Fast Spin Research Articles

Understanding How Fast Black Holes Spin by Analyzing Data from the Second Gravitational-wave Catalogue

Abstract The Advanced LIGO and Virgo detectors have now observed approximately 50 black hole binary mergers, from which we can begin to infer how rapidly astrophysical black holes spin. The LIGO-Virgo Collaboration (LVC) analysis of detections up to the end of the first half of the third observing run (O3a) appeared to uncover a distribution of spin magnitudes that peaks at ∼0.2. This is surprising: is there a black hole formation mechanism that prefers a particular, nonzero spin magnitude, or could this be the cumulative effect of multiple formation processes? We perform an independent analysis of the most recent gravitational-wave (GW) catalog, and find that (a) the support for the LVC spin magnitude is tenuous; in particular, adding or removing just one signal from the catalog can remove the statistical preference for this distribution; and (b) we find potential evidence for two spin subpopulations in the observed black holes: one with extremely low spins and one with larger spin magnitudes. We make the connection that these spin subpopulations could be correlated with the mass of the binary, with more massive binaries preferring larger spin magnitudes, and argue that this may provide evidence for hierarchical mergers in the second GW catalog.

Emergent linear Rashba spin-orbit coupling offers fast manipulation of hole-spin qubits in germanium

The electric dipole spin resonance (EDSR) combining strong spin-orbit coupling (SOC) and electric-dipole transitions facilitates fast spin control in a scalable way, which is the critical aspect of the rapid progress made recently in germanium (Ge) hole-spin qubits. However, a puzzle is raised because centrosymmetric Ge lacks the Dresselhaus SOC, a key element in the initial proposal of the hole-based EDSR. Here, we demonstrate that the recently uncovered finite $k$-linear Rashba SOC of 2D holes offers fast hole-spin control via EDSR with Rabi frequencies in excellent agreement with experimental results over a wide range of driving fields. We also suggest that the Rabi frequency can reach 500 MHz under a higher gate electric field or multiple GHz in a replacement by [110]-oriented quantum wells. These findings bring a deeper understanding for hole-spin qubit manipulation and offer design principles to boost the gate speed.

Quasi-periodic whispers from a transient ULX in M 101: signatures of a fast-spinning neutron star?

ABSTRACT We have studied the unusual time variability of an ultraluminous X-ray source in M 101, 4XMM J140314.2 + 541806 (henceforth, J1403), using Chandra and XMM-Newton data. Over the last two decades, J1403 has shown short-duration outbursts with an X-ray luminosity ∼1–3 × 1039 erg s−1, and longer intervals at luminosities ∼0.5–1 × 1038 erg s−1. The bimodal behaviour and fast outburst evolution (sometimes only a few days) are more consistent with an accretor/propeller scenario for a neutron star than with the canonical outburst cycles of stellar-mass black holes. If this scenario is correct, the luminosities in the accretor and propeller states suggest a fast spin (P ≈ 5 ms) and a low surface magnetic field (B ∼ 1010 G), despite our identification of J1403 as a high-mass X-ray binary. The most striking property of J1403 is the presence of strong ∼600-s quasi-periodic oscillations (QPOs), mostly around frequencies of ≈1.3–1.8 mHz, found at several epochs during the ultraluminous regime. We illustrate the properties of such QPOs, in particular their frequency and amplitude changes between and within observations, with a variety of techniques (Fast Fourier Transforms, Lomb–Scargle periodograms, weighted wavelet Z-transform analysis). The QPO frequency range <10 mHz is an almost unexplored regime in X-ray binaries and ultraluminous X-ray sources. We compare our findings with the (few) examples of very low frequency variability found in other accreting sources, and discuss possible explanations (Lense–Thirring precession of the inner flow or outflow; radiation pressure limit-cycle instability; marginally stable He burning on the neutron star surface).

Quantitative MRI Differentiates Electromyography Severity Grades of Denervated Muscle in Neuropathy of the Brachial Plexus.

