Purpose A new regularizer is proposed for the magnitude least‐squares optimization algorithm, to ensure robust parallel transmit RF shimming and small‐tip‐angle multispoke pulse designs for ultrahigh‐field MRI. Methods A finite‐difference regularization term is activated as an additional regularizer in the iterative magnitude‐least‐squares based pulse design algorithm when an unwanted flip angle null distribution is detected. Both simulated and experimental B1+ maps from different transmit arrays and different human subjects at 7 T were used to evaluate the proposed algorithm. The algorithm was further demonstrated in experiment with dynamic multislice RF shimming for a single‐shot gradient‐echo EPI for human functional MRI at 7 T. Results The proposed finite‐difference regularizer effectively prevented excitation null to be formed for RF shimming and small‐tip‐angle multispoke pulses, and improved the latter with a monotonic trade‐off relationship between flip angle error and RF power. The proposed algorithm was demonstrated to be effective with several head‐array geometries by simulation and with a commercial head array with 12 healthy human subjects by experiment. During a functional MRI scan at 7 T with dynamic RF shimming, the proposed algorithm ensured high image SNR throughout the human brain, compared with near‐complete local signal loss by the conventional magnitude‐least‐squares algorithm. Conclusion Using finite‐difference regularization to avoid unwanted solutions, the robustness of RF shimming and small‐tip‐angle multispoke pulse design algorithms are improved, with better flip angle homogeneity and a monotonic trade‐off relationship between flip angle error and RF power.

Cognitive impairment amongst Parkinson’s disease (PD) patients is highly prevalent and associated with an increased risk of dementia. There is growing evidence that altered cerebrovascular functions contribute to cognitive impairment. Few studies have compared cerebrovascular changes in PD patients with normal and impaired cognition and those with mild-cognitive-impairment (MCI) without movement disorder. Here, we investigated arteriolar-cerebral-blood-volume (CBVa), an index reflecting the homeostasis of the most actively regulated segment in the microvasculature, using advanced MRI in various brain regions in PD and MCI patients and matched controls. Our goal is to find brain regions with altered CBVa that are specific to PD with normal and impaired cognition, and MCI-without-movement-disorder, respectively. In PD patients with normal cognition (n=10), CBVa was significantly decreased in the substantia nigra, caudate and putamen when compared to controls. In PD patients with impaired cognition (n=6), CBVa showed a decreasing trend in the substantia nigra, caudate and putamen, but was significantly increased in the presupplementary motor area and intracalcarine gyrus compared to controls. In MCI-patients-without-movement-disorder (n=18), CBVa was significantly increased in the caudate, putamen, hippocampus and lingual gyrus compared to controls. These findings provide important information for efforts towards developing biomarkers for the evaluation of potential risk of PD dementia (PDD) in PD patients. The current study is limited in sample size and therefore is exploratory in nature. The data from this pilot study will serve as the basis for power analysis for subsequent studies to further investigate and validate the current findings.