Evaluation of a Gadolinium-Based Nanoparticle (AGuIX) for Contrast-Enhanced MRI of the Liver in a Rat Model of Hepatic Colorectal Cancer Metastases at 9.4 Tesla.

PURPOSE: The aim of this study was to compare a Gd-based nanoparticle (AGuIX) with a standard extracellular Gd-based contrast agent (Gd-DOTA) for MRI at 9.4 T in rats with hepatic colorectal cancer metastases. MATERIALS AND METHODS: 12 rats with hepatic metastases were subjected to MRI using a 9.4 T animal scanner. T1w self-gated FLASH sequences (TR/TE = 45/2.5 ms, alpha = 45°, TA = 1: 23 min, FOV = 5.12 × 5.12 cm(2), matrix = 256 × 256) were acquired before and at 10 time points after contrast injection. Each animal received 0.1 mmol/kg BW Gd-DOTA i.v. 2 days later AGuIX was applied at 0.01 mmol/kg BW (representing equal Gd doses). The SNR of normal liver (SNRliver), hyper- and hypoenhancing parts of tumors (SNRtumor, hyperenh/SNRtumor, hypoenhanc), erector spinae muscle (SNRmuscle), CNR and lesion enhancement (LE) were calculated based on ROI measurements. RESULTS: Mean SNRliver (Gd-DOTA: 14.6 +/- 0.7; AGuIX: 28.2+/- 2.6, p < 0.001), SNRtumor, hyperenhanc (Gd-DOTA: 18.6 +/- 1.2; AGuIX: 29.6 +/- 2.8, p < 0.001), SNRtumor, hypoenhanc (Gd-DOTA: 12.0 +/- 0.7; AGuIX: 15.4 +/- 0.7, p < 0.001), SNRmuscle (Gd-DOTA: 12.3 +/- 0.3; AGuIX: 14.0 +/- 0.7, p < 0.001), mean CNR (Gd-DOTA: -2.5 +/- 0.2; AGuIX: -7.5 +/- 1.0, p < 0.001) and LE (Gd-DOTA: 3.8 +/- 0.7; AGuIX: 14.9 +/- 2.8, p = 0.001) were significantly higher using AGuIX. Regardless of the larger molecular size, AGuIX demonstrates an early peak enhancement followed by a continuous washout. CONCLUSION: AGuIX provides better enhancement at 9.4 T compared to Gd-DOTA for equal doses of applied Gd. This is based on the molecule structure and the subsequent increased interaction with protons leading to a higher relaxivity. AGuIX potentially ameliorates the conspicuity of focal liver lesions and may improve the sensitivity in diagnostic imaging of malignant hepatic tumors. KEY POINTS: AGuIX provides superior enhancement as compared to the extracellular compound Gd-DOTA at 9.4 T. AGuIX may improve the detection and diagnostic sensitivity of malignant focal liver lesions. The small size of AGuIX allows for fast renal clearance and prevents undesirable accumulation in the body.

Novel neutron resonance mode in dx2-y2-wave superconductors.

We show that a new resonant magnetic excitation at incommensurate momenta, observed recently by inelastic neutron scattering experiments on YBa2Cu3O6.85 and YBa2Cu3O6.6, is a spin exciton. Its location in the Brillouin zone and its frequency are determined by the momentum dependence of the particle-hole continuum. We identify several features that distinguish this novel mode from the previous resonance mode observed near Q=(pi,pi).

Proximity effects and quantum dissipation in the chains of YBa2Cu3O6+x.

We argue that the results of recent scanning tunneling microscopy, angle-resolved photoemission, and infrared spectroscopy experiments on the CuO chains of YBa2Cu3O6+x are consistently explained within a proximity model by the interplay of a coherent chain-plane and an incoherent and indirect interchain coupling. We show that the CuO2 planes act as an Ohmic heat bath for the chain fermions and induce a substantial quantum dissipation. Below the planar T(c), charge excitations in the chains acquire a universal superconducting gap.

Local defect in metallic quantum critical systems.

We present a theory of a single point, line, or plane defect coupling to the square of the order parameter in a metallic system near a quantum critical point at or above its upper critical dimension. At criticality, a spin droplet is nucleated around the defect with its core size determined by the strength of the defect potential. Outside the core a universal slowly decaying tail of the droplet is found, leading to many dissipative channels coupling to the droplet and to a complete suppression of quantum tunneling. We propose an NMR experiment to measure the impurity-induced changes in the local spin susceptibility.

Resonance peak in Sr(2)RuO(4): signature of spin triplet pairing.

We study the dynamical spin susceptibility, chi(q,omega), in the normal and superconducting states of Sr(2)RuO(4). In the normal state, we find a peak in the vicinity of Q(i) approximately (0.72 pi,0.72 pi) in agreement with recent inelastic neutron scattering experiments. We predict that for spin triplet pairing in the superconducting state a resonance peak appears in the out-of-plane component of chi, but is absent in the in-plane component. In contrast, no resonance peak is expected for spin singlet pairing.