Quantitative MRI (qMRI) metrics reflect microstructural skeletal muscle changes secondary to denervation and may correspond to conventional electromyography (EMG) assessments of motor unit recruitment (MUR) and denervation. Differences in quantitative T2 , diffusion-based apparent fiber diameter (AFD), and fat fraction (FF) exist between EMG grades, in patients with clinically suspected neuropathy of the brachial plexus. Prospective. A total of 30 subjects (age=37.5 ± 17.5, 21M/9F) with suspected brachial plexopathy. 3-Tesla; qMRI using fast spin echo (T2 -mapping), multi-b-valued diffusion-weighted echo planar imaging (for AFD), and dual-echo Dixon gradient echo (FF-mapping) sequences. qMRI values were compared against EMG grades (MUR and denervation). qMRI values (T2 , AFD, and FF) were obtained for five regional shoulder muscles. A 4-point scale was used for MUR/denervation severity. Linear mixed models and least-squares pairwise comparisons were used to evaluate qMRI differences between EMG grades. Predictive accuracy of EMG grades from qMRI was quantified by 10-fold cross-validated logistic models. A P value < 0.05 was considered statistically significant. Mean (95% confidence interval) qMRI for "full" MUR were T2 =39.40 msec (35.72-43.08 msec), AFD=78.35 μm (72.52-84.19 μm), and FF=4.54% (2.11-6.97%). Significant T2 increases (+8.36 to +14.67 msec) and significant AFD decreases (-11.04 to -21.58 μm) were observed with all abnormal MUR grades as compared to "full" MUR. Significant changes in both T2 and AFD were observed with increased denervation (+9.59 to +15.04 msec, -16.25 to -18.66 μm). There were significant differences in FF between some MUR grades (-1.45 to +2.96%), but no significant changes were observed with denervation (P=0.089-0.662). qMRI prediction of abnormal MUR or denervation was strong (mean accuracy=0.841 and 0.810, respectively) but moderate at predicting individual grades (accuracy=0.492 and 0.508, respectively). Quantitative T2 and AFD differences were observed between EMG grades in assessing muscle denervation. 2 TECHNICAL EFFICACY: Stage 1.

Cine magnetic resonance imaging of the uterus for evaluation of abnormal uterine bleeding

To assess the potential role of cine magnetic resonance imaging (MRI) in the evaluation of uterine peristalsis in women classified with abnormal uterine bleeding - endometrial (AUB-E) by measuring frequency and directionality of waveforms. This was a prospective pilot study of seven women with normal menses and eight women with AUB-E, defined as regular but excessive flow causing anemia or interfering with daily activities. Exclusion criteria included other causes of AUB in the PALM-COEIN system. Subjects were evaluated using a modified Menstrual Impact Questionnaire (MIQ). MRI studies were performed within days 1-5 of the subject's menstrual cycle using a 3.0T MRI and 8-channel cardiac phased array coil. Axial and sagittal T2-weighted fast spin echo was obtained to evaluate uterine morphology. Cine MRI imaging was performed using a single shot fast spin echo with a temporal resolution of 2 to 3 seconds over a 2 minutes sequence to evaluate frequency and directionality of uterine waveforms, repeated 2-3 times, and maximum number of waveforms per two minutes reported. Images were reviewed independently by two expert radiologists blinded to patients’ histories. Primary outcome was peristaltic frequency of the subendometrium measured as number of waveforms per two minutes. Secondary outcome was directionality. Primary outcome and MRI morphology were compared by Mann-Whitney U test. MIQ responses were compared by Fischer’s exact test and Mann-Whitney U test. Normal subjects bled an average of 3.9 days and those with AUB-E bled an average of 6.4 days (p= 0.016). Normal subjects defined their flow as light or moderate. Six of seven normal subjects reported no impact on their work, physical or social activity. In comparison, all but one subject with AUB-E defined their flow as heavy or very heavy with passage of clots or flooding (p = 0.001). All subjects with AUB-E reported effect on their daily activities (p < 0.001) and were more likely to report effect on their social activity (p < 0.001) and physical activity (p < 0.001). Subjects with AUB-E were more likely to report dysmenorrhea (p=0.041). Thirteen of fifteen women demonstrated motility of the subendometrium during cine display. Two women with AUB-E did not demonstrate waveforms. There was complete agreement between readers with regard to maximum number of waveforms per two minute cycle and directionality. Median number of waveforms in subjects with normal menses was 3 per two minutes. In patients with AUB-E, the median number of waveforms was 1 per two minutes (p=0.009). All subjects with waveforms exhibited cervico-fundal directionality during menses. Cine MRI is a feasible modality for measuring differences in the frequency of uterine peristalsis in women with AUB-E. This pilot study supports further investigation into the endometrial and myometrial contributions to abnormal bleeding in women with AUB-E.

A 78Seconds Complete Brain MRI Examination in Ischemic Stroke: A Prospective Cohort Study.

