Mapping Sequence Research Articles

Bowen’s Formula for a Dynamical Solenoid

More than 50 years ago, Rufus Bowen noticed a natural relation between the ergodic theory and the dimension theory of dynamical systems. He proved a formula, known today as the Bowen’s formula, that relates the Hausdorff dimension of a conformal repeller to the zero of a pressure function defined by a single conformal map. In this paper, we extend the result of Bowen to a sequence of conformal maps. We present a dynamical solenoid, i.e., a generalized dynamical system obtained by backward compositions of a sequence of continuous surjections (fn:X→X)n∈N defined on a compact metric space (X,d). Under mild assumptions, we provide a self-contained proof that Bowen’s formula holds for dynamical conformal solenoids. As a corollary, we obtain that the Bowen’s formula holds for a conformal surjection f:X→X of a compact

The return of FarNet-II: Generation of solar far-side magnetograms from helioseismic data

The far-side activity of the Sun can be inferred by interpreting the near-side wave field using local helioseismic techniques. However, detections are limited to strongly active regions because signal-to-noise ratio of the data is low. Recently, we developed the FarNet and FarNet-II neural networks to improve the identification of active regions on far-side seismic maps. We aim to use FarNet-II to leverage seismic data to infer far-side magnetograms, including the magnetic field strength and polarity. We used FarNet-II to produce sequences of 11 consecutive binned magnetograms with a 12-hour cadence of a central section of the far side, where each pixel was assigned to one of nine possible classes that define its magnetic field and polarity. The inputs to the network are sequences of phase-shift maps of the same regions, computed using helioseismic holography. We trained the network using a cross-validation approach to estimate its reliability. The targets for the training and the cross-validation were obtained from near-side Helioseismic and Magnetic Imager magnetograms, taken half a rotation later than the seismic data. The metric we used for the evaluation is the volumetric Dice, a newly defined metric that measures the overlap between the outputs and the targets. The results were compared with Solar Orbiter data from a period with far-side coverage between May 2022 and September 2022. FarNet-II achieves an average volumetric Dice of 0.249, showing a good visual superposition between the targets and outputs of the network. The comparisons of the outputs and the Solar Orbiter magnetograms are also similar. FarNet-II can correctly predict the level of activity and the polarity of far-side regions using near-side seismic data. This capability can be leveraged in space-weather forecasting.

ENHANCING OTFS MODULATION FOR 6G THROUGH HYBRID PAPR REDUCTION TECHNIQUE FOR DIFFERENT SUB-CARRIERS

Peak-to-average power ratio (PAPR) in orthogonal time frequency space (OTFS) is vital for optimizing signal efficiency, minimizing distortion, and enhancing the performance of a beyond fifth-generation (B5G) system. The paper focuses on lowering the PAPR while retaining the bit error rate (BER) and power spectral density (PSD) for 64 and 256 sub-carriers. The PAPR is minimized by using a fractal optimization process known as selective mapping (SLM) and partial transmission sequence (PTS) at the transmitting block of the OTFS framework. The combination of SLM and PTS reduces peak power by selectively modifying the phase of transmitted symbols. SLM generates multiple versions of the signal, while PTS allocates power to these versions optimally, collectively mitigating amplitude peaks and minimizing PAPR. According to the simulation results, the suggested SLM+PTS works better than the traditional SLM and PTS, achieving low spectrum leakage and PAPR improvements of 5.5 dB and 4.9[Formula: see text]dB as well as SNR gains of 2.4[Formula: see text]dB and 2.1[Formula: see text]dB. In the future, SLM+PTS may work on lowering PAPR by making computers faster, researching adaptive algorithms, and combining machine learning methods for real-time optimization in various communication settings. Complex modeling, including fractal-based SLM and PTS approaches, provides a detailed understanding of waveform behavior and interference patterns, enabling more accurate and effective hybrid PAPR reduction techniques. This combination enhances the ability to manage to mitigate non-linear distortion across various sub-carriers, crucial for the performance and efficiency of 6G OTFS modulation.

