Mismatch Sign Research Articles

NI-09 CLINICAL SIGNIFICANCE OF T2-FLAIR MISMATCH SIGN IN LOWER GRADE GLIOMAS

Lower grade glioma is classified based on genetic information of mutation of IDH1/2 gene and co-deletion of chromosome 1p19q. Knowledge of these genetic information preoperatively is useful for making surgical planning, treatment strategy and prognostication. Recently, T2-FLAIR mismatch sign has been reported to be specific for astrocytoma with IDH mutation (mut) / non-1p19q co-deletion (co-del). This study aims to verify it in our patients. We retrospectively analyzed 152 patients aged over 15 years who were pathologically diagnosed with WHO grade 2 or 3 gliomas from April 2003 to December 2018. We excluded 88 patients without genetic information or without T2-weighted and FLAIR images. T2-FLAIR mismatch sign was defined as in the original description, namely, with homogeneously hyperintense signal on T2-weighted image and a peripheral hyperintense signal with central hypointensity signal on FLAIR image. Among 22 patients with IDH mut / non-1p19q codel, 10 were positive for T2-FLAIR mismatch sign. On the other hand, only one patient was positive for T2-FLAIR mismatch sign respectively in 19 with IDH mut / 1p19q codel and 23 patients with IDH wild-type. Sensitivity, specificity, positive predictive value, and negative predictive value of T2-FLAIR mismatch for the patients with IDH mut / non-1p19q codel are 0.46 (95% confidence interval: 0.24–0.68), 0.95 (0.84–0.99), 0.83 (0.52–0.98). and 0.77 (0.63–0.88), respectively. In 22 patients with IDH mut / non-1p19q codel, we compared 10 patients with and 12 without T2-FLAIR mismatch sign. Median age was 35 and 39 years old. WHO grade 3 was 3 patients each. Tumor location was frontal lobe in 9 (90%) and 10 patients (83%). A statistically significant difference was not found in these factors. PFS and OS were not reached in both groups. The specificity of the T2-FLAIR mismatch sign for astrocytoma with IDH mut / non-1p19q codel was very high, which may be helpful as preoperative imaging marker.

The T2-FLAIR-mismatch sign as an imaging biomarker for IDH and 1p/19q status in diffuse low-grade gliomas: a systematic review with a Bayesian approach to evaluation of diagnostic test performance.

With the revised WHO 2016 classification of brain tumors, there has been increasing interest in imaging biomarkers to predict molecular status and improve the yield of genetic testing for diffuse low-grade gliomas (LGGs). The T2-FLAIR-mismatch sign has been suggested to be a highly specific radiographic marker of isocitrate dehydrogenase (IDH) gene mutation and 1p/19q codeletion status in diffuse LGGs. The presence of T2-FLAIR mismatch indicates a T2-hyperintense lesion that is hypointense on FLAIR with the exception of a hyperintense rim. In accordance with PRISMA guidelines, we performed a systematic review of the Ovid Medline, Embase, Scopus, and Cochrane databases for reports of studies evaluating the diagnostic performance of T2-FLAIR mismatch in predicting the IDH and 1p/19q codeletion status in diffuse LGGs. Results were combined into a 2 × 2 format, and the following diagnostic performance parameters were calculated: sensitivity, specificity, positive predictive value, negative predictive value, and positive (LR+) and negative (LR-) likelihood ratios. In addition, we utilized Bayes theorem to calculate posttest probabilities as a function of known pretest probabilities from previous genome-wide association studies and the calculated LRs. Calculations were performed for 1) IDH mutation with 1p/19q codeletion (IDHmut-Codel), 2) IDH mutation without 1p/19q codeletion (IDHmut-Noncodel), 3) IDH mutation overall, and 4) 1p/19q codeletion overall. The QUADAS-2 (revised Quality Assessment of Diagnostic Accuracy Studies) tool was utilized for critical appraisal of included studies. A total of 4 studies were included, with inclusion of 2 separate cohorts from a study reporting testing and validation (n = 746). From pooled analysis of all cohorts, the following values were obtained for each molecular profile-IDHmut-Codel: sensitivity 30%, specificity 73%, LR+ 1.1, LR- 1.0; IDHmut-Noncodel: sensitivity 33.7%, specificity 98.5%, LR+ 22.5, LR- 0.7; IDH: sensitivity 32%, specificity 100%, LR+ 32.1, LR- 0.7; 1p/19q codeletion: sensitivity 0%, specificity 54%, LR+ 0.01, LR- 1.9. Bayes theorem was used to calculate the following posttest probabilities after a positive and negative result, respectively-IDHmut-Codel: 32.2% and 29.4%; IDHmut-Noncodel: 95% and 40%; IDH: 99.2% and 73.5%; 1p/19q codeletion: 0.4% and 35.1%. The T2-FLAIR-mismatch sign is an insensitive but highly specific marker of IDH mutation but not 1p/19q codeletion in diffuse LGGs, although there may be significant exceptions. These findings support the utility of T2-FLAIR mismatch as an imaging-based biomarker for positive selection of patients with IDH-mutant gliomas.

