[Spin echo and gradient echo : Methodological duo of MRI]. / Spinecho und Gradientenecho : Methodisches Duo der MR-Bildgebung.

Clinical magnetic resonance imaging (MRI) offers a multitude of different techniques with which anatomical, functional and metabolic information can be gained. The technical basis of an MRI method is the so-called pulse sequence, which determines the manner in which data is acquired. Pulse sequences are differentiated between gradient and spin echo sequences. The aim of this article is to present the principal physical properties of both techniques. From these properties, specific applications arise that are routinely used in clinical practice.

Precise localization of silicone-based intercranial planar electrodes in magnetic resonance imaging.

Intercranial planar electrodes enable neural recordings with high spatial resolution in diagnosis as well as for treatments. The value of the measurements increases with the precision of localization of the electrodes related to the individual anatomy. In this context, post-implantation MRI provides excellent soft tissue contrast, but the accurate localization of electrodes is impaired by magnetic susceptibility artifacts. We have addressed this problem without adding a substantial burden to the electrode fabrication process. Simple silicone reference structures were strategically placed on the implant surface to visualize the electrodes position in MRI. These reference structures allowed high precision electrode localization independently of electrode imaging artifacts. This implant manufacturing approach could prove extremely useful in combination with existing image processing pipelines.

Biomimetic optimisation of branched fibre-reinforced composites in engineering by detailed analyses of biological concept generators.

The aim of this study is the biomimetic optimisation of branched fibre-reinforced composites based on the detailed analysis of biological concept generators. The methods include analyses of the functional morphology and biomechanics of arborescent monocotyledons and columnar cacti as well as measurements and modelling of mechanical properties of biomimetic fibre-reinforced composites. The key results show evidence of notch stress reduction by optimised stem-branch-attachment morphology in monocotyledons and columnar cacti. It could be shown that some of these highly interesting properties can be transferred into biomimetic fibre-reinforced composites.

Phased-array of microcoils allows MR microscopy of ex vivo human skin samples at 9.4 T.

PURPOSE: The aim of this study was to demonstrate the feasibility of a custom-made phased-array microcoil within a 400 MHz animal system for the morphological characterization of human skin tissue in correlation with histopathology. MATERIALS AND METHODS: A dedicated 7-channel microcoil-based MR detector arranged in a phased-array geometry was developed to combine the advantages of both a large field of view and a high signal-to-noise ratio. Standard gradient echo sequences were adapted for the characterization of skin morphology ex vivo. RESULTS: In this study, the feasibility of using this type of microdetector, combined with specially manufactured sample holders, to achieve high-resolution MR images of fresh and formalin-fixed, normal and hidradenitis suppurativa diseased skin was successfully demonstrated. The setup presented in this work allows reliable acquisitions of high-resolution images with in-plane resolution up to 25 × 25 µm², and 100 µm in the orthogonal direction, thereby allowing the differentiation of typical layers of the skin, sebaceous glands and hair follicle. CONCLUSION: This study demonstrates that MR microscopy on skin biopsies can be applied at low cost on a standard animal MR imaging system. The successful imaging of different skin structures ex vivo is a prerequisite for non-invasive, in vivo application of skin MR microscopy for accurate complementary disease diagnosis in dermatology.

Fabrication and characterization of a high-resolution neural probe for stereoelectroencephalography and single neuron recording.

This paper reports on the design, fabrication, and characterization of neural probes for stereoelectroencephalography (SEEG). The probe specifically targets focal epilepsy as key application. However, probes of this type can also be used for the diagnosis and treatment of other neural dysfunctions such as Parkinson's disease or tremor, typically requiring deep brain probes. The probe fabrication, of which most processes are parallel batch processes, relies on a novel fabrication concept for rolling and gluing thin film polyimide sheets with integrated electrodes into permanent cylindrical shapes with diameters down to 800 µm. The SEEG probes, comprise several macro-electrodes designed to record local field potentials, and micro-electrodes positioned in-between, dedicated to monitoring single unit activity, with a total channel count of 32, despite the small diameter. While platinum micro-electrodes with a diameter of 35 µm have impedances of about 255 kΩ at 1 kHz, impedance values down to about 1.5 kΩ have been measured for the macro-electrodes. The devices have shown good compatibility with magnetic resonance imaging in a 9.4 T magnet, enabling the precise post-operative probe localization within the brain.

