•Magnetic contrast changes sign because of the energy-dependence of the spin reflectivity asymmetry.•Unexpected magnetic contrast is observed at magnetic domain boundary at the energy of zero ...asymmetry.•This contrast results from the finite energy width of the electron source, in combination with the dispersion of the magnetic prism array.
Important applications of spin polarized low energy electron microscopy (SPLEEM) employ this technique's vector imaging capability to resolve domain wall (DW) spin textures. Studying several thin film systems including Co/W(110), Co/Cu(001) and (Co/Ni)n/W(110), we show that an additional contrast can appear at magnetic DWs. By imaging the magnetization as a function of electron landing energy, electron energies are selected at which the magnetic domain contrast vanishes. Surprisingly, under such conditions of zero contrast between magnetic domains, we observe the appearance of magnetic contrast outlining the DWs. This DW contrast does not depend on the DW spin texture. Instead, our measurements show that this DW contrast results from a combination of the energy-dependence of the spin reflectivity asymmetry of the magnetic film, the finite energy width of the spin polarized electron source, and the dispersion of the magnetic prism array that separates the illumination and imaging columns of the instrument. Awareness of this DW contrast mechanism is useful to aid correct interpretation of SPLEEM images.
The structure of magnetic domains, i.e. regions of uniform magnetization separated by domain walls, depends on the balance of competing interactions present in ferromagnetic (or ferrimagnetic) ...materials. When these interactions change then domain configurations also change as a result. Magnetite provides a good test bench to study these effects, as its magnetocrystalline anisotropy varies significantly with temperature. Using spin-polarized electron microscopy to map the micromagnetic domain structure in the (001) surface of a macroscopic magnetite crystal (~1 cm size) shows complex domain patterns with characteristic length-scales in the micrometer range and highly temperature dependent domain geometries. Although heating above the Curie temperature erases the domain patterns completely, cooling down reproduces domain patterns not only in terms of general characteristics: instead, complex microscopic domain geometries are reproduced in almost perfect fidelity between heating cycles. A possible explanation of the origin of the high-fidelity reproducibility is suggested to be a combination of the presence of hematite inclusions that lock bulk domains, together with the strong effect of the first order magnetocrystalline anisotropy which competes with the shape anisotropy to give rise to the observed complex patterns.
DNA sequencing by imaging in an electron microscope is an approach that holds promise to deliver long reads with low error rates and without the need for amplification. Earlier work using ...transmission electron microscopes, which use high electron energies on the order of 100 keV, has shown that low contrast and radiation damage necessitates the use of heavy atom labeling of individual nucleotides, which increases the read error rates. Other prior work using scattering electrons with much lower energy has shown to suppress beam damage on DNA. Here we explore possibilities to increase contrast by employing two methods, X-ray photoelectron and Auger electron spectroscopy. Using bulk DNA samples with monomers of each base, both methods are shown to provide contrast mechanisms that can distinguish individual nucleotides without labels. Both spectroscopic techniques can be readily implemented in a low energy electron microscope, which may enable label-free DNA sequencing by direct imaging.
Purpose
Radioguided sentinel lymph node biopsy (SLNB) is the standard of care in breast cancer and melanoma. Additional preoperative Single-photon emission computed tomography (SPECT/CT) for improved ...anatomical co-registration of the SLNs causes additional radiation exposure and is time-consuming and expensive. The aim of this prospective study was to evaluate a novel approach involving real-time fusion of freehand SPECT (fhSPECT) and ultrasound (US) for anatomical co-registration of SLNs.
Methods
From February 2015 to February 2016, 153 patients were included in this prospective study. All patients underwent lymphoscintigraphy according to
practical guidelines
and 151 (118 cases of breast cancer, 30 cutaneous malignancies, and three cases of vulvar cancer) of the 153 patients were additionally investigated with fhSPECT-US. FhSPECT connected to a hand-held gamma detector generates three-dimensional images of the radioactivity distribution in the scanned area. For co-registration and real-time fusion of fhSPECT and subsequently performed US, an infrared stereo tracking system was used.
Results
In all patients an SLN was found on lymphoscintigraphy, and the fhSPECT detected corresponding hotspots in all but one patient. In 72 % of patients and 73 % of lymph node basins, real-time anatomical co-registration with US was feasible. The rate of success in achieving good co-registration increased from 60 to 75 % after training by a radiologist specialized in breast imaging. A higher co-registration rate (78 %) was observed in patients with only one SLN than in those with two SLNs (68 %) or three or more SLNs (0 %).
Conclusions
Real-time fusion of fhSPECT and US for preoperative anatomical co-registration of SLNs is feasible. However, before this approach can completely replace preoperative lymphatic imaging, further technical developments are needed.
Purpose
Despite improved treatment options, multiple myeloma (MM) remains an incurable disease. The aim of this study was to investigate the prognostic value of positron emission tomography/computed ...tomography (PET/CT) using
18
F-2’-deoxy-2’-fluorodeoxyglucose (
18
FFDG) in MM patients shortly before and ~100 days after allogeneic hematopoietic cell transplantation (allo-HCT).
Methods
In this retrospective analysis, we evaluated
18
FFDG-PET/CT-scans of 45 heavily pre-treated MM patients before and 27 patients after scheduled allo-HCT. All scans were qualitatively and semi-quantitatively assessed for the presence of active disease. Serological response was recorded according to International Myeloma Working Group (IMWG) criteria. Progression-free (PFS) and overall survival (OS) were correlated with different PET/CT-derived parameters, such as presence, number and maximum standardized uptake value (SUV
max
) of focal myeloma lesions. The impact of extramedullary disease on patient outcome was also assessed.
