and brought into context in proposed diagnostic algorithms. © 2013 S. Karger AG, Basel
Introduction
Specific diagnostic algorithms should be followed for the diagnosis, staging and evaluation of possible complications in patients with inflammatory bowel diseases (IBD) [1, 2] (fig. 1, 2). Whereas the esophagus, stomach, duodenum, terminal ileum and colon are accessible by upper and lower gastrointestinal endoscopy, radiological evaluations including abdominal ultrasound (US) are generally used as first-line procedures for the assessment of the small bowel. Studies performed in the late 1980s demonstrated that scintigraphy using radioactively la© 2013 S. Karger AG, Basel 0257–2753/13/0314–0345$38.00/0 E-Mail [email protected] www.karger.com/ddi
beled technetium has comparable sensitivities and specificities for the detection of intestinal inflammation as computed tomography (CT), magnetic resonance imaging (MRI) and US [2, 3]. However, due to the inevitable exposure to radiation and the lack of visualization of the abdominal organs, this technique currently has no clinical value. Capsule endoscopy is used in specific clinical situations and in general a radiological evaluation of the small bowel is always recommended in patients with suspected or established IBD prior to capsule endoscopy to rule out small bowel stricturing disease. Interestingly, in many European countries the actual sequence of utilizing the various imaging techniques in the workup of suspected or established IBD is different compared to the USA. Whereas in the USA invariably a CT and occasionally a MRI is ordered as a first-line imaging modality, in countries where gastroenterologists are responsible for performing US examinations (e.g. Germany, Italy, Switzerland), an US examination of the abdomen is preferred as the first-line imaging method (fig. 3).
Imaging Modalities to Evaluate Patients Suspected Small Bowel Crohn’s Disease
Recently, both a meta-analysis and a systemic review concluded that for evaluation of suspected small bowel Crohn’s disease, the sensitivities and specificities of US, CT and MRI fall within the range of 80–90% [4, 5]. Small bowel follow-through examinations are equally as rigorous as Hans Herfarth, MD, PhD Department of Medicine, Division of Gastroenterology and Hepatology University of North Carolina, Bioinformatics Bldg, CB#7080 Chapel Hill, NC 27599 (USA) E-Mail hherf @ med.unc.edu
Downloaded by: UCSF Library & CKM 169.230.243.252 - 3/30/2015 3:38:00 PM
Key Words CT enterography · MR enterography · Computed tomography · Magnetic resonance imaging · Inflammatory bowel diseases · Crohn’s disease
CT and MRI in detecting location, extent and luminal complications of Crohn’s disease but extraintestinal complications such as abscesses, enlarged lymph nodes and other IBD- or non-IBD-related organ complications cannot be visualized [6, 7]. Studies comparing either CT or MRI with conventional enterography (oral application of contrast) or with conventional enteroclysis (nasojejunal tube placement and application of contrast) revealed additional pathological extraenteric abnormalities on CT or MRI in 11– 58% of the cases [8–14]. These extraintestinal findings can be of significant clinical importance, as shown in a retrospective single-center analysis comprising 710 patients with proven Crohn’s disease undergoing MRI. Of all patients, 12% were found to have extraintestinal findings with major clinical impact such as spondylitis or cancer [15].
Labs (CBC, CRP, LFTs, albumin) Stool studies (calprotectin in pediatric patients) Upper and lower GI endoscopy with duodenal + ileal/colonic biopsies, abdominal ultrasound* Ulcerative colitis
Normal
‘Staging’ Small bowel imaging (CT, MRI* or SBFT)
Findings suspicious of Crohn’s disease/ stricture: consider balloon enteroscopy
Small bowel imaging (CT, MRI* or SBFT) Normal, but still high suspicion of IBD Capsule endoscopy
* Depending on local availability
Fig. 1. Diagnostic algorithm in suspected IBD.
