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Objective: To compare quantitative measures of image quality, in terms of CT number accuracy, noise, signal-to-noise-ratios (SNRs), and contrast-to-noise ratios (CNRs), at different dose levels with filtered-back-projection (FBP), iterative reconstruction (IR), and model-based iterative reconstruction (MBIR) alone and in combination with orthopedic metal artifact reduction (O-MAR) in a total hip arthroplasty (THA) phantom.Materials and Methods: Scans were acquired from high- to low-dose (CTDIvol: 40.0, 32.0, 24.0, 16.0, 8.0, and 4.0 mGy) at 120- and 140- kVp. Images were reconstructed using FBP, IR (iDose4 level 2, 4, and 6) and MBIR (IMR, level 1, 2, and 3) with and without O-MAR. CT number accuracy in Hounsfield Units (HU), noise or standard deviation, SNRs, and CNRs were analyzed.Results: The IMR technique showed lower noise levels (p < 0.01), higher SNRs (p < 0.001) and CNRs (p < 0.001) compared with FBP and iDose4 in all acquisitions from high- to low-dose with constant CT numbers. O-MAR reduced noise (p < 0.01) and improved SNRs (p < 0.01) and CNRs (p < 0.001) while improving CT number accuracy only at a low dose. At the low dose of 4.0 mGy, IMR level 1, 2, and 3 showed 83%, 89%, and 95% lower noise values, a factor 6.0, 9.2, and 17.9 higher SNRs, and 5.7, 8.8, and 18.2 higher CNRs compared with FBP respectively.Conclusions: Based on quantitative analysis of CT number accuracy, noise values, SNRs, and CNRs, we conclude that the combined use of IMR and O-MAR enables a reduction in radiation dose of 83% compared with FBP and iDose4 in the CT imaging of a THA phantom. [ABSTRACT FROM AUTHOR]

Purpose: To quantify the impact of prosthesis material and design on the reduction of metal artefacts in total hip arthroplasties using virtual monochromatic dual-layer detector Spectral CT imaging.Methods: The water-filled total hip arthroplasty phantom was scanned on a novel 128-slice Philips IQon dual-layer detector Spectral CT scanner at 120-kVp and 140-kVp at a standard computed tomography dose index of 20.0mGy. Several unilateral and bilateral hip prostheses consisting of different metal alloys were inserted and combined which were surrounded by 18 hydroxyapatite calcium carbonate pellets representing bone. Images were reconstructed with iterative reconstruction and analysed at monochromatic energies ranging from 40 to 200keV. CT numbers in Hounsfield Units (HU), noise measured as the standard deviation in HU, signal-to-noise-ratios (SNRs) and contrast-to-noise-ratios (CNRs) were analysed within fixed regions-of-interests placed in and around the pellets.Results: In 70 and 74keV virtual monochromatic images the CT numbers of the pellets were similar to 120-kVp and 140-kVp polychromatic results, therefore serving as reference. A separation into three categories of metal artefacts was made (no, mild/moderate and severe) where pellets were categorized based on HU deviations. At high keV values overall image contrast was reduced. For mild/moderate artefacts, the highest average CNRs were attained with virtual monochromatic 130keV images, acquired at 140-kVp. Severe metal artefacts were not reduced. In 130keV images, only mild/moderate metal artefacts were significantly reduced compared to 70 and 74keV images. Deviations in CT numbers, noise, SNRs and CNRs due to metal artefacts were decreased with respectively 64%, 57%, 62% and 63% (p<0.001) compared to unaffected pellets. Optimal keVs, based on CNRs, for different unilateral and bilateral metal hip prostheses consisting of different metal alloys varied from 74 to 150keV. The Titanium alloy resulted in less severe artefacts and were reduced more effectively compared to the Cobalt alloy.Conclusions: Virtual monochromatic dual-layer Spectral CT imaging results in a significant reduction of streak artefacts produced by beam-hardening in mild and moderate artefacts by improving CT number accuracy, SNRs and CNRs, while decreasing noise values in a total hip arthroplasty phantom. An optimal monochromatic energy of 130keV was found ranging from 74keV to 150keV for different unilateral and bilateral hip prostheses consisting of different metal alloys. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to assess leg muscle quality and give a detailed description of leg muscle involvement in a series of Duchenne muscular dystrophy patients using quantitative MRI and strength measurements. Fatty infiltration, as well as total and contractile (not fatty infiltrated) cross sectional areas of various leg muscles were determined in 16 Duchenne patients and 11 controls (aged 8–15). To determine specific muscle strength, four leg muscle groups (quadriceps femoris, hamstrings, anterior tibialis and triceps surae) were measured and related to the amount of contractile tissue. In patients, the quadriceps femoris showed decreased total and contractile cross sectional area, attributable to muscle atrophy. The total, but not the contractile, cross sectional area of the triceps surae was increased in patients, corresponding to hypertrophy. Specific strength decreased in all four muscle groups of Duchenne patients, indicating reduced muscle quality. This suggests that muscle hypertrophy and fatty infiltration are two distinct pathological processes, differing between muscle groups. Additionally, the quality of remaining muscle fibers is severely reduced in the legs of Duchenne patients. The combination of quantitative MRI and quantitative muscle testing could be a valuable outcome parameter in longitudinal studies and in the follow-up of therapeutic effects. [Copyright &y& Elsevier]

