Formulation of radiographically detectable gastrointestinal contrast agents for magnetic resonance imaging: effects of a barium sulfate additive on MR contrast agent effectiveness

Studies on the redox activity of iron N,O-complexes: Potential T1-contrast agents

OBJECTIVES

The goal of this study was to determine the redox activity of iron (ethylenebis[2-(o-hydroxyphenyl)glycine]) (EHPG) and (ethylenebis[2-(o-hydroxybenzyl)glycine]) (EHBG) (N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid) derivative complexes and of some N,O-salan complexes of iron. The hexadentate chelate (EHPG and EHBG) ligands varied in their substituents (polar OMe, NHAc, or lipophilic Ph), while the latter had different charge and lipophilicity. The low redox activity of these complexes is important in their potential applications as magnetic resonance imaging contrast agents.

METHODS

Redox activity was assessed in the entire Haber-Weiss cycle and separately in the Fenton reaction. The spin-trapping method with 5,5-dimethyl-1-pyrroline-N-oxide monitored in electron paramagnetic resonance was used. The standard Mn marker was applied as a reference for quantitative analysis. Additionally, ascorbate oxidation was analyzed with UV-Vis spectrophotometry.

RESULTS

Both the Haber-Weiss cycle and in particular the Fenton reaction showed low redox activity of the studied complexes, which did not exceed 30% of [Fe(EDTA)]- or FeCl3 activity. The N,O-salan complexes expressed even lower activity, i.e. 10-20% activity of [Fe(EDTA)]-.

DISCUSSION

For the EHPG and EHBG complexes, it is likely that hydrophobicity and the possibility of H-bond formation play a major role in the resulting redox effects. For this reason, chelates equipped with phenyl groups in the majority belong to less redox-active complexes. For N,O-salan complexes, activity is not correlated with the charge of the coordination sphere, but again, the highly hydrophobic character of the groups and the non-pendant substituents capable of H-bonding that are present in these ligands limit the affinity of hydrophilic species.

Magnetic resonance imaging of the small bowel in children with idiopathic inflammatory bowel disease: evaluation of disease activity

BACKGROUND

Examinations using ionizing radiation are frequently used in the evaluation of disease activity in children affected by idiopathic inflammatory bowel disease (IBD).

OBJECTIVE

To develop an MR imaging protocol without the need for fluoroscopic insertion of an enteral tube and to assess the disease activity in children with IBD.

MATERIALS AND METHODS

Included in the study were 37 children (22 girls and 15 boys; age range 7-15 years, mean 11.67 years) with IBD who underwent MR imaging of the small bowel. Of these 37 children, 32 had Crohn disease and 5 had indeterminate colitis. A water solution containing herbal fibres was administered orally or through a nasogastric tube. Patients were imaged on a 1.5-T MR scanner with T1-weighted and Tau2-weighted sequences followed by a dynamic study using 3-D T1-W images after intravenous administration of gadolinium.

RESULTS

The percentage enhancement of the bowel wall was significantly increased in patients with abnormal C-reactive protein (CRP) values compared to patients with CRP values in the normal range (P<0.001). A relatively weak but significant correlation between percentage enhancement of the bowel wall and CRP values was noted during all phases of enhancement.

CONCLUSION

This MR imaging protocol is a safe and well-tolerated method for evaluating disease activity and extraintestinal manifestations of IBD in children.

Magnetic resonance imaging of the small bowel in children with idiopathic inflammatory bowel disease: evaluation of disease activity

BACKGROUND

Examinations using ionizing radiation are frequently used in the evaluation of disease activity in children affected by idiopathic inflammatory bowel disease (IBD).

OBJECTIVE

To develop an MR imaging protocol without the need for fluoroscopic insertion of an enteral tube and to assess the disease activity in children with IBD.

MATERIALS AND METHODS

Included in the study were 37 children (22 girls and 15 boys; age range 7-15 years, mean 11.67 years) with IBD who underwent MR imaging of the small bowel. Of these 37 children, 32 had Crohn disease and 5 had indeterminate colitis. A water solution containing herbal fibres was administered orally or through a nasogastric tube. Patients were imaged on a 1.5-T MR scanner with T1-weighted and Tau2-weighted sequences followed by a dynamic study using 3-D T1-W images after intravenous administration of gadolinium.

RESULTS

The percentage enhancement of the bowel wall was significantly increased in patients with abnormal C-reactive protein (CRP) values compared to patients with CRP values in the normal range (P<0.001). A relatively weak but significant correlation between percentage enhancement of the bowel wall and CRP values was noted during all phases of enhancement.

CONCLUSION

This MR imaging protocol is a safe and well-tolerated method for evaluating disease activity and extraintestinal manifestations of IBD in children.

