Scientists specializing in breast MRIOur goal was to evaluate the feasibility of glycosaminoglycan (GAG) hydroxyl proton chemical exchange saturation transfer (gagCEST) imaging in detection and characterization of breast lesions in human patients at 7 Tesla. gagCEST - MRI may provide biochemical information on tissue status via altered proteoglycan content (1). This is supported by elevated proteoglycan concentrations found in mammary tumors (2), indicating its involvement in neoplastic cell behavior (3). Eleven female patients (age 60±16 years, range 23-74 years) with 15 histologically verified breast lesions (nine malignant and six benign) were examined. Institutional Review Board approval and written informed consent were obtained prior to the measurements. The mean size of malignant and benign lesions was 13±4 mm and 20±12 mm, respectively. Patient measurements were performed on a 7.0 T MRI scanner (Siemens, Erlangen, Germany) with a bilateral dual tuned ¹H/³¹P phased array breast coil with patients in a prone position. For gagCEST imaging, CEST effects were induced by a train of Gaussian RF pulses followed by image acquisition using a 3D turboFLASH sequence. The saturation pulse was applied at 17 saturation-offset frequencies (Δω) between ±3 ppm, with following characteristics: B1-CWAE (continuous wave amplitude equivalent) = 0.8 μT, pulse duration PD = 99 ms, interpulse delay IPD = 100 ms, number of CEST pulses = 5. Selective fat saturation was applied before readout. After gagCEST, contrast enhanced (CE)-MRI was performed with the following imaging parameters: FOV=179x319mm², slice thickness = 3 mm, TR/TE = 5 ms /2.2 ms, spatial resolution = 1.7×1.7 mm², flip angle = 11°, total acquisition duration = 9:37 min. Z-spectra were calculated for each pixel and were shifted for the water resonance to appear at 0 ppm. MTRasym (∂) was calculated as MTR(+∂)-MTR(-∂) integrated over the offset range ∂ from 0.5 to 2 ppm, which corresponds to the resonance frequencies of exchangeable hydroxyl protons of GAG. Regions of interests (ROI) were placed in the tumors and statistical analysis was performed (Games-Howell test, SPSS16; Chicago, IL, USA).In all carcinomas, the gagCEST maps showed higher values compared to healthy tissue (Fig. 1). MTRasym measured in the healthy glandular tissue (1.8±0.5%, range: 0.5-3.2%) was not significantly different from that in benign lesions (CI=95%, p=0.159) (Fig.2). The mean measured MTRasym value in breast carcinomas was (9.6±2.6% range: 6.6-13.3%), and was significantly higher than in benign lesions (3.3±0.9% range: 1.5-5.3%, (CI=95%, p=0.001) (Fig.3).Our preliminary data showed that gagCEST MRI has a great potential in biochemical investigation of breast lesions at 7 Tesla. In this pilot study we showed that the gagCEST effect in malignant lesion is significantly higher than in benign ones, which can be explained by the changed metabolism of the pathological tissue. However, the accuracy and reproducibility of this technique need to be further evaluated. The measured quantitative values should be compared with the content of proteoglycans found in tumors, using histological techniques. We believe that CEST MRI may become an attractive tool for the investigation of breast tumors, because it provides substantially different information than that obtained with established quantitative techniques.