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Purpose To dynamically minimize radiofrequency (RF)-induced heating of an active catheter through an automatic change of the termination impedance. Methods A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔTmax . The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built-in thermistor or external data from a fiber-optical thermometer. It automatically changes the catheter input impedance until the temperature rise during MRI is minimized. If ΔTmax is exceeded, RF transmission is blocked by a feedback system. Results The thermistor and fiber-optical thermometer provided consistent temperature data in a phantom experiment. During MRI, the MRsWD was able to reduce the maximum temperature rise by 25% when operated in real-time feedback mode. Conclusion This study demonstrates the technical feasibility of an MRsWD as an alternative or complementary approach to reduce RF-induced heating of active interventional devices. The automatic MRsWD can reduce heating using direct temperature measurements at the tip of the catheter. Given that temperature measurements are intrinsically slow, for a clinical implementation, a faster feedback parameter would be required such as the RF currents along the catheter or scattered electric fields at the tip.

Purpose To investigate the effect of the termination impedance on the RF-induced heating of active catheters using analytical modeling. Theory and methods Interaction of an arbitrary electric (E) field and an isolated transmission line (TL) embedded in cascaded lossy media was analytically modeled. Termination impedances at the tip and the input sides were expressed as distinct parameters in the current and voltage distribution formulae that are obtained by solving the inhomogeneous wave equations using the Green's function approach. The tip specific absorption rate (SAR) was calculated for different E field configurations. The tip SAR was displayed on a color-coded Smith chart in terms of the normalized input reflection coefficient. Results of the analytical calculations were compared to transfer function (TF) measurements. An input impedance control unit that is integrated to the interface circuit was introduced. Results TFs from analytical model and measurements exhibited similar behaviors. Color-coded Smith charts shows that the analytical model and measured TF-based tip SAR depends strongly on the input reflection coefficient. Both for measured and analytical TFs, SAR can deviate up to 70% from the mean value for different input impedance values. Conclusion This study shows that it is possible to change the RF-induced heating characteristics of an active catheter by adjusting the input impedance, and the presented analytical model is in good agreement with TF measurements.

PURPOSE To provide a data post-processing method that corrects for partial volume effects (PVE) and fast T 2 * decay in dynamic 17 O MRI for the mapping of cerebral metabolic rates of oxygen consumption (CMRO2 ). METHODS CMRO2 is altered in neurodegenerative diseases and tumors and can be measured after 17 O gas inhalation using dynamic 17 O MRI. CMRO2 quantification is difficult because of PVE. To correct for PVE, a direct estimation of the MR images (DIESIS) method is proposed and used in 4 dynamic 17 O MRI data sets of a healthy volunteer acquired on a 3T MRI system. With DIESIS, 17 O MR signal time curves in selected regions were directly estimated based on parcellation of a coregistered 1 H MPRAGE image. RESULTS Profile likelihood analysis of the DIESIS method showed identifiability of CMRO2 . In white matter (WM), DIESES reduced CMRO2 from 0.97 ± 0.25 µmol/gtissue /min with Kaiser-Bessel gridding reconstruction to 0.85 ± 0.21 µmol/gtissue /min, whereas in gray matter (GM) it increases from 1.3 ± 0.31 µmol/gtissue /min to 1.86 ± 0.36 µmol/gtissue /min; both values are closer to the literature values from the 15 O-PET studies. CONCLUSION DIESIS provided an increased separation of CMRO2 values in GM and WM brain regions and corrected for partial volume effects in 17 O-MRI inhalation experiments. DIESIS could also be applied to more heterogeneous tissues such as glioblastomas if subregions of the tumor can be represented as additional parcels.

Purpose Optimization of timing parameters for MR-guided ARFI to achieve the highest displacement signal-to-noise ratio (SNRd). Theory and Methods In MR-guided ARFI the phase change induced by motion encoding gradients (MEGs) is measured to assess tissue displacement. The sensitivity of this encoding procedure depends on several timing parameters, such as the MEG duration and the offset time between ultrasound (US) and MEG. Furthermore, mechanical and MR tissue constants and MEG schemes (bipolar or three-lobed) influence SNRd. Optimal timing parameters were determined in simulations for bipolar and three-lobed MEGs, and the results were compared with measurements. To provide clinically usable timing parameters, physiologically relevant ranges of tissue constants were considered. Results For the considered ranges of tissue constants, optimal timing parameters provide only 6% higher SNRd for bipolar than for three-lobed MEG. Three-lobed MEG is less sensitive to motion as confirmed in phantom experiments. Bipolar MEG can use approximately 1.5-fold shorter MEG durations. Conclusion Both bipolar and three-lobed MEGs can yield approximately the same SNRd if the optimal timing parameters are chosen. Bipolar MEG allows for shorter durations, which is preferable if deposition of US energy needs to be minimized, and three-lobed MEG is more suitable when residual motion compensation is necessary. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

PURPOSE Parameter identifiability and confidence intervals were determined using a profile likelihood (PL) analysis method in a quantification model of the cerebral metabolic rate of oxygen consumption (CMRO2 ) with direct 17 O MRI. METHODS Three-dimensional dynamic 17 O MRI datasets of the human brain were acquired after inhalation of 17 O2 gas with the help of a rebreathing system, and CMRO2 was quantified with a pharmacokinetic model. To analyze the influence of the different model parameters on the identifiability of CMRO2 , PLs were calculated for different settings of the model parameters. In particular, the 17 O enrichment fraction of the inhaled 17 O2 gas, α, was investigated assuming a constant and a linearly varying model. Identifiability was analyzed for white and gray matter, and the dependency on different priors was studied. RESULTS Prior knowledge about only one α-related parameter was sufficient to resolve the CMRO2 nonidentifiability, and CMRO2 rates (0.72-0.99 µmol/gtissue /min in white matter, 1.02-1.78 µmol/gtissue /min in gray matter) are in a good agreement with the results of 15 O positron emission tomography studies. Nonconstant α values significantly improved model fitting. CONCLUSION The profile likelihood analysis shows that CMRO2 can be measured reliably in 17 O gas MRI experiment if the 17 O enrichment fraction is used as prior information for the model calculations. Magn Reson Med 78:1157-1167, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

PURPOSE To present an image registration method for renal blood oxygen level-dependent (BOLD) measurements that enables semiautomatic assessment of parenchymal and medullary R2* changes under a functional challenge. METHODS In a series of breath-hold acquisitions, three-dimensional data were acquired initially for prospective image registration of subsequent BOLD measurements. An algorithm for kidney alignment for BOLD renal imaging (KALIBRI) was implemented to detect the positions of the left and right kidney so that the kidneys were acquired in the subsequent BOLD measurement at consistent anatomical locations. Residual in-plane distortions were corrected retrospectively so that semiautomatic dynamic R2* measurements of the renal cortex and medulla become feasible. KALIBRI was tested in six healthy volunteers during a series of BOLD experiments, which included a 600- to 1000-mL water challenge. RESULTS Prospective image registration and BOLD imaging of each kidney was achieved within a total measurement time of about 17 s, enabling its execution within a single breath-hold. KALIBRI improved the registration by up to 35% as found with mutual information measures. In four volunteers, a medullary R2* decrease of up to 40% was observed after water ingestion. CONCLUSION KALIBRI improves the quality of two-dimensional time-resolved renal BOLD MRI by aligning local renal anatomy, which allows for consistent R2* measurements over many breath-holds. Magn Reson Med 77:1573-1582, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