The role of cardiac magnetic resonance in patients with an angiographically diagnosed SCAD

Abstract Background/Introduction Spontaneous coronary artery dissection (SCAD) characterized by its non-atherosclerotic nature, poses challenges in diagnosis and management. While recent efforts shed light on SCAD's clinical aspects, the specific utility of CMR demands deeper investigation for enhanced diagnosis and patient care. Purpose This study aims to analyze the characteristics of patients with an angiographically diagnosed SCAD, evaluate qualitative and quantitative parameters of baseline CMR and investigate predictors of myocardial injury and the association between CMR parameters and clinical outcome (major adverse cardiac events, MACE). Methods The study is a prospective single-center analysis of 59 patients, presented acutely in our hospital, from March 2018 to November 2023, with an angiographically detected SCAD. CMR was performed after a median of 4 days (IQR 1.5-7) from the acute onset of symptoms. SCAD Types were angiographically categorized according to the Yip-Saw classification. Most patients (71%) were screened for fibromuscular dysplasia (FMD) with a brain MR and at least one contrast-enhanced abdominal vessels investigation (CT or MR). CMR imaging was performed on a clinical 1.5 T Scanner. T1-weighted, T2-weighted turbo-spin-echo (TSE) Black-Blood (BB) and Short-Tau-Inversion-Recovery (STIR) sequences in short-axis orientation were acquired. The scan protocol included standard cine and T1/T2-weighted TSE BB and Mapping sequences. Late gadolinium enhanced (LGE) images were acquired ≏10 min after the contrast injection and were visually assessed for the presence and extension of LGE areas. LGE quantification was assessed semiautomatically. Results 40 (68%) were females. 54(92%) complained of chest pain, in 55 (93%) high-sensitive Troponin T was eleveted (>14 ng/l) and 24 (41%) presented with the clinical picture of STEMI on admission. From an angiographic point of view, the majority (69.5%) were classified as SCAD Type 2 (a+b). Among patients who underwent a proper screening, 7 patients (16%) were diagnosed with FMD. Baseline CMR showed signs of active injury in 81% and LGE in 93% of the population; however, it was often moderate in size (median of LGE segments 3, IQR 2-5). Most patients had a preserved LVEF (55±10%). STEMI presentation is an independent predictor of LGE extension (p=0.02, OddsRatio(95% CI)=7(2-24)). ScadType1 (p=0.01, OR=10( 2-39)) and N°LGE transmural segments >3 (p=0.03, OR=5.4(1.2-25)) were found to be significant predictor of MACE. 6 of the 11 MACEs were SCAD recurrence/progression, and 4 out of these 11 had already shown signs of previous myocardial injury in the baseline CMR. Conclusion(s) This study emphasized the significance of CMR, which may provide further insights into extend of myocardial damage and may aid in patients’ risk stratification.

Prognostic value of multiparametric cardiac magnetic resonance after revascularized STEMI

Abstract Despite early revascularization of STEMI through angioplasty, the prognosis following STEMI remains poor for a non-negligible percentage of patients (1). In this setting, multiple imaging parameters have demonstrated their prognostic value. The aim of the present study is to evaluate which of these parameters are the most potent predictors of events following revascularized STEMI. Methods A prospective observational study was conducted, including a cohort of revascularized STEMI patients and who underwent cardiac MRI during the first week. The protocol included cardiac functional analysis and with b-SSFP sequences for evaluation of volumes, mass, ejection fraction and also circumferential and radial strain with feature tracking. STIR sequences were used to assess edema and salvaged myocardium, IR-FGE sequences were employed for evaluation of necrosis size and microvascular obstruction. Intra-infarct hemorrhage assessment was performed using T2* mapping sequences as previosly described (2,3,4) . A semi-automatic analysis was conducted, considering as microvascular obstruction segments with hypointensity in the infarct core and as segments with hemorrhage those with a T2* less than 20 ms. The association of imaging parameters with cardiovascular events in the first year following STEMI was studied using ROC curves. Variables with significant association were analyzed using a multivariate logistic regression model. Results Ninety-four patients with a mean age of 63 (SD 13) years were included. Nine of them had cardiovascular events in the first year and two of them died. The relative extent of necrosis and microvascular obstruction, minimal radial strain, left ventricular ejection fraction (LVEF) and indexed left ventricular end- systolic volume (ILVESV) showed significant association with cardiovascular events after STEMI. Variables with significant association were entered into a multivariate predictive model, revealing that the extent of microvascular obstruction (OR: 1.9, p=0.02) and the left ventricular end-systolic volume (OR: 1.04, p<0.01) are the only independent predictors of cardiovascular events following STEMI. Conclusion Although multiple imaging parameters have shown prognostic value after STEMI, the ILVESV and the extent of microvascular obstruction are the only independent predictors of events following STEMI.Multiparametric cardiac MR in STEMIAREA UNDER ROC CURVE OF CMR PARAMETERS

Association between objectively-measured sleep duration and early cardiac and hepatic imaging changes in adolescents: insights from the EnIGMA study