BackgroundFast 78‐second multicontrast echo‐planar MRI (EPIMix) has shown good diagnostic performance for detecting infarctions at a comprehensive stroke center, but its diagnostic performance has not been evaluated in a prospective study at a primary stroke center.PurposeTo prospectively determine whether EPIMix was noninferior in detecting ischemic lesions compared to routine clinical MRI.Study typeProspective cohort study.PopulationA total of 118 patients with acute MRI and symptoms of ischemic stroke.Field Strength and SequenceA 3 T. EPIMix (echo‐planar based: T1‐FLAIR, T2‐weighted, T2‐FLAIR, T2*, DWI) and routine clinical MRI sequences (T1‐weighted fast spin echo, T2‐weighted PROPELLER, T2‐weighted‐FLAIR fast spin echo, T2* gradient echo echo‐planar, and DWI spin echo echo‐planar).AssessmentThree radiologists, blinded for clinical information, assessed signs of ischemic lesions (DWI↑, ADC↓, and T2/T2‐FLAIR↑) on EPIMix and routine clinical MRI, with disagreements solved in consensus with a fourth reader to establish the reference standard.Statistical testsDiagnostic performance including sensitivity and specificity against the reference standard was evaluated. EPIMix sensitivity was tested for noninferiority compared to the reference standard using Nam's restricted maximum likelihood estimation (RMLE) Score. A P‐value < 0.05 was considered statistically significant.ResultsOf 118 patients (mean age 62 ± 16 years, 58% males), 25% (n = 30) had MRI signs of acute infarcts. EPIMix was noninferior with 97% (95% CI 83–100) sensitivity for reader 1, 100% (95% CI 88–100) sensitivity for reader 2, and 90% (95% CI 88–98) sensitivity for reader 3 vs. 93% (95% CI 78–99) sensitivity for readers 1 and 2 and 90% (95% CI 74–98) for reader 3 on routine clinical MRI. Specificity was 99% (95% CI 94–100) for reader 1, 100% (95% CI 96–100) for reader 2, and 98% (95% CI 92–100) for reader 3 on EPIMix vs. 100% (95% CI 96–100) for all readers on routine clinical MRI.ConclusionEPIMix was noninferior to routine clinical MRI for the diagnosis of acute ischemic stroke.Evidence Level2Technical EfficacyStage 2

Gadolinium Retention in the Brain of Mother and Pup Mouse: Effect of Pregnancy and Repeated Administration of Gadolinium-Based Contrast Agents.

BackgroundThe association of repeated administration of gadolinium‐based contrast agents (GBCAs) with the gadolinium (Gd) retention in the brains of mother and fetus remains unclear.PurposeTo investigate the effects of pregnancy and repeated administration of GBCAs on Gd retention in the brains of mother and pup mice.Study typeCross‐sectional cohort toxicity study.Animal ModelFrom gestational days 16–19, pregnant (n = 48) BALB/c mice.Field StrengthA 9.4 T and fast spin echo sequence.AssessmentHalf of the mother mice (n = 24) were killed at postnatal day 1 (P1) for inductively coupled plasma mass spectrometry (ICP‐MS) and transmission electron microscopy (TEM). Besides the ICP‐MS and TEM, four pups were randomly selected from each mother and killed at P1 for ultraperformance liquid chromatography mass spectrometry (UPLC‐MS) and Nissl staining.Statistical TestsOne‐way analysis of variance and unpaired t‐test.ResultsIn the group of gadodiamide, retention of Gd in the brains of pregnant mice was significantly lower than that of nonpregnant mice in the area of the deep cerebellar nuclei (DCN) (10.35 ± 2.16 nmol/g vs. 18.74 ± 3.65 nmol/g). Retention of Gd in the DCN of pups whose mothers were administered gadoterate meglumine was significantly lower than that of pups whose mothers were administered gadodiamide (0.21 ± 0.09 nmol/g vs. 6.15 ± 3.21 nmol/g) at P1. In mice treated with gadodiamide, most of the retained Gd in the brain tissue was insoluble (19.5% ± 9.5% of the recovered amount corresponded to the intact complex in the DCN).Data ConclusionIn different brain areas of the mother and pup mice, the retention of Gd after gadoterate meglumine administration was lower than that of gadodiamide and gadopentetate dimeglumine administration, and almost all the detected Gd in pups' brains was intact soluble GBCAs.Evidence Level1Technical EfficacyStage 2

Structure and Gating Behavior of the Human Integral Membrane Protein VDAC1 in a Lipid Bilayer.

