First experimental observations on melting and chemical modification of volcanic ash during lightning interaction.

Electrification in volcanic ash plumes often leads to syn-eruptive lightning discharges. High temperatures in and around lightning plasma channels have the potential to chemically alter, re-melt, and possibly volatilize ash fragments in the eruption cloud. In this study, we experimentally simulate temperature conditions of volcanic lightning in the laboratory, and systematically investigate the effects of rapid melting on the morphology and chemical composition of ash. Samples of different size and composition are ejected towards an artificially generated electrical arc. Post-experiment ash morphologies include fully melted spheres, partially melted particles, agglomerates, and vesiculated particles. High-speed imaging reveals various processes occurring during the short lightning-ash interactions, such as particle melting and rounding, foaming, and explosive particle fragmentation. Chemical analyses of the flash-melted particles reveal considerable bulk loss of Cl, S, P and Na through thermal vaporization. Element distribution patterns suggest convection as a key process of element transport from the interior of the melt droplet to rim where volatiles are lost. Modeling the degree of sodium loss delivers maximum melt temperatures between 3290 and 3490 K. Our results imply that natural lighting strikes may be an important agent of syn-eruptive morphological and chemical processing of volcanic ash.

Systemic treatment of advanced differentiated and medullary thyroid cancer. Overview and practical aspects.

In the last few years, three new drugs for targeted systemic therapies have been approved for advanced and progressive thyroid cancer, namely vandetanib and cabozantinib for medullary and sorafenib for radioiodine refractory differentiated thyroid cancer. Patient selection by an interdisciplinary team and education of patients by the treating physicians play a major role when such a treatment is considered and initiated. Only patients with significant tumor burden and/or symptomatic disease or progression, which cannot be controlled by local therapies, should be treated. In order to preserve quality of life, the management of adverse effects is of utmost importance. Due to the mechanism of action of these tyrosine kinase inhibitors, the reliability of serum tumour markers, calcitonin and thyroglobulin, is limited for the assessment of response and follow-up, therefore morphological and metabolic imaging is of great importance. Minor or localized progression should not automatically trigger the termination of treatment or change of drug. In the near future, it is expected that additional drugs become available.

The rheology of three-phase suspensions at low bubble capillary number.

We develop a model for the rheology of a three-phase suspension of bubbles and particles in a Newtonian liquid undergoing steady flow. We adopt an 'effective-medium' approach in which the bubbly liquid is treated as a continuous medium which suspends the particles. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and particle suspension rheology, which are taken from the literature. The model is validated against new experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction ([Formula: see text]) and bubble volume fraction ([Formula: see text]). Consistent with model predictions, experimental results demonstrate that adding bubbles to a dilute particle suspension at low capillarity increases its viscosity, while adding bubbles to a concentrated particle suspension decreases its viscosity. The model accounts for particle anisometry and is easily extended to account for variable capillarity, but has not been experimentally validated for these cases.

[Selective internal radiotherapy (SIRT) for hepatocellular carcinoma]. / Selektive interne Radiotherapie (SIRT) beim hepatozellulären Karzinom.

Microsphere-based radioembolization represents a new generation of therapeutics in interventional oncology. The intrahepatic application of radioactive microspheres via the hepatic artery allows locoregional therapy of diffuse or multifocal liver tumors, for which to date systemic therapy was the only remaining option. The current standard for this selective internal radiotherapy or radioembolization is yttrium-90 glass or resin microspheres. This review discusses the indications, the technique, and the therapeutic results of microsphere-based radioembolization.

The human cerebellum and temporal information processing--results from a PET experiment.

Changes of cerebellar blood flow were studied in normal humans using positron emission tomography (PET). A motor driven peg marked pairs of lines on subjects' right hands at different velocities. Subjects had to decide whether the second line was marked slower or faster than the first. Estimation of velocity (compared with control, i.e. presentation of lines at constant velocity) led to increases of regional cerebral blood flow (rCBF) in the left cerebellar hemisphere and vermis. Presentation of lines at constant velocity (compared with rest) activated the right cerebellar hemisphere. We conclude that the cerebellum is involved in temporal information processing even in the absence of motor output. This process can be separated from mere presentation of somatosensory stimuli.

