Peter M Jakob

Publications of Peter M Jakob

• Reducing RF-related heating of cardiac pacemaker leads in MRI: Implementation and experimental verification of practical design changes.

  Authors: Peter Nordbeck, Florian Fidler, Michael T Friedrich, Ingo Weiss, Marcus Warmuth, Daniel Gensler, Volker Herold, Wolfgang Geistert, Peter M Jakob, Georg Ertl, Oliver Ritter, Mark E Ladd, Wolfgang R Bauer, Harald H Quick

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 03/2012;

  There are serious concerns regarding safety when performing magnetic resonance imaging in patients with implanted conductive medical devices, such as cardiac pacemakers, and associated leads, asThere are serious concerns regarding safety when performing magnetic resonance imaging in patients with implanted conductive medical devices, such as cardiac pacemakers, and associated leads, as severe incidents have occurred in the past. In this study, several approaches for altering an implant's lead design were systematically developed and evaluated to enhance the safety of implanted medical devices in a magnetic resonance imaging environment. The individual impact of each design change on radiofrequency heating was then systematically investigated in functional lead prototypes at 1.5 T. Radiofrequency-induced heating could be successfully reduced by three basic changes in conventional pacemaker lead design: (1) increasing the lead tip area, (2) increasing the lead conductor resistance, and (3) increasing outer lead insulation conductivity. The findings show that radiofrequency energy pickup in magnetic resonance imaging can be reduced and, therefore, patient safety can be improved with dedicated construction changes according to a "safe by design" strategy. Incorporation of the described alterations into implantable medical devices such as pacemaker leads can be used to help achieve favorable risk-benefit-ratios when performing magnetic resonance imaging in the respective patient group. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

• IR TrueFISP with a golden-ratio-based radial readout: Fast quantification of T(1) , T(2) , and proton density.

  Authors: Philipp Ehses, Nicole Seiberlich, Dan Ma, Felix A Breuer, Peter M Jakob, Mark A Griswold, Vikas Gulani

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 02/2012;

  A promising approach for the simultaneous quantification of relative proton density (M(0) ), T(1) , and T(2) is the inversion-recovery TrueFISP sequence, consisting of an inversion pulse followed byA promising approach for the simultaneous quantification of relative proton density (M(0) ), T(1) , and T(2) is the inversion-recovery TrueFISP sequence, consisting of an inversion pulse followed by a series of balanced steady-state free precession acquisitions. Parameters can then be obtained from a mono-exponential fit to the series of images. However, a segmented acquisition is usually necessary, which increases the total acquisition time considerably. The goal of this study is to obtain M(0) , T(1) , and T(2) maps using a single-shot acquisition, with T(1) and T(2) measurements in brain that are consistent with the published literature, with a 20-fold speed improvement over the segmented approach, and at a clinically relevant spatial resolution. To this end, a single-shot inversion-recovery TrueFISP sequence was combined with a radial view-sharing technique. The parameters M(0) , T(1) , and T(2) were then obtained on a pixel-wise basis from a three fit parameter to the signal evolution. The accuracy of this method for quantifying these parameters is demonstrated in vivo. In addition, further corrections to the quantification necessary owing to other experimental factors, namely magnetization transfer and imperfect slice profiles, were developed. Including additional scans necessary for these corrections in the measurement protocol, the required scan time is increased from approximately 6 to 18-28 s per slice. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

• Signal evolution in the local magnetic field of a capillary - analogy to the damped driven harmonic oscillator.

  Authors: Christian H Ziener, Thomas Kampf, Gerd Melkus, Peter M Jakob, Heinz-Peter Schlemmer, Wolfgang R Bauer

  Magnetic resonance imaging. 02/2012;

  The temporal behavior of the magnetization decay caused by the local inhomogeneous magnetic field of a capillary is analyzed. Respecting the diffusion of the spins surrounding the capillary and theThe temporal behavior of the magnetization decay caused by the local inhomogeneous magnetic field of a capillary is analyzed. Respecting the diffusion of the spins surrounding the capillary and the strength of the susceptibility difference between the capillary and the surrounding medium, it is possible to distinguish different dephasing regimes. Each dephasing regime can be related to a certain characteristic form of the magnetization decay. If the influence of the diffusion dominates, the magnetization exhibits a monotonic decay. In the opposite case of dominating influence of the susceptibility effects, the magnetization shows an oscillating behavior. It can be shown that the dephasing process is closely related to the behavior of a damped driven harmonic oscillator.

