In vitro evaluation of alternative oral contrast agents for MRI of the gastrointestinal tract

Abstract: Purpose: In vitro evaluation of different materials as potential alternative oral contrast agents for small bowel MRI. Materials and methods: The T1 and T2 relaxation times of rose hip syrup, black currant extract, cocoa, iron-deferoxamine solution and a commonly used oral contrast material (1mM Gd-DTPA) were determined in vitro at different concentrations on a 1.0T clinical MR scanner. T1 values were obtained with an inversion prepared spoiled gradient echo sequence. T2 values were obtained using multiple echo sequences. Finally the materials were visualized on T1-, T2- and T2*-weighted MR images. Results: The relaxation times of the undiluted rose hip syrup (T1=110±5ms, T2=86±3ms), black currant extract (T1=55±3ms, T2=39±2ms) and 5mM iron-deferoxamine solution (T1=104±4ms, T2=87±2ms) were much shorter than for a 1mM Gd-DTPA solution (T1=180±8ms, T2=168±5ms). Dilution of black currant extract to 30% or a 3mM iron-deferoxamine solution conducted to T1 relaxation times which are quite comparable to a 1mM Gd-DTPA solution. Despite its much lower metal content an aqueous cocoa suspension (100g/L) produced T2 relaxation times (T1=360±21ms, T2=81±3ms) more or less in the same range like the 5mM iron-deferoxamine solution. Imaging of our in vitro model using clinical sequences allowed to anticipate the T1-, T2- and T2*-depiction of all used substances. Cocoa differed from all other materials with its low to moderate signal intensity on T1- and T2-weighted sequences. While all substances presented a linear 1/T1 and 1/T2 relationship towards concentration, rose hip syrup broke ranks with a disproportionately high increase of relaxation at higher concentrations. Conclusions: Rose hip syrup, black currant extract and iron-deferoxamine solution due to their positive T1 enhancement characteristics and drinkability appear to be valuable oral contrast agents for T1-weighted small bowel MRI. Cocoa with its differing relaxation and signal enhancement properties is a promising oral contrast agent but needs further clinical evaluation. [Copyright &y& Elsevier]