Medical_Physics RSS : Gourt

Structural–acoustic modal analysis of cylindrical shells: application to MRI scanner systems

Abstract Object The acoustic noise in a magnetic resonance imaging (MRI) scanner bore is mainly introduced by the vibration of gradient coils. The interaction between acoustic modes in the scanner bore and structure modes in the coil structure leads to structural–acoustic coupling. In order to implement quiet MRI design, the structural–acoustic coupling mechanism in MRI machines needs to be fully investigated. Materials and method Structural analysis was first implemented using Love’s classical shell theory. The concept of a “virtually closed cavity” was used in the acoustic modal analysis of the gradient coil duct. The dispersion curves and the number of modes per frequency band were used to reveal modal distribution properties for both structural modes and acoustic modes. Structural–acoustic coupling modes were identified by superposition of the dispersion diagrams of the structural waves and acoustic waves. Experimental validation was implemented separately for the structural analysis and acoustic analysis. Results Independent structural modes and acoustic modes and their distribution patterns were calculated up to 3000Hz with various boundary conditions. Coupling modes were clearly revealed using the analysis procedures presented in this paper and were found to be in agreement with the ones identified from experimental measurements. Conclusion These methods are effective for coupled and uncoupled modal analysis of MRI scanner systems and can be used for quiet MRI design or sound absorber design for existing MRI systems. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0185-zAuthors Gemin Li, Queen’s University Department of Mechanical Engineering McLaughlin Hall Kingston ON K7L 3N6 CanadaChris K. Mechefske, Queen’s University Department of Mechanical Engineering McLaughlin Hall Kingston ON K7L 3N6 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Quantitative metabolic profiles of 2nd and 3rd trimester human amniotic fluid using 1H HR-MAS spectroscopy

Abstract Object To establish and compare normative metabolite concentrations in 2nd and 3rd trimester human amniotic fluid samples in an effort to reveal metabolic biomarkers of fetal health and development. Materials and methods Twenty-one metabolite concentrations were compared between 2nd (15–27 weeks gestation, N = 23) and 3rd (29–39 weeks gestation, N = 27) trimester amniotic fluid samples using 1H high resolution magic angle spinning (HR-MAS) spectroscopy. Data were acquired using the electronic reference to access in vivo concentrations method and quantified using a modified semi-parametric quantum estimation algorithm modified for high-resolution ex vivo data. Results Sixteen of 21 metabolite concentrations differed significantly between 2nd and 3rd trimester groups. Betaine (0.00846±0.00206 mmol/kg vs. 0.0133±0.0058 mmol/kg, P < 0.002) and creatinine (0.0124±0.0058 mmol/kg vs. 0.247±0.011 mmol/kg, P < 0.001) concentrations increased significantly, while glucose (5.96±1.66 mmol/kg vs. 2.41±1.69 mmol/kg, P < 0.001), citrate (0.740±0.217 mmol/kg vs. 0.399±0.137 mmol/kg, P < 0.001), pyruvate (0.0659±0.0103 mmol/kg vs. 0.0299±0.286 mmol/kg, P < 0.001), and numerous amino acid (e.g. alanine, glutamate, isoleucine, leucine, lysine, and valine) concentrations decreased significantly with advancing gestation. A stepwise multiple linear regression model applied to 50 samples showed that gestational age can be accurately predicted using combinations of alanine, glucose and creatinine concentrations. Conclusion These results provide key normative data for 2nd and 3rd trimester amniotic fluid metabolite concentrations and provide the foundation for future development of magnetic resonance spectroscopy (MRS) biomarkers to evaluate fetal health and development. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0184-0Authors Brad R. Cohn, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USABonnie N. Joe, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAShoujun Zhao, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJohn Kornak, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAVickie Y. Zhang, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USARahwa Iman, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJohn Kurhanewicz, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAKiarash Vahidi, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USAJingwei Yu, University of California Department of Laboratory Medicine San Francisco CA USAAaron B. Caughey, University of California Department of Obstetrics & Gynecology San Francisco CA USAMark G. Swanson, University of California Department of Radiology & Biomedical Imaging 1600 Divisadero Street, Room C-250 Box 1667 San Francisco CA 94115 USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Thursday