• Direct cooling of the catheter tip increases safety for CMR-guided electrophysiological procedures.

  Authors: Theresa Reiter, Daniel Gensler, Oliver Ritter, Ingo Weiss, Wolfgang Geistert, Ralf Kaufmann, Sabine Hoffmeister, Michael T Friedrich, Stefan Wintzheimer, Markus Düring, Peter Nordbeck, Peter M Jakob, Mark E Ladd, Harald H Quick, Wolfgang R Bauer

  Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance. 01/2012; 14:12.

  ABSTRACT: One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter beingABSTRACT: One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter being exposed to the radiofrequency (RF) field of the RF transmitting body coil. Ablation procedures that use catheters with irrigated tips are well established therapeutic options for the treatment of cardiac arrhythmias and when used in a modified mode might offer an additional system for suppressing passive catheter heating. A two-step approach was chosen. Firstly, tests on passive catheter heating were performed in a 1.5 T Avanto system (Siemens Healthcare Sector, Erlangen, Germany) using a ASTM Phantom in order to determine a possible maximum temperature rise. Secondly, a phantom was designed for simulation of the interface between blood and the vascular wall. The MR-RF induced temperature rise was simulated by catheter tip heating via a standard ablation generator. Power levels from 1 to 6 W were selected. Ablation duration was 120 s with no tip irrigation during the first 60 s and irrigation at rates from 2 ml/min to 35 ml/min for the remaining 60 s (Biotronik Qiona Pump, Berlin, Germany). The temperature was measured with fluoroscopic sensors (Luxtron, Santa Barbara, CA, USA) at a distance of 0 mm, 2 mm, 4 mm, and 6 mm from the catheter tip. A maximum temperature rise of 22.4°C at the catheter tip was documented in the MR scanner. This temperature rise is equivalent to the heating effect of an ablator's power output of 6 W at a contact force of the weight of 90 g (0.883 N). The catheter tip irrigation was able to limit the temperature rise to less than 2°C for the majority of examined power levels, and for all examined power levels the residual temperature rise was less than 8°C. Up to a maximum of 22.4°C, the temperature rise at the tissue surface can be entirely suppressed by using the catheter's own irrigation system. The irrigated tip system can be used to increase MR safety of EP catheters by suppressing the effects of unwanted passive catheter heating due to RF exposure from the MR scanner.

• T-one insensitive steady state imaging: A framework for purely T(2) -weighted TrueFISP.

  Authors: Peter Schmitt, Peter M Jakob, Markus Kotas, Michael Flentje, Axel Haase, Mark A Griswold

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 11/2011;

  A new conceptual framework called T-one insensitive steady state imaging is proposed for fast generation of MR images with pure T(2) contrast. This is accomplished by imaging between nonequallyA new conceptual framework called T-one insensitive steady state imaging is proposed for fast generation of MR images with pure T(2) contrast. This is accomplished by imaging between nonequally spaced inversion pulses, with the magnetization vector alternatively residing in states parallel and antiparallel to B(0) for durations TP(i) and TA(i) , respectively. With TP(i) and TA(i) adequately chosen, identical signal time evolution can be obtained for different T(1) values, i.e., T(1) contrast can efficiently be removed from resultant images. As a specific realization of this principle, T-one insensitive steady state imaging sequences are presented which use True free induction steady precession readout blocks between the inversion pulses. While the conventional True free induction steady precession signal time course would be determined by both T(2) and T(1) , a pure T(2) dependence is realized with successfully suppressed influence of longitudinal relaxation, and images with essentially T(2) contrast alone are obtained. Analytical expressions are provided for the description of the ideal signal behavior, which help in creating pathways for sequence parameter optimization. The performance of the technique is analyzed with Bloch equation simulations. In vivo results obtained in healthy volunteers and brain tumor patients are presented. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

• Correcting slice selectivity in hard pulse sequences.

  Authors: David M Grodzki, Peter M Jakob, Bjoern Heismann

  Journal of magnetic resonance (San Diego, Calif. : 1997). 10/2011; 214(1):61-7.

