[MRI-Interactions with magnetically active and electrically conductive material]. / MRT ­ Wechselwirkungen mit magnetisch aktivem und elektrisch leitfähigem Material.

BACKGROUND: Patients undergoing MRI examinations are exposed to a strong static magnetic field and powerful electromagnetic alternating fields. Undesired or even dangerous effects could be caused if implants or objects with magnetic or electrically conductive elements are accidentally brought into the examination area. METHODS: Relevant interactions in MRI between magnetic/electric fields and body tissue as well as foreign materials are systematically presented, based on proven physical principles. RESULTS OF PRACTICAL RELEVANCE: Natural components of the human body are mainly diamagnetic leading to only hardly perceptible magnetic forces in MRI. In contrast, ferromagnetic items as iron show translational forces of more than hundred times their weight force when brought to the entry of the bore. Lengthy ferromagnetic items are additionally subjected to torque. Materials with high electrical conductivity as metals and carbon fibre-reinforced plastic are also safety relevant. Especially long conductive structures as often present in implants are prone to induced strong electrical currents and high voltages at their end portions. Maximum voltages occurring at the implants and current density in adjacent tissue which might cause significant heating are hardly predictable for individual cases. Implants providing extended conductive loops for ring currents often show strong vibrations due to gradient switching. Counter forces must be considered when tilting conductive plates or ring structures inside the magnetic field area.

MR-based in vivo follow-up study of Achilles tendon volume and hydration state after ankle-loading activity.

The purpose of this study was to evaluate temporal alterations of the Achilles tendon volume and hydration state after cross-country-running. Achilles tendons of six untrained participants were examined on a 3T MR-scanner before running, immediately afterwards, and in the following 24, 48, and 72 h. Using a 3D-UTE sequence, caudal (CA) and cranial (CR) mid-portion tendon areas were examined with off-resonance saturation ratios (OSR) and T2* relaxation times. Tendon volume was measured with a self-written Matlab-based automated contour detection algorithm (AVAT) in submillimeter T2-weighted MR images. A significant influence of running in caudal (P = 0.017) and cranial OSR values (P = 0.001), tendon volume (P = 0.024), and cranial T2* measurements (P = 0.046), but not in caudal T2* values (P = 0.298) were found. In detail, mean individual OSR and tendon volume measurements demonstrated a similar but inverted course in their values after exercise: initially, OSR values increased after running (and tendon volume decreased), while subsequently a decrease of OSR values (with an increase of tendon volume) could be observed. OSR and tendon volume measurements are able to detect a physiological response of tendons to a mechanical stimulus. After a transient decrease of free water in the Achilles tendon, an increase with a maximum free water content 48 h after ankle loading and a tendency toward normalization after 72 h was found.

[Liver volume, intrahepatic fat and body weight in the course of a lifestyle interventional study: Analysis with quantitative MR-based methods]. / Lebervolumen, Leberfettanteil und Körpergewicht im Verlauf einer Lebensstilinterventionsstudie : Eine Analyse mit quantitativen MR-basierten Methoden.

OBJECTIVES: The aim of this study was to investigate potential associations between changes in liver volume, the amount of intrahepatic lipids (IHL) and body weight during lifestyle interventions. MATERIAL AND METHODS: In a prospective study 150 patients with an increased risk for developing type 2 diabetes mellitus were included who followed a caloric restriction diet for 6 months. In the retrospective analysis 18 women and 9 men (age range 22-71 years) with an average body mass index (BMI) of 32 kg/m(2) were enrolled. The liver volume was determined at the beginning and after 6 months by three-dimensional magnetic resonance imaging (3D-MRI, echo gradient, opposed-phase) and IHLs were quantified by volume-selective MR spectroscopy in single voxel stimulated echo acquisition mode (STEAM). Univariable and multivariable correlation analyses between changes of liver volume (Δliver volume), intrahepatic lipids (ΔIHL) and body weight (ΔBW) were performed. RESULTS: Univariable correlation analysis in the whole study cohort showed associations between ΔIHL and ΔBW (r = 0.69; p < 0.0001), ΔIHL and Δliver volume (r = 0.66; p = 0.0002) as well as ΔBW and Δliver volume (r = 0.5; p = 0.0073). Multivariable correlation analysis revealed that changes of liver volume are primarily determined by changes in IHL independent of changes in body weight (ß = 0.0272; 95% CI: 0.0155-0.034; p < 0.0001). CONCLUSION: Changes of liver volume during lifestyle interventions are independent of changes of body weight primarily determined by changes of IHL. These results show the reversibility of augmented liver volume in steatosis if it is possible to reduce IHLs during lifestyle interventions.

