A longitudinal study of MARS MRI scanning of soft-tissue lesions around metal-on-metal total hip arthroplasties and disease progression.

We investigated the changes seen on serial metal artefact reduction magnetic resonance imaging scans (MARS-MRI) of metal-on-metal total hip arthroplasties (MoM THAs). In total 155 THAs, in 35 male and 100 female patients (mean age 70.4 years, 42 to 91), underwent at least two MRI scans at a mean interval of 14.6 months (2.6 to 57.1), at a mean of 48.2 months (3.5 to 93.3) after primary hip surgery. Scans were graded using a modification of the Oxford classification. Progression of disease was defined as an increase in grade or a minimum 10% increase in fluid lesion volume at second scan. A total of 16 hips (30%) initially classified as 'normal' developed an abnormality on the second scan. Of those with 'isolated trochanteric fluid' 9 (47%) underwent disease progression, as did 7 (58%) of 'effusions'. A total of 54 (77%) of hips initially classified as showing adverse reactions to metal debris (ARMD) progressed, with higher rates of progression in higher grades. Disease progression was associated with high blood cobalt levels or an irregular pseudocapsule lining at the initial scan. There was no association with changes in functional scores. Adverse reactions to metal debris in MoM THAs may not be as benign as previous reports have suggested. Close radiological follow-up is recommended, particularly in high-risk groups.

On the capabilities and computational costs of neuron models.

We review the Hodgkin-Huxley, Izhikevich, and leaky integrate-and-fire neuron models in regular spiking modes solved with the forward Euler, fourth-order Runge-Kutta, and exponential Euler methods and determine the necessary time steps and corresponding computational costs required to make the solutions accurate. We conclude that the leaky integrate-and-fire needs the least number of computations, and that the Hodgkin-Huxley and Izhikevich models are comparable in computational cost.

A pain in the neck--imaging in neck sepsis.

Deep neck infection has a high morbidity and mortality and the extent of infection is often difficult to estimate clinically. The complex anatomy and the communication between neck spaces means that infection can spread along fascial planes leading to life-threatening complications such as airway compromise, vascular erosion/thrombosis, neural dysfunction, and ultimately descending necrotizing mediastinitis. Imaging has an important role to play in identifying the extent of infection and the presence of complications.

GSTT1 and GSTM1 gene deletions are not associated with hepatotoxicity caused by antitubercular drugs.

BACKGROUND AND OBJECTIVE: Susceptibility to antitubercular drug (ATD)-induced hepatotoxicity may be genetically mediated, with variant alleles of genes such as N-acetyltransferase (NAT2) and CYP2E1 reported as risk factors. Two studies of Asian populations have reported that GSTM1*0 / *0 (null) genotype was a likely predictor of hepatotoxicity, whereas another of a Caucasian population implicated GSTT1*0 / *0. We undertook a prospective case-control study to investigate whether GSTM*0 / *0 and GSTT1*0 / *0 were risk factors for ATD-induced hepatotoxicity. METHODS: Pulmonary tuberculosis patients on isoniazid, rifampicin and pyrazinamide who developed hepatotoxicity using defined criteria were prospectively identified. These cases were then matched with at least one control subject on the same drugs but without hepatotoxicity. Genotyping for GSTM1 and GSTT1 was performed by multiplex PCR on genomic DNA. The odds ratios for the frequency of specific GSTM1 and GSTT1 homozygotes in the case and control subjects were calculated to test for association between the genotypes and hepatotoxicity. RESULTS AND DISCUSSION: Hundred and fifty-one subjects (51 cases, 100 controls) were enrolled. Odds ratio for GSTM1 null genotype was 1.00 (95% CI 0.51-1.97) and GSTT1 null was 2.02 (95% CI 0.39-10.39), respectively, showing that these genotypes are not associated with hepatotoxicity. CONCLUSION: GSTM1 *0 / *0 or GSTT1 *0 / *0 or both null genotypes, do not appear to be associated with ATD-induced hepatotoxicity in our Indian population.

The direct simulation of acoustics on Earth, Mars, and Titan.

With the recent success of the Huygens lander on Titan, a moon of Saturn, there has been renewed interest in further exploring the acoustic environments of the other planets in the solar system. The direct simulation Monte Carlo (DSMC) method is used here for modeling sound propagation in the atmospheres of Earth, Mars, and Titan at a variety of altitudes above the surface. DSMC is a particle method that describes gas dynamics through direct physical modeling of particle motions and collisions. The validity of DSMC for the entire range of Knudsen numbers (Kn), where Kn is defined as the mean free path divided by the wavelength, allows for the exploration of sound propagation in planetary environments for all values of Kn. DSMC results at a variety of altitudes on Earth, Mars, and Titan including the details of nonlinearity, absorption, dispersion, and molecular relaxation in gas mixtures are given for a wide range of Kn showing agreement with various continuum theories at low Kn and deviation from continuum theory at high Kn. Despite large computation time and memory requirements, DSMC is the method best suited to study high altitude effects or where continuum theory is not valid.

Accuracy of liver-specific magnetic resonance imaging as a predictor of chemotherapy-associated hepatic cellular injury prior to liver resection.