Abstract Introduction Inadequate sleep duration (SD) has been associated with adverse cardiovascular (CV) events in adults and adiposity in all life stages. Furthermore, previous cross-sectional studies have shown a possible association between self-reported SD and cardiac structural alterations as detected with echocardiography and cardiovascular magnetic resonance (MR), even in young healthy people. However, there is a lack of longitudinal studies demonstrating an association between objectively-measured SD and structural cardiac alterations. Purpose To assess the association between SD and MR-derived cardiac and hepatic parameters in adolescents. Methods This study used longitudinal data collected as part of the SI! Program for Secondary Schools trial in Spain (2017-2021), which enrolled 1326 participants (mean age: 12.5±0.5 years at baseline). Measurements were taken at three different time-points: baseline, 2-year follow-up and 4-year follow-up. SD and physical activity were assessed by accelerometry for seven consecutive days at each follow-up. The participants were offered to undergo a MR scan in the final follow-up as part of the Early imaging markers of unhealthy lifestyles in adolescents (EnIGMA) study. The imaging protocol included a cine SSFP to provide images for chamber size and function, myocardial tagging acquisitions to assess myocardial strain, T1 and T2 mapping sequences to provide precise myocardial relaxation time properties, and a liver mDixonQuant sequence to obtain liver fat content, using a 3-T scanner. The cumulative effect of the independent variable (SD) and the covariates was assessed using the area under the curve (AUC) method, calculating the integral of the curve parameters during the follow-up period for each subject. To facilitate interpretation, AUC values were divided by the years of follow-up. The participants were included in the analysis if they had available data for SD in at least 2 of the 3 time-points. The association between SD and the MR parameters was assessed by linear regression models. Results 109 participants (61 girls [56.0%]; mean age=16.0±0.5 years) were included in this study. Indexed left ventricular (LV) mass, as well as indexed end-diastolic biventricular volumes were higher in boys than in girls (Figure 1). SD AUC (hours/day) was independently and inversely associated with indexed LV mass and liver fat fraction in the unadjusted and adjusted (age, gender, physical activity, body mass index percentile, and systolic and diastolic blood pressure percentiles AUCs) models (Figure 2). There were no significant associations between the SD AUC and other MR-derived parameters. Conclusion Shorter SD is independently associated with initial stages of cardiac remodeling and liver fat accumulation as assessed with state-of-the-art MR as early as in adolescence. Considering these results, health promotion programs should be implemented early in life emphasizing the importance of good sleep habits.Participant characteristicsAssociation between SD and MR

Extracellular Volume and Fibrosis Volume of Left Ventricular Myocardium Assessed by Cardiac Magnetic Resonance in Vaccinated and Unvaccinated Patients with a History of SARS-CoV-2 Infection.

Cardiac magnetic resonance (CMR) enables the assessment of tissue characteristics of the myocardium. Changes in the extracellular volume (ECV) and fibrosis volume (FV) of the myocardium are sensitive and early pathogenetic markers and have prognostic significance. The aim of the study was to assess ECV and FV of left ventricular myocardium in T1 mapping sequence in patients with a history of SARS-CoV-2 infection, considering vaccination status against COVID-19. The study group consisted of 97 patients (52.54 ± 8.31years, 53% women and 47% men). The participants were divided into three subgroups: A) patients with a history of symptomatic SARS-CoV-2 infection, unvaccinated against COVID-19 (n = 39), B) patients with a history of symptomatic SARS-CoV-2 infection, with a full vaccination schedule against COVID-19 (n = 22), and C) persons without a history of SARS-CoV-2 infection constituting the control subgroup (C, n = 36). All patients underwent 1.5T cardiac magnetic resonance. In subgroup A compared to subgroups B and C, both the ECV whole myocardium and ECV segments 2, 5-6, 8, and 10-11 were statistically significantly higher. In addition, the ECV segment 16 was statistically significantly higher in subgroup A than in subgroup C. Also, the FV whole myocardium was statistically significantly higher in subgroup A in comparison to subgroups B and C. There were no significant differences in ECV and FV between subgroups B and C. In summary, unvaccinated against COVID-19 patients with a history of symptomatic SARS-CoV-2 infection have higher myocardial ECV and FV values in the T1 mapping sequence, compared to those without COVID-19 and those suffering from COVID-19, previously vaccinated with the full vaccination schedule.

Quantitative brain T1 maps derived from T1-weighted MRI acquisitions: a proof-of-concept study.

