Image technique optimization in MR imaging of a titanium alloy joint prosthesis

The purpose of this study was to explore systematically the effect of the imaging parameters changeable by the user in spin-echo (SE) imaging sequences to minimize image distortion when imaging joint prostheses. A titanium alloy hip joint prosthesis was studied at 1.0 T. The SE imaging parameters were bandwidth/pixel (BW/p), TE, strength of encoding gradients (matrix size), echo train length (ETL), and direction of phase and frequency encoding. The effect of ETL in rapid acquisition relaxation enhanced (RARE) sequences was also evaluated with a turbo-SE sequence using a different ETL with the same TR and an effective TE. It is concluded that an optimized image quality can be achieved in SE imaging by using a high bandwidth/pixel value (at least 130 Hz/pixel), a high resolution matrix (256–512), sequences with multiple refocusing, and a frequency-encoding axis parallel to the long axis of the prosthesis. The degree of distortion is reduced with this optimized technique.     

Deficiencies in the transfer and availability of clinical trials evidence: a review of existing systems and standards

ABSTRACT: BACKGROUND: Decisions concerning drug safety and efficacy are generally based on pivotal evidence provided by clinical trials. Unfortunately, finding the relevant clinical trials is difficult and their results are only available in text-based reports. Systematic reviews aim to provide a comprehensive overview of the evidence in a specific area, but may not provide the data required for decision making. METHODS: We review and analyze the existing information systems and standards for aggregate level clinical trials information from the perspective of systematic review and evidence-based decision making. RESULTS: The technology currently used has major shortcomings, which cause deficiencies in the transfer, traceability and availability of clinical trials information. Specifically, data available to decision makers is insufficiently structured, and consequently the decisions cannot be properly traced back to the underlying evidence. Regulatory submission, trial publication, trial registration, and systematic review produce unstructured datasets that are insufficient for supporting evidence-based decision making. CONCLUSIONS: The current situation is a hindrance to policy decision makers as it prevents fully transparent decision making and the development of more advanced decision support systems. Addressing the identified deficiencies would enable more efficient, informed, and transparent evidence-based medical decision making.     

Influence of physical activity on vertebral strength during late adolescence

Background contextReduced vertebral strength is a clear risk factor for vertebral fractures. Men and women with vertebral fractures often have reduced vertebral size and bone mineral density (BMD). Vertebral strength is controlled by both genetic and developmental factors. Malnutrition and low levels of physical activity are commonly considered to result in reduced bone size during growth. Several studies have also demonstrated the general relationship between BMD and physical activity in the appendicular skeleton.PurposeIn this study, we wanted to clarify the role of physical activity on vertebral bodies. Vertebral dimensions appear to generally be less pliant than long bones when lifetime changes occur. We wanted to explore the association between physical activity during late adolescence and vertebral strength parameters such as cross-sectional size and BMD.Study designThe association between physical activity and vertebral strength was explored by measuring vertebral strength parameters and defining the level of physical activity during adolescence.Patient sampleThe study population consisted of 6,928 males and females who, at 15 to 16 and 19 years of age, responded to a mailed questionnaire inquiring about their physical activity. A total of 558 individuals at the mean age of 21 years underwent magnetic resonance imaging (MRI) scans.MethodsWe measured the dimensions of the fourth lumbar vertebra from the MRI scans of the Northern Finland Birth Cohort 1986 and performed T2* relaxation time mapping, reflective of BMD. Vertebral strength was based on these two parameters. We analyzed the association of physical activity on vertebral strength using the analysis of variance.Results and conclusionsWe observed no association between the level of physical activity during late adolescence and vertebral strength at 21 years.     

The effect of model order selection in group PICA

Independent component analysis (ICA) of functional MRI data is sensitive to model order selection. There is a lack of knowledge about the effect of increasing model order on independent components' (ICs) characteristics of resting state networks (RSNs). Probabilistic group ICA (group PICA) of 55 healthy control subjects resting state data was repeated 100 times using ICASSO repeatability software and after clustering of components, centrotype components were used for further analysis. Visual signal sources (VSS), default mode network (DMN), primary somatosensory (S₁), secondary somatosensory (S₂), primary motor cortex (M₁), striatum, and precuneus (preC) components were chosen as components of interest to be evaluated by varying group probabilistic independent component analysis (PICA) model order between 10 and 200. At model order 10, DMN and VSS components fuse several functionally separate sources that at higher model orders branch into multiple components. Both volume and mean z‐score of components of interest showed significant (P < 0.05) changes as a function of model order. In conclusion, model order has a significant effect on ICs characteristics. Our findings suggest that using model orders ≤20 provides a general picture of large scale brain networks. However, detection of some components (i.e., S₁, S₂, and striatum) requires higher model order estimation. Model orders 30–40 showed spatial overlapping of some IC sources. Model orders 70 ± 10 offer a more detailed evaluation of RSNs in a group PICA setting. Model orders > 100 showed a decrease in ICA repeatability, but added no significance to either volume or mean z‐score results. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

MR perfusion, diffusion and BOLD imaging of methotrexate-exposed swine brain

PURPOSE: To evaluate the methotrexate (MTX)-exposed swine brain, functional magnetic resonance imaging (MRI), including perfusion, diffusion, and blood-oxygen-level-dependent (BOLD) contrast imaging, was used. MATERIAL AND METHODS: Juvenile pigs received either 2 x 5 g/m(2), or 5 x 2 g/m(2) MTX intravenously within one month. MRI was performed (sedative: propofol) before (14-17 kg, N = 6) and after (21-27 kg, N = 4) the MTX exposure. Also, age-matched controls (22-27 kg, N = 4) were imaged. RESULTS: After the MTX exposure, reduced (from 2%-4% to 0%-1%) or negative (-2% to -3%) BOLD responses were detected; apparent diffusion coefficient (ADC) or relative perfusion values did not change. CONCLUSION: This study suggests that MTX-related changes in the brain may be detected as changes in flow-metabolism coupling as reduced or negative response (for somatosensory activation) in the BOLD contrast MRI. The contrast agent perfusion MRI, without absolute quantification, may not show global damage in brain perfusion related to the MTX exposure in the swine model used. ADC (in one direction) may not indicate MTX-related changes in the brain.