Purpose

To develop a deep-learning-based method to quantify multiple parameters in the brain from conventional contrast-weighted images.

Methods

Eighteen subjects were imaged using an MR Multitasking sequence to generate reference T₁ and T₂ maps in the brain. Conventional contrast-weighted images consisting of T₁ MPRAGE, T₁ GRE, and T₂ FLAIR were acquired as input images. A U-Net-based neural network was trained to estimate T₁ and T₂ maps simultaneously from the contrast-weighted images. Six-fold cross-validation was performed to compare the network outputs with the MR Multitasking references.

Results

The deep-learning T₁ /T₂ maps were comparable with the references, and brain tissue structures and image contrasts were well preserved. A peak signal-to-noise ratio >32 dB and a structural similarity index >0.97 were achieved for both parameter maps. Calculated on brain parenchyma (excluding CSF), the mean absolute errors (and mean percentage errors) for T₁ and T₂ maps were 52.7 ms (5.1%) and 5.4 ms (7.1%), respectively. ROI measurements on four tissue compartments (cortical gray matter, white matter, putamen, and thalamus) showed that T₁ and T₂ values provided by the network outputs were in agreement with the MR Multitasking reference maps. The mean differences were smaller than ± 1%, and limits of agreement were within ± 5% for T₁ and within ± 10% for T₂ after taking the mean differences into account.

Conclusion

A deep-learning-based technique was developed to estimate T₁ and T₂ maps from conventional contrast-weighted images in the brain, enabling simultaneous qualitative and quantitative MRI without modifying clinical protocols.

Purpose

To develop a simultaneous T₁ , T₂ , and ADC mapping method that provides co-registered, distortion-free images and enables multiparametric quantification of 3D brain coverage in a clinically feasible scan time with the MR Multitasking framework.

Methods

The T₁ /T₂ /diffusion weighting was generated by a series of T₂ preparations and diffusion preparations. The underlying multidimensional image containing 3 spatial dimensions, 1 T₁ weighting dimension, 1 T₂ -preparation duration dimension, 1 b-value dimension, and 1 diffusion direction dimension was modeled as a 5-way low-rank tensor. A separate real-time low-rank model incorporating time-resolved phase correction was also used to compensate for both inter-shot and intra-shot phase inconsistency induced by physiological motion. The proposed method was validated on both phantom and 16 healthy subjects. The quantification of T₁ /T₂ /ADC was evaluated for each case. Three post-surgery brain tumor patients were scanned for demonstration of clinical feasibility.

Results

Multitasking T₁ /T₂ /ADC maps were perfectly co-registered and free from image distortion. Phantom studies showed substantial quantitative agreement ( R2=0.999 ) with reference protocols for T₁ /T₂ /ADC. In vivo studies showed nonsignificant T₁ (P = .248), T₂ (P = .97), ADC (P = .328) differences among the frontal, parietal, and occipital regions. Although Multitasking showed significant differences of T₁ (P = .03), T₂ (P < .001), and ADC (P = .001) biases against the references, the mean bias estimates were small (ΔT₁ % < 5%, ΔT₂ % < 7%, ΔADC% < 5%), with all intraclass correlation coefficients greater than 0.82 indicating "excellent" agreement. Patient studies showed that Multitasking T₁ /T₂ /ADC maps were consistent with the clinical qualitative images.

Conclusion

The Multitasking approach simultaneously quantifies T₁ /T₂ /ADC with substantial agreement with the references and is promising for clinical applications.

Importance

Developing more and better diagnostic and therapeutic tools for central nervous system disorders is an ethical imperative. Human research with neural devices is important to this effort and a critical focus of the National Institutes of Health Brain Research Through Advancing Innovative Neurotechnologies (BRAIN) Initiative. Despite regulations and standard practices for conducting ethical research, researchers and others seek more guidance on how to ethically conduct neural device studies. This article draws on, reviews, specifies, and interprets existing ethical frameworks, literature, and subject matter expertise to address 3 specific ethical challenges in neural devices research: analysis of risk, informed consent, and posttrial responsibilities to research participants.