NIMG-14. THE RELATION BETWEEN T2-FLAIR MISMATCH SIGN AND ADC VALUES REFLECTING PATHOLOGICAL MICROSTRUCTURE IN LOWER-GRADE GLIOMAS

Abstract BACKGROUND Although the recent studies have identified “T2-FLAIR mismatch sign” specific to IDH-mutant and 1p/19q-intact gliomas, it is unclear what the mismatch sign represents. We aimed to investigate the mechanisms and validate the clinical utility. METHODS We identified 79 lower-grade gliomas treated at Kobe University Hospital, and classified into three groups: (i) LGGIDH(m),1p19q(-) (n = 18): IDH-mutant and 1p/19q-intact, (ii) LGGIDH(m),1p19q(+) (n=26): IDH-mutant and 1p/19q co-deleted, (iii) LGGIDH(w) (n=35): IDH wild-type. We retrospectively analyzed the relation with apparent diffusion coefficient (ADC) values, metabolites in magnetic resonance spectroscopy and pathological features, and examined the influence of the presence of the mismatch sign on progression-free survival (PFS) and overall survival in LGGIDH(m),1p19q(-). RESULTS Compared to the rim presenting hyperintense on T2WI and FLAIR, the core presenting hyperintense on T2WI and reversely hypointense on FLAIR had significantly higher ADC values (p = 0.002). The core/rim ratios of ADC values were significantly higher in the cases with the mismatch sign (p = 0.001), not depending on IDH status, 1p/19q status and WHO grade. There was no significant difference in metabolites changing between the presence and absence of the mismatch sign. The cases with the mismatch sign in LGGIDH(m),1p19q(-) had abundant microcysts as a pathological feature, and longer PFS than those without the mismatch sign (5-yr PFS: 100% vs 37.5%). Multivariate analysis found the mismatch sign to be the only significant predictor for preferable PFS in LGGIDH(m),1p19q(-) (p = 0.044). CONCLUSION Our study provided the new evidence that the T2-FLAIR mismatch sign had the significantly different ADC values between the core and the rim, suggesting that the mismatch sign reflected the difference of the tumor cellularity and the microenvironment.