Magnetic resonance imaging evaluation of small intestinal Crohn's disease

Imaging evaluation in patients with Crohn's disease is based on morphological abnormalities, traditionally disclosed by barium studies including conventional enteroclysis, and more recently by cross-sectional imaging. A major prerequisite for optimal image quality and a more confident diagnosis is the adequate luminal distension of the bowel, which is usually achieved by administering an intraluminal contrast agent through a nasojejunal catheter. Magnetic resonance enteroclysis is a new technique that combines the advantages of volume challenge with state-of-the-art ultrafast pulse sequences, resulting in an excellent demonstration of the anatomy of the small bowel. Magnetic resonance enteroclysis compares favourably with conventional enteroclysis in detecting, localising and assessing the extent of involved small bowel segments. Luminal narrowing and extramural manifestations or complications of the disease can also be accurately assessed by the technique. Imaging features including the presence of deep ulcers, extensive wall thickening and mesenteric lymph nodes exhibiting marked gadolinium enhancement correlate strongly with disease activity. Although the clinical utility of magnetic resonance enteroclysis in Crohn's disease has been widely recognised, its routine application is currently limited to academic centres. Its clinical indications may include follow-up studies of known disease, the classification of Crohn's disease subtypes, an estimation of disease activity and a determination of the extramucosal extent and spread of the disease process.

Magnetic Resonance Enteroclysis

MR enteroclysis (MRE) is an emerging technique for the evaluation of small intestinal diseases. Administration of an iso-osmotic water solution through a nasojejunal catheter can guarantee adequate luminal distention, and in combination with ultrafast sequences, such as single shot TSE, true FISP, HASTE and 3D FLASH, results in excellent anatomic demonstration of the small intestine. MR fluoroscopy can be performed during MRE examination to monitor the filling process and might be useful in studying low-grade stenosis or motility related disorders. MRE is a very promising technique for the detection and characterization of involved small bowel segments in patients with Crohn's disease while its diagnostic performance in disclosing lumen narrowing and extramural manifestations and complications of the disease is outstanding. Initial experience shows that MRE is very efficient in the diagnosis of small bowel tumors and can be used in the evaluation of small bowel obstruction.

IRM et exploration du tube digestif — Aspects techniques et perspectives d’évolution

Barium enema remains the reference method for the detection of morphological intraluminal alterations of the bowel. Optimal filling of intestinal loops allows high diagnostic sensitivity and specificity. US, CT and MRI are useful diagnostic procedures in the evaluation of mural and extramural alterations. In recent years, MR-enteroclysis and MR colonography have been developed, both enable the evaluation of luminal, extraluminal and mural alterations of the bowel. While these modalities provide good imaging evaluation of the bowel, visualization of the different layers, as seen on US, is still not available. Use of high resolution endoluminal coil on MR could improve mural evaluation of bowel to differentiate inflammatory diseases and provide accurate TNM classification of tumoral lesion with minimally invasive procedure.

Exploration de l’intestin grêle par les techniques d’imagerie en coupes

Recent advances of cross sectional imaging allow optimal evaluation of the small bowel. This chapter will detail technical considerations and emphasize the role of imaging in the evaluation of the most common diseases of the small bowel.

Technical challenges and clinical applications of magnetic resonance enteroclysis

With the advent of gradient systems the image quality of ultrafast pulse sequences, i.e., half Fourier acquisition single shot turbo spin echo (HASTE), true fast imaging with steady-state processing and fast low angle shot (FLASH), improved substantially and clinical applications including small bowel imaging became feasible. Within this context, magnetic resonance enteroclysis was developed as a comprehensive examination of the small bowel, providing luminal, transmural, and exoenteric diagnostic information of small bowel abnormalities. Clinical applications of magnetic resonance enteroclysis include diagnostic evaluation and follow-up of patients with inflammatory or neoplastic diseases and small bowel obstruction.

BaSO4-loaded agarose: a construction material for multimodality imaging phantoms

RATIONALE AND OBJECTIVES

Phantom studies are an important part of the evaluation of imaging techniques; however, presently available phantom construction materials are not adequate for studies involving both magnetic resonance (MR) imaging and computed tomography (CT). The purpose of this study was to design a phantom construction material useful for multimodality imaging experiments.

MATERIALS AND METHODS

Iodinated contrast agent or BaSO4 was added during the formation of agarose gels. Both CT and MR imaging were performed, and T1 and T2 values and CT numbers (in Hounsfield units) were obtained for multiple combinations of contrast material and agarose. Results. The T2 values of agarose gels span the range of those values found in biologic tissues. Phantoms containing iodinated contrast agent were not stable; contrast agent diffused across concentration gradients. BaSO4-loaded agarose phantoms were stable, however, and varying barium concentrations produced phantoms that spanned the range of CT numbers found in biologic tissues. Addition of BaSO4 did not substantially alter T1 or T2 values of agarose gels. Agarose concentration had only a small effect on the CT numbers of BaSO4 suspensions.

CONCLUSION

BaSO4-loaded agarose is an effective material for construction of multimodality imaging phantoms. It provides adequate signal intensity for MR imaging and attenuation for CT, with independently variable contrast in both modalities.