How force plate size influences the probability of valid gait data acquisition.

Acquiring valid data is one of the major difficulties in gait analysis. Our previous study proved that, using the currently commercially available force plates, there is a low probability that every trial will be successful, and some subjects will have to alter their gait pattern to have a successful trial. In the present study the possibility of using an instrumented floor consisting of more than two force places of small size was investigated. This appears as the most promising solution to simultaneously solve the contrasting requirements of avoiding double contact on each element while acquiring complete gait cycles. In this work the set of mathematical equations previously developed for systems of two force plates was extended to consider any number of plates. Using gait data of 280 subjects from The Ohio State University Gait Laboratory, a software simulation was developed and performed to analyze different combinations of element and system sizes, and to calculate the probability of a successful gait analysis trial.

Average power spectral density of physiological tremor in normal subjects.

The measurement technologies currently available to quantitatively evaluate neurological tremors have several limitations. For this reason the assessment of disorders involving tremor is largely based on subjective clinical evaluation of the patient. The availability of a high-sensitivity, portable and easy to use instrument based on force plate technology, coupled with a customized data analysis protocol could represent a useful tool for the clinician. To verify such a hypothesis, baseline physiological tremor information in a standing posture was collected from normal subjects. A lightweight portable force plate was built and used in collecting vertical ground reaction force data, which was subsequently analyzed for frequency content and power spectral distribution. Repeatability of results in a group of subjects without any diagnosed neurological disorders, and intra-subject repeatability, as well as influence of footwear were investigated.

Oversampling data acquisition to improve resolution of digitized signals.

The ability to capture analog signals in a digital format suitable for subsequent storage, processing and analysis by a computer has revolutionized many scientific fields, including biomechanics. In the process of going from the analog signal to its digital representation, it is essential to maintain as much of the original signal content as possible. There is always a loss of information associated with the conversion from analog to digital, independently of how it is actually performed. The only possibility to reduce the loss of information is to increase the number of states or the resolution of the digital signal. The method presented here, based on the same theory used in oversampling analog to digital converters, is applicable to digital signals acquired using any converter. In most situations this method provides a feasible and inexpensive technique to significantly improve the amplitude resolution of the analog to digital conversion. This can be of fundamental importance when the information of interest is small in amplitude compared to the overall signal, or when subsequent ill-conditioned operations, like the computation of the derivatives of the signal, are to be performed.

Probability of valid gait data acquisition using currently available force plates.

A major difficulty in using force plates for gait analysis is to have a foot fall completely on the instrument while not having the other foot in contact with the same device. This translates into more trials (and time) required to obtain valid data. In order to estimate the probability of a successful trial, which is related to the overall number of trials required, the dimensional relationships between force plate, foot and gait cycle were investigated. In particular, it was analyzed how the dimensions of the plate, the size of foot, the step length and width affect the probability of having a successful trial when acquiring one or two subsequent foot falls using one or two force plates respectively. The equations obtained can also be used to estimate the force plate dimensions that allow for the minimum number of trials for a specific group of subjects. To illustrate this approach, commercially available force plate sizes were statistically evaluated using gait data collected in recent years at The Ohio State University Gait Laboratory from patients with different pathologies. The force plate length maximizing the probability of a successful trial was identified for this specific population.

The realization of a haptic (force feedback) interface device for the purpose of angioplasty surgery simulation.

Simulation is becoming an increasingly accepted method for training personnel for complex or high risk tasks. With the advent of modern Virtual Reality (VR) technology, such simulations are becoming more and more immersive. One significant limitation to the advance of this science is the challenges associated with simulating the touch or feel of various tasks in conjunction with VR simulations. This work has focused on creating and assessing the feasibility of haptic technology for high fidelity surgery simulation. It has culminated in a prototypical interface device to provide tactile feedback during the simulation of complex interventional radiology procedures such as Angioplasty. This device extends state of the art motion control, distributed computing processes, high resolution sensors for real-time feedback, and modular design techniques to accomplish these goals. The realization of the device, its capabilities, interfacing requirements, its limitations, and future extensions will be presented here.

The mechanics of drop landing on a flat surface--a preliminary study.

In an effort to investigate the mechanics of drop landing on a flat surface, bilateral performance characteristics during the landing were investigated. Two force plates were used as landing surfaces, and the six component kinetic time histories and the path of the center of pressure were measured for both feet. The forces were combined to obtain the resultant ground reaction force, allowing comparison between the global resultant and the forces developed by each leg. The results highlighted an asymmetry, and the presence of one dominant leg during the landing: the contact with the plate occurred with a delay between the dominant and non-dominant legs, and the forces applied to the plate were also unequal. Furthermore, due to the high rate of data acquisition and sensitivity of the force plates used, it was possible to correlate the peaks present in the global vertical reaction force with the impact of the different anatomical segments of each foot. The availability of such high resolution information presents to researchers and clinicians with more key identifiers to quantify various phenomena, potentially injury prevention, pathological diagnosis or quantification, and others.