1,720,966 research outputs found
A novel algorithm to detect the baseline value of a time signal in Dynamic Contrast Enhanced-Computed Tomography
No full textDynamic Contrast Enhanced-Computed Tomography (DCE-CT) is a functional imaging technique that has aroused a great interest in several clinical applications. The unenhanced portion of DCE-CT signal, the baseline, plays a fundamental role for signal analysis as well as to achieve accurate clinical parameter values, such as perfusion ones, used for diagnosis and prognosis purposes. In this study, a new adaptive iterative algorithm to compute voxel-based baseline values exploiting the maximum number of samples, adaptively for each voxel, is proposed and compared against the three main approaches used in the literature, over a dataset of 30 DCE-CT perfusion (briefly, CTp) liver examinations. Results were evaluated according to classical statistical indexes and tests. The experiments show that voxel-based results achieved by applying the four approaches significantly differ and the error indexes related to our method
are the lowest ones. Our results would expectedly improve the accuracy of all methods, including CTp, relying on the whole signal for computation of clinical parameters
Liver CT Perfusion: which is the relevant delay that reduces radiation dose and maintains diagnostic accuracy?
No full textObjectives: High radiation dose during CT perfusion (CTp) studies contributes to prevent CTp application in daily clinical practice. This work evaluates the consequences of scan delay on perfusion parameters and provides guidelines to help reducing the radiation dose by choosing the most appropriate delay. Methods: 59 patients (34 men, 25 women; mean age 68±12) with colorectal cancer, without underlying liver disease, underwent liver CTp, with the acquisition starting simultaneously with iodinated contrast agent injection. Blood flow (BF) and hepatic perfusion index (HPI) were computed on the acquired examinations, and compared with those of the same examinations when a variable scan delay (τ) is introduced. Dose length product, CT dose index, and effective dose were also computed on original and delayed examinations. Results: Altogether, three groups of delays (τ≤4s, 5s≤τ≤9s, τ≥10s) were identified, yielding increasing radiation dose saving (RDS) (RDS≤9.5%, 11.9%≤RDS≤21.4%, RDS≥23.8%) and decreasing perfusion accuracy (high (τ≤4s), medium (5s≤τ≤9s), low (τ≥10s)). In particular, single-input and arterial BF, and HPI were more insensitive to delay as regards the absolute variations (only 1ml/min/100g and 1%, respectively, for τ≤9s), than portal and total BF. Conclusion: Using delays lower than 4s does not change perfusion accuracy and convey unnecessary dose to patients. Conversely, starting the acquisition 9s after contrast agent injection yields a RDS of about 21%, with no significant losses in perfusion accuracy
The Effects of Baseline Length in Computed Tomography Perfusion of Liver
Full text linkObjective: Computed Tomography perfusion (CTp) of liver is very attractive for predictive and prognostic purposes, but motion artefacts and radiation dose connected to duration of examinations jeopardize the reproducibility of perfusion values, thwarting CTp daily application in clinics. The goal is showing to what extent these issues can be faced by shortening the CTp unenhanced stage (i.e., the baseline).
Methods: 59 patients with colorectal cancer underwent undelayed hepatic CTp examinations. For each patient, fifteen virtual examinations Eτ simulating different scan delays τ∈[1..15] s were achieved from the undelayed original sequence E0. Absolute (AD), percentage (PD) and compound differences (CDτ ) were computed between E0 and each Eτ for baseline and perfusion values and measured in HU and arbitrary units (a.u.), respectively. Patients were grouped and counted based on the differences achieved.
Results: Maximum perfusion CDτ<10 a.u. and baseline CDτ<7 HU were achieved. For τ≤10 s, maximum perfusion CDτ∈[5,6) a.u. was found in one patient only as well as maximum baseline CDτ∈[2,3) HU. Blood flow (BF), hepatic perfusion index and arterial BF showed the lowest CDτ , while portal BF and total BF the highest ones. PD is practically always higher than AD.
Conclusion: The approach presented allows clinicians to design the shortest CTp acquisition protocol, selecting the highest delay compliant with the required accuracy for the chosen perfusion parameters, to limit patient’s motion and improve image quality.
