Dr. Elizabeth Squirell

Intestinal ultrasound

A painless scan of your bowel, often done right in the IBD clinic. You can eat as usual, there are no needles and no radiation, and you can talk about the results the same day.

Reviewed October 2026 6 min read

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At a glance

  • Intestinal ultrasound is a painless scan of your bowel through the skin of your belly. It uses sound waves, not radiation.
  • You can eat and drink as you usually would. Sometimes your team may ask you to take one dose of a laxative drink (RestoraLAX) before the scan.
  • The doctor checks how thick your bowel wall is. In most of the bowel, 3 mm or less is normal.
  • The doctor also looks for extra blood flow, swollen fat around the bowel, and whether the wall layers look normal.
  • A thick wall alone does not mean you have a stricture (a narrow spot). That needs other signs too.
  • Ultrasound can be repeated often and is safe in pregnancy, so it is good for checking if a treatment is working.
  • It does not replace colonoscopy. You still need a colonoscopy for cancer checks and biopsies.

What is it?

Intestinal ultrasound (IUS) is a scan of your bowel. It is like the ultrasound used in pregnancy. A doctor moves a small probe over your belly with some gel. Sound waves make a live picture of your bowel on a screen.

In IBD, it is often done by your gastroenterologist during your clinic visit. Dr. Squirell is trained and certified in this scan by the International Bowel Ultrasound Group (IBUS).

Why it helps in IBD

  • No bowel clean-out. You do not need to empty your bowel, as you would for a colonoscopy.
  • No radiation and no needles. It is safe to repeat as often as needed, and safe in pregnancy.
  • Results in the room. The doctor can show you the pictures and talk about them right away.
  • It sees the whole wall. A colonoscopy sees the inside lining. Ultrasound sees how thick the whole wall is, and the tissue around it.
  • It shows change quickly. It can show if a new treatment is working within weeks. This helps your team decide sooner whether to change your medicine.

Ultrasound finds Crohn’s disease in the small bowel well. In a large study, it found it in 92 of 100 people who had it. An MRI scan found it in 97 of 100. MRI is better at measuring how much bowel is affected.

What to expect

  1. Before

    Eat and drink as you usually would. Sometimes your team may ask you to take one dose of a laxative drink beforehand. This is RestoraLAX (PEG 3350) mixed in water. It fills the small bowel with fluid, which can make it easier to see. Follow your clinic’s instructions.

  2. During

    You lie on your back with your belly showing. The doctor puts warm gel on your skin and presses gently with the probe. They follow your bowel from one side of your belly to the other. You may be asked to roll a little or take a breath.

    It should not hurt. If a spot is sore, say so. The doctor can press more gently.

  3. After

    Wipe off the gel and go about your day. The doctor will tell you what they saw.

What the doctor looks at

Healthy bowelA round bowel with a thin wall made of clear stripes, a thin ring of fat around it, and an open channel in the middle.Healthy bowelchannelThin wallClear layersThin ring of fat3 mm or lessaround the bowelInflamed bowelA round bowel with a much thicker wall, faint blurred stripes, small spots of extra blood flow in the wall, and a wide ring of swollen fat around it. The channel in the middle is the same size as in the healthy bowel.Inflamed bowelchannelThick wallSpots of extraBlurred layersSwollen fatmore than 3 mmblood flowaround the bowel
A simple drawing, not to scale. It shows the bowel cut across, like a slice. A healthy bowel has a thin wall and clear layers. An inflamed bowel has a thick wall, spots of extra blood flow, blurred layers and swollen fat around it.

The doctor checks four main things:

  • How thick the bowel wall is. This is the most important sign. In the small bowel and colon, a wall of 3 mm or less is normal. In the sigmoid colon (the last bend of the colon), up to 4 mm can be normal. A thicker wall usually means inflammation.
  • Blood flow in the wall. A setting called Doppler shows blood flow as coloured spots. Inflamed bowel has extra blood flow.
  • The fat around the bowel. Inflammation can make this fat swollen and bright on the scan.
  • The layers of the wall. A healthy wall has clear layers, like stripes. Strong inflammation can blur them.

The doctor also looks for problems such as a narrow spot (stricture), an abscess (a pocket of pus) or a fistula (a tunnel from the bowel to somewhere else).

Try the slider to see how wall thickness is judged.

2.0 mm · Normal
channel

Normal thickness. In the small bowel and colon, a wall of 3 mm or less is normal.

The channel in the middle stays the same size here on purpose. A thick wall does not by itself mean a stricture (a narrow spot). To find a stricture, the doctor looks for a narrow channel with a widened stretch of bowel just before it.

A teaching drawing, not to scale. Your own result depends on where in the bowel it was measured.

A thick wall is not the same as a stricture

A stricture is a narrow spot in the bowel. It can cause cramps, bloating and vomiting after meals. On a scan, a stricture means three things together:

  1. The channel inside the bowel is narrow.
  2. The wall there is thick.
  3. The bowel just before it is widened, because food backs up behind the narrow spot.

So a thick wall alone, even a very thick one, does not mean you have a stricture. The doctor checks for the narrowing separately.

When your result is good

When the wall is back to normal thickness with normal blood flow, it is called transmural healing. “Transmural” means through the whole wall. It is a deeper kind of healing than feeling well, and a newer goal that your team may aim for.

What ultrasound cannot do

Ultrasound is a great tool, but it has limits.