Computer-based quantification of the Achilles tendon thickness in sequential B-mode ultrasound images: a study of feasibility and reliability.

INTRODUCTION: Assessment of the Achilles tendon thickness (ATT) using B-mode ultrasound is a common technique for clinical evaluation of chronic mid-part tendinosis. Currently used image-based assessment is limited by relatively high inter- and intra-observer variability. In this study, it was tested whether a new sequence-based automated assessment of ATT provides more reliable and reproducible results than the standard image-based procedure. MATERIALS AND METHODS: A total of 118 non-operated tendons of 59 healthy subjects (44, range 28-50 years) were analysed using an automated image based as well as a newly developed automated sequence-based method. Correlation and agreement of both methods were evaluated. The root mean square deviation (RMSD) and a Bland-Altman analysis were performed to highlight observer (n = 18 tendons) as well as reader (n = 40 tendons) dependent variabilities of both methods. RESULTS: A strong correlation was found between image and sequence-based ATT assessment (p = 0.92). The Bland-Altman analysis showed a good agreement between both methods (mean difference 0.0018, 95 % CI: -0.046; 0.05). In repetitive examinations, sequence-based analysis showed a significant reduction concerning reader- and observer-dependent variability compared to image-based assessment. The RMSD for repetitive sequence-based measurements was approximately 0.3 mm (compared to 0.6 mm for image-based measurement), respectively. CONCLUSIONS: The study shows sequence-based automated assessment of ATT being clearly superior to the standard image-based procedure. The new method provides a clear reduction of reader as well as observer-dependent variability. Due to the decreased scattering of measurement data sequence-based measurement seems especially valuable for quantification of small tendon thickness changes such as exercise-induced hypertrophy.

In vitro stent lumen visualisation of various common and newly developed femoral artery stents using MR angiography at 1.5 and 3 tesla.

OBJECTIVES: To evaluate stent lumen assessment of various commonly used and newly developed stents for the superficial femoral artery (SFA) using MR angiography (MRA) at 1.5 and 3 T. METHODS: Eleven nitinol stents and one cobalt-chromium stent were compared regarding stent lumen visualisation using a common three-dimensional MRA sequence. Maximum visible stent lumen width and contrast ratio were analysed in three representative slices for each stent type. A scoring system for lumen visualisation was applied. RESULTS: Nitinol stents showed significantly better performance than the cobalt chromium stent (P < 0.05) at 1.5 and 3 T. Maximum visible stent lumen ranged between 43.4 and 95.5 %, contrast ratio between 7.2 and 110.6 %. Regarding both field strengths, seven of the nitinol stents were classified as "suitable". Three nitinol stents were "limited", and one nitinol stent and the cobalt chromium stent were "not suitable". CONCLUSIONS: Intraluminal loss of signal and artefacts of most of the SFA stents do not markedly limit assessment of stent lumen by MRA at 1.5 and 3 T. MRA can thus be considered a valid technique for detection of relevant in-stent restenosis. Applied field strength does not strongly influence stent lumen assessment in general, but proper choice of field strength might be helpful.

