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MDCT as a Diagnostic Tool in
Evaluating Small Bowel
Rania Mohammed Refaat Abd El-Hamid
(MSc. )
Imaging the small bowel is challenging technically:
-The organ is long and serpentine
-A large field of view and a large volume is needed to display
in entirety.
-Another problem for imaging is motion, both intrinsic
motion of peristalsis and the positional changes caused by
breathing making their tracing very difficult.
In addition, because small bowel diseases have a low
incidence, their appearance is less well known and there is
an increased risk of missing them. Ever most of the
common diseases in the small bowel, early changes are
subtle making their diagnoses difficult
The availability of MDCT along with advancements in 3D
CT imaging systems has greatly expanded the role of CT in
evaluation of suspected small bowel pathology.
Applications which were once routinely performed with
barium studies (e.g. evaluate suspected small bowel
obstruction) or modality angiography (e.g. evaluate for
mesenteric ischemia) have now been replaced with CT
scans. CT is now considered a first line for the evaluation
of a wide variety of small bowel diseases
For an optimal display of the bowel, two things
are essential in imaging: intraluminal contrast and
distension. Intraluminal contrast is needed to
delineate bowel loops in the abdominal cavity and
to depict the bowel wall. Distension in small
bowel imaging is essential to unfold the bowel
tube and separate out the bowel wall. In imaging
the small bowel, intraluminal contrast and
distension are inseparable.
Positive intraluminal contrast
Positive oral contrast are Barium sulfate or iodinated solutions.
Barium should only be used in very low doses to prevent artifacts.
The iodinated contrast agent meglumine diatrizoate (Gastrographin) is the
most widely used agent for CT.
They have wide acceptance and a low adverse-event rate.
Their use leads to a diminished display of the bowel wall because of the high
density of the lumen and hence to miss an enhancing tumour. One of the other
problems with these agents is their relatively low distending capability. These
positive oral contrast agents can be problematic when performing 3D imaging
and 3D angiography in particular since the high-density bowel contents can
obscure the opacified blood vessels and therefore need to be edited.
Use of positive intraluminal contrast medium
Furukawa, A. et al. Radiographics 2004;24:689-702
Copyright ©Radiological Society of North America, 2004
Use of positive intraluminal contrast medium
Furukawa, A. et al. Radiographics 2004;24:689-702
Copyright ©Radiological Society of North America, 2004
Neutral intraluminal contrast
Contrast agents that have an intermediate density (10-30 HU). They
are used with increasing frequency.
with IV contrast, they provide very good display of the bowel wall and
thus better visualization of the enhancing bowel wall is obtained.
The most widely used neutral oral contrast agent is water. it is
inexpensive and universally available and well tolerated but water
alone is not an ideal contrast agent, because it is absorbed early in the
gastrointestinal system and is not available in the mid and distal
section of the small bowel so it does not always result in optimal
distention of the distal small bowel. The administration of agents such
as Glucagon may improve distension but is not routinely done.
To overcome early absorption of water as a neutral contrast
agent, additives that increase the osmolarity of the water
are used without changing the contrast characteristics.
Mannitol or other long- chain sugars can be used. The
adverse effects of these additives are nausea and diarrhea.
A newly introduced neutral oral contrast agent (VoLumen) is used
which is based in oral barium sulfate solutions containing all the
additives but with only 0.1 % of barium sulfate. With such a low
concentration of barium it has no possible contrast effect in MDCT and
even though containing barium, it is considered a neutral contrast
agent. Compared with water or meglumine diatrizoate, this contrast
agent creates for better distension and the display of the bowel wall is
very clear compared with these intraluminal contrast agents.
Milk has been used by some groups in order to distend the small bowel
in patients undergoing CT angiography. Whole milk has a CT density
similar to water, but has a slower small bowel transit time and should
therefore result in better distention of the bowel.
Small bowel strictures in a 39-year-old man with Crohn disease and vomiting
Paulsen, S. R. et al. Radiographics 2006;26:641-657
Copyright ©Radiological Society of North America, 2006
Negative intraluminal contrast
 Negative contrast agents display a density below 10 HU in
MDCT and are normally fat based. Although they provide
a good distension and can result in good visualization of
the enhancing bowel wall they are not so widely used.
Carbon dioxide could work as a negative contrast but
patient tolerance is low. It is very difficult to apply as there
is currently no easy way to non invasively distend the
small intestine with air
Between 1,500 and 2,000 mL (or more) of contrast
material is administered orally 45–90 minutes prior to the
examination. To provide adequate and uniform distention
of the bowel loops, patients are asked to steadily ingest the
contrast material over a 20–60-minute period .