Off-resonance-dependent slice profile effects in balanced steady-state free precession imaging.

The purpose of this study was the simulation and measurement of balanced steady-state free precession (bSSFP) slice profiles for a detailed analysis of the influence of off-resonance effects on slice profile shape and bSSFP signal intensity. Due to the frequency response function of the bSSFP sequence, measurements that are not on-resonance result in broadened effective slice profiles with different off-resonance-dependent shapes and signal intensities. In this study, bSSFP slice profile effects and their dependence on off-resonance were investigated based on bSSFP signal simulations of phantom data as well as blood and tissue. For a better assessment of the similarity of measured and simulated slice profiles the field map was integrated in the slice profile simulations. The results demonstrate that simulations can accurately predict bSSFP slice profiles. Both measurements and simulations indicate that there is a substantial increase in signal intensity close to the banding artifacts, i.e., at spatial locations with off-resonance frequencies corresponding to a dephasing/TR = +/- pi resulting in signal void (bands). For routine bSSFP imaging, off-resonance-dependent slice broadening may thus result in a substantial difference between nominal and true slice thickness and lead to spatially varying slice thickness and signal intensities across the imaging slice.

MicroRNA-21 (miR-21) post-transcriptionally downregulates tumor suppressor Pdcd4 and stimulates invasion, intravasation and metastasis in colorectal cancer.

Tumor-suppressor Pdcd4 inhibits transformation and invasion and is downregulated in cancers. So far, it has not been studied as to whether miRNAs, suppressing target expression by binding to the 3'-UTR, regulate Pdcd4 or invasion. The present study was conducted to investigate the regulation of Pdcd4, and invasion/intra-vasation, by miRNAs. A bioinformatics search revealed a conserved target-site for miR-21 within the Pdcd4-3'-UTR at 228-249 nt. In 10 colorectal cell lines, an inverse correlation of miR-21 and Pdcd4-protein was observed. Transfection of Colo206f-cells with miR-21 significantly suppressed a luciferase-reporter containing the Pdcd4-3'-UTR, whereas transfection of RKO with anti-miR-21 increased activity of this construct. This was abolished when a construct mutated at the miR-21/nt228-249 target site was used instead. Anti-miR-21-transfected RKO cells showed an increase of Pdcd4-protein and reduced invasion. Moreover, these cells showed reduced intra-vasation and lung metastasis in a chicken-embryo-metastasis assay. In contrast, overexpression of miR-21 in Colo206f significantly reduced Pdcd4-protein amounts and increased invasion, while Pdcd4-mRNA was unaltered. Resected normal/tumor tissues of 22 colorectal cancer patients demonstrated an inverse correlation between miR-21 and Pdcd4-protein. This is the first study to show that Pdcd4 is negatively regulated by miR-21. Furthermore, it is the first report to demonstrate that miR-21 induces invasion/intravasation/metastasis.

Tumor suppressor Pdcd4 inhibits invasion/intravasation and regulates urokinase receptor (u-PAR) gene expression via Sp-transcription factors.

