OAR@UM Community:

Comparison of arterial spin-labeling and DSC perfusion MR imaging in pediatric brain tumors : a systematic review and meta-analysis

2025-12-16T14:01:57Z

Title: Comparison of arterial spin-labeling and DSC perfusion MR imaging in pediatric brain tumors : a systematic review and meta-analysis Authors: Vella, Stephanie; Lauri, Josef; Grech, Reuben Abstract: BACKGROUND: Brain tumors are a leading cause of mortality in children. Accurate tumor grading is essential to plan treatment and for prognostication. Perfusion imaging has been shown to correlate well with tumor grade in adults, however there are fewer studies in pediatric patients. Moreover, there is no consensus regarding which MR perfusion technique demonstrates the highest accuracy in the latter population. PURPOSE: We sought to compare the diagnostic test accuracy of DSC and arterial spin-labeling (ASL), in their ability to differentiate between low- and high-grade pediatric brain tumors at first presentation. DATA SOURCES: Articles were retrieved from online electronic databases: MEDLINE (Ovid), Web of Science Core Collection, and Scopus. STUDY SELECTION: Studies in pediatric patients with a treatment-naïve diagnosed brain tumor and imaging including either ASL or DSC or both, together with a histologic diagnosis were included. Studies involving adult patient or mixed age populations, studies with incomplete data, and those that used dynamic contrast-enhanced perfusion were excluded. DATA ANALYSIS: The sensitivities and specificities obtained from each study were used to calculate the true-positive, true-negative, false-positive, and false-negative count. A case was defined as a histologically proved high-grade tumor. The random-effect model was used to merge statistics. Significance level was set at P < .05. DATA SYNTHESIS: Forest plots showing pairs of sensitivity and specificity, with their 95% CIs, were constructed for each study. The bivariate model was applied to account for between-study variability. The summary receiver operating characteristics (SROC) plots were constructed from the obtained data sets. The area under the curve for the SROC of all studies was estimated to determine the overall diagnostic test accuracy of perfusion MRI, followed by a separate comparison of the SROC of ASL versus DSC studies. LIMITATIONS: There was a small and heterogeneous sample size. CONCLUSIONS: The diagnostic accuracy of ASL was found to be comparable and not inferior to DSC, thus its use in the diagnostic assessment of pediatric patients should continue to be supported.

On (r,c)-constant, planar and circulant graphs

2025-11-06T10:56:40Z

Title: On (r,c)-constant, planar and circulant graphs Authors: Caro, Yair; Mifsud, Xandru Abstract: This paper concerns (r, c)-constant graphs, which are r-regular graphs in which the subgraph induced by the open neighbourhood of every vertex has precisely c edges. The family of (r, c)-graphs contains vertex-transitive graphs (and in particular Cayley graphs), graphs with constant link (sometimes called locally isomorphic graphs), (r, b)-regular graphs, strongly regular graphs, and much more. This family was recently introduced in [6], serving as an important tool in constructing flip graphs [6, 14]. In this paper we shall mainly deals with the following. (i) Existence and non-existence of (r, c)-planar graphs. We completely determine the cases of existence and non-existence of such graphs and supply the smallest order in the case when they exist. (ii) We consider the existence of (r, c)-circulant graphs. We prove that for c ≡ 2 (mod 3) no (r, c)-circulant graph exists and that for c ≡ 0, 1 (mod 3), c > 0 and r ≥ 6 + √8c−5/3 there exist (r, c)-circulant graphs. Moreover for c = 0 and r ≥ 1, (r, 0)-circulants exist. (iii) We consider the existence and non-existence of small (r, c)-constant graphs, supplying a complete table of the smallest order of graphs we found for 0 ≤ c ≤ C(r, 2) and r ≤ 6. We shall also determine all the cases in this range for which (r, c)-constant graphs do not exist. We establish a public database of (r, c)-constant graphs for varying r, c and order.

Approximating photon trajectories in spherically symmetric spacetimes

2025-11-03T14:57:17Z

Title: Approximating photon trajectories in spherically symmetric spacetimes Authors: Sultana, Joseph Abstract: In this paper we use the Homotopy analysis method to obtain an analytic approximation for the entire photon trajectory in the Schwarzschild spacetime. This is usually expressed exactly in terms of an elliptic integral. We compare our approximation with other formulae found in the literature, which were specifically obtained for the Schwarzschild solution. Unlike some of these formulae, our approximation can be applied and maintains a good accuracy for emission point close to the event horizon and also for emission angles close to and greater than π/2. We show that our method can easily be applied to other spherically symmetric solutions such as the Reissner-Nordström solution. Such an approximation would be useful when accurate determination of the light trajectories around compact objects is required without the need to revert to time consuming numerical integration of elliptic integrals.

Reconstruction of shear force in atomic force microscopy from measured displacement of the cone-shaped cantilever tip

2025-09-22T12:27:35Z

Title: Reconstruction of shear force in atomic force microscopy from measured displacement of the cone-shaped cantilever tip Authors: Hasanov, Alemdar; Kawano, Alexandre; Baysal, Onur Abstract: In this paper, a dynamic model of reconstruction of the shear force g(t) in the Atomic Force Microscopy (AFM) cantilever tip-sample interaction is proposed. The interaction of the cone-shaped cantilever tip with the surface of the specimen (sample) is modeled by the damped Euler-Bernoulli beam equation ρ A ( x ) u t t + μ ( x ) u t + ( r ( x ) u x x + κ ( x ) u x x t ) x x = 0 , ( x , t ) ∈ ( 0 , ℓ ) × ( 0 , T ) , subject to the following initial, u(x,0)=0, u t ( x , 0 ) = 0 and boundary, u(0,t)=0, u x ( 0 , t ) = 0 , ( r ( x ) u x x ( x , t ) + κ ( x ) u x x t ) x = ℓ = M ( t ) , ( − ( r ( x ) u x x + κ ( x ) u x x t ) x ) x = ℓ = g ( t ) conditions, where M ( t ) : = 2 h cos ⁡ θ g ( t ) / π is the momentum generated by the transverse shear force g(t). For the reconstruction of g(t) the measured displacement ν ( t ) : = u ( ℓ , t ) is used as an additional data. The least square functional J ( F ) = 1 2 ∥ u ( ℓ , ⋅ ) − ν ∥ L 2 ( 0 , T ) 2 is introduced and an explicit gradient formula for the Fr\'echet derivative through the solution of the adjoint problem is derived. This allows to construct a gradient based numerical algorithm for the reconstructions of the shear force from noise free as well as from random noisy measured output ν ( t ) . Computational experiments show that the proposed algorithm is very fast and robust. This allows to develop a numerical "gadget" for computational experiments of generic AFMs.