NanoSQUID Magnetometry on Individual As-grown and Annealed Co Nanowires at Variable Temperature.

Performing magnetization studies on individual nanoparticles is a highly demanding task, especially when measurements need to be carried out under large sweeping magnetic fields or variable temperature. Yet, characterization under varying ambient conditions is paramount in order to fully understand the magnetic behavior of these objects, e.g., the formation of nonuniform states or the mechanisms leading to magnetization reversal and thermal stability. This, in turn, is necessary for the integration of magnetic nanoparticles and nanowires into useful devices, e.g., spin-valves, racetrack memories, or magnetic tip probes. Here, we show that nanosuperconducting quantum interference devices based on high critical temperature superconductors are particularly well suited for this task. We have successfully characterized a number of individual Co nanowires grown through focused electron beam induced deposition and subsequently annealed at different temperatures. Magnetization measurements performed under sweeping magnetic fields (up to ∼100 mT) and variable temperature (1.4-80 K) underscore the intrinsic structural and chemical differences between these nanowires. These point to significant changes in the crystalline structure and the resulting effective magnetic anisotropy of the nanowires, and to the nucleation and subsequent vanishing of antiferromagnetic species within the nanowires annealed at different temperatures.

Bile duct tumors.

Bile duct tumors are benign or malignant lesions which may be associated to risk factors or potentially malignant lesions. They constitute an heterogenous entities group with a different biological behavior and prognosis according to location and growth pattern. We revise the role of the radiologist in order to detect, characterize and stage these tumors, specially the importance of their classification when deciding an appropriate management and treatment.

Lanthanoid single-ion magnets based on polyoxometalates with a 5-fold symmetry: the series [LnP5W30O110]12- (Ln3+ = Tb, Dy, Ho, Er, Tm, and Yb).

A robust, stable and processable family of mononuclear lanthanoid complexes based on polyoxometalates (POMs) that exhibit single-molecule magnetic behavior is described here. Preyssler polyanions of general formula [LnP(5)W(30)O(110)](12-) (Ln(3+) = Tb, Dy, Ho, Er, Tm, and Yb) have been characterized with static and dynamic magnetic measurements and heat capacity experiments. For the Dy and Ho derivatives, slow relaxation of the magnetization has been found. A simple interpretation of these properties is achieved by using crystal field theory.

Gd-based single-ion magnets with tunable magnetic anisotropy: molecular design of spin qubits.

We report ac susceptibility and continuous wave and pulsed EPR experiments performed on GdW10 and GdW30 polyoxometalate clusters, in which a Gd3+ ion is coordinated to different polyoxometalate moieties. Despite the isotropic character of gadolinium as a free ion, these molecules show slow magnetic relaxation at very low temperatures, characteristic of single molecule magnets. For T≲200 mK, the spin-lattice relaxation becomes dominated by pure quantum tunneling events, with rates that agree quantitatively with those predicted by the Prokof'ev and Stamp model [Phys. Rev. Lett. 80, 5794 (1998)]. The sign of the magnetic anisotropy, the energy level splittings, and the tunneling rates strongly depend on the molecular structure. We argue that GdW30 molecules are also promising spin qubits with a coherence figure of merit Q(M)≳50.

Strong paramagnetism of gold nanoparticles deposited on a Sulfolobus acidocaldarius S layer.

Magnetic properties of Au nanoparticles deposited on an archaeal S layer are reported. X-ray magnetic circular dichroism and superconducting quantum interference device magnetometries demonstrate that the particles are strongly paramagnetic, without any indication of magnetic blocking down to 16 mK. The average magnetic moment per particle is M(part)=2.36(7) µ(B). This contribution originates at the particle's Au 5d band, in which an increased number of holes with respect to the bulk value is observed. The magnetic moment per Au atom is 25 times larger than any measured in other Au nanoparticles or any other configurations up to date.

Molecular prototypes for spin-based CNOT and SWAP quantum gates.

We show that a chemically engineered structural asymmetry in [Tb2] molecular clusters renders the two weakly coupled Tb3+ spin qubits magnetically inequivalent. The magnetic energy level spectrum of these molecules meets then all conditions needed to realize a universal CNOT quantum gate. A proposal to realize a SWAP gate within the same molecule is also discussed. Electronic paramagnetic resonance experiments confirm that CNOT and SWAP transitions are not forbidden.