Results
PET/CT negativity -prior to or following allo-HCT- was a favorable prognostic factor for progression-free and overall survival (both, PFS and OS: pre-HSCT
p
< 0.001, post-HCT
p
< 0.005). High FDG-uptake (SUV
max
> 6.5) revealed a significantly shortened survival compared to patients with a lower SUV
max
(<6.5) (OS, 5.0 ± 1.1 m vs. not reached - longest 122.0 m;
p
< 0.001). Moreover, our data prove that a higher number (>3) of focal lesions (pre-HCT: both PFS and OS:
p
< 0.001; post-HCT PFS:
p
< 0.001, OS:
p
= 0.139) as well as the presence of extramedullary disease serve as adverse prognostic factors prior to and after allo-HCT. At response assessment after allo-HCT,
18
FFDG-PET/CT had a complementary value in prognostication in addition to IMWG criteria alone.
Conclusion
18
FFDG-PET/CT before and shortly after allogeneic HCT is a powerful predictor for progression-free and overall survival in MM patients.
Tiger man sign in sarcoid myopathy Dierks, Alexander; Kircher, Malte; Schmid, Stefan J. ...
European journal of nuclear medicine and molecular imaging,
1/4, Letnik:
46, Številka:
4
Journal Article
Recently, Ftetrafluoroborate (FTFB) has been introduced as a versatile PET probe for imaging the human sodium/iodide symporter activity. This pilot study aimed to compare FTFB-PET/CT with INaI-PET/CT ...imaging in thyroid cancer patients.
Nine patients with newly diagnosed differentiated thyroid cancer underwent both FTFB- and INaI-PET/CT after total thyroidectomy. PET/CT scans were visually analyzed for the presence of remnant thyroid tissue and for metastatic lesions on a patient and lesion basis. For semiquantitative analysis, thyroid remnant/tumor to blood pool ratios were calculated.
All patients presented with positive FTFB and INaI-PET/CT scans. Retention of I in remnant thyroid tissue was significantly higher as compared with FTFB (P < 0.01). In a lesion-based analysis, both tracers identified an almost equal number of foci with FTFB depicting a total of 41 foci and I a total of 40 foci, respectively. In 6 of 9 patients, both radiopharmaceuticals returned an identical number of foci. Two I-positive benign thyroid remnants were missed by FTFB-PET/CT in a single patient. In another case, both tracers identified different thyroid remnant tissues in the cervical region. Notably, FTFB demonstrated additional (I-negative) cervical lymph node metastases in 2 patients, leading to an overall agreement between the radiotracers of 91% (74/81 foci).
In this pilot study, FTFB-PET was not inferior to INaI-PET for detecting thyroid cancer and its metastases and was able to detect INaI-PET-negative viable differentiated thyroid cancer metastases. Further clinical evaluation as a PET tracer for imaging thyroid pathophysiology and human sodium/iodide symporter expressing neoplasms is highly warranted.
Biodistribution of nanoencapsulated bioactive compounds is primarily determined by the size, shape, chemical composition and surface properties of the encapsulating nanoparticle, and, thus, less ...dependent on the physicochemical properties of the active pharmaceutical ingredient encapsulated. In the current work, we aimed to investigate the impact of formulation type on biodistribution profile for two clinically relevant nanoformulations. We performed a comparative study of biodistribution in healthy rats at several dose levels and durations up to 14-day post-injection. The studied nanoformulations were nanostructured lipid carriers incorporating the fluorescent dye IR780-oleyl, and polymeric nanoparticles containing the anticancer agent cabazitaxel. The biodistribution was approximated by quantification of the cargo in blood and relevant organs. Several clear and systematic differences in biodistribution were observed, with the most pronounced being a much higher (more than 50-fold) measured concentration ratio between cabazitaxel in all organs vs. blood, as compared to IR780-oleyl. Normalized dose linearity largely showed opposite trends between the two compounds after injection. Cabazitaxel showed a higher brain accumulation than IR780-oleyl with increasing dose injected. Interestingly, cabazitaxel showed a notable and prolonged accumulation in lung tissue compared to other organs. The latter observations could warrant further studies towards a possible therapeutic indication within lung and conceivably brain cancer for nanoformulations of this highly antineoplastic compound, for which off-target toxicity is currently dose-limiting in the clinic.
Graphical abstract
•LaB6–VB2 eutectic shown to have low work function at phase boundary.•Vanadium dosing yielded work function values as low as 1.1eV.•Thermionic emission imaging showed primary emission to be on the ...VB2 phase
With its low work function and high mechanical strength, the LaB6/VB2 eutectic system is an interesting candidate for high performance thermionic emitters. For the development of device applications, it is important to understand the origin, value, and spatial distribution of the work function in this system. Here we combine thermal emission electron microscopy and low energy electron microscopy with Auger electron spectroscopy and physical vapor deposition of the constituent elements to explore physical and chemical conditions governing the work function of these surfaces. Our results include the observation that work function is lower (and emission intensity is higher) on VB2 inclusions than on the LaB6 matrix. We also observe that the deposition of atomic monolayer doses of vanadium results in surprisingly significant lowering of the work function with values as low as 1.1eV.
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