Pure Ir Research Articles

NiIr nanowireassembles as an efficient electrocatalyst towards oxygen evolution reaction in both acid and alkaline media.

Oxygen evolution reaction (OER) is the rate-limiting step in water electrolysis due to its sluggish kinetic, and it is challenging to develop an OER catalyst that could work efficiently in both acid and alkaline environment. Herein, NiIr nanowire assembles (NAs) with unique nanoflower morphology were prepared by a facile hydrothermal method. As a result, the NiIr NAs exhibited superior OER activity in both acid and alkaline media. Specifically, in 0.1 M HClO4, NiIr NAs presented a superior electrocatalytic performance with a low overpotential of merely 242 mV at 10 mA cm-2 and a Tafel slope of only 58.1 mV dec-1, surpassing that of commercial IrO2 and pure Ir NAs. And it achieved a significantly higher mass activity of 148.40 A/g at -1.5 V versus RHE. In 1.0 M KOH, NiIr NAs has an overpotential of 291 mV at 10 mA cm-2 and a Tafel slope of 42.1 mV dec-1. Such remarkable activity makes the NiIr NAs among the best of recently reported representative Ir-based OER electrocatalysts. Density functional theory (DFT) calculations confirmed alloying effect promotes surface bonding of NiIr with oxygen-containing reactants, resulting in excellent catalytic properties.

High resistance towards electrochemical dissolution of cubic Rh@Ir core shell in acidic water splitting

The industrial development of acidic water splitting significantly counts on the activity associated with stability of oxygen evolution reaction (OER) electrocatalyst. In this work, we have constructed cubic Rh@Ir core–shell for acidic water splitting. The formed Rh@Ir electrocatalyst shows a high HER performance with only 29 mV overpotential for 10 mA cm−2, stemming from the upshifted and downshifted d band center of Ir and Rh, leading to a moderate hydrogen binding strength. The Ir atom donates its electrons to nearby Rh atoms triggering a high susceptibility in nucleophilic attack by H2O to generate *OOH; thereby, the overpotential required to achieve 10 mA cm−2 is 216 mV for Rh@Ir core–shell, better than commercial IrO2. Moreover, the stability is superior to commercial IrO2 and pure Ir electrocatalyst due to the strong electronic interplay in Rh@Ir contributing to a better resistance towards electrochemical dissolution proved by operando Raman and electrochemical impedance spectroscopies. Only 1.55 V is needed for Rh@Ir to drive overall water splitting at 10 mA cm−2.

Robust superconductivity and the suppression of charge-density wave in the quasi-skutterudites Ca3(Ir1−xRhx)4Sn13 single crystals at ambient pressure

Single crystals of the quasi-skutterudite compounds Ca3(Ir1-xRhx)4Sn13 (3–4–13) were synthesized by flux growth and characterized by x-ray diffraction, energy dispersive x-ray spectroscopy, magnetization, resistivity, and radio frequency magnetic susceptibility techniques. The coexistence and competition between the charge density wave (CDW) and superconductivity was studied by varying the Rh/Ir ratio. The superconducting transition temperature, Tc , varies from 7 K in pure Ir (x = 0) to 8.3 K in pure Rh (x = 1). Temperature-dependent electrical resistivity reveals monotonic suppression of the CDW transition temperature, T CDW(x). The CDW starts in pure Ir, x = 0, at T CDW ≈ 40 K and extrapolates roughly linearly to zero at xc≈ 0.53–0.58 under the superconducting dome. Magnetization and transport measurements show a significant influence of CDW on superconducting and normal states. Meissner expulsion is substantially reduced in the CDW region, indicating competition between the CDW and superconductivity. The low-temperature resistivity is higher in the CDW part of the phase diagram, consistent with the reduced density of states due to CDW gapping. Its temperature dependence just above Tc shows signs of non-Fermi liquid behavior in a cone-like composition pattern. We conclude that the Ca3(Ir1-xRhx)4Sn13 alloy is a good candidate for a composition-driven quantum critical point at ambient pressure.