NIMG-01. T2WI-FLAIR MISMATCH SIGN IN LOWER GRADE GLIOMA AND DYSEMBRYOPLASTIC NEUROEPITHELIAL TUMOR

Abstract BACKGROUND T2-FLAIR mismatch sign was reported as a specific imaging marker for diffuse astrocytoma with IDH-mutant and 1p/19q non-codeletion. However, most of the previous studies for T2-FLAIR mismatch were confirmed only among lower grade glioma (LGG). The purpose of this study is to explore the T2-FLAIR mismatch sing in supratentorial non-enhancing tumor including LGG and dysembryoplastic neuroepithelial tumor (DNET) and to unveil the exception rules of the sign. METHODS Forty-four patients of non-enhancing LGG and DNET were included in this study. LGG（diffuse astrocytoma with IDH mutant (IDHmut-Noncodel), oligodendroglioma with IDH-mutant and 1p19q codeletion (IDHmut-Codel), diffuse astrocytoma with IDH wildtype (IDHwt)）and DNET were diagnosed based on WHO 2016 classification. The tumors were evaluated MRI by 2 independent reviewers to assess presence or absence of T2-FLAIR mismatch sign. CT was also performed to evaluate the localized thinning of the skull bone. Inter-reviewer agreement with Cohen’s kappa (κ) was calculated. RESULT: Ten out of 18 cases (55.6%) of IDHmut-Noncodel presented T2-FLAIR mismatch sign. None of the other LGG (IDHmut-Codel and IDHwt) presented T2-FLAIR mismatch. Eight out of 11 cases (72.7%) of DNET also present the T2-FLAIR mismatch. The overlying part of the skull bone thinning was observed in 5 cases of DNET, but none of LGG presented the localized skull bone thinning. The inter-rater agreement for the T2-FLAIR mismatch and the localized thinning of the skull bone were excellent (κ= 1.00). CONCLUSION The T2-FLAIR mismatch sign was specific marker for IDHmut-Noncodel among LGG. However, DNET also presented the T2-FLAIR mismatch sign. The localized skull bone thinning could be useful for differentiating between IDHmut-Noncodel and DNET

NIMG-05. THE T2-FLAIR MISMATCH SIGN IN IDH-MUTANT ASTROCYTOMAS - IS THERE AN ASSOCIATION WITH FET PET UPTAKE?

Abstract BACKGROUND The purpose of this study was (i) to assess the reproducibility of the previously described T2-FLAIR mismatch sign as a highly specific MR imaging marker in non-enhancing IDH-mutant, 1p/19q non-codeleted lower-grade gliomas (LGG) of the WHO grades II or III, and (ii) its association with the uptake of the radiolabeled amino acid O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) in PET to further metabolically characterize that sign, which is currently poorly understood. METHODS Consecutive MRI and dynamic FET PET scans (n=134) from newly diagnosed and neuropathologically confirmed IDH-mutant LGG (n=65) and IDH-wildtype gliomas as control group (n=69) were evaluated by two independent raters to assess presence/absence of the T2-FLAIR mismatch sign as well as FET uptake. Interrater agreement was assessed using Cohen’s kappa (κ), as well as diagnostic performance (i.e., positive/negative predictive value; PPV, NPV) of the T2-FLAIR mismatch sign to identify IDH-mutant astrocytomas. RESULTS In the LGG group, 13 patients (20%) had a T2-FLAIR mismatch sign, which could be identified with a substantial interrater agreement (κ=0.75). In contrast, that sign was absent in IDH-wildtype gliomas. All 13 cases that were positive for the T2/FLAIR mismatch sign were IDH-mutant, 1p/19q non-codeleted tumors (PPV=100%, NPV=57%). Interestingly, compared to IDH-mutant gliomas without the T2-FLAIR mismatch sign, the sign was significantly (P=0.027; 10 of 13 patients) associated with a negative FET PET scan (i.e., 5 tumors with indifferent FET uptake comparable to the background activity, or FET uptake below background activity (photopenic defect) in 5 tumors). CONCLUSIONS With a robust interrater agreement, our findings are in line with previously reported findings regarding the T2-FLAIR mismatch sign. Additionally, the T2-FLAIR mismatch sign seems to be significantly related with a lack of increased FET uptake in PET, which may help to further characterize patients with that sign. Notwithstanding, the clinical relevance of this imaging constellation warrants further investigation.

