Download CT colonography: an update

Eur Radiol (2008) 18: 429–437
DOI 10.1007/s00330-007-0764-1
Andrik J. Aschoff
Andrea S. Ernst
Hans-Juergen Brambs
Markus S. Juchems
Received: 8 February 2007
Revised: 25 July 2007
Accepted: 24 August 2007
Published online: 25 September 2007
# European Society of Radiology 2007
A. J. Aschoff (*) . A. S. Ernst .
H.-J. Brambs . M. S. Juchems
Diagnostic and Interventional Radiology,
University Hospitals of Ulm,
Steinhoevelstr. 9,
89070 Ulm, Germany
e-mail: [email protected]
Tel.: +40-731-50061003
Fax: +40-731-50061005
GASTRO INTESTINAL
CT colonography: an update
Abstract Computed tomographic
(CT) colonography (CTC)—also
known as “virtual colonoscopy”—was
first described more than a decade
ago. As advancements in scanner
technology and three-dimensional
(3D) postprocessing helped develop
this method to mature into a potential
option in screening for colorectal
cancer, the fundamentals of the examination remained the same. It is a
minimally invasive, CT-based procedure that simulates conventional
colonoscopy using 2D and 3D com-
Introduction
“Virtual colonoscopy” was first described by David Vining
more than a decade ago [1]. Its potential was quickly
evident and it developed from a research tool to a potential
screening method for colorectal cancer. The basic approach
of acquiring a three-dimensional (3D) dataset after colon
distension in combination with 2D/3D postprocessing has
not changed, though. The preferred terminology for this
method should be computed tomographic colonography
(CTC) [2].
Epidemiology
Colorectal cancer is one of the most common causes for
cancer deaths. With an estimated number of 106,680 new
cases in 2006 and 55,170 estimated deaths in the same year,
it is the third most frequent cancer found among men and
women in the United States and the third most common
cause of death among cancers [3].
A variety of predisposing factors for developing colorectal cancer are known. These include: a first-degree
puterized reconstructions. The primary aim of CTC is the detection of
colorectal polyps and carcinomas.
However, studies reveal a wide performance variety in regard to polyp
detection, especially for smaller
polyps. This article reviews the available literature, discusses established
indications as well as open issues and
highlights potential future developments of CTC.
Keywords CT colonography .
Screening . Colon cancer
relative in whom colon cancer or a large adenomatous
polyp was diagnosed before the age of 60 years; inflammatory bowel disease; a history of familial adenomatous
polyposis or hereditary nonpolyposis; colorectal cancer
syndromes and prior adenomatous polyps or colon cancers.
In developing colorectal cancer, the colonic polyps—in
particular the adenomatous polyps—play a key role.
Through a genetic mutation, normal colon cells may
transform into hyperproliverative epithelium, adenomas
and finally into colorectal cancer [4]. Colorectal polyps can
be removed endoscopically (polypectomy), and colonoscopic polypectomy results in a lower than expected
incidence of colorectal cancer [5] (Fig. 1).
The symptoms of colorectal cancer are often uncharacteristic (obstipation, diffuse pain, loss of weight) and
may delay the final diagnosis. Therefore tests are desired to
detect colon cancer in its early stages or—even better—its
precursors, the adenomatous polyps.
Various screening tests for colorectal cancer are
available—fecal occult blood test (FOBT), sigmoidoscopy
and colonoscopy are the most important ones. Each of these
methods has its limitations. FOBT is a very specific but not
sensitive test [6] and sigmoidoscopy does not assess the
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single breath hold without respiration artifacts is an
advantage that is particularly beneficial for CTC.
Patient preparation
Fig. 1 a Normal colon as seen in optical colonoscopy and b corresponding endoluminal CTC reconstruction
whole colon. Nevertheless, even sigmoidoscopy leads to a
decrease of mortality [7], although up to 52% of the
colorectal polyps are located proximal to the rectosigmoid
[8] and significant polyps can be overseen if located
proximal to the rectosigmoid [9].
Colonoscopy is considered the “gold standard” of
screening for colorectal polyps and endoscopy incorporates
the possibility to perform a biopsy or excision of a polyp
[10, 11]. It offers high sensitivity and specificity, but some
limitations apply to this method as well, including the
invasiveness with a low but existent complication rate and
the inconvenience patients have to suffer [12–14]. The rate
of serious complications during or immediately after
colonoscopy has been reported to be below 0.1% [15].
