In this report, a Ti:Sapphire oscillator was utilized to realize synchronization-free stimulated emission depletion (STED) microscopy. With pump power of 4.6 W and sample irradiance of 310 mW, we achieved super-resolution as high as 71 nm. With synchronization-free STED, we imaged 200 nm nanospheres as well as all three cytoskeletal elements (microtubules, intermediate filaments, and actin filaments), clearly demonstrating the resolving power of synchronization-free STED over conventional diffraction limited imaging. It also allowed us to discover that, Dylight 650, exhibits improved performance over ATTO647N, a fluorophore frequently used in STED. Furthermore, we applied synchronization-free STED to image fluorescently-labeled intracellular viral RNA granules, which otherwise cannot be differentiated by confocal microscopy. Thanks to the widely available Ti:Sapphire oscillators in multiphoton imaging system, this work suggests easier access to setup super-resolution microscope via the synchronization-free STED.
Background: Anterior cruciate ligament (ACL) injury and reconstruction in the skeletally immature patient are becoming more common. The purpose of this study was to develop a reproducible anatomic ACL reconstruction technique, based on intra-articular and extra-articular landmarks, that reliably produces a femoral tunnel of adequate length and diameter while avoiding the distal femoral physis. Methods: Magnetic resonance images (MRIs) of one hundred and eighty-eight children (age range, six to seventeen years) were evaluated. Two extra-articular landmarks, the femoral insertion of the popliteus tendon and the lateral femoral epicondyle, and one intra-articular landmark, the central portion of the femoral footprint of the ACL, were identified. Computer software was used to plot these landmarks in all three planes and to draw lines representing two potential femoral tunnels. The first line connected the center of the ACL femoral footprint with the insertion of the popliteus tendon, and the second connected the center of the ACL femoral footprint with the lateral femoral epicondyle. The length of each tunnel, the shortest distance from the center of each tunnel to the distal femoral physis, and the height of the lateral femoral condyle from the physis to the chondral surface and to the base of the cartilage cap were calculated. A threedimensional MRI reconstruction was used to confirm that placement of a femoral tunnel with use of the chosen landmarks would avoid the distal femoral physis. Results: The mean distance from the center of the preferred ACL tunnel, which connected the center of the ACL femoral footprint with the insertion of the popliteus tendon, to the distal femoral physis was 12 mm, independent of sex (p = 0.94) or age, and the shortest distance was 8 mm. The length of this proposed tunnel averaged 30.1 mm in the boys and 27.4 mmin the girls (p < 0.001), and it averaged 25.4mmat an age of six years and 29.7mmat an age of seventeen years. The mean distance from the center of the alternative tunnel, which connected the center of the ACL femoral footprint with the lateral epicondyle, to the distal femoral physis was 8.8mmin the boys and 8.9mmin the girls (p = 0.55). The mean length of this alternative tunnel was 34.3 mm in the boys and 31.6 mm in the girls (p < 0.001). Conclusions: Drilling from the center of the ACL femoral footprint to the insertion of the popliteus tendon would have resulted in a mean tunnel length of 27 to 30 mm, and it would have allowed the safe placement of a femoral tunnel at least 7 mm in diameter in a patient six to seventeen years old. The center of the ACL femoral footprint and the popliteus insertion are easily identifiable landmarks and will allow safe, reproducible, anatomic ACL reconstruction in the skeletally immature patient. Copyright
by
Kartik S. Sundareswaran;
Christopher M. Haggerty;
Diane de Zelicourt;
Lakshmi P. Dasi;
Kerem Pekkan;
David H. Frakes;
Andrew J. Powell;
Kirk R Kanter;
Mark A. Fogel;
Ajit Yoganathan
Objective: Our objective was to analyze 3-dimensional (3D) blood flow patterns within the total cavopulmonary connection (TCPC) using in vivo phase contrast magnetic resonance imaging (PC MRI).
Methods: Sixteen single-ventricle patients were prospectively recruited at 2 leading pediatric institutions for PC MRI evaluation of their Fontan pathway. Patients were divided into 2 groups. Group 1 comprised 8 patients with an extracardiac (EC) TCPC, and group 2 comprised 8 patients with a lateral tunnel (LT) TCPC. A coronal stack of 5 to 10 contiguous PC MRI slices with 3D velocity encoding (5-9 ms resolution) was acquired and a volumetric flow field was reconstructed.
Results: Analysis revealed large vortices in LT TCPCs and helical flow structures in EC TCPCs. On average, there was no difference between LT and EC TCPCs in the proportion of inferior vena cava flow going to the left pulmonary artery (43% ± 7% vs 46% ± 5%; P = .34). However, for EC TCPCs, the presence of a caval offset was a primary determinant of inferior vena caval flow distribution to the pulmonary arteries with a significant bias to the offset side.
Conclusions: 3D flow structures within LT and EC TCPCs were reconstructed and analyzed for the first time using PC MRI. TCPC flow patterns were shown to be different, not only on the basis of LT or EC considerations, but with significant influence from the superior vena cava connection as well. This work adds to the ongoing body of research demonstrating the impact of TCPC geometry on the overall hemodynamic profile.
Total cavopulmonary connection is the result of a series of palliative surgical repairs performed on patients with single ventricle heart defects. The resulting anatomy has complex and unsteady hemodynamics characterized by flow mixing and flow separation. Although varying degrees of flow pulsatility have been observed in vivo, non-pulsatile (time-averaged) boundary conditions have traditionally been assumed in hemodynamic modeling, and only recently have pulsatile conditions been incorporated without completely characterizing their effect or importance. In this study, 3D numerical simulations with both pulsatile and non-pulsatile boundary conditions were performed for 24 patients with different anatomies and flow boundary conditions from Georgia Tech database. Flow structures, energy dissipation rates and pressure drops were compared under rest and simulated exercise conditions. It was found that flow pulsatility is the primary factor in determining the appropriate choice of boundary conditions, whereas the anatomic configuration and cardiac output had secondary effects. Results show that the hemodynamics can be strongly influenced by the presence of pulsatile flow. However, there was a minimum pulsatility threshold, identified by defining a weighted pulsatility index (wPI), above which the influence was significant. It was shown that when wPI < 30%, the relative error in hemodynamic predictions using time-averaged boundary conditions was less than 10% compared to pulsatile simulations. In addition, when wPI < 50, the relative error was less than 20%. A correlation was introduced to relate wPI to the relative error in predicting the flow metrics with non-pulsatile flow conditions.