Longitudinal T1 relaxation time is a key imaging biomarker. In addition, T1 values are modulated by the administration of T1 contrast agents used in patients with tumors and metastases. However, in clinical practice, dedicated T1 mapping sequences are often not included in brain MRI protocols. The aim of this study is to address the absence of dedicated T1 mapping sequences in imaging protocol by deriving T1 maps from standard T1-weighted sequences. A phantom, composed of 144 solutions of paramagnetic agents at different concentrations, was imaged with a three-dimensional (3D) T1-weighed turbo spin-echo (TSE) sequence designed for brain imaging. The relationship between the T1 values and the signal intensities was established using this phantom acquisition. T1 mapping derived from 3D T1-weighted TSE acquisitions in four healthy volunteers and one patient with brain metastases were established and compared to reference T1 mapping technique. The concentration of Gd-based contrast agents in brain metastases were assessed from the derived T1 maps. Based on the phantom acquisition, the relationship between T1 values and signal intensity (SI) was found equal to T1 = 0.35 × SI-1.11 (R2 = 0.97). TSE-derived T1 values measured in white matter and gray matter in healthy volunteers were equal to 0.997 ± 0.096 s and 1.358 ± 0.056 s (mean ± standard deviation), respectively. Mean Gd3+ concentration value in brain metastases was 94.7 ± 30.0 μM. The in vivo results support the relevance of the phantom-based approach: brain T1 maps can be derived from T1-weighted acquisitions. High-resolution brain T1 maps can be generated, and contrast agent concentration can be quantified and imaged in brain metastases using routine 3D T1-weighted TSE acquisitions. Quantitative T1 mapping adds significant value to MRI diagnostics. T1 measurement sequences are rarely included in routine protocols. T1 mapping and concentration of contrast agents can be derived from routine standard scans. The diagnostic value of MRI can be improved without additional scan time.

Whole-brain T2 mapping with radial sampling and retrospective motion correction at 3T.

Several barriers prevent the use of whole-brain T2 mapping in routine use despite increasing interest in this parameter. One of the main barriers is the long scan time resulting in patient discomfort and motion corrupted data. To address this challenge, a method for accurate whole-brain T2 mapping with a limited acquisition time and motion correction capabilities is investigated. A 3D radial multi-echo spin-echo sequence was implemented with optimized sampling trajectory enabling the estimation of intra-scan motion, subsequently used to correct the raw data. Motion corrected echo images are then reconstructed with linear subspace constrained reconstruction. Experiments were carried out on phantom and volunteers at 3T to evaluate the accuracy of the T2 estimation, the sensitivity to lesions and the efficiency of the correction on motion corrupted data. Whole-brain T2 mapping acquired in less than 7 min enabled the depiction of lesions in the white matter with longer T2. Data retrospectively corrupted with typical motion traces of pediatric patients highly benefited from the motion correction by reducing the error in T2 estimates within the lesions. All datasets acquired on seven volunteers, with deliberate motion, also showed that motion corrupted T2 maps could be improved with the retrospective motion correction both at the voxel level and the structure level. A whole-brain T2 mapping sequence with retrospective intra-scan motion correction and reasonable acquisition time is proposed. The method necessitates advanced iterative reconstruction strategies but no additional navigator, external device, or increased scan time is required.

Early detection of myocardial iron overload in patients with β-thalassemia major using cardiac magnetic resonance T1 mapping

BackgroundThe T2* technique, used for quantifying myocardial iron content (MIC), has limitations in detecting early myocardial iron overload (MIO). The in vivo mapping of the myocardial T1 relaxation time is a promising alternative for the early detection and management of MIO. Methods32 β-thalassemia major (βTM) patients aged 11.5 ± 4 years and 32 healthy controls were recruited and underwent thorough clinical and laboratory assessments. The mid-level septal iron overload was measured through T1 mapping using a modified Look-Locker inversion recovery sequence with a 3 (3 s) 3 (3 s) 5 scheme. Septum was divided at the mentioned level into 3 zones corresponding to segments 8 and 9 in the cardiac segmentation model. Results21.9 % of βTM had clinical cardiac morbidity. The cut-off of T1 mapping of hepatic and myocardium to differentiate between the patients and control groups was ≤466 and ≥ 923 ms respectively. The T1 technique was able to detect 4 patients with high MIC, two of them were not detected by the T2* technique. There was a statistically significant correlation between the average T1 values of the studied zones in patients with βTM and the liver iron content (LIC), the T1 values within segment 8 of the liver, age of patients, the age at first transfusion, age of splenectomy and serum ferritin value. ConclusionThe addition of the T1 mapping sequence to the conventional T2* technique was able to increase the efficacy of the MIC detection protocol by earlier detection of MIO. This would guide chelation therapy to decrease myocardial morbidity.