[Contrast in static images in clinical magnetic resonance imaging. Part 2: Sequences for various contrast weightings and applications]. / Bildkontraste bei statischen Aufnahmen in der klinischen Magnetresonanztomographie. Teil 2: Sequenzen für verschiedene Kontraste und Anwendungen.

The second part of this educational article focuses on sequence techniques in magnetic resonance imaging (MRI) and on suitable parameter sets for different contrast weightings. The content is based on the recently published part 1 of this educational article providing a survey on tissue properties relevant for most important contrast mechanisms. Characteristics of contrast weightings are presented in exemplary images recorded from healthy volunteers. Typical clinical applications of the most commonly used contrast weightings are described and discussed. Sequences for the following contrast weightings are included: proton density (density of hydrogen in small mobile molecules), relaxation times T1 and T2, chemical shift (water and fat), effects of magnetic susceptibility, restricted diffusion of water molecules and magnetization transfer between macromolecules and water molecules.

[Contrast in static images in clinical magnetic resonance imaging : Part 1: Contrast properties of tissue]. / Bildkontraste bei statischen Aufnahmen in der klinischen Magnetresonanztomographie : Teil 1: Kontrastgebende Gewebeeigenschaften.

In comparison to roentgen-based radiological examination techniques, magnetic resonance imaging (MRI) provides a wide variety of tissue contrast. This can be utilized for better detection and characterization of pathological findings. The basis of image contrast in MRI is the chemical and physical properties of the hydrogen atoms in tissue, in particular in their chemical bonds in water and lipid molecules and in the environment in which the hydrogen-containing molecules are contained. This environment is mainly determined by the composition of substances, viscosity and temperature as well as the microscopic geometrical conditions in tissue. Part 1 of this advanced education article describes those contrast mechanisms which are most commonly utilized in static clinical standard examinations of various organ systems.

Body adiposity index, body fat content and incidence of type 2 diabetes.

AIMS/HYPOTHESIS: The aim of this study was to compare estimates of body fat content, i.e. body adiposity index (BAI), BMI and waist and hip circumferences, with respect to their ability to predict the percentage of body fat (PBF; confirmed by magnetic resonance tomography) and incident type 2 diabetes. METHODS: Associations between anthropometric measurements and PBF were evaluated in the Tübingen Lifestyle Intervention Program (TULIP; 138 men, 222 women), and between these measurements and incident type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam study (9,729 men, 15,438 women) and the Cooperative Health Research in the Region of Augsburg (KORA) study (5,573 men, 5,628 women), using correlation and multivariate Cox regression analyses. RESULTS: BMI more strongly correlated with PBF (men: r = 0.81, women: r = 0.84) than BAI (r = 0.68 and 0.81, respectively), while waist circumference among men (r = 0.84) and hip circumference among women (r = 0.88) showed the strongest correlations. BAI overestimated PBF among men (mean difference -3.0%), and this error was dependent on the value of PBF. BAI was more weakly associated with diabetes risk (RRs for 1 SD, EPIC-Potsdam men: 1.62 [95% CI 1.52, 1.72], women: 1.67 [95% CI 1.55, 1.80]; KORA men: 1.62 [95% CI 1.48, 1.78], women: 1.82 [95% CI 1.65, 2.02]) compared with BMI (RRs, EPIC-Potsdam men: 1.95 [95% CI 1.83, 2.09], women 1.88 [95% CI 1.76, 2.02], KORA men 1.75 [95% CI 1.62, 1.89], women 2.00 [95% CI 1.81, 2.22]), while waist circumference showed the strongest associations (RRs: 2.17 [95% CI 2.01, 2.35], 2.33 [95% CI 2.15, 2.53], 1.81 [95% CI 1.66, 1.96] and 2.29 [95% CI 2.05, 2.57] for EPIC-Potsdam men and women and KORA men and women, respectively). CONCLUSIONS/INTERPRETATION: Waist circumference in men and hip circumference in women are better predictors of PBF than BAI and BMI. BAI was not as strong a predictor of diabetes as BMI, while waist circumference was the strongest predictor.