PURPOSE To combine vocal tract measurements with dynamic MRI of the lungs to provide fundamental insights into the lung physiology during singing. METHODS To analyze vocal fold oscillatory patterns during dynamic lung MRI, an electroglottography (EGG) system was modified to allow for simultaneous EGG measurements during MR image acquisitions. A low-pass filter was introduced to suppress residual radiofrequency (RF) coupling into the EGG signal. RF heating was tested in a gel phantom to ensure MR safety, and functionality of the EGG device was assessed in a volunteer experiment at singing frequencies from A5 to A3. In the recorded EGG signals, remaining RF interferences were removed by independent component analysis post processing, and standard EGG parameters such as fundamental frequency, contact quotient and jitter were calculated. In a second volunteer experiment, EGG recordings were compared with lung diameter measurements from 2D time-resolved trueFISP acquisitions. RESULTS RF heating measurements resulted in less than 1.2°C temperature increase in the gel phantom. EGG parameters measured during MR imaging are within the range of ideal values. In the lung measurement, both the lung diameter and the EGG recordings could be successfully performed with only minimal interference. CONCLUSION EGG recording is pos sible during dynamic lung MRI, and glottal activity can be studied safely at 1.5T. Magn Reson Med 76:1629-1635, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

PURPOSE Precise temperature measurements in the magnetic field are indispensable for MR safety studies and for temperature calibration during MR-guided thermotherapy. In this work, the interference of two commonly used fiber-optical temperature measurement systems with the static magnetic field B0 was determined. METHODS Two fiber-optical temperature measurement systems, a GaAs-semiconductor and a phosphorescent phosphor ceramic, were compared for temperature measurements in B0 . The probes and a glass thermometer for reference were placed in an MR-compatible tube phantom within a water bath. Temperature measurements were carried out at three different MR systems covering static magnetic fields up to B0 = 9.4T, and water temperatures were changed between 25°C and 65°C. RESULTS The GaAs-probe significantly underestimated absolute temperatures by an amount related to the square of B0 . A maximum difference of ΔT = -4.6°C was seen at 9.4T. No systematic temperature difference was found with the phosphor ceramic probe. For both systems, the measurements were not dependent on the orientation of the sensor to B0 . CONCLUSION Temperature measurements with the phosphor ceramic probe are immune to magnetic fields up to 9.4T, whereas the GaAs-probes either require a recalibration inside the MR system or a correction based on the square of B0 . Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.

Purpose To increase the signal-to-noise ratio (SNR) and to reduce artifacts in non-proton magnetic resonance imaging (MRI) by incorporation of a priori information from 1H MR data in an iterative reconstruction. Methods An iterative reconstruction algorithm for 3D projection reconstruction (3DPR) is presented that combines prior anatomical knowledge and image sparsity under a total variation (TV) constraint. A binary mask (BM) is used as an anatomical constraint to penalize non-zero signal intensities outside the object. The BM&TV method is evaluated in simulations and in MR measurements in volunteers. Results In simulated BM&TV brain data, the artifact level was reduced by 20% while structures were well preserved compared to gridding. SNR maps showed a spatially dependent SNR gain over gridding reconstruction, which was up to 100% for simulated data. Undersampled 3DPR 23Na MRI of the human brain revealed an SNR increase of 29 ± 7%. Small anatomical structures were reproduced with a mean contrast loss of 14%, whereas in TV-regularized iterative reconstructions a loss of 66% was found. Conclusion The BM&TV algorithm allows reconstructing images with increased SNR and reduced artifact level compared to gridding and performs superior to an iterative reconstruction using an unspecific TV constraint only. Magn Reson Med 71:1720–1732, 2014. © 2013 Wiley Periodicals, Inc.

Purpose To evaluate a novel imaging sequence termed crushed rephased orthogonal slice selection (CROSS) that uses the available time in long echo time (TE) gradient echo (GRE) imaging—as employed for proton resonance frequency (PRF) shift thermometry—to simultaneously acquire two orthogonal magnetic resonance imaging (MRI) temperature maps around the target region. Materials and Methods The CROSS sequence encodes a second orthogonal slice between excitation and data readout in long-TE imaging and applies dedicated crusher (CR) gradients to separate the signals from the two slices. Numerical simulations of the Bloch equations and phantom experiments were performed to analyze the MR signal. In phantom and in vivo experiments with two domestic pigs, the applicability of the CROSS sequence for temperature mapping of thermal therapies with focused ultrasound and laser was studied. Results A successful separation of the signals from the two slices was achieved for CR dephasing lengths approaching the in-plane resolution. In the two animal experiments, CROSS temperature mapping could be successfully demonstrated at a temporal resolution of 2–3 seconds and a temperature uncertainty of 3–4K. Conclusion At the expense of a reduced signal in the overlap of the two slices, the CROSS sequence achieves an improvement of temporal resolution by 50%, without requiring further acceleration techniques such as parallel imaging, over conventional sequential GRE sequences employing the same repetition time as the CROSS sequence acquires two slices within one repetition interval. J. Magn. Reson. Imaging 2013;38:1510–1520. © 2013 Wiley Periodicals, Inc.

Cerebral three-dimensional time of flight (TOF) angiography significantly benefits from ultrahigh fields, mainly due to higher signal-to-noise ratio and to longer T1 relaxation time of static brain tissues; however, specific absorption rate (SAR) significantly increases with B0. Thus, additional radiofrequency pulses commonly used at lower field strengths to improve TOF contrast such as saturation of venous signal and improved background suppression by magnetization transfer typically cannot be used at higher fields. In this work, we aimed at reducing SAR for each radiofrequency pulse category in a TOF sequence. We use the variable-rate selective excitation principle for the slab selective TOF excitation as well as the venous saturation radiofrequency pulses. In addition, magnetization transfer pulses are implemented by sparsely applying the pulses only during acquisition of the central k-space lines to limit their SAR contribution. Image quality, angiographic contrast, and SAR reduction were investigated as a function of variable-rate selective excitation parameters and of the total number of magnetization transfer pulses applied. Based on these results, a TOF protocol was generated that increases the angiographic contrast by more than 50% and reduces subcutaneous fat signal while keeping the resulting SAR within regulatory limits. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.

As ultrahigh-field MR imaging systems suffer from the standing wave problems of conventional coil designs, the use of antenna systems that generate travelling waves was suggested. As a modification to the original approach, we propose the use of a coaxial waveguide configuration with interrupted inner conductor. This concept can focus the radiofrequency energy to the desired imaging region in the human body and can operate at different Larmor frequencies without hardware modifications, as it is not limited by a lower cut-off frequency. We assessed the potential of the method with a hardware prototype setup that was loaded with a tissue equivalent phantom and operated with imaging areas of different size. Signal and flip angle distributions within the phantom were analyzed, and imaging at different Larmor frequencies was performed. Results were compared to a finite difference time domain simulation of the setup that additionally provides information on the spatial distribution of the specific absorption rate load. Furthermore, simulation results with a human model (virtual family) are presented. It was found that the proposed method can be used for MRI at multiple frequencies, achieving transmission efficiencies similar to other travelling wave approaches but still suffers from several limitations due to the used mode of wave propagation. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

An efficient breathing system was designed for direct 17O MRI to perform oxygen metabolism studies of the human brain. The breathing system consists of a demand oxygen delivery device for 17O2 supply and a custom-built re-breathing circuit with pneumatic switching valve. To efficiently deliver the 17O gas to the alveoli of the lungs, the system applies short gas pulses upon an inspiration trigger via a nasal cannula. During and after 17O2 administration, the exhaled gas volumes are stored and filtered in the re-breathing section to make the most efficient use of the rare 17O gas. In an inhalation experiment, 2.2 ± 0.1 L of 70%-enriched 17O2 were administered to a healthy volunteer and direct 17O MRI was performed for a total imaging time of 38 min with a temporal resolution of 50 s per 3D data set. Mapping of the maximum signal increase was carried out showing regional variations of oxygen concentration of up to 30% over the natural abundance of 17O water. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc.

