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Plaehn NMJ, Mayer S, Jakob PM, Gutjahr FT. T 1-independent exchange rate quantification using saturation- or phase sensitive-water exchange spectroscopy. J Magn Reson 2022; 335:107141. [PMID: 35051740 DOI: 10.1016/j.jmr.2021.107141] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 12/17/2021] [Accepted: 12/23/2021] [Indexed: 06/14/2023]
Abstract
PURPOSE Water Exchange Spectroscopy (WEX) is a direct measurement of the exchange rate ksw of labile protons from a solute to water in which the exchange time is varied. However the useful information can be masked by the T1-decay of the solvent pool. We propose Saturation-WEX and Phase Sensitive WEX (PS-WEX) as an extension upon the WEX approach to reduce T1-masking. Additionally PS-WEX takes advantage of the phase information contained in the WEX signal to improve the dynamic range. METHODS By introducing an additional RF-pulse and fixing the exchange time delay the T1-dependence of the signal is reduced. By exploiting the phase sensitivity of the WEX pathway the dynamic range can be increased. This approach is validated using simulations as well as phantom measurements. RESULTS The improved dynamic range is demonstrated in measurements. The fixed exchange time reduces the influence of the T1-decay on the signal curve leading to improved fit quality. CONCLUSION Sat-WEX and PS-WEX are an extension to the well established WEX approach with a less complex fit equation and in the case of PS-WEX improved dynamic range, allowing more accurate quantification.
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Affiliation(s)
- N M J Plaehn
- Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Am Hubland, 97074 Würzburg, Germany
| | - S Mayer
- Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Am Hubland, 97074 Würzburg, Germany; Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Correnstrasse 3, 06466 Gatersleben, Germany
| | - P M Jakob
- Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Am Hubland, 97074 Würzburg, Germany
| | - F T Gutjahr
- Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Am Hubland, 97074 Würzburg, Germany.
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Gensler D, Salinger T, Muentze J, Wech T, Frantz S, Jakob PM, Nordbeck P. P3702Self-navigated myocardial T2* mapping under free breathing using a radial multi gradient echo sequence. Eur Heart J 2018. [DOI: 10.1093/eurheartj/ehy563.p3702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- D Gensler
- University Hospital of Wurzburg, Comprehensive Heart Failure Center (CHFC) and Department of Internal Medicine I - Cardiology, Wurzburg, Germany
| | - T Salinger
- University Hospital of Wurzburg, Comprehensive Heart Failure Center (CHFC) and Department of Internal Medicine I - Cardiology, Wurzburg, Germany
| | - J Muentze
- University Hospital of Wurzburg, Comprehensive Heart Failure Center (CHFC) and Department of Internal Medicine I - Cardiology, Wurzburg, Germany
| | - T Wech
- University Hospital of Wurzburg, Comprehensive Heart Failure Center (CHFC) and Department of Diagnostic and Interventional Radiology, Wurzburg, Germany
| | - S Frantz
- University Hospital of Wurzburg, Comprehensive Heart Failure Center (CHFC) and Department of Internal Medicine I - Cardiology, Wurzburg, Germany
| | - P M Jakob
- University of Wuerzburg, Experimental Physics 5, Wurzburg, Germany
| | - P Nordbeck
- University Hospital of Wurzburg, Comprehensive Heart Failure Center (CHFC) and Department of Internal Medicine I - Cardiology, Wurzburg, Germany
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Vogel P, Rückert MA, Klauer P, Kullmann WH, Jakob PM, Behr VC. First in vivo traveling wave magnetic particle imaging of a beating mouse heart. Phys Med Biol 2016; 61:6620-6634. [PMID: 27541258 DOI: 10.1088/0031-9155/61/18/6620] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Magnetic particle imaging (MPI) is a non-invasive imaging modality for direct detection of superparamagnetic iron-oxide nanoparticles based on the nonlinear magnetization response of magnetic materials to alternating magnetic fields. This highly sensitive and rapid method allows both a quantitative and a qualitative analysis of the measured signal. Since the first publication of MPI in 2005 several different scanner concepts have been presented and in 2009 the first in vivo imaging results of a beating mouse heart were shown. However, since the field of view (FOV) of the first MPI-scanner only covers a small region several approaches and hardware enhancements were presented to overcome this issue and could increase the FOV on cost of acquisition speed. In 2014 an alternative scanner concept, the traveling wave MPI (TWMPI), was presented, which allows scanning an entire mouse-sized volume at once. In this paper the first in vivo imaging results using the TWMPI system are presented. By optimizing the trajectory the temporal resolution is sufficiently high to resolve the dynamic of a beating mouse heart.
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Affiliation(s)
- P Vogel
- Department for Experimental Physics 5 (Biophysics), Universität of Würzburg, Würzburg, Germany. Institute of Medical Engineering, University of Applied Sciences Würzburg-Schweinfurt, Schweinfurt, Germany. Research Center for Magnetic Resonance Bavaria e.V. (MRB), Würzburg, Germany
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Hopfgartner AJ, Tymofiyeva O, Ehses P, Rottner K, Boldt J, Richter EJ, Jakob PM. Dynamic MRI of the TMJ under physical load. Dentomaxillofac Radiol 2013; 42:20120436. [PMID: 23975114 PMCID: PMC3828022 DOI: 10.1259/dmfr.20120436] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 08/12/2013] [Accepted: 08/19/2013] [Indexed: 11/05/2022] Open
Abstract
OBJECTIVES The objective of this study was to examine the kinematics of structures of the temporomandibular joint (TMJ) under physiological load while masticating. METHODS Radial MRI was chosen as a fast imaging method to dynamically capture the motions of the joint's anatomy. The technique included a golden ratio-based increment angle and a sliding window reconstruction. The measurements were performed on 22 subjects with and without deformation/displacement of the intra-articular disc while they were biting on a cooled caramel toffee. RESULTS The reconstructed dynamic images provided sufficient information about the size and localization of the disc as well as the change of the intra-articular distance with and without loading. CONCLUSIONS The feasibility of the golden ratio-based radial MRI technique to dynamically capture the anatomy of the TMJ under physical load was demonstrated in this initial study.
