Broadband inversion pulses that rotate all magnetization components 180• about a given fixed axis are necessary for refocusing and mixing in highresolution NMR spectroscopy. The relative merits of various methodologies for generating pulses suitable for broadband refocusing are considered. The de novo design of 180• universal rotation pulses (180 • U R ) using optimal control can provide improved performance compared to schemes which construct refocusing pulses as composites of existing pulses. The advantages of broadband universal rotation by optimized pulses (BURBOP) are most evident for pulse design that includes tolerance to RF inhomogeneity or miscalibration. We present new modifications of the optimal control algorithm that incorporate symmetry principles and relax conservative limits on peak RF pulse amplitude for short time periods that pose no threat to the probe. We apply them to generate a set of 180• BU RBOP pulses suitable for widespread use in 13 C spectroscopy on the majority of available probes.

Using optimal control methods, robust broadband excitation pulses can be designed with a defined linear phase dispersion. Applications include increased bandwidth for a given pulse length compared to equivalent pulses requiring no phase correction, selective pulses, and pulses that mitigate the effects of relaxation. This also makes it possible to create pulses that are equivalent to ideal hard pulses followed by an effective evolution period. For example, in applications, where the excitation pulse is followed by a constant delay, e.g. for the evolution of heteronuclear couplings, part of the pulse duration can be absorbed in existing delays, significantly reducing the time overhead of long, highly robust pulses. We refer to the class of such excitation pulses with a defined linear phase dispersion as ICEBERG pulses (Inherent Coherence Evolution optimized Broadband Excitation Resulting in constant phase Gradients). A systematic study of the dependence of the excitation efficiency on the phase dispersion of the excitation pulses is presented, which reveals surprising opportunities for improved pulse sequence performance.

ObjectivesTo implement and evaluate a dedicated receive array coil for simultaneous PET/MR in breast cancer. MethodsThe 16 receiver channel coil design was optimized for simultaneous PET/MR. To assess MR performance, signal-to-noise ratio, parallel imaging capability and image quality was evaluated in phantoms, volunteers and patients and compared to clinical standard protocols. For PET evaluation, quantitative 18 F-FDG PET scans of phantoms and seven patients (14 lesions) were compared to scans without coil. In PET image reconstruction, a CT-based template of the coil was combined with the MR-acquired attenuation correction (AC) map of the phantom / patient. ResultsMR image quality was comparable to clinical MR-only exams. PET evaluation in phantoms showed regionally varying SUV underestimation (mean 22%) due to attenuation caused by the coil. This was improved by implementing the CT-based coil template in the AC (< 2% SUV underestimation). Patient data showed that including the coil in the AC increased SUV values in lesions (21% ± 9 %). ConclusionsUsing a dedicated PET/MR breast coil, state-of-the-art MRI was possible. In PET accurate quantification and image homogeneity could be achieved, if a CT-template of this coil was included in the attenuation correction for PET image reconstruction. KeywordsMagnetic Resonance Imaging, Positron-Emission Tomography, Breast cancer, Bilateral breast imaging, RF coil array Key Points• State-of-the-art breast MRI using a dedicated PET/MR breast coil is feasible.• A multi-channel design facilitates shorter MR acquisition times through parallel imaging.• The MR coil inside a simultaneous PET/MR system causes PET photon attenuation.• Including a coil CT-template in PET image reconstruction, accurate quantification is recovered. [2][3][4]. Although successfully applied in many oncologic applications, simultaneous PET/MR in breast cancer has so far been delayed due to the need for a dedicated breast coil, which enables prone positioning and achieves high image quality, as a precondition for state-of-the-art breast MRI [5]. However, the presence of MR related hardware, such as a breast coil, in the PET field-of-view (FOV) causes significant attenuation of the 511 keV annihilation photons, therefore hampering PET image quality [6]. Studies found, that the presence of MR head coils, which contain a substantial amount of plastic housing material, lead to 13-19% underestimation of PET activity concentration, if not accounted for during image reconstruction [7]. The attenuation effects for "lighter" or more "transparent" MR surface coils were only 4% overall, but up to 10-15% closer to the coil surface [8]. These results demonstrate that disregarding the presence of MR coils leads to substantial regional bias in PET quantification and illustrate the importance of accurate implementation of methodology for MR coil attenuation correction (AC) in simultaneous PET/MR applications. Even though MR coils are invisible in the conventional MR-acquired AC maps, it was shown that coil A...

FIG. 4. A linear four-spin chain has only direct couplings J 12 , J 23 , and J 34 between neighboring spins. We split the corresponding four-spin chain control problem into two subproblems for three-spin chains.