In arterial spin labeling (ASL) a perfusion weighted image is achieved by subtracting a label image from a control image. This perfusion weighted image has an intrinsically low signal to noise ratio and numerous measurements are required to achieve reliable image quality, especially at higher spatial resolutions. To overcome this limitation various denoising approaches have been published using the perfusion weighted image as input for denoising. In this study we propose a new spatio-temporal filtering approach based on total generalized variation (TGV) regularization which exploits the inherent information of control and label pairs simultaneously. In this way, the temporal and spatial similarities of all images are used to jointly denoise the control and label images. To assess the effect of denoising, virtual ground truth data were produced at different SNR levels. Furthermore, high-resolution in-vivo pulsed ASL data sets were acquired and processed. The results show improved image quality, quantitative accuracy and robustness against outliers compared to seven state of the art denoising approaches.

In the current paper a vertebral bone model is introduced that can be used for studying trabecular thinning and the formation of trabecular disconnections. Magnetostatic simulations are applied in MR-osteodensitometry to deduce the quality of trabecular bone from experimentally obtained susceptibility effects. The course of trabecular bone loss, which results in distinct interruptions and consequently severe mechanical impairment, is not assessable in the majority of such applied models. In the novel approach introduced here, analytical solutions of prolate ellipsoids were used to compute the disturbed magnetic fields within the proposed 3D model. The performed simulations focused on two variants of the vertebral model: an intact model and a pathological model accounting for microdamage. For both variants, magnetic resonance spectra were simulated for different bone volume fractions. Subsequently, resonance signals were obtained from the Fourier transform of the distribution with respect to time. The resonance time courses were analyzed through common signal models to estimate the relaxation time [Formula: see text] of the corresponding free induction decay. Detailed computations revealed the significant contribution of the microdamage to the susceptibility effect. Further, when comparing the line broadening effect between the intact and disrupted models a contradictory outcome was found. The damaged osseous network for the lower bone fraction resulted in faster decay of the transverse magnetization. In conclusion, a significant contribution of trabecular disconnections to the susceptibility effect has been shown by the presented model. Future dedicated MRI experiments can explore the use of this effect to assess the integrity of cancellous bone.

Novel analytical solutions suitable for computing field inhomogeneities induced by introducing prolate and oblate spheroids into a homogeneous field are presented. Exemplary an application in the field of magnetic resonance osteodensitometry is given.The authors believe that these findings have the potential to improve the modeling of magnetic resonance signal formation and spectral line broadening under the impact of susceptibility effects within biological structures.

One major source affecting the precision of bone structure analysis in quantitative magnetic resonance imaging (qMRI) is inter- and intraoperator variability, inherent in delineating and tracing regions of interest along longitudinal studies. In this paper an automated analysis tool, featuring bone marrow segmentation, region of interest generation, and characterization of cancellous bone of articular joints is presented. In evaluation studies conducted at the knee joint the novel analysis tool significantly decreased the standard error of measurement and improved the sensitivity in detecting minor structural changes. It further eliminated the need of time-consuming user interaction, and thereby increasing reproducibility.

The aim of this study was to evaluate a variety of phase- and magnitude-based MRI methods at 1.5 T and 3 T regarding their sensitivity and accuracy with respect to the quantification of electrical direct current via the induced magnetic field inhomogeneity. For this, a phantom was constructed which was specially designed to reduce RF effects and which provided a one-dimensional electrical direct current in a thin copper conductor perpendicular to the static magnetic field of the scanner. The current was varied between 4 mA and 472 mA. The analysis of FLASH phase images as well as trueFISP and MAGSUS images revealed that the accuracy of the MR current measurement depended on the method and the field strength: the mean of the absolute deviations of the measured current values from the adjusted current values varied between 9% and 21%. The phase measurement with a FLASH sequence was found to be more sensitive than the trueFISP and MAGSUS measurements. In FLASH magnitude images as well as in images of spin echo sequences with on- and off-resonant frequency selective saturation pulses the extension of the artifact increased with the electrical current. MRI methods for the quantification of electrical direct current might e.g. play a role in functional testing of electrically active devices in the human body in terms of measuring the present current. One-dimensional electrical direct current in a thin, straight conductor could also be applied to the visualization of instruments in interventional MRI procedures. Currents below 100 mA would be sufficient to create distinct artifacts, at least under simplified conditions (homogeneous background etc.).

Nonlinear parallel imaging reconstruction using an iterative regularized Gauss Newton method (IRGN) has shown its potential in several applications. This technique acquires data using array coils were the coil sensitivites and the image are both computed from the under sampled data. Several normalization steps for each image and each receiver coil are necessary prior image reconstruction. In the current work it was examined if the complex reconstruction process limits the applicability of this method for quantitative determination of NMR parameters (T2). Hence measurements with full encoding using the established parallel imaging method „Grappa“ were compared with the IRGN reconstruction. It was shown that both parallel imaging techniques are in principle applicable for quantitative determination. In the case of the applied cartesian image encoding certain advantages of the IRGN reconstruction in comparison to the applied „Grappa“ implementation were found in areas with low SNR. Further examinations are necessary for radial k-space sampling.

