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Purpose: Customizing a Siemens 32‐channel coil for use in a Philips 3T MRI system with incorporated magnetic field probes for collecting high‐quality MRI and magnetic‐field monitoring data concurrently. Methods: The development process of the custom coil involved several (iterative) phases. Standard temporal SNR and B1+ data were collected with the 32‐channel Siemens and for reference the 32‐channel/8‐channel Philips head coils before and after the custom coil was made compatible with the 3T Philips Achieva system, and magnetic field probes were installed into it along with ancillary electronics around it. Quality assurance tests were conducted in each of the build phases to ensure that the modifications did not affect MRI or field‐monitoring data negatively. To test the finished custom coil, we collected high angular resolution diffusion imaging (HARDI) datasets on a spherical silicon oil phantom both with and without concurrent field monitoring and a 32‐channel Philips coil without concurrent field monitoring, where the latter two served as reference scans to assess the improved performance of the custom coil with field monitoring. Similar HARDI‐MRI data were also collected in vivo with the finished custom coil together with field monitoring data. Results: The custom coil provided excellent temporal SNR especially at the edges where cortical gray matter is expected. When using concurrent field monitoring in HARDI acquisitions, the custom coil alleviated ghosting artifacts in phantom data and provided in vivo images with 1.4‐mm isotropic resolution. Conclusion: The custom MRI coil with integrated magnetic‐field monitoring probes provided improved imaging performance. [ABSTRACT FROM AUTHOR]

Purpose: This article presents a novel 14‐channel receive‐only array for 13C human head imaging at 3 T that explores the SNR gain by operating at cryogenic temperature cooled by liquid nitrogen. Methods: Cryostats are developed to evaluate single‐coil bench SNR performance and cool the 14‐channel array with liquid nitrogen while having enough thermal insulation between the coils and the sample. The temperature distribution for the coil array is measured. Circuits are adapted to the −189°C environment and implemented in the 14‐channel array. 13C images are acquired with the array at cryogenic and room temperature in a 3T scanner. Results: Compared with room temperature, the array at cryogenic temperature provides 27%–168% SNR improvement over all voxels and 47% SNR improvement near the image center. The measurements show a decrease of the element noise correlation at cryogenic temperature. Conclusion: It is demonstrated that higher SNR can be achieved by cryogenically cooling the 14‐channel array. A cryogenic array suitable for clinical imaging can be further developed on the array proposed. The cryogenic coil array is most likely suited for scenarios in which high SNR deep in a head and decent SNR on the periphery are required. [ABSTRACT FROM AUTHOR]

Individuals differ in their functional connectome, which can be demonstrated using a “fingerprinting” analysis in which the connectome from an individual in one dataset is used to identify the same person from an independent dataset. Recently, the origin of these fingerprints has been studied by examining if they are present in infants. The results have varied considerably, with identification rates from 10 to 90%. When fingerprinting has been performed by splitting a single imaging session into two split-sessions (within session), identification rates were higher than when two full-sessions (between sessions) were compared. This study examined whether a methodological difference could account for this variation. It was hypothesized that the infant's exact head position in the head coil may affect the measured connectome, due to the gradual inhomogeneity of signal-to-noise in phased-array coils and the breadth of possible positions for a small infant head in a head coil. This study examined the impact of this using resting state functional MRI data from the Developing Human Connectome Project second release. Using functional timeseries, fingerprinting identification was high (84-91%) within a session while between sessions it was low (7%).Using N = 416 infants’ head positions, a map of the average signal-to-noise across the physical volume of the head coil was calculated and was used (independent group of 44 infants with two scan sessions) to demonstrate a significant relationship between head position in the head coil and functional connectivity. Using only the head positions (signal-to-noise values extrapolated from the group average map) of the independent group of 44 infants, high identification success was achieved across split-sessions (within session) but not full-sessions (between sessions). Using a model examining factors influencing the stability of the functional connectome, head position was seen as the strongest of the explanatory variables. We conclude within-session fingerprinting is affected by head position and future infant functional fingerprint analyses must use a different strategy or account for this impact.

