*2.1.1.1 Examination technique and ultrasound findings*

After the conventional abdominal ultrasound with a convex probe within the range of 2–5 MHz, the gastrointestinal tract examination is continued with highfrequency linear probes in the field of 5–10 MHz.

When inspecting the intestinal vortices, the gradual compression technique is used to expel air from the intestines.

Incompressibility and thickening are vital signs of a pathomorphological change of the wall. The intestine's pathomorphological altered segment is characterized by concentric wall thickening, absence or reduction of peristalsis, and lack of compressibility under pressure with an ultrasound probe [19] (**Figure 1**).

A wall thickness above 3 mm can be considered a pathological finding [20]. The discovery of a "pseudo-kidney" or "target sign" is the thickened, relatively hypoechoic intestinal wall surrounding the hyperechoic lumen, which is not specific and can be caused by other pathological conditions (neoplasms, intussusception, wall hematomas, hypertrophic pyloric ischemia, appendicitis, diverticulitis, etc.) [21]. A longitudinal view shows the tubular structure.

Some authors report a high percentage of detection of thickened intestinal convolutions (up to 90%) by high-resolution ultrasound, making it more challenging to determine the affected segment's exact length [22].

Therefore, the determination of the affected segment's length is estimated more reliably by other radiological methods [20].

An increasing number of authors emphasize the value of ultrasound in detecting and monitoring chronic inflammatory bowel disease, and in evaluating drug therapy

**Figure 1.** *Thickening of the terminal ileum wall.*

#### *Endoscopy in Small Bowel Diseases*

effectiveness and presenting extramural complications (fistulas, abscesses, lymph nodes, free fluid) [23, 24] (**Figures 2** and **3**).

There are observations related to Crohn's disease that the loss of stratification due to wall edema correlates with the disease's active phase. In contrast, in the subacute and chronic phases, due to fibrosis, recognizable stratification from all five layers prevails [25].

### *2.1.2 CT enterography*

It is a fast, non-invasive technique that uses a large amount of intestinal contrast material to better display the small intestine wall and lumen [26, 27].

CT enterography is not as sensitive as standard radiological methods in detecting mucosal damage. In comparison between them, it is superior in showing intramural and extraluminal changes [28] (**Figure 4**).

CT-proven mural thickening of the intestinal wall is the most crucial indicator of a pathological finding [29].

In the active inflammatory phase of the disease, contrast imbibition shows CT thickening of the wall and "stratification", which is indicated by a double halo - the "target sign" [29].

**Figure 2.** *Enterocutaneous fistula.*

**13**

*Role of Imaging in Small Bowel Crohn's Disease DOI: http://dx.doi.org/10.5772/intechopen.96098*

The main limiting factor in CT enterography is ionizing radiation, and it is

Magnetic resonance imaging was introduced as an alternative method for detecting Crohn's disease and can be performed as MR enterography, or as MR

MR enteroclysis is more demanding to perform and uncomfortable for the patient because it involves using a nasojejunal tube, and nowadays it is being avoided [35]. Technical advances with rapid sequences (GRE and EPI sequences, particularly HASTE) have minimized artifacts problem due to respiration and peristalsis [36]. Fat signal suppression is one of the technical modifications to better contrast the

The examination involves applying a more considerable amount of fluid orally to ensure the distension of the intestinal vortices, after which the MRI imaging itself is approached. Before the native and contrast sequences, an antispasmodic is administered intravenously to slow down the peristalsis and avoid bowel movement artifacts. After that, axial and coronal T1 and T2 sequences are recorded, as well as

The fair spatial and temporal resolution of MR images, combined with a large amount of oral contrast agent that provides intestinal curvature distension, allows good visualization of the intestinal wall thickening, and edema thereof, which is

A high signal in the T2 measured image as a well-known indicator of inflammation in human tissue should be a good indicator of inflammation in Crohn's disease. The inflamed bowel wall in the T2-weighted image has a low-contrast resolution because the inflamed wall is more difficult to distinguish from the high signal of

unsuitable for the follow-up of patients with Crohn's disease.

useful for assessing Crohn's disease activity [38] (**Figure 5**).

intraluminal fluid and perivisceral fatty tissue T2W sequence.