Usefulness of intestinal ultrasound in inflammatory bowel disease. / Utilidad de la ecografía intestinal en la enfermedad inflamatoria intestinal.

Imaging techniques play a fundamental role in the initial diagnosis and follow-up of inflammatory bowel disease. Intestinal ultrasound has high sensitivity and specificity in patients with suspected Crohn's disease and in the detection of inflammatory activity. This technique enables the early diagnosis of intra-abdominal complications such as stenosis, fistulas, and abscesses. It has also proven useful in monitoring the response to treatment and in detecting postsurgical recurrence. Technical improvements in ultrasound scanners, technological advances such as ultrasound contrast agents and elastography, and above all increased experience have increased the role of ultrasound in the evaluation of the gastrointestinal tract. The features that make ultrasound especially attractive include its wide availability, its noninvasiveness and lack of ionizing radiation, its low cost, and its good reproducibility, which is important because it is easy to repeat the study and the study is well tolerated during follow-up. This review summarizes the role of intestinal ultrasound in the detection and follow-up of inflammatory bowel disease.

Size-dependent properties of magnetoferritin.

We report a detailed experimental study of maghemite nanoparticles, with sizes ranging from 1.6 to 6 nm, synthesized inside a biological mould of apoferritin. The structural characterization of the inorganic cores, using TEM and x-ray diffraction, reveals a low degree of crystalline order, possibly arising from the nucleation and growth of multiple domains inside each molecule. We have also investigated the molecular structure by means of atomic force microscopy in liquid. We find that the synthesis of nanoparticles inside apoferritin leads to a small, but measurable, decrease in the external diameter of the protein, probably associated with conformational changes. The magnetic response of the maghemite cores has been studied by a combination of techniques, including ac susceptibility, dc magnetization and Mössbauer spectroscopy. From the equilibrium magnetic response, we have determined the distribution of magnetic moments per molecule. The results show highly reduced magnetic moments. This effect cannot be ascribed solely to the canting of spins located at the particle surface but, instead, it suggests that magnetoferritin cores have a highly disordered magnetic structure in which the contributions of different domains compensate each other. Finally, we have also determined, for each sample, the distribution of the activation energies required for the magnetization reversal and, from this, the size-dependent magnetic anisotropy constant K. We find that K is enormously enhanced with respect to the maghemite bulk value and that it increases with decreasing size. The Mössbauer spectra suggest that low-symmetry atomic sites, probably located at the particle surface and at the interfaces between different crystalline domains, are the likely source of the enhanced magnetic anisotropy.

Magnetic vortex nucleation and annihilation in bi-stable ultra-small ferromagnetic particles.

Vortex-mediated magnetization reversal in individual ultra-small (∼100 nm) ferromagnetic particles at low temperatures is studied by nanoSQUID magnetometry. At zero applied bias field, the flux-closure magnetic state (vortex) and the quasi uniform configuration are bi-stable. This stems from the extremely small size of the nanoparticles that lies very close to the limit of single-domain formation. The analysis of the temperature-dependent (from 0.3 to 70 K) hysteresis of the magnetization allows us to infer the nature of the ground state magnetization configuration. The latter corresponds to a vortex state as also confirmed by electron holography experiments. Based on the simultaneous analysis of the vortex nucleation and annihilation data, we estimate the magnitude of the energy barriers separating the quasi single-domain and the vortex state and their field dependence. For this purpose, we use a modified power-law scaling of the energy barriers as a function of the applied bias field. These studies are essential to test the thermal and temporal stability of flux-closure states stabilized in ultra-small ferromagnets.

Bowel ultrasound: examination techniques and normal and pathologic patterns. / Ecografía intestinal: técnicas de examen, patrones normales y patológicos.

Ultrasound is being increasingly used to study the digestive tract because it has certain advantages over other techniques such as endoscopy, CT enterography, and MR enterography. Ultrasound can be used to evaluate the bowel wall and the elements that surround it without the need for contrast agents; its ability to evaluate the elasticity and peristalsis of these structures is increasing interest in its use. This article describes the techniques and modalities of bowel ultrasound, as well as the normal features of the bowel wall and contiguous structures. It uses a practical approach to review the main pathological findings and their interpretation, and the different patterns of presentation, which will help orient the diagnosis.