The voltage-dependent anion channel (VDAC), the most abundant protein in the outer mitochondrial membrane, is responsible for the transport of all ions and metabolites into and out of mitochondria. Larger than any of the β-barrel structures determined to date by magic-angle spinning (MAS) NMR, but smaller than the size limit of cryo-electron microscopy (cryo-EM), VDAC1’s 31 kDa size has long been a bottleneck in determining its structure in a near-native lipid bilayer environment. Using a single two-dimensional (2D) crystalline sample of human VDAC1 in lipids, we applied proton-detected fast magic-angle spinning NMR spectroscopy to determine the arrangement of β strands. Combining these data with long-range restraints from a spin-labeled sample, chemical shift-based secondary structure prediction, and previous MAS NMR and atomic force microscopy (AFM) data, we determined the channel’s structure at a 2.2 Å root-mean-square deviation (RMSD). The structure, a 19-stranded β-barrel, with an N-terminal α-helix in the pore is in agreement with previous data in detergent, which was questioned due to the potential for the detergent to perturb the protein’s functional structure. Using a quintuple mutant implementing the channel’s closed state, we found that dynamics are a key element in the protein’s gating behavior, as channel closure leads to the destabilization of not only the C-terminal barrel residues but also the α2 helix. We showed that cholesterol, previously shown to reduce the frequency of channel closure, stabilizes the barrel relative to the N-terminal helix. Furthermore, we observed channel closure through steric blockage by a drug shown to selectively bind to the channel, the Bcl2-antisense oligonucleotide G3139.

Indirect NMR detection via proton of nuclei subject to large anisotropic interactions, such as 14N, 195Pt, and 35Cl, using the T-HMQC sequence.

Recently, the T-hetero-nuclear multiple quantum coherence (T-HMQC) sequence using the TRAPDOR (transfer of population in double resonance) recoupling has been introduced for the indirect detection via protons of quadrupolar nuclei with spin I = 1 (14N) or 3/2 (35Cl) in solids at fast magic-angle spinning (MAS). The sequence is simple as it only uses four rectangular pulses and exhibits low t1-noise because the recoupling pulses are applied to the indirectly detected isotope, I. We demonstrate that this sequence is applicable for the detection via protons of spin-1/2 nuclei subject to large chemical shift anisotropy, such as 195Pt. We also report the proton detection of double-quantum (2Q) coherences of 14N nuclei using this sequence. This 2Q version is more robust to the adjustment of the magic angle and the instabilities of the MAS frequencies than its parent single-quantum (1Q) version since the 2Q coherences are not broadened by the first-order quadrupole interaction. In practice, than its 1Q counterpart for the indirect detection of 14N nuclei, the 2Q variant benefits from a slightly higher resolution and comparable sensitivity. In this article, we derive for the first time the Hamiltonian that describes the spin dynamics during the TRAPDOR recoupling. This Hamiltonian demonstrates the importance of the adiabaticity parameter as well as the role of third-order terms in the effective Hamiltonian. The effects of offsets, radio-frequency field, and recoupling time on the efficiency of the T-HMQC sequence are analyzed numerically as well as with experimental detection via protons of 195Pt nuclei in a mixture of cis- and trans-platin and that of 14N and 35Cl isotopes in l-histidine HCl.

Selecting Candidates for Organ-Preserving Strategies After Neoadjuvant Chemoradiotherapy for Rectal Cancer: Development and Validation of a Model Integrating MRI Radiomics and Pathomics.

