Stricturing Crohn*s Disease assessment using advanced ultrasound and magnetic resonance imaging techniques for evaluation of inflammation and fibrosis

Crohn*s disease is a chronic inflammatory disease characterised by episodes of
relapse and periods of remission. Patients predominantly present with
inflammatory disease, although approximately 11% of patients already exhibit
strictures at diagnosis. Additionally, later during the disease course more
than 30% of the patients develop intestinal strictures.1,6*8 As a consequence
patients may present with symptoms of intestinal obstruction, such as bloating,
abdominal pain, vomiting, inability to pass stool and restricted dietary
intake.1,9 The treatment of strictures could be surgical or alternatively
medical or endoscopic. In general, predominant-inflammatory strictures likely
benefit from medical therapy whereas predominant-fibrotic strictures often
require a surgical approach.1,3,6 Rarely is a stricture identified as merely
inflammatory or fibrotic: a mixture of inflammation, muscular hypertrophy,
collagen disposition and fibrosis has previously been identified in
histological assessment of strictures.1,5,10 Consequently, the most optimal
treatment has to be determined individually for each patient developing
strictures. Furthermore, the development of antifibrotic medical therapies may
offer an additional modality of treatment in the future.2 Therefore it is
necessary to characterize predominant components of the stricture to guide
clinical decision and identifying relevant parameters to use as endpoints for
future clinical trials. Cross-sectional imaging techniques have high potential
to satisfy this unmet need.2,3 Ultrasound and MRI can adequately characterize
general features of a stricture, such as bowel wall thickening, luminal
narrowing and the presence of a prestenotic dilation3. However, conventional
imaging techniques are inconclusive in characterizing the stricture
composition.3,5 However, advanced ultrasonography and MRI modalities may have
the capability to adequately distinguish between fibrotic and inflammatory
components.11*18 These modalities are well-tolerated, highly accessible and
without radiation exposure, which makes them attractive for frequent use in
patients with CD.3,19,20 Regarding advanced MRI-techniques, magnetization
transfer, Intravoxel Incoherent Motion (IVIM) and T2*-mapping showed promising
results when correlated with the resection specimen of stricturing CD patients.
Magnetization transfer MRI can indirectly measure macromolecules, such as
collagen, and it was shown to be accurate in grading different
histopathological fibrosis classifications.12 IVIM is a sequence that measures
both diffusion and perfusion, influenced by changes in tissue composition due
to inflammation and fibrosis. A recent study showed that IVIM was able to
differentiate between four histopathological grades of fibrosis.11 T2*-mapping
uses susceptibility differences and heterogeneities in the magnetic field that
reflect the microstructure of the tissue. This sequence also showed promising
results in measurement of fibrosis in the resection specimen of patients with
stricturing CD.14 Both magnetization transfer, IVIM and T2*-mapping
outperformed the more traditional contrast-enhanced (CE) imaging and
diffusion-weighted imaging (DWI).11,12,14 Furthermore, quantified terminal
ileal motility of Crohn*s disease patients has been shown to correlate with
disease activity in the terminal ileum and was altered in stricturing
segments.28,29 However, no data on correlation with histopathologic fibrosis is
available. Advanced ultrasound modalities, such as contrast-enhanced ultrasound
(CEUS), shear-wave elastography (SWE) and small intestinal contrast ultrasound
(SICUS) recently became available and could improve the assessment of
strictures.15*18,21*24 During CEUS intravascular contrast is injected and
subsequently the vascularization of the bowel wall is analysed. 15,16,25 A
recent study showed that blood volume and flow is lower in fibrotic resection
specimens compared to non-fibrotic specimens16. SWE analyses stiffness of
tissue, by measuring reverberation of sonographic waves on the tissue of
interest. Consequently, it is possible to distinguish stiff from elastic tissue
by measuring velocity of the shear waves. A few studies show promising value of
SWE in stricturing disease and were found to correlate with muscular
hypertrophy and fibrosis in surgical resection specimens. 15,18,26,27
Furthermore, CEUS peak flow enhancement was inversely correlated with SWE
indicating less blood flow through stiffer tissue15. During SICUS, the small
intestine is examined by using oral contrast, which improves detection of
inflammatory lesions and strictures of the small bowel.21*24 The flow of
contrast through the stenotic segment could indicate the severity of the
stricture and improve further characterization of the stricture although no
previous studies have investigated this. Histopathology of the resection
specimen remains the ultimate reference standard for characterization of a
stricture, however in studies this inherently creates a selection bias towards
severe or predominant-fibrotic disease. Therefore, to evaluate
predominant-inflammatory strictures, it is important to include patients that
respond to anti-inflammatory treatment. To further establish the clinical
impact, parameters that distinguish patients responding to anti-inflammatory
treatment and patients requiring surgery need to be identified. This can
identify novel biomarkers to guide clinical decision-making and to use in
clinical trials regarding anti-fibrotic therapies. To date, no studies focused
on cross-sectional imaging parameters in a broad spectrum of stricturing
disease, both correlating findings to the composition of the resection specimen
and the response to anti-inflammatory treatment. Therefore, it is important to
conduct an all-encompassing study assessing imaging parameters according to a
histopathological and a clinical reference standard. In conclusion, the aim of
this study is to evaluate parameters of advanced ultrasound and MRI techniques
to explore both the correlation with histology and to identify biomarkers that
distinguish patients responding to anti-inflammatory treatment and those
requiring surgery.