NIMG-02. NON-INVASIVE DETECTION OF IDH MUTANT 1p19q NON-CODELETED GLIOMAS USING THE T2-FLAIR MISMATCH SIGN

Abstract OBJECTIVE To assess the validity and pathophysiology of the T2/FLAIR mismatch sign for non-invasive identification of IDH-mutant 1p/19q non-codeleted glioma. METHODS MRI scans from 408 consecutive patients with newly diagnosed glioma (113 lower-grade glioma and 295 glioblastoma) were evaluated for the presence of a T2/FLAIR-mismatch sign (defined as complete/near-complete hyperintense signal on T2w, simultaneous hypointense signal on FLAIR except for a hyperintense peripheral rim) by two independent reviewers. Sensitivity, specificity, accuracy, positive and negative predictive value (PPV, NPV) were calculated to assess the performance of the T2/FLAIR-mismatch sign for identifying IDH-mutant 1p/19q non-codeleted tumors. An exploratory analysis of spatial differences in ADC and rCBV values comparing the FLAIR-hypointense core vs. hyperintense rim in cases with presence of a T2/FLAIR-mismatch sign was performed. RESULTS There was substantial interrater agreement to identify the T2/FLAIR-mismatch sign (Cohen’s Kappa = 0.75 [95% CI 0.57–0.93]). The T2/FLAIR-mismatch sign was present in 12 cases with lower-grade glioma (10.6%), all of them were IDH-mutant, 1p/19q non-codeleted tumors (sensitivity=10.9%, specificity=100%, PPV=100%, NPV=3.0%, accuracy=13.3%). The T2/FLAIR-mismatch sign was not identified in any other molecular subgroup, especially not in any of the IDH-mutant glioblastoma cases (n=5). In tumors with T2/FLAIR-mismatch sign the ADC values were significantly lower in the rim as compared to the core (p=0.0005) whereas there was no difference in rCBV values (p=0.4258). CONCLUSION This study confirms the high specificity of the T2/FLAIR-mismatch sign for non-invasive identification of IDH-mutant 1p/19q non-codeleted gliomas, although sensitivity is low and applicability is limited to lower-grade gliomas. The identified spatial differences in ADC values between the core and rim of tumors with a T2/FLAIR-mismatch sign potentially reflects differences in tumor cellularity and microenvironment.

When Less Is More: Why Extubation With Less Than Routine 100% Oxygen May Be a Reasonable Strategy.

When Less Is More: Why Extubation With Less Than Routine 100% Oxygen May Be a Reasonable Strategy.

Advanced imaging parameters improve the prediction of diffuse lower-grade gliomas subtype, IDH mutant with no 1p19q codeletion: added value to the T2/FLAIR mismatch sign

A combination of T2/FLAIR mismatch sign and advanced imaging parameters may improve the determination of molecular subtypes of diffuse lower-grade glioma. We assessed the diagnostic value of adding the apparent diffusion coefficient (ADC) and cerebral blood volume (CBV) to the T2/FLAIR mismatch sign for differentiation of the IDH mutation or 1p/19q codeletion. Preoperative conventional, diffusion-weighted, and dynamic susceptibility contrast imaging were performed on 110 patients with diffuse lower-grade gliomas. The study population was classified into three groups using molecular subtype, namely IDH mutation and 1p/19q codeletion (IDHmut-Codel), IDH wild type (IDHwt) and IDH mutation and no 1p/19q codeletion (IDHmut-Noncodel). T2/FLAIR mismatch sign and the histogram parameters of apparent diffusion coefficient (ADC) and normalised cerebral blood volume (nCBV) values were assessed. A multivariate logistic regression model was constructed to distinguish IDHmut-Noncodel from IDHmut-Codel and IDHwt and from IDHwt, and the performance was compared with that of single parameters using the area under the receiver operating characteristics curve (AUC). Positive visual T2/FLAIR mismatch sign and higher nCBV skewness were significant variables to distinguish IDHmut-Noncodel from the other two groups (AUC, 0.88; 95% CI, 0.81-0.96). A lower ADC10 was a significant variable for distinguishing IDHmut-Noncodel from the IDHwt group (AUC, 0.75; 95% CI, 0.62-0.89). Adding ADC or CBV histogram parameters to T2/FLAIR mismatch sign improved performance in distinguishing IDHmut-Noncodel from the other two groups (AUC 0.882 vs. AUC 0.810) or from IDHwt (AUC 0.923 vs. AUC 0.868). The combination of the T2/FLAIR mismatch sign with ADC or CBV histogram parameters can improve the identification of IDHmut-Noncodel diffuse lower-grade gliomas, which can be easily applied in clinical practice. • The combination of the T2/FLAIR mismatch sign with the ADC or CBV histogram parameters can improve the identification of IDHmut-Noncodel diffuse lower-grade gliomas. • The multivariable model showed a significantly better performance for distinguishing the IDHmut-Noncodel group from other diffuse lower-grade gliomas than the T2/FLAIR mismatch sign alone or any single parameter. • The IDHmut-Noncodel type was associated with intermediate treatment outcomes; therefore, the identification of IDHmut-Noncodel diffuse lower-grade gliomas could be helpful for determining the clinical approach.