Exercise-induced albuminuria is associated with perivascular renal sinus fat in individuals at increased risk of type 2 diabetes.

AIMS/HYPOTHESIS: Microalbuminuria represents an established surrogate marker of early diabetic nephropathy and glomerular microangiopathy. Increasing evidence is emerging of a role of perivascular adipose tissue (PVAT) as an important link between obesity, insulin resistance and both macro- and microangiopathy. It is not known whether perivascular renal sinus fat (RSF) has an impact on microalbuminuria in the prediabetic stage. We investigated whether RSF quantified by MRI is associated with microalbuminuria before or after exercise. METHODS: Non-diabetic individuals at increased risk of type 2 diabetes were recruited into the Tübingen Lifestyle Intervention Program (TULIP); 146 participants took part in the analysis. RSF was measured in axial MRI sections at the level of the renal artery. Urine was collected before and after exercise stress testing. RESULTS: Participants (age 47 ± 12 years; mean ± SD) reached a mean exercise load of 176 ± 49 W, with a mean arterial peak pressure (MAPP) of 112 ± 14 mmHg. After adjusting for sex, age, visceral adipose tissue (VAT) and MAPP during exercise, RSF was significantly associated with postexercise albumin/creatinine ratio (ACR; p = 0.006). No association between RSF and baseline BP could be observed after adjusting for confounders (p = 0.26), and there was no association between RSF and baseline ACR either (p = 0.2). CONCLUSIONS: RSF is associated with exercise-induced albuminuria independently of sex, age, VAT and MAPP in a non-diabetic cohort at diabetic risk. We conclude that PVAT in the renal sinus may play a role in the pathogenesis of microalbuminuria.

The secretion pattern of perivascular fat cells is different from that of subcutaneous and visceral fat cells.

AIMS/HYPOTHESIS: We have previously found that the mass of perivascular adipose tissue (PVAT) correlates negatively with insulin sensitivity and post-ischaemic increase in blood flow. To understand how PVAT communicates with vascular vessels, interactions between perivascular, subcutaneous and visceral fat cells with endothelial cells (ECs) were examined with regard to inflammatory, metabolic and angiogenic proteins. To test for possible in vivo relevance of these findings, circulating levels of the predominant secretion product, hepatocyte growth factor (HGF), was measured in individuals carefully phenotyped for fat distribution patterns. METHODS: Mono- and co-cultures of human primary fat cells with ECs were performed. mRNA expression and protein production were studied using Luminex, cytokine array, RealTime Ready and ELISA systems. Effects of HGF on vascular cells were determined by WST assays. In patients, HGF levels were measured by ELISA, and the mass of different fat compartments was determined by whole-body MRI. RESULTS: In contrast with other fat cell types, PVAT cells released higher amounts of angiogenic factors, e.g. HGF, acidic fibroblast growth factor, thrombospondin-1, serpin-E1, monocyte chemotactic protein-1 and insulin-like growth factor-binding protein -3. Cocultures showed different expression profiles from monocultures, and mature adipocytes differed from pre-adipocytes. HGF was preferentially released by PVAT cells and stimulated EC growth and smooth muscle cell cytokine release. Finally, in 95 patients, only PVAT, not visceral or subcutaneous mass, correlated independently with serum HGF levels (p = 0.03; r = 0.225). CONCLUSIONS: Perivascular (pre-)adipocytes differ substantially from other fat cells with regard to mRNA expression and protein production of angiogenic factors. This may contribute to fat tissue growth and atherosclerotic plaque complications. Higher levels of angiogenic factors, such as HGF, in patients with increased perivascular fat mass may have pathological relevance.

Visceral obesity modulates the impact of apolipoprotein C3 gene variants on liver fat content.