Theoretical study of N2 adsorption and dissociation on Ir/Cu loaded Ir(100) catalyst

Electrocatalytic nitrogen reduction (NRR) is a promising method for NH3 synthesis. However, the design of catalysts with high activity for N2 dissociation remains a key challenge. Herein, we have designed several catalysts based on Ir, including pure Ir(100), and Ir(100) with Ir (Cu) atom loaded on it (denoted as Ir(a)@Ir(100) and Cu(a)@Ir(100)), to study the reactivity of N2 dissociation. The results showed that Ir(a)@Ir(100) and Cu(a)@Ir(100) can effectively activate NN bond with ultralow dissociation barriers of 0.31 eV and 0.61 eV. However, the adsorption strength of N2 is significantly poor on Ir(a)@Ir(100) (−0.24 eV) compared to that on Cu(a)@Ir(100) (−0.62 eV). This can be interpreted from the electronic properties: The Ir-5d states can hybridize with N-2π* states significantly near the Fermi level, which is absence for Cu-3d states. Therefore, the loaded Cu atom on Cu@Ir(100) can effectively decrease the occupation of N2 antibonding orbitals (ICOHP = −7.68) compared to the situation on Ir@Ir(100) (ICOHP = −7.35). Therefore, Cu(a)@Ir(100) can be screened as the favorable candidate although a little higher dissociation barrier of N2 (0.61 eV), compared to the situation on Ir(a)@Ir(100) (0.31 eV). However, a barrier of 0.61 eV can also be easily overcome at room temperature as 0.31 eV on Ir(a)@Ir(100). We firmly believe that this work can not only open a novel way for the design of Ir-based catalysts, but also provide a promising strategy of N2 dissociation for experimental works.

High-Performance Iridium-Molybdenum Oxide Electrocatalysts for Water Oxidation in Acid: Bayesian Optimization Discovery and Experimental Testing.

Ir oxides are costly and scarce catalysts for oxygen evolution reaction (OER) in acid. There has been extensive interest in developing alternatives that are either Ir-free or require smaller amounts of Ir to drive the reactions at acceptable rates. One design strategy is to identify Ir-based mixed oxides that achieve similar performance while requiring smaller amounts of Ir. The obstacle to this strategy has been a very large phase space of the Ir-based mixed metal oxides, in terms of the metals combined with Ir and the different crystallographic structures of the mixed oxides, which prevents a thorough exploration of possible materials. In this work, we developed a workflow that uses machine-learning-aided Bayesian optimization in combination with density functional theory to make the exploration of this phase space plausible. This screening identified Mo as a promising dopant for forming acid-tolerant Ir-based oxides for the OER. We synthesized and characterized the Ir-Mo mixed oxides in the form of thin-film electrocatalysts with a known surface area. We show that these mixed oxides exhibited overpotentials ∼30 mV lower than a pure Ir control while maintaining 24% lower Ir dissolution rates than the Ir control. These findings suggest that Mo is a promising dopant and highlight the promise of machine learning to guide the experimental exploration and optimization of catalytic materials.

Supported-Ir Catalysts: The Impact of the Supports' Chemical Composition on the Oxygen Evolution Reaction