A General Fixed Point Theorem for a Sequence of Multivalued Mappings in S-Metric Spaces

A General Fixed Point Theorem for a Sequence of Multivalued Mappings in S-Metric Spaces

A threefold chaotic image encryption technique for efficacious image data protection

With the profound use of digital contents in education and social media, multimedia content have become a prevalent means of communication and with such rapid increase, information security is still a major concern. This paper provides a summary of the techniques of securing image data focusing primarily on encryption. This paper additionally also explores the contribution of chaos theory in the domain of image encryption and applies a threefold chaotic map sequence to design an image encryption technique. This chaos-based encryption technique renders characteristics like sensitivity, determinacy, and ergodicity, and hence provides a better trade-off between security and computational speed. The efficacy of proposed algorithm is also evaluated based on well-known statistical metrics like Number of Changing Pixel Rate (NPCR), Unified Average Changing Intensity (UACI), Information Entropy, local Entropy, Correlation analysis, key sensitivity analysis, and NIST Randomness test. Furthermore, the key sensitivity analysis is also discussed which is a major part of any encryption algorithm analysis.

Changes in inflammatory edema and fat fraction of thigh muscles following a half-marathon in recreational marathon runners.

It is known that microtrauma exists in the thigh muscles after long-distance running such as the half-marathon. Moreover, training characteristics of long-distance runners may influence the specificity of the distribution of muscle fiber types in the thigh and affect muscle responses to lipid metabolism. However, the specific changes in microtrauma and intramuscular lipid in thigh muscles after a half-marathon are unknown. A cohort of 20 healthy recreational marathon runners was recruited to complete a half-marathon. MRI T2 mapping and 6-echo q-Dixon sequences were employed at baseline (P1), 2-3h after running (P2), and 1day after running (P3). Inflammatory markers (the T2 values) and intramuscular fat fraction (the proton density fat fraction, PDFF) were measured in thigh muscles to detect microtrauma and intramuscular lipid changes, respectively. One-way analysis of variance showed significant time effects for T2 values and PDFF. Post hoc analysis of the 14 datasets collected at three time points revealed significantly higher T2 values in all thigh muscles after running (all p<0.05). Significant differences in T2 values persisted for all thigh muscles at P3 compared to P1 (all p<0.05). The PDFF of the vastus lateralis and vastus medialis was significantly decreased at P2 compared to P1 (p<0.05). No significant differences in PDFF were observed for the thigh muscles at P3 compared to P1. The manifestations of inflammation edema and intramuscular lipid investigated through MRI may offer valuable insights for recreational marathon runners regarding the lower limb movement characteristics during half-marathon running.

Evaluation of Myocarditis with a Free-breathing 3D Isotropic Whole-Heart Joint T1 and T2 Mapping Sequence

BackgroundThe diagnosis of myocarditis by CMR requires the use of T2 and T1 weighted imaging, ideally incorporating parametric mapping. Current 2D mapping sequences are acquired sequentially and involve multiple breath-holds resulting in prolonged scan times and anisotropic image resolution. We developed an isotropic free-breathing 3D whole-heart sequence which allows simultaneous T1 and T2 mapping and validated it in patients with suspected acute myocarditis. MethodsEighteen healthy volunteers and 28 patients with suspected myocarditis underwent conventional 2D T1 and T2 mapping with whole heart coverage and 3D joint T1/T2 mapping on a 1.5T scanner. Acquisition time, image quality, and diagnostic performance were compared. Qualitative analysis was performed using a 4-point Likert scale. Bland-Altman plots were used to assess the quantitative agreement between 2D and 3D sequences. ResultsThe 3D T1/T2 sequence was acquired in 8mins 26s under free breathing, whereas 2D T1 and T2 sequences were acquired with breath holds in 11mins 44s (p=0.0001). All 2D images were diagnostic. For 3D images, 89% of T1 and 96% of T2 images were diagnostic with no significant difference in the proportion of diagnostic images for the 3D and 2D T1 (p=0.2482) and T2 maps (p=1.0000). Systematic bias in T1 was noted with biases of 102ms, 115ms, and 152ms for basal-apical segments, with a larger bias for higher T1 values. Good agreement between T2 values for 3D and 2D techniques was found (bias of 1.8ms, 3.9ms, and 3.6ms for basal-apical segments). The sensitivity and specificity of the 3D sequence for diagnosing acute myocarditis was 74% (95% confidence interval [CI] 49-91%) and 83% (36-100%) respectively, with an estimated c-statistic (95% CI) of 0.85 (0.79-0.91) and no statistically significant difference between the 2D and 3D sequences for the detection of acute myocarditis for T1 (p=0.2207) or T2 (p=1.0000). ConclusionFree-breathing whole heart 3D joint T1/T2 mapping was comparable to 2D mapping sequences with respect to diagnostic performance, but with the added advantages of free-breathing, and shorter scan times. Further work is required to address the bias noted at high T1 values, but this did not significantly impact on diagnostic accuracy.