Efficacy and safety of mangafodipir trisodium (MnDPDP) injection for hepatic MRI in adults: results of the U.S. Multicenter phase III clinical trials. Efficacy of early imaging

The efficacy of contrast-enhanced magnetic resonance imaging (MRI) for detecting and characterizing, or excluding, hepatic masses was assessed in 404 patients, following the intravenous administration of mangafodipir trisodium (MnDPDP) injection, a hepatic MRI contrast agent. An initial contrast-enhanced computed tomography (CT) examination was followed by unenhanced MRI, injection of MnDPDP (5 micromol/kg IV), and enhanced MRI at 15 minutes post injection. Agreement of the radiologic diagnoses with the patients' final diagnoses was higher for enhanced MRI and for the combined unenhanced and enhanced MRI evaluations than for unenhanced MRI alone or enhanced CT using the clinical diagnosis as the gold standard. Mangafodipir-enhanced MRI uniquely provided additional diagnostic information in 48% of the patients, and patient management was consequently altered in 6% of the patients. MnDPDP-enhanced MRI was comparable or superior to unenhanced MRI and enhanced CT for the detection, classification, and diagnosis of focal liver lesions in patients with known or suspected focal liver disease.

Magnetic resonance imaging of the hepatobiliary system: intestinal absorption studies of manganese mesoporphyrin

RATIONALE AND OBJECTIVES

We studied the intestinal absorption of manganese mesoporphyrin (Mn-mesoporphyrin), a potential oral hepatobiliary contrast agent.

METHODS

Mn-mesoporphyrin was complexed with monoolein and taurocholate (mixed micelles). Portal venous delivery and biliary excretion were measured after intestinal administration in rats and rabbits, and the mechanism of intestinal transport was studied in a combined lymph-bile fistula model in rats. T1-weighted magnetic resonance (MR) images of the liver were obtained in rats and domestic pigs before and after gastric administration of Mn-mesoporphyrin in mixed micelles.

RESULTS

A 2.2-fold increase of portal venous Mn concentration was found 90 min after intestinal administration of the complex. None was found in the lymph collected from the thoracic duct, indicating a transcellular transport mechanism through the intestinal mucosa with portal venous delivery. Mn-mesoporphyrin levels in bile peaked between 240 and 270 min after administration (200-fold increase). The greatest liver enhancement (20-90%) was measured 360 min after administration.

CONCLUSION

The feasibility of intestinal delivery of Mn-mesoporphyrin, a lipophilic hepatobiliary contrast agent was demonstrated.

Safety and optimum concentration of a manganese chloride-based oral MR contrast agent

To determine the safety of a manganese chloride-based oral magnetic resonance (MR) contrast agent and the ideal concentration of the agent for marking in three different anatomic sites (stomach, middle of the small bowel, and ileocecal region), six healthy volunteers were evaluated before and after administration of 900 mL of three different concentrations of the contrast agent. Images were evaluated subjectively and objectively. No adverse events were noted. There was a minimal rise in manganese blood levels at 6 hours after administration, with a return to baseline at 24 hours. The imaging data demonstrated good-to-excellent bowel marking on T1-weighted images at all three concentrations. However, on T2-weighted images, the 40 mg Mn+2/L concentration provided improved hypointense bowel marking relative to the 20 mg/L concentration. Little difference was seen between the 40 and 60 mg/L concentrations. Fast T1- and T2-weighted sequences provided superior image quality to that of conventional spin-echo sequences.

Methods for the systematic investigation of gastrointestinal contrast media for MRI: evaluation of intestinal distribution by radiographic monitoring

Comparison of the effectiveness of various gastrointestinal (GI) contrast agents for magnetic resonance (MR) imaging is often complicated by varying amounts intraluminal filling with the orally administered agents. To achieve more uniform and reproducible imaging results with GI contrast agents for MR imaging (GICMR), we evaluated a radiographic method for monitoring intraluminal filling and distribution. Solutions of Mn-DPDP (2 mM), to which a small amount of barium sulfate (6 wt/vol%) was added, were administered orally to dogs. Gastric emptying and small bowel transit were monitored fluoroscopically. MR imaging was performed either 1) at a fixed time after administration of the contrast agent or 2) at a variable interval when the contrast agent was observed fluoroscopically to be in the terminal ileum. When initiation of MR imaging was guided by fluoroscopic monitoring of intestinal contrast distribution, uniform and reproducible intestinal contrast enhancement by GICMR was achieved. However, when MR imaging was performed at a fixed time interval after oral administration, non-uniform and variable GI visualization was obtained, and this corresponded to the variable intestinal distribution observed fluoroscopically. We conclude that reproducible intestinal filling with orally administered contrast agents can be accomplished with a radiographic monitoring technique, and this promotes more consistent GI visualization on MR images. Such standardized and reproducible methods are necessary for studies in which the effectiveness of GI contrast media for MR imaging is evaluated and compared.