CTC
Indications
Besides the potential of a screening option for colorectal
polyps and cancer, which is still controversial, CTC has
increasingly established clinical indications, including
incomplete colonoscopy, evaluation of the colon proximal
to a stenosing lesion, and investigation of patients that are
not in a suitable condition for undergoing a conventional
colonoscopy (e.g., patients with bleeding disorders), or for
patients refusing conventional colonoscopy [16–19].
CT equipment
CTC has benefited greatly from developments in computed
tomography (CT) scanner technology and new methods of
3D image processing. The introduction of spiral CT in the
early 1990s culminated in the development of multidetector (MD) CT systems that allow scanning of greater
volumes with thinner slices in less time. The possibility to
perform an examination of the whole abdomen within a
Various studies have been published on how to prepare
patients prior to the examination. A well-distended,
virtually stool- and fluid-free colon is the traditional way
to perform a CTC [20, 21]. The cathartic cleansing keeps
the reader from misinterpreting residual feces and helps to
investigate as much colonic surface as possible. Unfortunately, this is highly dependent on patient compliance.
Other publications emphasize that it is possible to
perform a CTC without cathartic cleansing by using stooland fluid-tagging [22, 23]. Fecal- and fluid-tagging is
achieved by fractionated oral administration of contrast
agent (barium, sodium/meglumine diatrizoate). This helps
to improve discrimination between stool residues and
genuine polyps, and thus potentially improves the specificity of CTC [23, 24].
Different regimes and medications to perform a cathartic
bowel cleansing are in use. A lot of experience with these
medications exists because most of them are also used prior
to optical colonoscopy. In addition to home-made cleansing solutions that some favor, most institutions rely on one
of three commercially available groups of cleansing
solutions: polyethylene glycol [PEG; e.g., GoLytely
preparations (Delcoprep) and NuLytely preparations
(Endofalk)]-based, phospho-soda-based solutions (e.g.,
Fleet Phospho-soda) and magnesium citrate (e.g., LoSoPrep). Although some studies show an advantage for
phospho-soda, we favor a NuLytely PEG-based cleansing
protocol as we are constantly able to achieve sufficient
cleansing with this preparation regime [25].
Macari et al. [20] compared phospho-soda-based (‘dry’)
cathartic preparation with PEG-electrolyte-based solutions
(‘wet’) for CTC and found significantly less residual fluid
and a drier mucosal surface using phospho-soda. Although
preparations from both groups have been demonstrated
safe for use in healthy individuals, caution should be taken
in selecting a bowel preparation for individuals with
significant comorbid conditions [26]. Sodium phosphate is
contraindicated in patients with serum electrolyte imbalances, advanced hepatic dysfunction, acute and chronic
renal failure, recent myocardial infarction, unstable angina,
congestive heart failure, ileus, malabsorption, and ascites
[26].
As mentioned above, it is possible to perform CTC
without cathartic cleansing (“dry” preparation) [22, 27].
Bielen et al. [24] reported high patient compliance and
acceptance using a “dry” bowel preparation. Especially
noncompliant, elderly patients could benefit from a dry
preparation. Combined with fecal tagging the use of
automated cleansing techniques [28, 29] seems to be very
promising.
431
After colonic cleansing, good bowel distension during
scanning is required to further enhance visualization of the
colonic surface. The easiest and most inexpensive way of
achieving a pneumocolon is insufflating room air through a
rectal enema tube into the colon using a manual balloon
pump. This can be performed physician or patient
controlled. We routinely achieve satisfactory results using
the later approach [25].
CO2 administration instead of room air can be done
automatically and patient controlled as well [30]. Some
favor CO2 over room air as it is supposed to be better
tolerated by means of patient comfort and potentially
provides better colonic distension [31].
Several studies showed that it is imperative to perform
the CT scan in the prone and supine patient positions [32–
35]. This helps to reallocate fluid to reveal previously
hidden colonic surface, and insufflated air is redistributed
during patient repositioning to further improve sensitivity
and specificity in detecting colorectal polyps.
Another controversially discussed issue is the use of
spasmolytics (glucagon, N-butylscopolamin) prior to the
scan to improve colonic distension. While some studies
clearly show beneficial results in regard to bowel
distension and patient comfort when using spasmolytics
[36, 37], others failed to do so [35, 38]. Nevertheless, we
routinely use spasmolytics.
2D and 3D data work-up
The most important 2D procedures are the evaluation of the
axial images and multiplanar reconstructions (MPR) that
can be used to reconstruct any required scan orientation.
In early studies on CTC, the complementary use of 2D
and 3D images together was assumed to provide the
highest sensitivity [45, 46]. Although some of the newer
studies still favor a solitary 2D interpretation over 3D
viewing [47, 48], some studies yielded low sensitivities for
large polyps, ranging from 55% to 64% [49–51] using a
primary 2D approach. On the other hand, some authors
prefer primary 3D work-up [52, 53]. The impressive results
(sensitivity 93.8% for lesions >10 mm) achieved in the
latter study all go along with further improved CTC
software as well as in CT scanner hardware.