Magnetic resonance-guided percutaneous interventions with needles require fast pulse sequences with acquisition times less than 1 s to image the needle trajectory within moving organs. To guide the movement of a rigid instrument with high sampling rate, an magnetic resonance imaging method was developed that reduces the acquisition time down to a few hundred milliseconds by restricting the field of view to a small stripe around the instrument trajectory. To maintain the dynamic steady state, saturation pulses for outer volume suppression were inserted into additional repetition time-intervals. These saturation intervals were combined with three sequence variants: a spoiled gradient echo sequence, an echo-shifted steady state free precession and a balanced steady state free precession sequence. The magnetization dynamics were analyzed by means of numerical optimized simulations. Results were compared with phantom experiments and an average signal-to-suppression-ratio of 15.5 could be achieved. With a field of view reduction of up to 12.5% an update rate of six images per second could be achieved. Finally, animal experiments demonstrated the fast and reliable needle tip visualization during percutaneous magnetic resonance-guided interventions with the help of a robotic assistance system.

An inductively coupled coil concept is presented, which improves the compensation of physiological motion by the self-gating (SG) technique. The animal is positioned in a conventional volume coil encompassing the whole animal. A small, resonant surface coil (SG-coil) is placed on the thorax so that its sensitive region includes the heart. Via inductive coupling the SG-coil amplifies selectively the MR signal of the beating heart. With an optical detuning mechanism, this coupling can be switched off during acquisition of the MR image information, whereas it is active during SG data sampling to provide the physiological information. In vivo experiments on a mouse show an amplification of the SG signal by at least 40%. Magn Reson Med, 2011. © 2010 Wiley-Liss, Inc.

Variable-rate selective excitation RF pulses modulate the slice selection gradients during RF transmission, especially to reduce the total RF power. Amplitude-modulated slice selection gradients can lead to increased gradient noise, in particular in high-field MRI where variable-rate selective excitation techniques are often used. In this work, an algorithm is presented that calculates a variable-rate selective excitation pulse modulation from given RF pulses with constant slice selection gradient. The algorithm avoids the known acoustic resonance frequencies of the gradient system to minimize sound pressure levels. It was tested with four different slice-selective RF pulse shapes (Sinc, Gaussian, and two Shinnar-LeRoux). Sound measurements revealed a reduction of the mean sound pressure level by up to 13 dB, and simultaneously, the specific absorption rate was reduced by 55%.

A new method to localize and track medical devices in air-filled body cavities is proposed that uses active microcoils with a semisolid filling. In air spaces, e.g., the lung, microcoils require an independent signal source, which should be made of a biocompatible, solid and sterilizable material with a long shelf time. In a measurement of the T(1) and T*(2) and the relative spin density of several semisolid materials, latex was identified as a suitable material from which a prototype catheter was constructed with a microcoil at its tip. In a dual-echo tracking pulse sequence, the very short T*(2) of the rubber material allowed suppressing the background signal from surrounding tissue with a subtraction technique and additional dephasing gradients. With a roadmapping reconstruction, the microcoil's trajectory could be visualized on a previously acquired reference image set with a tracking rate of up to 60 Hz at a spatial resolution of better than 2mm. In a real-time tracking implementation, an image update rate of 4 Hz was achieved by combining the tracking with a fast real-time imaging sequence. Both methods were successfully applied in vivo to track the catheter in the lung of a pig.

Purpose: Focused ultrasound surgery (FUS) is a highly precise noninvasive procedure to ablate pathogenic tissue. FUS therapy is often combined with magnetic resonance (MR)imaging as MRimaging offers excellent target identification and allows for continuous monitoring of FUS induced temperature changes. As the dimensions of the ultrasound(US) focus are typically much smaller than the targeted volume, multiple sonications and focus repositioning are interleaved to scan the focus over the target volume. Focal scanning can be achieved electronically by using phased-array UStransducers or mechanically by using dedicated mechanical actuators. In this study, the authors propose and evaluate the precision of a combined robotic FUS setup to overcome some of the limitations of the existing MRgFUS systems. Such systems are typically integrated into the patient table of the MRscanner and thus only provide an application of the US wave within a limited spatial range from below the patient. Methods: The fully MR-compatible robotic assistance system InnoMotion™ (InnoMedic GmbH, Herxheim, Germany) was originally designed for MR-guided interventions with needles. It offers five pneumatically driven degrees of freedom and can be moved over a wide range within the bore of the magnet. In this work, the robotic system was combined with a fixed-focus UStransducer (frequency: 1.7 MHz; focal length: 68 mm, and numerical aperture: 0.44) that was integrated into a dedicated, in-house developed treatment unit for FUS application. A series of MR-guided focal scanning procedures was performed in a polyacrylamide-egg white gel phantom to assess the positioning accuracy of the combined FUS setup. In animal experiments with a 3-month-old domestic pig, the system’s potential and suitability for MRgFUS was tested. Results: In phantom experiments, a total targeting precision of about 3 mm was found, which is comparable to that of the existing MRgFUS systems. Focus positioning could be performed within a few seconds. Duringin vivo experiments, a defined pattern of single thermal lesions and a therapeutically relevant confluent thermal lesion could be created. The creation of local tissue necrosis by coagulation was confirmed by post-FUS MRimaging and histological examinations on the treated tissue sample. During all sonications in phantom and in vivo, reliable MRimaging and online MR thermometry could be performed without compromises due to operation of the combined robotic FUS setup. Conclusions: Compared to the existing MRgFUS systems, the combined robotic FUS approach offers a wide range of spatial flexibility so that highly flexible application of the US wave would be possible, for example, to avoid risk structures within the US field. The setup might help to realize new ways of patient access in MRgFUS therapy. The setup is compatible with any closed-bore MR system and does not require an especially designed patient table.

Air enclosures in polar ice cores represent the only direct paleoatmospheric archive. Analysis of the entrapped air provides clues to the climate system of the past in decadal to centennial resolution. A wealth of information has been gained from measurements of concentrations of greenhouse gases; however, little is known about their isotopic composition. In particular, stable isotopologues (dD and d 13 C) of methane (CH4) record valuable information on its global cycle as the different sources exhibit distinct carbon and hydrogen isotopic composition. However, CH4 isotope analysis is limited by the largesample size requiredand thedemandinganalysis as highprecision is required.Herewe present a highly automated, high-precision online gas chromatography/pyrolysis/isotope ratio monitoring mass spectrometry (GC/P/irmMS) technique for the analysis of dD(CH4). It includes gas extraction from ice, preconcentration, gas chromatographic separation and pyrolysis of CH4 from roughly 500g of ice with CH4 concentrations as low as 350ppbv. Ice samples with approximately 40mL air and only � 1nmol CH4 can be measured with a precision of 3.4%. The precision for 65mL air samples with recent atmospheric concentration is 1.5%. The CH4 concentration can be obtained along with isotope data which is crucial for reporting ice core data on matched time scales and enables us to detect flaws in the measurement procedure. Custom-made script-based processing of MS raw and peak data enhance the system’s performance with respect to stability, peak size dependency, hence precision and accuracy and last but not least time requirement. Copyright # 2010 John Wiley & Sons, Ltd.