Purpose: To compare the performance of a 12-channel flexible head coil (HFC12) with commercial 16-channel (HRC16) and 24-channel (HRC24) rigid coils. Methods: The phantom study was performed on a 1.5 T MR scanner with HFC12, HRC16, and HRC24. The SNR and noise correlation matrix of T1WI, T2WI, and diffusion weighted imaging (DWI) were measured. The SNR profiles were created according to the SNR. In addition, 1/g-factors were calculated in different acceleration directions. In the in vivo study, T1WI, T2WI, and DWI were performed in one healthy volunteer with three different coils. The SNR and noise correlation matrix were measured. Results: In the phantom study and in vivo study, the SNR of HFC12 in the transverse, sagittal, and coronal planes was the highest, followed by HRC24, and that of HRC16 was the lowest. The SNR profiles showed that the SNR at the edge of HFC12 was the highest. The mean value of the noise correlation matrix of HFC12 was the highest. The 1/g-factor results showed that HFC12 obtained the best acceleration ability in the head--foot acceleration direction when the reduction factor was set to two. The SNR of HFC12 in most cortices was significantly higher than that of HRC16 and HRC24, except in the occipital cortex. The SNR of HRC24 in the occipital cortex was higher than that of HFC12. Conclusion: The SNR of HFC12 in T1WI, T2WI, and DWI was better than that of the HRC24 and HFC16. The SNR of HFC12 in the cortex was significantly higher than that of the commercial rigid head coil, except in the occipital cortex. [ABSTRACT FROM AUTHOR]

Purpose: To theoretically describe, design, and test the new geometry of the birdcage coil for 7 Tesla anatomical brain imaging, which includes a large window on top, without deliberately jeopardizing its homogeneity and efficiency. This opencage will not only improve patient comfort but also enable the volunteer to follow functional MRI stimuli. This design could also facilitate the tracking of patient compliance and enable better correction of the movement. Methods: Via the transfer matrix approach, a birdcage‐like coil with a nonperiodic distribution of rungs is constructed with optimized currents in the coil rungs. Subsequently, the coil is adjusted in full‐wave simulations. Then, the coil is assembled, fine‐tuned, and matched on the bench. Finally, these results are confirmed experimentally on a phantom and in vivo. Results: Indeed, the computed isolation of −14.9 dB between the feeding ports of the coil and the symmetry of the circular polarized mode pattern transmit RF magnetic field (B1+) showed that the coil was properly optimized. An experimental assessment of the developed coil showed competitive transmit efficiency and coverage compared with the conventional birdcage coil of similar size. Conclusion: The proposed opencage coil can be designed and work without a dramatic drop of performance in terms of the B1+ field homogeneity, transmit efficiency (B1+/Pref), peak local specific absorption rate (SAR10g) and SAR efficiency (B1+/SAR10g). [ABSTRACT FROM AUTHOR]

Abstract Purpose To offer the new head coil option (with a lower channel count) of an RF coil array that provides comparable performance to the commercial 32-channel head coil. Methods The coil system comprised an upper shield (ten channels) and bottom section (fourteen channels). Signal-to-noise ratio (SNR) values for 2D unaccelerated imaging and the g-factor with an acceleration factor of 2–4 were evaluated in a phantom study. SNR performance and human brain and intracranial vessel wall imaging were conducted as part of the in vivo study. Both studies were conducted using the commercial head coil on the Siemens Tim Trio 3 T system for comparison. Results In the phantom study, the new head coil had an 8% higher SNR than the commercial head coil and demonstrated less than a 1% difference in the g-factor with the acceleration factor 2–4 in the right-to-left and anterior-to-posterior directions. In the in vivo study, the performance matched the results seen in the phantom study and showed high reproducibility in several human experiments. Structural images of the brain and intracranial vessel wall with an isotropic spatial resolution of 0.5 mm can be acquired with the new head coil. Conclusion This study demonstrates that the new head coil is capable of providing good SNR performance in both phantom and human experiments, can achieve similar acceleration ability compared to the commercial head coil, and is capable of obtaining brain and intracranial vessel wall images. [ABSTRACT FROM AUTHOR]

