Delayed Contrast Enhanced MRI of Cartilage: Comparison of Ionic and Non-ionic Contrast Agents

Hypothesis: Delayed Gd(DTPA) enhanced MRI of cartilage (dGEMRIC) is a method designed to image the distribution of fixed charge density in cartilage, based on the premise that mobile ions will distribute in cartilage in relation to the concentration of the charged glycosoaminoglycan (GAG) molecules. The hypothesis to be tested here is whether the variation of T1 values post-Gd is a true reflection of charge distribution or if there may be other competing or synergistic effects that may influence the post-Gd T1 within the cartilage. To accomplish this, T1 maps were obtained in the same individuals after administration of Gd(DTPA) 2(Berlex, NJ) as an ionic contrast agent or gadodiamide (GE Healthcare, WI) as non-ionic contrast agent. The expectation would be that gadodiamide T1 values would be uniformly low (as it would penetrate cartilage uniformly at higher concentration, irrelevant of charge), while Gd(DTPA) T1s would have a distribution of values due to variations in its distribution due to the cartilage matrix fixed charge. Materials & Methods: Subjects: Twenty seven subjects, including 15 patients with self reported OA (5 men and 10 women, aged 40-86, average age of 60.1 years) and 12 volunteers without OA symptoms (controls, 4 men and 8 women, aged 18-40, average age of 29.9 years), participated in this study. Imaging: Data were acquired on 1.5T GE Signa short bore Twin speed system (GE Healthcare, Milwaukee, WI) using a commercial transmit/receive extremity coil. Each subject had two imaging sessions, using 0.2 mmol/kg Gd(DTPA) (Magnevist, Berlex, NJ) or gadodiamide (Omniscan, GE Healthcare, WI) respectively. The time interval between the two imaging sessions was no less than 3 days. Sagittal images were acquired with a 3D look locker (3DLL) sequence, started at 90 (n=4), 120 (n=12), or135 min (n=11) post contrast injection. For each subject, the acquisition start time in the 2 imaging sessions were identical. Parameters for the sequence included: slices prescribed=32, flip angle =5°, TR=2.2 s, τ=5.693 ms, bandwidth = +/-62.5 kHz, Matrix = 256x256. Eleven echoes with TIs ranged from 20 to 1839 ms were obtained. The acquisition time was 9 min 24 sec. Data analysis: T1 mapping was performed for both medial and lateral condyles of the femur, with a custom software analysis routine written in MATLAB (The Mathworks; Natick, MA). ROIs were placed at the central region of the cartilage between the outer edges of the meniscus horns in central slices of the condyles. Results: Gd(DTPA) Gadodiamide Gd(DTPA) Gadodiamide Gd(DTPA) Gadodiamide Gd(DTPA) Gadodiamide