In water electrolyzer cells, the anode electrode is one of the most important components, where the oxygen evolution reaction (OER) takes place. In this process, the water molecules split into oxygen ions, protons, and electrons, and the oxygen gas is produced on the anode surface [1]. The most suitable materials that catalyze OER are ruthenium, iridium, and their oxides, but their cost and scarcity require reduction and enhancement of their utilization [2]. One morphological strategy consists of the dispersion of the active nanoparticles in supportive nanoparticles made of less expensive materials to increase their mass activity. In addition, due to the high potential reached during operating conditions for water splitting, supportive materials have to possess a high corrosion resistance. Titanium oxides are good candidates because of their high thermal and chemical stability, low cost, and commercial availability [3]. But their poor electric conductivity (∼10−6 S cm−1) makes the design of an active and stable catalyst a complex task. In this work, Ir nanoparticles have been synthesized on the surface of several Ti-based nanoparticles and a complete analysis of their physicochemical properties have been carried out ( Fig. 1a-b ). In addition, electrochemical behaviour has been tested ex-situ in a half cell by the rotating disk electrode technique and after, the catalysts have been deposited in a polymer membrane for testing in-situ in a single cell proton exchange membrane water electrolyzer. The results show a successful performance of the supported Ir/TiO2 nanoparticles comparable to the pure Ir black nanoparticles but with an active metal loading five times lower. Differently, even though TiC showed excellent electrical conductivity during the ex-situ characterization, Ir/TiC nanoparticles had a poor activity after just one day of performance in the WE due to the complete oxidation of the TiC into TiO2 ( Fig. 1c-d ). Finally, Ir/TiB2 showed a balanced result in terms of activity and stability, showing promising properties as a catalyst for PEM-WE. Sadhasivam T., Ho-Young J. Chapter 3 - Nanostructured bifunctional electrocatalyst support materials for unitized regenerative fuel cells// Nanostructured, Functional, and Flexible Materials for Energy Conversion and Storage Systems- 2020.- 69-103. Antolini E. Iridium as Catalyst and Cocatalyst for Oxygen Evolution /Reduction in Acidic Polymer Electrolyte Membrane Electrolyzers and Fuel Cells // ACS Catal. - 2014.- 4, N 5.- P. 1426-1440. Van Pham C., Bühler M. IrO2 coated TiO2 core-shell microparticles advance performance of low loading proton exchange membrane water electrolyzers// Applied Catalysis B: Environmental-2020.- P 269.- P. 118762. Figure 1. TEM image of Ir/TIO2 (a), EDX mapping of Ir/TiO2(b), linear sweep voltammetry of catalysts (c), the current density at given potential 1.80 V (d). Figure 1

Oxidation behaviors of Ir[sbnd]Hf and Ir[sbnd]Zr coatings under different air pressures at 1800 °C

In order to improve the oxidation resistance of Ir, multilayer IrHf and IrZr coatings with gradually increasing content of alloying elements from inside out were formed in situ on Ir by pack cementation. The oxidation behaviors and microstructural evolution of the IrHf and IrZr coatings oxidized under different air pressures at 1800 °C for 1 h were explored and the oxidation mechanisms were revealed. The results showed that the oxidation resistances of the IrHf and IrZr coatings at 1800 °C were much better than that of pure Ir and increased with the decrease of pressure. At 101 kPa, the mass loss rates of the IrHf and IrZr coatings were 0.52 × 10−3 and 0.48 × 10−3 mg·cm−2·s−1, respectively. The as-oxidized IrHf and IrZr coatings mostly exhibited morphologies of internal oxidation with a quasi-gradient transition structure and both coatings were prone to external oxidation with decreasing pressure. The critical pressure for the internal to external oxidation transition of the IrZr coatings was ~1 kPa and higher than that of the IrHf coatings.

Tailoring the Electronic Structure of Ir Alloy Electrocatalysts through Lanthanide (La, Ce, Pr, and Nd) for Acidic Oxygen Evolution Enhancement

The oxygen evolution reaction (OER) is critical for renewable energy conversion and storage devices. However, the rational design of electrocatalysts with suitably high efficiency and stability in strongly acidic electrolytes remains a major challenge. Herein, a solid‐phase synthesis strategy is developed for the preparation of Ir‐Ln (Ln = La, Ce, Pr, Nd) alloy nanoparticles with uniform particle size on carbon supports as superior acidic OER catalysts. Tailoring by the rare earth (RE) elements, Ir2Pr achieves a maximum mass activity of 2.10 A mg−1Ir at 300 mV overpotential and stability over 200 h at 10 mA cm−2 in 0.5 m H2SO4, which is 9.5 and 20 times higher to pure Ir nanoparticles. Furthermore, Ir2Pr alloy nanoparticles exhibit excellent durability in strongly acidic electrolytes. Theoretical calculations have confirmed that the OER performances are strongly related to the RE elements in the alloy, where the d‐band centers show a consistent trend with the overpotential. Moreover, the highest electroactivity of Ir2Pr is attributed to the improved electron transfer by 4f orbitals and the suitable binding strength of intermediates. Herein, a fundamental understanding of the lanthanide–electrochemical performance relationship is provided and will also inspire the rational design of efficient nanoscale RE alloy electrocatalysts.

