Model for b1 imaging in MRI using the rotating RF field

The componential nature of arithmetical cognition: some important questions

Research on typically developing children and adults and people with developmental and acquired dyscalculia converges in indicating that arithmetical ability is not unitary but is made up of many different components. Categories of components include non-symbolic quantity representation and processing; symbolic quantity representation and processing; counting procedures and principles; arithmetic operations; arithmetical knowledge and understanding; multiple forms and applications of conceptual knowledge of arithmetic; and domain-general abilities such as attention, executive functions and working memory. There is much evidence that different components can and often do show considerable functional independence, not only in developmental and acquired dyscalculia, but in typically achieving children and adults. At the same time, it is possible to find complex interactions and bidirectional relationships between the different components, including between domain-specific and apparently domain-general abilities. There is a great deal that still needs to be discovered. In particular, we need to learn more about the origins in infancy of subitizing and approximate magnitude comparison, the extent to which these interact, the extent to which they may be further divisible, and the extent and ways in which they themselves may develop with age and the extent to which they may influence later-developing components. There also needs to be a lot more research on exactly how domain-general and domain-specific abilities contribute to mathematical development, and how they interact with one another.

Fast spin-echo approach for accelerated B1 gradient-based MRI

PURPOSE

To expand on the previously developedB 1 + $$ {\mathrm{B}}_1^{+} $$ -encoding technique, frequency-modulated Rabi-encoded echoes (FREE), to perform accelerated image acquisition by collecting multiple lines of k-space in an echo train.

METHODS

FREE uses adiabatic full-passage pulses and a spatially varying RF field to encode unique spatial information without the use of traditional B0 gradients. The original implementation relied on acquiring single lines of k-space, leading to long acquisitions. In this work, an acceleration scheme is presented in which multiple echoes are acquired in a single shot, analogous to conventional fast spin-echo sequences. Theoretical analysis and computer simulations investigated the feasibility of this approach and presented a framework to analyze important imaging parameters of FREE-based sequences. Experimentally, the multi-echo approach was compared with conventional phase-encoded images of the human visual cortex using a simple surface transceiver coil. Finally, different contrasts demonstrated the clinical versatility of the new accelerated sequence.

RESULTS

Images were acquired with an acceleration factor of 3.9, compared with the previous implementation of FREE, without exceeding specific absorption rate limits. Different contrasts can easily be acquired without major modifications, including inversion recovery-type images.

CONCLUSION

FREE initially illustrated the feasibility of performing slice-selective 2D imaging of the human brain without the need for a B0 gradient along the y-direction. The multi-echo version maintains the advantages thatB 1 + $$ {\mathrm{B}}_1^{+} $$ encoding provides but represents an important step toward improving the clinical feasibility of such sequences. Additional acceleration and more advanced reconstruction techniques could further improve the clinical viability of FREE-based techniques.

Clinically feasible B1 field correction for multi-organ sodium imaging at 3 T

Sodium MRI allows the non-invasive quantification of intra-organ sodium concentration. RF inhomogeneity introduces uncertainty in this estimated concentration. B₁ field corrections can be used to overcome some of these limitations. However, the low signal-to-noise ratio in sodium MRI makes accurate B₁ mapping in reasonable scan times challenging. The study aims to evaluate Bloch-Siegert off-resonance (BLOSI) B₁ field correction for sodium MRI using a 3D Fermat looped, orthogonally encoded trajectories (FLORET) read-out trajectory. We propose a clinically feasible B₁ field map correction method for sodium imaging at 3 T, evaluating five healthy subjects' brain, heart blood, kidneys, and thigh muscle. We scanned the subjects twice for repeatability measures and used sodium phantoms to determine organ total sodium concentration. Conventional proton scans were compared with sodium images for organ structural integrity. The BLOSI approach based on the 3D FLORET read-out trajectory was used in B₁ field correction and 3D density-adapted radial acquisition for sodium imaging. Results indicate improvements in sodium imaging based on B₁ field correction in a clinically feasible protocol. Improvements are determined in all organs by enhanced anatomical representation, organ homogeneity, and an increase in the total sodium concentration after applying a B₁ field correction. The proposed BLOSI-based B₁ field correction using a 3D FLORET read-out trajectory is clinically feasible for sodium imaging, which is shown in the brain, heart, kidney, and thigh muscle. This supports using fast B₁ field mapping in the clinical setting.

A preference for mathematical processing outweighs the selectivity for Arabic numbers in the inferior temporal gyrus

A region in the posterior inferior temporal gyrus (ITG), referred to as the number form area (NFA, here ITG-numbers) has been implicated in the visual processing of Arabic numbers. However, it is unknown if this region is specifically involved in the visual encoding of Arabic numbers per se or in mathematical processing more broadly. Using functional magnetic resonance imaging (fMRI) during experiments that systematically vary tasks and stimuli, we find that mathematical processing, not preference to Arabic numbers, consistently drives both mean and distributed responses in the posterior ITG. While we replicated findings of higher responses in ITG-numbers to numbers than other visual stimuli during a 1-back task, this preference to numbers was abolished when participants engaged in mathematical processing. In contrast, an ITG region (ITG-math) that showed higher responses during an adding task vs. other tasks maintained this preference for mathematical processing across a wide range of stimuli including numbers, number/letter morphs, hands, and dice. Analysis of distributed responses across an anatomically-defined posterior ITG expanse further revealed that mathematical task but not Arabic number form can be successfully and consistently decoded from these distributed responses. Together, our findings suggest that the function of neuronal regions in the posterior ITG goes beyond the specific visual processing of Arabic numbers. We hypothesize that they ascribe numerical content to the visual input, irrespective of the format of the stimulus.