Ultrafast Sequences Research Articles

Single-subject Single-session Temporally-Independent Functional Modes of Brain Activity

Temporally independent functional modes (TFMs) are functional brain networks identified based on their temporal independence. The rationale behind identifying TFMs is that different functional networks may share a common anatomical infrastructure yet display distinct temporal dynamics. Extracting TFMs usually require a larger number of samples than acquired in standard fMRI experiments, and thus have therefore previously only been performed at the group level. Here, using an ultra-fast fMRI sequence, MESH-EPI, with a volume repetition time of 158 ​ms, we conducted an exploratory study with n ​= ​6 subjects and computed TFMs at the single subject level on both task and resting-state datasets. We identified 6 common temporal modes of activity in our participants, including a temporal default mode showing patterns of anti-correlation between the default mode and the task-positive networks, a lateralised motor mode and a visual mode integrating the visual cortex and the visual streams. In alignment with other findings reported recently, we also showed that independent time-series are largely free from confound contamination. In particular for ultra-fast fMRI, TFMs can separate the cardiac signal from other fluctuations. Using a non-linear dimensionality reduction technique, UMAP, we obtained preliminary evidence that combinations of spatial networks as described by the TFM model are highly individual. Our results show that it is feasible to measure reproducible TFMs at the single-subject level, opening new possibilities for investigating functional networks and their integration. Finally, we provide a python toolbox for generating TFMs and comment on possible applications of the technique and avenues for further investigation.

Dynamic channel selection in wireless communications via a multi-armed bandit algorithm using laser chaos time series

Dynamic channel selection is among the most important wireless communication elements in dynamically changing electromagnetic environments wherein, a user can experience improved communication quality by choosing a better channel. Multi-armed bandit (MAB) algorithms are a promising approach that resolve the trade-off between channel exploration and exploitation of enhanced communication quality. Ultrafast solution of MAB problems has been demonstrated by utilizing chaotically oscillating time series generated by semiconductor lasers. In this study, we experimentally demonstrate a MAB algorithm incorporating laser chaos time series in a wireless local area network (WLAN). Autonomous and adaptive dynamic channel selection is successfully demonstrated in an IEEE802.11a-based, four-channel WLAN. Although the laser chaos time series is arranged prior to the WLAN experiments, the results confirm the usefulness of ultrafast chaotic sequences for real wireless applications. In addition, we numerically examine the underlying adaptation mechanism of the significantly simplified MAB algorithm implemented in the present study compared with the previously reported chaos-based decision makers. This study provides a first step toward the application of ultrafast chaotic lasers for future high-performance wireless communication networks.

Combination of an ultrafast TWIST-VIBE Dixon sequence protocol and diffusion-weighted imaging into an accurate easily applicable classification tool for masses in breast MRI.

This study aimed to develop a tool for the classification of masses in breast MRI, based on ultrafast TWIST-VIBE Dixon (TVD) dynamic sequences combined with DWI. TVD sequences allow to abbreviate breast MRI protocols, but provide kinetic information only on the contrast wash-in, and because of the lack of the wash-out kinetics, their diagnostic value might be hampered. A special focus of this study was thus to maintain high diagnostic accuracy in lesion classification. Sixty-one patients who received breast MRI between 02/2014 and 04/2015 were included, with 83 reported lesions (60 malignant). Our institute's standard breast MRI protocol was complemented by an ultrafast TVD sequence. ADC and peak enhancement of the TVD sequences were integrated into a generalised linear model (GLM) for malignancy prediction. For comparison, a second GLM was calculated using ADC and conventional DCE curve type. The resulting GLMs were evaluated for standard diagnostic parameters. For easy application of the GLMs, nomograms were created. The GLM based on peak enhancement of the TVD and ADC was as equally accurate as the GLM based on conventional DCE and ADC, with no significant differences (sensitivity, 93.3%/93.3%; specificity, 91.3%/87.0%; PPV, 96.6%/94.9%; NPV, 84.0%/83.3%; all, p ≥ 0.315). This study presents a method to integrate ultrafast TVD sequences into a breast MRI protocol, allowing a reduction of the examination time while maintaining diagnostic accuracy. A GLM based on the combination of TVD-derived peak enhancement and ADC provides high diagnostic accuracy, and can be easily applied using a nomogram. • Ultrafast TWIST-VIBE Dixon sequence protocols in combination with diffusion-weighted imaging allow to shorten breast MRI examinations, while diagnostic accuracy is maintained. • Integrating peak enhancement from the TWIST-VIBE Dixon sequence and the apparent diffusion coefficient into a generalised linear model provides a comprehensible image evaluation approach. • This approach is further facilitated by nomograms.

Silent T1 mapping using the variable flip angle method with B1 correction.

To compare the silent rotating ultrafast imaging sequence (RUFIS) to a traditional Cartesian spoiled gradient-echo (SPGR) acquisition scheme for variable flip angle (VFA) mapping. A two-point VFA measurement was performed using RUFIS and Cartesian SPGR in a quantitative phantom and healthy volunteers. To correct for errors, a novel silent magnetization prepared map acquisition (SIMBA) was developed, which combined with RUFIS VFA allows for a completely silent mapping protocol. The silent protocol was found to have comparable repeatability but higher reproducibility in vivo compared to the standard SPGR protocol, and showed no increase in acoustic noise levels above background noise levels compared to a 33 dBA increase for the SPGR acquisition. VFA mapping using RUFIS is a feasible alternative to SPGR, achieving silent mapping with comparable acquisition time.

Fetal Magnetic Resonance Imaging of Choledochal Cyst

ABSTRACTCholedochal cysts (CCs) are rare congenital anomaly with characterized dilatation of intra- or extrahepatic biliary duct or both. Prenatal diagnosis is increasing due to high resolution of ultrasound (US) and ultrafast sequences of magnetic resonance imaging (MRI) showing better delineation of the cyst to the adjacent structure. Considering the additional value of the fetal MRI report is still infrequent to confirm the CC case, we therefore report the type I of CC, which was previously diagnosed as a cystic biliary atresia (CBA) from US result. Postnatal MRI and histopathology prove it.How to cite this article:Wirasasmita DA, Abdurrazak G, Yani A. Fetal Magnetic Resonance Imaging of Choledochal Cyst. Int J Infertil Fetal Med 2020;11(1):27–29.

Breast MRI: Is Faster Better?

OBJECTIVE. Fast breast MRI protocols have the same sensitivity as conventional protocols, but their specificity is variable and can be inadequate. An ultrafast sequence provides early enhancement of lesion characteristics that optimize the characterization of the fast protocol, increasing positive predictive values without increasing time. CONCLUSION. These new abbreviated protocols could constitute a viable screening tool both for women at high risk of breast cancer and for those at intermediate risk with high breast density.

Near-silent distortionless DWI using magnetization-prepared RUFIS.

To develop a near-silent and distortionless DWI (sd-DWI) sequence using magnetization-prepared rotating ultrafast imaging sequence. A rotating ultrafast imaging sequence was modified with driven-equilibrium diffusion preparation, including eddy-current compensation methods. To compensate for the T1 recovery during readout, a phase-cycling method was used. Both compensation methods were validated in phantoms. The optimized sequence was compared with an EPI diffusion sequence for image distortion, contrast, ADC, and acoustic noise level in phantoms. The sequence was evaluated in 1 brain volunteer, 5 prostate volunteers, and 10 pediatric patients with joint diseases. Combination of several eddy-current compensation methods reduced the artifact to an acceptable level. Phase cycling reduced T1 recovery contamination during readout. In phantom scans, the optimized sequence generated similar image contrast to the EPI diffusion sequence, and ADC maps between the sequences were comparable; sd-DWI had significantly lower acoustic noise (P < .05). In vivo brain scan showed reduced image distortion in sd-DWI compared with the EPI diffusion, although residual motion artifact remains due to brain pulsation. The prostate scans showed that sd-DWI can provide similar ADC compared with EPI diffusion, with no image distortion. Patient scans showed that the sequence can clearly depict joint lesions. An sd-DWI sequence was developed and optimized. Compared with conventional EPI diffusion, sd-DWI provided similar diffusion contrast, accurate ADC measurement, improved image quality, and minimal ambient scanning noise. The sequence showed the ability to obtain in vivo diffusion contrast in relatively motion-free body regions, such as prostate and joint.

Detection of Crohn's disease with diffusion images versus contrast-enhanced images in pediatric using MR enterography with histopathological correlation.

The purpose of this study was to determine whether MRE performed with diffusion-weighted imaging (DWI) sequences is comparable to contrast-enhanced MRE in the detection of active small-bowel inflammation in pediatric patients with Crohn's disease (CD). We included in our study 68 patients with diagnosis of CD between April 2015 and June 2018 that underwent MRE examination. Examination protocol includes coronal and axial FISP, T2-w half-Fourier RARE and DWI sequences, a baseline coronal T1-w fat-saturated ultrafast (GRE) sequence followed by contrast 3D T1-w GRE. All images were assessed by two radiologists who graded each of bowel segments for the presence of inflammation on a four-point confidence scale on the basis of wall thickening and wall signal on DWI and ADC maps and comparing their results with post-contrast images. When considering all bowel segments, we found 41 true positive and 25 true negative on DWI. One false positive case corresponded to the absence of inflammatory histopathology changes at the level of the terminal ileum in a 15-year-old male, and one false negative case was in a 10-year-old female with only jejunal lesion. The corresponding sensitivity, specificity, PPV, NPV and accuracy were 97.6% (95% CI 67.7-99.7), 96.1% (95% CI 66.7-98.5), 97.6% (95% CI 70.8-98.4), 96.1% (95% CI 64.2-90.6) and 97% (95% CI 84.2-97.5), respectively. Analyzing the gadolinium-enhanced set, 35 true positive and 25 true negative results were found. One false positive case was found, and it was the same as with DWI. The corresponding sensitivity, specificity, PPV, NPV and accuracy were 83.3% (95% CI 65.9-86.7), 96.1% (95% CI 68.7-88.9), 97.2% (95% CI 84.3-98.7), 78.1% (95% CI 27.9-72.1) and 88.2% (95% CI 41.2-85.6), respectively. Sensitivity for the detection of active IBD lesion was significantly better with DWI than with CE-T1-w imaging (p = 0.002), whereas the specificity was similar (p = 0.743). Our study has shown that DWI sequences have a high accuracy in detecting the bowel segment affected by CD. These results emphasize the utility to include the DWI/ADC in standard MR enterography protocols and suggest that DWI could replace T1-weighted post-contrast sequences.

Nonuniform Fourier-decomposition MRI for ventilation- and perfusion-weighted imaging of the lung.

PurposeTo improve the robustness of pulmonary ventilation‐ and perfusion‐weighted imaging with Fourier decomposition (FD) MRI in the presence of respiratory and cardiac frequency variations by replacing the standard fast Fourier transform with the more general nonuniform Fourier transform.Theory and MethodsDynamic coronal single‐slice MRI of the thorax was performed in 11 patients and 5 healthy volunteers on a 1.5T whole‐body scanner using a 2D ultra‐fast balanced steady‐state free‐precession sequence with temporal resolutions of 4‐9 images/s. For the proposed nonuniform Fourier‐decomposition (NUFD) approach, the original signal with variable physiological frequencies that was acquired with constant sampling rate was retrospectively transformed into a signal with (ventilation or perfusion) frequency‐adapted sampling rate. For that purpose, frequency tracking was performed with the synchro‐squeezed wavelet transform. Ventilation‐ and perfusion‐weighted NUFD amplitude and signal delay maps were generated and quantitatively compared with regularly sampled FD maps based on their signal‐to‐noise ratio (SNR).ResultsVolunteers and patients showed statistically significant increases of SNR in frequency‐adapted NUFD results compared to regularly sampled FD results. For ventilation data, the mean SNR increased by 43.4%±25.3% and 24.4%±31.9% in volunteers and patients, respectively; for perfusion data, SNR increased by 93.0%±36.1% and 75.6%±62.8%. Two patients showed perfusion signal in pulmonary areas with NUFD that could not be imaged with FD.ConclusionThis study demonstrates that using nonuniform Fourier transform in combination with frequency tracking can significantly increase SNR and reduce frequency overlaps by collecting the signal intensity onto single frequency bins.

Evaluation of Skull Base Tumors with Dynamic TurboFLASH MRI during Gadolinium Injection.

Background and Purpose This study was aimed to investigate the role of dynamic TurboFLASH gadolinium (Gd) magnetic resonance (MR) imaging in improving the differential diagnosis of skull base tumors. Methods Eleven patients with skull base tumors underwent standard MR and ultrafast TurboFLASH sequence during gadolinium injection. Results The characterization of tumor vascularity was performed. Different patterns of gadolinium uptake for each tumor type were observed. This is particularly important to identify tumors at high risk of intraoperative bleeding. All glomus tumors, typically highly vascularized, showed an enhancement at the arterial phase, reflecting the arterialization of these tumors which is not detectable on conventional MR. No signal increase at the arterial phase was instead observed in other cases in which the ruling out of a glomus tumor was important because of the location of the lesion. Moreover TurboFLASH identified the pathognomonic "filling-in" profile of cavernous sinus cavernous hemangiomas (CSCH), that is, the progressive centripetal enhancement of the lesion at the beginning of the venous phase. Conclusion The dynamic analysis of tumor contrast enhancement with the TurboFLASH sequence provides useful additional information to that obtained with conventional MR, improving the differential diagnosis of skull base tumors, particularly in the distinction between glomus and nonglomus tumors and in diagnosing CSCH.

Ultrafast Sequence in Fetal Magnetic Resonance Imaging for Evaluation Chiari III Malformation

Ultrafast Sequence in Fetal Magnetic Resonance Imaging for Evaluation Chiari III Malformation

Pathogen Species Identification from Metagenomes in Ancient Remains: The Challenge of Identifying Human Pathogenic Species of Trypanosomatidae via Bioinformatic Tools.

Accurate species identification from ancient DNA samples is a difficult task that would shed light on the evolutionary history of pathogenic microorganisms. The field of palaeomicrobiology has undoubtedly benefited from the advent of untargeted metagenomic approaches that use next-generation sequencing methodologies. Nevertheless, assigning ancient DNA at the species level is a challenging process. Recently, the gut microbiome analysis of three pre-Columbian Andean mummies (Santiago-Rodriguez et al., 2016) has called into question the identification of Leishmania in South America. The accurate assignment would be important because it will provide some key elements that are linked to the evolutionary scenario for visceral leishmaniasis agents in South America. Here, we recovered the metagenomic data filed in the metagenomics RAST server (MG-RAST) to identify the different members of the Trypanosomatidae family that have infected these ancient remains. For this purpose, we used the ultrafast metagenomic sequence classifier, based on an exact alignment of k-mers (Kraken) and Bowtie2, an ultrafast and memory-efficient tool for aligning sequencing reads to long reference sequences. The analyses, which have been conducted on the most exhaustive genomic database possible on Trypanosomatidae, show that species assignments could be biased by a lack of some genomic sequences of Trypanosomatidae species (strains). Nevertheless, our work raises the issue of possible co-infections by multiple members of the Trypanosomatidae family in these three pre-Columbian mummies. In the three mummies, we show the presence of DNA that is reminiscent of a probable co-infection with Leptomonas seymouri, a parasite of insect’s gut, and Lotmaria.

Looping Star.

To introduce a novel MR pulse sequence, termed Looping Star, for fast, robust, and yet quiet, 3D radial multi-gradient echo T2* MR imaging. The Looping Star pulse sequence is based on the 3D radial Rotating Ultra-Fast Imaging Sequence (RUFIS) extended by a time-multiplexed gradient-refocusing mechanism. First, multiple magnetic coherences are excited, which are subsequently gradient-refocused in form of a looping k-space trajectory. Accordingly, Looping Star captures an initial FID image followed by gradient echo images at equidistant echo times. Looping Star was demonstrated in phantom and in vivo volunteer experiments for 3D, high resolution T2* weighted imaging, T2* mapping, and quantitative susceptibility mapping (QSM). The method is fast, quiet, and robust against imperfections including Eddy currents, motion, and geometric distortions. When applied to a motor task fMRI experiment a BOLD sensitivity of 5% was achieved at minimal acoustic noise (i.e. 2.7dB(A) above ambient noise) and with images congruent to other anatomical scans. Looping Star imaging provides new and exciting opportunities for fast, robust and yet quiet T2* MR imaging. Potential applications include T2*-weighted imaging, T2* mapping, QSM, and fMRI.

Functional magnetic resonance imaging for clinical evaluation of uterine contractility.

ABSTRACTUterine contractility out of the gestational phase, during the menstrual cycle and the habitual functional variations of the organ, this is one of the responsible mechanisms for reproduction and fertility, due to its direct action in the mechanisms conducting the spermatozoa to the ovule and in the decidual implantation. Pathologies such as uterine leiomyoma, endometriosis, adenomyosis, polycystic ovarian syndrome, as well as the use of intrauterine devices and oral contraceptives, may alter a functionality of uterine contractility. Thus, magnetic resonance imaging with ultrafast sequences provides a dynamic evaluation (cine-MRI) and thus the correlation of uterine contractility quality in patients with current infertility or pathologies.

Ultrafast fMRI sequences for studying the cognitive brain architectures

The purpose of this work was to test the ultrafast fMRI sequences for the study of the sensorimotor and cognitive functions of the human brain. In a series of test tasks for performing motor movements, the obtained fMRI data showed similar results of brain activity for the block paradigm with standard sequences (TR = 2000 ms) and ultrafast (TR = 300 ms) and event-related paradigm with the use of ultra-fast sequences. In the emotional task, fMRI data was performed in three scan modes: TR=2000 ms, TR=1000 ms, TR=700 ms. The obtained data show the promise of using in cognitive studies of ultrafast sequences, which opens up fundamentally new opportunities for fully non-invasive visualization of networks in the brain.

Utility of Various Ultrafast Magnetic Resonance Sequences in the Detection of Fetal Intracranial Hemorrhage.

Objective:The aim of this study is to compare the images obtained from standard ultrafast magnetic resonance (MR) imaging sequences with gradient (GRE) sequence images in identifying fetal intracranial hemorrhage (ICH).Materials and Methods:MR images of fetal brains with ICH done between October 2012 and September 2015 were reviewed. The images obtained from four ultrafast MR sequences– Turbo Fast Low Angle Shot (Turbo FLASH) T1-weighted images, Half Fourier Acquisition single-shot turbo spin echo (HASTE) T2-weighted images, b0 images of diffusion-weighted imaging (DWI) and b800 images of DWI were compared with images obtained from GRE sequence in depicting fetal ICH.Results:Out of the 212 fetuses during the study period, 15 fetuses had ICH. In the 15 fetuses with ICH as detected on GRE, Grade1 germinal matrix hemorrhage was seen in 5 fetuses, Grade 2 in 4 fetuses, Grade 3 in 3 fetuses, and Grade 4 in two fetuses. Subdural hemorrhage was seen in 1 fetus. In comparison to GRE sequence, b0 of DWI sequence was almost equal in the depiction of ICH. T2 HASTE sequence also delineated hemorrhage, although not as effectively as GRE and b0 images of images DWI. T1 Turbo FLASH and b800 images of DWI were less reliable in the depiction of fetal ICH but were useful in predicting the stage of hemorrhage.Conclusion:As compared to GRE sequence, b0 images of DWI followed by HASTE are the two preferred ultrafast sequences in the diagnosis of fetal ICH.

Evaluation of the fetal abdomen by magnetic resonance imaging. Part 1: malformations of the abdominal cavity.

Although ultrasound continues to be the mainstay modality for the evaluation of fetal disorders, fetal magnetic resonance imaging (MRI) has often been used as a valuable adjunct in recent years. The exponential growth of the use of fetal MRI has been facilitated by technological advancements such as ultrafast T2-weighted sequences and diffusion-weighted imaging. Fetal MRI can achieve results that are comparable to or better than those of ultrasound, particularly in cases of maternal obesity, severe oligohydramnios, or abnormal fetal position. Because of its superior soft tissue contrast, wide field of view, and multiplanar imaging, fetal MRI is able to evaluate the large fetal organs, such as the lungs, liver, bowel, and kidneys. In addition, fetal MRI allows large or complex malformations to be examined, facilitating the understanding of the malformation within the context of the body as a whole. Initial fetal MRI studies were focused on the central nervous system. With advances in software and hardware, fetal MRI gained importance in the evaluation of the fetal abdomen. The purpose of this article is to review the recent literature and developments in MRI evaluation of the fetal abdomen, with an emphasis on imaging aspects, protocols, and common clinical indications.

Chapter 1 - Fetal cerebellar disorders

The embryologic development of the cerebellum extends over a long time period, thus making it vulnerable to a broad spectrum of malformations and disruptions. Knowledge of the main steps of fetal posterior fossa development; the normal imaging patterns at different stages of embryogenesis; the large spectrum of cerebellar malformations; and their clinical presentations enables diagnosis and precise counseling of parents. Sonography is the most important imaging method for the screening of cerebellar malformations since it is noninvasive, widely available, and safe for both mother and child. The ultrasonographic approach for the evaluation of the fetal posterior fossa is based on the classic transabdominal visualization of axial planes with addition when indicated of a more comprehensive, multiplanar transvaginal or transfundal approach, including coronal and sagittal imaging planes. Fetal magnetic resonance imaging (MRI) has become an adjunct to prenatal ultrasound since the 1980s. Good-quality images have been obtained thanks to the implementation of fast and ultrafast MRI sequences. Fetal MRI has higher-contrast resolution than prenatal sonography and may contribute to the differentiation of normal from abnormal tissue. Both prenatal neurosonography and fetal MRI enable accurate prenatal diagnosis of most posterior fossa anomalies.

The Small Bowel: An Imaging Guide

Background: This article reviews the latest radiological advances in the evaluation of small bowel disease. MRI and CT have been optimized in recent years for small bowel imaging including the development of enteric agents to distend the bowel, multiplanar thin-section imaging, advanced imaging applications, and radiation dose optimization techniques. Discussion: MR enterography, with the absence of ionizing radiation exposure, excellent tissue contrast, ultrafast breath-holding pulse sequences, and the ability to perform real-time functional imaging, has become the first-line imaging modality for the evaluation of the majority of small bowel disorders. Advanced MR applications including diffusion-weighted imaging, dynamic contrast-enhanced MRI, and motility imaging are becoming central in the imaging evaluation of small bowel disease. Conclusion: CT enterography is the preferred modality in patients with known or suspected inflammatory bowel disease in the acute setting to assess for extra-luminal complications. The enteroclysis technique is of use in selected cases in which adequate small bowel distention is not achieved with oral enteral contrast administration. Capsule endoscopy is reserved for patients in whom the clinical suspicion of small bowel disease remains high despite negative evaluations with endoscopy and imaging. Keywords: Small bowel, MR enterography, CT enterography, enteroclysis, dose optimization, Crohn's disease.

Functional connectivity during affective mentalizing in criminal offenders with psychotic disorders: Associations with clinical symptoms

Psychotic disorders are associated with neurobehavioral impairments in mental state attribution (mentalizing). These impairments are most severe in psychotic patients with elevated symptom levels, particularly negative and cognitive symptoms. There have been few studies of functional connectivity related to mentalizing in psychotic disorders and associations with symptoms. We conducted a functional MRI study of affective mentalizing in individuals with psychotic disorders and varying symptom levels (positive, negative, cognitive). Participants were drawn from an adjudicated inpatient forensic psychiatric population (criminal offenders). Functional MRI scans were acquired using a 32-channel ultra-fast multiband imaging sequence. Mentalizing task performance and functional connectivity were assessed in psychotic criminal offenders (n = 46) and nonpsychotic offenders (n = 41). Temporal coherent brain networks were estimated with group independent component analysis (ICA). Relative to nonpsychotic offenders, psychotic offenders showed impaired task performance and reduced activation in a component comprising the dorsomedial prefrontal cortex, superior temporal gyrus, and ventrolateral prefrontal cortex. Positive and cognitive symptoms were inversely correlated with component activity and task performance. The results are discussed with reference to potential mechanisms underlying impaired social cognition in psychotic disorders and across symptom types.