  Many MRI sequences use non-selective hard pulse excitation in the presence of imaging gradients. In this work, we investigate to which extent the sinc-shaped frequency excitation profiles of theMany MRI sequences use non-selective hard pulse excitation in the presence of imaging gradients. In this work, we investigate to which extent the sinc-shaped frequency excitation profiles of the pulse can be used for imaging without the generation of artefacts. A correction algorithm is proposed that eliminates the influence of the excitation profile. Phantom as well as in vivo measurements prove that enhanced image quality can be obtained as long as the first minimum of the excitation profile lies outside the imaged object.

• Association between reward-related activation in the ventral striatum and trait reward sensitivity is moderated by dopamine transporter genotype.

  Authors: Tim Hahn, Sebastian Heinzel, Thomas Dresler, Michael M Plichta, Tobias J Renner, Falko Markulin, Peter M Jakob, Klaus-Peter Lesch, Andreas J Fallgatter

  Human brain mapping. 10/2011; 32(10):1557-65.

  The impact of individual differences on human reward processing has been a focus of research in recent years, particularly, as they are associated with a variety of neuropsychiatric diseasesThe impact of individual differences on human reward processing has been a focus of research in recent years, particularly, as they are associated with a variety of neuropsychiatric diseases including addiction and attention-deficit/hyperactivity disorder. Studies exploring the neural basis of individual differences in reward sensitivity have consistently implicated the ventral striatum (VS) as a core component of the human reward system. However, the mechanisms of dopaminergic neurotransmission underlying ventral striatal activation as well as trait reward sensitivity remain speculative. We addressed this issue by investigating the triadic interplay between VS reactivity during reward anticipation using functional magnetic resonance imaging, trait reward sensitivity, and dopamine (DA) transporter genotype (40-bp 3'VNTR of DAT, SLC6A3) affecting synaptic DA neurotransmission. Our results show that DAT variation moderates the association between VS-reactivity and trait reward sensitivity. Specifically, homozygote carriers of the DAT 10-repeat allele exhibit a strong positive correlation between reward sensitivity and reward-related VS activity whereas this relationship is absent in the DAT 9-repeat allele carriers. We discuss the possibility that this moderation of VS-trait relation might arise from DAT-dependent differences in DA availability affecting synaptic plasticity within the VS. Generally, studying the impact of dopaminergic gene variations on the relation between reward-related brain activity and trait reward sensitivity might facilitate the investigation of complex mechanisms underlying disorders linked to dysregulation of DA neurotransmission.

• Contrast agent derived determination of the total circulating blood volume using magnetic resonance.

  Authors: Kerstin Pannek, Florian Fidler, Ralf Kartäusch, Peter M Jakob, Karl-Heinz Hiller

  Magma (New York, N.Y.). 09/2011;

  OBJECT: Knowledge of the total circulating blood volume (TCBV) is essential for the treatment of a variety of medical conditions and blood disorders. To date, blood volume analysis is rarely carriedOBJECT: Knowledge of the total circulating blood volume (TCBV) is essential for the treatment of a variety of medical conditions and blood disorders. To date, blood volume analysis is rarely carried out due to the disadvantages of available methods. Our aim was to develop a widely available, simple, fast, yet accurate method for the determination of the total circulating blood volume. MATERIALS AND METHODS: Magnetic resonance (MR) is a well-established, non-invasive technique. In this article, we present a method that uses MR contrast agents for the determination of the blood volume. The dependence of MR relaxation times on the concentration of MR contrast agents allows the calculation of the volume the contrast agent has been diluted in. RESULTS: In phantom and in vivo experiments we could demonstrate that TCBV can be determined with high accuracy and precision. CONCLUSION: This work introduces a novel method for the determination of the total circulating blood volume using magnetic resonance contrast agents as tracers.

• Randomness of resting-state brain oscillations encodes Gray's personality trait.

  Authors: Tim Hahn, Thomas Dresler, Ann-Christine Ehlis, Martin Pyka, Alica C Dieler, Claudia Saathoff, Peter M Jakob, Klaus-Peter Lesch, Andreas J Fallgatter

  NeuroImage. 08/2011; 59(2):1842-5.

