Optimization of indirect arthrography of the knee by application of external heat: initial experience

To examine the potential utility of applying heat to increase the uptake of intravenous gadolinium (Gd) contrast into the knee joint in order to optimize MR arthrography.

At 1.5T, 16 knees in eight patients without prior surgery, injury, or pain were examined before and 30 minutes after intravenous administration of Gd contrast (0.1 mM/kg). Between scans a heating pad was applied to the anterior aspect of eight randomly selected knees (the contralateral knee served as the control). Initial and postcontrast imaging consisted of identical axial T1-weighted sequences (TR/TE = 500/14 msec) without fat suppression. On the initial and postcontrast images, regions of interest (ROIs) were placed at identical locations in the suprapatellar pouch and the intercondylar notch by a reader blinded to the treated side. The values at these two locations were averaged and the change in joint signal intensity was calculated. The differences between the heated and unheated knees were also calculated.

Seven of the eight knees treated with heat had increased joint enhancement compared to the contralateral control, with percentage changes in joint signal intensity (heated knee vs. control) of +38%, +80%, +121%, +145%, +150%, +164%, and +177%. Overall there was a doubling of signal intensity (125%) on the heated side compared to the contralateral control (with significance at P = 0.039). One patient was excluded because of a prior knee injury.

The application of external heat increases uptake of intravenously administered Gd contrast into the knee joint, and may help to optimize indirect MR arthrography at a relatively low cost.