Finely-tuned heteroleptic phosphorescent Ir(III) complexes for CIEy < 0.2-based pure blue organic light-emitting diodes with external quantum efficiencies > 30%

Three pure blue phosphorescent Ir (III) complexes F5OFpt, F5MFpt and F5SiFpt with the amazing CIEy coordinate value<0.2 have been obtained by introducing different electron-donating groups (-OMe, -Me and -TMS) into the corresponding C^N ligands. Based on a well matched mixed host combination of mCBP and TSPO1, all the emitting systems achieve quite high maximum EQE > 30% with low efficiency roll-off and ideal blue color with the CIEy < 0.2.

General Synergistic Hybrid Catalyst Synthesis Method Using a Natural Enzyme Scaffold-Confined Metal Nanocluster.

Due to differences in the chemical properties or optimal reaction conditions of the catalysts, the challenge in the design of bio-chemical hybrid catalysts is that the bio-catalysts or chemical catalysts usually cannot maintain the initial catalytic performance. Herein, we report a general bio-chemical hybrid catalyst synthesis method using a natural enzyme scaffold-confined metal nanocluster. A redox-active enzyme is a nanoreactor that allows access to and reduces metal ions into metal nanoclusters in situ, resulting in the enzyme-confined metal nanocluster hybrid catalyst with a synergistic effect to boost catalytic performance. Specifically, bilirubin oxidase-Ir nanoclusters (BOD-Ir NCs) with catalytic properties for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are designed. The BOD-Ir NCs exhibit an approximately 2-fold ORR activity compared with pure BOD and a 4-fold OER activity compared with pure Ir NCs. BOD-Ir NCs exhibit stability for over 50,000 s, exceeding that of pure Ir NCs (22,000 s). The synergistic catalytic performance is attributed to the following: the mild preparation condition and matched sizes of BOD and the Ir NCs maintain the natural activity of BOD; the highly conductive Ir NCs improve the ORR activity of BOD; and the confining effect of BOD, which improves the stability and activity of the Ir NCs during the OER. In particular, BOD-Ir NCs exhibit a high half-wave potential of 0.97 V for the ORR and a low overpotential of 319 mV at 10 mA cm-2 for the OER, surpassing most of reported catalysts under neutral conditions. Furthermore, laccase-Ir NCs and glucose oxidase-Pd NCs with synergistic catalytic performances are fabricated, proving the universality of this synthetic method. This facile strategy for designing synergistic hybrid catalysts is expected to be applied to more complex chemical transformations.

IrPt Alloy Nanoparticles with Controllable Compositions as Catalysts for Electrochemical Oxygen and Hydrogen Evolution

When two metal precursors are reduced to form alloy nanoparticles (NPs), the final size usually varies by the composition because the reduction rate is different for each precursor. In this study, we report that the composition of IrPt alloy NPs can be easily controlled without affecting the size using an antisolvent crystallization-based method owing to the separation of the particle growth and precursor reduction steps. The synthesized IrPt alloy NPs displayed low overpotentials in both hydrogen evolution reaction (65 mV with a Tafel slope of 32.2 mV dec–1) and oxygen evolution reaction (240 mV with a Tafel slope of 77.9 mV dec–1) to deliver a current density of 10 mA cm–2 in H2SO4 (0.5 M), showing their enhanced electrocatalytic activities compared with the pure Pt and Ir catalysts.

Pollen-like self-supported FeIr alloy for improved hydrogen evolution reaction in acid electrolyte

Ir is recognized as efficient catalyst for hydrogen evolution reaction (HER). The high price, however, has hindered its application in the production of hydrogen. In this work, we prepared the self-supported FeIr alloy nanoparticles, taking advantage of solid-state synthesis method. The as-prepared FeIr alloy possesses a novel morphology of pollen, which is consist of smaller FeIr nanoparticles. DFT calculations reveal that the change of the free Gibbs for Ir is negative after the adsorption of active H, while it is positive for the case of Fe. Thus, the alloying of Fe and Ir not only effectively reduces the cost, but also can achieve more adequate adsorption of active H species. Benefitting from this, the as-prepared FeIr alloy nanoparticle exhibits superior HER performance with an overpotential of 19 mV at a current density of 10 mV/cm2 and a Tafel slope of 32 mV/dec, when tested in 0.5 M H2SO4, better than pure Ir and Pt/C. This work paves the way to the exploration of efficient alloy electrocatalysts for HER.