BACKGROUND/AIMS: To evaluate the diagnostic precision of chemical-shift imaging MRI and ferucarbotran-enhanced MRI for hepatic parenchymal injury prior to hepatic resection for colorectal metastases. METHODS: Preoperative MRI criteria were used to score 37 patients with colorectal liver metastases by two independent radiologists, blinded to outcomes, for signal drop-out on chemical-shift imaging MRI and ferucarbotran uptake and compared to blinded standardized histopathological endpoints of steatosis, steatohepatitis and sinusoidal dilatation. Sensitivity, specificity, predictive values and the area under the receiver operating characteristic curve (AUC) were calculated for the MRI sequences. RESULTS: On histology, severe steatosis, steatohepatitis and sinusoidal dilation were evident in 6 (16.2%), 4 (10.8%) and 9 (24.3%) patients respectively. Chemical-shift imaging MRI had a positive predictive value (PPV) of 100% for severe steatosis, 80% for steatohepatitis and zero for sinusoidal dilatation, with an AUC of 1.0, 0.99 and 0.36 respectively. Ferucarbotran-enhanced MRI had a 100% PPV for the detection of severe sinusoidal dilatation, with an AUC of 0.61. CONCLUSIONS: This study demonstrates that liver-specific MRI can accurately predict the severity of pre-existing hepatic injury. Moreover, it may play a key role in planning the timing and extent of chemotherapy and hepatic resection for colorectal metastases.

MRI of intermittent meniscal dislocation in the knee.

The aim of this work was to demonstrate meniscal dislocation on magnetic resonance (MR) imaging, in cases with no meniscal tear but a strongly suggestive clinical history of reproducible intermittent locking of the knee. Three patients with a strong history of intermittent knee locking had negative initial MR scans but were able to reproduce locking of their knee voluntarily. A further MR study involving T(2) weighted sagittal and coronal imaging of the knee was performed in the "locked" position using either a standard knee coil if the joint was straight or a flexible coil if flexed. MR demonstrated meniscal dislocation in all three patients when they intentionally adopted the "locked" knee position. On review of the initially negative scans, the menisci were confirmed to be normal in appearance. All three were confirmed arthroscopically to have deficiency of the corresponding meniscocapsular ligaments with instability of the meniscus to direct probing, but no meniscal tear. A normal conventional MR may not detect the cause of intermittent locking, particularly in the absence of a meniscal tear. When patients are able to intentionally adopt the "locked" position at will, a further study in the "locked" position can be diagnostic.

Predicting absorption and dispersion in acoustics by direct simulation Monte Carlo: Quantum and classical models for molecular relaxation.

In the current study, real gas effects in the propagation of sound waves are simulated using the direct simulation Monte Carlo method for a wide range of frequencies. This particle method allows for treatment of acoustic phenomena at high Knudsen numbers, corresponding to low densities and a high ratio of the molecular mean free path to wavelength. Different methods to model the internal degrees of freedom of diatomic molecules and the exchange of translational, rotational and vibrational energies in collisions are employed in the current simulations of a diatomic gas. One of these methods is the fully classical rigid-rotor/harmonic-oscillator model for rotation and vibration. A second method takes into account the discrete quantum energy levels for vibration with the closely spaced rotational levels classically treated. This method gives a more realistic representation of the internal structure of diatomic and polyatomic molecules. Applications of these methods are investigated in diatomic nitrogen gas in order to study the propagation of sound and its attenuation and dispersion along with their dependence on temperature. With the direct simulation method, significant deviations from continuum predictions are also observed for high Knudsen number flows.

RanGAP-mediated nuclear protein import in vascular smooth muscle cells is augmented by lysophosphatidylcholine.

The intracellular mechanism responsible for the mitogenic effects of lysophosphatidylcholine (LPC) is unclear. Import of proteins from the cytoplasm into the cell nucleus is integral to the regulation of gene expression and cell growth. We hypothesized that LPC exerts its intracellular effects through alterations in nuclear protein import. Rabbit aortic smooth muscle cells incubated with LPC induced a significant increase in cell proliferation in both quiescent cells (63.2+/-6.48% of control) and cells grown in 1% fetal bovine serum (FBS) (28.3+/-7.35% of control). Vascular smooth muscle cells were preincubated with LPC then microinjected with a marker protein for nuclear import. A significant stimulation of nuclear protein transport was observed. Using a conventional nuclear protein import assay in permeabilized cells, a significant stimulation of import (72.3+/-5.2% of control) was again observed when the cytosolic nuclear import cocktail was treated with LPC. This effect was not observed with other lysophosphatidyl species. LPC also activated the extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase (MAPK) pathway, and this was blocked by 2'-amino-3'-methoxyflavone (PD98059), which inhibits the activation of ERK 1/2. The stimulation of nuclear import was also blocked by PD98059. LPC-induced MAPK activation augmented GTP hydrolysis by RanGAP, a RanGTPase activating protein and a critical regulatory component of nuclear protein import, and this stimulation was again blocked by PD98059. We conclude that LPC alters gene expression and cell proliferation through striking effects on nuclear protein import via a MAP kinase-induced activation of RanGAP. This may play an important role in cancer and atherosclerosis and other disorders involving accelerated cell growth/proliferation.

A comparison of voluntary versus stimulated strength training of the human adductor pollicis muscle.

The effects of voluntary versus electrically stimulated isometric strength training of the adductor pollicis on muscle strength were compared. The adductor pollicis of one hand was trained using voluntary contractions at 50% of the maximum voluntary contraction force, and the other with 30 Hz tetani (stimulated contractions), which produced a force equivalent to 30-50% of the maximum voluntary force. Tetani were delivered with surface electrodes placed over the ulnar nerve at the wrist. Both protocols resulted in large, significant increases in maximum voluntary strength of 79+/-44% (voluntary) and 74+/-41% (stimulated) (mean+/-s; P< 0.002). The time course of the changes was very similar for both protocols and there was no significant difference between the strength increases produced by the two protocols. The large gains resulting from stimulated training argues against central adaptations as a major contributor to the strength increases following training.