The Impact of Nanostructuring on the Thermal Conductivity of Thermoelectric CoSb3

The high concentration of grain boundaries provided by nanostructuring is expected to lower the thermal conductivity of thermoelectric materials, which favors an increase in their thermoelectric figure‐of‐merit, ZT. A novel chemical alloying method has been used for the synthesis of nanoengineered‐skutterudite CoSb₃. The CoSb₃ powders were annealed for different durations to obtain a set of samples with different particle sizes. The samples were then compacted into pellets by uniaxial pressing under various conditions and used for the thermoelectric characterization. The transport properties were investigated by measuring the Seebeck coefficient and the electrical and thermal conductivities in the temperature range 300 K to 650 K. A substantial reduction in the thermal conductivity of CoSb₃ was observed with decreasing grain size in the nanometer region. For an average grain size of 140 nm, the thermal conductivity was reduced by almost an order of magnitude compared to that of a single crystalline or highly annealed polycrystalline material. The highest ZT value obtained was 0.17 at 611 K for a sample with an average grain size of 220 nm. The observed decrease in the thermal conductivity with decreasing grain size is quantified using a model that combines the macroscopic effective medium approaches with the concept of the Kapitza resistance. The compacted samples exhibit Kapitza resistances typical of semiconductors and comparable to those of Si–Ge alloys.     

Properties of Sn-doped Bi2Te3 − x Sex single crystals

The effect of Sn doping (0.2 and 0.4 at %) on the properties of Czochralski-grown single crystals of n-type Bi₂Te_2.85Se_0.15 solid solutions is studied. Thermoelectric power, electrical conductivity, thermal conductivity, and Hall effect measurements in the range 77–400 K demonstrate that Sn doping has a significant effect on the transport properties of the solid solutions. Between 300 and 370 K, the thermoelectric figure of merit of Bi_1.996Sn_0.004Te_2.85Se_0.15 single crystals is higher than that of the Sn-free solid solution. In addition, hot-microprobe thermoelectric power measurements, highly sensitive to variations in carrier concentration, indicate that the Sn-doped single crystals are very uniform in electrical properties, both along the growth direction and radially.     

PET/MR for therapy response evaluation in malignant lymphoma: initial experience

Object

To evaluate the feasibility of positron emission tomography/magnetic resonance imaging (PET/MR) with ¹⁸fluoro-2-deoxyglucose (FDG) for therapy response evaluation of malignant lymphoma.

Materials and methods

Nine patients with malignant lymphoma who underwent FDG-PET/MR before and after chemotherapy were included in this retrospective study. Average time between the two scans was 70 days. The scans were evaluated independently by two nuclear medicine physicians. The Ann Arbor classification was used to describe lymphoma stage. Furthermore, the readers also rated PET image quality using a five point scale. Weighted kappa (κ) was used to calculate interrater agreement.

Results

The initial scan showed foci of increased FDG uptake in all patients, with Ann Arbor stage varying between I and IV. In the follow-up examination, all but one patient showed complete response to chemotherapy. PET image quality was rated as very good or excellent for all scans. Interrater agreement was excellent regarding Ann Arbor stage (κ = 0.97) and good regarding image quality (κ = 0.41).

Conclusion

PET/MR shows promising initial results for therapy response evaluation in lymphoma patients.     

Overestimation of grey matter atrophy in glioblastoma patients following radio(chemo)therapy

Objective

Brain atrophy has the potential to become a biomarker for severity of radiation-induced side-effects. Particularly brain tumour patients can show great MRI signal changes over time caused by e.g. oedema, tumour progress or necrosis. The goal of this study was to investigate if such changes affect the segmentation accuracy of normal appearing brain and thus influence longitudinal volumetric measurements.

Materials and methods

T1-weighted MR images of 52 glioblastoma patients with unilateral tumours acquired before and three months after the end of radio(chemo)therapy were analysed. GM and WM volumes in the contralateral hemisphere were compared between segmenting the whole brain (full) and the contralateral hemisphere only (cl) with SPM and FSL. Relative GM and WM volumes were compared using paired t tests and correlated with the corresponding mean dose in GM and WM, respectively.