*2.1.3 Contrast MR enterography*

*CT enterography - thickening of the terminal ileum wall.*

dynamic post-contrast recordings.

enteroclysis [30–34].

**Figure 4.**

MR image [37].

**Figure 3.** *Hypoechogenic, reactively altered lymph nodes.*

*Role of Imaging in Small Bowel Crohn's Disease DOI: http://dx.doi.org/10.5772/intechopen.96098*

#### **Figure 4.**

*Endoscopy in Small Bowel Diseases*

layers prevails [25].

*2.1.2 CT enterography*

a pathological finding [29].

"target sign" [29].

nodes, free fluid) [23, 24] (**Figures 2** and **3**).

and extraluminal changes [28] (**Figure 4**).

effectiveness and presenting extramural complications (fistulas, abscesses, lymph

There are observations related to Crohn's disease that the loss of stratification due to wall edema correlates with the disease's active phase. In contrast, in the subacute and chronic phases, due to fibrosis, recognizable stratification from all five

It is a fast, non-invasive technique that uses a large amount of intestinal contrast

CT enterography is not as sensitive as standard radiological methods in detecting mucosal damage. In comparison between them, it is superior in showing intramural

CT-proven mural thickening of the intestinal wall is the most crucial indicator of

In the active inflammatory phase of the disease, contrast imbibition shows CT thickening of the wall and "stratification", which is indicated by a double halo - the

material to better display the small intestine wall and lumen [26, 27].

**12**

**Figure 3.**

*Hypoechogenic, reactively altered lymph nodes.*

**Figure 2.**

*Enterocutaneous fistula.*

*CT enterography - thickening of the terminal ileum wall.*

The main limiting factor in CT enterography is ionizing radiation, and it is unsuitable for the follow-up of patients with Crohn's disease.

#### *2.1.3 Contrast MR enterography*

Magnetic resonance imaging was introduced as an alternative method for detecting Crohn's disease and can be performed as MR enterography, or as MR enteroclysis [30–34].

MR enteroclysis is more demanding to perform and uncomfortable for the patient because it involves using a nasojejunal tube, and nowadays it is being avoided [35].

Technical advances with rapid sequences (GRE and EPI sequences, particularly HASTE) have minimized artifacts problem due to respiration and peristalsis [36]. Fat signal suppression is one of the technical modifications to better contrast the MR image [37].

The examination involves applying a more considerable amount of fluid orally to ensure the distension of the intestinal vortices, after which the MRI imaging itself is approached. Before the native and contrast sequences, an antispasmodic is administered intravenously to slow down the peristalsis and avoid bowel movement artifacts. After that, axial and coronal T1 and T2 sequences are recorded, as well as dynamic post-contrast recordings.

The fair spatial and temporal resolution of MR images, combined with a large amount of oral contrast agent that provides intestinal curvature distension, allows good visualization of the intestinal wall thickening, and edema thereof, which is useful for assessing Crohn's disease activity [38] (**Figure 5**).

A high signal in the T2 measured image as a well-known indicator of inflammation in human tissue should be a good indicator of inflammation in Crohn's disease.

The inflamed bowel wall in the T2-weighted image has a low-contrast resolution because the inflamed wall is more difficult to distinguish from the high signal of intraluminal fluid and perivisceral fatty tissue T2W sequence.

#### **Figure 5.**

*T2 blade coronal mbh sequence: Distended intestinal loops with visible thickening of the terminal ileal wall.*

Suppression of perivisceral adipose tissue signals with the "fat suppression" technique amplifies signal intensity of the inflamed intestine level. Also, superparamagnetic contrast (iron oxide particles) reduces the high intraluminal signal in the T2W-measured image.

Combining the above (fat suppression and superparamagnetic contrast) maximally improves the intestinal wall's high T2 signal. In other words, the mesenteric adipose tissue signal and the intraluminal content signal are "subtracted" from the display, which amplifies the inflamed intestinal wall signal in the T2W sequence.