OBJECTIVE: It has not been solved whether subjects carrying the minor alleles of the -455T>C or -482C>T single nucleotide polymorphisms (SNPs) in the apolipoprotein-C3-gene (APOC3) have an increased risk for developing fatty liver and insulin resistance. We investigated the relationships of the SNPs with hepatic APOC3 expression and hypothesized that visceral obesity may modulate the effects of these SNPs on liver fat and insulin sensitivity (IS). METHODS: APOC3 mRNA expression and triglyceride content were determined in liver biopsies from 50 subjects. In a separate group (N=330) liver fat was measured by (1)H-magnetic resonance spectroscopy. IS was estimated during an oral glucose tolerance test (OGTT) and the euglycemic, hyperinsulinemic clamp (N=222). RESULTS: APOC3 mRNA correlated positively with triglyceride content in liver biopsies (r=0.29, P=0.036). Carriers of the minor alleles (-455C and -482T) tended to have higher hepatic APOC3 mRNA expression (1.80 (0.45-3.56) vs 0.77 (0.40-1.64), P=0.09), but not higher triglyceride content (P=0.76). In 330 subjects the genotype did not correlate with liver fat (P=0.97) or IS (OGTT: P=0.41; clamp: P=0.99). However, a significant interaction of the genotype with waist circumference in determining liver fat was detected (P=0.02) in which minor allele carriers had higher liver fat only in the lowest tertile of waist circumference (P=0.01). In agreement, during a 9-month lifestyle intervention the minor allele carriers of the SNP -482C>T in the lowest tertile also had less decrease in liver fat (P=0.04). CONCLUSIONS: APOC3 mRNA expression is increased in fatty liver and is regulated by SNPs in APOC3. The impact of the APOC3 SNPs on fatty liver is small and depends on visceral obesity.

Effects of a lifestyle intervention in metabolically benign and malign obesity.

AIMS/HYPOTHESIS: We and others recently characterised metabolically benign or healthy obesity (MHO). In the present study we investigated whether a lifestyle intervention is sufficient to place obese insulin-resistant (OIR) individuals in a position where the possible metabolic consequences are similar to those for MHO individuals. METHODS: A total of 262 non-diabetic individuals participated in a 9 month lifestyle intervention programme. Obese individuals (BMI ≥ 30.0 kg/m(2)) were stratified, based on their insulin sensitivity (IS) estimated from an OGTT, into MHO (IS in the upper quartile, n = 26) and OIR (IS in the lower three quartiles, n = 77). Total body and visceral fat were measured by magnetic resonance (MR) tomography and liver fat by (1)H-MR spectroscopy. RESULTS: During the intervention, visceral fat decreased significantly in both groups (both p ≤ 0.009), whereas total body and liver fat decreased only in the OIR group (p < 0.0001; MHO p = 0.12 for total body fat and p = 0.47 for liver fat). IS improved in the OIR group (p < 0.0001), but remained essentially unchanged in the MHO group (p = 0.30). However, despite the significant increase in the OIR group, IS at follow-up barely exceeded 50% of the IS of the MHO group (OIR 9.30 ± 0.53 arbitrary units [AU]; MHO 16.41 ± 1.05 AU; p < 0.0001). CONCLUSIONS/INTERPRETATION: IS improves during the lifestyle intervention in OIR individuals. However, it does not reach a level where adequate protection from type 2 diabetes and cardiovascular disease is expected. Thus, stratification of obese individuals based on their metabolic phenotype is important to identify those who are likely to need early pharmacological treatment in addition to the lifestyle intervention.

Quantitative diffusion imaging of adipose tissue in the human lower leg at 1.5 T.