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Thursday Content Type Journal ArticleDOI 10.1007/s10334-009-0175-1 Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Saturday

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Saturday Content Type Journal ArticleDOI 10.1007/s10334-009-0177-z Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Friday

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Abstracts, Friday Content Type Journal ArticleDOI 10.1007/s10334-009-0176-0 Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: EPOStm Posters / Paper Posters / Info-RESO

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: EPOStm Posters / Paper Posters / Info-RESO Content Type Journal ArticleDOI 10.1007/s10334-009-0178-y Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Author Index

ESMRMB 2009 Congress, Antalya, Turkey, 1–3 October: Author Index Content Type Journal ArticleDOI 10.1007/s10334-009-0179-x Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Supplement 1 / October, 2009

A digital receiver with fast frequency- and gain-switching capabilities for MRI systems

Abstract Object In this article, two issues pertaining to MRI digital receivers are addressed. One is the maintenance of phase coherence between the transmitter and the receiver—an effective solution is proposed, in which the receiver frequency is switched synchronously with the transmitter frequency. The other is the dynamic range of the receiver—gain-switching technique is utilized to improve the dynamic range. To meet the hardware requirements of these solutions, a digital receiver with fast frequency- and gain-switching capabilities was implemented. Materials and methods The primary components of the proposed digital receiver are a variable gain amplifier, a high-speed analog-to-digital converter and a single-chip digital receiver core. The radio-frequency magnetic resonance signal is directly sampled by the analog-to-digital converter and processed in the digital receiver core. By pre-storing the receiver waveform in the on-board SDRAM, the frequency and gain of the receiver may be switched very quickly. Results The performance of the proposed digital receiver is verified by embedding it in an imaging spectrometer. It is then demonstrated by conducting experiments on a home-built 0.3-T magnetic resonance imaging system. Conclusion The results show that the phase coherence between the transmitter and the receiver and the dynamic range of the receiver are greatly improved. Consequently, the proposed digital receiver may be useful for obtaining multiple-slice two-dimensional magnetic resonance images with very high resolution. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0182-2Authors Ning Ruipeng, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of ChinaDai Yidong, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of ChinaYang Guang, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of ChinaLi Gengying, East China Normal University Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics 3663 North Zhong-Shan Road 200062 Shanghai People’s Republic of China Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

Influence of cardiac motion on diffusion-weighted magnetic resonance imaging of the liver

Abstract Purpose To assess cardiac motion-induced signal loss in diffusion-weighted magnetic resonance imaging (DWI) of the liver using dynamic DWI. Materials and methods Three volunteers underwent dynamic coronal DWI of the liver under breathholding, in the diastolic (DWIdiast) or systolic (DWIsyst) cardiac phase, and with motion probing gradients (MPGs) in phase encoding (P, left–right), frequency encoding (M, superior–inferior), or slice select (S, anterior–posterior) direction. Liver-to-background contrasts (LBCs) of DWIsyst were compared to those of DWIdiast, for both the left and right liver lobes, using nonparametric tests. Signal decrease ratios (SDRs) were calculated as (1−(LBCDWIsyst/LBCDWIdiast)) × 100%. DWIsyst was further analyzed to determine which direction of MPGs was most affected by cardiac motion. Results In the left liver lobe, LBCs of DWIsyst (median 3.35) were significantly lower (P < 0.0001) than those of DWIdiast (median 4.84). In the right liver lobe, LBCs of DWIsyst (median 4.17) were also significantly lower (P < 0.0001) than those of DWIdiast (median 5.35 ). SDRs of the left and right liver lobes were 25.5% and 17.3%, respectively. In DWIsyst, the significantly lowest (P < 0.05) LBCs were observed in the M direction (left liver lobe) and P direction (right liver lobe) of MPGs. Conclusion Signal intensity of both liver lobes are affected by cardiac motion in DWI. In the left liver lobe, signal loss especially occurs in the superior–inferior direction of MPGs, whereas in the right lobe, signal loss especially occurs in the left-right direction of MPGs. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0183-1Authors Thomas C. Kwee, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The NetherlandsTaro Takahara, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The NetherlandsTetsu Niwa, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The NetherlandsMarko K. Ivancevic, University of Michigan Medical Center Department of Radiology Ann Arbor MI USAGwenael Herigault, Philips Healthcare Best The NetherlandsMarc Van Cauteren, Philips Healthcare Asia Pacific Tokyo JapanPeter R. Luijten, University Medical Center Utrecht Department of Radiology Heidelberglaan 100 3584 CX Utrecht The Netherlands Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Rapid 3-D mapping of hyperpolarized 3He spin-lattice relaxation times using variable flip angle gradient echo imaging with application to alveolar oxygen partial pressure measurement in rat lungs