Triclosan, an antimicrobial compound used in personal care products, occurs in the aquatic environment due to residual concentrations in municipal wastewater treatment effluent. We evaluate triclosan-related risks to the aquatic environment, for aquatic and sediment-dwelling organisms and for aquatic-feeding wildlife, based on measured and modeled exposure concentrations. Triclosan concentrations in surface water, sediment, and biota tissue are predicted using a fugacity model parameterized to run probabilistically, to supplement the limited available measurements of triclosan in sediment and tissue. Aquatic toxicity is evaluated based on a species sensitivity distribution, which is extrapolated to sediment and tissues assuming equilibrium partitioning. A probabilistic wildlife exposure model is also used, and estimated doses are compared with wildlife toxicity benchmarks identified from a review of published and proprietary studies. The 95th percentiles of measured and modeled triclosan concentrations in surface water, sediment, and biota tissues are consistently below the 5th percentile of the respective species sensitivity distributions, indicating that, under most scenarios, adverse affects due to triclosan are unlikely. Integr Environ Assess Manag 2010;6:419–440. © 2010 SETAC

The fate and partitioning of the antimicrobial compound, triclosan, in wastewater treatment plants (WWTPs) is evaluated using a probabilistic fugacity model to predict the range of triclosan concentrations in effluent and secondary biosolids. The WWTP model predicts 84% to 92% triclosan removal, which is within the range of measured removal efficiencies (typically 70% to 98%). Triclosan is predominantly removed by sorption and subsequent settling of organic particulates during primary treatment and by aerobic biodegradation during secondary treatment. Median modeled removal efficiency due to sorption is 40% for all treatment phases and 31% in the primary treatment phase. Median modeled removal efficiency due to biodegradation is 48% for all treatment phases and 44% in the secondary treatment phase. Important factors contributing to variation in predicted triclosan concentrations in effluent and biosolids include influent concentrations, solids concentrations in settling tanks, and factors related to solids retention time. Measured triclosan concentrations in biosolids and non-United States (US) effluent are consistent with model predictions. However, median concentrations in US effluent are over-predicted with this model, suggesting that differences in some aspect of treatment practices not incorporated in the model (e.g., disinfection methods) may affect triclosan removal from effluent. Model applications include predicting changes in environmental loadings associated with new triclosan applications and supporting risk analyses for biosolids-amended land and effluent receiving waters. Integr Environ Assess Manag 2010;6:393–404. © 2010 SETAC

Triclosan is an antimicrobial compound found in many consumer products including soaps and personal care products. Most triclosan is disposed of down household drains, whereupon it is conveyed to wastewater treatment plants. Although a high percentage of triclosan biodegrades during wastewater treatment, most of the remainder is adsorbed to sludge, which may ultimately be applied to land as biosolids. We evaluated terrestrial ecological risks related to triclosan in land-applied biosolids for soil microbes, plants, soil invertebrates, mammals, and birds. Exposures are estimated using a probabilistic fugacity-based model. Triclosan concentrations in biosolids and reported biosolids application rates are compiled to support estimation of triclosan concentrations in soil. Concentrations in biota tissue are estimated using an equilibrium partitioning model for plants and worms and a steady-state model for small mammals; the resulting tissue concentrations are used to model mammalian and avian dietary exposures. Toxicity benchmarks are identified from a review of published and proprietary studies. The results indicate that adverse effects related to soil fertility (i.e., disruption of nitrogen cycling) would be expected only under "worst-case" exposures, under certain soil conditions and would likely be transient. The available data indicate that adverse effects on plants, invertebrates, birds, and mammals due to triclosan in land-applied biosolids are unlikely.

The present study proposes a catheter system with an expandable coil etched on a polyimide foil. The catheter system combines the advantages of a small insertion diameter when the coil is rolled up in a protective carrier sheath with an increased signal-to-noise ratio (SNR) and penetration depth when the coil is pushed out. After imaging, the coil can be retracted into the sheath and folded back into the initial rolled-up configuration due to the tapered geometry of the carrier foil. The catheter system was tested on two healthy anesthetized pigs, including tracking and high-resolution intravascular imaging. To reduce artifacts in high-resolution images induced by catheter motion in the pulsatile blood flow, a motion-gating method was implemented that combines a flow-compensated two-dimensional fast low angle shot (FLASH) imaging sequence with the acquisition of projection data for retrospective gating. Using the projection data for motion detection, image SNR was increased by up to 500% over uncorrected images, and anatomic structures of 150 μm size could be differentiated in the aorta. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc.

Purpose: To measure longitudinal relaxation rate (R1) changes during contrast agent studies using a driven equilibrium single pulse observation of T1 (DESPOT) method with a sliding window (sw) acquisition. Materials and Methods: A sw-DESPOT technique was implemented that uses several three-dimensional (3D) image data sets to calculate R1 with a temporal resolution of only a single data set. Different sources of systematic errors were studied in simulations, and the technique was tested in a tumor-bearing mouse using an intravascular contrast agent. Results: Consistent concentration distributions of the CA were calculated with a temporal resolution of 10 s. Conclusion: Sw-DESPOT offers a precise and fast method to monitor the CA dynamics in 3D volumes. J. Magn. Reson. Imaging 2009;30:1163–1170. © 2009 Wiley-Liss, Inc.

There is significant clinical interest in primers which are specific for fungi and do not hybridize to DNA of other eukaryotes or prokaryotes. Such primers would allow specific amplification of fungal DNA from human tissue samples containing fungi. Fungal identification to the species level could follow by direct sequencing or restriction analysis. Several previously described primer systems cross-react with DNA of plants and animals. We have designed a primer system that amplifies a fragment of the gene coding for the small ribosomal subunit 18S rRNA. Database searches and sequence analyses were performed using the HUSAR (Heidelberg Unix Sequence Analysis Resources) computer system at the German Cancer Research Centre, Heidelberg, Germany. Primers TR1 (5'-GTTTCTAGGACCGCCGTA) and TR2 (5'-CTCAAACTTCCATCGACTTG) bind to sequences which are homologous within the fungi, but differ from corresponding DNA fragments of plants and animals. The amplified fragment is 581 base pairs in length and contains variable, and therefore species-specific, regions. The DNA of Trichophyton rubrum, Trichophyton mentagrophytes, Trichophyton verrucosum, Trichophyton terrestre, Microsporum canis, Microsporum gypseum and Epidermophyton floccosum and of several yeast species was amplified by the primers, but not the DNA from 42 normal human skin samples. Furthermore, other DNA preparations from plants and animals, including those from radish, cabbage, wheat and mouse, did not show amplification reactions.