Diffusion-weighted spin-echo echo-planar imaging was developed and applied for assessment of diffusion coefficients of adipose tissue in human lower leg on a 1.5-T whole-body MR scanner. Because of the higher molecular weight of triglycerides, apparent diffusion coefficients (ADCs) of adipose tissue are approximately two orders of magnitude smaller compared with water, leading to the necessity of using high b-values up to 50,000 sec/mm(2) and an echo time of 240 msec for sufficient diffusion-related signal attenuation. ADC maps of adipose tissue in the human lower leg were derived for diffusion encoding along orthogonal spatial directions in six healthy volunteers. Mean diffusion coefficients in the tibial bone marrow amounted to (1.81 ± 0.10) × 10(-5) mm(2) /sec (left-right), (1.96 ± 0.10) × 10(-5) mm(2) /sec (anterior-posterior), and (1.96 ± 0.20) × 10(-5) mm(2) /sec (head-feet), respectively. Pixel-wise calculated ADC values of subcutaneous adipose tissue showed a distinctly higher variation with the smallest ADC values similar to those measured for tibial bone marrow. Some subcutaneous adipose tissue regions showed increased signal attenuation at higher b-values resulting in ADC coefficients up to 4.2 × 10(-5) mm(2) /sec. It must be noted that diffusion measurements with extremely high b-values in vivo are extremely sensitive to incoherent motion effects in tissue. Nonetheless, it could be shown that in vivo diffusion imaging of adipose tissue in human lower leg is possible at 1.5 T in acceptable measurement time of a few minutes. Potential future applications of fat diffusion imaging are seen in temperature measurements in adipose tissue, detection of free fatty acids in white or brown adipose tissue in case of high lipolysis, differentiation of macro- and microvesicular steatosis, or assessment of the mobility of intramyocellular lipids.

The impact of liver fat vs visceral fat in determining categories of prediabetes.

AIMS/HYPOTHESIS: Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are risk factors for type 2 diabetes and cardiovascular disease; however, their impact on these endpoints differs. Because liver fat and visceral fat are important determinants of glucose and lipid metabolism, we investigated whether these fat compartments and their humoral products, the adipokine adiponectin and the hepatokine fetuin-A, differ in their impact on the glucose categories. METHODS: In 330 individuals at risk of type 2 diabetes, glucose tolerance status was determined by a 2 h 75 g OGTT. Total-body and visceral fat were precisely quantified by magnetic resonance (MR) tomography and liver fat by (1)H-MR spectroscopy. RESULTS: A total of 210 individuals had normal glucose tolerance (NGT), 41 isolated IFG, 43 isolated IGT and 36 IFG+IGT. Total-body fat was not different (p = 0.51), although a small but continuous increase in visceral fat was found among the categories after adjustment for age and sex (NGT: 3.07 +/- 0.10 kg; IFG: 3.11 +/- 0.21 kg; IGT: 3.61 +/- 0.21 kg; IFG+IGT: 3.84 +/- 0.23 kg [SEs], p = 0.03). A larger difference was found for liver fat (NGT: 4.73 +/- 0.42%; IFG: 5.86 +/- 0.92%; IGT: 8.65 +/- 0.92%; IFG + IGT: 11.11 +/- 1.01%, p < 0.0001). The differences among the categories were small for adiponectin (p = 0.14), but larger for fetuin-A (p = 0.015). Among fat compartments, liver fat (p < 0.0001) and among circulating variables fetuin-A (p = 0.016) were the strongest determinants of the categories. CONCLUSIONS/INTERPRETATION: Liver fat, more than visceral fat, strongly increases when glycaemia and glucose tolerance move from NGT to isolated IFG, isolated IGT and IFG+IGT. Because liver-derived circulating fetuin-A determines, although weakly, prediabetes categories, it is worth searching for hepatokines more strongly predicting prediabetes.

High cardiorespiratory fitness is an independent predictor of the reduction in liver fat during a lifestyle intervention in non-alcoholic fatty liver disease.