Histopathologic evaluation after surgery is the gold standard to evaluate treatment response to neoadjuvant chemoradiotherapy (nCRT) in locally advanced rectal cancer (LARC). However, it cannot be used to guide organ-preserving strategies due to poor timeliness. To develop and validate a multiscale model incorporating radiomics and pathomics features for predicting pathological good response (pGR) of down-staging to stage ypT0-1N0 after nCRT. Retrospective. A total of 153 patients (median age, 55 years; 109 men; 107 training group; 46 validation group) with clinicopathologically confirmed LARC. A 3.0-T; fast spin echo T2 -weighted and single-shot EPI diffusion-weighted images. The differences in clinicoradiological variables between pGR and non-pGR groups were assessed. Pretreatment and posttreatment radiomics signatures, and pathomics signature were constructed. A multiscale pGR prediction model was established. The predictive performance of the model was evaluated and compared to that of the clinicoradiological model. The χ2 test, Fisher's exact test, t-test, the minimum redundancy maximum relevance algorithm, the least absolute shrinkage and selection operator logistic regression algorithm, regression analysis, receiver operating characteristic curve (ROC) analysis, Delong method. P < 0.05 indicated a significant difference. Pretreatment radiomics signature (odds ratio [OR]=2.53; 95% CI: 1.58-4.66), posttreatment radiomics signature (OR=9.59; 95% CI: 3.04-41.46), and pathomics signature (OR=3.14; 95% CI: 1.40-8.31) were independent factors for predicting pGR. The multiscale model presented good predictive performance with areas under the curve (AUC) of 0.93 (95% CI: 0.88-0.98) and 0.90 (95% CI: 0.78-1.00) in the training and validation groups, those were significantly higher than that of the clinicoradiological model with AUCs of 0.69 (95% CI: 0.55-0.82) and 0.68 (95% CI: 0.46-0.91) in both groups. A model incorporating radiomics and pathomics features effectively predicted pGR after nCRT in patients with LARC. 3 TECHNICAL EFFICACY: Stage 4.

Left-Right Intensity Asymmetries Vary Depending on Scanner Model for FLAIR and T1 Weighted MRI Images.

BackgroundLocalized regions of left–right image intensity asymmetry (LRIA) were incidentally observed on T2‐weighted (T2‐w) and T1‐weighted (T1‐w) diagnostic magnetic resonance imaging (MRI) images. Suspicion of herpes encephalitis resulted in unnecessary follow‐up imaging. A nonbiological imaging artifact that can lead to diagnostic uncertainty was identified.PurposeTo investigate whether systematic LRIA exist for a range of scanner models and to determine if LRIA can introduce diagnostic uncertainty.Study TypeA retrospective study using the Alzheimer's Disease Neuroimaging Initiative (ADNI) data base.SubjectsOne thousand seven hundred fifty‐three (median age: 72, males/females: 878/875) unique participants with longitudinal data were included.Field Strength3T.SequencesT1‐w three‐dimensional inversion‐recovery spoiled gradient‐echo (IR‐SPGR) or magnetization‐prepared rapid gradient‐echo (MP‐RAGE) and T2‐w fluid‐attenuated inversion recovery (FLAIR) long tau fast spin echo inversion recovery (LT‐FSE‐IR). Only General Electric, Philips, and Siemens' product sequences were used.AssessmentLRIA was calculated as the left–right percent difference with respect to the mean intensity from automated anatomical atlas segmented regions. Three neuroradiologists with 37 (**), 32 (**), and 3 (**) years of experience rated the clinical impact of 30 T2‐w three‐dimensional FLAIR exams with LRIA to determine the diagnostic uncertainty. Statistical comparisons between retrospective intensity normalized T1m and original T1‐w images were made.Statistical TestsFor each image type, a linear mixed effects model was fit using LRIA scores from all scanners, regions, and participants as the outcome and age and sex as predictors. Statistical significance was defined as having a P‐value <0.05.ResultsLRIA scores were significantly different from zero on most scanners. All clinicians were uncertain or recommended definite diagnostic follow‐up in 62.5% of cases with LRIA >10%. Individuals with acute brain pathology or focal neurologic deficits are not enrolled in ADNI; therefore, focal signal abnormalities were considered false positives.Data ConclusionLRIA is system specific, systematic, creates diagnostic uncertainty, and impacts IR‐SPGR, MP‐RAGE, and LT‐FSE‐IR product sequences.Level of Evidence: 2Technical Efficacy Stage: 3

Highly Efficient Polarizing Agents for MAS‐DNP of Proton‐Dense Molecular Solids

AbstractEfficiently hyperpolarizing proton‐dense molecular solids through dynamic nuclear polarization (DNP) solid‐state NMR is still an unmet challenge. Polarizing agents (PAs) developed so far do not perform well on proton‐rich systems, such as organic microcrystals and biomolecular assemblies. Herein we introduce a new PA, cAsymPol‐POK, and report outstanding hyperpolarization efficiency on 12.76 kDa U‐13C,15N‐labeled LecA protein and pharmaceutical drugs at high magnetic fields (up to 18.8 T) and fast magic angle spinning (MAS) frequencies (up to 40 kHz). The performance of cAsymPol‐POK is rationalized by MAS‐DNP simulations combined with electron paramagnetic resonance (EPR), density functional theory (DFT) and molecular dynamics (MD). This work shows that this new biradical is compatible with challenging biomolecular applications and unlocks the rapid acquisition of 13C–13C and 15N–13C correlations of pharmaceutical drugs at natural isotopic abundance, which are key experiments for structure determination.

