Purpose Cardiac pulsation increases the noise level in brain maps of the MRI parameter R2*. Cardiac-induced noise is challenging to mitigate during the acquisition of R2* mapping data because the characteristics of this noise remain largely unknown. In this work, we characterize cardiac-induced noise in brain maps of the MRI parameter R2*. Methods We introduce a sampling strategy that enables the acquisition of multi-echo data in several intervals of the cardiac cycle. From this data, we estimate the variability of brain R2* maps due to cardiac-induced fluctuations and identify the most sensitive area of k-space. From these characteristics, we derive a novel sampling strategy that successfully mitigates cardiac-induced noise in R2* maps of the brain. Results In inferior brain regions, cardiac pulsation accounts for R2* variations of up to 3s-1 across the cardiac cycle, i.e. ~35% of the overall variability. Cardiac-induced fluctuations occur throughout the cardiac cycle and exhibit a reduced intensity during the first quarter of the cycle after the detection of the systole at the finger. 50-60% of the overall cardiac-induced noise is contained near the k-space centre (k < 0.074 mm-1), corresponding to 22% of voxels at 4mm resolution. The proposed cardiac noise mitigation strategy reduces the variability of R2* estimates across repetitions by 11% in the brainstem and 6% across the whole brain. Conclusion We provide characteristics of cardiac-induced noise in brain maps of the MRI parameter R2* that constitute a basis for the design of mitigation strategies during data acquisition.

Purpose To introduce the dipolectric antenna: a novel RF coil design for high‐field MRI using a combination of a dipole antenna with a loop‐coupled dielectric resonator antenna. Methods Simulations in human voxel model Duke involving 8‐, 16‐, and 38‐channel dipolectric antenna arrays for brain MRI were conducted. An 8‐channel dipolectric antenna for occipital lobe MRI at 7 T was designed and constructed. The array was built of four dielectric resonator antennas (dielectric constant = 1070) and four segmented dipole antennas. In vivo MRI experiments were conducted in one subject, and the SNR performance was benchmarked against a commercial 32‐channel head coil. Results A 38‐channel dipolectric antenna array provided the highest whole‐brain SNR (up to a 2.3‐fold SNR gain in the center of the Duke's head vs. an 8‐channel dipolectric antenna array). Dipolectric antenna arrays driven in dipole‐only mode (with dielectric resonators used as receive‐only) yielded the highest transmit performance. The constructed 8‐channel dipolectric antenna array provided up to threefold higher in vivo peripheral SNR when compared with a 32‐channel commercial head coil. Conclusion Dipolectric antenna can be considered a promising approach to enhance SNR in human brain MRI at 7 T. This strategy can be used to develop novel multi‐channel arrays for different high‐field MRI applications.