Abstract Objective The purpose of this work was to develop a rapid 3-D, variable flip angle (VFA) method for measurement of hyperpolarized 3He T 1 which accounts for the effects of radiofrequency (RF) pulses without the need for additional flip angle information. Materials and methods The 3-D, VFA method was validated in vitro over a range of oxygen partial pressures ranging from 0.04 to 0.52 atm. The approach was also tested in vivo in five healthy rats as a function of increasing number of wash-out breaths. The T 1 accuracy of the VFA method in the presence of flip angle mis-setting and RF field non-uniformity was compared with the CFA method using simulations and experiments. Results T 1 measurements were found to provide pAO2 estimates, both in vitro and in vivo consistent with those predicted based on gas dilution and/or ventilation para- meters. For the RF pulse mis-setting (4%) and RF field non-uniformity (3%) used here, the VFA method provided a T 1 accuracy of better than 5% compared to 12% for the CFA method. Conclusion With sufficient RF field homogeneity (3%) and proper calibration (4%), the VFA approach can provide rapid and reliable 3-D T 1 mapping of hyperpolarized 3He without the need for additional flip angle information. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0181-3Authors Alexei V. Ouriadov, Robarts Research Institute Imaging Research Laboratories P.O. Box 5015 100 Perth Drive London ON N6A 5K8 CanadaWilfred W. Lam, Sunnybrook Health Sciences Centre Imaging Research Toronto ON M4N 3M5 CanadaGiles E. Santyr, Robarts Research Institute Imaging Research Laboratories P.O. Box 5015 100 Perth Drive London ON N6A 5K8 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Utilizing different methods for visualizing susceptibility from a single multi-gradient echo dataset

Abstract Purpose Objects that cause a susceptibility gradient can generate regions of hypo-intensity in MRI. MR techniques developed for positive enhancement of such objects require sequence parameter optimization. Thus comparison of images acquired successively using different techniques is difficult since different parameter settings result in variations in signal and noise. A new method is presented that allows production of positive contrast images, a relaxation rate R2* -map and negative contrast images from a single dataset by post-processing. Methods Positive contrast techniques considered include the “white marker” technique, inversion-recovery on-resonance (IRON) and susceptibility gradient mapping (SGM). The new method was tested in phantoms of iron-oxide agent gel solutions and prostate marker seeds. Images produced by post-processing were compared with those obtained directly. The post-processing technique was applied in vivo for the visualization of iron-oxide contrast agent uptake in a balloon-injured swine carotid model. Results The images produced in the post-processing step allowed determination of optimal parameter settings for each technique. SGM was found to provide the greatest positive contrast, whilst the T2* -weighted images provide more sensitivity to regions that exhibited weaker susceptibility effects. Conclusions Combined T2* -weighted imaging and SGM using the same complex image data was found to provide complementary information and high sensitivity to detect distortion inducing agents. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0180-4Authors Gopal Varma, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UKSteen Fjord Pedersen, University of Aarhus, Aarhus University Hospital The MR Research Centre Skejby, Brendstrupgaardsvej 8200 Aarhus N DenmarkMatthias Taupitz, Charite-Universitatsmedizin Berlin Department of Radiology Campus Charite Mitte, Chariteplatz 1 10117 Berlin GermanyRene Michael Botnar, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UKHannes Dahnke, Philips Research Europe Roentgenstrasse 24-26 22335 Hamburg GermanyStephen Frederick Keevil, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UKTobias Schaeffter, King’s College London, St Thomas’ Hospital Division of Imaging Sciences Westminster Bridge Road London SE1 7EH UK Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Influence of selecting EPI readout-encoding bandwidths on arterial spin labeling perfusion MRI