Neuroimaging-Based Classification Algorithm for Predicting 1p/19q-Codeletion Status in IDH-Mutant Lower Grade Gliomas.

Isocitrate dehydrogenase (IDH)-mutant lower grade gliomas are classified as oligodendrogliomas or diffuse astrocytomas based on 1p/19q-codeletion status. We aimed to test and validate neuroradiologists' performances in predicting the codeletion status of IDH-mutant lower grade gliomas based on simple neuroimaging metrics. One hundred two IDH-mutant lower grade gliomas with preoperative MR imaging and known 1p/19q status from The Cancer Genome Atlas composed a training dataset. Two neuroradiologists in consensus analyzed the training dataset for various imaging features: tumor texture, margins, cortical infiltration, T2-FLAIR mismatch, tumor cyst, T2* susceptibility, hydrocephalus, midline shift, maximum dimension, primary lobe, necrosis, enhancement, edema, and gliomatosis. Statistical analysis of the training data produced a multivariate classification model for codeletion prediction based on a subset of MR imaging features and patient age. To validate the classification model, 2 different independent neuroradiologists analyzed a separate cohort of 106 institutional IDH-mutant lower grade gliomas. Training dataset analysis produced a 2-step classification algorithm with 86.3% codeletion prediction accuracy, based on the following: 1) the presence of the T2-FLAIR mismatch sign, which was 100% predictive of noncodeleted lower grade gliomas, (n = 21); and 2) a logistic regression model based on texture, patient age, T2* susceptibility, primary lobe, and hydrocephalus. Independent validation of the classification algorithm rendered codeletion prediction accuracies of 81.1% and 79.2% in 2 independent readers. The metrics used in the algorithm were associated with moderate-substantial interreader agreement (κ = 0.56-0.79). We have validated a classification algorithm based on simple, reproducible neuroimaging metrics and patient age that demonstrates a moderate prediction accuracy of 1p/19q-codeletion status among IDH-mutant lower grade gliomas.

Radiographic assessment of contrast enhancement and T2/FLAIR mismatch sign in lower grade gliomas: correlation with molecular groups.

With the updated World Health Organization (WHO) 2016 neuropathological diagnostic criteria, radiographic prognostic associations in lower-grade gliomas (LGG, WHO grade II and III) are undergoing re-evaluation. We identified 316 LGG patients (151 grade II and 165 grade III) for a combined cohort from three independent databases. We analyzed the preoperative axial FLAIR, axial T2-weighted and post-gadolinium volumetric T1-weighted MR images. The molecular data collected included the status of IDH1/2, TP53, TERT promoter and ATRX mutations, in addition to 1p/19q co-deletions. In a subset of cases (n = 133), we assessed the "T2-FLAIR mismatch" sign. Gliomas were assigned to one of the three molecular groups: Group O (IDH-mutant, 1p/19q co-deleted oligodendrogliomas, n = 95), Group A (IDH-mutant, ATRX inactivated astrocytomas, n = 175) and Group G (IDH wild-type, GBM-like, n = 46). A contrast-enhancing tumor was seen in 98 patients (31%), most frequently in Group G (n = 28/45, 57%), when compared to Group A (n = 49/175, 28%) and Group O (n = 24/95, 25.3%) tumors (p = 0.008 and p = 0.0011, respectively). Consistent with previous reports, T2-FLAIR mismatch was preferentially found in Group A tumors (73.1%, 60 of 82), although its presence was not associated with survival, after controlling for molecular group. False positive mismatch sign was noted in 28.5% (12/42) Group O tumors, but none of the tumors in Group G. A combination of all three factors: age under 40years at first diagnosis, a tumor size larger than 6cm and T2-FLAIR mismatch was highly specific for IDH mutant astrocytoma (Group A). We identify radiographic correlates of molecular groups in lower-grade gliomas, which join clinical demographic features in defining the characteristic presentation of these tumors. Radiographic correlates of prognosis in LGG require re-evaluation within molecular group.