A major disadvantage of a primary 3D endoluminal
approach—similar to conventional colonoscopy—is the
lack of ability to look behind haustral folds. Ante- and
retrograde fly-throughs are therefore mandatory, resulting
in increased interpretation time. New visualization methods like an unfolded cube projection [54] and virtual
dissection displays (e.g., Philips Filet view, Fig. 2, [47, 55,
56]) have the potential to overcome this limitation.
Significant decrease of evaluation time down to 10 min
per case could be observed with these techniques.
Although it is our personal experience that lesion
detection is best performed using a 3D approach, it is
CTC scanning protocols
necessary to further evaluate detected lesions in a 2D or
MPR work-up to avoid pitfalls caused by misinterpreting
Both collimation and pitch may influence the sensitivity for stool residuals, inverted diverticula, etc. as genuine colopolyp detection [39].
rectal polyps (Fig. 3).
In the recent literature a clear trend for recommending
Much emphasis has been put into CTC research, but there
lower collimations can be recognized [18, 47, 48]. has been much unsteadiness in the results obtained with
According to the “Consensus statement on CT colonography” regard to sensitivity and specificity, as outlined below. It
of the European society of gastrointestinal and abdominal seems clear that reader performance increases with experadiology ESGAR [40], a collimation of less than 3 mm is rience [57, 58], and physicians who do CTC should receive
currently recommended.
appropriate training to perform and evaluate CTC datasets.
The downside of acquiring thinner slices may be
A lot of research [59–63] has been performed on
increased radiation dose. As radiation is of serious concern automated polyp detection [computer-aided detection
when performing CTC, exposure has to be kept as low as (CAD), Fig. 4], using different approaches: CAD as a “first
possible. Consequently many studies investigated so-called reader”, as a “concurrent reader,” or as a “second reader.” As
low-dose protocols [41–44]. In a study that was published a “first reader”, CAD separates out negative cases before
by Macari et al. in 2002 [44], 50 mAs tube current, 120 kV physicians read the cases. However, this paradigm bears the
voltage and a collimation of 4×1 mm were used. Large risk of missing colorectal lesions. CAD as a “concurrent
polyps (>10 mm) were detected with a sensitivity of 93%, reader” presents suspect lesions to the physician, who can
whereas the detection of intermediate size polyps (6–9 mm) then further evaluate the presented lesion and decide whether
was compromised totaling in a sensitivity of 70%. Even it is a genuine polyp or not. It is unclear whether this type of
more encouraging results were published by Iannacone et evaluation biases the reader by drawing attention to CAD
al. in 2003 [43]. With a current of 10 mAs and a voltage of findings. Finally CAD as “second reader” re-reviews CTC
140 kVp, 100% sensitivity was reached for large polyps cases. Thus, CAD findings can be used to alter a report if
(>10 mm) as well as for intermediate sized ones (6–9 mm). lesions have been missed in first place. Using CAD as a
The “Consensus statement” mentioned above [44] “second reader” in this specific setting may lead to an
currently recommends for supine and prone non-IV contrast increase in reading time, though [64].
enhanced acquisition with a tube current of 100 mAs or less
Recently published data showed encouraging results
(50 mAs or less), dependent on available CT technology.
using CAD. In a study performed by Taylor et al. [62],
432
Fig. 2 Principle of a colon
dissection display. The colon,
previously reconstructed as
a tube, is cut at one side (a),
unrolled (b) and presented
similar to a pathological
specimen (c)
CAD reached a sensitivity of 92% for polyps >10 mm.
Overall the CAD performance was comparable and in
some parts even better than that of expert readers.
If a robust CAD algorithm can be found, a further
decrease in interpretation time may be on the horizon, and
inexperienced readers might miss less polyps.
Although so-called “flat” adenomas are not considered to
have a markedly increased risk of developing into invasive
cancer compared with sessile or pedunculated polyps by
some researchers [65], they still remain problematic to be
detected in CTC [66, 67]. Since up to 27% of all baseline
adenomas may be flat [65], this remains a problem that
needs researchers’ attention in the future. One possible
Fig. 3 Pitfall in CTC.
a Polypoid lesion as seen in
endoluminal and dissection 3D
reconstructions. b The corresponding MPR discriminates
residual feces (arrow) containing air from a genuine polyp
approach is using a “translucency view” (Fig. 5). This
postprocessing algorithm assigns colors to the mucosa
based on HU values. Besides ruling out false positives by
helping to differentiate between stool residuals and colorectal polyps, this might (especially if used in conjunction
with IV contrast media) help to reveal flat adenomas.
