INTRODUCTION

The chemical exchange saturation transfer (CEST) MRI technique is evolving as an attractive molecular imaging approach with the ability to provide valuable metabolic information. The efficacy of glucosamine (GlcN) as an agent for CEST MR molecular imaging of tumors was recently demonstrated in several animals' tumor models^1,2. The potential of a clinical application of CEST MRI with GlcN is strengthened by its lack of toxicity as can be indicated from its wide use as a food supplement³. Here, the translation of the GlcN CEST MRI method to a clinical MRI set-up was examined, in order to evaluate the feasibility of obtaining a new class of contrast agent for breast cancer MR imaging that enables the tumor to be distinguished from the surrounding tissue and to compare it to the conventional MRI method.

METHODS

Twelve patients with newly-diagnosed breast tumors (median age, 53 years) were recruited in this prospective IRB-approved study. Informed consent was obtained from all patients. GlcN CEST-MRI scans were conducted at a 3T clinical scanner (PRISMA, Siemens, Germany) using a bilateral diagnostic breast coil (16 channels, Siemens, Germany) after a minimum of a 6 hour fast. The patients were scanned with the CEST MRI protocol before and two hours after drinking a solution of 7.5 g of GlcN sulfate (Arthryl, Rafa, Jerusalem, Israel) in 150 ml water. Optimal slice positioning of the CEST sequence (with 8 slices) was supported by high-resolution T₂W images acquired at the beginning of the examination. Pre-saturation of the CEST sequence consisted of 5 Gaussian-shaped RF pulses (pulse length tp=100ms, inter-pulse delay=61ms, 2s between measurements, B₁=2.5μT, recover time=5s) at 17-24 frequency offsets sampled in the range of ±6ppm. Fully relaxed images were acquired for normalization. CEST sequence was followed by a spiral-reordered 3D single-slice GRE read-out (TE=2.2ms; TR=5.0ms; FA=10^o; FoV, 280; matrix, 264×320; slice thickness=2.5mm; bandwidth=660Hz/Px, fat suppression-on). To improve B₀ homogeneity, unilateral shimming was performed. CEST signal intensities were quantified in the tumor and in the surrounding tissue after the correction of B₀ field inhomogeneity. Data interpretation was done by magnetization transfer asymmetry ratio (MTRasym) and a multi-Gaussian fitting⁴. The routine breast MR protocol also included T₁W- dynamic contrast-enhanced (DCE) imaging with the injection of gadolinium contrast agent following the CEST scans.

RESULTS

Analysis of signal intensities from ROIs in the tumors and the surrounding breast tissue revealed higher CEST values in the tumor tissue (MTRasym effect of 8.1±4.1%, N=12, P<0.05 with the incremental increase due to the GlcN administration of 3.4±0.8%, N=12, P<0.05), which correlated well with tumor areas as demonstrated by DCE MRI (Figs.1,2). The Z-spectra of breast tumors had distinct GlcN CEST peaks corresponding to the presence of hydrogen exchange between free water and hydroxyl, amide/amine, and relayed nuclear Overhauser enhancement (NOE) from aliphatic groups, all yielded larger CEST integrals in the tumor tissue after GlcN uptake by an averaged factor of 2.2±1.2 (P<0.01),1.4±0.4 (P=0.2) and 1.6±0.6 (P=0.05), respectively (Fig.3).

DISCUSSION

To our knowledge, this is the first time to investigate the detection of human breast cancer with the GlcN CEST MRI method at a clinical set-up. This study reveals the feasibility of the technique to differentiate between breast cancer and normal-appearing breast tissue. Both the asymmetry analysis and the multi-pool Gaussian fitting may assist in detecting dynamic changes of the CEST signal upon administration of GlcN in breast cancer. The contrast may arise from GlcN or its metabolic products accumulation in the tumor, as was previously shown for a murine model^1,2. The enhanced CEST effect can also be explained by tissue acidosis associated with lactate buildup². The NOE effect indicates that the CEST arises from intracellular GlcN and its metabolites.

CONCLUSION

The results of this initial feasibility study indicate the potential of GlcN CEST MRI to diagnose breast cancer in a clinical setting.

Acknowledgements

No acknowledgment found

References

1. Rivlin, M, et al. Glucosamine and N-acetyl glucosamine as new CEST MRI agents for molecular imaging of tumors. Scientific Reports Nature 2016; 6 (32648) doi:10.1038/srep32648 2. Rivlin M, et al. Molecular imaging of cancer by glucosamine chemical exchange saturation transfer MRI: A preclinical study. NMR in Biomedicine. 2021;34(2):e4431. 3. Anderson, JW et al. Glucosamine effects in humans: a review of effects on glucose metabolism, side effects, safety considerations, and efficacy. Food Chem Toxicol 2005;43(2):187-201. 4. Zaiss M, et al. Quantitative separation of CEST effect from magnetization transfer and spillover effects by Lorentzian-line-fit analysis of z-spectra. J Magn Reson. 2011;211(2):149-155.