Patterns of cerebral damage in multiple sclerosis and aquaporin-4 antibody-positive neuromyelitis optica spectrum disorders-major differences revealed by non-conventional imaging.

Multiple sclerosis and aquaporin-4 antibody neuromyelitis optica spectrum disorders are distinct autoimmune CNS disorders with overlapping clinical features but differing pathology. Multiple sclerosis is primarily a demyelinating disease with the presence of widespread axonal damage, while neuromyelitis optica spectrum disorders is characterized by astrocyte injury with secondary demyelination. Diagnosis is typically based on lesion characteristics observed on standard MRI imaging and antibody testing but can be challenging in patients with in-between clinical presentations. Non-conventional MRI techniques can provide valuable diagnostic information by measuring disease processes at the microstructural level. We used non-conventional MRI to measure markers of axonal loss in specific white matter tracts in multiple sclerosis and neuromyelitis optica spectrum disorders, depending on their relationship with focal lesions. Patients with relapsing-remitting multiple sclerosis (n = 20), aquaporin-4 antibody-associated neuromyelitis optica spectrum disorders (n = 20) and healthy controls (n = 20) underwent a 3T brain MRI, including T1-, T2- and diffusion-weighted sequences, quantitative susceptibility mapping and phase-sensitive inversion recovery sequence. Tractometry was used to differentiate tract fibres traversing through white matter lesions from those that did not. Neurite density index was assessed using neurite orientation dispersion and density imaging model. Cortical damage was evaluated using T1 relaxation rates. Cortical lesions and paramagnetic rim lesions were identified using phase-sensitive inversion recovery and quantitative susceptibility mapping. In tracts traversing lesions, only one out of 50 tracts showed a decreased neurite density index in multiple sclerosis compared with neuromyelitis optica spectrum disorders. Among 50 tracts not traversing lesions, six showed reduced neurite density in multiple sclerosis (including three in the cerebellum and brainstem) compared to neuromyelitis optica spectrum disorders. In multiple sclerosis, reduced neurite density was found in the majority of fibres traversing (40/50) and not traversing (37/50) white matter lesions when compared to healthy controls. A negative correlation between neurite density in lesion-free fibres and cortical lesions, but not paramagnetic rim lesions, was observed in multiple sclerosis (39/50 tracts). In neuromyelitis optica spectrum disorders compared to healthy controls, decreased neurite density was observed in a subset of fibres traversing white matter lesions, but not in lesion-free fibres. In conclusion, we identified significant differences between multiple sclerosis and neuromyelitis optica spectrum disorders corresponding to their distinct pathologies. Specifically, in multiple sclerosis, neurite density reduction was widespread across fibres, regardless of their relationship to white matter lesions, while in neuromyelitis optica spectrum disorders, this reduction was limited to fibres passing through white matter lesions. Further studies are needed to evaluate the discriminatory potential of neurite density measures in white matter tracts for differentiating multiple sclerosis from neuromyelitis optica spectrum disorders.

Simultaneous Multiparameter Mapping of the Liver in a Single Breath-Hold or Respiratory-Triggered Acquisition Using Multi-Inversion Spin and Gradient Echo MRI.