  Randomness of functional Magnetic Resonance Imaging (fMRI) resting-state time-series has recently been used as a biomarker for numerous disorders including Alzheimer's and Parkinson's disease as wellRandomness of functional Magnetic Resonance Imaging (fMRI) resting-state time-series has recently been used as a biomarker for numerous disorders including Alzheimer's and Parkinson's disease as well as autism. To date, however, it remains unknown whether and to what degree personality traits are associated with the randomness of resting-state temporal dynamics. To investigate this question, we estimated the Hurst exponent - a measure of the randomness of a time-series - during resting-state fMRI in brain areas previously associated with trait Impulsivity as defined in Gray's Reinforcement Sensitivity Theory of Personality in 15 healthy individuals. The Hurst exponent in the ventral striatum as well as in the orbitofrontal cortex (OFC) was significantly associated with the measure of Gray's trait Impulsivity. Specifically, more random resting-state neural dynamics corresponded to higher Impulsivity scores both in the ventral striatum (r(15)=-.71; p=.003) and the OFC (r(15)=-.81; p<.001). In summary, we provide evidence for an association between individual differences in Gray's Impulsivity and randomness in key areas of the reward system which have previously been associated with this personality trait. Based on evidence from fMRI and electroencephalographical studies, we suggest that this association might arise from resting-state fluctuations constraining task-related neural responsiveness. Thereby, we outline a potential mechanism linking randomness of resting-state dynamics and personality.

• Combined noninvasive imaging and modeling approaches reveal metabolic compartmentation in the barley endosperm.

  Authors: Hardy Rolletschek, Gerd Melkus, Eva Grafahrend-Belau, Johannes Fuchs, Nicolas Heinzel, Falk Schreiber, Peter M Jakob, Ljudmilla Borisjuk

  The Plant cell. 08/2011; 23(8):3041-54.

  The starchy endosperm of cereals is a priori taken as a metabolically uniform tissue. By applying a noninvasive assay based on (13)C/(1)H-magnetic resonance imaging (MRI) to barley (Hordeum vulgare)The starchy endosperm of cereals is a priori taken as a metabolically uniform tissue. By applying a noninvasive assay based on (13)C/(1)H-magnetic resonance imaging (MRI) to barley (Hordeum vulgare) grains, we uncovered metabolic compartmentation in the endosperm. (13)C-Suc feeding during grain filling showed that the primary site of Ala synthesis was the central region of the endosperm, the part of the caryopsis experiencing the highest level of hypoxia. Region-specific metabolism in the endosperm was characterized by flux balance analysis (FBA) and metabolite profiling. FBA predicts that in the central region of the endosperm, the tricarboxylic acid cycle shifts to a noncyclic mode, accompanied by elevated glycolytic flux and the accumulation of Ala. The metabolic compartmentation within the endosperm is advantageous for the grain's carbon and energy economy, with a prominent role being played by Ala aminotransferase. An investigation of caryopses with a genetically perturbed tissue pattern demonstrated that Ala accumulation is a consequence of oxygen status, rather than being either tissue specific or dependent on the supply of Suc. Hence the (13)C-Ala gradient can be used as an in vivo marker for hypoxia. The combination of MRI and metabolic modeling offers opportunities for the noninvasive analysis of metabolic compartmentation in plants.

• Temporal filtering effects in dynamic parallel MRI.

  Authors: Martin Blaimer, Irene P Ponce, Felix A Breuer, Peter M Jakob, Mark A Griswold, Peter Kellman

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 07/2011; 66(1):192-8.

  Autocalibrated parallel MRI methods such as TSENSE or k-t SENSE have been presented for dynamic imaging studies as they are able to provide images with high temporal resolution. One key element ofAutocalibrated parallel MRI methods such as TSENSE or k-t SENSE have been presented for dynamic imaging studies as they are able to provide images with high temporal resolution. One key element of these techniques is the temporal averaging of the undersampled raw data to obtain an unaliased image. This image represents the temporal average (also known as direct current, DC) and is used to derive the reconstruction parameters. In this work, we show that aliasing artifacts can be introduced in the DC signal obtained from the undersampled raw data. These artifacts lead to undesired temporal filtering effects when the DC signal is used for coil sensitivity calibration or when the DC signal is subtracted from the raw data. It is demonstrated that the temporal filtering effects can be reduced significantly by filtering the DC signal.

• Ultrashort echo time imaging using pointwise encoding time reduction with radial acquisition (PETRA).

  Authors: David M Grodzki, Peter M Jakob, Bjoern Heismann

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 06/2011; 67(2):510-8.