Capsule Endoscopy for Suspected Small Bowel Crohn’s Disease
Unexplained clinical symptoms (bleeding, diarrhea, pain, obstructive symptoms) despite presumably adequate therapy Abdominal ultrasound*, Upper and lower GI endoscopy, small bowel imaging (MR*, CT) Pathologies explaining symptoms
Normal
Adaption medical therapy Endoscopic therapy of strictures Surgery
Patency capsule+ Capsule endoscopy Normal
Strictures Inflammation
Adaption medical therapy for IBS/IBD
* Depending on local availability
Fig. 2. Diagnostic algorithm in established Crohn’s disease and
Capsule endoscopy
Fourth line
MRI or CT
Third line
Ultrasound
Second line
First line
Europe Enteroscopy
(single or double balloon, spiral technique)
Capsule endoscopy
Third line
CT or MRI
Second line
First line
USA
Color version available online
unexplained clinical symptoms.
Enteroscopy
(single or double balloon, spiral technique)
Fig. 3. Comparison of diagnostic imaging approach in Europe and
the USA.
346
Dig Dis 2013;31:345–350 DOI: 10.1159/000354690
For the initial evaluation of small bowel involvement in patients with IBD, one has to keep in mind that either CT or MRI might not visualize superficial ulcers in the small bowel. Capsule endoscopy has been proven to be superior to both modalities in patients with suspected Crohn’s disease [16–18]. However, due to the risk of concurrent strictures even in clinically asymptomatic patients, a radiological evaluation of the small intestine is always recommended before performing capsule endoscopy [19]. Using an ‘imaging-first approach’ with conventional enteroclysis and MR enterography, it has been demonstrated that only about 10% of all patients with negative upper endoscopy and ileocolonoscopy might obtain a diagnostic benefit with capsule endoscopy after negative radiological imaging [20]. The main difficulties of identifying Crohn’s disease utilizing capsule endoscopy in patients with otherwise negative previous workup are (a) the lack of histological verification of the findings, which can be only achieved with a balloon enteroscopy, and (b) the lack of validated ‘diagnostic criteria’. The limitations of the characterization of capsule endoscopy findings were illustrated by a recent study [21]. A total of 102 patients with suspicion of Crohn’s disease underwent capsule endoscopy following normal or equivocal findings on colonoscopy and radiological small bowel imaging. After 12 months of follow-up, only 13% of patients, who were found to have small bowel ulcerations had been diagnosed with Crohn’s disease by subsequent endoscopic or radiographic re-evaluations. The overall sensitivity of capsule endoscopy, using the presence of any small Herfarth
Downloaded by: UCSF Library & CKM 169.230.243.252 - 3/30/2015 3:38:00 PM
Crohn’s disease
Table 1. Published prospective and retrospective studies comparing CT and MRI in the evaluation of patients with IBD
Reference (first author)
Study design
Patients, n
Result
Papadia, 2013 [48]
prospective
186
No difference between CT and MRI in detection of internal fistulas
Jensen, 2011 [49]
prospective
50
Sensitivities for small bowel inflammation and stenosis similar between CT and MRI
Gee, 2011 [50]
prospective
21
Sensitivities for small bowel inflammation and stenosis similar between CT and MRI
Fiorino, 2011 [51]
prospective
44
No significant difference in sensitivity except small advantage for MRI in detection of fistulae
Schreyer, 2010 [52]
retrospective
53
No difference in sensitivity to detect small bowel inflammation, but CT scans better in visualization of lymph nodes and colonic inflammation
33
Similar sensitivity to detect small bowel disease, but MRI with inferior image quality
Lee, 2009 [6]
prospective
30
No significant difference in sensitivity to detect small bowel inflammation
Schmidt, 2003 [54]
prospective
55 (not all IBD)
CT better than MRI in detecting small bowel inflammation and better inter-observer agreement
Low, 2000 [55]
prospective
26
MRI superior in detection of mild inflammation, (MRI scans were compared to images obtained by a helical CT scanner)
bowel ulcers as criterion for the diagnosis of Crohn’s disease (within 12 months of capsule endoscopy) was 85%, the specificity was 73%, the positive predictive value was 31%, and the negative predictive value was 97%. The positive predictive value increased to 50% if >3 ulcers were used as a criterion for Crohn’s disease on the initial capsule study. Given the high negative predictive value of a normal capsule endoscopy study, the real value is the exclusion of the diagnosis of Crohn’s disease in patients with suspected small bowel inflammation and otherwise negative previous workup.
