Multispectral 3D phase-encoded turbo spin-echo for imaging near metal: Limitations and possibilities demonstrated by simulations and phantom experiments Jetse S. van Gorp a, ⁎, Razmara Nizak b , Job G. Bouwman a , Daniël B.F. Saris b , Peter R. Seevinck a a Image Sciences Institute, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands b Department of Orthopedics, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands abstract article info Article history: Received 18 June 2016 Received in revised form 23 January 2017 Accepted 24 January 2017 Available online xxxx To see improvements in the imaging performance near biomaterial implants we assessed a multispectral fully phase-encoded turbo spin-echo (ms3D-PE-TSE) sequence for artifact reduction capabilities and scan time effi- ciency in simulation and phantom experiments. For this purpose, ms3D-PE-TSE and ms3D-TSE sequences were implemented to obtain multispectral images (±20 kHz) of a cobalt-chromium (CoCr) knee implant embedded in agarose. In addition, a knee implant comput- er model and the acquired ms3D-PE-TSE images were used to investigate the possibilities for scan time acceler- ation using field-of-view (FOV) reduction for off-resonance frequency bins and compressed sensing reconstructions of undersampled data. Both acceleration methods were combined to acquire a +10 kHz frequen- cy bin in a second experiment. The obtained ms3D-PE-TSE images showed no susceptibility related artifacts, while ms3D-TSE images suf- fered from hyper-intensity artifacts. The limitations of ms3D-TSE were apparent in the far off-resonance re- gions (±[10–20] kHz) located close to the implant. The scan time calculations showed that ms3D-PE-TSE can be applied in a clinically relevant timeframe (~12 min), when omitting the three central frequency bins. The feasibility of CS acceleration for ms3D-PE-TSE was demonstrated using retrospective reconstruc- tions before combining CS and rFOV imaging to decrease the scan time for the + 10 kHz frequency bin from ~10.9 min to ~ 3.5 min, while also increasing the spatial resolution fourfold. The temporally resolved signal of ms3D-PE-TSE proved to be useful to decrease the intensity ripples after sum-of-squares reconstructions and increase the signal-to-noise ratio. The presented results suggest that the scan time limitations of ms3D-PE-TSE can be sufficiently addressed when focusing on signal acquisitions in the direct vicinity of metal implants. Because these regions cannot be measured with existing multispectral methods, the presented ms3D-PE-TSE method may enable the detection of inflamma- tion or (pseudo-)tumors in locations close to the implant. © 2017 Elsevier Inc. All rights reserved. Keywords: Near-metal imaging Implants Fully phase-encoded MRI Multispectral 3D phase-encoded turbo spin-echo Susceptibility Field inhomogeneities 1. Introduction The incidence of knee and hip replacements [1,2] but also of trauma related procedures, have been steadily increasing in recent years. With the increasing number of metal implants, there is a growing need for ac- curate imaging in patients with substantial implants. There is an unmet medical need for imaging around implants and the assistance in fre- quently complex diagnostic dilemmas. Ideally, the soft-tissue contrast of MRI is exploited for the detection of complications [3–8] (e.g. osteolysis, infection, implant loosening, pseudo-tumors) [9,10] near metal implants. To accurately perform post-operative MRI, multispectral turbo spin- echo (msTSE) techniques (e.g. MAVRIC, SEMAC) have been developed for metal artifact reduction caused by the paramagnetic nature of the implants [5,6,11]. To a large extent these methods have been successful in improving the diagnostic image quality surrounding metal implants. However, in the case of extreme susceptibility induced field gradients, equal or larger than the frequency encoding readout gradient, such techniques still result in signal hyper-intensities and signal voids [12]. In a recent study it was calculated that multispectral techniques are fun- damentally limited in regions close to the implants where metal in- duced off-resonance offsets exceed ± 12 kHz, when applied as in the clinic [13]. To overcome these remaining fundamental limitations, fully phase- encoded techniques have been suggested [14–16]. These techniques Magnetic Resonance Imaging 39 (2017) 31–43 ⁎ Corresponding author. E-mail address: sjoerdvangorp@gmail.com (J.S. van Gorp). http://dx.doi.org/10.1016/j.mri.2017.01.016 0730-725X/© 2017 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Magnetic Resonance Imaging journal homepage: www.mrijournal.com