  • Some parts are hard to see. The rectum and the deep pelvis are hard to see from the belly. So are parts of the upper small bowel.
  • Gas and body shape can block the view. Gas in the bowel, or a thicker belly, can make the pictures less clear.
  • Late pregnancy. Ultrasound works best in the first two trimesters. Later, the growing uterus can block the view.
  • It cannot take biopsies. Only a scope can take small tissue samples or remove polyps.
  • It does not replace colonoscopy for cancer checks. If you need regular colonoscopies to look for early signs of cancer, you still need them.
  • Skill matters. The scan is best when done by someone trained in bowel ultrasound.

If ultrasound cannot answer the question, your team may suggest an MRI or a scope.

Does it matter if I have a flare when I come in?

No. Come to your appointment. The scan can help show how active your IBD is right now.

Can I have an ultrasound if I am pregnant?

Yes. It uses sound waves, not radiation. It works best in the first two trimesters.

Read next

Sources for this guide

Sources

  1. Ilvemark JFKF, Hansen T, Goodsall TM, et al. Defining transabdominal intestinal ultrasound treatment response and remission in inflammatory bowel disease: systematic review and expert consensus statement. J Crohns Colitis 2022;16(4):554–80. PMID 34614172 International IUS (IBUS) expert consensus. Transmural remission = bowel wall thickness ≤3 mm with normal colour Doppler in small bowel and colon; sigmoid up to 4 mm can be normal. Response judged by fall in wall thickness; early scans at weeks 4–8 can help; UC remission may be seen as early as week 4.
  2. Bettenworth D, Bokemeyer A, Baker M, et al. Assessment of Crohn's disease-associated small bowel strictures and fibrosis on cross-sectional imaging: a systematic review. Gut 2019;68(6):1115–26. PMID 30944110 Three key items define a stricture on imaging: luminal narrowing, wall thickening and pre-stenotic dilation. Thickness alone is not a stricture.
  3. Kucharzik T, Taylor S, Allocca M, et al. ECCO-ESGAR-ESP-IBUS Guideline on Diagnostics and Monitoring of Patients with Inflammatory Bowel Disease: Part 1. J Crohns Colitis 2025;19(7):jjaf106. PMID 40741688 Current European guideline (replaces the 2019 ECCO-ESGAR guideline), written with IBUS. IUS bowel wall thickness shows treatment response within 2–6 weeks in UC and 4–8 weeks in Crohn's; IUS is an alternative to MRE for monitoring Crohn's; accuracy is lower in the rectum, which lies deep in the pelvis; MRE is better for mapping disease extent; colon cancer surveillance is by colonoscopy, starting 8 years after first symptoms.
  4. Yanai H, Feakins R, Allocca M, et al. ECCO-ESGAR-ESP-IBUS Guideline on Diagnostics and Monitoring of Patients with Inflammatory Bowel Disease: Part 2. J Crohns Colitis 2025;19(7):jjaf107. PMID 40742985 Recommendation 54: fasting is usually not required for IUS; routine oral contrast is not recommended but may be used in specific scenarios to improve views of the small bowel (small intestine contrast ultrasound: PEG solution, typically 250–500 mL, range 125–800 mL, drunk 30–40 minutes before). Dr. Squirell's clinic: patients eat as usual and occasionally take one dose of RestoraLAX (PEG 3350) beforehand.
  5. Maaser C, Sturm A, Vavricka SR, et al. ECCO-ESGAR Guideline for Diagnostic Assessment in IBD Part 1: Initial diagnosis, monitoring of known IBD, detection of complications. J Crohns Colitis 2019;13(2):144–64. PMID 30137275 Earlier version, now updated by the 2025 guideline above; cited here for the upper small bowel point. IUS has significant limits for the rectum; lower accuracy in the upper small bowel; less accurate than MR enterography for extent of Crohn's; useful for monitoring and transmural healing; non-invasive and well tolerated.
  6. Taylor SA, Mallett S, Bhatnagar G, et al. Diagnostic accuracy of magnetic resonance enterography and small bowel ultrasound for the extent and activity of newly diagnosed and relapsed Crohn's disease (METRIC): a multicentre trial. Lancet Gastroenterol Hepatol 2018;3(8):548–58. PMID 29914843 Sensitivity for small bowel Crohn's presence: ultrasound 92%, MRE 97%. Both valid first-line tests; MRE more accurate for extent.
  7. Chavannes M, Dolinger MT, Cohen-Mekelburg S, Abraham B. AGA Clinical Practice Update on the role of intestinal ultrasound in inflammatory bowel disease: commentary. Clin Gastroenterol Hepatol 2024;22(9):1790–5.e1. PMID 39001773 AGA summary table: no preparation, no procedural risk; limited view of rectum; may be limited by body habitus and bowel gas; no ability to take biopsies or treat during the scan (via gastro.org summary).
  8. Mahadevan U, Seow CH, Barnes EL, et al. Global Consensus Statement on the Management of Pregnancy in Inflammatory Bowel Disease. Inflamm Bowel Dis 2025;31(10):2615–64. PMID 40874613 IUS preferred over CT in pregnancy; accurate in trimesters 1 and 2, technically harder in trimester 3.
  9. Squirell E, Meade S, Leung Y. The fundamentals of inflammatory bowel disease management in pregnancy: a practical review for the gastroenterologist. J Can Assoc Gastroenterol 2024;7(1):121–31. PMID 38314178 IUS is non-invasive and safe in pregnancy; detects disease location, strictures, abscesses and fistulas; the pregnant uterus can limit views of the terminal ileum and sigmoid later in pregnancy; reliability depends on operator expertise.
  10. Gordon H, Biancone L, Fiorino G, et al. ECCO Guidelines on Inflammatory Bowel Disease and Malignancies. J Crohns Colitis 2023;17(6):827–54. PMID 36528797 Colon cancer surveillance in IBD is done by colonoscopy.

This guide is for general education. It can't replace advice from your own care team, who know your health history.

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