Imaging Modalities in Established Crohn’s Disease
There seems to be no significant difference with regard to the clinical diagnostic value (sensitivity, specificity and accuracy) between US, CT and MRI for the evaluation of the extent of inflammation, stricturing or penetrating disease or extraintestinal complications [5, 22]. Comparing only CT and MRI, more recent studies have indisputably established that both imaging modalities have similar sensitivities for detection of intestinal inflammation and extraintestinal complications of IBD (table 1). Most of the Update Imaging in IBD
differences found in the tabulated studies might be explained by the technical capabilities of the imaging systems at the time of the study (e.g. single versus multidetector spiral CT, different image processing in MRI) and the experience of the reader with either CT or MRI. Capsule endoscopy can be performed in patients with established Crohn’s disease in cases in which imaging results from CT or MRI or other radiological methods are not conclusive enough to explain the symptoms (e.g. continuing diarrhea despite negative upper and lower gastrointestinal endoscopy and negative CT enterography). A retrospective single-center analysis including 128 capsule endoscopies in patients with IBD reported a change in medication in 62% of the patients in the 3 months after the capsule endoscopy, with 40% initiating a new IBD medication [23].
Advantages and Disadvantages of Imaging Modalities
Before choosing a particular imaging technique, one should be aware of its advantages and disadvantages (table 2). The major disadvantage of CT scans is the expoDig Dis 2013;31:345–350 DOI: 10.1159/000354690
347
Downloaded by: UCSF Library & CKM 169.230.243.252 - 3/30/2015 3:38:00 PM
Siddiki, 2009 [53]
Table 2. Advantages and disadvantages of different imaging modalities for evaluation of small bowel involvement
on patients with IBD Advantages of individual techniques MRI, CT, US: visualization of extraluminal pathologies US: cheap and fast, feasible technique for intervention (abscess drainage) MRI, US: no radiation Small bowel follow-through: information about small bowel motility (adhesions) Disadvantages of individual techniques MRI, CT: no information about small bowel motility (except for MRI if locally MRI fluoroscopy is available) US: operator-dependent, no standardized documentation, quantification of inflammation often difficult MRI: long acquisition time, higher costs compared to CT, limited availability
Perspectives in Imaging of IBD Patients
Radiation Exposure with CT Undoubtedly, the primary advantage of MRI is the lack of radiation exposure. Given the need for repeat imaging due to the chronic nature of IBD, MRI lacks the long-term risk of radiation-induced cancers, whereas the lasting risk of multiple CT scans is broadly acknowledged [24, 25]. Radiation is an important concern, particularly in pediatric patients, in young or pregnant women and in patients with IBD who require frequent repeated imaging examinations. No estimates are currently available for the future risk for cancer in relation to previous abdominal CT scans [26]. The latest epidemiological study in the UK conducted in children receiving head CTs estimated the lifetime risk for leukemia as 1:10,000 and a lifetime risk for brain cancer as 1:2,000 [27]. Estimates for the USA suggest that radiation exposure from CT examinations may be responsible for 0.5–2% of all cancers [28, 29]. Similar estimates for other countries revealed a cumulative cancer risk of 0.6% in the United Kingdom, 1.5% in 348
Dig Dis 2013;31:345–350 DOI: 10.1159/000354690
Germany and 3.2% in Japan [30]. It is important to note that these estimates are derived proposing a linear dose effect (‘linear no-threshold dose-effect model’), which postulates the possibility of carcinogenesis even with an exposure to low-dose radiation. Opponents to this model argue that extrapolating the cancer risk from high-dose exposure (>100 mSv) to lower doses may result in overestimation of the overall cancer risk. More recently, studies have demonstrated that by using multidetector CT scans and specific algorithms for image processing, a substantial radiation dose reduction without compromising diagnostic information can be achieved [31–33]. Lee et al. [34] determined that the effective dose of a standard CT enterography of 4.7 ± 1.1 mSv could be reduced to 2.4 ± 0.5 mSv. However, there were some drawbacks in image quality between normal and reduced dose CT scans. Without a doubt, further technical evolution of CT scanners and imaging software will solve issues of poor image quality by low-dose radiation approaches [35]. Hence, despite the presence of, albeit low, overall cancer risk due to cumulative radiation exposure, the lower costs of CT compared to MRI will be a compelling consideration in the choice of imaging at least in the USA. A Markov analysis taking into account cumulative radiation-induced cancers with yearly or every 2-year CT scans versus MRI examinations revealed that CT would be more cost-effective than MRI if CT is performed with radiation doses
