|ECR 2019 / C-3199|
|MR Enterography: beyond the acquisition|
Findings and procedure details
Diagnostic images of polyps, inflammatory pathologies, fistulas, abscesses, jejunal stenosis, transient invaginations in celiac disease, among others, were obtained by applying acquisition techniques using oral and intravenous contrast, MR sequences: Balanced, T2, DWI + ADC and dynamic T1 volumetric 3D with fat suppression pre- and post-intravenous contrast.
At our institution, we use oral contrast (a single 500 cm3 packet of Mannitol 15% diluted in 1500 ml of water) to achieve optimal distension of the bowel. The patient is indicated to swallow contrast material over a 40-minute period.
Prior to acquisition, peristalsis was suppressed by an intramuscular injection of 40 mg hyoscine butylbromide (Buscopan®; Boehringer Ingelheim, Ingelheim, Germany).
Prone or Supine?
While the supine position is more comfortable for the patient, it remains unknown whether one position surpasses the other in terms of bowel distention and lesion detection. However, prone position has been favored as it exerts mild pressure on the anterior abdominal wall, facilitating separation of small-bowel loops (better mural evaluation) and decreasing the volume of the peritoneal cavity, thus the number of slices in each sequence.
Positive: (appearing bright on MRI) Increased T1 signal intensity causes by paramagnetic effect and detect wall thickening. Example: gadolinium chelates. At our institution, we use gadoterate meglumine with 0.2 mg/kg body weight at 5 ml/s followed by a 30 ml saline flush.
Negative: (appearing predominantly dark on MRI) Induce local field inhomogeneity and shorten T1 and T2 relaxation. Bowel inflammation, more detectable interloop abscesses. Example: superparamagnetic particles (perfluorooctyl bromide)
Biphasic: (appearing dark on T1-weighted and bright on T2-weighted images) Low-signal T1 & high-signal T2 resulting in decreased intraluminal signal on T1 weighted images and increased signal on T2-weighted images . Clear demonstration of pathology and extraluminal abscess. Example: Mannitol 15%.
MRE Protocol (Sequences)
We use a 1.5 T MRI Scanner with a phase array flex coil.
True FISP - Balanced- (with and without fat-sat) – (axial and coronal) Insensitive to flow artefact. Evaluation of mechanical bowel obstruction, strictures, areas of diminished motility.
T2 Haste (axial and coronal) : To assess mural inflammation and changes in peri-enteric fat. Sensitive to flow voids but poor mesenteric information.
-without fat-sat: to see anatomy
-with fat-sat: disease activity.
DWI (3 b-values: 0-300-600) + ADC map - axial: Due to the suppression of T2 shine-through effect from bowel contents and enteral contrast material, high b-values are favoured to image the bowel. Additionally, high b-values contribute to negate high-signal intensity of normal bowel mucosa regularly detected on DWI.
Malignant tumors have high-signal intensity on high-b-value images and low ADC values.
The signal intensity on regional DWI images may then be assessed to determine whether restricted diffusion is present in abnormal tissues, such as tumor, inflammation, or abscess.
DWI may be superimposed on anatomic images and viewed as a fusion resulting from b-value and anatomic images or blending gray-scale with color-coded images.
Dynamic Contrast Enhancement (DCE) T1 Volumetric 3D – axial
It requires the use of serial 3D acquisitions before, during and after a bolus of low-molecular-weight gadolinium contrast media.
Qualitative, or Visual, Analysis of DCE-MRI: used for some of the first signs of active disease such as mucosal hyperenhancement and tumoral pathologies on mesentery or small bowel.
Complications in Crohn’s disease, including abscess, adenopathies or fistula formation, are also more prominent on post-gadolinium imaging.
Quantitative: we can also use the dynamic sequence to make T1 perfusion curves for a posterior analysis and classification on tumoral mass. The quantitative approach is based on modeling the concentration change of the contrast agent using pharmacokinetic modeling techniques.
Curves provide parameters that may include Arrival Time (AT), Time To Peak (TTP), Wash-In Rate (WIR), Wash-Out Rate (WOR), Area Under Contrast Curve (AUC), Maximum Enhancement (ME) and Percent Maximum Enhancement (%ME) compared to baseline. This values may be useful when compared to signal intensity changes in other lesions or to the normal tissue background.
Thematically related posters
ECR 2019 / C-1453
Review of the Utility of Diffusion Weighted Sequences in Abdominal and Pelvic Magnetic Resonance Imaging for Junior Trainee Radiologists.