Spin Hall effect in a non-equilibrium Cu76Ir24 alloy measured at various temperatures

Non-equilibrium Cu–Ir binary alloys are interesting materials because these alloys show a large spin Hall effect (SHE) despite the non-remarkable spin Hall angles of pure Cu and pure Ir. In this study, the temperature dependence of the SHE on a non-equilibrium Cu–Ir binary alloy was investigated in order to understand the mechanism of its large SHE. We measured the spin Hall magnetoresistance for the Cu76Ir24/CoFeB bilayer at various measurement temperatures. The spin Hall conductivity remains practically constant against temperature and electrical conductivity, indicating that the side jump or the intrinsic process based on the band structure is dominant for the SHE in the present Cu76Ir24.

Iridium‐cobalt alloy nanotubes as a bifunctional electrocatalyst for pH‐universal overall water splitting

AbstractBimetallic IrxCo1−x alloy nanotubes (x = 0.25, 0.50 and 0.75, the atomic ratios of Ir precursor out of the total metal precursor) were prepared via the thermal H2‐reduction of IrxCo1−xOy nanotubes which were synthesized by electrospinning and post calcination. Ir and Co atoms were well mixed to form the alloy in IrxCo1−x nanotubes. Their phase structures were different depending on the composition ratios. Ir0.75Co0.25 and Ir0.50Co0.50 had Ir fcc phase where some Ir atoms were substituted with Co. In contrast, Ir0.25Co0.75 was in Ir‐substituting Co hcp phase. Among the IrxCo1−x alloy nanotubes, Ir0.50Co0.50 showed the highest catalytic activity for overall electrochemical water splitting in acidic, neutral, and alkaline conditions, better than pure metallic Ir and Co counterparts. The activity and stability of Ir0.50Co0.50 nanotubes for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) were superior to commercial Ir/C and Pt/C, respectively.

Magnetron Sputtered Iridium-Ruthenium Thin-Film Catalyst for Oxygen Evolution Reaction

In today´s developed world, there is a huge pressure on increasing the amount of electricity produced by renewable sources. With growing percentage of electricity from wind and solar power plants, new challenges arise. The biggest issue seems to be the instability of generated electricity during the days. Possible solution can be offered by Proton Exchange Membrane Water Electrolyzers (PEM-WE) and Proton Exchange Membrane Fuel Cell (PEM-FC) through electricity-hydrogen-electricity conversion cycle. Although PEM-WE technology is well suited for scale-up, one major drawback – its dependence on noble metal catalysts remains to be solved. Both, Ir on the anode and Pt on the cathode, which are traditionally used, are extremely rare and expensive, thus their partial replacement by other materials can lead to the noticeable decrease of PEM-WE price. More focus is usually laid on the anodic oxygen evolution reaction (OER) which is catalytically much more demanding. Ruthenium catalyst appears to be an interesting alternative due to its high activity towards OER. However, low electrochemical stability of Ru renders it inapplicable in its pure form. This problem can be solved by using mixed iridium-ruthenium catalyst which benefits from stability of iridium and from the lower price and high activity of ruthenium.In this work we present magnetron sputtered thin-film iridium-ruthenium mixed catalyst for the OER on the anode of PEM-WE. Magnetron sputtering is a mean of catalyst deposition which allows the preparation of a thin films of exact concentration and thickness. Moreover, it is also possible to use it on industrial scales. Usage of magnetron sputtering provides several important advantages. Firstly, we are able to cut down the amount of used catalyst significantly -- usually 10 times less than in the case of powder catalyst. Secondly, it is possible to prepare small systems for detailed electrochemical and surface analysis and also bigger systems for testing of our catalysts at real electrolyzer. This allows us to narrow the gap between the model and controlled studies and real industrial systems.In our work, we present four concentration of mixed iridium-ruthenium catalyst prepared by magnetron sputtering. Each catalyst was prepared either on Glassy Carbon electrode, or on Nafion® NR212. Measurement on Nafion® NR212 helps us to pick the industrially most suitable candidate. Measurements on the Glassy Carbon electrodes allows to investigate the activity and stability of given catalysts and correlate it with their structural and chemical properties. Numerous techniques were used, specifically Rotation Disk Electrode (RDE), Potential Electrochemically Impedance Spectroscopy (PEIS), Scanning Electron Microscopy, Energy Dispersive X-Ray spectroscopy (EDX), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD). Combination of these techniques revealed that 25:75 Ir:Ru sputtered thin-film catalyst outperforms the benchmark pure Ir counterpart while retaining comparable electrochemical stability. Figure 1