Highly Efficient Polarizing Agents for MAS-DNP of Proton-Dense Molecular Solids.

Efficiently hyperpolarizing proton-dense molecular solids through dynamic nuclear polarization (DNP) solid-state NMR is still an unmet challenge. Polarizing agents (PAs) developed so far do not perform well on proton-rich systems, such as organic microcrystals and biomolecular assemblies. Herein we introduce a new PA, cAsymPol-POK, and report outstanding hyperpolarization efficiency on 12.76 kDa U-13 C,15 N-labeled LecA protein and pharmaceutical drugs at high magnetic fields (up to 18.8 T) and fast magic angle spinning (MAS) frequencies (up to 40 kHz). The performance of cAsymPol-POK is rationalized by MAS-DNP simulations combined with electron paramagnetic resonance (EPR), density functional theory (DFT) and molecular dynamics (MD). This work shows that this new biradical is compatible with challenging biomolecular applications and unlocks the rapid acquisition of 13 C-13 C and 15 N-13 C correlations of pharmaceutical drugs at natural isotopic abundance, which are key experiments for structure determination.

Accelerating Knee MRI: 3D Modulated Flip-Angle Technique in Refocused Imaging with an Extended Echo Train and Compressed Sensing.

PurposeThe three-dimensional (3D) sequence of magnetic resonance imaging (MRI) plays a critical role in the imaging of musculoskeletal joints; however, its long acquisition time limits its clinical application. In such conditions, compressed sensing (CS) is introduced to accelerate MRI in clinical practice. We aimed to investigate the feasibility of an isotropic 3D variable-flip-angle fast spin echo (FSE) sequence with CS technique (CS-MATRIX) compared to conventional 2D sequences in knee imaging.MethodsImages from different sequences of both the accelerated CS-MATRIX and the corresponding conventional acquisitions were prospectively analyzed and compared. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the structures within the knees were measured for quantitative analysis. The subjective image quality and diagnostic agreement were compared between CS-MATRIX and conventional 2D sequences. Quantitative and subjective image quality scores were statistically analyzed with the paired t-test and Wilcoxon signed-rank test, respectively. Diagnostic agreements of knee substructure were assessed using Cohen’s weighted kappa statistic.ResultsFor quantitative analysis, images from the CS-MATRIX sequence showed a significantly higher SNR than T2-fs 2D sequences for visualizing cartilage, menisci, and ligaments, as well as a higher SNR than proton density (pd) 2D sequences for visualizing menisci and ligaments. There was no significant difference between CS-MATRIX and 2D T2-fs sequences in subjective image quality assessment. The diagnostic agreement was rated as moderate to very good between CS-MATRIX and 2D sequences.ConclusionThis study demonstrates the feasibility and clinical potential of the CS-MATRIX sequence technique for detecting knee lesions The CS-MATRIX sequence allows for faster knee imaging than conventional 2D sequences, yielding similar image quality to 2D sequences.

A revisit of the k-space filtering effects of magnetization-prepared 3D FLASH and balanced SSFP acquisitions: Analytical characterization of the point spread functions

Purpose3D FLASH and balanced SSFP (bSSFP) are increasingly used in quantitative MRI after contrast preparation. The acquired k-space data are modulated by T1 relaxation (or additional T2 for bSSFP). Three separate sequence parameters including the number of phase-encoding steps per shot (N), flip angle (FA), and TR have made the transient state of rapid gradient echo (GRE) imaging difficult for analysis and optimization. Here we aim to analytically characterize the k-space filtering effect of magnetization-prepared FLASH and bSSFP with the point spread functions (PSF). MethodsThe amplitude effect is characterized with the peak magnitude of the PSF, i.e. PSF(0), which, due to their approaching from transient state to steady-state for the GRE acquisitions, obeys a linear (with a slope and an intercept, not proportional) relationship with the prepared longitudinal magnetization (Mprep). The blurring effect is characterized by the FWHM of the PSF. The magnetization-prepared acquisition-dependent image contrast efficiency is characterized with the relative contrast-to-noise ratio (CNR) per unit time (ruCNR). ResultsThe slope of PSF(0) characterizes the relative contrast between different Mprep levels. The intercept of PSF(0) could lead to quantification bias for magnetization-prepared imaging. FLASH and bSSFP experience very little blurring effect, which is to the contrary of conventional fast spin echo (FSE). Analytical selections of N, FA, and TR are provided to optimize ruCNR for different scenarios. ConclusionsPSFs of the FLASH and bSSFP acquisitions are analytically derived and numerically validated, and compared with the FSE acquisition, thus providing a useful tool for optimizing magnetization-prepared GRE acquisitions.

