Contrast Leakage Patterns from Dynamic Susceptibility Contrast Perfusion MRI in the Grading of Primary Pediatric Brain Tumors

BACKGROUND AND PURPOSE: The pattern of contrast leakage from DSC tissue signal intensity time curves have shown utility in distinguishing adult brain neoplasms, but has limited description in the literature for pediatric brain tumors. The purpose of this study is to evaluate the utility of grading pediatric brain tumors with this technique. MATERIALS AND METHODS: A retrospective review of tissue signal-intensity time curves from 63 pediatric brain tumors with preoperative DSC perfusion MR imaging was performed independently by 2 neuroradiologists. Tissue signal-intensity time curves were generated from ROIs placed in the highest perceived tumor relative CBV. The postbolus portion of the curve was independently classified as returning to baseline, continuing above baseline (T1-dominant contrast leakage), or failing to return to baseline (T2*-dominant contrast leakage). Interobserver agreement of curve classification was evaluated by using the Cohen κ. A consensus classification of curve type was obtained in discrepant cases, and the consensus classification was compared with tumor histology and World Health Organization grade. RESULTS: Tissue signal-intensity time curve classification concordance was 0.69 (95% CI, 0.54–0.84) overall and 0.79 (95% CI, 0.59–0.91) for a T1-dominant contrast leakage pattern. Twenty-five of 25 tumors with consensus T1-dominant contrast leakage were low-grade (positive predictive value, 1.0; 95% CI, 0.83–1.00). By comparison, tumors with consensus T2*-dominant contrast leakage or return to baseline were predominantly high-grade (10/15 and 15/23, respectively) with a high negative predictive value (1.0; 95% CI, 0.83–1.0). For pilomyxoid or pilocytic astrocytomas, a T1-dominant leak demonstrated high sensitivity (0.91; 95% CI, 0.70–0.98) and specificity (0.90, 95% CI, 0.75–0.97). CONCLUSIONS: There was good interobserver agreement in the classification of DSC perfusion tissue signal-intensity time curves for pediatric brain tumors, particularly for T1-dominant leakage. Among patients with pediatric brain tumors, a T1-dominant leakage pattern is highly specific for a low-grade tumor and demonstrates high sensitivity and specificity for pilocytic or pilomyxoid astrocytomas

Magnetic resonance imaging findings in children with spasmus nutans

Background Spasmus nutans (SN) is a rare pediatric ophthalmologic syndrome characterized by nystagmus, head bobbing, and abnormal head positioning. Historically, SN has been associated with underlying optic pathway gliomas (OPG); however, evidence of this association is based primarily on a small number of isolated case reports. Prior retrospective analyses have found the rate of OPG to be <2%, but these studies only intermittently used neuroimaging with computed tomography, which has limited sensitivity for detection of small lesions in the optic pathway. The purpose of this study was to investigate the association of SN with intracranial abnormalities, particularly OPG, using magnetic resonance imaging of the brain and orbits. Methods Neuroradiology databases at three institutions spanning January 2010 to May 2016 were queried for examinations ordered for evaluation of SN; MRI examinations of the brain and/or orbits were included and evaluated for OPG and other structural abnormalities. Medical records were reviewed to confirm a diagnosis of SN, presence of other underlying neurological disease, or preexisting diagnoses. Results A total of 40 patients with eligible MRI examinations were identified. None had optic nerve pathway gliomas. Two children had optic nerve hypoplasia; no other patients had optic pathway abnormalities. None had intracranial or orbital masses. MRI examinations were normal in 25 patients. Conclusions This series represents the largest collection of MRI examinations for SN in the literature to date and shows no association between OPG and SN. In children presenting with SN but no other findings suggesting OPG or neurological abnormalities, neuroimaging may not be required

children: differentiation using diffusion-weighted magnetic resonance imaging

Purpose To evaluate differences in magnetic resonance imaging (MRI) appearance between infantile hemangiomas and rhabdomyosarcomas of the orbit in pediatric patients using diffusion-weighted imaging. Methods A multicenter retrospective review of MRIs of pediatric patients with infantile hemangiomas and rhabdomyosarcomas of the orbit was performed. MRI examinations from a total of 21 patients with infantile hemangiomas and 12 patients with rhabdomyosarcomas of the orbit were independently reviewed by two subspecialty board-certified neuroradiologists masked to the diagnosis. A freehand region of interest was placed in the mass to obtain the mean apparent diffusion coefficient (ADC) value of the mass as well as within the medulla to obtain a ratio of the ADC mass to the medulla. A t test was used to compare mean ADC and ADC ratios between the two groups. Receiver operating characteristic analysis was performed to determine ADC value and ADC ratio thresholds for differentiation of infantile hemangioma and rhabdomyosarcoma. Results There was a statistically significant difference in the mean ADC value of infantile hemangiomas compared to rhabdomyosarcomas (1527 × 10−6 mm2/s vs 782 × 10−6 mm2/s; P = 0.0001) and the ADC ratio of the lesion to the medulla (1.77 vs 0.92; P = 0.0001). An ADC threshold of <1159 × 10−6 mm2/sec and an ADC ratio of <1.38 differentiated rhabdomyosarcoma from infantile hemangioma (sensitivity 100% and 100%; specificity 100% and 100%) with area under the curve of 1.0 and 1.0, respectively. Conclusions In conjunction with conventional MRI sequences, ADC values obtained from diffusion-weighted MRI are useful to differentiate orbital infantile hemangiomas from rhabdomyosarcomas in pediatric patients

Evidence of early multi-strange hadron freeze-out in high energy nuclear collisions

Recently reported transverse momentum distributions of strange hadrons produced in Pb(158AGeV) on Pb collisions and corresponding results from the relativistic quantum molecular dynamics (RQMD) approach are examined. We argue that the experimental observations favor a scenario in which multi-strange hadrons are formed and decouple from the system rather early at large energy densities (around 1 GeV/fm$^3$). The systematics of the strange and non-strange particle spectra indicate that the observed transverse flow develops mainly in the late hadronic stages of these reactions.Comment: 4 pages, 4 figure

Study of a Nonlocal Density scheme for electronic--structure calculations

An exchange-correlation energy functional beyond the local density approximation, based on the exchange-correlation kernel of the homogeneous electron gas and originally introduced by Kohn and Sham, is considered for electronic structure calculations of semiconductors and atoms. Calculations are carried out for diamond, silicon, silicon carbide and gallium arsenide. The lattice constants and gaps show a small improvement with respect to the LDA results. However, the corresponding corrections to the total energy of the isolated atoms are not large enough to yield a substantial improvement for the cohesive energy of solids, which remains hence overestimated as in the LDA.Comment: 4 postscript figure

Optical application and measurement of torque on microparticles of isotropic nonabsorbing material

We show how it is possible to controllably rotate or align microscopic particles of isotropic nonabsorbing material in a TEM00 Gaussian beam trap, with simultaneous measurement of the applied torque using purely optical means. This is a simple and general method of rotation, requiring only that the particle is elongated along one direction. Thus, this method can be used to rotate or align a wide range of naturally occurring particles. The ability to measure the applied torque enables the use of this method as a quantitative tool--the rotational equivalent of optical tweezers based force measurement. As well as being of particular value for the rotation of biological specimens, this method is also suitable for the development of optically-driven micromachines.Comment: 8 pages, 6 figure