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Clinical Molecular PET/MRI Hybrid Imaging
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Since the appearance of the system on the market in 2014, it has been continuously investigated to test the interoperability of the components and to improve the hardware and software features. Recently, new reconstruction options using a Bayesian-penalized reconstruction iterative technique – well known from the PET/CT systems of GE – as well as Zero-time-Echo MR sequences to improve the attenuation correction by MRI-based detection and segmentation of bone, complement the formerly implemented atlas-based segmentation methods as well as the maximum likelihood reconstruction of attenuation and activity (MLAA) based quantification methods using the TOF information. No significant impact of the MRI- on the PET-performance and vice versa was found [65], not even when aggressive MR pulsing such as fast-recovery, fast-spin echo MR sequences (high RF power) and echo planar imaging sequences (heat-inducing gradients) were selected. Based on the aforementioned NEMA standards, the performance of the system has been thoroughly investigated [37, 66]. A comprehensive summary of the specifications and of the performance measurements are comprised in Table 22.6.
Magnetic Resonance Imaging
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The exact values for TE and TR are adjusted to create images with various types of weighting. For example, for T1-weighting, TE is chosen to be very short to minimize the effects of different T2 values, and several values of TR can be used to better determine T1. The time to take a complete scan also must allow for the system's inherent need to restore its dipoles to their initial state. In practice, for complete relaxation to occur, TR must be equal to several seconds in order to be several times the longest value of T1. This has traditionally placed a constraint on how quickly MRI scans can take place. Some MRI techniques work by exciting only a fraction of the available magnetization, sometimes in combination with flip angles of less than 90°; both maneuvers result in a faster spin recovery, permitting faster scans. Turbo MRI techniques fall into this category. However, by reducing scan times, these methods also lower the signals collected per slice, resulting in noisier, lower-quality images. At the end of this chapter we will discuss a method, echo-planar imaging, that allows reduced scanning times without sacrificing image quality.
IVIM in the Body: A General Overview
Published in Denis Le Bihan, Mami Iima, Christian Federau, Eric E. Sigmund, Intravoxel Incoherent Motion (IVIM) MRI, 2018
Matthew R. Orton, Neil P. Jerome, Mihaela Rata, Dow-Mu Koh
DWI is a challenging MR modality; it is notable, though not unique, among MR techniques in that contrast is introduced by actively destroying signal, specifically through diffusion-sensitizing gradients. When quantitative diffusion measurements are required, one must therefore be mindful of the available SNR and how it may influence signal modeling. Well-documented challenges of DWI are the dependence of minimum echo times on the maximum b value, distortion in echo-planar imaging (EPI) readouts from susceptibility boundaries, and artifacts arising from both cardiac and respiratory motion for extracranial targets.
Brain activity and connectivity changes in response to nutritive natural sugars, non-nutritive natural sugar replacements and artificial sweeteners
Published in Nutritional Neuroscience, 2021
Anna M. Van Opstal, Anne Hafkemeijer, Annette A. van den Berg-Huysmans, Marco Hoeksma, Theo. P. J. Mulder, Hanno Pijl, Serge A. R. B. Rombouts, Jeroen van der Grond
MRI scanning was performed on a Philips Achieva 3.0 T scanner using a 32-channel SENSE head coil (Philips Healthcare, Best, The Netherlands). Anatomical high-resolution 3DT1- weighted images of the whole brain were acquired (TR 9.8 ms, TE 4.6 ms, flip angle 8, 140 transverse slices, FOV 224 mm × 177 mm × 168 mm, reconstructed in-plane resolution 0.88 mm × 0.87 mm, slice thickness 1.2 mm) along with a high-resolution T2*-weighted EPI scan (EPI factor 35, TR 2200 ms, TE 30 ms, flip angle 80, 84 axial slices, FOV 220 mm × 220 mm, in-plane resolution 1.96 mm × 1.96 mm, slice thickness 2.0 mm) for registration purposes. Resting-state scans were acquired with T2*-weighted gradient echo-planar imaging (EPI factor 35, 160 dynamics, 37 transverse slices scanned in ascending order, TR 2200 ms, TE 30 ms, flip angle 80, FOV 220 mm × 220 mm, voxel size 2.75 × 2.75 × 2.50 mm with a 0.25 mm slice gap, total acquisition time: 6 min).
Multivariate associative patterns between the gut microbiota and large-scale brain network connectivity
Published in Gut Microbes, 2021
N. Kohn, J. Szopinska-Tokov, A. Llera Arenas, C.F. Beckmann, A. Arias-Vasquez, E Aarts
Participants were screened for compatibility with magnetic resonance imaging (MRI). MRI data were acquired using a 3 T MAGNETOM Prisma system, equipped with a 32-channel head coil. After three short task-related fMRI scans (see Papalini et al.), 9 min of resting state fMRI was acquired. 3D echo planar imaging (EPI) scans using a T2*weighted gradient echo multi-echo sequence (Poser, Versluis et al. 2006) were acquired (voxel size 3.5 × 3.5 × 3 mm isotropic, TR = 2070 ms, TE = 9 ms; 19.25 ms; 29.5 ms; 39.75 ms, FoV = 224 mm). The slab positioning and rotation (average angle of 14 degrees to AC axis) optimally covered both prefrontal and deep brain regions. Subjects were instructed to lie still with their eyes open and refrain from directed thought. A whole-brain high-resolution T1-weighted anatomical scan was acquired using a MPRAGE sequence (voxel size 1.0 × 1.0 × 1.0 isotropic, TR = 2300 ms, TE = 3.03 ms, 192 slices).
Brain activity and connectivity changes in response to glucose ingestion
Published in Nutritional Neuroscience, 2020
A. M. van Opstal, A. Hafkemeijer, A. A. van den Berg-Huysmans, M. Hoeksma, C. Blonk, H. Pijl, S. A. R. B. Rombouts, J. van der Grond
MRI scanning was performed on a Philips Achieva 3.0 T scanner using a 32-channel SENSE head coil (Philips Healthcare, Best, The Netherlands). Anatomical high-resolution 3D T1-weighted images of the whole brain were acquired (TR 9.8 ms, TE 4.6 ms, flip angle 8, 140 transverse slices, FOV 224 mm × 177 mm × 168 mm, reconstructed in-plane resolution 0.88 mm × 0.87 mm, slice thickness 1.2 mm) along with a high-resolution T2*-weighted EPI scan (EPI factor 35, TR 2200 ms, TE 30 ms, flip angle 80, 84 axial slices, FOV 220 mm × 220 mm, in-plane resolution 1.96 mm × 1.96 mm, slice thickness 2.0 mm) for registration purposes. Resting state scans were acquired with T2*-weighted gradient echo-planar imaging (EPI factor 35, 160 dynamics, 37 transverse slices scanned in ascending order, TR 2200 ms, TE 30 ms, flip angle 80, FOV 220 mm × 220 mm, voxel size 2.75 × 2.75 × 2.50 mm with a 0.25 mm slice gap, total acquisition time: 6 minutes).