Multi-Planar, Multi-Contrast and Multi-Time Point Analysis Tool (MOCHA) for Intracranial Vessel Wall Characterization.

Three-dimensional (3D) intracranial vessel wall (IVW) magnetic resonance imaging can reliably image intracranial atherosclerotic disease (ICAD). However, an integrated, streamlined, and optimized workflow for IVW analysis to provide qualitative and quantitative measurements is lacking. To propose and evaluate an image analysis pipeline (MOCHA) that can register multicontrast and multitime point 3D IVW for multiplanar review and quantitative plaque characterization. Retrospective. A total of 11 subjects with ICAD (68 ± 10 years old, 6 males). A 3.0 T, 3D time-of-flight gradient echo sequence and T1- and proton density-weighted fast spin echo sequences. Each participant underwent two IVW sessions within 2 weeks. Scan and rescan IVW images were preprocessed using MOCHA. The presence of atherosclerotic lesions was identified in different intracranial arterial segments by two readers (GC and JS, 12 years of vascular MR imaging experience each) following an established review protocol to reach consensus on each of the reviews. For all locations with identified plaques, plaque length, lumen and vessel wall areas, maximum and mean wall thickness values, normalized wall index and contrast enhancement ratio were measured. Percent agreement and Cohen's κ were used to test scan-rescan reproducibility of detecting plaques using MOCHA. Intraclass correlation coefficient (ICC) and Bland-Altman analysis were used to evaluate scan-rescan reproducibility for plaque morphologic and enhancement measurements. In 150 paired intracranial vessel segments, the overall agreement in plaque detection was 92.7% (κ=0.822). The ICCs (all ICCs > 0.90) and Bland-Altman plots (no bias observed) indicated excellent scan-rescan reproducibility for all morphologic and enhancement measurements. Findings from this study demonstrate that MOCHA provides high scan-rescan reproducibility for identification and quantification of atherosclerosis along multiple intracranial arterial segments and highlight its potential use in characterizing plaque composition and monitoring plaque development. 4 TECHNICAL EFFICACY: Stage 2.

T2 -Weighted MR Imaging-Derived Radiomics for Pretreatment Determination of Therapeutic Response to Glucocorticoid in Patients With Thyroid-Associated Ophthalmopathy: Comparison With Semiquantitative Evaluation.

MR imaging has been applied to determine therapeutic response to glucocorticoid (GC) before treatment in thyroid-associated ophthalmopathy (TAO), while the performance was still poor. To investigate the value of T2 -weighted imaging (T2 WI)-derived radiomics for pretreatment determination of therapeutic response to GC in TAO patients, and compare its diagnostic performance with that of semiquantitative parameters. Retrospective. A total of 110 patients (49 ± 12 years; male/female, n=48/62; responsive/unresponsive, n=62/48), divided into training (n=78) and validation (n=32) cohorts. 3.0 T, T2 -weighted fast spin echo. W.C. and H.H. (6 and 10 years of experience, respectively) performed the measurements. Maximum, mean, and minimum signal intensity ratios (SIRs) of extraocular muscle (EOM) bellies were collected to construct a semiquantitative imaging model. Radiomics features from volumes of interest covering EOM bellies were extracted and three machine learning-based (logistic regression [LR]; decision tree [DT]; support vector machine [SVM]) models were built. The diagnostic performances of models were evaluated using receiver operating characteristic curve analyses, and compared using DeLong test. Two-sided P < 0.05 was considered statistically significant. The responsive group showed higher minimum signal intensity ratio (SIRmin ) of EOMs than the unresponsive group (training: 1.46 ± 0.34 vs. 1.18 ± 0.39; validation: 1.44 ± 0.33 vs. 1.19 ± 0.20). In both cohorts, LR-based radiomics model demonstrated good diagnostic performance (area under the curve [AUC]=0.968, 0.916), followed by DT-based (AUC=0.933, 0.857) and SVM-based models (AUC=0.919, 0.855). All three radiomics models outperformed semiquantitative imaging model (SIRmin : AUC=0.805) in training cohort. In validation cohort, only LR-based radiomics model outperformed that of SIRmin (AUC=0.745). The nomogram integrating LR-based radiomics signature and disease duration further elevated the diagnostic performance in validation cohort (AUC: 0.952 vs. 0.916, P=0.063). T2 WI-derived radiomics of EOMs, together with disease duration, provides a promising noninvasive approach for determining therapeutic response before GC administration in TAO patients. 3 TECHNICAL EFFICACY: Stage 4.

