Diffusion-weighted MRI in the characterization of cystic pancreatic lesions: usefulness of ADC values

Purpose

To evaluate the usefulness of diffusion-weighted magnetic resonance imaging (DW-MRI) in the differentiation of cystic pancreatic lesions.

Materials and Methods

Institutional review board approval was obtained, and written informed consent was taken from all enrolled subjects. Fifty-four patients with cystic pancreatic lesions of at least 1 cm in diameter (range:10–96 mm) at ultrasonography and/or computed tomography and 10 normal subjects underwent MRI at 1.5 T. These subjects included thirty-four patients with intraductal papillary mucinous tumors (IPMTs), 10 with pseudocysts, 5 with serous cystoadenoma and 5 with mucinous cystoadenoma. The MR protocol included axial T1w and T2w sequences and coronal MR cholangiopancreatography images. DW-MRI was performed using a breath-hold single-shot echo-planar sequence with a b gradient factor value of 500 s/mm² in the three orthogonal axes. Apparent diffusion coefficient (ADC) was calculated for cerebrospinal fluid, normal pancreatic parenchyma, and for each focal pancreatic lesion. Imaging results were correlated with endoscopic retrograde cholangiopancreatography, endoscopic ultrasound-guided fine needle aspiration, surgery and/or imaging follow-up.

Results

Mean ADC value was 4.1×10⁻³ mm²/s for cerebrospinal fluid, 1.73×10⁻³ mm²/s for normal pancreatic parenchyma, 4.09×10⁻³ mm²/s for IPMT, 3.89×10⁻³ mm²/s for mucinous cystoadenoma, 3.65×10⁻³ mm²/s for serous cystoadenoma and 2.83×10⁻³ mm²/s for pseudocyst. Mean ADC values of each of the different types of pancreatic lesions were statistically different (P<.05).

Conclusion

DW-MRI may be helpful in the differential diagnosis of cystic pancreatic lesions.     

High-pressure phases of hydrogen cyanide: formation of hydrogenated carbon nitride polymers and layers and their electronic properties

We have performed a set of first-principles simulations to consider the possible phase transitions in molecular crystals of HCN under high pressure. Our calculations reveal several transition paths from the orthorhombic phase to tetragonal and then to triclinic phases. The transitions from the orthorhombic to the tetragonal phases are of the second order, whereas those from the tetragonal to the triclinic phases turn out to be of the first-order type and characterized by an abrupt decrease in volume. Our calculations show that, by adjustment of the temperature and pressure of the HCN molecular crystal, novel layered and polymeric crystals with insulating, semiconducting or metallic properties can be found. Based on our simulation results, two different crystal formation mechanisms are deduced. The stabilities of the predicted structures at ambient pressure are further assessed by performing phonon or MD simulations. In addition, the electron transport properties of the predicted polymers are obtained using the non-equilibrium Green's function technique combined with density functional theory. The results show that the polymers have metallic-like I-V characteristics.     

Evidence of Sn adatoms quantum tunneling at the alpha-Sn/Si(111) surface

We present a low-temperature scanning tunneling microscopy study of the alpha-Sn/Si(111) surface that demonstrates the fluctuating behavior of the Sn adatoms. The dynamical fluctuation model, successfully applied in describing the alpha-Sn/Ge(111) surface, is proposed for the related alpha-Sn/Si(111) surface too, although with a much lower transition temperature. In addition, a new phenomenon appears responsible for the unexpected evidence that the average oscillation frequency remains constant at temperatures lower than 15 K, in contradiction to the Arrhenius law. We explain this phenomenon as quantum tunneling of Sn adatoms.     

A Quantum-Like Description of the Planetary Systems

The Titius–Bode law for planetary distances is reviewed. A model describing the basic features of this rule in the “quantum-like” language of a wave equation is proposed. Some considerations about the ’t Hooft idea on the quantum behavior of deterministic systems with dissipation are discussed.     

Three qubits in a symmetric environment: Dissipatively generated asymptotic entanglement

We study the asymptotic entanglement of three identical qubits under the action of a Markovian open system dynamics that does not distinguish them. We show that by adding a completely depolarized qubit to a special class of two-qubit states, by letting them reach the asymptotic state and by finally eliminating the added qubit, can provide more entanglement than by direct immersion of the two qubits within the same environment.     

Adaptive field-of-view imaging for efficient receive beamforming in medical ultrasound imaging systems

Quadrature demodulation-based phase rotation beamforming (QD-PRBF) is commonly used to support dynamic receive focusing in medical ultrasound systems. However, it is computationally demanding since it requires two demodulation filters for each receive channel. To reduce the computational requirements of QD-PRBF, we have previously developed two-stage demodulation (TSD), which reduces the number of lowpass filters by performing demodulation filtering on summation signals. However, it suffers from image quality degradation due to aliasing at lower beamforming frequencies. To improve the performance of TSD-PRBF with reduced number of beamforming points, we propose a new adaptive field-of-view (AFOV) imaging method. In AFOV imaging, the beamforming frequency is adjusted depending on displayed FOV size and the center frequency of received signals. To study its impact on image quality, simulation was conducted using Field II, phantom data were acquired from a commercial ultrasound machine, and the image quality was quantified using spatial (i.e., axial and lateral) and contrast resolution. The developed beamformer (i.e., TSD-AFOV-PRBF) with 1024 beamforming points provided comparable image resolution to QD-PRBF for typical FOV sizes (e.g., 4.6% and 1.3% degradation in contrast resolution for 160 mm and 112 mm, respectively for a 3.5 MHz transducer). Furthermore, it reduced the number of operations by 86.8% compared to QD-PRBF. These results indicate that the developed TSD-AFOV-PRBF can lower the computational requirement for receive beamforming without significant image quality degradation.     

On absence of diffusion near the bottom of the spectrum for a random Schrödinger operator onL 2(ℝ)+

We consider a random Schrödinger operator onL ²(^v) of the form , {C _i} being a covering of ^v with unit cubes around the sites of ^v and {q _i} i.i.d. random variables with values in [0, 1]. We assume that theq _i's are continuously distributed with bounded densityf(q) and that 0<P(q ₀<1/2)=<1. Then we show that an ergodic mean of the quantity dx|x|²|(exp(itH ))(x)|²t ^–1 vanishes provided =g _E(H ), where is well-localized around the origin andg _E is a positiveC -function with support in (0,E),EE*(, |f|). Our estimate ofE*(, |f|) is such that the set {x ^v |V (x) E*(, |f|)} may contain with probability one an infinite cluster of cubes {C _i} which are nearest neighbours. The proof is based on the technique introduced by Fröhlich and Spencer for the analysis of the Anderson model.Work supported in part by C.N.R. (Italy) and NAVF (Norway)On leave of absence from Instituto di Fisica Università di Roma, Italia