OBJECTIVE: Lifestyle intervention with diet modification and increase in physical activity is effective for reducing hepatic steatosis in patients with non-alcoholic fatty liver disease (NAFLD). However, for a similar weight loss, there is a large variability in the change in liver fat. We hypothesised that cardiorespiratory fitness may predict the response to the intervention. DESIGN: Longitudinal study with increase in physical activity and diet modification. SETTING: University teaching hospital. PATIENTS: 50 adults with NAFLD and 120 controls at risk for metabolic diseases. MAIN OUTCOME MEASURES: Total-, subcutaneous abdominal- and visceral adipose tissue by magnetic resonance tomography, liver fat by 1HMR spectroscopy and cardiorespiratory fitness (VO(2,max)) by a maximal cycle exercise test at baseline and after 9 months of follow-up. RESULTS: In all subjects total-, subcutaneous abdominal- and visceral adipose tissue decreased and fitness increased (all p<0.0001) during the intervention. The most pronounced changes were found for liver fat (-31%, p<0.0001). Among the parameters predicting the change in liver fat, fitness at baseline emerged as the strongest factor, independently of total- and visceral adipose tissue as well as exercise intensity (p = 0.005). In the group of subjects with NAFLD at baseline, a resolution of NAFLD was found in 20 individuals. For 1 standard deviation increase in VO(2,max) at baseline the odds ratio for resolution of NAFLD was 2.79 (95% confidence interval, 1.43-6.33). CONCLUSIONS: Cardiorespiratory fitness, independently of total adiposity, body fat distribution and exercise intensity, determines liver fat content in humans, suggesting that fitness and liver fat are causally related to each other. Moreover, measurement of fitness at baseline predicts the effectiveness of a lifestyle intervention in reducing hepatic steatosis in patients with NAFLD.

A machine-learning framework for automatic reference-free quality assessment in MRI.

Magnetic resonance (MR) imaging offers a wide variety of imaging techniques. A large amount of data is created per examination which needs to be checked for sufficient quality in order to derive a meaningful diagnosis. This is a manual process and therefore time- and cost-intensive. Any imaging artifacts originating from scanner hardware, signal processing or induced by the patient may reduce the image quality and complicate the diagnosis or any image post-processing. Therefore, the assessment or the ensurance of sufficient image quality in an automated manner is of high interest. Usually no reference image is available or difficult to define. Therefore, classical reference-based approaches are not applicable. Model observers mimicking the human observers (HO) can assist in this task. Thus, we propose a new machine-learning-based reference-free MR image quality assessment framework which is trained on HO-derived labels to assess MR image quality immediately after each acquisition. We include the concept of active learning and present an efficient blinded reading platform to reduce the effort in the HO labeling procedure. Derived image features and the applied classifiers (support-vector-machine, deep neural network) are investigated for a cohort of 250 patients. The MR image quality assessment framework can achieve a high test accuracy of 93.7% for estimating quality classes on a 5-point Likert-scale. The proposed MR image quality assessment framework is able to provide an accurate and efficient quality estimation which can be used as a prospective quality assurance including automatic acquisition adaptation or guided MR scanner operation, and/or as a retrospective quality assessment including support of diagnostic decisions or quality control in cohort studies.

[Dynamic magnetic resonance nephrography and urography of uropathies in children]. / Dynamische Magnetresonanz-Nephrografie und -Urografie bei Kindern mit Harnwegserkrankungen.

PURPOSE: To evaluate an improved method of dynamic magnetic resonance (MR) nephrography with short acquisition time and compensation of breathing motion for assessment of renal excretion and split renal function in children with anomalies of the urinary tract. MATERIALS AND METHODS: A protocol for dynamic MR nephrography was implemented using a T1-weighted navigator-gated TurboFLASH sequence (TR/TE 498 ms/1.25 ms, saturation recovery time 300 ms, flip angle 8 degrees ). After bolus injection of 0.05 mmol/kg gadolinium dimeglumine (Gd-DTPA), split renal function was determined from the contrast-medium excretion. In 20 patients (ages between 3 months and 14 years), dynamic MR nephrography and MAG3 radionuclide scintigraphy as the gold standard were performed. RESULTS: In all children, T1-weighted images were able to be recorded over 40 minutes at a nearly identical diaphragm position using the TurboFLASH sequence, thus allowing for exact region-of-interest analysis of the excretion and split renal function. The course of the contrast-medium concentration was able to be measured in the renal pelvis with good accuracy due to the high spatial resolution and the lack of breathing artifacts. Excellent correlation to the MAG3 scintigraphy was demonstrated for the excretion and split renal function (correlation coefficient: 0.975). CONCLUSION: Dynamic MR nephrography allows for reliable assessment of renal function in children with anomalies of the urinary tract with higher spatial resolution as compared to radionuclide scintigraphy.