Significance: A short CTp protocol allows strengthening the reliability of perfusion values, and correctness of clinical outcomes, advancing CTp introduction in the standard clinical practice
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
Radiomic analysis could allow detecting misassigned bioptic grading when discriminating G1 and G2 primary pancreatic neuroendocrine tumours imaged with 68Ga-DOTANOC PET/CT
No full textPurpose or Learning Objective
Evaluating whether radiomic analysis applied to 68Ga-DOTANOC PET/CT examinations could allow detecting misassigned bioptic grading, when discriminating grade 1 (G1) and grade 2 (G2) pancreatic neuroendocrine
tumours (panNET).
Methods or Background
Thirty-three patients with low grade primary panNET assessed through pathological bioptic samples underwent 68Ga-DOTANOC PET/CT. Seven lesions with volume lower than 1cm3 were excluded from the study and standardized uptake value (SUV) maps were extracted for the remaining twenty-six patients (M:F=11:15; mean age:64 y.o. [48-85]; G1:G2=18:8). 60- first and second-order radiomic features (RFs) were computed on SUV maps of the whole tumour volume, discarding those showing high linear correlation. A discriminative radiomic model (RM) was generated for each of the surviving RFs. The area under the curve (AUC) were computed on the receiver operating characteristic curve. To evaluate models’ discrimination capability, the two-tail Wilcoxon rank-sum test was applied (p-value≤0.05) on the features space and the RF with the lowest p-values and the highest AUC were selected.
Results or Findings
The best performing RM is based on second-order correlation which provides a significant (p-value=0.028) separation between G2 and G1 panNET, with AUC=0.78, sensitivity=88%, specificity=78%, accuracy=81%. More importantly, the only FN is a lesion with borderline ki67=3 index, detected as FN in all the other RMs, this leading to questioning if it was correctly discriminated by the bioptical sample examination.
Conclusion
This preliminary study showed that this single RF well discriminates low grade panNET. Considering that tumour grade based on bioptical samples is not representative of the entire lesion, RFs may be used as tool to overcome this limitation, assigning a correct grade in all patients, especially in cases with borderline ki67.
Limitations
Reduced patients’ sample size and lack of grading assessment on tumour surgically excided
Comparing PET-derived semiquantitative parameters and radiomic features in discriminating G1 and G2 primary pancreatic neuroendocrine tumours in 68Ga-DOTANOC PET/CT
No full textPurpose or Learning Objective
To assess whether PET-derived semiquantitative parameters (PDSPs) extracted from 68Ga-DOTANOC PET/CT and single radiomic features (RFs) can differentiate low grade pancreatic neuroendocrine tumour (panNET).
Methods or Background
13 patients with G1 and 15 with G2 primary panNET demonstrated by pre-surgical 68Ga-DOTANOC PET/CT were included in this study (M:F=13:15; mean age: 56 years old [17-78]). Tumour grading was assessed after surgical excision evaluation. Total lesion receptorial expression (TLRE), Receptorial tumour volume (RTV), andSUVmax were analysed together with 60 first and second-order RFs computed on standardized uptake value (SUV) maps of the primary lesion whole volume. To prevent overfitting, only single RF were considered to generate discriminative radiomic models, where linearly correlated RFs were removed. Discrimination capability was assessed through the two-tail Wilcoxon rank-sum test with Bonferroni correction (pvalue<0.0031). Receiver operating characteristic and area under the curve (AUC) were computed. Features with the lowest p-values and highest AUC were selected.
Results or Findings
RTV is the only PDSP yielding a significant separation (p-value=0.03) between G2 and G1 panNET patients (Sensitivity=67%, Specificity=92%, Accuracy=79%). Indeed, SUVmax (Sensitivity=93%, Specificity=38%, Accuracy=68%, p-value=0.71) and TLRE (Sensitivity=87%, Specificity=54%, Accuracy=71%, p-value=0.20) were not significant and led to worse performance, accordingly. On the contrary, the first-order kurtosis provided the best performance (p-value=0.0009) at all, with Sensitivity=93%, Specificity=77%, Accuracy=86%.
Conclusion
Despite PDSPs are more easily accessible by clinicians, RFs proved to be more accurate in discriminating tumour grading in well-differentiated panNETs. The use of this radiomic model, if validated on a larger population, could represent a novel non-invasive approach to avoid biopsy before surgery, especially in selected patients not amenable to biopsy or with poor health conditions.
Limitations
Reduced patients’ sample size
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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