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Affiliation(s)
- A J Hopfgartner
- Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany;
| | - O Tymofiyeva
- Department of Prosthodontics, University of Wuerzburg, Wuerzburg, Germany
| | - P Ehses
- Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany;
| | - K Rottner
- Department of Prosthodontics, University of Wuerzburg, Wuerzburg, Germany
| | - J Boldt
- Department of Prosthodontics, University of Wuerzburg, Wuerzburg, Germany
| | - E-J Richter
- Department of Prosthodontics, University of Wuerzburg, Wuerzburg, Germany
| | - P M Jakob
- Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany;
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Tymofiyeva O, Vaegler S, Rottner K, Boldt J, Hopfgartner AJ, Proff PC, Richter EJ, Jakob PM. Influence of dental materials on dental MRI. Dentomaxillofac Radiol 2013; 42:20120271. [PMID: 23610088 DOI: 10.1259/dmfr.20120271] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
OBJECTIVES To investigate the potential influence of standard dental materials on dental MRI (dMRI) by estimating the magnetic susceptibility with the help of the MRI-based geometric distortion method and to classify the materials from the standpoint of dMRI. METHODS A series of standard dental materials was studied on a 1.5 T MRI system using spin echo and gradient echo pulse sequences and their magnetic susceptibility was estimated using the geometric method. Measurements on samples of dental materials were supported by in vivo examples obtained in dedicated dMRI procedures. RESULTS The tested materials showed a range of distortion degrees. The following materials were classified as fully compatible materials that can be present even in the tooth of interest: the resin-based sealer AH Plus(®) (Dentsply, Maillefer, Germany), glass ionomer cement, gutta-percha, zirconium dioxide and composites from one of the tested manufacturers. Interestingly, composites provided by the other manufacturer caused relatively strong distortions and were therefore classified as compatible I, along with amalgam, gold alloy, gold-ceramic crowns, titanium alloy and NiTi orthodontic wires. Materials, the magnetic susceptibility of which differed from that of water by more than 200 ppm, were classified as non-compatible materials that should not be present in the patient's mouth for any dMRI applications. They included stainless steel orthodontic appliances and CoCr. CONCLUSIONS A classification of the materials that complies with the standard grouping of materials according to their magnetic susceptibility was proposed and adopted for the purposes of dMRI. The proposed classification can serve as a guideline in future dMRI research.
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Affiliation(s)
- O Tymofiyeva
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA.
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Wild JM, Marshall H, Bock M, Schad LR, Jakob PM, Puderbach M, Molinari F, Van Beek EJR, Biederer J. MRI of the lung (1/3): methods. Insights Imaging 2012; 3:345-53. [PMID: 22695952 PMCID: PMC3481083 DOI: 10.1007/s13244-012-0176-x] [Citation(s) in RCA: 181] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Revised: 04/11/2012] [Accepted: 04/16/2012] [Indexed: 11/26/2022] Open
Abstract
Proton magnetic resonance imaging (MRI) has recently emerged as a clinical tool to image the lungs. This paper outlines the current technical aspects of MRI pulse sequences, radiofrequency (RF) coils and MRI system requirements needed for imaging the pulmonary parenchyma and vasculature. Lung MRI techniques are presented as a “technical toolkit”, from which MR protocols will be composed in the subsequent papers for comprehensive imaging of lung disease and function (parts 2 and 3). This paper is pitched at MR scientists, technicians and radiologists who are interested in understanding and establishing lung MRI methods. Images from a 1.5 T scanner are used for illustration of the sequences and methods that are highlighted. Main Messages • Outline of the hardware and pulse sequence requirements for proton lung MRI • Overview of pulse sequences for lung parenchyma, vascular and functional imaging with protons • Demonstration of the pulse-sequence building blocks for clinical lung MRI protocols
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Affiliation(s)
- J M Wild
- Academic Radiology, Royal Hallamshire Hospital Sheffield, University of Sheffield, Sheffield, S10 2JF, UK,
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Gensler D, Fidler F, Ehses P, Warmuth M, Reiter T, Düring M, Ritter O, Ladd ME, Quick HH, Jakob PM, Bauer WR, Nordbeck P. MR safety: Fast T
1
thermometry of the RF-induced heating of medical devices. Magn Reson Med 2012; 68:1593-9. [PMID: 22287286 DOI: 10.1002/mrm.24171] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 12/01/2011] [Accepted: 12/29/2011] [Indexed: 11/11/2022]
Affiliation(s)
- D Gensler
- Research Center for Magnetic Resonance Bavaria e.V., Würzburg, Germany.
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Sturm VJF, Basse-Lüsebrink TC, Kampf T, Stoll G, Jakob PM. Improved encoding strategy for CPMG-based Bloch-Siegert B(1)(+) mapping. Magn Reson Med 2011; 68:507-15. [PMID: 22190144 DOI: 10.1002/mrm.23232] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 08/11/2011] [Accepted: 09/04/2011] [Indexed: 11/05/2022]
Abstract
Bloch-Siegert (BS) based B(1)(+) mapping methods use off-resonant pulses to encode quantitative B(1)(+) information into the signal phase. It was recently shown that the principle behind BS-based B(1)(+) mapping can be expanded from spin echo (BS-SE) and gradient-echo (BS-FLASH) based BS B(1)(+) mapping to methods such as Carr, Purcell, Meiboom, Gill (CPMG)-based turbo-spin echo (BS-CPMG-TSE) and multi-spin echo (BS-CPMG-MSE) imaging. If CPMG conditions are preserved, BS-CPMG-TSE allows fast acquisition of the B(1)(+) information and BS-CPMG-MSE enables simultaneous mapping of B(1)(+), M(0), and T(2). To date, however, two separate MRI experiments must be performed to enable the calculation of B(1)(+) maps. This study investigated a modified encoding strategy for CPMG BS-based methods to overcome this limitation. By applying a "bipolar" off-resonant BS pulse before the refocusing pulse train, the needed phase information was able to be encoded into different echo images of one echo train. Thus, this technique allowed simultaneous B(1)(+) and T(2) mapping in a single BS-CPMG-MSE experiment. To allow single-shot B(1)(+) mapping, this method was also applied to turbo-spin echo imaging. Furthermore, the presented modification intrinsically minimizes phase-based image artifacts in BS-CPMG-TSE experiments.
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Affiliation(s)
- V J F Sturm
- Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany.
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Basse-Lüsebrink TC, Sturm VJF, Kampf T, Stoll G, Jakob PM. Fast CPMG-based Bloch-Siegert B
1
+
mapping. Magn Reson Med 2011; 67:405-18. [DOI: 10.1002/mrm.23013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2010] [Revised: 04/23/2011] [Accepted: 05/02/2011] [Indexed: 11/06/2022]
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Kampf T, Fischer A, Basse-Lüsebrink TC, Ladewig G, Breuer F, Stoll G, Jakob PM, Bauer WR. Application of compressed sensing to in vivo 3D ¹⁹F CSI. J Magn Reson 2010; 207:262-273. [PMID: 20932790 DOI: 10.1016/j.jmr.2010.09.006] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2010] [Revised: 09/13/2010] [Accepted: 09/13/2010] [Indexed: 05/30/2023]
Abstract
This study shows how applying compressed sensing (CS) to (19)F chemical shift imaging (CSI) makes highly accurate and reproducible reconstructions from undersampled datasets possible. The missing background signal in (19)F CSI provides the required sparsity needed for application of CS. Simulations were performed to test the influence of different CS-related parameters on reconstruction quality. To test the proposed method on a realistic signal distribution, the simulation results were validated by ex vivo experiments. Additionally, undersampled in vivo 3D CSI mouse datasets were successfully reconstructed using CS. The study results suggest that CS can be used to accurately and reproducibly reconstruct undersampled (19)F spectroscopic datasets. Thus, the scanning time of in vivo(19)F CSI experiments can be significantly reduced while preserving the ability to distinguish between different (19)F markers. The gain in scan time provides high flexibility in adjusting measurement parameters. These features make this technique a useful tool for multiple biological and medical applications.
