J.P.H.M. van den Wijngaard

Placental Characteristics of Monoamniotic Twin Pregnancies in Relation to Perinatal Outcome

OBJECTIVE To study placental characteristics in relation to perinatal outcome in 55 pairs of monochorionic monoamniotic (MA) twins. METHODS Between January 1998 and May 2008 55 pairs of MA twins were delivered in 4 tertiary care centers and analysed for mortality, birth weight discordancy and twin-to-twin transfusion syndrome (TTTS) in relation to type of anastomoses, type and distance between cord insertions and placental sharing. Five acardiac twins, 2 conjoined twins, 4 higher order multiples and one early termination of pregnancy were excluded, leaving 43 MA placentas for analysis. Of these 43, one placenta could not be analysed for placental vascular anastomoses due to severe maceration after single intra-uterine demise leaving 42 placentas for analysis of anastomoses. RESULTS Arterio-arterial (AA), venovenous (VV) and arteriovenous (AV) anastomoses were detected in 98%, 43% and 91% of MA placentas, respectively. Velamentous cord insertion was found in 4% of cases. Small distance between both umbilical cord insertions (<5 cm) was present in 53% of MA placentas. Overall perinatal loss rate was 22% (19/86). We found no association between mortality and type of anastomoses, type and distance between cord insertions and placental sharing. The incidence of TTTS was low (2%) and occurred in the only pregnancy with absent AA-anastomoses. CONCLUSION Perinatal mortality in MA twins was not related to placental vascular anatomy. The almost ubiquitous presence of compensating AA-anastomoses in MA placentas appears to prevent occurrence of TTTS.

Fetoscopic laser treatment of twin-to-twin transfusion syndrome followed by severe twin anemia-polycythemia sequence with spontaneous resolution

We present a case of twin anemia-polycythemia sequence after laser surgery for twin-to-twin transfusion syndrome which resolved spontaneously. No residual anastomoses were identified after placental injection with colored dye. We discuss the possible pathogenetic mechanisms that may have led to this remarkable clinical course and discuss the various management options.

Model-Based Vasculature Extraction From Optical Fluorescence Cryomicrotome Images

The aim of this study was to develop a novel method to reconstruct 3-D coronary vasculature from cryomicrotome images, comprised of two distinct sets of data-fluorescent microsphere beads and coronary vasculature. Fluorescent beads and cast injected into the vasculature were separately imaged with different filter settings to obtain the microsphere and vascular data, respectively. To extract the vascular anatomy, light scattering in the tissue was modelled using a point spread function (PSF). The PSF was parametrized by optical tissue excitation and emission attenuation coefficients, which were estimated by fitting simulated images of microspheres convolved with the PSF model to the experimental microsphere images. These parameters were then applied within a new model-based method for vessel radius estimation. Current state-of-the-art radii estimation methods and the proposed model-based method were applied on vessel phantoms. In this validation study, the full-width half-maximum method of radii estimation, when performed on the raw data without correcting for the optical blurring, resulted in 42.9% error on average for the 170&nbsp;μm vessel. In comparison, the model-based method resulted in 0.6% error on average for the same phantom. Whole-organ porcine coronary vasculature was automatically reconstructed with the new model-based vascular extraction method.

Simulated Sequential Laser Therapy of Twin–Twin Transfusion Syndrome

Sequential laser therapy of twin-twin transfusion syndrome (TTTS) includes laser obliteration of arteriovenous (AV) anastomoses from donor to recipient (AVDR) before obliterating AV anastomoses from recipient to donor (AVRD). This strategy allows for a beneficial intra-operative transfusion of blood from the hypervolemic recipient to the hypovolemic donor. In the present study, we sought to analyze the benefits and risks of sequential laser therapy with our computational model to aid its more widespread introduction. We simulated an equally shared placenta with an AVDR and a smaller diameter AVRD causing TTTS at 20 weeks. Laser coagulation and various volumes and directions of inter-twin transfusion were simulated at 21 weeks. A typical result is that when an AVDR is coagulated first, and 10 min later the AVRD with inner diameter of about 1 mm, an inter-twin transfusion of 25 ml may result from the recipient to the donor, based on literature data of AV flow versus diameter. This procedure causes a simulated loss of 50% of the recipients blood volume. The opposite coagulation sequence, thus coagulating the AVRD first, 10 min later followed by the AVDR of 1 mm inner diameter, causes a loss of the donors blood volume of 64%. In conclusion, our simulations support the concept of sequential laser therapy for TTTS and suggest directions for an improved safety and efficacy of this strategy.

Perfusion territories subtended by penetrating coronary arteries increase in size and decrease in number toward the subendocardium

Blood flow distribution within the myocardium and the location and extent of areas at risk in case of coronary artery disease are dependent on the distribution and morphology of intramural vascular crowns. Knowledge of the intramural vasculature is essential in novel multiscale and multiphysics modeling of the heart. For this study, eight canine hearts were analyzed with an imaging cryomicrotome, developed to acquire high-resolution spatial data on three-dimensional vascular structures. The obtained vasculature was skeletonized, and for each penetrating artery starting from the epicardium, the dependent vascular crown was defined. Three-dimensional Voronoi tessellation was applied with the end points of the terminal segments as center points. The centroid of end points in each branch allowed classification of the corresponding perfusion territories in subendocardial, midmyocardial, and subepicardial. Subendocardial regions have relatively few territories of about 0.5 ml in volume having their own penetrating artery at the epicardium, whereas the subepicardium is perfused by a multitude of small perfusion territories, in the order of 0.01 ml. Vascular volume density of small arteries up till 400 μm was 3.2% at the subendocardium territories but only 0.8% in the subepicardium territories. Their higher volume density corresponds to compensation for flow impeding forces by cardiac contraction. These density differences result in different scaling law properties of vascular volume and tissue mass per territory type. This novel three-dimensional quantitative analysis may form the basis for patient-specific computational models on coronary perfusion and aid the interpretation of image-based clinical methods for assessing the transmural perfusion distribution.