  Sequences with ultrashort echo times enable new applications of MRI, including bone, tendon, ligament, and dental imaging. In this article, a sequence is presented that achieves the shortest possibleSequences with ultrashort echo times enable new applications of MRI, including bone, tendon, ligament, and dental imaging. In this article, a sequence is presented that achieves the shortest possible encoding time for each k-space point, limited by pulse length, hardware switching times, and gradient performance of the scanner. In pointwise encoding time reduction with radial acquisition (PETRA), outer k-space is filled with radial half-projections, whereas the centre is measured single pointwise on a Cartesian trajectory. This hybrid sequence combines the features of single point imaging with radial projection imaging. No hardware changes are required. Using this method, 3D images with an isotropic resolution of 1 mm can be obtained in less than 3 minutes. The differences between PETRA and the ultrashort echo time (UTE) sequence are evaluated by simulation and phantom measurements. Advantages of pointwise encoding time reduction with radial acquisition are shown for tissue with a T(2) below 1 ms. The signal to noise ratio and Contrast-to-noise ratio (CNR) performance, as well as possible limitations of the approach, are investigated. In-vivo head, knee, ankle, and wrist examples are presented to prove the feasibility of the sequence. In summary, fast imaging with ultrashort echo time is enabled by PETRA and may help to establish new routine clinical applications of ultrashort echo time sequences.

• Magnetic resonance imaging (MRI) of inflamed myocardium using iron oxide nanoparticles in patients with acute myocardial infarction - Preliminary results.

  Authors: Ali Yilmaz, Sabine Rösch, Karin Klingel, Reinhard Kandolf, Xavier Helluy, Karl-Heinz Hiller, Peter M Jakob, Udo Sechtem

  International journal of cardiology. 06/2011;

  OBJECTIVES: Superparamagnetic iron oxide nanoparticle (SPIO)-based molecular imaging agents targeting macrophages have been developed and successfully applied in animal models of myocardialOBJECTIVES: Superparamagnetic iron oxide nanoparticle (SPIO)-based molecular imaging agents targeting macrophages have been developed and successfully applied in animal models of myocardial infarction. The purpose of this clinical trial was to investigate whether magnetic resonance imaging (MRI) of macrophages using ferucarbotran (Resovist®) allows improved visualisation of the myocardial (peri-)infarct zone compared to conventional gadolinium-based necrosis/fibrosis imaging in patients with acute myocardial infarction. MATERIAL AND METHODS: The clinical study NIMINI-1 was performed as a prospective, non-randomised, non-blinded, single agent phase III clinical trial (NCT0088644). Twenty patients who had experienced either an acute ST-elevation or non-ST-elevation myocardial infarction (STEMI/NSTEMI) were included to this study. Following coronary angiography, a first baseline cardiovascular magnetic resonance (CMR) study (pre-SPIO) was performed within seven days after onset of cardiac symptoms. A second CMR study (post-SPIO) was performed either 10min, 4h, 24h or 48h after ferucarbotran administration. The CMR studies comprised cine-CMR, T2-weighted "edema" imaging, T2*-weighted cardiac imaging and T1-weighted late-gadolinium-enhancement (LGE) imaging. RESULTS: The median extent of short-axis in-plane LGE was 28% (IQR 19-31%). Following Resovist® administration the median extent of short-axis in-plane T2*-weighted hypoenhancement (suggestive of intramyocardial haemorrhage and/or SPIO accumulation) was 0% (IQR 0-9%; p=0.68 compared to pre-SPIO). A significant in-slice increase (>3%) in the extent of T2*-weighted "hypoenhancement" (post-SPIO compared to pre-SPIO) was seen in 6/16 patients (38%). However, no patient demonstrated "hypoenhancement" in T2*-weighted images following Resovist® administration that exceeded the area of LGE. CONCLUSIONS: T2/T2*-weighted MRI aiming at non-invasive myocardial macrophage imaging using the approved dose of ferucarbotran does not allow improved visualisation of the myocardial (peri-) infarct zone compared to conventional gadolinium-based necrosis/fibrosis imaging.

• Ultra-high field diffusion tensor imaging of articular cartilage correlated with histology and scanning electron microscopy.

  Authors: José G Raya, Andreas P Arnoldi, Daniel L Weber, Lucianna Filidoro, Olaf Dietrich, Silvia Adam-Neumair, Elisabeth Mützel, Gerd Melkus, Reinhard Putz, Maximilian F Reiser, Peter M Jakob, Christian Glaser

  Magma (New York, N.Y.). 06/2011; 24(4):247-58.

