BOLD fMRI is hampered by dropout of signal in the orbitofrontal and parietal brain regions due to magnetic field gradients near air-tissue interfaces. This work reports the use of spiral-in trajectories that begin at the edge of k-space and end at the origin, and spiral in/out trajectories in which a spiral-in readout is followed by a conventional spiral-out trajectory. The spiral-in trajectory reduces the dropout and increases the BOLD contrast. The spiral-in and spiral-out images can be combined in several ways to simultaneously achieve increased signal-tonoise ratio (SNR) and reduced dropout artifacts. Activation experiments employing an olfaction task demonstrate significantly increased activation volumes due to reduced dropout, and overall increased SNR in all regions. The most widely used form of fMRI exploits BOLD contrast (1,2) to produce maps of neuronal activation. When the transverse magnetization decay is exponential, changes in BOLD contrast are maximized if the echo time (TE) is made equal to the susceptibility-mediated transverse relaxation time constant, T* 2 . In uniform brain the T* 2 for gray matter is about 50 ms at 3T (3,4); thus, in sensitizing the acquisition to BOLD changes from the microscopic gradients surrounding capillaries, the acquisition is also made exquisitely sensitive to intravoxel dephasing resulting from macroscopic field gradients established near air-tissue interfaces. These susceptibility-induced field gradients (SFGs) cause severe dropout of signal in the frontal orbital and lateral parietal brain regions due to the difference in magnetic susceptibility of tissue and air (ϳ -8 ppm). These dropouts can limit the applicability of fMRI for many cognitive experiments.Several methods have been proposed to reduce the effect of SFGs. One class of techniques corrects for dropouts caused when SFGs shift the center of excitation k-space (k z direction), by applying compensation gradients in the slice-selection direction to refocus the dephased spins (5,6). 3D compensation schemes were introduced by Yang et al. (7,8) in which multiple echoes and Fourier inversion are used to create compensated images, and by Glover (9), who used extended coverage of k z -space with windowed reconstruction to provide efficiency improvements in gathering the compensated images. A related method simply decreases the slice thickness and averages adjacent slices (10,11). However, each of these methods suffers from prolonged scan time and loss of SNR efficiency. Another class of methods uses tailored RF pulses to compensate the dephasing during excitation (12)(13)(14). The design of these pulses is complex and ideally must be tailored for each subject, and their effectiveness is reduced by gradient system limitations that cause the pulses to be lengthy. In addition, all of these compensation methods are effective only for SFGs in the slice-select direction, and they provide no mitigation for intravoxel dephasing caused by in-plane gradients.Spiral methods have several advantages over other techniques for ...

Quantitative spinal cord (SC) magnetic resonance imaging (MRI) is fraught with challenges, among which is the lack of standardized imaging protocols. Here we present a prospectively harmonized quantitative MRI protocol, which we refer to as the spine generic protocol, for the three main 3T MRI vendors: GE, Philips and Siemens. The protocol provides valuable metrics for assessing SC macrostructural and microstructural integrity: T1-weighted and T2-weighted imaging for SC cross-sectional area (CSA) computation, multi-echo gradient echo for gray matter CSA, as well as magnetization transfer and diffusion weighted imaging for assessing white matter microstructure. The spine generic protocol was used to acquire data across 42 centers in 260 healthy subjects, as detailed in the companion paper [REF-DATA]. The spine generic protocol is open-access and its latest version can be found at: https://spinalcordmri.org/protocols. The protocol will serve as a valuable starting point for researchers and clinicians implementing new SC imaging initiatives. Note to the reviewer/editor/publisher: the companion paper is referred to as [REF-DATA]6/52 121 122dealing with cervical myelopathy and MS populations. Applications of the MethodThe proposed protocol is not geared towards a specific disease and it is suitable for imaging WM pathology (demyelination and Wallerian degeneration via axon/myelin-sensitive 122 https://mssociety.ca/about-ms-research/about-our-research-program/research-we-fund/canadian-prospect ive-cohort-study-to-understand-progression-in-ms-canproco 121 https://www.wingsforlife.com/us/research/imaging-spinal-cord-injury-and-assessing-its-predictive-value-th e-inspired-study-2675/ 9/52

Purpose Simultaneous brain and spinal cord functional MRI is emerging as a new tool to study the central nervous system but is challenging. Poor B0 homogeneity and small size of the spinal cord are principal obstacles to this nascent technology. Here we extend a dynamic shimming approach, first posed by Finsterbusch, by shimming per slice for both the brain and spinal cord. Methods We shim dynamically by a simple and fast optimization of linear field gradients and frequency offset separately for each slice in order to minimize off‐resonance for both the brain and spinal cord. Simultaneous acquisition of brain and spinal cord fMRI is achieved with high spatial resolution in the spinal cord by means of an echo‐planar RF pulse for reduced FOV. Brain slice acquisition is full FOV. Results T2*‐weighted images of brain and spinal cord are acquired with high clarity and minimal observable image artifacts. Fist‐clenching fMRI experiments reveal task‐consistent activation in motor cortices, cerebellum, and C6‐T1 spinal segments. Conclusions High quality functional results are obtained for a sensory‐motor task. Consistent activation in both the brain and spinal cord is observed at individual levels, not only at group level. Because reduced FOV excitation is applicable to any spinal cord section, future continuation of these methods holds great potential.

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Dermatomal maps are a mainstay of clinical practice and provide information on the spatial distribution of the cutaneous innervation of spinal nerves. Dermatomal deficits can help isolate the level of spinal nerve root involvement in spinal conditions and guide clinicians in diagnosis and treatment. Dermatomal maps, however, have limitations, and the spatial distribution of spinal cord sensory activity in humans remains to be quantitatively assessed. Here we used spinal cord functional MRI to map and quantitatively compare the spatial distribution of sensory spinal cord activity during tactile stimulation of the left and right lateral shoulders (i.e. C5 dermatome) and dorsal third digits of the hands (i.e., C7 dermatome) in healthy humans (n = 24, age = 36.8 ± 11.8 years). Based on the central sites for processing of innocuous tactile sensory information, we hypothesized that the activity would be localized more to the ipsilateral dorsal spinal cord with the lateral shoulder stimulation activity being localized more superiorly than the dorsal third digit. The findings demonstrate lateralization of the activity with the left- and right-sided stimuli having more activation in the ipsilateral hemicord. Contradictory to our hypotheses, the activity for both stimulation sites was spread across the dorsal and ventral hemicords and did not demonstrate a clear superior-inferior localization. Instead, the activity for both stimuli had a broader than expected distribution, extending across the C5, C6, and C7 spinal cord segments. We highlight the complexity of the human spinal cord neuroanatomy and several sources of variability that may explain the observed patterns of activity. While the findings were not completely consistent with our a priori hypotheses, this study provides a foundation for continued work and is an important step towards developing normative quantitative spinal cord measures of sensory function, which may become useful objective MRI-based biomarkers of neurological injury and improve the management of spinal disorders.