Evaluation of upper tract urothelial carcinomas by contrast-enhanced ultrasound. / Valoración del carcinoma urotelial de vías superiores mediante ecografía con contraste.

AIM: To describe the findings and behaviour of contrast-enhanced ultrasound in the study of upper tract urothelial tumours and to assess its usefulness for diagnosis. MATERIAL AND METHODS: We reviewed our hospital's database over a period of 45 months to identify patients diagnosed with upper tract urothelial carcinomas. We reviewed the findings on mode B-ultrasound, contrast-enhanced ultrasound (location and qualitative assessment of intensity and washout of enhancement), and made a comparison with other techniques (computed tomography or magnetic resonance), and with the surgical specimen. RESULTS: We found 42 patients with a diagnosis of upper tract urothelial carcinoma confirmed with surgery over the period reviewed. Twenty-eight (67%) patients underwent contrast-enhanced ultrasound. Baseline ultrasound showed hydronephrosis with or without ureteral dilatation with echogenic content occupying the renal calyx (6), pelvis (10) or ureter (12). After injection of contrast, enhancement was noticed in 100% of the lesions, with similar intensity to the cortex in 23, and less in 5. Twenty-four lesions showed early washout, before the cortex, between 40 and 55seconds after the injection. The diagnosis was correct in 27 cases. Localisation coincided with the histological specimen in 28 cases, and 3 patients had additional distal carcinoma foci. CONCLUSION: Contrast-enhanced ultrasound is a useful technique for diagnosing upper tract urothelial tumours that increases confidence in the diagnosis.

Diseases that simulate acute appendicitis on ultrasound.

Ultrasound is useful in the assessment of patients with possible appendicitis. A diagnosis of appendicitis can be made in patients with persistent right lower quadrant pain when a non-compressible appendix greater than 6 mm in diameter is shown. When a normal appendix is affected by an adjacent lesion, reactive inflammation can cause secondary enlargement of the appendix. This article reviews ultrasound findings in conditions which can clinically mimic acute appendicitis. Examples of Crohn's disease, tuboovarian abscess, typhilitis, sigmoid diverticulitis, perforated sigmoid neoplasm, perforated peptic ulcer, perforated acute cholecystitis, caecal carcinoma and appendiceal tumours are included.

Note: Highly sensitive superconducting quantum interference device microsusceptometers operating at high frequencies and very low temperatures inside the mixing chamber of a dilution refrigerator.

We report the experimental results that show the operation of superconducting quantum interference device (SQUID) microsusceptometers immersed in the (3)He-(4)He mixture inside the mixing chamber of a dilution refrigerator at high frequency (1 MHz) and down to very low temperatures (13 mK). The devices are based on highly sensitive and easy-to-use commercial SQUID sensors. The integrated susceptometers are fabricated by rerouting some connections of the SQUID's input circuit. Examples of measurements on molecular magnets Mn(12) and HoW(10) are shown.

[Polygonal mosaic-like pattern of the colonic mucosa in cecal volvulus: CT findings]. / Patrón en mosaico de la pared del colon en un caso con vólvulo de ciego: hallazgos en TC.

A polygonal mosaic-like pattern of colonic mucosa is a rare radiological finding that was first described in studies using barium enema. We describe the CT findings of this pattern in a case of cecal volvulus.

[Cecal volvulus: imaging features]. / Vólvulo cecal: características en imagen.

OBJECTIVE: To determine the sensitivity of plain-film radiography and computed tomography (CT) in the diagnosis of cecal volvulus. MATERIAL AND METHODS: We reviewed the clinical histories of 11 patients diagnosed with cecal volvulus at endoscopy or surgery. Two radiologists working in consensus analyzed the findings at plain-film radiography and at CT and calculated the sensitivities. The plain-film and CT studies were retrospectively classified as certain, probable, or indeterminate for cecal volvulus on the basis of the presence or absence of previously reported signs. Signs of wall suffering at CT were compared to the histologic findings. RESULTS: The most sensitive findings at plain-film radiography were the presence of a disproportionately dilated bowel loop and a pattern of distal small bowel occlusion (91%), followed by a single air-fluid level in the cecum and collapse of the distal colon (82%). At CT, the "coffee bean" sign with a single air-fluid level and collapse of the left colon had a sensitivity of 100%. The whirl sign was present in 86%. Retrospectively, 36% of the plain-film studies and 86% of the CT studies were classified as certain for cecal volvulus. Although all cases with ischemia had signs of vascular compromise on CT, no significant correlation was observed between these variables. CONCLUSIONS: The plain-film signs reported for cecal volvulus enable a certain diagnosis in a third of all cases; the CT signs enable a certain diagnosis in most cases. The evaluation of additional findings increases the chances of reaching the correct diagnosis.