MR-guided transrectal prostate biopsy is currently a time-consuming procedure because the imaging slice is often manually realigned with the biopsy needle during lesion targeting. In this work a pulse sequence is presented that automatically follows a passive marker attached to a dedicated MR biopsy device holder, thus providing an alternative to existing active tracking methods. In two orthogonal tracking FLASH images of the marker the position of the needle axis is automatically identified using a phase-only cross-correlation (POCC) algorithm. The position information is then used to realign a trueFISP imaging slice in real time. In phantom experiments the sensitivity of this technique to initial misalignments of the marker and to the signal-to-noise ratio was evaluated. In several puncture experiments the precision of the needle placement was analyzed. The POCC algorithm allowed for a precise identification of the marker in the images even under severe initial misalignments of up to 45°. At a frame rate 1 image/s a precision of the needle placement of 1.5 ± 1.1 mm could be achieved. Magn Reson Med 59:1043–1050, 2008. © 2008 Wiley-Liss, Inc.

Temperate grasslands contribute about 20% to the global terrestrial carbon (C) budget with sugars contributing 10–50% to this soil C pool. Whether the observed increase of the atmospheric CO2 concentration (pCO2) leads to additional C sequestration into these ecosystems or enhanced mineralization of soil organic matter (SOM) is still unclear. Therefore, the aim of the presented study was to investigate the impact of elevated atmospheric pCO2 on C sequestration and turnover of plant- (arabinose and xylose) and microbially derived (fucose, rhamnose, galactose, mannose) sugars in soil, representing a labile SOM pool. The study was carried out at the Swiss Free Air Carbon Dioxide Enrichment (FACE) experiment near Zurich. For 7 years, Lolium perenne swards were exposed to ambient and elevated pCO2 (36 and 60 Pa, respectively). The additional CO2 in the FACE plots was depleted in 13C compared with ambient plots, so that ‘new’ (

A new reconstruction method for parallel MRI called PROBER is proposed. The method PROBER works in an image domain similar to methods based on Sensitivity Encoding (SENSE). However, unlike SENSE, which first estimates the spatial sensitivity maps, PROBER approximates the reconstruction coefficients directly by B-splines. Also, B-spline coefficients are estimated at once in order to minimize the reconstruction error instead of estimating the reconstruction in each pixel independently (as in SENSE). This makes the method robust to noise in reference images. No presmoothing of reference images is necessary. The number of estimated parameters is reduced, which speeds up the estimation process. PROBER was tested on simulated, phantom, and in vivo data. The results are compared with commercial implementations of the algorithms SENSE and GRAPPA (Generalized Autocalibrating Partially Parallel Acquisitions) in terms of elapsed time and reconstruction quality. The experiments showed that PROBER is faster than GRAPPA and SENSE for images wider than 150 × 150 pixels for comparable reconstruction quality. With more basis functions, PROBER outperforms both SENSE and GRAPPA in reconstruction quality at the cost of slightly increased computational time. Magn Reson Med 58:582–591, 2007. © 2007 Wiley-Liss, Inc.

MR-guided intravascular interventions require image update rates of up to 10 images per second, which can be achieved using parallel imaging. However, parallel imaging requires many coil elements, which increases reconstruction times and thus compromises real-time image reconstruction. In this study a dynamic coil selection (DCS) algorithm is presented that selects a subset of receive coils to reduce image reconstruction times. The center-of-sensitivity coordinates and the relative signal intensities are determined for each coil in a prescan. During the intervention m coils are selected for reconstruction using a coil ranking based on the distance to the current slice or catheter position. In a phantom experiment for m = 6, an optimal signal-to-background ratio (SBR) was achieved and foldover artifacts were avoided. In three animal experiments involving catheter manipulation in the aorta and the right heart chamber, the anatomy was successfully visualized at frame rates of about 5 Hz using active catheter tracking.

Percutaneous MR-guided interventions with needles require fast pulse sequences to image the needle trajectory with minimal susceptibility artifacts. Spin-echo pulse sequences are well suited for reducing artifact size; however, even with single-shot turbo spin-echo techniques, such as rapid acquisition with relaxation enhancement (RARE) or half-Fourier acquisition single-shot turbo spin-echo (HASTE), fast imaging remains challenging. In this work we present a HASTE pulse sequence that is combined with inner-volume excitation to reduce the scan time and limit the imaging field of view (FOV) to a small strip close to the needle trajectory (targeted-HASTE). To compensate for signal saturation from fast repeated acquisitions, a magnetization restore pulse (driven equilibrium Fourier transform (DEFT)) is used. The sequence is combined with dedicated active marker coils to measure the position and orientation of the needle so that the targeted-HASTE image slice is automatically repositioned. In an animal experiment the coils were attached to an MR-compatible robotic assistance system for MR-guided interventions. Needle insertion and infusion via the needle could be visualized with a temporal resolution of 1 s, and the needle tip could be localized even in the presence of a stainless steel mandrel.

Healthcare workers (HCW) have an increased risk of suffering from occupational skin diseases (OSDs). Therefore, we established special prevention and skin protection courses for HCW. Medical aims are to optimize diagnostic procedures and individual therapy, educational aims are to improve individual skin protection/skin care habits of the patient and also to influence the participants' attitudes towards health. Participants are patients that have been suspected to suffer from an OSD and are insured with the German Accident Prevention Insurance Association for Health Care Workers (BGW). Teaching units mainly focus on the texture and functioning of the skin, general aspects of OSDs, general information concerning skin protection, instructions about the correct use of skin cleansing and skin protection products. Besides, every participant is clinically examined by a dermatologist and a precise patient's history is obtained. Individually adapted skin protection strategies are developed. Patients can ask the dermatologist questions in confidence. 504 patients (mean age: 36.9 years, SD = 11.7) participated in the skin protection courses. 94.6% (n = 477) suffered from hand eczema frequently caused by a mixture of atopic, irritant and allergic contact dermatitis, but irritant contact dermatitis was the most frequent diagnosis (55.4%, n = 279). The participants rated the course as good to excellent. Health education and advisory services in occupational dermatology are still fragmentary. Prevention of OSD and maintenance of health through education are important complementary measures for dermatological care. In the future, similar educational programmes should be offered for employees of other professions with an increased risk for OSD.

(23)Na MRI has the potential to noninvasively detect sodium (Na) content changes in vivo. The goal of this study was to implement (23)Na MRI in a clinical setting for neurooncological and muscular imaging. Due to the biexponential T(2) decay of the tissue Na signal with a short component, which ranges between 0.5-8 ms, the measurement of total Na content requires imaging techniques with echo times (TEs) below 0.5 ms. A 3D radial pulse sequence with a TE of 0.2 ms at a spatial resolution of 4 x 4 x 4 mm(3) was developed that allows the acquisition and presentation of Na images on the scanner. This sequence was evaluated in patients with low- and high-grade gliomas, and higher (23)Na MR signals corresponding to an increased Na content were found in the tumor regions. The contrast-to-noise ratio (CNR) between tumor and white matter increased from 0.8 +/- 0.2 to 1.3 +/- 0.3 with tumor grade. In patients with an identified muscular (23)Na channelopathy (Paramyotonia congenita (PC)), induced muscle weakness led to a signal increase of approximately 18% in the (23)Na MR images, which was attributed to intracellular Na(+) accumulation in this region.