Quantitative parametric mapping is an increasingly important tool for noninvasive assessment of chronic liver disease. Conventional parametric mapping techniques require multiple breath-held acquisitions and provide limited anatomic coverage. To investigate a multi-inversion spin and gradient echo (MI-SAGE) technique for simultaneous estimation of T1, T2, and T2* of the liver. Prospective. Sixteen research participants, both adult and pediatric (age 17.5 ± 4.6 years, eight male), with and without known liver disease (seven asymptomatic healthy controls, two fibrotic liver disease, five steatotic liver disease, and two fibrotic and steatotic liver disease). 1.5 T, single breath-hold and respiratory triggered MI-SAGE, breath-hold modified Look-Locker inversion recovery (MOLLI, T1 mapping), breath-hold gradient and spin echo (GRASE, T2 mapping), and multiple gradient echo (mGRE, T2* mapping) sequences. Agreement between hepatic T1, T2, and T2* estimated using MI-SAGE and conventional parametric mapping sequences was evaluated. Repeatability and reproducibility of MI-SAGE were evaluated using a same-session acquisition and second-session acquisition. Bland-Altman analysis with bias assessment and limits of agreement (LOA) and intraclass correlation coefficients (ICC). Hepatic T1, T2, and T2* estimates obtained using the MI-SAGE technique had mean biases of 72 (LOA: -22 to 166) msec, -3 (LOA: -10 to 5) msec, and 2 (LOA: -5 to 8) msec (single breath-hold) and 36 (LOA: -43 to 120) msec, -3 (LOA: -17 to 11) msec, and 4 (LOA: -3 to 11) msec (respiratory triggered), respectively, in comparison to conventional acquisitions using MOLLI, GRASE, and mGRE. All MI-SAGE estimates had strong repeatability and reproducibility (ICC > 0.72). Hepatic T1, T2, and T2* estimates obtained using an MI-SAGE technique were comparable to conventional methods, although there was a 12%/6% for breath-hold/respiratory triggered underestimation of T1 values compared to MOLLI. Both respiratory triggered and breath-hold MI-SAGE parameter maps demonstrated strong repeatability and reproducibility. 1 TECHNICAL EFFICACY: Stage 2.

Feasibility of 3D MRI fingerprinting for rapid knee cartilage T1, T2, and T1ρ mapping at 0.55T: Comparison with 3T.

Low-field strength scanners present an opportunity for more inclusive imaging exams and bring several challenges including lower signal-to-noise ratio (SNR) and longer scan times. Magnetic resonance fingerprinting (MRF) is a rapid quantitative multiparametric method that can enable multiple quantitative maps simultaneously. To demonstrate the feasibility of an MRF sequence for knee cartilage evaluation in a 0.55T system we performed repeatability and accuracy experiments with agar-gel phantoms. Additionally, five healthy volunteers (age 32 ±4years old, 2 females) were scanned at 3T and 0.55T. The MRI acquisition protocols include a stack-of-stars T1ρ-enabled MRF sequence, a VIBE sequence with variable flip angles (VFA) for T1 mapping, and fat-suppressed turbo flash (TFL) sequences for T2 and T1ρ mappings. Double-Echo steady-state (DESS) sequence was also used for cartilage segmentation. Acquisitions were performed at two different field strengths, 0.55T and 3T, with the same sequences but protocols were slightly different to accommodate differences in signal-to-noise ratio and relaxation times. Cartilage segmentation was done using five compartments. T1, T2, and T1ρ values were measured in the knee cartilage using both MRF and conventional relaxometry sequences. The MRF sequence demonstrated excellent repeatability in a test-retest experiment with model agar-gel phantoms, as demonstrated with correlation and Bland-Altman plots. Underestimation of T1 values was observed on both field strengths, with the average global difference between reference values and the MRF being 151 ms at 0.55T and 337 ms at 3T. At 0.55T, MRF measurements presented significant biases but strong correlations with the reference measurements. Although a larger error was present in T1 measurements, MRF measurements trended similarly to the conventional measurements for human subjects and model agar-gel phantoms.

Oxygen extraction fraction change in M1-M6 brain regions of patients with unilateral or bilateral middle cerebral artery occlusion.

Cerebral blood flow (CBF) and oxygen extraction fraction (OEF) can be measured using arterial spin labeling (ASL) and quantitative susceptibility mapping (QSM) sequences, respectively. ASL and QSM sequences were performed on 13 healthy participants and 46 patients with unilateral or bilateral Middle cerebral artery (MCA) occlusion. M1-M3 and M4-M6 correspond to anterior, lateral, and posterior MCA territories within the insular ribbon and centrum semiovale, respectively. In patients with unilateral MCA occlusion, significant decreases in CBF were observed in the lesions in M1, M3, M5 and M6 regions, as well as in the contralateral M3 and M5 regions. The OEF of the lesion in the M1-M4 and M6 regions, and the contralateral M1-M3 regions were significantly higher. Additionally, the cerebral metabolic rate of oxygen (CMRO2) in the lesions of the M3 and M6 regions, and the contralateral M3 region, were significantly lower compared to the corresponding regions of healthy participants. For patients with bilateral MCA occlusion, the CMRO2 in the left M5 region and the right M3 and M6 regions were significantly lower than that in the corresponding regions of healthy participants. In conclusion, abnormal hemodynamics occur in the contralateral hemisphere of patients with unilateral MCA occlusion.