CTC performance
Pickhardt and coworkers published in 2003 the first large
prospective study in an average-risk screening population,
comparing more than 1,200 CT colonographies with
433
Fig. 4 CAD marked 8-mm polyp (blue) in endoluminal (a) and
dissection (b) display mode
optical colonography performed on the same day [53].
Their sensitivity of CTC in the detection of adenomatous
polyps was 93.8% for polyps at least 10 mm in diameter,
93.9% for polyps at least 8 mm in diameter, and 88.7% for
polyps at least 6 mm in diameter. The sensitivity of optical
colonoscopy for adenomatous polyps was 87.5%, 91.5%,
and 92.3% for the three sizes of polyps, respectively. They
concluded that CTC is an accurate screening method for
the detection of colorectal neoplasia in asymptomatic
Fig. 5 “Tranclucency view”
(shown in the middle of the
upper row). 1 untagged stool is
represented in green; 2 pedunculated polyp is shown in red
average-risk adults and compares favorably with optical
colonography (Fig. 6).
Not quite 2 years later, Rockey and coworkers published
their prospective results of more than 600 CTCs in
comparison with optical colonoscopy and air contrast
barium enema [51], using a similar study design to the one
used by Pickhardt et al. [53]. When analyzed on a perpatient basis, for lesions 10 mm or larger in size, the
sensitivity of CTC was 59% (compared with 93.8%
reported by Pickhardt and coworkers), and of colonoscopy
98%. For lesions 6–9 mm in size, sensitivity was 51% for
CTC and 99% for colonoscopy.
The exact reason for this striking difference in reported
performance of CTC is yet unclear, although both papers
were extensively discussed and commented in the scientific
community.
Three recent major meta-analysis publications tried to
systematically approach the CTC performance in the light
of the reported variability [68–70] (Table 1).
In the largest meta-analysis published up to now,
Mulhall et al. [69] systematically reviewed the test
performance of CTC, selecting prospective studies published before February 2005 from 33 studies (CTC after
full bowel preparation and insufflation of the colon, with
colonoscopy or surgery as the gold standard, collimation
smaller than 5 mm, both 2D and 3D for scan interpretation)
providing data on 6,393 patients. The sensitivity of CTC
434
account for this variability. Collimation, type of scanner,
and mode of imaging explain some of the discrepancy, but
not all of it.
Patients’ perception and tolerance of CTC compared
with conventional colonoscopy
Many comparisons of patients’ acceptance and tolerance
have been published, and researchers were able to show
that either CTC is better tolerated than colonoscopy [13,
14] or vice versa [71, 72]. The discussion is not very useful
because most colonoscopies are performed using sedatives,
which makes a direct comparison impossible. Nevertheless, bowel preparation seems to be the most uncomfortable issue for both CTC and colonoscopy from the patients’
point of view [14].
CTC in incomplete colonoscopy
CTC after incomplete colonoscopy may be especially
helpful for evaluation of the nonvisualized part of the colon
after incomplete colonoscopy, and it can increase the
diagnostic yield of masses and clinically important polyps
in this context [17, 19, 73]. The rate of incomplete
colonoscopies varies between 4% [74] and 19% [75–77].
This frequency serves as an important indication for
performing immediate CTC in order to avoid repeat bowel
preparation when possible.
Fig. 6 Colonic polyp. a Dissection view, b endoluminal view,
c endoscopic view. Note also diverticulae, especially apparent in a
was heterogeneous but improved as polyp size increased
[48% (95% CI, 25–70%) for detection of polyps <6 mm,
70% (95% CI, 55–84%) for polyps 6–9 mm, and 85%
(95% CI, 79–91%) for polyps >9 mm]. In contrast,
specificity was homogenous [92% (95% CI, 89–96%)
for detection of polyps <6 mm, 93% (95% CI, 91–95%)
for polyps 6–9 mm, and 97% (95% CI, 96–97%) for
polyps >9 mm]. They came to the conclusion that, although
CTC is highly specific, the range of reported sensitivities is
wide, and patient or scanner characteristics do not fully
CTC open issues
As discussed above and outlined in the meta-analysis by
Mulhall et al. [69], the wide range of reported sensitivities
that can not be completely explained must be resolved
before CTC can be advocated for generalized screening
for colorectal cancer. CTC has not yet been officially
accepted as a screening procedure in any country, mainly
because of the lack of reliable evidence resulting from
large trials.