In this study the contrast behaviour of five different musculoskeletal tissues of the knee (muscle, cartilage, bone marrow, synovial fluid and the Hoffa's fat body) were analysed for spinecho-and spoiled gradientecho sequences by means of computer simulations On the basis of tissue properties (spin density, T1, T2 and T2*) obtained from three healthy subjects optimal imaging parameters TR, TE and the flip angle (the latter only for GRE) were derived for separation between two tissue types. As a criterion for the ability to separate two tissues the ratio between signal intensity difference regarding the two tissues of interest and the used measuring time was applied. The paper presents the sequence type and parameters for optimal tissue contrast regarding all possible pairs of tissue. The applicability of the model was tested by comparing results with corresponding images recorded in a healthy subject. The long-term objective is the optimisation of imaging strategies for the so called "computer aided diagnostics", where reliable antomated tissue separation in huge radiological MR data sets is considered essential.

Object The objective of this study was to evaluate breathing influence on precision in temperature determination by using the proton resonance frequency (PRF) shift method depending on the location in abdominal organs at 0.2 and 1.5 T.Materials and Methods Phase images were acquired with gradient echo sequences in a total of 12 volunteers at 1.5 and 0.2 T. Different examination protocols were performed (each 8 measurements with (1) in-/expiration, (2) free breathing, (3) under breathhold, (4) with breathing belt triggering, and (5) with navigator triggering (integrated in MR signal acquisition). Regions of interest were placed on liver and kidneys, and the resulting phase differences between the measurements were transformed into corresponding temperature differences.Results Precision significantly varied depending on the liver segment or location in the kidney. Gating techniques were found better than breathhold techniques and clearly better than non-gated examinations. The most precise approach reached a standard deviation of 2.0 degrees C under continuous breathing when navigator gating was used at 1.5 T.Conclusion PRF temperature measurement is feasible even for moving organs in the abdomen at 0.2 and 1.5 T. The location of the target region and the required precision of the measurements should direct the choice of examination mode.

In this study the contrast behaviour of five different musculoskeletal tissues of the knee (muscle, cartilage, bone marrow, synovial fluid and the Hoffa's fat body) were analysed for spinecho-and spoiled gradientecho sequences by means of computer simulations On the basis of tissue properties (spin density, T1, T2 and T2*) obtained from three healthy subjects optimal imaging parameters TR, TE and the flip angle (the latter only for GRE) were derived for separation between two tissue types. As a criterion for the ability to separate two tissues the ratio between signal intensity difference regarding the two tissues of interest and the used measuring time was applied. The paper presents the sequence type and parameters for optimal tissue contrast regarding all possible pairs of tissue. The applicability of the model was tested by comparing results with corresponding images recorded in a healthy subject. The long-term objective is the optimisation of imaging strategies for the so called "computer aided diagnostics", where reliable automated tissue separation in huge radiological MR data sets is considered essential.

Zielsetzung: Thermographische Methoden sind zur Kontrolle thermoablativer Therapieverfahren wünschenswert; sie sind jedoch artefaktanfällig. Mit dieser Studie soll die Messungenauigkeit durch Atmung und Bewegung bei der Temperaturbestimmung an Leber und Niere mittels der Proton Resonance Frequency Shift (Phasenkontrast-)Methode bestimmt werden. Material und Methoden: Sechs Probanden wurden an einem 1,5 T MR-Tomographen mit einer Gradientenecho-Sequenz (TR 50 ms, TE 10 ms, Flipwinkel 35°, Matrix 256×256; für getriggerte Sequenzen mit TE 7,8 ms, TR 700 ms, Flipwinkel 8°, Matrix 128×128) untersucht. Jeweils acht Aufnahmen wurden in fünf Untersuchungsmodi durchgeführt: Inspirations-Expirations-Modus (IE) in Atemextremlagen, Continuous Breathing (CB), Expiration (8E), sowie Atemgurt (AG)- und Navigator (NA)-getriggerte Untersuchungen. Vier Probanden wurden an einem 0,2 T Kernspin-Tomographen mit einer Gradientenechosequenz (TR 60 ms, TE 30 ms, Flipwinkel 35°, Matrix192×192) mit den Modi IE, CB und 8E untersucht. Auswertung: In Leber und Nieren wurden segment- oder zonenspezifisch ROIs platziert. Die während der Untersuchung entstandene Phasenverschiebung wurde gemäß Δ((Phi))=δ γ B0 TE ΔT in eine Temperaturdifferenz ΔT umgerechnet. Es wurden jeweils die maximale Temperaturdifferenz und die mittlere Abweichung vom Mittelwert berechnet. Ergebnisse: Die Messungen mit dem 0,2 T-Kernspintomograph ergeben einen größeren Temperaturfehler. Der Temperaturfehler der Untersuchungsmodi ist signifikant unterschiedlich (IE 31°C, CB 7°C mittlere Abweichung vom Mittel, 8E 4°C, AG 1,9°C, NA 2,0°C). Die höchste Präzision zeigen die beiden getriggerten Untersuchungen; Atemgurt und Navigator sind nicht signifikant unterschiedlich. Die Lebersegmente 2, 4a und 8 zeigen signifikant die größte Ungenauigkeit in der Temperaturbestimmung. Schlussfolgerung: Die Temperaturbestimmung mit der PRF Methode ist sehr suszeptibel für Atem- und Bewegungsartefakte, die am 0,2 T-Kernspintomograph besonders ausgeprägt sind. Atemgurttriggerung und Navigatortechnik erhöhen die Genauigkeit der Temperaturbestimmung in den Bereich, der für den klinischen Einsatz notwendig ist.