Benjamin Schmitt, Presenter: Research support, Siemens AG

Goetz Hannes Welsch MD, Abstract Co-Author: Nothing to Disclose

Sebastian Apprich, Abstract Co-Author: Nothing to Disclose

Siegfried Trattnig MD, Abstract Co-Author: Nothing to Disclose

Evaluation of feasibility and the possible clinical relevance of glycosaminoglycan-dependent chemical exchange saturation transfer (gagCEST) imaging on a 3T MR system in knee cartilage of ten healthy volunteers and ten patients with focal cartilage defects.

Morphological MRI and gagCEST imaging were performed on a clinical 3T MR scanner. Scan time for 3D gagCEST of one knee was 10:30 min with a saturation module optimized by simulation of Bloch equations. As a reference for gagCEST at 3T, results were compared to gagCEST results obtained on a 7T whole-body system. Cartilage tissue from the loading area of the femoral condyles was segmented on representative sagittal slices for each volunteer and mean CEST signal intensities were calculated for the areas. The mean values were used for comparison between 3 and 7 Tesla, and corresponding correlation was analysed. ROI evaluation of cartilage lesions in patients was performed separately by two readers and evaluated by non-parametric statistical measures.

Healthy cartilage of volunteers exhibited mean gagCEST values of 0.7±1.9% (range: -6.7 – 3.5%, N=40) at 3T and 2.7±4.2% (range: -8.7 – 10.8%, N=40) at 7T. Comparison of the corresponding values for both field strengths yielded a strong linear correlation with Pearson’s r = 0.82 (p<0.01). Cartilage lesions (L) could be well delineated on CEST images and exhibited significantly (p<0.05) lower signals than native cartilage at both field strengths. At 3 T, the mean CEST signal in lesions was -2.1±1.3%, and 1.8±0.8% at 7 T. Intra-class correlation between readers yielded R² = 0.83 (p<0.001).

The strong correlation between gagCEST results obtained at 3T and those obtained at 7T clearly indicates clinical viability of the technique at 3T. Additionally, the correlation shows that negative asymmetries are actual effects, which occur at both field strengths and are attributed to compensation of CEST effects by magnetization transfer or NOE effects. Although feasible at 3T, gagCEST yields considerably lower signals at 3T compared to 7T. This restricts maximum sensitivity and spatial resolution, which can be obtained at 3T.

gagCEST imaging can be used for assessment of cartilage GAG content on clinical 3T MR scanners and is thus relevant for non-invasive monitoring of pathologic changes of GAG content.

Schmitt, B, Welsch, G, Apprich, S, Trattnig, S, gagCEST Imaging of Knee Cartilage on a Clinical 3T MRI System: Assessment of Feasibility and Clinical Relevance.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043436.html