In past decades, much effort has been invested in developing therapies for spinal injuries. Lack of standardization of clinical read-out measures, however, makes direct comparison of experimental therapies difficult. Damage and therapeutic effects in vivo are routinely evaluated using rather subjective behavioral tests. Here we show that manganese-enhanced magnetic resonance imaging (MEMRI) can be used to examine the extent of damage following spinal cord injury (SCI) in mice in vivo. Injection of MnCl2 solution into the cerebrospinal fluid leads to manganese uptake into the spinal cord. Furthermore, after injury MEMRI-derived quantitative measures correlate closely with clinical locomotor scores. Improved locomotion due to treating the detrimental effects of SCI with an established therapy (neutralization of CD95Ligand) is reflected in an increase of manganese uptake into the injured spinal cord. Therefore, we demonstrate that MEMRI is a sensitive and objective tool for in vivo visualization and quantification of damage and functional improvement after SCI. Thus, MEMRI can serve as a reproducible surrogate measure of the clinical status of the spinal cord in mice, potentially becoming a standard approach for evaluating experimental therapies.

In this work active MR catheter tracking with automatic slice alignment was combined with an autocalibrated parallel imaging technique. Using an optimized generalized autocalibrating partially parallel acquisitions (GRAPPA) algorithm with an acceleration factor of 2, we were able to reduce the acquisition time per image by 34%. To accelerate real-time GRAPPA image reconstruction, the coil sensitivities were updated only after slice reorientation. For a 2D trueFISP acquisition (160 x 256 matrix, 80% phase matrix, half Fourier acquisition, TR = 3.7 ms, GRAPPA factor = 2) real-time image reconstruction was achieved with up to six imaging coils. In a single animal experiment the method was used to steer a catheter from the vena cava through the beating heart into the pulmonary vasculature at an image update rate of about five images per second. Under all slice orientations, parallel image reconstruction was accomplished with only minor image artifacts, and the increased temporal resolution provided a sharp delineation of intracardial structures, such as the papillary muscle.

Zusammenfassung Hintergrund: Die Beschaftigten der Gesundheitsberufe haben ein erhohtes Risiko, eine Berufshautkrankheit zu entwickeln. Seit Januar 2002 werden in der Abteilung Klinische Sozialmedizin, Berufs- und Umweltdermatologie des Universitatsklinikums Heidelberg in Zusammenarbeit mit der Berufsgenossenschaft fur Gesundheitsdienst und Wohlfahrtspflege (BGW) Seminare zur sekundaren Pravention von berufsbedingten Hauterkrankungen bei Angehorigen von Gesundheitsberufen durchgefuhrt. Zielkriterien sind Veranderungen des individuellen Schutz- und Pflegeverhaltens, Empfehlungen bezuglich der weiteren Diagnostik und Therapie, langfristige Besserung und Stabilisierung des Hautzustandes und Vermeidung einer Berufskrankheit nach BK 5101. Patienten und Methodik: Bei den zweitagigen Seminaren nehmen bis zu 14 Hauterkrankte teil. Darin werden sie uber Aufbau und Funktion der Haut sowie notwendige Schutzmasnahmen informiert. In praktischen Seminarphasen uben die Teilnehmer, Hautschutzmasnahmen in ihre taglichen Arbeitslaufe zu integrieren. Ferner erfolgt eine ausfuhrliche arztliche Anamnese und Untersuchung. Diese ermoglicht dem Arzt, ein auf die individuellen Bedurfnisse angepasstes Hautschutz- und Hautpflegeprogramm auszuarbeiten und den Teilnehmern, alle anfallenden Fragen zu stellen. Ergebnisse: Von bisher 355 Teilnehmern (Stand: Mai 2004) waren 87,3 % Frauen mit dem durchschnittlichen Alter von 36,9 Jahren. 95 % der Betroffenen hatten ein Handekzem, das morphologisch haufig als dyshidrotischer Typ dominierte. Atiologisch bestand in vielen Fallen ein Mischbild aus irritativem, atopischem und kontaktallergischem Handekzem, wobei insgesamt die irritativen Kontaktekzeme (43 %) dominierten. 68 % der Teilnehmer hatten eine atopische Hautdiathese. Das Seminar wird von den Teilnehmern durchgehend als gut eingestuft. Positiv sind sogenannte Seiteneffekte wie z. B. die Weitergabe des Erlernten an Arbeitskollegen, Familienmitglieder und Freunde. Schlusfolgerungen: Berufsdermatologische Untersuchungen und Beratungen werden bisher nur luckenhaft durchgefuhrt sowie Hautschutz- und Hautpflegemasnahmen noch nicht ausreichend umgesetzt und angewandt. Es ist anzustreben, Hautschutzseminare zukunftig auch fur andere hautgefahrdende Berufszweige anzubieten. Summary Background: Healthcare workers have an increased risk of occupational dermatoses. In January 2002, the Department of Social Medicine, Occupational and Environmental Dermatology of the University of Heidelberg started organizing special prevention courses for this group of employees in cooperation with the Accident Prevention & Insurance Association for Health Care Workers (BGW). The major aims are to improve individual skin protection and skin care habits, as well as to optimize diagnostic procedures and therapy. Patients and Methods: The two-day course has up to 14 participants. Teaching units mainly focus on skin structure and function, general aspects of occupational skin diseases, general information concerning skin protection and practical exercises emphasizing the correct use of skin cleansing and skin protection products. Additionally, every participant undergoes a dermatological examination including a detailed history and skin inspection. Individual skin protection strategies are developed, and the participants are provided with the opportunity to ask the dermatologist questions in confidence. Results: Most of the 355 participants have been female (87,3 %) with a mean age of 36,9 years. 95 % had hand eczema, predominantly dyshidrotic morphology. In many cases, there was a mixture of atopic, irritant and allergic contact dermatitis but irritant contact dermatitis was most common (43 %). Atopy was present in 68 % of the patients. The participants rated the course as good to excellent. Other benefits are the exchange of experience between patients working in the same or similar occupations and transfer of the new knowledge to colleagues, family and friends. Conclusions: Examinations and advisory services in occupational dermatology are still fragmentary. Skin barrier creams and moisturizers are not sufficiently utilized in daily practice. In the future, similar courses should be offered for employees in other professions with an increased risk of occupational skin diseases.

Purpose To implement and optimize a real-time pulse sequence and user interface to perform intravascular interventions using active catheter tracking. Materials and Methods In magnetic resonance (MR)-guided interventions, small radio-frequency coils can be used to rapidly determine the device position (active tracking). In this work, active catheter tracking was combined with a dedicated real-time pulse sequence and user interface. The pulse sequence offered the imaging contrasts fast low angle shot (FLASH), true Fast imaging with steady state precession (TrueFISP), and projection MR digital subtraction angiography (MR-DSA), which could be selected by the radiologist from within the scanner room at any time during the intervention. Automatic slice positioning was added to the real-time pulse sequence so that the location of the tracking coils defined the image slice position and orientation. The technique was assessed in phantoms and animal experiments. Results At a reaction time of 24 msec and a frame rate of three images per second, the movement of an active intravascular catheter could be monitored in the aorta and the renal arteries of a pig. With interactive contrast and orientation changes, the renal vasculature could be assessed by a fully MR-guided catheterization in less than 10 minutes. Conclusion With carefully designed active catheters, a dedicated user interface, and an optimized pulse sequence intravascular interventions can successfully be performed by a single operator from within the MR scanner room. J. Magn. Reson. Imaging 2004;19:580–589. © 2004 Wiley-Liss, Inc.