  To investigate the relationship of the different diffusion tensor imaging (DTI) parameters (ADC, FA, and first eigenvector (EV)) to the constituents (proteoglycans and collagen), the zonalTo investigate the relationship of the different diffusion tensor imaging (DTI) parameters (ADC, FA, and first eigenvector (EV)) to the constituents (proteoglycans and collagen), the zonal arrangement of the collagen network, and mechanical loading of articular cartilage. DTI of eight cartilage-on-bone samples of healthy human patellar cartilage was performed at 17.6 T. Three samples were additionally imaged under indentation loading. After DTI, samples underwent biomechanical testing, safranin-O staining for semiquantitative proteoglycan estimation, and scanning electron microscopy (SEM) for depicting collagen architecture. From the articular surface to the bone-cartilage interface, ADC continuously decreased and FA increased. Cartilage zonal heights calculated from EVs strongly correlated with SEM-derived zonal heights (P < 0.01, r (2)=0.87). Compression reduced ADC in the superficial 30% of cartilage and increased FA in the superficial 5% of cartilage. Reorientation of the EVs indicative of collagen fiber reorientation under the indenter was observed. No significant correlation was found between ADC, FA, and compressive stiffness. Correlating ADC and FA with proteoglycan and collagen content suggests that diffusion is dominated by different depth-dependent mechanisms within cartilage. Knowledge of the spatial distribution of the DTI parameters and their variation contributes to form a database for future analysis of defective cartilage.

• Specific identification of iron oxide-labeled stem cells using magnetic field hyperthermia and MR thermometry.

  Authors: Daniel Haddad, Markus F Hildenbrand, Karl-Heinz Hiller, Meike Haddad-Weber, Peter M Jakob

  NMR in biomedicine. 05/2011; 25(3):402-9.

  Cell-based therapies represent important novel strategies for the improved treatment of various diseases. To monitor the progress of therapy and cell migration, noninvasive imaging methods areCell-based therapies represent important novel strategies for the improved treatment of various diseases. To monitor the progress of therapy and cell migration, noninvasive imaging methods are needed. MRI represents such a modality, allowing, for example, for the tracking of cells labeled with superparamagnetic iron oxide nanoparticles. Unfortunately, the labeled cells cannot always be identified nonambiguously in the MR images. In this article, we present the combination of two different types of MR experiment to identify iron oxide-labeled cells nonambiguously. The labeled cells appear as hypointense spots on standard T(2) *-weighted MR images. Furthermore, they can be heated magnetically and subsequently identified by MR thermometry as a result of their heat dissipation. Other hypointense regions in the MR images are not heated and do not show heat dissipation. A proof-of-principle study was successfully performed in vitro and in vivo. The positive identification of the iron oxide-labeled cells was demonstrated in collagen type I hydrogel phantoms and in living mice with high spatial and temporal accuracy. The motion of the in vitro samples was corrected in order to improve the specificity of the identification of labeled cells. Therefore, this method possesses the potential for cell tracking without prior knowledge about the cells, and thus allows the noninvasive monitoring of cell-based therapies, as long as the cells contain a sufficient amount of iron oxide for detection in MR thermometry and imaging. Copyright © 2011 John Wiley & Sons, Ltd.

• Dynamic ¹³C/¹ H NMR imaging uncovers sugar allocation in the living seed.

  Authors: Gerd Melkus, Hardy Rolletschek, Johannes Fuchs, Volodymyr Radchuk, Eva Grafahrend-Belau, Nese Sreenivasulu, Twan Rutten, Diana Weier, Nicolas Heinzel, Falk Schreiber, Thomas Altmann, Peter M Jakob, Ljudmilla Borisjuk

  Plant biotechnology journal. 04/2011; 9(9):1022-37.