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Affiliation(s)
- T Kampf
- Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany.
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Ziener CH, Kampf T, Jakob PM, Bauer WR. Diffusion effects on the CPMG relaxation rate in a dipolar field. J Magn Reson 2010; 202:38-42. [PMID: 19853483 DOI: 10.1016/j.jmr.2009.09.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 09/15/2009] [Accepted: 09/26/2009] [Indexed: 05/28/2023]
Abstract
The diffusion in the magnetic dipolar field around a sphere is considered. The diffusion is restricted to the space between two concentric spheres, where the inner sphere is the source of the magnetic dipolar field. Analytical expressions for the CPMG transverse relaxation rate as well as the free induction decay and the spin echo time evolution are given in the Gaussian approximation. The influence of the inter-echo time is analyzed. The limiting cases of small and large inter-echo times as well as the short and long time behavior are evaluated.
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Affiliation(s)
- C H Ziener
- Julius-Maximilians-Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Würzburg, Germany.
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Ziener CH, Glutsch S, Jakob PM, Bauer WR. Spin dephasing in the dipole field around capillaries and cells: numerical solution. Phys Rev E Stat Nonlin Soft Matter Phys 2009; 80:046701. [PMID: 19905476 DOI: 10.1103/physreve.80.046701] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Indexed: 05/28/2023]
Abstract
We numerically solve the Bloch-Torrey equation by discretizing the differential operators in real space using finite differences. The differential equation is either solved directly in time domain as initial-value problem or in frequency domain as boundary-value problem. Especially the solution in time domain is highly efficient and suitable for arbitrary domains and dimensions. As examples, we calculate the average magnetization and the frequency distribution for capillaries and cells which are idealized as cylinders and spheres, respectively. The solution is compared with the commonly used Gaussian approximation and the strong-collision approximation. While these approximations become exact in limiting cases (small or large diffusion coefficient), they strongly deviate from the numerical solution for intermediate values of the diffusion coefficient.
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Affiliation(s)
- C H Ziener
- Julius-Maximilians-Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Würzburg, Germany
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Weber T, Ziener CH, Kampf T, Herold V, Bauer WR, Jakob PM. Measurement of apparent cell radii using a multiple wave vector diffusion experiment. Magn Reson Med 2009; 61:1001-6. [DOI: 10.1002/mrm.21848] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Ziener CH, Kampf T, Herold V, Jakob PM, Bauer WR, Nadler W. Frequency autocorrelation function of stochastically fluctuating fields caused by specific magnetic field inhomogeneities. J Chem Phys 2008; 129:014507. [DOI: 10.1063/1.2949097] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Oechsner M, Stäb D, Pracht ED, Jakob PM, Köstler H, Hahn D, Beer M. Sauerstoffgestützte T2* Bildgebung der menschlichen Lunge bei 0.2 Tesla. ROFO-FORTSCHR RONTG 2008. [DOI: 10.1055/s-2008-1073589] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Ziener CH, Kampf T, Melkus G, Herold V, Weber T, Reents G, Jakob PM, Bauer WR. Local frequency density of states around field inhomogeneities in magnetic resonance imaging: effects of diffusion. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 76:031915. [PMID: 17930279 DOI: 10.1103/physreve.76.031915] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Revised: 04/27/2007] [Indexed: 05/25/2023]
Abstract
A method describing NMR-signal formation in inhomogeneous tissue is presented which covers all diffusion regimes. For this purpose, the frequency distribution inside the voxel is described. Generalizing the results of the well-known static dephasing regime, we derive a formalism to describe the frequency distribution that is valid over the whole dynamic range. The expressions obtained are in agreement with the results obtained from Kubos line-shape theory. To examine the diffusion effects, we utilize a strong collision approximation, which replaces the original diffusion process by a simpler stochastic dynamics. We provide a generally valid relation between the frequency distribution and the local Larmor frequency inside the voxel. To demonstrate the formalism we give analytical expressions for the frequency distribution and the free induction decay in the case of cylindrical and spherical magnetic inhomogeneities. For experimental verification, we performed measurements using a single-voxel spectroscopy method. The data obtained for the frequency distribution, as well as the magnetization decay, are in good agreement with the analytic results, although experiments were limited by magnetic field gradients caused by an imperfect shim and low signal-to-noise ratio.
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Affiliation(s)
- C H Ziener
- Julius-Maximilians-Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Am Hubland, 97074 Würzburg, Germany
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Wichmann T, Lanz T, Griswold M, Jakob PM. Highly accelerated imaging of cardiac function using a 32 channel cardiac phased array at 3 T. ROFO-FORTSCHR RONTG 2007. [DOI: 10.1055/s-2007-972144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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18
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Ziener CH, Kampf T, Melkus G, Jakob PM, Bauer WR. Scaling laws for transverse relaxation times. J Magn Reson 2007; 184:169-75. [PMID: 17045825 DOI: 10.1016/j.jmr.2006.09.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Revised: 09/18/2006] [Accepted: 09/22/2006] [Indexed: 05/12/2023]
Abstract
Simple scaling laws are useful tools in understanding the effect of changing parameters in MRI experiments. In this paper the general scaling behavior of the transverse relaxation times is discussed. We consider the dephasing of spins diffusing around a field inhomogeneity inside a voxel. The strong collision approximation is used to describe the diffusion process. The obtained scaling laws are valid over the whole dynamic range from motional narrowing to static dephasing. The dependence of the relaxation times on the external magnetic field, diffusion coefficients of the surrounding medium, and the characteristic scale of the field inhomogeneity is analyzed. For illustration the generally valid scaling laws are applied to the special case of a capillary, usually used as a model of the myocardial BOLD effect.
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Affiliation(s)
- C H Ziener
- Bayerische Julius-Maximilians-Universität Würzburg, Institut für Experimentelle Physik 5, Am Hubland, 97074 Würzburg, Germany.