The primary objectives of this study are to evaluate advanced MRI techniques
(IVIM, T2*-mapping, motility) and advanced ultrasound techniques (CEUS, SWE and
SICUS) to: 1. Identify advanced imaging techniques that correlate with
stricture composition as defined by the histopathologic degree of fibrosis and
inflammation in the resection specimen 2. Identify parameters that distinguish
patients responding to anti-inflammatory therapy and patients requiring surgery

Single-center, cross-sectional observational study Patients with proven Crohn*s
disease that present with symptoms of obstruction (abdominal pain, nausea,
vomiting, dietary restriction) and/or a small bowel stricture seen on endoscopy
and/or cross-sectional imaging will be identified in the outpatient clinic or
weekly multidisciplinary meeting. Patients will receive a conventional MRI,
which is standard clinical care, with the addition of advanced sequences for
the study (See *MR Imaging*). Then, all patients will receive advanced
ultrasonography (See *Ultrasound*) prior to treatment. The multidisciplinary
IBD team will be blind for the outcomes of all advanced imaging techniques for
both MRI and ultrasound and treatment strategy will therefore not be influenced
by these advanced imaging techniques. For optimal correlation with the
resection specimen in patients undergoing surgery, the interval between imaging
and surgery cannot exceed eight weeks. If this is the case, the MRI and
ultrasound will be repeated. To address the objectives, MRI and ultrasound
parameters are correlated with the histological outcome in those patients that
will have surgical resection. The MRI and ultrasound parameters are compared
between patients responding to anti-inflammatory treatment and patients having
surgery to identify distinctive markers. Clinical data Clinical data from the
medical records will be collected and will consist of medical history, gender,
age, smoking status, weight, height, clinical disease activity scores (HBI,
CDOS) and biochemical parameters in blood and stool. Clinical and biochemical
activity parameters will be collected at inclusion and at 26 weeks. The
clinical and biochemical assessment is part of the routine care and is not
influenced by this study. Anti-inflammatory treatment assessment In the
anti-inflammatory treatment group, patients will be divided in responders and
non-responders. Response is defined as no surgery or endoscopic balloon
dilatation, continuation of anti-inflammatory therapy and no clinical
deterioration based on an increase in HBI and/or CDOS at 26 weeks.
Non-responders can require surgery and may be transferred to the surgery group.
When the initial imaging was performed more than eight weeks prior to surgery,
imaging will be repeated for optimal correlation with histopathology. MR
Imaging Patient preparation Patients will be prepared using the standard
clinical MR enterography procedure, encompassing 4 hours of fasting after which
patients are requested to drink 1600 ml of a mannitol-solution as intraluminal
contrast medium in 60 minutes prior to the MRI examination. MRI scanning MRI
enterography will be performed on a 3.0 Tesla MRI (Ingenia, Philips, Best, The
Netherlands) using a 16 channel body coil. Scanning will be performed according
to the standard abdominal MRI protocol with antiperistaltic medication
(Buscopan, Boehringer-Ingelheim, Germany) and a contrast-agent (Gadolinium, 0.1
mmol/kg) intravenously. The conventional protocol consists of a coronal dynamic
motility sequence, coronal T2-weighted sequence, axial T2-weighted sequence
with fat suppression, coronal T1-weighted pre- and post-contrast sequences,
axial T1-weighted post contrast sequence. The additional research sequences
consist of , IVIM and T2*-mapping which will add 15 minutes to the conventional
protocol. Conventional parameters such as bowel wall thickness, bowel wall
edema, prestenotic dilatation, bowel wall enhancement, bowel wall
stratification, fatty wrapping, fistulas and abscesses will be reported.
Intravoxel Incoherent Motion (IVIM) is a sequence that measures both perfusion
and diffusion parameters, without the use of an intravenous contrast-agent,
reflecting tissue characteristics that can be altered by inflammation and
fibrosis. A recent study showed that IVIM fractional perfusion was able to
differentiate between histopathological grades of fibrosis with a better
accuracy than DWI and CE in stricturing Crohn*s disease patients.11 The
sequence is safe and does not increase the burden for the patient. T2*-mapping
reflects the microstructure of a tissue by using local susceptibility
differences and inhomogeneities in the magnetic field. This sequence was able
to accurately distinguish different grades of fibrosis and also outperformed
more traditional sequences. Quantitated motility in the terminal ileum, has
been shown to correlate with disease activity measured by endoscopy and
histology from a biopsy in Crohn*s disease patients and is altered in
stricturing disease. Changes might be different beween inflammation and
fibrosis but It has not been evaluated in correlation with histopathology yet.