  Seed growth and accumulation of storage products relies on the delivery of sucrose from the maternal to the filial tissues. The transport route is hidden inside the seed and has never been visualizedSeed growth and accumulation of storage products relies on the delivery of sucrose from the maternal to the filial tissues. The transport route is hidden inside the seed and has never been visualized in vivo. Our approach, based on high-field nuclear magnetic resonance and a custom made (13)C/(1) H double resonant coil, allows the non-invasive imaging and monitoring of sucrose allocation within the seed. The new technique visualizes the main stream of sucrose and determines its velocity during the grain filling in barley (Hordeum vulgare L.). Quantifiable dynamic images are provided, which allow observing movement of (13)C-sucrose at a sub-millimetre level of resolution. The analysis of genetically modified barley grains (Jekyll transgenic lines, seg8 and Risø13 mutants) demonstrated that sucrose release via the nucellar projection towards the endosperm provides an essential mean for the control of seed growth by maternal organism. The sucrose allocation was further determined by structural and metabolic features of endosperm. Sucrose monitoring was integrated with an in silico flux balance analysis, representing a powerful platform for non-invasive study of seed filling in crops.

• Fast MR parameter mapping using k-t principal component analysis.

  Authors: Frederike H Petzschner, Irene P Ponce, Martin Blaimer, Peter M Jakob, Felix A Breuer

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 03/2011; 66(3):706-16.

  Quantification of magnetic resonance parameters plays an increasingly important role in clinical applications, such as the detection and classification of neurodegenerative diseases. The majorQuantification of magnetic resonance parameters plays an increasingly important role in clinical applications, such as the detection and classification of neurodegenerative diseases. The major obstacle that remains for its widespread use in clinical routine is the long scanning times. Therefore, strategies that allow for significant decreases in scan time are highly desired. Recently, the k-t principal component analysis method was introduced for dynamic cardiac imaging to accelerate data acquisition. This is done by undersampling k-t space and constraining the reconstruction of the aliased data based on the k-t Broad-use Linear Acquisition Speed-up Technique (BLAST) concept and predetermined temporal basis functions. The objective of this study was to investigate whether the k-t principal component analysis concept can be adapted to parameter quantification, specifically allowing for significant acceleration of an inversion recovery fast imaging with steady state precession (TrueFISP) acquisition. We found that three basis functions and a single training data line in central k-space were sufficient to achieve up to an 8-fold acceleration of the quantification measurement. This allows for an estimation of relaxation times T(1) and T(2) and spin density in one slice with sub-millimeter in-plane resolution, in only 6 s. Our findings demonstrate that the k-t principal component analysis method is a potential candidate to bring the acquisition time for magnetic resonance parameter mapping to a clinically acceptable level.

• Feasibility of contrast-enhanced and nonenhanced MRI for intraprocedural and postprocedural lesion visualization in interventional electrophysiology: animal studies and early delineation of isthmus ablation lesions in patients with typical atrial flutter.

  Authors: Peter Nordbeck, Karl-Heinz Hiller, Florian Fidler, Marcus Warmuth, Natalie Burkard, Matthias Nahrendorf, Peter M Jakob, Harald H Quick, Georg Ertl, Wolfgang R Bauer, Oliver Ritter

  Circulation. Cardiovascular imaging. 03/2011; 4(3):282-94.

  Imaging of myocardial ablation lesions during electrophysiology procedures would enable superior guidance of interventions and immediate identification of potential complications. The aim of thisImaging of myocardial ablation lesions during electrophysiology procedures would enable superior guidance of interventions and immediate identification of potential complications. The aim of this study was to establish clinically suitable MRI-based imaging techniques for intraprocedural lesion visualization in interventional electrophysiology. Interventional electrophysiology was performed under magnetic resonance guidance in an animal model, using a custom setup including magnetic resonance-conditional catheters. Various pulse sequences were explored for intraprocedural lesion visualization after radiofrequency ablation. The developed visualization techniques were then used to investigate lesion formation in patients immediately after ablation of atrial flutter. The animal studies in 9 minipigs showed that gadolinium-DTPA-enhanced T1-weighted and nonenhanced T2-weighted pulse sequences are particularly suitable for lesion visualization immediately after radiofrequency ablation. MRI-derived lesion size correlated well with autopsy (R(2)=0.799/0.709 for contrast-enhanced/nonenhanced imaging). Non-contrast agent-enhanced techniques were suitable for repetitive lesion visualization during electrophysiological interventions, thus allowing for intraprocedural monitoring of ablation success. The patient studies in 24 patients with typical atrial flutter several minutes to hours after cavotricuspid isthmus ablation confirmed the results from the animal experiments. Therapeutic lesions could be visualized in all patients using contrast-enhanced and also nonenhanced MRI with high contrast-to-noise ratio (94.6±35.2/111.1±32.6 versus 48.0±29.0/68.0±37.3 for ventricular/atrial lesions and contrast-enhanced versus nonenhanced imaging). MRI allows for precise lesion visualization in electrophysiological interventions just minutes after radiofrequency ablation. Nonenhanced T2-weighted MRI is particularly feasible for intraprocedural delineation of lesion formation as lesions are detectable within minutes after radiofrequency delivery and imaging can be repeated during interventions.