Observations

Research with humans proceeds after careful assessment of the risks and benefits. In assessing whether risks are justified by potential benefits in both invasive and noninvasive neural device research, the following categories of potential risks should be considered: those related to surgery, hardware, stimulation, research itself, privacy and security, and financial burdens. All 3 of the standard pillars of informed consent-disclosure, capacity, and voluntariness-raise challenges in neural device research. Among these challenges are the need to plan for appropriate disclosure of information about atypical and emerging risks of neural devices, a structured evaluation of capacity when that is in doubt, and preventing patients from feeling unduly pressured to participate. Researchers and funders should anticipate participants' posttrial needs linked to study participation and take reasonable steps to facilitate continued access to neural devices that benefit participants. Possible mechanisms for doing so are explored here. Depending on the study, researchers and funders may have further posttrial responsibilities.

Conclusions and relevance

This ethical analysis and points to consider may assist researchers, institutional review boards, funders, and others engaged in human neural device research.

The physics case and an experimental overview of the MOLLER (Measurement Of a Lepton Lepton Electroweak Reaction) experiment at the 12 GeV upgraded Jefferson Lab are presented. A highlight of the Fundamental Symmetries subfield of the 2007 NSAC Long Range Plan was the SLAC E158 measurement of the parity-violating asymmetry $A_{PV}$ in polarized electron-electron (M{\o}ller) scattering. The proposed MOLLER experiment will improve on this result by a factor of five, yielding the most precise measurement of the weak mixing angle at low or high energy anticipated over the next decade. This new result would be sensitive to the interference of the electromagnetic amplitude with new neutral current amplitudes as weak as $\sim 10^{-3}\cdot G_F$ from as yet undiscovered dynamics beyond the Standard Model. The resulting discovery reach is unmatched by any proposed experiment measuring a flavor- and CP-conserving process over the next decade, and yields a unique window to new physics at MeV and multi-TeV scales, complementary to direct searches at high energy colliders such as the Large Hadron Collider (LHC). The experiment takes advantage of the unique opportunity provided by the upgraded electron beam energy, luminosity, and stability at Jefferson Laboratory and the extensive experience accumulated in the community after a round of recent successfully completed parity-violating electron scattering experiments

We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of x_{B} (0.36, 0.48, and 0.60) and Q^{2} (3.1 to 8.4  GeV^{2}) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions dσ_{T}/dt+εdσ_{L}/dt, dσ_{TT}/dt, dσ_{LT}/dt, and dσ_{LT^{'}}/dt are extracted as a function of the proton momentum transfer t-t_{min}. The results suggest the amplitude for transversely polarized virtual photons continues to dominate the cross section throughout this kinematic range. The data are well described by calculations based on transversity generalized parton distributions coupled to a helicity flip distribution amplitude of the pion, thus providing a unique way to probe the structure of the nucleon.

We report high-precision measurements of the deeply virtual Compton scattering (DVCS) cross section at high values of the Bjorken variable x_{B}. DVCS is sensitive to the generalized parton distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross section for all possible polarization states of the initial and final electron and nucleon, and final state photon, we present the first experimental extraction of all four helicity-conserving Compton form factors (CFFs) of the nucleon as a function of x_{B}, while systematically including helicity flip amplitudes. In particular, the high accuracy of the present data demonstrates sensitivity to some very poorly known CFFs.

We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of $x_B$ (0.36, 0.48 and 0.60) and $Q^2$ (3.1 to 8.4 GeV$^2$) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions $d\sigma_L/dt+\epsilon d\sigma_T/dt$, $d\sigma_{TT}/dt$, $d\sigma_{LT}/dt$ and $d\sigma_{LT'}/dt$ are extracted as a function of the proton momentum transfer $t-t_{min}$. The results suggest the amplitude for transversely polarized virtual photons continues to dominate the cross-section throughout this kinematic range. The data are well described by calculations based on transversity Generalized Parton Distributions coupled to a helicity flip Distribution Amplitude of the pion, thus providing a unique way to probe the structure of the nucleon.