The contrast material may be administered through a
nasojejunal catheter at a rate of 100–250 mL/min with the
help of a roller pump and the technique is called CT
enteroclysis. An increased rate of infusion or dual-phase
intubation with an initial flow rate of 80–120 mL/min
followed by a rate of 200 mL/min is recommended to
achieve reflex intestinal atony and thereby minimize
motion artifact. Use of a nasojejunal catheter allows better
luminal distention but causes patient discomfort.
If necessary, 300– 1,000 mL of contrast agent can be
administered transrectally.
CT scans are obtained from the dome of the liver to the
level of the perineum to cover the entire course of the
intestine. Imaging with the patient in the prone position is
recommended to disperse the small bowel loops.
IV contrast
The peroral contrast must be combined with IV contrast. Specially, the
combination of neutral oral contrast and IV contrast gives a good
display of the bowel wall.
Inflammatory bowel disease and neoplasm are optimally displayed
with the use of IV contrast. Non ionic iodinated contrast is most widely
used today.
The ideal volume and injection rate are 125 mL and 3 to 4 mL/ s,
respectively. For detailed display of the mesenteric vasculature, a
higher volume (150 mL) and a higher flow rate 4-5 mL/ s are chosen.
A 60 second scan delay is ideal to acquire the small bowel wall in its
best enhancement phase
Copyright ©Radiological Society of North America, 2004
CT enterography differs from routine abdominopelvic CT in
that it makes use of thin sections (2 to 2.5 mm section thickness
and reconstruction intervall 1 to 1.5) and large volumes of
enteric contrast material to better display the small bowel lumen
and wall. Although CT enteroclysis profits from excellent
distension of the entire small bowel and precise evaluation of
the entire small bowel and precise evaluation of the extent of
extraluminal disease, it has the major drawbacks of invasiveness
and high radiation exposure.
Compared with the traditional small bowel follow-through
examination, CT enterography has several advantages: (a) it
displays the entire thickness of the bowel wall
 (b) it allows examination of deep ileal loops in the pelvis
without superimposition
 (c) it permits evaluation of the surrounding mesentery and
perienteric fat. CT enterography also allows assessment of
solid organs and provides a global overview of the abdomen.
CT Enterography with the Use of neutral intraluminal contrast medium
Furukawa, A. et al. Radiographics 2004;24:689-702
Copyright ©Radiological Society of North America, 2004
The clinical efficacy of MR imaging has been investigated,
and favorable results have been reported
High soft-tissue contrast, static and dynamic imaging
capabilities, and the absence of ionizing radiation exposure
represent advantages of MR imaging over CT.
On the other hand, MR imaging is more time consuming,
less readily available, and more expensive.
Advantages of CT over MR imaging include greater
availability, shorter examination times, flexibility in
choosing imaging thickness and planes after data
acquisition with multi–detector row CT, and higher spatial
Capsule endoscopy is a revolutionary new diagnostic tool for the
detection of small bowel disease that makes use of a swallowable
video capsule. Unlike conventional endoscopy, capsule endoscopy
allows examination of the entire small bowel and does not require
sedation.The main disadvantage of capsule endoscopy are:
(a) The inability to definitively localize or treat small bowel lesions. The
method of roughly approximating capsule location described earlier is
obviously prone to inaccuracy due to differences in small bowel transit time or
variant anatomy.
(b) It does not allow treatment or biopsy sampling of abnormalities.
(c) Battery failure in prolonged transit and also the false negative
results if there is rapid peristalsis at the lesion site or if there is bowel
angulation at a lesion that impairs the camera view
Figure 1. Photograph shows the capsule (26 x 11 mm) in relation to a dime
Hara, A. K. et al. Radiographics 2005;25:697-711
Copyright ©Radiological Society of North America, 2005
Figure 2. Drawing illustrates sensors attached to the abdomen, along with the battery pack and
Hara, A. K. et al. Radiographics 2005;25:697-711
Copyright ©Radiological Society of North America, 2005
Capsule endoscopy appears to be most useful in the
difficult evaluation of obscure gastrointestinal bleeding
when barium examinations and standard endoscopy are
A known small bowel stricture or obstruction is a
contraindication for capsule endoscopy, since capsules
that are not excreted naturally will require surgical
Disadvantages of conventional endoscopic techniques such
as push enteroscopy and colonoscopy with ileoscopy
include :
-limited endoscopic examination of the small bowel
-sedation requirements.
A complete endoscopic evaluation was previously possible
only with intraoperative endoscopy.