Wall thickening, length of inflamed bowel and mural signal enhancement after intravenous administration of gadolinium correlate with Crohn's disease activity [39] (**Figure 6**).

MR enterography is easy to perform and has been proven to be useful for detecting active ileitis, assessing disease activity in the area of anastomoses, and identifying extraenteric complications [40–44] (**Figures 7**–**13**).

One of the earliest papers indicated a high sensitivity of over 90% in detecting fistulas in Crohn's disease [45].

The advantages of MRI imaging are:


**15**

*Role of Imaging in Small Bowel Crohn's Disease DOI: http://dx.doi.org/10.5772/intechopen.96098*

*postcontrast: Thickening of the ileal wall in Crohn's disease.*

**Figure 6.**

**Figure 7.**

**Figure 8.**

*fistula.*

The disadvantages of MRI imaging are:

• metal side of the body,

• lower spatial resolution.

*diffusion coefficient (ADC)*

• high search price, and difficult availability,

• prolonged search time, and related claustrophobia,

*2.1.4 Diffusion-weighted magnetic resonance imaging (DW MRI) and apparent* 

*(A) T2 blade fs axial multi breathe hold (mbh), (B) T1 vibe fs axial mbh, and (C) T1 vibe fs axial mbh* 

*(A) T1 vibe fs coronal mbh native and (B) T1 vibe fs coronal mbh after paramagnetic contrast agent* 

*application: Thickening of the ileal wall in the area of ileotransverso anastomosis.*

Diffusion-weighted imaging (DWI) provides unique information about the observed tissue because the image contrast between different structures

*(A) T2 blade transverse mbh and (B) T1 vibe transverse mbhpostcontrast: Perianal abscesses fused by retroanal* 

• high reliability to show fistulas.

#### **Figure 6.**

*Endoscopy in Small Bowel Diseases*

T2W-measured image.

activity [39] (**Figure 6**).

population,

technique,

fistulas in Crohn's disease [45].

activity (T2 sequence),

changes of the intestinal wall,

• high reliability to show fistulas.

The advantages of MRI imaging are:

sequence.

**Figure 5.**

Suppression of perivisceral adipose tissue signals with the "fat suppression" technique amplifies signal intensity of the inflamed intestine level. Also, superparamagnetic contrast (iron oxide particles) reduces the high intraluminal signal in the

*T2 blade coronal mbh sequence: Distended intestinal loops with visible thickening of the terminal ileal wall.*

Combining the above (fat suppression and superparamagnetic contrast) maximally improves the intestinal wall's high T2 signal. In other words, the mesenteric adipose tissue signal and the intraluminal content signal are "subtracted" from the display, which amplifies the inflamed intestinal wall signal in the T2W

Wall thickening, length of inflamed bowel and mural signal enhancement after intravenous administration of gadolinium correlate with Crohn's disease

MR enterography is easy to perform and has been proven to be useful for detecting active ileitis, assessing disease activity in the area of anastomoses, and

• absence of ionizing radiation, which is especially crucial for the young

• high signal intensity after the application of gadolinium in pathological

• fair contrast resolution (display of wall edema) using fat suppression

• potential for making multiplanar and coronal representations,

• possibility of using different parameters for the evaluation of inflammatory

One of the earliest papers indicated a high sensitivity of over 90% in detecting

identifying extraenteric complications [40–44] (**Figures 7**–**13**).

**14**

*(A) T2 blade fs axial multi breathe hold (mbh), (B) T1 vibe fs axial mbh, and (C) T1 vibe fs axial mbh postcontrast: Thickening of the ileal wall in Crohn's disease.*

#### **Figure 7.**

*(A) T1 vibe fs coronal mbh native and (B) T1 vibe fs coronal mbh after paramagnetic contrast agent application: Thickening of the ileal wall in the area of ileotransverso anastomosis.*

#### **Figure 8.**

*(A) T2 blade transverse mbh and (B) T1 vibe transverse mbhpostcontrast: Perianal abscesses fused by retroanal fistula.*

The disadvantages of MRI imaging are:

