1,721,002 research outputs found
FID-calibrated simultaneous multi-slice fast spin echo with long trains of hard pulses
No full textObjective. 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.N
High-resolution Magnetic Resonance Imaging Reveals Hidden Etiologies of Symptomatic Vertebral Arterial Lesions
No full textBackground: Symptomatic intracranial vertebral artery (VA) disease has various clinical features and poor neurological outcomes. The disease is believed to result from atherosclerotic stenosis, occlusion, or spontaneous VA dissection. The underlying histopathology of symptomatic intracranial VA disease has only been studied at postmortem, and no in vivo imaging investigation has been conducted despite the increased sophistication of imaging techniques. Methods: The authors performed high-resolution magnetic resonance imaging (HR-MRI) of intracranial vertebral arteries in 9 patients, suspected of a VA pathology by magnetic resonance imaging (MRI), magnetic resonance angiography, and digital subtraction angiography. Results: HR-MRI allowed the authors to determine the following: (1) atherosclerotic plaque is composed of a large lipid core with intraplaque hemorrhage and calcification, (2) nonstenotic atherosclerosis exhibits diffuse vessel wall thickening and plaque protruding toward perforating arteries, and (3) spontaneous VA dissection exhibits large intramural hematoma in a false lumen with complete occlusion of the true lumen. In addition, VA hypoplasia was easily differentiated from atherosclerotic stenosis, by direct visualization of a narrow lumen diameter without arterial wall thickening. Furthermore, etiologic diagnoses based on classical MRI, angiography, and digital subtraction angiography were changed in 3 patients after HR-MRI. Additional information on plaque stability, indicating the possibility of unstable plaque, was found in 4 patients. Conclusions: The application of HR-MRI in stroke patients with VA pathologies enabled the authors to determine the underlying pathophysiologies. These findings could be used to improve risk stratification and treatment decision making in symptomatic intracranial VA disease.N
Critical Test Result Notification via Mobile Phone-Based Automated Text Message System in the Radiologic Field: Single Institutional Experience
No full textPurpose: To investigate the feasibility of sharing critical test result (CTR) notifications (CTRNs) via automated text messaging. Materials and methods: CTRNs via automated text messaging was used to notify physicians of CTRs in a tertiary hospital with 1,786 beds. From June 2016 to September 2016, notifications for 545 CTRs were given via a CTRN system. Among them, 490 CTRs (292 male and 198 female patients; mean age, 53.6 years old [range, 1-88]) were included in analysis. CTR levels (CTRLs) were assigned to four categories (CTRL1 to CTRL3 and unclassified) when reported, and reclassified into three CTRLs according to their clinical relevance and urgency. Response time was defined as time lapse between CTR reporting and documentation by physicians. Analysis of variance was performed to compare response times according to CTRLs and patients' location. Results: Corresponding actions were taken in 404 of 490 cases (82.4%) without any delayed CTRN-related morbidity. There were 15 CTRL1 (3.1%), 50 CTRL2 (10.2%), 112 CTRL3 (22.9%) cases, and the remaining 313 CTRL cases were unclassified. After reclassification, CTRL1, CTRL2, and CTRL3 were 81 (16.5%), 177 (36.1%), and 232 cases (47.3%), respectively. Response time of reclassified CTRL3 was significantly longer than that of reclassified CTRL1 (median 23.0, [interquartile range 2.0-133.5] hours versus 4.0 [0.0-22.0] hours; P < .001). Response time of outpatient cases (80.0 [6.0 to 157.0] hours) was significantly longer (P < .001) than those of inpatient (3.0 [0.0-16.01) and emergency department cases (5.0 [1.0-21.0]). Conclusion: Automated text messaging could be a feasible option for CTRNs in the radiologic field. Further large-scale investigations regarding efficiency of this system are warranted.N
Association Between Enlarged Perivascular Spaces and Cognition in a Memory Clinic Population
No full textBACKGROUND AND OBJECTIVES: Although enlarged perivascular spaces (EPVS) have been suggested as an emerging measure of small vessel disease (SVD) in the brain, their association with cognitive impairment is not yet clearly understood. We aimed to examine the relationship between each EPVS in the basal ganglia (BG-EPVS) and centrum semiovale (CSO-EPVS) with cognition in a memory clinic population. METHODS: Participants with a diverse cognitive spectrum were recruited from a university hospital memory clinic. They underwent comprehensive clinical and neuropsychological assessments and brain MRI. BG-EPVS and CSO-EPVS were measured on T2-weighted MRI and then dichotomized into low and high degrees for further analyses. Other SVD markers were assessed using validated rating scales. RESULTS: A total of 910 participants were included in this study. A high degree of BG-EPVS was significantly associated with poorer scores on the executive function domain, but not with other cognitive domains, when age, sex, education, MRI scanner type, and cognitive diagnosis were controlled as covariates. However, the association between BG-EPVS and executive function was no longer significant after controlling for other markers of SVD, such as lacunar infarcts and periventricular white matter hyperintensities, as additional covariates. CSO-EPVS did not have a significant relationship with any cognitive scores, regardless of the covariates. DISCUSSION: Our findings from a large memory clinic population suggest that EPVS, regardless of the topographical location, may not be used as a specific SVD marker for cognitive impairment, although an apparent association was observed between a high degree of BG-EPVS and executive dysfunction before controlling other SVD markers that share a common pathophysiologic process with BG-EPVS
The Effect of Varying Slice Thickness and Interslice Gap on T-1 and T-2 Measured with the Multidynamic Multiecho Sequence
No full textPurpose: The purpose of our study was to investigate the effect of different slice thicknesses and/or interslice gaps on longitudinal and transverse relaxation times (T-1 and T-2) measured by a multi-dynamic, multi-echo (MDME) sequence. Materials and Methods: This retrospective study included nine healthy subjects who underwent MDME sequence (at 3T) with four different combinations of slice thicknesses and/or interslice gaps: slice thickness of 4 mm and interslice gap of 0 mm (TH4/G0), TH4/G1, TH5/G0, and TH5/G1. T-1 and T-2 were measured in various brain regions by a qualified neuroradiologist with 8 years of clinical experience: the frontal white matter (WM), occipital WM, genu, splenium, frontal cortex, thalamus, putamen, caudate head, and cerebrospinal fluid (CSF). The paired samples t-test was used to investigate the effect of different slice thicknesses and interslice gaps (TH4/G0 versus TH4/G1 and TH5/G0 versus TH5/G1). P 0.013). In addition, T-1 in all brain regions of interest did not significantly change between TH4/G0, TH4/G1, TH5/G0 and TH5/G1. However, T-1 in some of the brain regions was higher with TH4/G0 than with TH5/G0 (occipital WM, frontal cortex, and caudate head) and with TH4/G1 than with TH5/G1 (occipital WM, genu, splenium and thalamus, all Ps < 0.013). Conclusion: T-2 estimated using the MDME sequence was stable regardless of slice thickness or gap. Although the sequence seems to provide stable relaxation values, identical slice thicknesses need to be used for follow-up to prevent potential T-1 changes. ©2018 Japanese Society for Magnetic Resonance in Medicine11sci
Recurrent ischemic lesions after acute atherothrombotic stroke: clopidogrel plus aspirin versus aspirin alone
No full textBackground and Purpose In patients with acute ischemic stroke caused by large artery atherosclerosis, clopidogrel plus aspirin versus aspirin alone might be more effective to prevent recurrent cerebral ischemia. However, there is no clear evidence. Methods In this multicenter, double-blind, placebo-controlled trial, we randomized 358 patients with acute ischemic stroke of presumed large artery atherosclerosis origin within 48 hours of onset to clopidogrel (75 mg/d without loading dose) plus aspirin (300-mg loading followed by 100 mg/d) or to aspirin alone (300-mg loading followed by 100 mg/d) for 30 days. The primary outcome was new symptomatic or asymptomatic ischemic lesion on magnetic resonance imaging within 30 days. Secondary outcomes were 30-day functional disability, clinical stroke recurrence, and composite of major vascular events. Safety outcome was any bleeding. Results Of 358 patients enrolled, 334 (167 in each group) completed follow-up magnetic resonance imaging. The 30-day new ischemic lesion recurrence rate was comparable between the clopidogrel plus aspirin and the aspirin monotherapy groups (36.5% versus 35.9%; relative risk, 1.02; 95% confidence interval, 0.77-1.35; P=0.91). Of the recurrent ischemic lesions, 94.2% were clinically asymptomatic. There were no differences in secondary outcomes between the 2 groups. Any bleeding were more frequent in the combination group than in the aspirin monotherapy group, but the difference was not significant (16.7% versus 10.7%; P=0.11). One hemorrhagic stroke occurred in the clopidogrel plus aspirin group. Conclusions Clopidogrel plus aspirin might not be superior to aspirin alone for preventing new ischemic lesion and clinical vascular events in patients with acute ischemic stroke caused by large artery atherosclerosis.N
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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