Results

Mean GM atrophy was significantly higher for full segmentation compared to cl segmentation when using SPM (mean ± std: ΔV_GM,full = − 3.1% ± 3.7%, ΔV_GM,cl = − 1.6% ± 2.7%; p < 0.001, d = 0.62). GM atrophy was significantly correlated with the mean GM dose with the SPM cl segmentation (r = − 0.4, p = 0.004), FSL full segmentation (r = − 0.4, p = 0.004) and FSL cl segmentation (r = -0.35, p = 0.012) but not with the SPM full segmentation (r = − 0.23, p = 0.1).

Conclusions

For accurate normal tissue volume measurements in brain tumour patients using SPM, abnormal tissue needs to be masked prior to segmentation, however, this is not necessary when using FSL.

     

Biocatalysis at Work: Applications in the Development of Sagopilone

For the antitumour agent sagopilone, an epothilone analogue, a large‐scale synthesis was developed to synthesise the active pharmaceutical ingredient for clinical trials, exploring enzymatic and microbial methods to produce chiral building blocks on a multi‐kilogram scale. The three building blocks were identified as key intermediates in the synthesis and needed to be produced with high optical purity in yields higher than those previously published. The improved syntheses of two of these building blocks are detailed herein. For building block A, the chemical research synthesis was abandoned, and a novel chemical route was developed leading to building block A via an enzymatic hydrolysis process. For building blocks C, replacement of a chemical catalytic procedure by a microbial process meant that the development of a new starting material could be avoided, thereby accelerating the development process. For the clinical development process, a human metabolite of sagopilone was required as a reference. To accelerate the synthesis of the metabolite, no chemical synthesis was investigated; rather, we relied solely on oxidoreductases. The human metabolite of sagopilone was synthesised on a multi‐gram scale in a single‐step process using genetically engineered E. coli expressing human cytochrome P450 enzyme 2C19. The integration of enzymatic and microbial processes provided tools that enable the synthesis of highly functionalised intermediates and metabolites.     

Gadofluorine 8: initial experience with a new contrast medium for interstitial MR lymphography

Rationale and objectives: Differential diagnosis of malignant and benign lymph nodes is still a problem in lymphographic imaging modalities. Plain magnetic resonance imaging (MRI) and computed tomography (CT) are inadequate for detecting metastases in normal-sized lymph nodes and for differentiating enlarged nodes. Therefore it is important to have a contrast agent that accumulates in healthy lymphatic tissue but does not accumulate in metastatic deposits.Methods: The lymphographic constrast agent Gadofluorine 8 (Schering AG, Berlin, Germany) is a lipophilic but water-soluble gadolinium complex. Lymphographic effects were investigated in guinea pigs, dogs, and tumor-bearing rabbits after interstitial (subcutaneous or intracutaneous) injection. MR imaging was performed using T₁-weighted gradient-echo sequences until 120 min after administration.Results: After interstitial injection Gadofluorine 8 accumulates in regional, lymph nodes, resulting in a pronounced increase in signal intensity in the lymph nodes. Differentiation between normal and metastatic lymph nodes was achieved.Conclusions: Gadofluorine 8 is an innovative contrast agent that can distinguish between normal and tumorous lymph nodes in interstitial MR lymphography.     

Scalable Silicon Nanostructuring for Thermoelectric Applications

The current limitations of commercially available thermoelectric (TE) generators include their incompatibility with human body applications due to the toxicity of commonly used alloys and possible future shortage of raw materials (Bi-Sb-Te and Se). In this respect, exploiting silicon as an environmentally friendly candidate for thermoelectric applications is a promising alternative since it is an abundant, ecofriendly semiconductor for which there already exists an infrastructure for low-cost and high-yield processing. Contrary to the existing approaches, where n/p-legs were either heavily doped to an optimal carrier concentration of 10¹⁹ cm^?3 or morphologically modified by increasing their roughness, in this work improved thermoelectric performance was achieved in smooth silicon nanostructures with low doping concentration (1.5 × 10¹⁵ cm^?3). Scalable, highly reproducible e-beam lithographies, which are compatible with nanoimprint and followed by deep reactive-ion etching (DRIE), were employed to produce arrays of regularly spaced nanopillars of 400 nm height with diameters varying from 140 nm to 300 nm. A potential Seebeck microprobe (PSM) was used to measure the Seebeck coefficients of such nanostructures. This resulted in values ranging from ?75 μV/K to ?120 μV/K for n-type and 100 μV/K to 140 μV/K for p-type, which are significant improvements over previously reported data.