• Change of diffusion tensor imaging parameters in articular cartilage with progressive proteoglycan extraction.

  Authors: José G Raya, Gerd Melkus, Silvia Adam-Neumair, Olaf Dietrich, Elisabeth Mützel, Bart Kahr, Maximilian F Reiser, Peter M Jakob, Reinhard Putz, Christian Glaser

  Investigative radiology. 03/2011; 46(6):401-9.

  To investigate changes of diffusion tensor imaging (DTI) parameters (mean apparent diffusion coefficient [ADC], fractional anisotropy [FA], and first eigenvector) with increasing proteoglycan (PG)To investigate changes of diffusion tensor imaging (DTI) parameters (mean apparent diffusion coefficient [ADC], fractional anisotropy [FA], and first eigenvector) with increasing proteoglycan (PG) extraction of articular cartilage. Twelve cylindrical cartilage-on-bone samples were drilled from 4 human patellae (3 per patella). Each sample was divided into 2 pieces. One piece underwent histologic examination to assess the PG content of the native sample by safranin-O staining and its collagen architecture by polarized light microscopy. The other underwent magnetic resonance imaging (MRI) at 17.6 T for DTI measurement. After MRI, 2 of the 3 samples from each patella were immersed in a dilute trypsin solution (0.1 mg/mL), whereas the third sample was kept as a negative control in physiological saline. After incubation (6, 48, 72, and 96 hours), the samples were reimaged, stained for PG content and for the collagen orientation. Maps of ADC, FA, and the orientation of the first eigenvector as well as histology were available for each sample before and after incubation. PG loss led to increased ADC and reduced safranin-O staining from the articular surface to the bone-cartilage interface. A significant correlation (r(2) = 0.86, P < 0.01) was observed between the change in bulk ADC and PG loss. Regional analysis from the articular surface to the tide mark demonstrated depth dependent significant correlations of ADC and PG loss. FA and first eigenvector as well as polarized light microscopy showed only small changes in the order of magnitude of measurement errors, not correlating with PG loss. Mean diffusivity evidence by the ADC is linearly correlated to progressive PG extraction in articular cartilage. FA and the first eigenvector seem to be specific to the collagen architecture of cartilage. DTI has the potential to become a valuable biomarker for the workup of cartilage degeneration in osteoarthritis, since evaluation of the PG content and collagen architectural properties of cartilage can be performed with a single, non–contrast-enhanced proton-based MRI measurement.

• Impact of imaging landmark on the risk of MRI-related heating near implanted medical devices like cardiac pacemaker leads.

  Authors: Peter Nordbeck, Oliver Ritter, Ingo Weiss, Marcus Warmuth, Daniel Gensler, Natalie Burkard, Volker Herold, Peter M Jakob, Georg Ertl, Mark E Ladd, Harald H Quick, Wolfgang R Bauer

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 01/2011; 65(1):44-50.

  Implanted medical devices such as cardiac pacemakers pose a potential hazard in magnetic resonance imaging. Electromagnetic fields have been shown to cause severe radio frequency-induced tissueImplanted medical devices such as cardiac pacemakers pose a potential hazard in magnetic resonance imaging. Electromagnetic fields have been shown to cause severe radio frequency-induced tissue heating in some cases. Imaging exclusion zones have been proposed as an instrument to reduce patient risk. The purpose of this study was to further assess the impact of the imaging landmark on the risk for unintended implant heating by measuring the radio frequency-induced electric fields in a body phantom under several imaging conditions at 1.5T. The results show that global radio frequency-induced coupling is highest with the torso centered along the superior-inferior direction of the transmit coil. The induced E-fields inside the body shift when changing body positioning, reducing both global and local radio frequency coupling if body and/or conductive implant are moved out from the transmit coil center along the z-direction. Adequate selection of magnetic resonance imaging landmark can significantly reduce potential hazards in patients with implanted medical devices.