Variable (phaseand gap-dependent) skewand normal-quadrupole focusing effects of APPLE-II undulators on electron beam are reportedly complicating practical use of this type of insertion devices in many synchrotron radiation sources. We show that these undesirable effects, whatever their physical “origin”, can be well controlled and in many cases efficiently compensated during the standard “virtu...

PURPOSE To design array-compressed parallel transmit radiofrequency (RF) pulses and compare them to pulses designed with existing transmit array compression strategies. THEORY AND METHODS Array-compressed parallel RF pulse design is proposed as the joint optimization of a matrix of complex-valued compression weights that relate a full-channel physical array to a reduced-channel virtual array,...

Introduction Whole body MRI at 3T may be impeded by B1 transmit field inhomogeneities caused by the dielectric shortening of the RF wavelength [1]. RF shimming techniques based on parallel transmission [2,3] can strongly improve the image quality in clinical whole body applications [4]. In this context, it is an important question, how the RF shimming performance depends on the chosen coil topo...

Recently, the MRI-linac prototype at UMC Utrecht was upgraded with a ring-based gantry, where all linac components are mounted on a ring around the MR scanner. Although adaptations have been made to both linac and MR magnets in order to account for mutual magnetic interference, interference problems cannot be ruled out completely. Therefore, in this paper the impact of gantry position dependent...

The high-field permanent magnetic circuits of 1.2 T and 1.5 T with novel magnetic focusing and curved-surface correction are developed. The permanent magnetic circuit comprises a magnetic yoke, main magnetic steel, nonspherical curved-surface magnetic poles, plugging magnetic steel, and side magnetic steel. In this work, a novel shimming method is proposed for the effective correction of base m...

The diamagnetism of biological tissues reduces the homogeneity of the magnetic field and may limit the number of samples in multi-sample gradient-recalled echo (GRE) experiments. This study aims to 1) evaluate the magnetic field distortions and signal loss artifacts in GRE images of proximal water samples, and 2) develop a passive shimming device to overcome this limitation. The magnetic field ...

Introduction: The increased longitudinal relaxation time of the blood at ultrahigh field (UHF) can improve non-contrast enhanced perfusion imaging using arterial spin labeling (ASL), especially for targeted tissues with long arterial transit times and/or intrinsic low perfusion, such as the prostate. One well-known challenge for UHF imaging is the destructive interference of RF pulses (1), whic...