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Abstract
PURPOSE Gas exchange is the primary function of the lung and the transport of oxygen plays a key role in pulmonary physiology and pathophysiology. MATERIALS AND METHODS Molecular oxygen is weakly paramagnetic, so that an increase in oxygen concentration results in shortening T1 relaxation time and thus increasing signal intensity in T1 weighted images. The calculation of parameter maps may allow deeper insights into relaxation mechanisms. T1 maps based on a snapshot FLASH sequence obtained during the inhalation of various oxygen concentrations allow the creation of an oxygen transfer function, providing a measurement of local oxygen transfer. T1 weighted single shot TSE sequences demonstrate the signal changing effects during inhalation of pure oxygen. RESULTS The average of the mean T1 values over the entire lung during inspiration was 1,199+/-117 ms, the average of these values during expiration was 1,333+/-167 ms. T1 maps of patients with emphysema and lung fibrosis show fundamentally different values and respiratory dependence compared to healthy individuals. Oxygen enhanced MR has the potential to assess reduced diffusion capacity and decreased transport of oxygen in patients with emphysema and cystic fibrosis. DISCUSSION Results published in the literature indicate that T1 mapping and oxygen enhanced MR are promising new methods in functional imaging of the lung.
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Affiliation(s)
- A Stadler
- Universitätsklinik für Radiodiagnostik, Medizinische Universität Wien.
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Schmitt P, Griswold MA, Gulani V, Haase A, Flentje M, Jakob PM. A simple geometrical description of the TrueFISP ideal transient and steady-state signal. Magn Reson Med 2006; 55:177-86. [PMID: 16323155 DOI: 10.1002/mrm.20738] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
An intuitive approach is presented for assessment of the TrueFISP signal behavior in the transient phase and the steady state, based on geometrical considerations in combination with the Bloch equations. Short formulations are derived for the zenith and phase angle determining the direction of the magnetization vector for which a smooth monoexponential decay is obtained even at considerable off-resonance frequencies, thus compactly defining the target of various preparation schemes proposed in literature. A pictorial explanation is provided to illustrate how the interplay between RF excitation and relaxation governs the TrueFISP transient phase and steady state. Closed form expressions are developed that describe the signal evolution, accounting for the influence of T(1), T(2), flip angle, and resonance frequency offset in agreement with recently published studies. These results are obtained directly from basic assumptions, without the need for abstract mathematical treatment or further approximations. The validity of the conceptual framework and the analytical description is verified by simulations based on the Bloch equations as well as with MR phantom experiments. The theory may be used for contrast calculations and has the potential to facilitate improved parameter quantification with magnetization prepared TrueFISP experiments accounting for off-resonance effects.
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Affiliation(s)
- P Schmitt
- Department of Experimental Physics 5, University of Würzburg, Germany.
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Oechsner M, Jakob PM, Pracht ED, Köstler H, Weininger M, Beissert M, Hahn D, Beer M. Optimierte FLASH Sequenzen zur Lungenbildgebung bei 0,2 Tesla mit MRI. ROFO-FORTSCHR RONTG 2006. [DOI: 10.1055/s-2006-940672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Ziener CH, Bauer WR, Jakob PM. Frequency distribution and signal formation around a vessel. MAGMA 2005; 18:225-30. [PMID: 16175391 DOI: 10.1007/s10334-005-0122-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2005] [Revised: 07/19/2005] [Accepted: 07/19/2005] [Indexed: 10/25/2022]
Abstract
We describe the NMR signal formation properties of a single vessel. Instead of assuming the frequency distribution to be a simple Lorentzian or Gaussian one, we take into account that the frequency distribution around the vessel is a complex function. Considering the static dephasing regime we find a relationship between signal formation and frequency distribution. Analytical expressions for the frequency distribution in a voxel and the magnetization decay are obtained. In the case of small volume fractions of blood and week magnetic fields the results can be used for describing signal formation processes in a vascular network. A relationship between the frequency distribution and the properties of the vascular network is derived. The magnetization decay in different time regimes is discussed. The result is relevant for describing signal formation processes around a vessel for arbitrary pulse sequences.
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Affiliation(s)
- C H Ziener
- Bayerische Julius-Maximilians-Universität Würzburg, Lehrstuhl für Experimentelle Physik 5, Am Hubland, 97074, Würzburg, Germany.
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23
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Abstract
We describe the NMR relaxation properties of magnetically labeled cells. The cells are labeled with magnetic nanoparticles (SPIO, USPIO), which generate susceptibility contrast. The geometry of the labeled cells and the surrounding tissue is considered. We assume that the magnetic nanoparticles accumulate to form a magnetic core of radius RC inside the cell. The correlation time tau, which describes the motion of spins around this core, is analyzed. Using the strong collision approach, explicit expressions are derived for the transverse relaxation rate R2* for tissue containing labeled cells as a function of the core radius, the diffusion coefficient, and the concentration of the nanoparticles. The predictions of this model agree well with numerical simulations and experimental data.
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Affiliation(s)
- C H Ziener
- Bayerische Julius-Maximilians-Universität Würzburg, Institut für Experimentelle Physik 5, Am Hubland, 97074 Würzburg, Germany.
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24
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Neuberger T, Greiser A, Nahrendorf M, Jakob PM, Faber C, Webb AG. 23Na microscopy of the mouse heart in vivo using density-weighted chemical shift imaging. MAGMA 2004; 17:196-200. [PMID: 15580377 DOI: 10.1007/s10334-004-0048-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2004] [Revised: 06/18/2004] [Accepted: 07/02/2004] [Indexed: 10/26/2022]
Abstract
The mouse has become an important animal model for human cardiac disease, and the development of techniques for non-invasive imaging of the mouse heart in vivo is, therefore, of great potential interest. Previous magnetic resonance imaging studies have concentrated on pathologically induced changes in cardiac structure and dynamics by acquiring proton images. Further information can be gained by studying cardiac function and physiology using other nuclei, for example, sodium. Sodium imaging of such a small structure presents considerable technical challenges. In this work we show the first sodium images of the mouse heart, with an isotropic spatial resolution of 1 x 1 x 1 mm, acquired in a time of 1.5 h. The ventricles, septum and myocardium are readily distinguishable in these images, which were acquired through the combination of 3D density-weighted chemical shift imaging, optimized instrumentation, and a high magnetic field strength (17.6 T). Measurements of the myocardial:blood sodium concentration in the left and right ventricles agree well with theoretical values.
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Affiliation(s)
- T Neuberger
- Department of Physics, EP5 (Biophysics), University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
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25
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Behr VC, Weber T, Neuberger T, Vroemen M, Weidner N, Bogdahn U, Haase A, Jakob PM, Faber C. High-resolution MR imaging of the rat spinal cord in vivo in a wide-bore magnet at 17.6 Tesla. MAGMA 2004; 17:353-8. [PMID: 15517470 DOI: 10.1007/s10334-004-0057-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2004] [Revised: 07/19/2004] [Accepted: 07/29/2004] [Indexed: 11/25/2022]
Abstract
The objective was to demonstrate the feasibility and to evaluate the performance of high-resolution in vivo magnetic resonance (MR) imaging of the rat spinal cord in a 17.6-T vertical wide-bore magnet. A probehead consisting of a surface coil that offers enlarged sample volume suitable for rats up to a weight of 220 g was designed. ECG triggered and respiratory-gated gradient echo experiments were performed on a Bruker Avance 750 wide-bore spectrometer for high-resolution imaging. With T*2 values between 5 and 20 ms, good image contrast could be obtained using short echo times, which also minimizes motion artifacts. Anatomy of healthy spinal cords and pathomorphological changes in traumatically injured rat spinal cord in vivo could be visualized with microscopic detail. It was demonstrated that imaging of the rat spinal cord in vivo using a vertical wide-bore high-magnetic-field system is feasible. The potential to obtain high-resolution images in short scan times renders high-field imaging a powerful diagnostic tool.