Localization of a cerebellar timing process using PET.

We used positron emission tomography (PET) to localize a cerebellar timing function. Six healthy volunteers estimated time differences by comparing a test interval (defined by two tones) with a standard interval. In the timing condition, subjects lifted their right index finger if the test interval was shorter and their right middle finger if it was longer than the standard interval. In the control condition, the two intervals were identical and subjects had to alternate between lifting their index and middle fingers. We examined regional cerebral blood flow (rCBF) using the standard C15O2 inhalation technique. Comparison of control and rest conditions revealed significant increases of rCBF during the control condition in the inferior parts of the ipsilateral cerebellar hemisphere, reflecting finger movements. Comparison of timing and control conditions showed additional activations of the cerebellar vermis and hemispheres bilaterally during the timing condition, reflecting the cerebellar timing process. We conclude that the cerebellum is involved in time-critical perception ("timing"). This nonmotor task can be separated from a motor task (finger movement).

Collimator optimization for lesion detection incorporating prior information about lesion size.

A Bayesian estimator has been developed as a paradigm for human observer performance in detecting lesions of unknown size in a uniform noisy background. The Bayesian observer used knowledge of the range of possible lesion sizes as a prior; its predictions agreed well with the results of a six-observer perceptual study. The average human response to changes in collimator resolution, as measured by the detectability index, dA, was tracked by the Bayesian detector's signal-to-noise ratio (SNR) somewhat better than by two other estimation models based, respectively, on lesser and greater degrees of lesion size uncertainty. As the range of possible lesion sizes increased, the Bayesian detector's SNR decreased and the optimal collimator resolution shifted towards better resolution. An analytic approximation for the variance of lesion activity estimates (which included the same prior) was shown to predict the variance of the Bayesian estimator over a wide range of collimator resolution values. Because the bias of the Bayesian estimator was small (< 1%), the analytic variance estimate permitted a rapid and convenient prediction of the Bayesian detection SNR. This calculation was then used to optimize the geometric parameters of a two-layer tungsten collimator being constructed from crossed grids for a new imaging detector. A Monte Carlo program was first run to estimate all contributions to the radial point-spread function for collimators of differing tungsten contents and spatial resolution values, imaging 140-keV photons emitted from the center of a 15-cm-diameter, water-filled attenuator. The optimal collimator design for detecting lesions with unknown diameters in the range 2.5-7.5 mm yielded a system resolution of approximately 8.5-mm FWHM, a geometric collimator efficiency of 1.21 x 10(-4), and a single-septum penetration probability of 1%.

Development and validation of a Monte Carlo simulation of photon transport in an Anger camera.

The geometric component of the point spread function (PSF) of a gamma camera collimator can be determined analytically, and the penetration component can be calculated readily by numerical ray-tracing. A Monte Carlo simulation of photon transport which includes collimator scatter is developed. The simulation was implemented with an array processor which propagates up to 1024 photons in parallel, allowing accurate estimates of the total radial PSF in less than a day. The simulation was tested by imaging monoenergetic point sources of Tc-99m, Cr-51, and Sr-85 (140, 320, and 514 keV, respectively) on a General Electric Star Cam with low-energy, general-purpose, and medium-energy collimators. Comparisons of measured and simulated PSFs demonstrate the validity of the model and the significance of collimator scatter in the degradation of image quality.

Increased iofetamine I 123 brain uptake in metastatic melanoma.

Four of five patients with brain metastases from melanoma had increased lofetamine I 123 uptake in the region of the tumor deposits. A comparison group of five patients with melanoma with no clinical or radiologic evidence of brain involvement and 46 of 47 patients without malignant melanoma but with known brain tumors of other histologic types had normal or decreased iofetamine I 123 brain uptake in the region of the tumor. An exception was one patient whose metastatic small cell lung cancer to the brain showed focally increased uptake. These findings suggest that certain brain tumors such as melanoma are capable of selectively binding iofetamine I 123 because of specific chemical properties of the radiopharmaceutical. Increased uptake of iofetamine I 123 in brain lesions in a patient at risk for metastatic melanoma may be a useful aid to differential diagnosis.