Purpose To compare contrast characteristics and image quality of 1.0 M gadobutrol with 0.5 M Gd-DTPA for time-resolved three-dimensional pulmonary magnetic resonance angiography (MRA). Materials and Methods Thirty-one patients and five healthy volunteers were examined with a contrast-enhanced time-resolved pulmonary MRA protocol (fast low-angle shot [FLASH] three-dimensional, TR/TE = 2.2/1.0 msec, flip angle: 25°, scan time per three-dimensional data set = 5.6 seconds). Patients were randomized to receive either 0.1 mmol/kg body weight (bw) or 0.2 mmol/kg bw gadobutrol, or 0.2 mmol/kg bw Gd-DTPA. Volunteers were examined three times, twice with 0.2 mmol/kg bw gadobutrol using two different flip angles and once with 0.2 mmol/kg bw Gd-DTPA. All contrast injections were performed at a rate of 5 mL/second. Image analysis included signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements in lung arteries and veins, as well as a subjective analysis of image quality. Results In patients, significantly higher SNR and CNR were observed with Gd-DTPA compared to both doses of gadobutrol (SNR: 35–42 vs.17–25; CNR 33–39 vs. 16–23; P ≤ 0.05). No relevant differences were observed between 0.1 mmol/kg bw and 0.2 mmol/kg bw gadobutrol. In volunteers, gadobutrol and Gd-DTPA achieved similar SNR and CNR. A significantly higher SNR and CNR was observed for gadobutrol-enhanced MRA with an increased flip angle of 40°. Image quality was rated equal for both contrast agents. Conclusion No relevant advantages of 1.0 M gadobutrol over 0.5 M Gd-DTPA were observed for time-resolved pulmonary MRA in this study. Potential explanations are T2/T2*-effects caused by the high intravascular concentration when using high injection rates. J. Magn. Reson. Imaging 2004;19:202–208. © 2004 Wiley-Liss, Inc.

Flow measurements can be used to quantify blood flow during MR-guided intravascular interventional procedures. In this study, a fast flow measurement technique is proposed that quantifies flow velocities in the vicinity of a small RF coil attached to an intravascular catheter. Since the small RF coil receives signal from only a limited volume around the catheter, a spatially nonselective signal reception is employed. To enhance signal from flowing blood, and suppress unwanted signal contributions from static material, a slice-selective RF excitation is used. At a velocity sensitivity of 150 cm/s, a temporal resolution of 2 x TR = 10.2 ms can be achieved. The flow measurement is combined with an automatic slice positioning to facilitate measurements during interventional procedures. The influence of the catheter position in the blood vessel on the velocity measurement was analyzed in simulations. For blood vessels with laminar flow, the simulation showed a systematic deviation between catheter measurement and true flow between -15% and 80%. In four animal experiments, the catheter velocity measurement was compared with results from a conventional ECG-triggered 2D phase-contrast (PC) technique. The shapes of the velocity time curves in the abdominal aorta were nearly identical to the conventional measurements. A relative scaling factor of 0.69-1.19 was found between the catheter velocity measurement and the reference measurement, which could be partly explained by the simulation results.

In this work absolute values of regional renal blood volume (rRBV) and flow (rRBF) are assessed by means of contrast-enhanced (CE) MRI using an intravascular superparamagnetic contrast agent. In an animal study, eight foxhounds underwent dynamic susceptibility-weighted MRI upon injection of contrast agent. Using principles of indicator dilution theory and deconvolution analysis, parametric images of rRBV, rRBF, and mean transit time (MTT) were computed. For comparison, whole-organ blood flow was determined invasively by means of an implanted flow probe, and the weight of the kidneys was evaluated postmortem. A mean rBV value of 28 ml/100 g was found in the renal cortex, with a corresponding mean rBF value of 524 ml/100 g/min and an average MTT of about 3.4 s. Although there was a systematic difference between the absolute blood flow values determined by MRI and the ultrasonic probe, a significant correlation (rs = 0.72, P < 0.05) was established. The influence of the arterial input function (AIF), T1 relaxation effects, and repeated measurements on the precision of the perfusion quantitation is discussed. Magn Reson Med 49:276-287, 2003. © 2003 Wiley-Liss, Inc.

The interrelation between the morphologic degree of renal artery stenosis and changes in parenchymal perfusion is assessed using an intravascular contrast agent. In seven adult foxhounds, different degrees of renal artery stenosis were created with an inflatable clamp implanted around the renal artery. Dynamic susceptibility-weighted gradient-echo imaging was used to measure signal-time curves in the renal artery and the renal parenchyma during administration of 1.5 mg/kg BW of an intravascular ultrasmall particle iron oxide (USPIO) contrast agent. From the dynamic series, regional renal blood volume (rRBV), regional renal blood flow (rRBF), and mean transit time (MTT) were calculated. The morphologic degree of stenosis was measured in the steady state using a high-resolution 3D contrast-enhanced (CE) MR angiography (MRA) sequence (voxel size = 0.7 x 0.7 x 1 mm(3)). Five patients with renoparenchymal damage due to long-standing renal artery stenosis were evaluated. In the animal stenosis model, cortical perfusion remained unchanged for degrees of renal artery stenosis up to 80%. With degrees of stenoses > 80%, cortical perfusion dropped to 151 +/- 54 ml/100 g of tissue per minute as compared to a baseline of 513 +/- 76 ml/100 g/min. In the patients, a substantial difference in the cortical perfusion of more than 200 +/- 40 ml/100 g/min between the normal and the ischemic kidneys was found. The results show that quantitative renal perfusion measurements in combination with 3D-CE-MRA allow the functional significance of a renal artery stenosis to be determined in a single MR exam. Differentiation between renovascular and renoparenchymal disease thus becomes feasible.

Arteriovenous malformations (AVM) can be treated with stereotactic radiosurgery. An infrequent, but important complication of this treatment is radionecrosis, which can be detected by MRI. However, the imaging characteristics of necrosis are unspecific in conventional MRI. Here, we report a case of necrosis after radiotherapy of an AVM to illustrate the potential of 7 Tesla MRI including amide proton transfer (APT) for necrosis imaging.

The aim of this pilot study in humans was to investigate the effect of an intravascular contrast agent (CA) on relaxation rate in myocardium (R(1,myo)) in the steady state. The dependence of R(1,myo) on R(1,blood) was characterized and compared with a theoretical model which allowed determination of the intra- extracapillary water proton exchange frequency (f = 0.48 s(-1)) and the intracapillary blood volume (RBV = 12.9 %). A linear response range of DeltaR(1,myo) on DeltaR(1,blood) was estimated which in future studies will allow the determination of RBV with intravascular CA.

In this initial work, the in vivo degradation of 17 O-labeled glucose was studied during cellular glycolysis. To monitor cellular glucose metabolism, direct 17 O-magnetic resonance spectroscopy (MRS) was used in the mouse brain at 9.4 T. Non-localized spectra were acquired with a custom-built transmit/receive (Tx/Rx) two-turn surface coil and a free induction decay (FID) sequence with a short TR of 5.4 ms. The dynamics of labeled oxygen in the anomeric 1-OH and 6-CH2 OH groups was detected using a Hankel-Lanczos singular value decomposition (HLSVD) algorithm for water suppression. Time-resolved 17 O-MRS (temporal resolution, 42/10.5 s) was performed in 10 anesthetized (1.25% isoflurane) mice after injection of a 2.2 M solution containing 2.5 mg/g body weight of differently labeled 17 O-glucose dissolved in 0.9% physiological saline. From a pharmacokinetic model fit of the H217 O concentration-time course, a mean apparent cerebral metabolic rate of 17 O-labeled glucose in mouse brain of CMRGlc = 0.07 ± 0.02 μmol/g/min was extracted, which is of the same order of magnitude as a literature value of 0.26 ± 0.06 μmol/g/min reported by 18 F-fluorodeoxyglucose (18 F-FDG) positron emission tomography (PET). In addition, we studied the chemical exchange kinetics of aqueous solutions of 17 O-labeled glucose at the C1 and C6 positions with dynamic 17 O-MRS. In conclusion, the results of the exchange and in vivo experiments demonstrate that the C6-17 OH label in the 6-CH2 OH group is transformed only glycolytically by the enzyme enolase into the metabolic end-product H217 O, whereas C1-17 OH ends up in water via direct hydrolysis as well as glycolysis. Therefore, dynamic 17 O-MRS of highly labeled 17 O-glucose could provide a valuable non-radioactive alternative to FDG PET in order to investigate glucose metabolism.