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Affiliation(s)
- V C Behr
- Department of Physics, EP5 (Biophysics), University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
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26
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Abstract
In medical magnetic resonance imaging (MRI) it is standard to use MR scanners with a field strength of 1.5 Tesla. Recently, an ongoing development to higher field strength can be observed and a new clinical standard at 3.0 Tesla seems to be established. High field MRI with its intrinsic higher signal to noise ratio (SNR) can enable new applications of MRI in medical diagnosis, or can serve to improve existing methods. It is important to note, that the use of high field MRI is not without its limitations. Besides the SNR, other unwanted effects increase with a higher field strength. Without correction, these high field problems cause a serious loss in image quality. An elegant way to address these problems is the use of parallel imaging. In many clinical applications, parallel MRI (pMRI) is part of the standard protocol, because pMRI can enhance virtually every MRI application, without necessarily affecting the contrast behavior of the underlying imaging sequence. In high field MRI, besides the speed advantage of pMRI, the positive influence on high field specific problems and therefore on the image quality will be of major importance.
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Affiliation(s)
- R M Heidemann
- Physikalisches Institut-EP5, Universität Würzburg, Wuerzburg.
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27
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Arnold JFT, Fidler F, Wang T, Pracht ED, Schmidt M, Jakob PM. Imaging lung function using rapid dynamic acquisition of T 1-maps during oxygen enhancement. Magn Reson Mater Phy 2004; 16:246-53. [PMID: 15042464 DOI: 10.1007/s10334-004-0034-z] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2003] [Accepted: 12/19/2003] [Indexed: 10/26/2022]
Abstract
This paper describes imaging of lung function with oxygen-enhanced MRI using dynamically acquired T1 parameter maps, which allows an accurate, quantitative assessment of time constants of T1-enhancement and therefore lung function. Eight healthy volunteers were examined on a 1.5-T whole-body scanner. Lung T1-maps based on an IR Snapshot FLASH technique (TE = 1.4 ms, TR = 3.5 ms, FA = 7 (composite function )) were dynamically acquired from each subject. Without waiting for full relaxation between subsequent acquisition of T1-maps, one T1-map was acquired every 6.7 s. For comparison, all subjects underwent a standard pulmonary function test (PFT). Oxygen wash-in and wash-out time course curves of T1 relaxation rate (R1)-enhancement were obtained and time constants of oxygen wash-in (w(in)) and wash-out (w(out)) were calculated. Averaged over the whole right lung, the mean w(out) was 43.90 +/- 10.47 s and the mean (w(in)) was 51.20 +/- 15.53 s, thus about 17% higher in magnitude. Wash-in time constants correlated strongly with forced expired volume in one second in percentage of the vital capacity (FEV1 % VC) and with maximum expiratory flow at 25% vital capacity (MEF25), whereas wash-out time constants showed only weak correlation. Using oxygen-enhanced rapid dynamic acquisition of T1-maps, time course curves of R1-enhancement can be obtained. With w(in) and w(out) two new parameters for assessing lung function are available. Therefore, the proposed method has the potential to provide regional information of pulmonary function in various lung diseases.
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Affiliation(s)
- J F T Arnold
- Department of Physics, University of Würzburg, 97074 Würzburg, Germany.
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28
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Heidemann RM, Griswold MA, Kiefer B, Nittka M, Wang J, Jellus V, Jakob PM. Resolution enhancement in lung 1H imaging using parallel imaging methods. Magn Reson Med 2003; 49:391-4. [PMID: 12541262 DOI: 10.1002/mrm.10349] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Resolution in (1)H lung imaging is limited mainly by the acquisition time. Today, half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences, with short echo time (TE) and short interecho spacing (T(inter)) have found increased use in lung imaging. In this study, a HASTE sequence was used in combination with a partially parallel acquisition (PPA) strategy to increase the spatial resolution in single-shot (1)H lung imaging. To investigate the benefits of using a combination of single-shot sequences and PPA, five healthy volunteers were examined. Compared to conventional imaging methods, substantially increased resolution is obtained using the PPA approach. Representative in vivo (1)H lung images acquired with a HASTE sequence in combination with the generalized autocalibrating partially parallel acquisition (GRAPPA) method, up to an acceleration factor of three, are presented.
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Affiliation(s)
- R M Heidemann
- Department of Physics, Universität Würzburg, Physikalisches Institut, Würzburg, Germany
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29
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Abstract
MR-CAT (combined acquisition technique), a modular hybrid imaging concept, was introduced recently. In this article it is demonstrated that the CAT principles can be applied to form a versatile combination of spin and gradient echoes for abdominal imaging. This CAT approach, which essentially integrates RARE and EPI modules in a sequential fashion, was used to implement a set of segmented and single-shot RARE/EPI-CAT imaging techniques. CAT was used in in vivo studies to perform high-resolution abdominal imaging in five healthy subjects. The results demonstrate the feasibility of abdominal imaging using the proposed CAT approach and the potential of this technique to reduce imaging time while preserving image quality.
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Affiliation(s)
- P M Jakob
- Physikalisches Institut, Universität Würzburg, Würzburg, Germany.
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30
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Abstract
In this contribution, a rapid and robust technique for quantitative T(1) mapping of the human lung is presented. Based on a series of Snapshot FLASH tomograms acquired after a single inversion pulse, high quality and quantitative T(1) parameter maps acquired in under five seconds were obtained from six healthy volunteers. The measured T(1) values are in good agreement with previously reported literature values. T(1) maps were also acquired with the volunteers breathing room air or 100% O(2). The T(1) difference between breathing room air and 100% O(2) is statistically significant at P < 0.0001.
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Affiliation(s)
- P M Jakob
- Department of Physics, University of Würzburg, Würzburg, Germany.
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31
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Abstract
SMASH (SiMultaneous Acquisition of Spatial Harmonics) was recently introduced as a novel rapid-imaging technique. The SMASH technique uses a partially parallel acquisition strategy, using spatial information from a radiofrequency coil array to accelerate imaging. This study constitutes the first application of SMASH to cardiac magnetic resonance imaging. The increased imaging speed provided by SMASH was used to obtain images with reduced breathhold duration, enhanced spatial resolution, and increased temporal resolution in healthy volunteers. The results obtained demonstrate the feasibility and potential clinical utility of cardiac magnetic resonance imaging using the SMASH technique.