[Ultrasound, CT, and MRI in Crohn's disease]. / Técnicas seccionales de imagen en la enfermedad de Crohn: ecografía, tomografía computarizada y resonancia magnética.

Colonoscopy and Barium contrast studies continue to be the techniques of choice for the evaluation of mucosal lesions in Crohn's disease. However, these techniques have limited capacity for demonstrating the transmural and extramural extension of the disease. Although ultrasound, CT, and MRI cannot detect early lesions, these techniques satisfactorily show parietal and extraparietal changes caused by the disease, thus complementing the information provided in conventional studies. These three techniques enable the evaluation of the pathological segments, the presence of stenosis and dilatation, and extramural disease (fibrofatty proliferation, fistulae, phlegmons, and abscesses). This information is essential for classifying each patient into one of the three subtypes of Crohn's disease (inflammatory, stenotic, or fistulating). These techniques also enable the evaluation of signs that indicate inflammatory activity (hyperemia, wall enhancement, and increased mesenteric vascularization), and this information, together with the subtype, will determine the treatment. Ultrasound, CT, and MRI should be included in the complete evaluation of the patient with Crohn's disease, together with clinical examination, laboratory tests, and conventional imaging studies. We review the role of ultrasound, CT, and MRI in the diagnosis and evaluation of Crohn's disease, describing patient preparation and examination protocols, as well as the findings in these three techniques. We also discuss the advantages and limitations of each of these techniques and their current clinical roles in this context.

Pancreatic pseudotumor in Meckel diverticulum.

This report describes the ultrasonic appearance of an ectopic pancreatic rest presenting as a mass within an intussusception due to an inverted Meckel diverticulum. Familiarity with the ultrasound appearance of this entity may be useful to obviate unnecessary imaging workup.

Tumores de la vía biliar / Bile duct tumors

Los tumores de la vía biliar son lesiones benignas o malignas que pueden asociarse a factores de riesgo o a lesiones con potencial de malignización. Constituyen un grupo heterogéneo de entidades con diferente comportamiento biológico y pronóstico dependiendo de su localización y del tipo de crecimiento. En este artículo revisamos el papel del radiólogo para detectar, caracterizar y estadificar estos tumores y, sobre todo, la importancia de clasificarlos para planificar el manejo y el tratamiento (AU)

Bile duct tumors are benign or malignant lesions which may be associated to risk factors or potentially malignant lesions. They constitute an heterogenous entities group with a different biological behavior and prognosis according to location and growth pattern. We revise the role of the radiologist in order to detect, characterize and stage these tumors, specially the importance of their classification when deciding an appropriate management and treatment (AU)

Appendicular involvement in perforated sigmoid disease: US and CT findings.

We describe four patients in whom ultrasound (US) and/or computed tomography (CT) demonstrated a thickened appendix, secondarily enlarged due to perforated sigmoid diverticulitis (n = 2) or carcinoma (n = 2). The underlying pathology was correctly recognized in all cases. Secondary thickening of the appendix due to perforated sigmoid disease provides a potential pitfall mainly on US and may lead to an incorrect diagnosis and thus to unnecessary surgery or a wrong surgical intervention. Although US alone is enough to diagnose periappendicitis and sigmoid disease, combined use of US and CT may improve assessment of its origin and extension.

Patrón en mosaico de la pared del colon en un caso con vólvulo de ciego: hallazgos en TC / Polygonal mosaic-like pattern of the colonic mucosa in cecal volvulus: CT findings

El patrón en mosaico de la mucosa colónica es un hallazgo radiológico poco frecuente, que se ha descrito previamente en los estudios de enema de bario. Describimos la apariencia de este patrón en la TC en un paciente con vólvulo de ciego (AU)

A polygonal mosaic-like pattern of colonic mucosa is a rare radiological finding that was first described in studies using barium enema. We describe the CT findings of this pattern in a case of cecal volvulus (AU)