Purpose The goal of the Developing Human Connectome Project is to acquire MRI in 1000 neonates to create a dynamic map of human brain connectivity during early development. High-quality imaging in this cohort without sedation presents a number of technical and practical challenges. Methods We designed a neonatal brain imaging system (NBIS) consisting of a dedicated 32-channel receive array coil and a positioning device that allows placement of the infant's head deep into the coil for maximum signal-to-noise ratio (SNR). Disturbance to the infant was minimized by using an MRI-compatible trolley to prepare and transport the infant and by employing a slow ramp-up and continuation of gradient noise during scanning. Scan repeats were minimized by using a restart capability for diffusion MRI and retrospective motion correction. We measured the 1) SNR gain, 2) number of infants with a completed scan protocol, and 3) number of anatomical images with no motion artifact using NBIS compared with using an adult 32-channel head coil. Results The NBIS has 2.4 times the SNR of the adult coil and 90% protocol completion rate. Conclusion The NBIS allows advanced neonatal brain imaging techniques to be employed in neonatal brain imaging with high protocol completion rates. Magn Reson Med 78:794-804, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. [ABSTRACT FROM AUTHOR]

In this paper, a new design for transverse asymmetric head gradient coils is proposed for Magnetic Resonance Imaging (MRI). Unlike the conventional coil designs where the x and y coils are placed onto separate radial layers, the new design has windings for both the x and y coils in each transverse coil layer. The coil performance using the new design was compared with the conventional coils with the same dimensions and constraints. The results showed that the new design can improve coil performance in terms of a lower inductance, lower resistance and a higher figure of merit. [ABSTRACT FROM AUTHOR]

Purpose: To compare the performance of a 12-channel flexible head coil (HFC12) with commercial 16-channel (HRC16) and 24-channel (HRC24) rigid coils., Methods: The phantom study was performed on a 1.5 T MR scanner with HFC12, HRC16, and HRC24. The SNR and noise correlation matrix of T1WI, T2WI, and diffusion weighted imaging (DWI) were measured. The SNR profiles were created according to the SNR. In addition, 1/g-factors were calculated in different acceleration directions. In the in vivo study, T1WI, T2WI, and DWI were performed in one healthy volunteer with three different coils. The SNR and noise correlation matrix were measured., Results: In the phantom study and in vivo study, the SNR of HFC12 in the transverse, sagittal, and coronal planes was the highest, followed by HRC24, and that of HRC16 was the lowest. The SNR profiles showed that the SNR at the edge of HFC12 was the highest. The mean value of the noise correlation matrix of HFC12 was the highest. The 1/g-factor results showed that HFC12 obtained the best acceleration ability in the head-foot acceleration direction when the reduction factor was set to two. The SNR of HFC12 in most cortices was significantly higher than that of HRC16 and HRC24, except in the occipital cortex. The SNR of HRC24 in the occipital cortex was higher than that of HFC12., Conclusion: The SNR of HFC12 in T1WI, T2WI, and DWI was better than that of the HRC24 and HFC16. The SNR of HFC12 in the cortex was significantly higher than that of the commercial rigid head coil, except in the occipital cortex.

Array coils can potentially offer increased signal-to-noise ratio (SNR) over standard coils adjacent to the array elements, while preserving the SNR at the center of the volume. The SNR advantage should theoretically increase with the number of array elements. Parallel acquisition techniques (PAT), on the other hand, can benefit acquisition times or spatial resolution at a cost to SNR as well as image quality. This study examines the question of whether SNR and image quality are still acceptable with two different array coils (four and eight channels) in conjunction with PAT when compared to standard imaging with a volume coil. All imaging was on a 1.5 T MR scanner. T2-weighted, FLAIR, diffusion-weighted, and time of flight (TOF) angiography images were performed with and without PAT in a phantom and in ten healthy volunteers. The phantom measurements demonstrated superior SNR for the eight-channel coil versus the four-channel and standard head coils. Using the eight-channel head coil for in vivo imaging, image quality with PAT (acceleration factor=2) was scored similar to images without PAT using the volume coil. The four-channel head coil suffered from inhomogeneity, lower SNR and poorer image quality when using PAT compared to standard imaging with the volume head coil. Both the in vivo and the phantom results indicate that the eight-channel head coil should be used for the highest quality brain images; this coil can be combined with PAT sequences for shorter acquisition time without a significant decrease in image quality relative to a volume coil without PAT. [ABSTRACT FROM AUTHOR]