Background Magnetisation transfer imaging (MTI) has the potential to quantify pathological changes in CNS disorders before conventional MRI sequences can detect abnormalities. This makes MTI an attractive technique to apply in both premanifest and manifest HD as an addition to volumetric measures. Aim To investigate MTI parameters and their clinical correlates in premanifest and manifest HD. Method From the TRACK-HD study, 78 participants (28 controls, 25 premanifest gene carriers and 25 manifest HD) were scanned using MTI and T1 weighted MRI. Brain regions were segmented using FSL's automated tools FAST and FIRST on T1 images. This approach yields separate segmentations of grey matter, white matter, caudate nucleus, putamen, pallidum, thalamus, amygdala and hippocampus, of which individual magnetic transfer ratio (MTR) values were calculated. Regression analysis with clinical measures of motor (UHDRS total motor score, speeded tapping, tongue force), cognitive (MMSE, SDMT, Stroop, TMT, Verbal fluency), behavioural functioning (BDI, FrSBe, PBA-s) and the disease burden was performed on gene carriers. Results MTR peak height was reduced in both grey (p<0.004) and white matter (p<0.006) in manifest HD compared with controls. Mean MTR was also reduced in grey matter (p<0.001) and showed a trend in white matter (p<0.052) in manifest HD. No differences between premanifest gene carriers and controls were found. The deep grey matter structures showed a uniform pattern of significantly reduced MTR values in manifest HD (p<0.05) but not in premanifest HD. MTR values correlated with disease burden, motor and cognitive impairment. Conclusion Throughout the brain, disturbances in MTI parameters are apparent in manifest HD and are homogeneous across (subcortical) grey and white matter. The correlation of MTI with clinical features indicates the potential to act as a disease monitor in future clinical trials. [ABSTRACT FROM PUBLISHER]

Abstract: Huntington''s disease (HD) is characterized by brain atrophy. Localized atrophy of a specific structure could potentially be a more sensitive biomarker reflecting neuropathologic changes rather than global volume variation. We examined 90 TRACK-HD participants of which 30 were premanifest HD, 30 were manifest HD and 30 were controls. Using FMRIB''s Integrated Registration and Segmentation Tool, segmentations were obtained for the pallidum, caudate nucleus, putamen, thalamus, accumbens nucleus, amygdala, and hippocampus and overall volumes were calculated. A point distribution model of each structure was obtained using Growing and Adaptive Meshes. Permutation testing between groups was performed to detect local displacement in shape between groups. In premanifest HD overall volume loss occurred in the putamen, accumbens and caudate nucleus. Overall volume reductions in manifest HD were found in all subcortical structures, except the amygdala, as compared to controls. In premanifest HD shape analysis showed small areas of displacement in the putamen, pallidum, accumbens and caudate nucleus. When the premanifest group was split into two groups according to predicted disease onset, the premanifest HD group close to expected disease onset showed more pronounced displacements in caudate nucleus and putamen compared to premanifest HD far from disease onset or the total premanifest group. Analysis of shape in manifest HD showed widespread shape differences, most prominently in the caudal part of the accumbens nucleus, body of the caudate nucleus, putamen and dorsal part of the pallidum. We conclude that shape analysis provides new insights in localized intrastructural atrophy patterns in HD, but can also potentially serve as specific target areas for disease tracking. [Copyright &y& Elsevier]