Abstract Object The objective of this study was to investigate effects of varying readout bandwidths on the arterial spin labeling (ASL)-perfusion MRI measurements at a high magnetic field MRI system. Materials and methods Brain perfusion studies were performed on nine volunteers (four males, five females) using flow sensitive alternating inversion recovery (FAIR) ASL single-shot echo-planar imaging (EPI)-MRI. To investigate EPI bandwidth effects on the time-series perfusion-weighted imaging (PWI) data, two regions-of-interest (ROI) were placed outside the brain to determine the level of noise and another ROI inside the brain to determine the level of signal. Coefficients of variations (CoV) were calculated for the time-series PWI data. One-way analysis of variance (ANOVA) was used to investigate voxel-wise differences in the time-series PWI data between two different bandwidth values. Results At the level of ROI, there was no significant effect of changing EPI bandwidths on the time-series PWI data in any of the volunteers (P > 0.031). In contrast, CoV values over the dynamic PWI data varied with depending on selecting EPI bandwidths and voxel-based tests showed that N2 ghosting, modulated by EPI bandwidth, can appear in some brain regions, especially in areas that overlap with the spatial distribution of N2 ghosting artifacts. Conclusions Although N2 ghosting can be reduced by adjusting the bandwidth of EPI on the time-series of PWI data, the effects cannot be entirely eliminated. In particular, N2 ghosting can bias CBF quantification if EPI control scans to determine the equilibrium-state signal are confounded by N2 ghosting. Therefore, careful tuning of the bandwidth of EPI is necessary to avoid artifacts in the ASL signal from N2-ghosting. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0174-2Authors Geon-Ho Jahng, Kyung Hee University Department of Radiology, School of Medicine, East-West Neo Medical Center 149 Sangil-dong, Gangdong-gu Seoul 134-090 South KoreaNorbert Schuff, University of California, San Francisco Department of Radiology, Center for Imaging of Neurodegenerative Diseases, VA Medical Center 4150 Clement Street, 114M San Francisco CA 94121 USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Echo-dephased steady state free precession

Abstract Objective To introduce a novel positive contrast method for passive localization and visualization of paramagnetic susceptibility markers. Materials and methods The novel approach is based on an echo-dephased steady-state free precession (SSFP) sequence. Gradients dephase any signal by ±π at the centered echo-time (TE = TR/2) and induce a total dephasing of ±2π per pixel within TR. This ensures that background tissues do not contribute to signal formation and thus appear dark. However, within the close vicinity of the paramagnetic marker, local gradient fields compensate for the intrinsic dephasing to form an echo. Conceptual issues of gradient compensation and its visualization characteristics are analyzed. The feasibility of the proposed technique for MR-guided intravascular interventions is demonstrated using flow phantom. Results Echo-dephased SSFP is able to localize and visualize paramagnetic marker with excellent suppression of the background signals. The flow phantom experiments concluded that reliable tracking of the interventional guidewire is feasible using echo-dephased SSFP. Conclusion With newly introduced echo-dephased SSFP approach, accurate and reliable visualization of paramagnetic interventional device is feasible. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0173-3Authors Sunil Patil, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel SwitzerlandOliver Bieri, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel SwitzerlandKlaus Scheffler, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel Switzerland Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Monitoring the survival of islet transplants by MRI using a novel technique for their automated detection and quantification