Microstructure evolution and mechanical properties of a novel γ′ phase-strengthened Ir-W-Al-Th superalloy

The present work introduces a novel γ′ phase-strengthened Ir-W-Al-Th superalloy for ultrahigh-temperature applications. First, the as-cast microstructure and phase transformation of Ir-13W-6Al-0.15Th (at%) alloy during solid solution and aging were investigated. Phase transformation was observed during heat treatment. The primary γ′ phase disappeared via the redissolution of γ′ → γ at 1800 °C. The recrystallization took place at 1450 °C and very fine equiaxed γ′/γ grains formed after 240 h. The cold-rolled microstructure indicated that the room-temperature γ phase was brittle and cracks mainly emerged along grain boundaries. Ir-13W-6Al-0.15Th alloy exhibited a higher nanohardness than other Ir-based superalloys and pure Ir, which can be attributed to the solid solution and precipitation (γ′) strengthening. In addition, the as-cast Ir-13W-6Al-0.15Th alloy shows a medium room-temperature compressive yield strength and good ductility.

Electrocatalytic oxidation of 2-propanol on PtxIr100-x bifunctional electrocatalysts – A thin-film materials library study

Due to the high demand for renewable and infrastructure compatible energy conversion and storage technologies, research on organic fuel cells receives increasing interest again recently. Organic fuels such as alcohols provide an attractive avenue to overcome the drawbacks of hydrogen as an energy carrier. Particularly interesting are secondary alcohols that almost exclusively form ketones as the final oxidation product, as they can be utilized in “zero emission” concepts without CO2 as a by-product. The state-of-the-art electrocatalyst in secondary alcohol oxidation is Pt-Ru, which demonstrates low onset potentials for the oxidation of the most facile secondary alcohol isopropanol. Yet, the achievable current densities are still relatively low and decrease rapidly due to the formed product acetone, which can poison the catalyst surface over time. Therefore, there is an inevitable need for the development of novel electrocatalyst materials circumventing these challenges. In this study, we employ a high-throughput electrochemical approach coupled to on-line inductively-coupled plasma mass spectrometry to map the composition-dependent activity and stability of PtxIr100-x alloy electrocatalysts toward the electro-oxidation of isopropanol. The activity and stability of magnetron sputtered PtxIr100-x material libraries are studied in 0.1 M HClO4 both in the absence and presence of isopropanol. The highest current densities are achieved for the sample containing the least amount of Ir (3.4 at.%), with a continuous decrease with the increasing amount of Ir. The alloys are inactive towards the oxidation of isopropanol when the amount of Ir exceeded 80 at%. The presence of isopropanol also has a notable effect on stability: while dissolution rates do not change in the case of pure Pt and Ir, a significant increase in stability is observed for the PtxIr100-x thin-film samples at all applied upper potential limits. This is explained by the strong adsorption of acetone on the surface of the catalyst that inhibits the formation of surface oxides.