Single photon emission computed tomography in Alzheimer's disease. Abnormal iofetamine I 123 uptake reflects dementia severity.

To determine whether abnormalities in regional cerebral functional activity estimated by iofetamine hydrochloride I 123 and single photon emission computed tomography can be detected in mild or moderate as well as severe cases of Alzheimer's disease (AD), we performed iofetamine I 123-single photon emission computed tomography in 37 patients with probable AD (nine patients with mild, 18 patients with moderate, and ten patients with severe dementia) and nine age-matched control subjects. Iofetamine I 123 uptake was measured in right and left frontal, temporal, parietal, and occipital cortices. Mean (right and left) iofetamine I 123 activity was lowest in the parietal region of patients with AD and was significantly reduced in the other three regions compared with control subjects. Only in the parietal region was lower relative iofetamine I 123 activity associated with an impaired level of patient function and with cognitive deficit.

Collimator selection for SPECT brain imaging: the advantage of high resolution.

We compared a prototype long-bore (LB) high-resolution collimator with a low-energy, general-purpose collimator (LEGP) using 99mTc and 123I. The LB collimator provided a 56% improvement in tomographic resolution (autocorrelation width) over the LEGP for 99mTc; for 123I, the gain was 79%, providing substantially improved contrast for small structures. The sensitivity of the LB collimator, however, is only 32% of that of the LEGP. The imaging tasks to be performed on [123I]IMP brain scans involve localization and discrimination of small, high-contrast brain structures and detection of abnormalities in shape, size, or uptake, rather than simple detection of lesions. Observer performance in such higher-order imaging tasks is known to depend on high spatial resolution, even at the cost of sensitivity. Patient studies confirmed that, for resolution-limited tasks, the increase in resolution outweighs the increased noise due to a loss in sensitivity. When the tomographic resolution of the LB collimator was degraded by smoothing to that of the LEGP, the noise in the LB images was lower than that of the LEGP by a factor of 2.9 for the same imaging time, demonstrating the advantage of high-resolution detectors and a smooth reconstruction filter over low-resolution detectors without smoothing. Therefore, collimators designed for high resolution, even at substantial cost in sensitivity, are expected to yield significant improvements for brain SPECT. Geometric calculations show that commercially available low-energy, high-resolution cast collimators promise to meet these requirements.

Caudate nucleus infarction demonstrated by N-isopropyl-p iodoamphetamine SPECT imaging using a rotating gamma camera.

N-isopropyl p-iodoamphetamine (I-123 IMP) was used in two patients with previous unilateral basal ganglia infarcts documented by CT of the head. Tomographic images obtained with a commercially available rotating gamma camera equipped with a long-bore collimator showed corresponding areas of decreased uptake in the head of the caudate nuclei. Detection of such small areas of decreased perfusion is possible using SPECT and I-123 radiolabeled IMP.

Inversion of the 3D Radon transform for a multidetector, point-focused SPECT brain scanner.

The Radon transform is presented for unattenuated projection data acquired with a multidetector, point-focused SPECT brain scanner. The three-dimensional (3D) integral transform is shown to be exactly invertible only for the case of an ideal machine whose detectors scan away from the source to infinity in all directions. The two-dimensional (2D) ramp filter reconstruction algorithm previously used for this scanner is a limiting case of the 3D method and is exact only for sources with cylindrical symmetry, (f(x,y,z) = f(x,y) for all z). Projection data from a long cylinder and a 1.5 cm thick disc of equal diameters and activity concentrations were simulated by computer for the same scan pattern used on the machine. The data were reconstructed with both the 2D and 3D analytic methods. The 2D method produced a 20% bowl-shaped dip in the centre of the disc, whereas the central slice of the 3D reconstruction was more than 97% accurate. The effective, noise-equivalent sensitivity when reconstructing the central slice of the disc with the necessary 3D method is 10.1 times lower than the sensitivity obtained for the long cylindrical source when reconstructing with the 2D method.