Another important open issue concerns the relevance of
small polyps. The overall prevalence of colorectal polyps
independent of size and histology in an average risk
screening population is estimated to be in the range of 25–
Table 1 CTC performance as calculated in meta-analyses
Authors
Year
Number
of studies
included
Number
of patients
included
Per patient sensitivity;
polyps >9 mm
(95% CI)
Per patient sensitivity;
polyps 6–9 mm
(95% CI)
Per patient sensitivity;
polyps <6 mm
(95% CI)
Sosna et al. [68]
Mulhall et al. [69]
2003
2005
14
33
1,324
6,393
88% (84–93%)
85% (79–91%)
84% (80–89%)
70% (55–84%)
65% (57–73%)
48% (25–70%)
435
30% [78–80]. The current concept of polypectomy is to
remove all polyps detected during optical colonoscopy
(independent of size and histology). This results in a
significant decrease in mortality from colorectal cancer, as
shown by the National Polyp Study Workgroup [5].
Although some authors argue that polyps of less than
5 mm [81] or 10 mm [82] in size may not need immediate
polypectomy, the majority of gastroenterologists disagree
[83], and no prospective study has shown a decrease in the
mortality of colorectal cancer using any threshold size for
polypectomy. This has several implications for CTC.
Even if CTC would be capable of detecting all or at least
the majority of the polyps smaller than 10 mm and no falsepositive findings would occur, approximately every third or
fourth patient would still have to undergo interventional
optical colonoscopy with polypectomy after CTC. Since
this seems to be an unacceptably high rate of follow-up
endoscopies and the known lower sensitivity of CTC in the
detection of smaller polyps, a threshold size for “relevant”
polyps would have to be defined before CTC could be used
in large screening settings.
The other major implication relates to the fact that CTC
performs poorer in the detection of smaller polyps and
relates to the clinical value of a “negative” CTC in terms of
need for follow-up exams, and the definition of a
reasonable time interval to do so.
Addressing the significance of missed or found small
polyps on CTC, Macari et al. [84] recommend a CTC
follow-up after 3 years for lesions smaller than 6 mm. The
ESGAR consensus statement recommends that polyps less
than 5 mm in size should not even be reported, providing
that agreement for such a reporting policy has been made
with those referring patients [40], but no general
recommendation regarding follow-up intervals was made.
In a consensus proposal, the Working Group on Virtual
Colonoscopy discusses the so called “clinically important
polyp and the rationale for surveillance” and discriminates
between “diminuitive”, “intermediate”, “multiple intermediate” and “lesions that are 1 cm in size or larger” [85].
In their opinion, “diminuitive” lesions (smaller than
5 mm) should not be reported, similar to the approach
suggested by the ESGAR consensus [40]. Patients with one
or two “intermediate” lesions (6–9 mm) should be
recommended interval surveillance after up to three years
depending on several factors, including patient age, sex,
comorbidities, and preference and local practice. More than
three lesions of 6–9 mm or one lesion of at least 10 mm
require immediate colonoscopy.
Although aspects of this proposal may be discussed
controversially, the proposed framework addresses the
definite need to have a reference guide for interpretation of
CTC results.
Conclusion
CTC offers high sensitivity and specificity for the detection
of colon cancer and polyps larger than 10 mm in size, given
suitable equipment and experienced investigators. It is the
method of choice for incomplete colonoscopies and for
patients that to some reason can not undergo optical
colonoscopy. Nevertheless, its use in routine screening
should be subject to the introduction of quality controls
with prescribed examination standards. For screening
purposes, the wide range of reported sensitivities that can
not be completely explained must be resolved and a
threshold size for clinically relevant polyps has to be
defined, and its application backed by prospective studies.
In particular, multicenter trials are necessary to achieve this
goal. Computer-assisted evaluation has the potential to
shorten the examination time and may further increase
sensitivity in the near future.
References
1. Vining D, Shifrin R, Grishaw E (1994)
Virtual colonoscopy. Radiology
193:446
2. Johnson CD, Hara AK, Reed JE (1998)
Virtual endoscopy: what’s in a name? AJR
Am J Roentgenol 171(5):1201–1202
3. Jemal A et al (2006) Cancer statistics,
2006. CA Cancer J Clin 56(2):106–130
4. Fearon ER, Vogelstein B (1990) A
genetic model for colorectal tumorigenesis. Cell 61(5):759–767
5. Winawer SJ et al (1993) Prevention of
colorectal cancer by colonoscopic
polypectomy. The National Polyp
Study Workgroup. N Engl J Med 329
(27):1977–1981
6. Rockey DC et al (1998) Relative
frequency of upper gastrointestinal and
colonic lesions in patients with positive
fecal occult-blood tests. N Engl J Med
339(3):153–159
7. Selby JV et al (1992) A case-control
study of screening sigmoidoscopy and
mortality from colorectal cancer.