The T2-FLAIR mismatch sign as an imaging marker for non-enhancing IDH-mutant, 1p/19q-intact lower-grade glioma: a validation study.

The purpose of this study was to assess the reproducibility of the previously described T2-fluid attenuated inversion recovery (FLAIR) mismatch sign as a specific imaging marker in non-enhancing isocitrate dehydrogenase (IDH) mutant, 1p/19q non-codeleted lower-grade glioma (LGG), encompassing both diffuse and anaplastic astrocytoma. MR scans (n = 154) from 3 separate databases with genotyped LGG were evaluated by 2 independent reviewers to assess (i) presence/absence of "T2-FLAIR mismatch" sign and (ii) presence/absence of homogeneous signal on T2-weighted images. Interrater agreement with Cohen's kappa (κ) was calculated, as well as diagnostic test performance of the T2-FLAIR mismatch sign to identify IDH-mutant astrocytoma. There was substantial interrater agreement for the T2-FLAIR mismatch sign [κ = 0.75 (0.64-0.87)], but only fair agreement for T2 homogeneity [κ = 0.38 (0.25-0.52)]. The T2-FLAIR mismatch sign was present in 38 cases (25%) and had a positive predictive value of 100%, negative predictive value of 68%, a sensitivity of 51%, and a specificity of 100%. With a robust interrater agreement, our study confirms that among non-enhancing LGG the T2-FLAIR mismatch sign represents a highly specific imaging marker for IDH-mutant astrocytoma. This non-invasive marker may enable a more informed patient counsel and can aid in the treatment decision processes in a significant proportion of patients presenting with non-enhancing, LGG-like lesions.

T2-FLAIR Mismatch, an Imaging Biomarker for IDH and 1p/19q Status in Lower-grade Gliomas: A TCGA/TCIA Project.

Purpose: Lower-grade gliomas (WHO grade II/III) have been classified into clinically relevant molecular subtypes based on IDH and 1p/19q mutation status. The purpose was to investigate whether T2/FLAIR MRI features could distinguish between lower-grade glioma molecular subtypes.Experimental Design: MRI scans from the TCGA/TCIA lower grade glioma database (n = 125) were evaluated by two independent neuroradiologists to assess (i) presence/absence of homogenous signal on T2WI; (ii) presence/absence of "T2-FLAIR mismatch" sign; (iii) sharp or indistinct lesion margins; and (iv) presence/absence of peritumoral edema. Metrics with moderate-substantial agreement underwent consensus review and were correlated with glioma molecular subtypes. Somatic mutation, DNA copy number, DNA methylation, gene expression, and protein array data from the TCGA lower-grade glioma database were analyzed for molecular-radiographic associations. A separate institutional cohort (n = 82) was analyzed to validate the T2-FLAIR mismatch sign.Results: Among TCGA/TCIA cases, interreader agreement was calculated for lesion homogeneity [κ = 0.234 (0.111-0.358)], T2-FLAIR mismatch sign [κ = 0.728 (0.538-0.918)], lesion margins [κ = 0.292 (0.135-0.449)], and peritumoral edema [κ = 0.173 (0.096-0.250)]. All 15 cases that were positive for the T2-FLAIR mismatch sign were IDH-mutant, 1p/19q non-codeleted tumors (P < 0.0001; PPV = 100%, NPV = 54%). Analysis of the validation cohort demonstrated substantial interreader agreement for the T2-FLAIR mismatch sign [κ = 0.747 (0.536-0.958)]; all 10 cases positive for the T2-FLAIR mismatch sign were IDH-mutant, 1p/19q non-codeleted tumors (P < 0.00001; PPV = 100%, NPV = 76%).Conclusions: Among lower-grade gliomas, T2-FLAIR mismatch sign represents a highly specific imaging biomarker for the IDH-mutant, 1p/19q non-codeleted molecular subtype. Clin Cancer Res; 23(20); 6078-85. ©2017 AACR.