Abstract Object There is a clinical need to be able to assess graft loss of transplanted pancreatic islets (PI) non-invasively with clear-cut quantification of islet survival. We tracked transplanted PI in diabetic mice during the early post-transplant period by magnetic resonance imaging (MRI) and quantified the islet loss using automatic segmentation technique. Materials and methods Magnetically labeled islet iso-, allo- and xenografts were injected into the right liver lobes. Animals underwent MRI scanning during 14 days after PI transplantation. MR images were processed using custom-made software, which automatically detects hypointense regions representing PI. It is based on morphological top-hat and bottom-hat transforms. Results Manually and automatically detected areas, corresponding to PI, differed by 4% in phantoms. Signal loss regions due to PI decreased comparably in all groups during the first week post transplant. Throughout the second week post-transplant, the signal loss area continued in a steep decline in case of allografts and xenografts, whereas the decline in case of isografts slowed down. Conclusion Automatic segmentation allows for the more reproducible, objective assessment of transplanted PI. Quantification confirms the assumption that a significant number of islets are destroyed in the first week following transplantation irrespective of allografts, xenografts or isografts. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0172-4Authors Daniel Jirak, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 CanadaJan Kriz, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 CanadaMichal Strzelecki, Technical University of Lodz Institute of Electronics Lodz PolandJiabi Yang, Robarts Research Institute Transplantation Group London ON CanadaCraig Hasilo, Robarts Research Institute Transplantation Group London ON CanadaDavid J. White, Robarts Research Institute Transplantation Group London ON CanadaPaula J. Foster, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009

Detection and quantification of d-glucuronic acid in human bile using 1H NMR spectroscopy: relevance to the diagnosis of pancreatic cancer

Abstract Objective There are no specific biomarkers available for the definitive diagnosis of pancreatic cancer. Analysis of d-glucuronic acid (GlcUA) in bile could be valuable in this regard. Materials and methods Bile samples obtained from patients with pancreatic cancer (n = 4), chronic pancreatitis (n = 3) and control patients with biliary obstruction (n = 10) were analyzed by 1H NMR spectroscopy. GlcUA was quantified from the peak area of the α-1CH signal (at 5.24 ppm) obtained by deconvolution. Results GlcUA was detected in human bile by one-dimensional 1H NMR and two-dimensional 1H–1H COSY and TOCSY experiments. Quantification of GlcUA was achieved by measuring the peak area of the α-1CH signal using CPMG experiment, and the quantities of GlcUA were calibrated to account for the attenuation due to T 2 relaxation. GlcUA was observed at elevated levels in bile samples obtained from pancreatic cancer patients, whereas it was either absent or found in negligible amounts in control and chronic pancreatitis patients. The reason for the presence of elevated levels of GlcUA could be the hydrolysis of biliary bilirubin diglucuronide by β-glucuronidase, released excessively from pancreatic tissue during the course of malignancy. Conclusion Analysis of d-glucuronic acid in bile could be valuable in the detection of pancreatic cancer, and detecting GlcUA by in vivo 1H MRS has the potential to help in the non-invasive diagnosis of pancreatic cancer. Given that only four cancer patients have been studied so far, the new biomarker is regarded as a preliminary finding, but one that warrants further investigation. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0171-5Authors Tedros Bezabeh, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 CanadaOmkar B. Ijare, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 CanadaNils Albiin, CLINTEC, Karolinska Institutet Division of Radiology Stockholm SwedenUrban Arnelo, CLINTEC, Karolinska Institutet Division of Surgery Stockholm SwedenBo Lindberg, CLINTEC, Karolinska Institutet Division of Radiology Stockholm SwedenIan C. P. Smith, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 5 / October, 2009

Extraction of the first bolus passage in dynamic susceptibility contrast perfusion measurements