N Engl J Med 326(10):653–657
8. Bernstein MA et al (1985) Distribution
of colonic polyps: increased incidence
of proximal lesions in older patients.
Radiology 155(1):35–38
9. Imperiale TF et al (2000) Risk of
advanced proximal neoplasms in
asymptomatic adults according to the
distal colorectal findings. N Engl J Med
343(3):169–174
10. Ransohoff DF, Sandler RS (2002)
Clinical practice. Screening for
colorectal cancer. N Engl J Med 346
(1):40–44
11. Rockey DC (2005) Colon imaging:
computed tomographic colonography.
Clin Gastroenterol Hepatol 3(7 Suppl
1):S37–S41
12. Juchems MS, Ehmann J, Brambs H-J,
Aschoff AJ (2005) A retrospective
evaluation of patient acceptance of CT
colonography (“virtual colonoscopy”)
in comparison to conventional colonoscopy in an average risk screening
population. Acta Radiol 46(7):664–670
436
13. Svensson MH et al (2002) Patient
acceptance of CT colonography and
conventional colonoscopy: prospective
comparative study in patients with or
suspected of having colorectal
disease. Radiology 222(2):337–345
14. Thomeer M et al (2002) Patient acceptance for CT colonography: what is
the real issue? Eur Radiol
12(6):1410–1415
15. Rainis T et al (2007) Diagnostic yield
and safety of colonoscopy in Israeli
patients in an open access referral
system. J Clin Gastroenterol 41
(4):394–399
16. Fenlon HM et al (1999) Occlusive
colon carcinoma: virtual colonoscopy
in the preoperative evaluation of the
proximal colon. Radiology
210(2):423–428
17. Morrin MM et al (1999) Endoluminal
CT colonography after an incomplete
endoscopic colonoscopy. AJR Am J
Roentgenol 172(4):913–918
18. Neri E et al (2002) Colorectal cancer:
role of CT colonography in preoperative evaluation after incomplete
colonoscopy. Radiology
223(3):615–619
19. Gryspeerdt S et al (2005) CT
colonography with fecal tagging after
incomplete colonoscopy. Eur Radiol 15
(6):1192–1202
20. Macari M et al (2001) Effect of
different bowel preparations on residual
fluid at CT colonography. Radiology
218(1):274–277
21. Yee J et al (2001) Colorectal neoplasia:
performance characteristics of CT
colonography for detection in 300
patients. Radiology 219(3):685–692
22. Lefere PA et al (2002) Dietary fecal
tagging as a cleansing method before
CT colonography: initial results polyp
detection and patient acceptance.
Radiology 224(2):393–403
23. Callstrom MR et al (2001) CT
colonography without cathartic preparation: feasibility study. Radiology 219
(3):693–698
24. Bielen D et al (2003) Dry preparation
for virtual CT colonography with fecal
tagging using water-soluble contrast
medium: initial results. Eur Radiol 13
(3):453–458
25. Juchems MS et al (2006) Bowel
preparation for CT-colonography:
comparison of two different cleansing
protocols. Eur J Radiol 60(3):460–464
26. Wexner SD et al (2006) A consensus
document on bowel preparation before
colonoscopy: prepared by a task force
from the American Society of Colon
and Rectal Surgeons (ASCRS), the
American Society for Gastrointestinal
Endoscopy (ASGE), and the Society of
American Gastrointestinal and
Endoscopic Surgeons (SAGES). Dis
Colon Rectum 49(6):792–809
27. Lefere P et al (2005) CT colonography
after fecal tagging with a reduced
cathartic cleansing and a reduced volume of barium. AJR Am J Roentgenol
184(6):1836–1842
28. Zalis ME, Hahn PF (2001) Digital
subtraction bowel cleansing in CT
colonography. AJR Am J Roentgenol
176(3):646–648
29. Zalis ME et al (2003) CT
colonography: digital subtraction bowel
cleansing with mucosal reconstruction
initial observations. Radiology 226
(3):911–917
30. Shinners TJ et al (2006) Patientcontrolled room air insufflation versus
automated carbon dioxide delivery for
CT colonography. AJR Am J
Roentgenol 186(6):1491–1496
31. Burling D et al (2006) Automated
insufflation of carbon dioxide for
MDCT colonography: distension and
patient experience compared with
manual insufflation. AJR Am J
Roentgenol 186(1):96–103
32. Chen SC et al (1999) CT colonography:
value of scanning in both the supine
and prone positions. AJR Am J
Roentgenol 172(3):595–599
33. Yee J et al (2003) Comparison of
supine and prone scanning separately
and in combination at CT
colonography. Radiology
226(3):653–661
34. Fletcher JG et al (2000) Optimization
of CT colonography technique:
prospective trial in 180 patients.