Fast cardiac T1ρ,adiab mapping using slice-selective adiabatic spin-lock preparation pulses.

Myocardial T1ρ mapping techniques commonly acquire multiple images in one breathhold to calculate a single-slice T1ρ map. Recently, non-selective adiabatic pulses have been used for robust spin-lock preparation (T1ρ,adiab). The objective of this study was to develop a fast multi-slice myocardial T1ρ,adiab mapping approach. The proposed-sequence reduces the number of breathholds required for whole-heart 2D T1ρ,adiab mapping by acquiring multiple interleaved slices in each breathhold using slice-selective T1ρ,adiab preparation pulses. The proposed-sequence was implemented with two interleaved slices per breathhold scan and was quantitatively evaluated in phantom experiments and 10 healthy-volunteers against a single-slice T1ρ,adiab mapping sequence. The sequence was demonstrated in two patients with myocardial scar. The phantom experiments showed the proposed-sequence had slice-to-slice variation of 1.62% ± 1.05% and precision of 4.51 ± 0.68 ms. The healthy volunteer cohort subject-wise mean relaxation time was lower for the proposed-sequence than the single-slice sequence (137.7 ± 5.3 ms vs. 148.4 ± 8.3 ms, p < 0.001), and spatial-standard-deviation was better (18.7 ± 1.8 ms vs. 21.8 ± 3.4 ms, p < 0.018). The mean within-subject, coefficient of variation was 5.93% ± 1.57% for the proposed-sequence and 6.31% ± 1.92% for the single-slice sequence (p = 0.35) and the effect of slice variation (0.81 ± 4.87 ms) was not significantly different to zero (p = 0.61). In both patient examples increased T1ρ,adiab (maximum American Heart Association-segment mean = 174 and 197 ms) was measured within the myocardial scar. The proposed sequence provides a twofold acceleration for myocardial T1ρ,adiab mapping using a multi-slice approach. It has no significant difference in within-subject variability, and significantly better precision, compared to a 2D T1ρ,adiab mapping sequence based on non-selective adiabatic spin-lock preparations.

The Generic Failure of Lower-Semicontinuity for the Linear Distortion Functional

AbstractWe consider the convexity properties of distortion functionals, particularly the linear distortion, defined for homeomorphisms of domains in Euclidean n-spaces, $$n\ge 3$$ n ≥ 3 . The inner and outer distortion functionals are lower semi-continuous in all dimensions and so for the curve modulus or analytic definitions of quasiconformality it ifollows that if $$ \{ f_{n} \}_{n=1}^{\infty } $$ { f n } n = 1 ∞ is a sequence of K-quasiconformal mappings (here K depends on the particular distortion functional but is the same for every element of the sequence) which converges locally uniformly to a mapping f, then this limit function is also K-quasiconformal. Despite a widespread belief that this was also true for the geometric definition of quasiconformality (defined through the linear distortion $$H({f_{n}})$$ H ( f n ) ), T. Iwaniec gave a specific and surprising example to show that the linear distortion functional is not always lower-semicontinuous on uniformly converging sequences of quasiconformal mappings. Here we show that this failure of lower-semicontinuity is common, perhaps generic in the sense that under mild restrictions on a quasiconformal f, there is a sequence $$ \{f_{n} \}_{n=1}^{\infty } $$ { f n } n = 1 ∞ with $$ {f_{n}}\rightarrow {f}$$ f n → f locally uniformly and with $$\limsup _{n\rightarrow \infty } H( {f_{n}})&lt;H( {f})$$ lim sup n → ∞ H ( f n ) &lt; H ( f ) . Our main result shows this is true for affine mappings. Addressing conjectures of Gehring and Iwaniec we show the jump up in the limit can be arbitrarily large and give conjecturally sharp bounds: for each $$\alpha &lt;\sqrt{2}$$ α &lt; 2 there is $${f_{n}}\rightarrow {f}$$ f n → f locally uniformly with f affine and $$\begin{aligned} \alpha \; \limsup _{n\rightarrow \infty } H( {f_{n}}) &lt; H( {f}) \end{aligned}$$ α lim sup n → ∞ H ( f n ) &lt; H ( f ) We conjecture $$\sqrt{2}$$ 2 to be best possible.