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Affiliation(s)
- P M Jakob
- Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
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32
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Abstract
Recently a self-calibrating SMASH technique, AUTO-SMASH, was described. This technique is based on PPA with RF coil arrays using auto-calibration signals. In AUTO-SMASH, important coil sensitivity information required for successful SMASH reconstruction is obtained during the actual scan using the correlation between undersampled SMASH signal data and additionally sampled calibration signals with appropriate offsets in k-space. However, AUTO-SMASH is susceptible to noise in the acquired data and to imperfect spatial harmonic generation in the underlying coil array. In this work, a new modified type of internal sensitivity calibration, VD-AUTO-SMASH, is proposed. This method uses a VD k-space sampling approach and shows the ability to improve the image quality without significantly increasing the total scan time. This new k-space adapted calibration approach is based on a k-space-dependent density function. In this scheme, fully sampled low-spatial frequency data are acquired up to a given cutoff-spatial frequency. Above this frequency, only sparse SMASH-type sampling is performed. On top of the VD approach, advanced fitting routines, which allow an improved extraction of coil-weighting factors in the presence of noise, are proposed. It is shown in simulations and in vivo cardiac images that the VD approach significantly increases the potential and flexibility of rapid imaging with AUTO-SMASH.
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Affiliation(s)
- R M Heidemann
- Department of Physics, University of Würzburg, Würzburg, Germany
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33
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Jakob PM, Griswold M, Hillenbrand C, Heidemann R, Hahn D, Haase A. High speed and high resolution cardiac MRI (parallel acquisition techniques & modular imaging). MAGMA 2000; 11:52-4. [PMID: 11186987 DOI: 10.1007/bf02678494] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- P M Jakob
- Lehrstuhl für Experimentelle Physik, University of Würzburg, Germany.
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34
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Abstract
In this study a novel partially parallel acquisition method is presented, which can be used to accelerate image acquisition using an RF coil array for spatial encoding. In this technique, Parallel Imaging with Localized Sensitivities (PILS), it is assumed that the individual coils in the array have localized sensitivity patterns, in that their sensitivity is restricted to a finite region of space. Within the PILS model, a detailed, highly accurate RF field map is not needed prior to reconstruction. In PILS, each coil in the array is fully characterized by only two parameters: the center of coil's sensitive region in the FOV and the width of the sensitive region around this center. In this study, it is demonstrated that the incorporation of these coil parameters into a localized Fourier transform allows reconstruction of full FOV images in each of the component coils from data sets acquired with a reduced number of phase encoding steps compared to conventional imaging techniques. After the introduction of the PILS technique, primary focus is given to issues related to the practical implementation of PILS, including coil parameter determination and the SNR and artifact power in the resulting images. Finally, in vivo PILS images are shown which demonstrate the utility of the technique.
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Affiliation(s)
- M A Griswold
- Department of Physics, University of Würzburg, Würzburg, Germany.
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35
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Abstract
In this study, a modular concept for NMR hybrid imaging is presented. This concept essentially integrates different imaging modules in a sequential fashion and is therefore called CAT (combined acquisition technique). CAT is not a single specific measurement sequence, but rather a sequence design concept whereby distinct acquisition techniques with varying imaging parameters are employed in rapid succession in order to cover k-space. The power of the CAT approach is that it provides a high flexibility toward the acquisition optimization with respect to the available imaging time and the desired image quality. Important CAT sequence optimization steps include the appropriate choice of the k-space coverage ratio and the application of mixed bandwidth technology. Details of both the CAT methodology and possible CAT acquisition strategies, such as FLASH/EPI-, RARE/EPI- and FLASH/BURST-CAT are provided. Examples from imaging experiments in phantoms and healthy volunteers including mixed bandwidth acquisitions are provided to demonstrate the feasibility of the proposed CAT concept.
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Affiliation(s)
- C Hillenbrand
- Physikalisches Institut, EP5, Universit]at W]urzburg, Am Hubland, 97074, W]urzburg, Germany.
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36
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Abstract
We demonstrate the feasibility of a new versatile hybrid imaging concept, the combined acquisition technique (CAT), for cardiac imaging. The cardiac CAT approach, which combines new methodology with existing technology, essentially integrates fast low-angle shot (FLASH) and echoplanar imaging (EPI) modules in a sequential fashion, whereby each acquisition module is employed with independently optimized imaging parameters. One important CAT sequence optimization feature is the ability to use different bandwidths for different acquisition modules. Twelve healthy subjects were imaged using three cardiac CAT acquisition strategies: a) CAT was used to reduce breath-hold duration times while maintaining constant spatial resolution; b) CAT was used to increase spatial resolution in a given breath-hold time; and c) single-heart beat CAT imaging was performed. The results obtained demonstrate the feasibility of cardiac imaging using the CAT approach and the potential of this technique to accelerate the imaging process with almost conserved image quality.
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Affiliation(s)
- C Hillenbrand
- Physikalisches Institut, Universität Würzburg, 97074 Würzburg, Germany
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37
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Seifert MH, Jakob PM, Jellus V, Haase A, Hillenbrand C. High-resolution diffusion imaging using a radial turbo-spin-echo sequence: implementation, eddy current compensation, and self-navigation. J Magn Reson 2000; 144:243-254. [PMID: 10828192 DOI: 10.1006/jmre.2000.2041] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
This work describes a segmented radial turbo-spin-echo technique (DW-rTSE) for high-resolution multislice diffusion-weighted imaging and quantitative ADC mapping. Diffusion-weighted images with an in-plane resolution of 700 microm and almost free of bulk motion can be obtained in vivo without cardiac gating. However, eddy currents and pulsatile brain motion cause severe artifacts when strong diffusion weighting is applied. This work explains in detail the artifacts in projection reconstruction (PR) imaging arising from eddy currents and describes an effective eddy current compensation based on the adjustment of gradient timing. Application of the diffusion gradients in all three orthogonal directions is possible without degradation of the images due to eddy current artifacts, allowing studies of the diffusional anisotropy. Finally, a self-navigation approach is proposed to reduce residual nonrigid body motion artifacts. Five healthy volunteers were examined to show the feasibility of this method.
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Affiliation(s)
- M H Seifert
- Lehrstuhl für Experimentelle Physik V, Physikalisches Institut der Universität Würzburg, Germany
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38
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Abstract
Recently, several partially parallel acquisition (PPA) techniques have been presented which use spatial information inherent in an RF coil array to reconstruct an image from a reduced set of phase encoding steps. PPAs represent a change in paradigm for the RF coil designer since the focus for arrays to be used with PPAs is to optimize the spatial encoding that is provided by the array. One of the first practical implementations of PPA imaging was demonstrated using the SMASH technique. In this study, we present our results from the construction of the first array designed specifically for cardiac SMASH imaging. Additional design criteria are presented for SMASH arrays that are not considered in conventional array design. Using these design criteria, a four-element array was constructed and then tested in SMASH imaging experiments in the heart. This array has been used in all of our initial cardiac and head SMASH studies with good results.