Radiology 216(3):704–711
35. Morrin MM et al (2002) CT
colonography: colonic distention improved by dual positioning but not
intravenous glucagon. Eur Radiol 12
(3):525–530
36. Taylor SA et al (2003) Optimizing
colonic distention for multi-detector
row CT colonography: effect of hyoscine butylbromide and rectal balloon
catheter. Radiology 229(1):99–108
37. Rogalla P et al (2005) Spasmolysis at
CT colonography: butyl scopolamine
versus glucagon. Radiology 236
(1):184–188
38. Bruzzi JF et al (2003) Efficacy of IV
Buscopan as a muscle relaxant in CT
colonography. Eur Radiol 13
(10):2264–2270
39. Taylor SA et al (2003) Multi-detector
row CT colonography: effect of collimation, pitch, and orientation on polyp
detection in a human colectomy
specimen. Radiology 229(1):109–118
40. Taylor SA et al (2007) European
society of gastrointestinal and abdominal radiology (ESGAR): Consensus
statement on CT colonography. Eur
Radiol 17(2):575–579
41. Cohnen M et al (2003) Effective doses
in standard protocols for multi-slice CT
scanning. Eur Radiol 13(5):1148–1153
42. Cohnen M et al (2004) Feasibility of
MDCT Colonography in ultra-low-dose
technique in the detection of colorectal
lesions: comparison with highresolution video colonoscopy. AJR Am
J Roentgenol 183(5):1355–1359
43. Iannaccone R et al (2003) Feasibility of
ultra-low-dose multislice CT
colonography for the detection of colorectal lesions: preliminary experience.
Eur Radiol 13(6):1297–1302
44. Macari M et al (2002) Colorectal
neoplasms: prospective comparison of
thin-section low-dose multi-detector
row CT colonography and conventional
colonoscopy for detection. Radiology
224(2):383–392
45. Hara AK et al (2001) Colorectal polyp
detection with CT colography: twoversus three-dimensional techniques.
Work in progress. Radiology 200
(1):49–54
46. Royster AP et al (1997) CT colonoscopy of colorectal neoplasms:
two-dimensional and three-dimensional
virtual-reality techniques with colonoscopic correlation. AJR Am J
Roentgenol 169(5):1237–1242
47. Hoppe H et al (2004) Virtual colon
dissection with CT colonography compared with axial interpretation and
conventional colonoscopy: preliminary
results. AJR Am J Roentgenol 182
(5):1151–1158
48. Bruzzi JF et al (2004) Colonic surveillance by CT colonography using axial
images only. Eur Radiol 14(5):763–767
49. Cotton PB et al (2004) Computed
tomographic colonography (virtual
colonoscopy): a multicenter comparison with standard colonoscopy for
detection of colorectal neoplasia. Jama
291(14):1713–1719
50. Johnson CD et al (2003) Prospective
blinded evaluation of computed tomographic colonography for screen detection of colorectal polyps.
Gastroenterology 125(2):311–319
437
51. Rockey DC et al (2005) Analysis of air
contrast barium enema, computed
tomographic colonography, and
colonoscopy: prospective comparison.
Lancet 365(9456):305–311
52. Beaulieu CF et al (1999) Display
modes for CT colonography. Part II.
Blinded comparison of axial CT and
virtual endoscopic and panoramic endoscopic volume-rendered studies. Radiology 212(1):203–212
53. Pickhardt PJ et al (2003) Computed
tomographic virtual colonoscopy to
screen for colorectal neoplasia in
asymptomatic adults. N Engl J Med
349(23):2191–2200
54. Vos FM et al (2003) Three-dimensional
display modes for CT colonography:
conventional 3D virtual colonoscopy
versus unfolded cube projection. Radiology 228(3):878–885
55. Johnson KT et al (2006) CT
colonography using 360-degree virtual
dissection: a feasibility study. AJR Am
J Roentgenol 186(1):90–95
56. Juchems MS et al (2006) CT
colonography: comparison of a colon
dissection display versus 3D
endoluminal view for the detection of
polyps. Eur Radiol 16(1):68–72
57. Soto JA, Barish MA, Yee J (2005)
Reader training in CT colonography:
how much is enough? Radiology 237
(1):26–27
58. Taylor SA et al (2004) CT
colonography: effect of experience and
training on reader performance. Eur
Radiol 14(6):1025–1033
59. Jerebko AK et al (2003) Computerassisted detection of colonic polyps
with CT colonography using neural
networks and binary classification
trees. Med Phys 30(1):52–60
60. Luboldt W et al (2005) Automated
mass detection in contrast-enhanced CT
colonography: an approach based on
contrast and volume. Eur Radiol 15
(2):247–253
61. Summers RM et al (2002) Colonic
polyps: complementary role of computer-aided detection in CT colonography.