Strain Softening of Bimodal Isoprene Rubber Vulcanizates

AbstractIsoprene rubber (IR) vulcanizates soften upon large‐amplitude oscillational shear and large‐strain cyclic tensile deformation. The mechanisms of these two strain softening behaviors remain unclarified and methods for reducing the accompanied mechanical dissipations are not well established. Herein IR/liquid isoprene rubber bimodal blends are cured into vulcanizates with similar cross‐linking densities. The results indicate that, in comparison with the pure IR network, the bimodal networks demonstrate lowered loss modulus and loss tangent at low strain amplitudes during oscillational shear and reduced loading−unloading dissipation energy at large strains during cyclic tensile deformation. The latter is ascribed to the weakened strain‐induced crystallization (SIC) as disclosed by in situ wide angle X‐ray diffraction. To the best of the current knowledge, the depression of SIC and thus dissipation energy in cyclic deformation is seldom reported for rubber materials. This work provides a new perspective for preparing rubber materials with balanced deformation resistance and mechanical hysteresis.

Ultra-low-dose thoracic CT with model-based iterative reconstruction (MBIR) in cystic fibrosis patients undergoing treatment with cystic fibrosis transmembrane conductance regulators (CFTR)

To assess the utility of a volumetric low-dose computed tomography (CT) thorax (LDCTT) protocol at a dose equivalent to a posteroanterior (PA) and lateral chest radiograph for surveillance of cystic fibrosis (CF) patients. A prospective study was undertaken of 19 adult patients with CF that proceeded to LDCTT at 12 and 24 months following initiation of ivacaftor. A previously validated seven-section, low-dose axial CT protocol was used for the 12-month study. A volumetric LDCTT protocol was developed for the 24-month study and reconstructed with hybrid iterative reconstruction (LD-ASIR) and pure iterative reconstruction (model-based IR [LD-MBIR]). Radiation dose was recorded for each scan. Image quality was assessed quantitatively and qualitatively, and disease severity was assessed using a modified Bhalla score. Statistical analysis was performed and p-values of <0.05 were considered statistically significant. Volumetric LD-MBIR studies were acquired at a lower radiation dose than the seven-section studies (0.08±0.01 versus 0.10±0.02 mSv; p=0.02). LD-MBIR and seven-section ASIR images had significantly lower levels of image noise compared with LD-ASIR images (p<0.0001). Diagnostic acceptability scores and depiction of bronchovascular structures were found to be acceptable for axial and coronal LD-MBIR images. LD-MBIR images were superior to LD-ASIR images for all qualitative parameters assessed (p<0.0001). No significant change was observed in mean Bhalla score between 1-year and 2-year studies (p=0.84). The use of a volumetric LDCTT protocol (reconstructed with pure IR) enabled acquisition of diagnostic quality CT images, which were considered extremely useful for surveillance of CF patients, at a dose equivalent to a PA and lateral chest radiograph.

Image Quality Assessment of Low-Dose CT using Hybrid Iterative Reconstruction

Background: X-ray computed tomography is the first imaging technology that supports accurate nondestructive interior image reconstruction of an object from sufficient projection data. Low-dose computed tomography (LDCT) has been considered to relieve the harm to patients caused by X-ray radiation. However, LDCT images can be degraded by quantum noise and streak artifacts. Methods: The objective of the authors’ study is to evaluate the optimal level of the hybrid iterative reconstruction (HIR) that generates images with the best diagnostic quality on different dose and noise levels. HIR with optimizations is proposed to reduce image noise and provide better performance at a low dose. The Catphan R 504 phantom is employed to assess various image qualities (IQ). Results: For any given scanning protocols, there is linear noise reduction and linear increase of contrast-to- noise ratio (CNR) using optimal HIR. The evidence from various module tests demonstrates that the shape of the noise power spectrum is continuously shifted to low frequency with increasing HIR levels compared with that of filtered-back-projection (FBP). This may describe the difference between the human observer performance and features of the ideal low-contrast objects. Conclusion: Optimal HIR is clearly demonstrated to be a superior method for reducing image noise and improving CNR compared to FBP. Optimal HIR also inhibits texture change or spectrum shift compared with the pure IR method. Even though there are continuous noise reduction and CNR increase with HIR at increasing levels, the human observer performance does not seem to improve simultaneously due to coarser noise (low-frequency noise). HIR level 3 to 5 is optimal for their study. It is possible for the optimal HIR to offer equivalent diagnostic IQ at a lower dose compared with FBP at a routine dose.