Diffusion tensor imaging of the spinal cord at 1.5 and 3.0 Tesla.

PURPOSE: The feasibility of highly resolved diffusion tensor imaging (DTI) of the human cervical spinal cord was tested on a clinical MR unit operating at 3.0 Tesla. DTI parametrical maps and signal-to-noise ratios (SNRs) were compared to results recorded at 1.5 Tesla. MATERIALS AND METHODS: Eight healthy volunteers and one patient participated in the study. A transverse oriented single-shot ECG-triggered echo-planar imaging (EPI) sequence with double spin-echo diffusion preparation was applied for highly resolved DTI of the spinal cord. The signal yield, fractional anisotropy (FA), and mean diffusivity (MD) were compared for both field strengths. The clinical applicability of the protocol was also tested in one patient with amyotrophic lateral sclerosis (ALS) at 3.0 T. RESULTS: A mean increase in SNR of 95.7 +/- 4.6 % was found at 3.0 Tesla compared to 1.5 Tesla. Improved quality of the DTI parametrical maps was observed at higher field strength (p < 0.02). Comparable FA and MD (reported in units of 10 (-3) mm (2)/s) values were computed in the dorsal white matter at both field strengths (1.5 T: FA = 0.75 +/- 0.08, MD = 0.84 +/- 0.12, 3.0 T: FA = 0.74 +/- 0.04, MD = 0.93 +/- 0.14). The DTI images exhibited diagnostic image quality in the patient. At the site of the diseased corticospinal tract, a decrease of 46.0 +/- 3.8 % in FA (0.40 +/- 0.03) and an increase of 50.3 +/- 5.6 % in MD (1.40 +/- 0.05) were found in the ALS patient. CONCLUSION: The 3.0 Tesla field strength provides higher image quality in DTI of the spinal cord compared to 1.5 T. The proposed DTI protocol seems adequate for the assessment of spinal cord diseases.

[The bases of magnetic resonance tomography]. / Grundlagen der Magnetresonanztomographie.

Magnetic resonance tomography (MRT) has advanced to be an important pillar of radiological diagnostics, along side of x-rays and ultrasound. In the present work, the technical requirements for carrying out modern MRT diagnostics are discussed as are the principles of locally generated signal registration. Typical problems in the use of MRT as well as strategies for improving image quality and for the correct interpretation of the images are detailed. Consideration is also given to how existing image problems can be eliminated by the adjustment of the in put parameters.

Intramyocellular lipids and their dynamics assessed by 1 H magnetic resonance spectroscopy.

This report provides an overview on the present knowledge on intramyocellular lipids (IMCL) and their dynamics in the course of interventions with physical activity of variable type and intensity in different population groups, as accessible by examinations using non-invasive volume-selective 1 H magnetic resonance spectroscopy (1 H MRS). IMCL serve as energy source in skeletal muscle for fat oxidation in the mitochondria and became intensively studied after discovery of their relation with insulin sensitivity. While baseline levels of IMCL concentration have been shown to be mainly dependent on the metabolic status (insulin sensitivity), on the level of training and on fibre composition in the muscles, studies applying different physical activity protocols revealed the dynamic of their depletion and replenishment. From the findings in human studies, it can be concluded that IMCL levels are potentially useful markers for monitoring metabolic adaptation of skeletal muscle to sportive activities and training.