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Affiliation(s)
- M A Griswold
- Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
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39
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Lövblad KO, Thomas R, Jakob PM, Scammell T, Bassetti C, Griswold M, Ives J, Matheson J, Edelman RR, Warach S. Silent functional magnetic resonance imaging demonstrates focal activation in rapid eye movement sleep. Neurology 1999; 53:2193-5. [PMID: 10599807 DOI: 10.1212/wnl.53.9.2193] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Functional imaging of human sleep has been performed with nuclear medicine methods, but MRI has been difficult to implement, in part because of the noise associated with echo-planar imaging as well as the difficulty in reading physiologic signals in the MRI environment. We describe a silent MR sequence that can record brain activation over many hours with simultaneous acquisition of an EEG. This shows activation of occipital cortex and deactivation of frontal cortex during REM sleep, in agreement with previous studies using other techniques. MRI-Sleep-REM sleep.
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Affiliation(s)
- K O Lövblad
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
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40
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Chen Q, Levin DL, Kim D, David V, McNicholas M, Chen V, Jakob PM, Griswold MA, Goldfarb JW, Hatabu H, Edelman RR. Pulmonary disorders: ventilation-perfusion MR imaging with animal models. Radiology 1999; 213:871-9. [PMID: 10580969 DOI: 10.1148/radiology.213.3.r99dc31871] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To demonstrate the capability of magnetic resonance (MR) imaging to assess alteration in regional pulmonary ventilation and perfusion with animal models of airway obstruction and pulmonary embolism. MATERIALS AND METHODS Airway obstruction was created by inflating a 5-F balloon catheter into a secondary bronchus. Pulmonary emboli were created by injecting thrombi into the inferior vena cava. Regional pulmonary ventilation was assessed with 100% oxygen as a T1 contrast agent. Regional pulmonary perfusion was assessed with a two-dimensional fast low-angle shot, or FLASH, sequence with short repetition and echo times after intravenous administration of gadopentetate dimeglumine. RESULTS Matched ventilation and perfusion abnormalities were identified in all animals with airway obstruction. MR perfusion defects without ventilation abnormalities were seen in all animals with pulmonary emboli. CONCLUSION Ventilation and perfusion MR imaging are able to provide regional pulmonary functional information with high spatial and temporal resolution. The ability of MR imaging to assess both the magnitude and regional distribution of pulmonary functional impairment could have an important effect on the evaluation of lung disease.
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Affiliation(s)
- Q Chen
- Dept of Radiology, Beth Israel Deaconess Medical Center, Boston, MA 02215 USA.
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41
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Griswold MA, Jakob PM, Chen Q, Goldfarb JW, Manning WJ, Edelman RR, Sodickson DK. Resolution enhancement in single-shot imaging using simultaneous acquisition of spatial harmonics (SMASH). Magn Reson Med 1999; 41:1236-45. [PMID: 10371457 DOI: 10.1002/(sici)1522-2594(199906)41:6<1236::aid-mrm21>3.0.co;2-t] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Spatial resolution in single-shot imaging is limited by signal attenuation due to relaxation of transverse magnetization. This effect can be reduced by minimizing acquisition times through the use of short interecho spacings. However, the minimum interecho spacing is constrained by limits on gradient switching rates, radiofrequency (RF) power deposition and RF pulse length. Recently, simultaneous acquisition of spatial harmonics (SMASH) has been introduced as a method to acquire magnetic resonance images at increased speeds using a reduced number of phase-encoding gradient steps by extracting spatial information contained in an RF coil array. In this study, it is shown that SMASH can be used to reduce the effects of relaxation, resulting in single-shot images with increased spatial resolution without increasing imaging time. After a brief theoretical discussion, two strategies to reduce signal attenuation and increase spatial resolution in single-shot imaging are introduced and their performance is evaluated in phantom studies. In vivo single-shot echoplanar imaging (EPI), BURST, and half-Fourier single-shot turbo spin-echo (HASTE) images are then presented demonstrating the practical implementation of these resolution enhancement strategies. Images acquired with SMASH show increased spatial resolution and improved image quality when compared with images obtained with the conventional acquisitions. The general principles presented for imaging with SMASH can also be applied to other partially parallel imaging techniques.
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Affiliation(s)
- M A Griswold
- Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
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42
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Sodickson DK, Griswold MA, Jakob PM. SMASH imaging. Magn Reson Imaging Clin N Am 1999; 7:237-54, vii-viii. [PMID: 10382159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
SMASH imaging is a new MR imaging technique that can be used to multiply the speed of existing imaging sequences. It operates by using an array of radiofrequency (RF) detection coils to perform some of the spatial encoding normally accomplished with magnetic field gradients. The speed of the SMASH technique results from appropriate combinations of coil array RF signals in which multiple lines of image data are gathered simultaneously, rather than one after another. SMASH can be used in conjunction with most rapid imaging sequences, including EPI, resulting in multiplicative gains in imaging speed. This article reviews the basic principles of SMASH imaging, outlines requirements for practical implementation, and presents a variety of in vivo results, highlighting ways in which SMASH may be used to increase imaging speed and to improve image quality for clinical MR imaging applications.
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Affiliation(s)
- D K Sodickson
- Department of Medicine, Harvard University Medical School, Boston, Massachusetts, USA.
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43
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Abstract
A general theory of signal-to-noise ratio (SNR) in simultaneous acquisition of spatial harmonics (SMASH) imaging is presented, and the predictions of the theory are verified in imaging experiments and in numerical simulations. In a SMASH image, multiple lines of k-space are generated simultaneously through combinations of magnetic resonance signals in a radiofrequency coil array. Here, effects of noise correlations between array elements as well as new correlations introduced by the SMASH reconstruction procedure are assessed. SNR and SNR efficiency in SMASH images are compared with results using traditional array combination strategies. Under optimized conditions, SMASH achieves the same average SNR efficiency as ideal pixel-by-pixel array combinations, while allowing imaging to proceed at otherwise unattainable speeds. The k-space nature of SMASH reconstructions can lead to oscillatory spatial variations in noise standard deviation, which can produce local enhancements of SNR in particular regions.
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Affiliation(s)
- D K Sodickson
- Charles A. Dana Research Institute and Harvard-Thorndike Laboratory of the Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.