Abstract Object The processing of dynamic susceptibility contrast perfusion measurements requires an extraction of the first bolus passage of the injected contrast agent. State-of-the-art methods employ the fit of a gamma variate function to the measured data. The use of a gamma variate function is motivated by its shape similarity to the expected relaxation rate time-course during the first bolus passage. However, the quality of this result is strongly influenced by the amount of overlap of the first and second bolus passage. In this work we present an alternative, data-driven method for the extraction of the first bolus passage from a measured relaxation time-course. Materials and methods By using prior knowledge of the injection function, the measured time-courses can be transformed to time-courses that would occur at a shorter injection duration where the two bolus passages have less overlap. This time-course is found by Tikhonov regularized deconvolution of the measured time-courses with an injection function that bases on the measurement protocol. A minimum search yields the cut-off point at which the first bolus can be extrapolated to zero. The gamma variate fit is performed using Powells algorithm. The proposed approach is compared to the gamma variate fit approach using simulations and an exemplary dataset from one healthy volunteer. Results The new method performs comparably stable as the gamma variate function fit approach in simulations. Both methods are superior to a simple exponential extrapolation approach. Applied to volunteer data, the new method performs much faster than the gamma variate fit approach. The results obtained from both methods correspond well. Conclusion The new method offers a conceptual understanding of the first bolus passage and yields similar results to the gamma variate function fit approach but performs much faster. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0170-6Authors Peter Gall, University Medical Center Freiburg Department of Diagnostic Radiology, Medical Physics Hugstetterstrasse 55 79106 Freiburg GermanyIrina Mader, University Medical Center Freiburg Department of Neuroradiology Breisacher Strasse 64 79106 Freiburg GermanyValerij G. Kiselev, University Medical Center Freiburg Department of Diagnostic Radiology, Medical Physics Hugstetterstrasse 55 79106 Freiburg Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009

Fast multiecho balanced SSFP metabolite mapping of 1H and hyperpolarized 13C compounds

Abstract Object To investigate the feasibility of multiecho balanced steady-state free precession (bSSFP)-based fast chemical shift mapping hyperpolarized 13C metabolites. The overall goal was to reduce total imaging time and to increase spatial resolution compared to common chemical shift imaging (CSI). Materials and methods A multiecho bSSFP sequence in combination with an iterative reconstruction algorithm was implemented. 1H experiments were performed on phantoms and on a human volunteer in order to investigate the feasibility of the method on a system with metabolite maps that are known beforehand. 13C experiments were performed in vivo on pigs, where CSI images were acquired also for comparison. Results Chemical shift images of three and four distinct 1H resonance frequencies as well as chemical shift images of up to five hyperpolarized 13C metabolites were successfully obtained. Conclusion Fast metabolite mapping based on multiecho balanced SSFP in combination with an iterative reconstruction approach could successfully separate several 1H resonances and hyperpolarized 13C metabolites. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0169-zAuthors Jochen Leupold, University Hospital Freiburg Department of Diagnostic Radiology, Medical Physics Freiburg GermanySven Månsson, Lund University, Malmö University Hospital Medical Radiation Physics and Radiology, Department of Clinical Sciences Malmö Malmö SwedenJ. Stefan Petersson, GE Healthcare Helsingborg SwedenJürgen Hennig, University Hospital Freiburg Department of Diagnostic Radiology, Medical Physics Freiburg GermanyOliver Wieben, University of Wisconsin-Madison Departments of Medical Physics and Radiology, Wisconsin Institutes for Medical Research (WIMR) 1111 Highland Ave. Madison WI 53705-2275 USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009

Voxel-based reproducibility of T2 relaxation time in patellar cartilage at 1.5 T with a new validated 3D rigid registration algorithm

Abstract Object T2 relaxation time is a promising MRI parameter for the early diagnosis and follow-up of osteoarthritis. Assessing the evolution of osteoarthritis needs exact comparison of datasets acquired at different times and knowledge of the T2 reproducibility. The aims of this work were to establish a method for voxel-wise comparison of T2 datasets and to assess voxel-based T2 reproducibility in healthy patellar cartilage. Materials and methods A new rigid 3D-registration algorithm was developed. The precision of the registration algorithm was calculated with numerical simulations and in vitro measurements. In vivo T2 reproducibility was assessed in six volunteers measured at seven different times. The voxel-based reproducibility was characterized with the coefficient of variation (CV) of T2, and its regional variations were analyzed. Results The registration algorithm showed an average registration precision lower than 25% of the voxel size. In vivo voxel-based T2 reproducibility exhibited a median CV of 10.1%. Reproducibility showed significant regional differences. Largest CVs (15.4%) were found near the articular surface. The central regions showed the lowest CVs (7.2%) and the lateral regions intermediate CVs (11.2%). Conclusion Using a rigid 3D-registration algorithm provides voxel-based T2 reproducibility errors comparable to former, 2D region-based approaches, thus opening the possibility of voxel-based monitoring of cartilage degradation in osteoarthritis. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0168-0Authors José G. Raya, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyAnnie Horng, Ludwig Maximilian University of Munich Department of Clinical Radiology, Großhadern Munich GermanyOlaf Dietrich, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyJürgen Weber, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyJulia Dinges, Klinikum rechts der Isar der Technischen Universität München Institut für Röntgendiagnostik Munich GermanyElisabeth Mützel, Ludwig Maximilian University of Munich Department of Forensic Medicine Munich GermanyMaximilian F. Reiser, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyChristian Glaser, Ludwig Maximilian University of Munich Department of Clinical Radiology, Großhadern Munich Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009