How do people with weak and strong pro-environmental worldviews process visual climate change information? An EEG study / ¿Cómo procesan la información visual relacionada con el cambio climático las personas con una visión del mundo ambiental arraigada o sin ella? Un estudio con EEG

In a pioneering work, this study explores the potential that may be found in combining the environmental psychological concept environmental worldview with the neurocognitive study technique electroencephalography (EEG). With this research, we aim to bridge between the research traditions of environmental communication and neuro-cognition by investigating in an qEEG experiment (N = 19) if different levels of environmental worldview, measured by the NEP, influence the processing of visual climate change imagery, reflected by the theta and gamma oscillations in the frontal and parietal areas. Our results confirm the assumptions that there is a relationship between the degree of environmental worldview and visual environmental communication processing. The pattern is interpreted as an indication that people with weak pro-environmental worldviews show cognitive signs of mismatch between what is in line with their environmental worldview and what they are confronted with in the visual stimulus.

Parametric reflection phenomenon in quadratic uniaxial crystals with birefringence

Effects of parametric refraction and reflection of optical beams in uniaxial crystals have been considered with allowance for birefringence. The equation of the signal wave trajectory, taking into account the medium anisotropy, has been obtained and analyzed. Pecularities of these effects for different types of three-frequency interaction of ordinary and extraordinary waves are shown. In the presence of birefringence, the effective mismatch sign can change and consequently the cascade nonlinearity can become focusing; in this case, the effect of reflection disappears.

Radiology: Beyond Borders

HomeRadiologyVol. 237, No. 1 PreviousNext ArticlesPresident's AddressRadiology: Beyond BordersBrian C. LentleBrian C. LentleAuthor Affiliations1From Saanichton, British Columbia, Canada. From the 2004 RSNA Annual Meeting. Received January 4, 2005; accepted January 14.Address correspondence to the author (e-mail: [email protected]).Brian C. LentlePublished Online:Oct 1 2005https://doi.org/10.1148/radiol.2371050014MoreSectionsFull textPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In Reference1 Patel V, Sumathipala A. International representation in psychiatric literature: survey of six leading journals. Br J Psychiatry 2001;178:406–409. Medline, Google ScholarArticle HistoryPublished in print: Oct 2005 FiguresReferencesRelatedDetailsRecommended Articles RSNA Committee on International Radiology Education: 25 Years of Global Education OutreachRadioGraphics2020Volume: 40Issue: 7pp. 1938-19522017: A Look BackRadiology2017Volume: 285Issue: 3pp. 702-7042018 in Review and Plans for 2019RadioGraphics2019Volume: 39Issue: 1pp. 1-6Frederick J. Bonte, MDRadiology2017Volume: 286Issue: 1pp. 366James G. Kereiakes, PhDRadiology2017Volume: 286Issue: 1pp. 367See More RSNA Education Exhibits Anatomy of a Deep Learning Project for Breast Cancer Prognosis Prediction: From Collecting Data to Building a PipelineDigital Posters2019Imaging-Guided Precision Medicine in Cancer Patients Treated with Immune Checkpoint BlockersDigital Posters2019The T2-FLAIR Mismatch Sign in Diffuse Gliomas: From Top to BottomDigital Posters2020 RSNA Case Collection Fourth branchial cleft cystRSNA Case Collection2021Dedifferentiated Thyroid CancerRSNA Case Collection2020Osteoid OsteomaRSNA Case Collection2020 Vol. 237, No. 1 Metrics Altmetric Score PDF download

Effective lensing effects in parametric frequency conversion

We show that, in the high wave-vector-mismatch (cascading) limit, the well-known paraxial description of parametric frequency conversion in quadratic media entails effective lensing effects, which can have a self-focusing or a self-defocusing nature, critically depending on the mismatch sign, the selected wave, and the launching condition (second-harmonic generation or downconversion). Numerical and experimental evidence of this behavior is reported.