Laser-induced (endo)vascular photothermal effects studied by combined brightfield and fluorescence microscopy in hamster dorsal skin fold venules

The putative features of the (endo)vascular photothermal response, characterized by laser-induced thermal denaturation of blood and vessel wall constituents, have been elucidated individually, but not simultaneously in dynamic, isolated in vivo systems. A hamster dorsal skin fold model in combination with brightfield/fluorescence intravital microscopy was used to examine the effect of laser pulse duration and blood flow velocity on the size of the thermal coagulum, its attachment behavior, and laser-mediated vasomotion. The size of the coagulum and the extent of vasoconstriction and latent vasodilation were proportional to the laser pulse duration, but pulse duration had no effect on coagulum attachment/dislodgement. Blood flow velocity exhibited no significant effect on the studied parameters. The (endo)vascular photothermal response is governed predominantly by laser energy deposition and to a marginal extent by blood flow velocity.

Intrauterine transfusion combined with partial exchange transfusion for twin anemia polycythemia sequence: Modeling a novel technique

INTRODUCTION Twin anemia-polycythemia sequence (TAPS) is a newly described disease in monochorionic twin pregnancies, characterized by large inter-twin hemoglobin differences. Optimal management for TAPS is not clear. One of the possible treatment modalities is intrauterine blood transfusion (IUT) in the donor with or without combination of partial exchange transfusion (PET) in the recipient. METHODS We applied a computational model simulation to illustrate the mechanism of IUT with and without PET in TAPS occurring after laser surgery for twin-twin transfusion syndrome (TTTS). Model simulations were performed with the representative anastomotic pattern as observed during laser intervention, and after placental dye injection. RESULTS The model was tested against different cases where IUT was combined with PET for the treatment of post-laser TAPS. Model simulations using the observed anastomotic pattern showed a significant reduction of hyperviscosity in the recipient after IUT/PET compared to IUT without PET. DISCUSSION In this model simulation we show that the addition of PET to IUT reduces the severity of polycythemia in the recipient. PET may thus be important to prevent complications of hyperviscosity. CONCLUSION This model simulation shows the beneficial effect of PET for the recipient in TAPS cases treated with IUT.

Influence of segmented vessel size due to limited imaging resolution on coronary hyperemic flow prediction from arterial crown volume

Computational predictions of the functional stenosis severity from coronary imaging data use an allometric scaling law to derive hyperemic blood flow (Q) from coronary arterial volume (V), Q = αV(β) Reliable estimates of α and β are essential for meaningful flow estimations. We hypothesize that the relation between Q and V depends on imaging resolution. In five canine hearts, fluorescent microspheres were injected into the left anterior descending coronary artery during maximal hyperemia. The coronary arteries of the excised heart were filled with fluorescent cast material, frozen, and processed with an imaging cryomicrotome to yield a three-dimensional representation of the coronary arterial network. The effect of limited image resolution was simulated by assessing scaling law parameters from the virtual arterial network at 11 truncation levels ranging from 50 to 1,000 μm segment radius. Mapped microsphere locations were used to derive the corresponding relative Q using a reference truncation level of 200 μm. The scaling law factor α did not change with truncation level, despite considerable intersubject variability. In contrast, the scaling law exponent β decreased from 0.79 to 0.55 with increasing truncation radius and was significantly lower for truncation radii above 500 μm vs. 50 μm (P< 0.05). Hyperemic Q was underestimated for vessel truncation above the reference level. In conclusion, flow-crown volume relations confirmed overall power law behavior; however, this relation depends on the terminal vessel radius that can be visualized. The scaling law exponent β should therefore be adapted to the resolution of the imaging modality.

P06.08: Monitoring of sacrococcygeal teratoma: clinical evaluation of a computerised model

I Portal sinus 2 (12.5%) Persistent right umbilical vein II Ductus venosus 0 III Hepatic veins 0 IV Four chambers 5 (31.3%) Ventricular septal defect Auriculoventricular asymmetry Dilated coronary sinus Tricuspid insufficiency (2) V Left ventricular outflow tract 2 (12.5%) Truncus vs pulmonary atresia Dilated aorta VI Right ventricular outflow tract 2 (12.5%) Truncus vs pulmonary atresia Dilated pulmonary artery VII Three vessels-trachea 11 (68.8%) Aberrant right subclavian artery (6) Persistent left superior vena cava (2) Truncus vs pulmonary atresia Dilated aorta Dilated pulmonary artery VIII Thy-box 2 (12.5%) Absence of innominate vein Impossible to see thymus IX Subclavian arteries 6 (37.5%) Aberrant right subclavian artery

High-Resolution Spatial Quantification of Coronary Collaterals with an Imaging Cryomicrotome

Ischemia and subsequent infarction may occur when blood supply to the heart is impeded by coronary artery disease. Stimulating coronary collateral formation may provide a last resort in patients were the cardiac muscle cannot be successfully reperfused by conventional surgery. However, detailed information on the mechanism of collateral formation is needed. Therefore, we propose a new method of acquiring information on the spatial organization of vascular beds and the distribution of collateral-dependent perfusion of myocardial tissue.