To evaluate the feasibility of 7T breast magnetic resonance imaging (MRI) by determining the intrinsic sensitivity gain compared with 3T in healthy volunteers and to explore clinical application of 7T MRI in breast cancer patients receiving neoadjuvant chemotherapy (NAC).
Materials and Methods:
In 5 volunteers, the signal-to-noise ratio (SNR) was determined on proton density MRI at 3T using a conventional 4-channel bilateral breast coil and at 7T using a dedicated 2-channel unilateral breast coil, both obtained at identical scan parameters. Subsequently, consecutive breast cancer patients on NAC were included. The 7T breast MRI protocol consisted of diffusion-weighted imaging, 3D high-resolution (450 μm isotropic) T1-weighted fat-suppressed gradient-echo sequences and quantified single voxel 1H-magnetic resonance spectroscopy. Morphology was scored according to the MRI Breast Imaging-Reporting and Data System (BI-RADS)-lexicon, and the images were compared with 3T and histopathologic findings. Image quality was evaluated using a 5-point scale.
A 5.7-fold higher SNR was measured at 7T than at 3T, which reflects the advantages of a higher field strength and the use of optimized radiofrequency coils. Three breast cancer patients were included and received a total of 13 7T MRI examinations. The image quality of the high-resolution examinations was at least satisfactory, and good to excellent in 9 of the 13 examinations performed. More anatomic detail was depicted at 7T than at 3T. In 1 case, a fat plane between the muscle and tumor was visible at 7T, but not at the clinically performed 3T examination, suggesting that there was no muscle invasion, which was confirmed by pathology. Changes in tumor apparent diffusion coefficient values could be monitored in 2 patients and were found to increase during NAC, consistent with published results from studies at lower field strengths. Apparent diffusion coefficient values increased respectively from 0.33 × 10−3 mm2/s to 1.78 × 10−3 mm2/s after NAC and from 1.20 × 10−3 mm2/s to 1.44 × 10−3 mm2/s during NAC. Choline concentrations as low as 0.77 mMol/kgwater could be detected. In 1 patient, choline levels showed an overall decrease from 4.2 mMol/kwwater to 2.6 mMol/kgwater after NAC and the tumor size decreased correspondingly from 3.9 × 4.1 × 5.6 cm3 to 2.0 × 2.7 × 2.4 cm3. All 7T MRI findings were consistent with pathology analysis.
Dedicated 7T breast MRI is technically feasible, can provide more SNR than at 3T, and has diagnostic potential.