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44
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Abstract
The current work is a continuation of a new MRI technique that was proposed for the non-invasive assessment of regional lung ventilation using inhaled molecular oxygen as a T1 contrast agent. Several improvements of this technique are described in this work. The signal-to-noise ratio in the ventilation-scan images was optimized using a centrically reordered single-shot RARE sequence with a short effective echo time and short inter-echo spacing. The contrast-to-noise ratio was improved using an optimized inversion delay time. The optimized MR-ventilation-scan was successfully performed in healthy volunteers and in an animal model with airway obstruction. The experimental results demonstrate the feasibility and clinical potential of the MR ventilation imaging technique for assessment of regional pulmonary function.
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Affiliation(s)
- Q Chen
- Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
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45
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Jakob PM, Griswold MA, Edelman RR, Sodickson DK. AUTO-SMASH: a self-calibrating technique for SMASH imaging. SiMultaneous Acquisition of Spatial Harmonics. MAGMA 1998; 7:42-54. [PMID: 9877459 DOI: 10.1007/bf02592256] [Citation(s) in RCA: 184] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Recently a new fast magnetic resonance imaging strategy, SMASH, has been described, which is based on partially parallel imaging with radiofrequency coil arrays. In this paper, an internal sensitivity calibration technique for the SMASH imaging method using self-calibration signals is described. Coil sensitivity information required for SMASH imaging is obtained during the actual scan using correlations between undersampled SMASH signal data and additionally sampled calibration signals with appropriate offsets in k-space. The advantages of this sensitivity reference method are that no extra coil array sensitivity maps have to be acquired and that it provides coil sensitivity information in areas of highly non-uniform spin-density. This auto-calibrating approach can be easily implemented with only a small sacrifice of the overall time savings afforded by SMASH imaging. The results obtained from phantom imaging experiments and from cardiac studies in nine volunteers indicate that the self-calibrating approach is an effective method to increase the potential and the flexibility of rapid imaging with SMASH.
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Affiliation(s)
- P M Jakob
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
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Laubach HJ, Jakob PM, Loevblad KO, Baird AE, Bovo MP, Edelman RR, Warach S. A phantom for diffusion-weighted imaging of acute stroke. J Magn Reson Imaging 1998; 8:1349-54. [PMID: 9848751 DOI: 10.1002/jmri.1880080627] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A tissue phantom for diffusion-weighted imaging was developed, basing its contrast between two compartments on different apparent diffusion coefficients, without contrast due to T2 relaxation and proton density. These contrast properties of the phantom simulate the situation found in normal gray matter and areas of acute ischemia. A possible application of the phantom was demonstrated for the investigation of the accuracy of volume measurements based on diffusion-weighted images.
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Affiliation(s)
- H J Laubach
- Department of Neurology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
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Abstract
A quiet magnetic resonance (MR) imaging technique for detecting changes in cerebral activity functions is presented. This single-shot method, functional Burst imaging (FBI), combines elements of Burst imaging with an offset technique known as asymmetric spin echo (ASE). The FBI sequence has the unique feature of being nearly silent, because of the low number of gradient switching steps involved. Furthermore, this approach has the key advantage that it can be implemented on conventional MR systems. Established auditory and visual paradigms were used to evaluate whether FBI can detect changes in cerebral activity using a 1.5 Tesla MR system. In a second set of experiments, the FBI technique was used to evaluate cerebral activity changes during different sleep stages in humans. The results obtained demonstrate that the FBI sequence provides an alternative approach for functional imaging of brain activity in primary and secondary sensory areas of the human brain. Furthermore, in using this quiet MR technique, it was possible to scan continuously during different stages of human sleep without acoustic noise perturbation.
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Affiliation(s)
- P M Jakob
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA
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Abstract
Technical challenges of cardiac MRI include minimizing the effects of cardiac and respiratory motion and developing techniques that allow for both high spatial resolution and high SNR given the small size of small structures such as the coronary vessels. Fast imaging techniques provide considerable time savings and increased flexibility which allow to further optimize image quality.
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Affiliation(s)
- P M Jakob
- Physikalisches Institut der Universität Würzburg, Germany
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Jakob PM, Lövblad KO, Weber J, Laubach HJ, Remonda L, Gönner F, Heid O, Mattle HP, Schroth G, Edelman RR, Warach S. [Diffusion-weighted imaging in acute stroke]. Nervenarzt 1998; 69:683-93. [PMID: 9757420 DOI: 10.1007/s001150050329] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Magnetic resonance imaging represents today the most important tool in neuroradiology for both clinical practice and research. MRI allows imaging of the human body in 2 or 3 dimensions with variable tissue contrast. The natural diffusion of tissue protons can now be used as a supplementary contrast mechanism. Different MRI techniques can be used to obtain clinically useful diffusion-weighted images. These techniques all require the use of strong gradient pulses in order to obtain the diffusion contrast. In the current article, the most important physical principles of diffusion measurement are presented. After a short introduction into the basic physical principles, we will present the prerequisites and limitations of clinically relevant applications today. Finally a few select examples of clinical use of these techniques in the acute diagnosis of stroke will be presented.
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Affiliation(s)
- P M Jakob
- Radiology Department, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
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Lövblad KO, Jakob PM, Chen Q, Baird AE, Schlaug G, Warach S, Edelman RR. Turbo spin-echo diffusion-weighted MR of ischemic stroke. AJNR Am J Neuroradiol 1998; 19:201-8; discussion 209. [PMID: 9504466 PMCID: PMC8338180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
PURPOSE Our objective was to determine whether a multisection technique, diffusion-weighted half-Fourier single-shot turbo spin-echo (HASTE) imaging, can compensate for the drawbacks common to other diffusion-weighted techniques; specifically, the need for echo-planar technology and the presence of susceptibility artifacts in areas close to the skull base. METHODS Forty subjects who were referred to the stroke service with signs of acute (less than 24 hour) neurologic dysfunction were included in this prospective study. MR imaging of the brain was performed with diffusion-weighted echo-planar and diffusion-weighted HASTE sequences. The images obtained with both sequences were analyzed for the presence of hyperintensities corresponding to ischemic lesions as well as for the presence of image artifacts and distortions. RESULTS Diffusion-weighted HASTE images showed areas of hyperintensity corresponding to the infarcts present on diffusion-weighted echo-planar imaging studies without distortion or susceptibility artifacts in all the patients who had a stroke. Twelve patients had no acute ischemic lesions; of these, five had other findings, six had normal findings, and in one patient, a hyperintensity seen on diffusion-weighted echo-planar images proved to be an artifact on diffusion-weighted HASTE images. CONCLUSIONS Diffusion-weighted HASTE is equal to diffusion-weighted echo-planar imaging in the detection of early ischemia. Because of the absence of significant image distortions and other artifacts, diffusion-weighted HASTE permits fast multiplanar imaging in artifact-prone regions, such as the posterior fossa and the inferior frontal and temporal lobes. Diffusion imaging can be performed on conventional systems with strengths of 1.5 T that do not have echo-planar imaging capabilities.
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Affiliation(s)
- K O Lövblad
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Mass, USA
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