Tumor suppressor Pdcd4 has recently been shown to inhibit invasion by activating activator protein-1 (AP-1); however, little is known of the functionally significant Pdcd4-target genes. The urokinase receptor (u-PAR) promotes invasion/metastasis, and is associated with poor cancer-patient survival. The present study was conducted (1) to investigate a role for Pdcd4 in intravasation, invasion and u-PAR regulation, and (2) to describe mechanisms by which this is achieved. Fourteen cell lines showed reciprocal expression of u-PAR/Pdcd4. Resected tumor/normal tissues of 29 colorectal cancer patients demonstrated a significant inverse correlation between Pdcd4/u-PAR. siRNA-Pdcd4-transfected GEO cells significantly increased endogenous u-PAR mRNA/protein. A u-PAR-promoter-chloramphenicol acetyl transferase (CAT)-reporter was reduced in activity with increasing Pdcd4 expression in RKO. Deletion of a putative Sp-1-binding site (-402/-350) inhibited u-PAR promoter regulation by Pdcd4, this being paralleled by a reduction of Sp1 binding to this region in pdcd4-transfected cells. Pdcd4-transfected cells showed an increase in Sp3 binding to u-PAR promoter region -152/-135, the deletion of which reduces the ability of Pdcd4 to suppress u-PAR promoter activity. Surprisingly, the u-PAR-AP-1 site was not targeted by Pdcd4. Finally, RKO cells overexpressing Pdcd4 showed an inhibition of invasion/intravasation (chicken embryo metastasis assay). These data suggest Pdcd4 as a new negative regulator of intravasation, and qas the invasion-related gene u-PAR. It is the first study to implicate Pdcd4 regulation of gene expression via Sp1/Sp3.

Alternating repetition time balanced steady state free precession.

A novel balanced SSFP technique for the separation or suppression of different resonance frequencies (e.g., fat suppression) is presented. The method is based on applying two alternating and different repetition times, TR(1) and TR(2). This RF scheme manipulates the sensitivity of balanced SSFP to off-resonance effects by a modification of the frequency response profile. Starting from a general approach, an optimally broadened stopband within the frequency response function is designed. This is achieved with a TR(2) being one third of TR(1) and an RF-pulse phase increment of 90 degrees . With this approach TR(2) is too short ( approximately 1 ms) to switch imaging gradients and is only used to change the frequency sensitivity. Without a significant change of the spectral position of the stopband, TR(1) can be varied over a range of values ( approximately 2.5-4.5 ms) while TR(2) and phase cycling is kept constant. On-resonance spins show a magnetization behavior similar to balanced SSFP, but with maximal magnetization at flip angles about 10 degrees lower than in balanced SSFP. The total scan time is increased by about 30% compared to conventional balanced SSFP. The new technique was applied on phantoms and volunteers to produce rapid, fat suppressed images.

Double average parallel steady-state free precession imaging: optimized eddy current and transient oscillation compensation.

Balanced steady-state free precession (SSFP) imaging is sensitive to off-resonance effects, which can lead to considerable artifacts during a transient phase following magnetization preparation or steady-state interruption. In addition, nonlinear k-space encoding is required if contrast-relevant k-space regions need to be acquired at specific delays following magnetization preparation or for transient artifact reduction in cardiac-gated k-space segmented CINE imaging. Such trajectories are problematic for balanced SSFP imaging due to nonconstant eddy current effects and resulting disruption of the steady state. In this work, a novel acquisition strategy for balanced SSFP imaging is presented that utilizes scan time reduction by parallel imaging for optimized "double average" eddy current compensation and artifact reduction during the transient phase following steady-state storage and magnetization preparation. Double average parallel SSFP imaging was applied to k-space segmented CINE SSFP tagging as well as nongated centrically encoded SSFP imaging. Phantom and human studies exhibit substantial reduction in steady-state storage and eddy current artifacts while maintaining spatial resolution, signal-to-noise ratio, and similar total scan time of a standard SSFP acquisition. The proposed technique can easily be extended to other acquisition schemes that would benefit from nonlinear reordering schemes and/or rely on interruption of the balanced SSFP steady state.

Long-term results following ankle arthrodesis for post-traumatic arthritis.