Role of surface energy and surface reconstructions on the 2D-to-3D growth-mode transition of strainedInxGa1−xAslayers on InP(001)

We show that the role played by surface energy in the total-energy balance between the initial twodimensional ~2D! state and the final three-dimensional ~3D! state is of prime importance to explain morphologies observed during the molecular-beam epitaxy growth of strained materials. This was established by analyzing differences in 2D-3D transition onsets for 2% mismatched InxGa12xAs films grown on InP~001! substrates when changing the mismatch sign ~compression or tension!, the film doping, and the type of surface stabilization ~anion or cation!. The 2D-3D onsets were measured by reflection high-energy electron diffraction and the corresponding surface morphologies characterized by scanning tunneling microscopy

Effect of the arterial oxygenation level on cardiac output, oxygen extraction, and oxygen consumption in low birth weight infants receiving mechanical ventilation

Objective: To investigate the effects on oxygenation of targeting the higher versus the lower end of the currently recommended range for pulse oximetry (Sp o 2 ). Design: Nonrandomized crossover trial with the use of within-subject comparisons (two-tailed paired t test). Setting: Level III neonatal intensive care unit of a university hospital. Patients: Twenty infants whose lungs were mechanically ventilated (mean ± SD: birth weight, 1192 ± 396 gm; gestational age, 28.7 ± 2.7 weeks; age at time of study, 42 ± 26 hours). Interventions: The inspired oxygen concentration was adjusted to achieve Sp o 2 readings of 93% to 96% versus 89% to 92% (Ohmeda pulse oximeter) or 95% to 98% versus 91% to 94% (Nellcor oximeter). Measurements: Cardiac output was measured by echocardiography, oxygen content of arterial blood samples by cooximetry, and oxygen consumption by indirect calorimetry. Results: The inspired oxygen concentrations required to achieve the Sp o 2 target ranges were 39.8% ± 8.3% versus 28.7% ± 6.1% ( p <0.001). The respective arterial oxygen contents were 18.0 ± 2.6 ml/dl versus 16.9 ± 2.5 ml/dl ( p <0.001). Oxygen consumption was unchanged. In the lower-oxygen condition no compensatory increase in cardiac output was detected; thus the estimated mixed venous oxygen tension decreased and the oxygen extraction ratio increased. Venous admixture increased from 15% ± 6% to 31% ± 9% in the lower-oxygen condition ( p <0.001). Conclusions: The ”low normal“ Sp o 2 target range allowed for less oxygen exposure. No signs of mismatch between systemic oxygen delivery and demand could be detected. (J P EDIATR 1995;126:777-84)

Bright solitons with second-order nonlinearities

We investigate the mutual trapping of intense fundamental and second-harmonic waves propagating in materials with second-order nonlinearity. Consistent with Menyuk’s robustness hypothesis of solitons, we numerically observe that solitonlike waves emerge from the input signal over a wide range of excitation conditions for both signs of the phase mismatch and in the presence of moderate linear walk-off between the interacting waves. The solitons exist above a threshold intensity and in general arise as oscillating states. The trapping of the waves is governed by the sign of the phase mismatch, by the beam or pulse width, and by the absolute value of the phase mismatch through the ratios among the characteristic lengths of the wave evolution, namely, the diffractive, walk-off, and nonlinear interaction lengths.

Pulmonary embolism: increased ventilation in areas of decreased perfusion.

An abnormal finding that is considered characteristic of large or extensive pulmonary embolism has been observed on ventilation-perfusion (V-P) lung scans. This observation is a regional area of increased ventilation radioactivity in the embolized region of the lung that is more than the normal ventilation radioactivity in the adjacent or contralateral normally perfused lung. It has been designated the "enhanced V-P mismatch sign." This sign was noted in 15 cases among approximately 700 routine V-P lung scans interpreted by a nuclear radiologist. Of these, large or extensive emboli were confirmed in only 10 cases, nine by means of angiography and one by means of autopsy studies. The remaining five cases demonstrated clinical correlation only and are not included in this report. Of the 10 confirmed cases with enhanced V-P mismatch sign, increased ventilation radioactivity involved unilateral lung distribution in five and zonal or lobar distribution in five. The Westermark sign was seen in only seven of the 10 cases. It is hoped that this observation will prove useful in the diagnosis of large or extensive pulmonary emboli.