title: Multispectral 3D phase-encoded turbo spin-echo for imaging near metal: Limitations and possibilities demonstrated by simulations and phantom experiments.
abstract: 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 efficiency in simulation and phantom experiments. For this purpose, ms3D-PE-TSE and ms3D-TSE sequences were implemented to obtain multispectral images (±20kHz) of a cobalt-chromium (CoCr) knee implant embedded in agarose. In addition, a knee implant computer model and the acquired ms3D-PE-TSE images were used to investigate the possibilities for scan time acceleration 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 +10kHz frequency bin in a second experiment. The obtained ms3D-PE-TSE images showed no susceptibility related artifacts, while ms3D-TSE images suffered from hyper-intensity artifacts. The limitations of ms3D-TSE were apparent in the far off-resonance regions (±[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 (~12min), when omitting the three central frequency bins. The feasibility of CS acceleration for ms3D-PE-TSE was demonstrated using retrospective reconstructions before combining CS and rFOV imaging to decrease the scan time for the +10kHz frequency bin from ~10.9min to ~3.5min, 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 inflammation or (pseudo-)tumors in locations close to the implant.
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands. Electronic address: sjoerdvangorp@gmail.com.
authors.forename: Jetse S
authors.initials: JS
authors.lastname: van Gorp
authors.affiliation: Department of Orthopedics, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands.
authors.forename: Razmara
authors.initials: R
authors.lastname: Nizak
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands.
authors.forename: Job G
authors.initials: JG
authors.lastname: Bouwman
authors.affiliation: Department of Orthopedics, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands.
authors.forename: Daniël B F
authors.initials: DBF
authors.lastname: Saris
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, Heidelberglaan 100, 3584CX Utrecht, The Netherlands.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Seevinck
mesh_terms: D016477:Artifacts; D002857:Chromium / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D005269:Femur / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007717:Knee / Q000601:surgery; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008670:Metals; D019047:Phantoms, Imaging; D019736:Prostheses and Implants; D012189:Retrospective Studies; D059629:Signal-To-Noise Ratio
chemical_list: D008670:Metals; D002857:Chromium; D003035:Cobalt
keywords: Field inhomogeneities; Fully phase-encoded MRI; Implants; Multispectral 3D phase-encoded turbo spin-echo; Near-metal imaging; Susceptibility