FID-calibrated simultaneous multi-slice fast spin echo with long trains of hard pulses

Objective. To develop a novel, free-induction-decay (FID)-calibrated single-shot simultaneous multi-slice fast spin echo (SMS-FSE) with very long hard pulse trains for high encoding efficiency and low energy deposition. Approach. The proposed single-shot SMS-FSE employs a mixed pulse configuration in which a long excitation pulse that is spatially multi-band (MB) selective is used in conjunction with short spatially nonselective refocusing pulses. To alleviate energy deposition to tissues while reducing signal modulation along the echo train, variable low flip angles with signal prescription are utilized in the refocusing pulse train. A time-efficient FID calibration and correction method is introduced before aliased voxels in the slice direction are resolved. Simulations and experiments are performed to demonstrate the feasibility of the proposed method as an alternative to conventional HASTE for generating T 2-weighted images. Main results. Compared with conventional HASTE, the proposed method enhances imaging speed effectively by an MB factor up to 5 without apparent loss of image contrast while successfully eliminating FID artifacts. Significance. We successfully demonstrated the feasibility of the proposed method as an encoding- and energy-efficient alternative to conventional HASTE for generation of T 2-weighted contrast.

Imaging of equine septic discospondylitis using MRI, CT and post‐mortem radiographs

SummaryThis report describes a case of septic discospondylitis in an 11‐year‐old American Miniature stallion. Key imaging features are described here and include Fast Spin Echo T2/STIR hyperintensity on MRI of the intervertebral disc space and surrounding soft tissues as well as vertebral endplate destruction. Spinal cord deformation was seen concurrently and is considered likely secondary to either associated inflammatory granulation tissue or disc herniation. These findings most likely explain the apparent cervical pain and spinal ataxia grade 2/5 due to cervical spinal cord disease in this case.

Comparison of zero echo time MRI with T1-weighted fast spin echo for the recognition of sacroiliac joint structural lesions using CT as the reference standard.

To evaluate the diagnostic performance of zero echo time (ZTE) MRI in the depiction of structural lesions of sacroiliac joints (SIJs) in patients with the suspicion of sacroiliitis compared with T1-weighted fast spin echo (T1 FSE), using CT as the reference standard. Forty patients with suspicion of sacroiliitis underwent both CT and MR scans of SIJs with 80 SIJs (160 bone articular surfaces) included for analysis. Two readers independently scored SIJs for structural lesions on CT and MR images. The diagnostic capability of ZTE MRI and T1 FSE were compared by the McNemar test, using CT as the reference standard. Agreements of diagnosis and sum scores of lesions between MR sequences and CT as well as between readers were also investigated using Cohen's κappa tests and intraclass correlation coefficients. Diagnostic accuracy of ZTE MRI was higher than that of T1 FSE for erosions, sclerosis, and joint space changes (e.g., joint space changes: 91.3% vs 75.0%). ZTE MRI also improved sensitivity for detection of erosions and sclerosis (e.g., erosions at the joint level: 98.2% vs 80.0%) as well as specificity for detection of joint space changes (93.0% vs 67.4%). ZTE MRI had more consistency with CT than T1 FSE for both diagnosis and sum scores. Inter-reader agreements were higher for CT and ZTE MRI than those for T1 FSE. ZTE MRI showed superior diagnostic performance in the depiction of SIJ structural lesions compared with routine T1-weighted MRI and had reliability comparable to CT. • ZTE MRI can provide CT-like bone contrast for the depiction of osseous structural lesions of the sacroiliac joints. • ZTE MRI showed superior diagnostic performance than conventional T1 FSE in the detection of osseous structural lesions of sacroiliitis, using CT as the reference standard. • In terms of inter-reader reliability, ZTE MRI performed comparably to CT and better than conventional T1 FSE.