Kentaro Uesugi

Chondrulelike Objects in Short-Period Comet 81P/Wild 2

The Stardust spacecraft returned cometary samples that contain crystalline material, but the origin of the material is not yet well understood. We found four crystalline particles from comet 81P/Wild 2 that were apparently formed by flash-melting at a high temperature and are texturally, mineralogically, and compositionally similar to chondrules. Chondrules are submillimeter particles that dominate chondrites and are believed to have formed in the inner solar nebula. The comet particles show oxygen isotope compositions similar to chondrules in carbonaceous chondrites that compose the middle-to-outer asteroid belt. The presence of the chondrulelike objects in the comet suggests that chondrules have been transported out to the cold outer solar nebula and spread widely over the early solar system.

Low core-mantle boundary temperature inferred from the solidus of pyrolite

Melting Moments The boundary between Earths core and mantle defines where the iron-rich liquid outer core meets the more chemically heterogeneous solid lower mantle and is marked by a sharp thermal gradient of nearly 1500 kelvin. The precise relationship between temperature and melting of the lowermost mantle constrains the structure and heat flow across the core-mantle boundary. In order to identify trace amounts of liquid as melting initiates, Nomura et al. (p. 522, published online 16 January) performed x-ray microtomographic imaging of rocks of a primitive mantle composition that had been subjected to high pressures and temperatures in a diamond anvil cell. The experimentally determined maximum melting point of 3570 kelvin suggests that some phases typically thought to lose stability in the lowermost mantle, such as MgSiO3-rich post-perovskite, may be more widely distributed than expected. High-pressure experiments suggest that Earth’s mantle melts at lower temperatures than previously predicted. The melting temperature of Earth’s mantle provides key constraints on the thermal structures of both the mantle and the core. Through high-pressure experiments and three-dimensional x-ray microtomographic imaging, we showed that the solidus temperature of a primitive (pyrolitic) mantle is as low as 3570 ± 200 kelvin at pressures expected near the boundary between the mantle and the outer core. Because the lowermost mantle is not globally molten, this provides an upper bound of the temperature at the core-mantle boundary (TCMB). Such remarkably low TCMB implies that the post-perovskite phase is present in wide areas of the lowermost mantle. The low TCMB also requires that the melting temperature of the outer core is depressed largely by impurities such as hydrogen.

Effect of Sustained Inflation Length on Establishing Functional Residual Capacity at Birth in Ventilated Premature Rabbits

The effect of inflation length on lung aeration pattern, tidal volumes, and functional residual capacity (FRC) immediately after birth was investigated. Preterm rabbits (28 d), randomized into four groups, received a 1-, 5-, 10-, or 20-s inflation (SI) followed by ventilation with 5 cm H2O end-expiratory pressure. Gas volumes were measured by plethysmography and uniformity of lung aeration by phase contrast x-ray imaging for 7 min. The first inspiratory volume significantly (p < 0.001) increased with inflation duration from a median (IQR) of 0.2 (0.1–3.1) mL/kg for 1-s inflation to 23.4 (19.3–30.4) mL/kg for 20-s SI. The lung was uniformly aerated, and the FRC and tidal volume fully recruited after 20-s SI. A 10-s SI caused a higher FRC (p < 0.05) at 7 min, and a 20-s SI caused a higher FRC (p < 0.05) at 20 s and 7 min than a 1- or 5-s SI. The mean (SD) time for 90% of the lung to aerate was 14.0 (4.1) s using 35 cm H2O peak inflation pressure. In these rabbits, 10- and 20-s SI increased the inspiratory volume and produced a greater FRC, and a 20-s SI uniformly aerated the lung before ventilation started.

On the origin of speckle in x-ray phase contrast images of lung tissue

Phase contrast x-ray imaging of small animal lungs reveals a speckled intensity pattern not seen in other tissues, making the lungs highly visible in comparison to other organs. Although bearing a superficial resemblance to alveoli, the cause of this speckle has not been established. With a view to determining the mechanism for the formation of speckle, this paper details the results of propagation-based phase contrast experiments performed on mice lungs, together with packed glass microspheres used to emulate lung tissue. These experimental studies are compared to numerical simulations, based on wave propagation techniques. We find that speckle arises from focusing effects, with multiple alveoli acting as aberrated compound refractive lenses. Both experiments and modelling suggest that this speckle-formation phenomenon may lead to better screening methods for human lungs than conventional radiography.

Positive end-expiratory pressure enhances development of a functional residual capacity in preterm rabbits ventilated from birth

The factors regulating lung aeration and the initiation of pulmonary gas exchange at birth are largely unknown, particularly in infants born very preterm. As hydrostatic pressure gradients may play a role, we have examined the effect of a positive end-expiratory pressure (PEEP) on the spatial and temporal pattern of lung aeration in preterm rabbit pups mechanically ventilated from birth using simultaneous phase-contrast X-ray imaging and plethysmography. Preterm rabbit pups were delivered by caesarean section at 28 days of gestational age, anesthetized, intubated, and placed within a water-filled plethysmograph (head out). Pups were imaged as they were mechanically ventilated from birth with a PEEP of either 0 cmH(2)O or 5 cmH(2)O. The peak inflation pressure was held constant at 35 cmH(2)O. Without PEEP, gas only entered into the distal airways during inflation. The distal airways collapsed during expiration, and, as a result, the functional residual capacity (FRC) did not increase above the lungs anatomic dead space volume (2.5 +/- 0.8 ml/kg). In contrast, ventilation with 5-cmH(2)O PEEP gradually increased aeration of the distal airways, which did not collapse at end expiration. The FRC achieved in pups ventilated with PEEP (19.9 +/- 3.2 ml/kg) was significantly greater than in pups ventilated without PEEP (-2.3 +/- 3.5 ml/kg). PEEP greatly facilitates aeration of the distal airways and the accumulation of FRC and prevents distal airway collapse at end expiration in very preterm rabbit pups mechanically ventilated from birth.