Post-processing Post-processing of magnetization transfer, IVIM, T2*-mapping
will be performed with in-house developed software to obtain quantitated data.
Dynamic (motility) scans will be assessed with a previously validated algorithm
(GIQuant, Motilent, London, UK) which is based on non-rigid image registration
for automated motility analysis. Motility is quantified within a ROI
delineating the affected bowel segment to produce a single, numerical motility
score. Ultrasonography All ultrasonographic examinations will be executed using
a Philips EPIQ 5G device. A convex probe (C5-1 MHz) will be used for an
overview of the abdomen. Secondly, a linear probe (eL 18-4 MHz) will be used
for detailed examinations and for all the measurements involving
gastrointestinal ultrasound (GIUS), colour Doppler, CEUS, SWE and SICUS.
Participants will be asked to fast for at least six hours prior to the
examination. First, GIUS is performed to visualize colon, terminal ileum, ileum
and jejunum successively and measure bowel wall thickness, Doppler signal
according to the Limberg score, fatty wrapping, wall layer stratification,
motility, presence of lymph nodes, abscesses, fistulas, prestenotic dilatation
and narrowing of the lumen in all segments. The most narrowed part of the lumen
will be identified and considered the region of interest for ultrasound
(ROI-US). Subsequently, intravascular contrast (Sonovue) for CEUS is injected
and the ROI-US is visualized for 90 seconds. CEUS measurements will be
performed, cine-loops will be recorded and analysed by software (VueBox®,
Bracco, Italy) measuring flow through the bowel wall (mL/min per 100 mL
tissue), peak volume, time to peak volume and wash out time. Then, SWE is
performed where the velocity of shear waves (m/sec) will be measured. This will
be measured ten times successively in the ROI-US and an average will be
calculated. Then, SICUS will be performed. Participants ingest the oral
contrast (17.4 gram of polyethylene glycol, PEG 4000 powder, dissolved in 500
mL tap water). Subsequently, progression of contrast through the small bowel is
monitored. When contrast reaches the stricture, time between arrival of
contrast and passage through the stricture will be recorded. Furthermore, the
amount of bowel movements will be recorded before contrast passages the
stricture. All measurements will be noted on an ultrasound assessment form.
Regions of interest (ROI) for both MRI and ultrasound will be placed manually
by two, independent observers (experienced radiologists and/or
ultrasonographers) within the bowel wall of the strictured segment that is
location-matched with the resection specimen. Histopathology In patients
undergoing surgery, histological slides are retrieved in a predefined
standardized way and location matched with MRI and ultrasound. Location
matching of MRI and histopathology will be based on anatomical landmarks such
as the most stictured part and the ileocecal valve, performed by the research
coordinators, together with the radiologist and/or surgeon and/or pathologist.
Histological evaluation of surgical specimens will be performed by two
experienced gastrointestinal pathologists, independently, according to an
adapted histological score by Chen et al.

Most of the MRI scans will be performed within routine clinical care with the
addition of 15 minutes scanning time to the 30-45 minutes for the conventional
protocol, resulting in a scanning protocol of maximally one hour. Routine
clinical oral preparation (mannitol), intravenous antiperistaltic medication
(buscopan) and contrast agent (gadolinium) are given. This requires one
venepuncture which is not influenced by the study. The total time of the visit
will be two hours due to the oral preparation, of which 15 minutes are added by
the study. In patients scheduled for surgery with an MRI that is more than 8
weeks old, an extra MRI will be performed with the previous protocol.. The
included patients will be subjected to an ultrasonographic exam: CEUS and
elastography will take 10 minutes each, SICUS will take between 30 and 45
minutes resulting in a total examination time of 60 to 90 minutes.
Ultrasonography itself is as safe procedure using sound waves to visualize
abdominal organs. Administration of oral and intravascular contrast is a very
safe procedure with hardly any side effects. In less than 1:10.000 patients an
allergic reaction is reported with regards to intravascular contrast. For oral
contrast no severe side effect have been reported. Regarding the contrast, oral
contrast is a dilution of macrogol in 500 mL of tap water. Intravascular
contrast will form microbubbles when it is injected in the blood stream and
will be breathed out within 15 minutes. No harmful effects to the lungs,
kidneys or liver have been reported. The treatment strategy (medication or
surgery) is decided within clinical care and is not influenced by the study.
Blood samples and a stool sample will be collected at inclusion and are part of
the standard clinical care.