Radiology 225(2):391–399
62. Taylor SA et al (2006) Computerassisted reader software versus expert
reviewers for polyp detection on CT
colonography. AJR Am J Roentgenol
186(3):696–702
63. Kiss G et al (2002) Computer-aided
diagnosis in virtual colonography via
combination of surface normal and
sphere fitting methods. Eur Radiol 12
(1):77–81
64. Mang T et al (2007) Effect of
computer-aided detection as a second
reader in multidetector-row CT colonography. Eur Radiol DOI 10.1007/
s00330-007-0608-z
65. O’Brien MJ et al (2004) Flat adenomas
in the National Polyp Study: is there
increased risk for high-grade dysplasia
initially or during surveillance? Clin
Gastroenterol Hepatol 2(10):905–911
66. Rex DK, Vining D, Kopecky KK
(1999) An initial experience with
screening for colon polyps using spiral
CT with and without CT colography
(virtual colonoscopy). Gastrointest Endosc 50(3):309–313
67. Van Gelder RE et al (2004) Computed
tomographic colonography compared
with colonoscopy in patients at increased risk for colorectal cancer. Gastroenterology 127(1):41–48
68. Sosna J et al (2003) CT colonography
of colorectal polyps: a metaanalysis.
AJR Am J Roentgenol 181(6):1593–
1598
69. Mulhall BP, Veerappan GR, Jackson JL
(2005) Meta-analysis: computed tomographic colonography. Ann Intern Med
142(8):635–650
70. Halligan S et al (2005) CT colonography in the detection of colorectal
polyps and cancer: systematic review,
meta-analysis, and proposed minimum
data set for study level reporting.
Radiology 237(3):893–904
71. Akerkar GA et al (2001) Patient experience and preferences toward colon
cancer screening: a comparison of virtual colonoscopy and conventional colonoscopy. Gastrointest Endosc 54
(3):310–315
72. Forbes GM, Mendelson RM (2000)
Patient acceptance of virtual colonoscopy. Endoscopy 32(3):274–275
73. Copel L et al (2007) CT colonography
in 546 patients with incomplete colonoscopy. Radiology 244(2):471–478
74. Marshall JB, Barthel JS (1993) The
frequency of total colonoscopy and
terminal ileal intubation in the 1990s.
Gastrointest Endosc 39(4):518–520
75. Shah HA et al (2007) Factors associated with incomplete colonoscopy: a
population-based study. Gastroenterology 132(7):2297–2303
76. Dafnis G et al (2005) Patient factors
influencing the completion rate in
colonoscopy. Dig Liver Dis
37(2):113–118
77. Cirocco WC, Rusin LC (1995) Factors
that predict incomplete colonoscopy.
Dis Colon Rectum 38(9):964–968
78. Correa P (1978) Epidemiology of
polyps and cancer. Major Probl Pathol
10:126–152
79. Williams AR, Balasooriya BA, Day
DW (1982) Polyps and cancer of the
large bowel: a necropsy study in
Liverpool. Gut 23(10):835–842
80. Winawer SJ et al (1992) The National
Polyp Study. Design, methods, and
characteristics of patients with newly
diagnosed polyps. The National Polyp
Study Workgroup. Cancer 70(5
Suppl):1236–1245
81. Aldridge AJ, Simson JN (2001) Histological assessment of colorectal adenomas by size. Are polyps less than
10 mm in size clinically important? Eur
J Surg 167(10):777–781
82. Ransohoff DF (2005) CON: Immediate
colonoscopy is not necessary in patients who have polyps smaller than
1 cm on computed tomographic colonography. Am J Gastroenterol 100
(9):1905–1907; discussion 1907–8
83. Rex DK (2005) PRO: Patients with
polyps smaller than 1 cm on computed
tomographic colonography should be
offered colonoscopy and polypectomy.
Am J Gastroenterol 100(9):1903–1905;
discussion 1907–8
84. Macari M et al (2004) Significance of
missed polyps at CT colonography.
AJR Am J Roentgenol 183(1):127–134
85. Zalis ME et al (2005) CT colonography
reporting and data system: a consensus
proposal. Radiology 236(1):3–9