Small Bowels

8/12/2019 Small Bowels

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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 displayin entirety.

-Another problem for imaging is motion, both intrinsicmotion of peristalsis and the positional changes caused by

breathing making their tracing very difficult.

In addition, because small bowel diseases have a lowincidence, their appearance is less well known and there is

an increased risk of missing them. Ever most of thecommon diseases in the small bowel, early changes aresubtle making their diagnoses difficult


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For an optimal display of the bowel, two things

are essential in imaging: intraluminal contrast and

distension. Intraluminal contrast is needed todelineate bowel loops in the abdominal cavity andto depict the bowel wall. Distension in small

bowel imaging is essential to unfold the bowel

tube and separate out the bowel wall. In imagingthe small bowel, intraluminal contrast anddistension are inseparable.


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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 themost 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 highdensity of the lumen and hence to miss an enhancing tumour. One of the otherproblems with these agents is their relatively low distending capability. Thesepositive oral contrast agents can be problematic when performing 3D imagingand 3D angiography in particular since the high-density bowel contents canobscure the opacified blood vessels and therefore need to be edited.


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Copyright Radiological Society of North America, 2004

Furukawa, A. et al. Radiographics 2004;24:689-702

Use of positive intraluminal contrast medium


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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 andthus better visualization of the enhancing bowel wall is obtained.

The most widely used neutral oral contrast agent is water. it isinexpensive and universally available and well tolerated but wateralone is not an ideal contrast agent, because it is absorbed early in thegastrointestinal system and is not available in the mid and distalsection of the small bowel so it does not always result in optimal

distention of the distal small bowel. The administration of agents suchas Glucagon may improve distension but is not routinely done.


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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.


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12/25Copyright Radiological Society of North America, 2006

Paulsen, S. R. et al. Radiographics 2006;26:641-657

Small bowel strictures in a 39-year-old man with Crohn disease and vomiting


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Negative intraluminal contrast Negative contrast agents display a density below 10 HU in

MDCT and are normally fat based. Although they providea good distension and can result in good visualization ofthe enhancing bowel wall they are not so widely used.

Carbon dioxide could work as a negative contrast butpatient tolerance is low. It is very difficult to apply as thereis currently no easy way to non invasively distend thesmall intestine with air


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Between 1,500 and 2,000 mL (or more) of contrast

material is administered orally 45

90 minutes prior to theexamination. To provide adequate and uniform distentionof the bowel loops, patients are asked to steadily ingest thecontrast material over a 2060-minute period .

The contrast material may be administered through anasojejunal catheter at a rate of 100250 mL/min with thehelp of a roller pump and the technique is called CTenteroclysis. An increased rate of infusion or dual-phaseintubation with an initial flow rate of 80120 mL/minfollowed by a rate of 200 mL/min is recommended toachieve reflex intestinal atony and thereby minimize

motion artifact. Use of a nasojejunal catheter allows betterluminal distention but causes patient discomfort.


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If necessary, 3001,000 mL of contrast agent can be

administered transrectally.

CT scans are obtained from the dome of the liver to thelevel 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.


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IV contrast The peroral contrast must be combined with IV contrast. Specially, the

combination of neutral oral contrast and IV contrast gives a gooddisplay of the bowel wall.

Inflammatory bowel disease and neoplasm are optimally displayedwith the use of IV contrast. Non ionic iodinated contrast is most widelyused today.

The ideal volume and injection rate are 125 mL and 3 to 4 mL/ s,respectively. For detailed display of the mesenteric vasculature, ahigher 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 itsbest enhancement phase


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CTenterographydiffers from routine abdominopelvic CTinthat it makes use of thin sections (2 to 2.5 mm section thicknessand reconstruction intervall 1 to 1.5) and large volumes ofenteric contrast material to better display the small bowel lumenand wall. Although CT enteroclysis profits from excellentdistension of the entire small bowel and precise evaluation ofthe entire small bowel and precise evaluation of the extent ofextraluminal disease, it has the major drawbacks of invasivenessand high radiation exposure.

Compared with the traditional small bowel follow-throughexamination, CTenterographyhas several advantages: (a)itdisplays the entire thickness of the bowel wall

(b)it allows examination of deep ileal loops in the pelviswithout superimposition

(c)it permits evaluation of the surrounding mesentery andperienteric fat. CTenterographyalso allows assessment ofsolid organs and provides a global overview of the abdomen.



Furukawa, A. et al. Radiographics 2004;24:689-702

CT Enterography with the Use of neutral intraluminal contrast medium


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The clinical efficacy of MR imaging has been investigated,and favorable results have been reported

High soft-tissue contrast, static and dynamic imagingcapabilities, 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 greateravailability, shorter examination times, flexibility in

choosing imaging thickness and planes after dataacquisition with multi

detector row CT, and higher spatialresolution.


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Capsuleendoscopyis a revolutionary new diagnostic tool for thedetection of small bowel disease that makes use of a swallowablevideo capsule.Unlike conventional endoscopy,capsuleendoscopyallows examination of the entire small bowel and does not requiresedation.The main disadvantage of capsule endoscopy are:

(a) The inability to definitively localize or treat small bowel lesions. Themethod of roughly approximating capsule location described earlier isobviously prone to inaccuracy due to differences in small bowel transit time orvariant anatomy.

(b) It does not allow treatment or biopsy sampling of abnormalities.

(c) Battery failure in prolonged transit and also the false negativeresults if there is rapid peristalsis at the lesion site or if there is bowel

angulation at a lesion that impairs the camera view


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Copyright Radiological Society of North America, 2005

Hara, A. K. et al. Radiographics 2005;25:697-711

Figure 2. Drawing illustrates sensors attached to the abdomen, along with the battery pack andrecorder


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Capsuleendoscopyappears to be most useful in the

difficult evaluation of obscure gastrointestinal bleeding

when barium examinations and standard endoscopyare

negative.

A known small bowel stricture or obstruction is a

contraindication for capsuleendoscopy, since capsules

that are not excreted naturally will require surgical

removal.


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Small Bowels

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