Dynamic imaging of the lungs using x-ray phase contrast

High quality real-time imaging of lungs in vivo presents considerable challenges. We demonstrate here that phase contrast x-ray imaging is capable of dynamically imaging the lungs. It retains many of the advantages of simple x-ray imaging, whilst also being able to map weakly absorbing soft tissues based on refractive index differences. Preliminary results reported herein show that this novel imaging technique can identify and locate airway liquid and allows lung aeration in newborn rabbit pups to be dynamically visualized.

Electron density measurement with dual-energy x-ray CT using synchrotron radiation.

Monochromatic x-ray computed tomography (CT) at two different energies provides information about electron density of human tissue without ambiguity due to the beam hardening effect. This information makes the treatment planning for proton and heavy-ion radiotherapy more precise. We have started a feasibility study on dual energy x-ray CT by using synchrotron radiation. A translation-rotation scanning CT system was developed for quantitative measurement in order to clarify what precision in the measurement was achieved. Liquid samples of solutions of K2HPO4 and solid samples of tissue equivalent materials were used to simulate human tissue. The experiments were carried out using monochromatic x-rays with energies of 40, 70 and 80 keV produced by monochromatizing synchrotron radiation. The solid samples were also measured in a complementary method using high-energy carbon beams to evaluate the electron densities. The measured electron densities were compared with the theoretical values or the values measured in the complementary method. It was found that these values were in agreement in 0.9% on average. Effective atomic numbers were obtained as well from dual-energy x-ray CT. The tomographic image based on each of the electron densities and the effective atomic number presents a different feature of the material, and its contrast drastically differs from that in a conventional CT image.

X-ray refraction-enhanced imaging and a method for phase retrieval for a simple object.

Refraction-enhanced imaging is now widely used for imaging low-absorption-contrast specimens in the hard X-ray region. However, the interpretation of the details of a refraction-enhanced image is not always clear. In this paper the theoretical treatment of refraction-enhanced imaging and a method for phase retrieval from refraction-contrast images are discussed in comparison with angular-deflection mapping of the transmitting beam. The problems of thick and complicated objects are also discussed.

Inspiration regulates the rate and temporal pattern of lung liquid clearance and lung aeration at birth

At birth, the initiation of pulmonary gas exchange is dependent on air entry into the lungs, and recent evidence indicates that pressures generated by inspiration may be involved. We have used simultaneous plethysmography and phase-contrast X-ray imaging to investigate the contribution of inspiration and expiratory braking maneuvers (EBMs) to lung aeration and the formation of a functional residual capacity (FRC) after birth. Near-term rabbit pups (n = 26) were delivered by cesarean section, placed in a water plethysmograph, and imaged during the initiation of spontaneous breathing. Breath-by-breath changes in lung gas volumes were measured using plethysmography and visualized using phase-contrast X-ray imaging. Pups rapidly (1-5 breaths) generate a FRC (16.2 +/- 1.2 ml/kg) by inhaling a greater volume than they expire (by 2.9 +/- 0.4 ml.kg(-1).breath(-1) over the first 5 breaths). As a result, 94.8 +/- 1.4% of lung aeration occurred during inspiration over multiple breaths. The incidence of EBMs was rare early during lung aeration, with most (>80%) occurring after >80% of max FRC was achieved. Although EBMs were associated with an overall increase in FRC, 34.8 +/- 5.3% of EBMs were associated with a decrease in FRC. We conclude that lung aeration is predominantly achieved by inspiratory efforts and that EBMs help to maintain FRC following its formation.

IMAGING LUNG AERATION AND LUNG LIQUID CLEARANCE AT BIRTH USING PHASE CONTRAST X‐RAY IMAGING

1 The transition to extra‐uterine life at birth is critically dependent on airway liquid clearance to allow the entry of air and the onset of gaseous ventilation. We have used phase contrast X‐ray imaging to identify factors that regulate lung aeration at birth in spontaneously breathing term and mechanically ventilated preterm rabbit pups. 2 Phase contrast X‐ray imaging exploits the difference in refractive index between air and water to enhance image contrast, enabling the smallest air‐filled structures of the lung (alveoli; < 100 µm) to be resolved. Using this technique, the lungs become visible as they aerate, allowing the air–liquid interface to be observed as it moves distally during lung aeration. 3 Spontaneously breathing term rabbit pups rapidly aerate their lungs, with most fully recruiting their functional residual capacity (FRC) within the first few breaths. The increase in FRC occurs mainly during individual breaths, demonstrating that airway liquid clearance and lung aeration is closely associated with inspiration. We suggest that transpulmonary pressures generated by inspiration provide a hydrostatic pressure gradient for the movement of water out of the airways and into the surrounding lung tissue after birth. 4 In mechanically ventilated preterm pups, lung aeration is closely associated with lung inflation and a positive end‐expiratory pressure is required to generate and maintain FRC after birth. 5 In summary, phase contrast X‐ray imaging can image the air‐filled lung with high temporal and spatial resolution and is ideal for identifying factors that regulate lung aeration at birth in both spontaneously breathing term and mechanically ventilated preterm neonates.