BACKGROUND: Ankle arthrodesis is considered by many to be the standard operative treatment for end-stage ankle arthritis; however, the long-term effect of ankle arthrodesis on other lower-extremity joints remains largely unknown. The purpose of this study was to perform a clinical and radiographic review to determine the effect of ankle arthrodesis on the development of osteoarthritis in other lower-extremity joints. METHODS: Twenty-three patients who had had an isolated ankle arthrodesis for the treatment of painful posttraumatic arthritis of the ankle were followed for a mean of twenty-two years (range, twelve to forty-four years) after the operation. Each completed standardized, self-reported outcome questionnaires (the Foot Function Index, Western Ontario and McMaster University Osteoarthritis Index [WOMAC], and Short Form-36 [SF-36]), was examined clinically by two of the investigators, and underwent complete radiographic examination of the knee, ankle, and foot bilaterally. The radiographic grade of osteoarthritis was determined for each joint, and the levels of overall activity limitation, pain, and disability were determined for each patient from the clinical findings and questionnaire information. RESULTS: Osteoarthritis of the ipsilateral subtalar (p<0.0001), talonavicular (p<0.0001), calcaneocuboid (p<0.0001), naviculocuneiform (p = 0.0012), tarsometatarsal (p = 0.0009), and first metatarsophalangeal joints (p = 0.0012) was consistently more severe than the osteoarthritis of those joints on the contralateral side. Osteoarthritis did not develop more frequently in the ipsilateral knee or lesser metatarsophalangeal joints than it did on the contralateral side. Significant differences between the two sides were found with regard to overall activity limitation (p<0.0001), pain (p<0.0001), and disability (p<0.0001), with the involved side consistently more symptomatic. CONCLUSIONS: To our knowledge, the present series represents the longest follow-up study of ankle arthrodesis to date. Our cohort of patients all had isolated post-traumatic ankle arthritis, and each underwent a successful isolated ankle arthrodesis. At a mean of twenty-two years, the majority of the patients had substantial, and accelerated, arthritic changes in the ipsilateral foot but not the knee. They were often limited functionally by foot pain. Although ankle arthrodesis may provide good early relief of pain, it is associated with premature deterioration of other joints of the foot and eventual arthritis, pain, and dysfunction.

Birth as a multidimensional experience: comparison of the English- and German-language versions of Salmon's Item List.

Results concerning satisfaction with the birth experience in different trials are difficult to compare, owing to a lack of internationally used research scales. Salmon's Item List (SIL) is easy-to-handle and would therefore be very helpful for research as well as for obstetric clinic quality control. Two hundred and fifty-one patients were investigated using a German-language version of SIL (SIL-ger); the statistical evaluation was carried out by means of a principal components analysis. Principal components analysis revealed two major findings: (1) as stated by other authors the birth experience is multidimensional, each aspect influencing the others in a non-linear way; (2) in addition to Salmon's dimensions (i.e. postnatal 'fulfillment', intranatal 'physical discomfort' and intranatal 'emotional distress') another postnatal dimension labeled 'negative emotional experience' was detected. Not only are intranatal experiences multidimensional, but so too are evaluative feelings afterwards. In addition to fulfillment, as developed by Salmon, a dimension of negative emotional experience needs to be taken into account. This dimension does not correlate in a linear way with fulfillment. It is appropriate to use SIL in research. Before using it for purposes of clinical quality control, however, larger samples need to be evaluated in order to prove the stability of the factor structure.

Sites of simian foamy virus persistence in naturally infected African green monkeys: latent provirus is ubiquitous, whereas viral replication is restricted to the oral mucosa.

Foamy viruses (FV), retroviruses of the genus Spumavirus, are able to infect a wide variety of animal species and replicate in nearly all types of cultured cells. To identify the cells targeted by FV in the natural host and define the sites of viral replication, multiple organs of four African green monkeys naturally infected with simian FV type 3 were investigated for the presence of FV proviral DNA and viral transcripts. All organs contained significant amounts of FV proviral DNA. In addition to proviruses containing the complete transactivator gene taf, proviral genomes carrying a specific 295-bp deletion in the taf gene were detected in all monkeys. As in the case of human foamy virus the deletion leads to the formation of the bet gene that is regarded to be instrumental in the regulation of viral persistence. FV RNA was detected by RT-PCR and in situ hybridization only in the oral mucosa of one monkey. No other samples contained detectable levels of viral transcripts. Histopathological changes were not observed in any of the tissue samples analyzed. Our results show that the natural history of FV is characterized by latent infection in all organs of the host and by minimal levels of harmless viral replication in the oral mucosa. The broad host cell range in vivo further encourages the development of FV-derived vectors for therapeutic gene delivery.