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Categories of negative oral contrast agents:
Negative oral contrast media are usually based on superparamagnetic particles and act by inducing local field inhomogeneities, which results in shortening of both T1 and T2 relaxation times. Superparamagnetic contrast agents have predominant T2 weighted effects.
Biphasic contrast media are agents that have different signal intensities on different sequences, depending on the concentration at which they are used.
Suitable materials for oral contrast agents should have little or no absorption by the stomach or intestines, complete excretion, no motion or susceptibility artifacts, affordability, and uniform marking of the gastrointestinal tract.
Benefits of negative oral contrast agents are the reduction of ghosting artifacts caused by the lack of signal. Superparamagnetic iron oxides produce also in low concentrations a noticeable signal loss; but can generate susceptibility artifacts especially in gradient echo sequences. Perfluorochemicals do not dilute in the bowel because they are not miscible with water.
High cost, poor availability, and limited evaluations of side effects are possible disadvantages.
Negative oral contrast agents are used e.g., in MRCP, where the ingestion of 600-900 ml of SPIO cancels out the signal intensity of the lumen (in addition after the injection of a gadolinium-based contrast medium, the enhancement of the inflammatory tissues is clearer seen), and in MR abdominal imaging of Crohn's disease in combination with mannitol.
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Drug Information and Specification T1, Predominantly positive enhancement PHARMACOKINETIC Intravascular, extracellular, renal excretion CONCENTRATION 287 mg/mL,0.5 mol/L DOSAGE 0.1-0.2 mmol/kg / 0.2-0.4 ml/kg PREPARATION Finished product INDICATION Neuro/whole body DEVELOPMENT STAGE For sale PRESENTATION Vials of 10 mL, 15 mL and 20 mL
DO NOT RELY ON THE INFORMATION PROVIDED HERE, THEY ARE NOT A SUBSTITUTE FOR THE ACCOMPANYING PACKAGE INSERT!
Distribution Information TERRITORY TRADE NAME DEVELOPMENT STAGE DISTRIBUTOR Australia Omniscan® for sale | | | | • View the DATABASE results for 'Omniscan®' (7).
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Drug Information and Specification NAME OF COMPOUND Barium suspensions, clay mineral particles, iron oxide crystals CENTRAL MOIETY Ba3+, Al3+, Si2+, Fe T2, Predominantly negative enhancement CONCENTRATION Various mixtures DOSAGE Depending on the mixture PREPARATION Depending on the product INDICATION Gastrointestinal bowel marking DEVELOPMENT STAGE No clinical development DO NOT RELY ON THE INFORMATION PROVIDED HERE, THEY ARE NOT A SUBSTITUTE FOR THE ACCOMPANYING PACKAGE INSERT! | | | | • View the DATABASE results for 'Oral Magnetic Particles' (4).
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(PEAKS) This function offers consistent arterial enhancement for contrast enhanced MRA studies, augmenting the k-space with filling flexibility. | | | | | |
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Types of oral contrast agents with positive signal enhancement:
Ideal oral contrast agents are immiscible with water, biologically inert, have a low viscosity and surface tension. Oral positive contrast agents may improve the separation of bowel loops, the detection of polyps in colon MRI or the assessment of inflammatory bowel in the small intestine.
Several positive oral contrast agents are available and they are safe to use, for example gadolinium solution, ferric ammonium citrate, different oil emulsions and pediatric formula.
Unfavorably motion artifacts caused by respiration and peristalsis may be increased in MR imaging. In addition, the signal of the positive contrast medium may decrease caused by dilution in gastrointestinal (GI) secretions. With the use of contrast agents that are immiscible with water, no dilution and accompanying signal loss occur even when the contrast agent is in contact with the intraluminal contents of the GI tract.
Another disadvantage may be residual substances in the bowel, resembling masses when enclosed by bright signal. In addition, positive contrast agents may have a similar signal as bright masses, which make their (e.g. lipoma) detection difficult.
See also Gastrointestinal Paramagnetic Contrast Agents, Combination Oral Contrast Agents, Gastrointestinal Diamagnetic Contrast Agents. | | | | | | • View the DATABASE results for 'Positive Oral Contrast Agents' (6).
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