Abstract: In recent years, graph theory has been successfully applied to study functional and anatomical connectivity networks in the human brain. Most of these networks have shown small-world topological characteristics: high efficiency in long distance communication between nodes, combined with highly interconnected local clusters of nodes. Moreover, functional studies performed at high resolutions have presented convincing evidence that resting-state functional connectivity networks exhibits (exponentially truncated) scale-free behavior. Such evidence, however, was mostly presented qualitatively, in terms of linear regressions of the degree distributions on log–log plots. Even when quantitative measures were given, these were usually limited to the r 2 correlation coefficient. However, the r 2 statistic is not an optimal estimator of explained variance, when dealing with (truncated) power-law models. Recent developments in statistics have introduced new non-parametric approaches, based on the Kolmogorov–Smirnov test, for the problem of model selection. In this work, we have built on this idea to statistically tackle the issue of model selection for the degree distribution of functional connectivity at rest. The analysis, performed at voxel level and in a subject-specific fashion, confirmed the superiority of a truncated power-law model, showing high consistency across subjects. Moreover, the most highly connected voxels were found to be consistently part of the default mode network. Our results provide statistically sound support to the evidence previously presented in literature for a truncated power-law model of resting-state functional connectivity. [Copyright &y& Elsevier]

The new SinMod method extracts motion from magnetic resonance imaging (MRI)-tagged (MRIT) image sequences. Image intensity in the environment of each pixel is modeled as a moving sine wavefront. Displacement is estimated at subpixel accuracy. Performance is compared with the harmonic-phase analysis (HARP) method, which is currently the most common method used to detect motion in MRIT images. SinMod can handle line tags, as well as speckle patterns. In artificial images (tag distance six pixels), SinMod detects displacements accurately (error < 0.02 pixels). Effects of noise are suppressed effectively. Sharp transitions in motion at the boundary of an object are smeared out over a width of 0.6 tag distance. For MRIT images of the heart, SinMod appears less sensitive to artifacts, especially later in the cardiac cycle when image quality deteriorates. For each pixel, the quality of the sine-wave model in describing local image intensity is quantified objectively. If local quality is low, artifacts are avoided by averaging motion over a larger environment. Summarizing, SinMod is just as fast as HARP, but it performs better with respect to accuracy of displacement detection, noise reduction, and avoidance of artifacts. [ABSTRACT FROM AUTHOR]

Aims Dyslipidaemia in Type 2 diabetes mellitus (T2DM) is one of the major contributors in the pathogenesis of atherosclerosis. Thiazolidinediones (TZD), a class of drugs used in the treatment of T2DM, also modify lipids, especially lowering serum triglycerides and raising high-density lipoprotein cholesterol (HDL-C). Methods We describe five patients taking rosiglitazone and a fibrate who showed a paradoxical fall in HDL-C, which would have been missed if HDL-C had not been routinely monitored. This could have had a major impact in increasing the cardiovascular risk in these patients. Results Our five patients showed marked variation in both the decrease in serum HDL-C (50–89%) and also in the time taken for recovery of HDL-C after withdrawal of rosiglitazone (between 5 and 20 weeks). Apolipoprotein A1 mirrored the drop in HDL-C in four of the five patients but in one subject this was not seen, suggesting the possibility of multiple mechanisms leading to the phenomenon described, perhaps involving HDL metabolism. Improvements in glycaemic control with rosiglitazone (absolute HbA1c reduction between 0.6 and 3.0%) were seen in four of our patients. This suggests that the peroxisomal proliferator-activated receptor γ signalling pathways relevant to glucose homeostasis were intact. Conclusion As atherosclerosis is associated with a decrease in the HDL-C level, our observations reinforce the message that HDL-C should be measured before and after the commencement of rosiglitazone and also on increasing the dosage [ABSTRACT FROM AUTHOR]

A letter to the editor is presented about exogenous Cushing's syndrome and topical ocular steroids.