Design of internal MRI coils using ultimate intrinsic SNR

Abstract Object Internal MRI coils have important applications in diagnostic and interventional studies. Since they can be placed very close to the region of interest in the body, they are favored over external coils in applications where high-resolution images are required. In this paper it is demonstrated that ultimate intrinsic SNR (UISNR) and the optimum coil sensitivity solutions can be used to make new coil designs with higher intrinsic SNR. Materials and methods In this study, UISNR, which is the maximum attainable value of the intrinsic SNR, is used as a measure of performance and as a design criterion. As an example, a novel endorectal MRI coil is designed. The design is tested with phantom and patient studies. Results An endorectal coil is built to demonstrate the effectiveness of the design strategy. ISNR of the endorectal coil approximates the UISNR to 72%. Conclusion An internal coil design method that takes advantage of the UISNR and optimum coil sensitivity calculations was presented. This method can also be used to design better internal MRI coils for different applications. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0167-1Authors Yiğitcan Eryaman, Bilkent University Department of Electrical and Electronics Engineering 06800 Ankara TurkeyYusuf Öner, Gazi University Department of Radiology Ankara TurkeyErgin Atalar, Bilkent University Department of Electrical and Electronics Engineering 06800 Ankara Turkey Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009

Metabolic changes in the rat brain after a photochemical lesion treated by stem cell transplantation assessed by 1H MRS

Abstract Object Metabolite changes in an experimental lesion in the rat cortex and in the contralateral hemisphere after the intravenous administration of mesenchymal stem cells (MSCs) were assessed by proton MR spectroscopy to verify the impact of the cell treatment on the brain tissue. Materials and methods Wistar rats with a photochemical cortical lesion and transplanted MSCs or sham transplanted rats were examined. Proton spectra were obtained from the lesion and from the contralateral cortex. Results Magnetic resonance spectroscopy revealed a gradual recovery of the damaged tissue; however, we found no significant differences in metabolite concentrations in the lesioned hemisphere between treated and untreated animals. Higher concentrations of glutamate and N-acetyl aspartate were found in the contralateral hemisphere in cell-treated animals compared to untreated ones. Lesioned animals showed neurogenesis in the contralateral hemisphere; the number of newly generated cells in stem cell-treated animals was 50% higher than those observed in untreated animals. Conclusion No direct impact of cell transplantation was observed in the lesion. However, changes in the contralateral hemisphere suggest that the transplanted MSCs might stimulate repair processes and plasticity resulting in the generation of newborn cells, which might enable the faster adoption of the damaged tissue’s function by healthy tissue. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0166-2Authors Vít Herynek, Institute for Clinical and Experimental Medicine MR-Unit, Department of Radiodiagnostic and Interventional Radiology Vídeňská 1958/9 140 21 Prague Czech RepublicKateřina Růžičková, Charles University Center for Cell Therapy and Tissue Repair, Second Medical Faculty V Úvalu 84 150 06 Prague Czech RepublicPavla Jendelová, Charles University Center for Cell Therapy and Tissue Repair, Second Medical Faculty V Úvalu 84 150 06 Prague Czech RepublicEva Syková, Charles University Center for Cell Therapy and Tissue Repair, Second Medical Faculty V Úvalu 84 150 06 Prague Czech RepublicMilan Hájek, Institute for Clinical and Experimental Medicine MR-Unit, Department of Radiodiagnostic and Interventional Radiology Vídeňská 1958/9 140 21 Prague Czech Republic Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243 Journal Volume Volume 22 Journal Issue Volume 22, Number 4 / August, 2009