Arterial spin labeling (ASL) permits quantification of tissue perfusion without the use of MR contrast agents. With standard ASL techniques such as flow-sensitive alternating inversion recovery (FAIR) the signal from arterial blood is measured at a fixed inversion delay after magnetic labeling. As no image information is sampled during this delay, FAIR measurements are inefficient and time-consuming. In this work the FAIR preparation was combined with a Look-Locker acquisition to sample not one but a series of images after each labeling pulse. This new method allows monitoring of the temporal dynamics of blood inflow. To quantify perfusion, a theoretical model for the signal dynamics during the Look-Locker readout was developed and applied. Also, the imaging parameters of the new ITS-FAIR technique were optimized using an expression for the variance of the calculated perfusion. For the given scanner hardware the parameters were: temporal resolution 100 ms, 23 images, flip-angle 25.4°. In a normal volunteer experiment with these parameters an average perfusion value of 48.2 ± 12.1 ml/100 g/min was measured in the brain. With the ability to obtain ITS-FAIR time series with high temporal resolution arterial transit times in the range of −138 − 1054 ms were measured, where nonphysical negative values were found in voxels containing large vessels. Magn Reson Med 46:974–984, 2001. © 2001 Wiley-Liss, Inc.

The foamy virus (FV) subgroup of Retroviridae reverse transcribe their RNA (pre-)genome late in the replication cycle before leaving an infected cell. We studied whether a marker gene-transducing FV vector is able to shuttle to the nucleus and integrate into host cell genomic DNA. While a potential intracellular retrotransposition of vectors derived from other retroviruses was below the detection limit of our assay, we found that up to 5% of cells transfected with the FV vector were stably transduced, harboring 1 to approximately 10 vector integrants. Generation of the integrants depended on expression of functional capsid, reverse transcriptase and integrase proteins, and did not involve an extracellular step. PCR analysis of the U3 region of the 5' long terminal repeat and determination of proviral integration sites showed that a reverse transcription step had taken place to generate the integrants. Co-expression of a mutated envelope allowing particle egress and avoiding extracellular infection resulted in a significantly increased rescue of cells harboring integrants, suggesting that accumulation of proviruses via intracellular retrotransposition represents an integral part of the FV replication strategy.

Multiphase contrast-enhanced 3D MR angiography (MRA) data sets allow the separate visualization of the arterial and venous pulmonary vasculature. However, due to short arterial-to-venous bolus transit times in the lung, the generation of pure venograms without arterial overlay is difficult. To suppress arterial signal in venograms, early arterial phase data are typically subtracted from peak venous phase images. In this study, a correlation algorithm is used to postprocess the multiphase 3D MRA data sets. The cross-correlation between a measured arterial or venous reference function and the local signal-time course is computed which highlights image locations with a similar signal-time curve as the reference function and suppresses constant signal. Conventional maximum intensity projections (MIP) are generated from the arterial and venous correlation maps. In a study with five volunteers, an increase in SNR by a factor of 2.1 (1.8) of arterial (venous) correlation MIP images over subtraction MIP images was observed.

Recently the blood oxygenation level–dependent (BOLD)-related T2* of myocardium was derived as an analytical function of intracapillary blood volume, blood oxygenation, and nuclear spin diffusion. The basis of this approach was to approximate the diffusion-induced field fluctuations a nuclear spin is subjected to by strong collision dynamics, i.e., the field fluctuations are uncorrelated. The same analysis is now performed for spin echo experiments that gives myocardial T2 as a function of the parameters above and the echotime. An analytical relationship between T2 and T2* relaxation is derived. The dependence of T2 on diffusion, echo time, and blood oxygenation is congruent with simulation and experimental data. Magn Reson Med 42:1004–1010, 1999. © 1999 Wiley-Liss, Inc.

The purpose of this study was to demonstrate selective visualization of pulmonary arteries and veins with high spatial resolution for improved detection of vascular pathologies. Time-resolved pulmonary three-dimensional gadolinium-enhanced magnetic resonance angiograms (3D-Gd-MRA) were acquired with an ultrashort 3D fast low-angle shot (FLASH) sequence (TR/TE 2.3/0.9 msec) using asymmetric k-space sampling in readout, phase-encoding, and partition directions. In a single breath-hold four consecutive acquisitions were performed with a scan time of 6.28 seconds for each phase. A spatial resolution of 1.9 x 1.4 x 2 mm(3) could be achieved for a 12 cm thick 3D volume. To exploit the intrinsic enhancement kinetics of the pulmonary vascular system, the infusion of two gadolinium chelate boli was synchronized with the acquisition of the first and third data sets. This infusion strategy created two predominantly pulmonary arterial and venous data sets with the arterial and venous signal being maximally anti-correlated in time. A further separation of arterial and venous signal could be achieved by means of a correlation analysis. Eight patients with suspected thrombi in the pulmonary veins were studied. The calculated correlation angiographies provided high-quality pulmonary arterio- and venograms. Background signal was completely eliminated, allowing maximum intensity projection analysis of the full data set. In 7/8 patients no venous contamination of the arterial phase and vice versa was found. Patency of the pulmonary arteries and veins could be reliably assessed to the level of the segmental vessels. The combination of ultrafast multiphase 3D-Gd-MRA and dual-bolus injection with a correlation analysis of vascular signal provides high-resolution pulmonary arterio- and venograms. This imaging strategy initiates a new competitor to X-ray angiography.

To detect a renal artery stenosis and assess its hemodynamic and functional significance in five breath holds. In a single MR exam, T1 weighted FLASH and T2 weighted fast spin echo techniques are used to assess renal morphology, multiphase 3D gadolinium (Gd) MRA to evaluate the renal arteries, and a segmented EPI cine phase-contrast technique to measure renal artery blood flow. A standardized image analysis is performed to assess kidney size, corticomedullar differentiation (CMD), parenchymal enhancement, the degree of renal artery stenosis, abnormalities in blood flow pattern, and any associated abdominal vascular disease. Multiphase 3D-Gd-MRA accurately assesses atherosclerotic renal artery disease particularly in the presence of an associated aortic aneurysm. Delayed parenchymal enhancement, loss of CMD, and decrease in kidney size can be detected. In combination with decreased systolic velocity components, the diagnosis of a hemodynamically and functionally significant stenosis can be made. High-resolution single-phase 3D-Gd-MRA is preferable for evaluation of fibromuscular dysplasia or hypoplastic vessels. The combination of different breath hold techniques in a single, standardized MR exam allows to detect the hemodynamic and functional significance of a renal artery stenosis. J. Magn. Reson. Imaging 1999;10:347–356. © 1999 Wiley-Liss, Inc.