[Technical considerations for injection of a mixture of iodinated contrast material and Artirem for combined CT and...

To determine the influence of 4 independent parameters on signal intensity and density measurements after injection of an arthrography-specific form of gadoterate meglumine and an iodinated contrast material for combined MR and CT arthrography. The parameters included: 1) variations of gadolinium and iodinated contrast agents within the mixture, 2) variations of concentration of the iodinated contrast agent, 3) variation of temperature of the mixture, 4) the type of MR pulse sequence acquired.

The study was performed on a CT using a phantom containing 47 different syringes. Ten separate mixtures of gadolinium and iodinated contrast agents were obtained, each with a 10% change in the respective proportion of each contrast agent. This was repeated 4 times for 4 iodinated contrast agents of different iodine concentration. Two control syringes, 4 mixtures containing 50% normal saline and 50% iodinated contrast material (one for each of the 4 concentrations of iodinated contrast material) and one with a mixture of 50% of normal saline and gadolinium contrast agent. For the MR acquisition, the syringes were separated into 4 groups for 4 phantoms. On a 1.5 T MR unit, SE T1W, FSE T2W, PD and 3D FIESTA sequences were acquired. All acquisitions were repeated 2 times, and a 3 different temperatures.

The progressive increase in the proportion of gadolinium contrast in the solution was associated with a non-linear increase of signal on T1W, 3D FIESTA, and PD images. The signal intensity reached a plateau at concentrations between 40-60%. Signal variations on the 3D FIESTA sequence were significant. On T2W images, there was an increase of measured signal intensity at low gadolinium concentrations. On CT, there was a linear relationship between density measurements and dilution of gadolinium. The progressive increase of the concentration of the iodinated contrast was associated with increased signal loss on MR and progressive increase of density values on CT. Temperature variations were associated with signal intensity changes on T2W and FIESTA images, but not on T1W images.

At 1.5 T, a mixture of 50% iodinated contrast and 50% gadolinium contrast corresponded to an acceptable compromise for combined acquisition of MR and CT arthrography.