2024-03-29T04:46:43Z
http://eprints.drcmr.dk/cgi/oai2
oai:www.drcmr.dk:3
2010-04-02T00:05:17Z
7374617475733D707562
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7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
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7375626A656374733D493032:49303278393033
74797065733D7465616368696E675F7265736F75726365
Introduktion til teknikken bag MR-skanning
Hanson, Lars G.
Teaching
Magnetic Resonance Imaging
Medical Illustration
Magnetic Resonance Spectroscopy
Man kan optage billeder med en MR-skanner uden at forstå princippet bag, men det kræver forståelse at opsøge de rette parametre og målemetoder, og at fortolke billeder og artefakter. Teksten her udgør en introduktion til teknikken bag magnetisk resonans (MR) skanning. Dele er møntet på begyndere med et minimum af teknisk baggrund, mens andre dele sigter lidt højere. Dette afspejler, at noterne er skrevet i forbindelse med undervisning af personer med blandet baggrund.
DRCMR homepage
2004
Teaching Resource
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/3/1/Intro.pdf
http://www.drcmr.dk/Intro.pdf
Hanson, Lars G. (2004) Introduktion til teknikken bag MR-skanning. [Teaching Resource]
http://eprints.drcmr.dk/3/
oai:www.drcmr.dk:10
2008-06-28T18:38:09Z
7374617475733D707562
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
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7375626A656374733D493032:49303278393033
74797065733D61727469636C65
A graphical simulator for teaching basic and advanced MR imaging techniques.
Hanson, Lars G.
Teaching
Magnetic Resonance Imaging
Medical Illustration
Teaching of magnetic resonance (MR) imaging techniques typically involves considerable handwaving, literally, to explain concepts such as resonance, rotating frames, dephasing, refocusing, sequences, and imaging. A proper understanding of MR contrast and imaging techniques is crucial for radiologists, radiographers, and technical staff alike, but it is notoriously challenging to explain spin dynamics by using traditional teaching tools. The author developed a freely available graphical simulator based on the Bloch equations to aid in the teaching of topics ranging from precession and relaxation to advanced concepts such as stimulated echoes, spin tagging, and k-space-methods. A graphical user interface provides the user with a three-dimensional view of spin isochromates that can be manipulated by selecting radiofrequency pulses and gradient events. Even complicated sequences can be visualized in an intuitive way. The cross-platform software is primarily designed for use in lectures, but is also useful for self studies and student assignments. Movies available at http://radiographics.rsnajnls.org/cgi/content/full/e27/DC1.
Radiological Society of North America, Inc (RSNA)
2007-08-10
Article
PeerReviewed
http://radiographics.rsnajnls.org/cgi/content/abstract/27/6/e27
Hanson, Lars G. (2007) A graphical simulator for teaching basic and advanced MR imaging techniques. Radiographics, 27 (6). e27. ISSN 1527-1323
http://eprints.drcmr.dk/10/
oai:www.drcmr.dk:18
2010-04-02T00:05:21Z
7374617475733D707562
7375626A656374733D453031:45303178333730:4530317833373078333736:453031783337307833373678333030
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030:45303178333730783335307835303078323030
7375626A656374733D453035:45303578303437
74797065733D61727469636C65
Encoding of electrophysiology and other signals in MR images.
Hanson, Lars G
Lund, Torben E
Hanson, Christian G
Electroencephalography
Echo-Planar Imaging
Artifacts
PURPOSE: To develop a gradient insensitive, generic technique for recording of non-MR signals by use of surplus scanner bandwidth. MATERIALS AND METHODS: Relatively simple battery driven hardware is used to transform one or more signals into radio waves detectable by the MR scanner. Similar to the "magstripe" technique used for encoding of soundtracks in motion pictures, the electrical signals are in this way encoded as artifacts appearing in the MR images or spectra outside the region of interest. The encoded signals are subsequently reconstructed from the signal recorded by the scanner. RESULTS: Electrophysiological (EP) eye and heart muscular recording (electrooculography [EOG] and electrocardiography [ECG]) during fast echo planar imaging (EPI) is demonstrated with an expandable, modular 8-channel prototype implementation. The gradient artifacts that would normally be dominating EOG are largely eliminated. CONCLUSION: The method provides relatively inexpensive sampling with inherent microsecond synchronization and it reduces gradient artifacts in physiological recordings significantly. When oversampling is employed, the method is compatible with all MR reconstruction and postprocessing techniques.
Wiley InterScience
2007
Article
PeerReviewed
application/pdf
http://eprints.drcmr.dk/18/1/article.pdf
http://dx.doi.org/10.1002/jmri.20906
Hanson, Lars G and Lund, Torben E and Hanson, Christian G (2007) Encoding of electrophysiology and other signals in MR images. Journal of Magnetic Resonance Imaging : JMRI, 25 (5). pp. 1059-66. ISSN 1053-1807
http://eprints.drcmr.dk/18/
oai:www.drcmr.dk:19
2010-04-02T00:05:23Z
7374617475733D707562
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7375626A656374733D453035:45303578313936:4530357831393678383637:453035783139367838363778353139
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078383235:45303178333730783335307838323578353030:4530317833373078333530783832357835303078323030
74797065733D61727469636C65
Reconstruction strategy for echo planar spectroscopy and its application to partially undersampled imaging.
Hanson, L G
Schaumburg, K
Paulson, O B
Metabolism
Magnetic Resonance Spectroscopy
Echo-Planar Imaging
The most commonly encountered form of echo planar spectroscopy involves oscillating gradients in one spatial dimension during readout. Data are consequently not sampled on a Cartesian grid. A fast gridding algorithm applicable to this particular situation is presented. The method is optimal, i.e., it performs as well as the full discrete Fourier transform for band limited signals while allowing for use of the fast Fourier transform. The method is demonstrated for reconstruction of data that are partially undersampled in the time domain. The advantages of undersampling are lower hardware requirements or fewer interleaves per acquisition. The method is of particular interest when large bandwidths are needed (e.g., for high field scanning) and for scanners with limited gradient performance. The unavoidable artifacts resulting from undersampling are demonstrated to be acceptable for spectroscopy with long echo times.
Wiley InterScience
2000
Article
PeerReviewed
application/pdf
http://eprints.drcmr.dk/19/1/article.pdf
http://dx.doi.org/10.1002/1522-2594(200009)44:3%3C412::AID-MRM11%3E3.0.CO;2-P
Hanson, L G and Schaumburg, K and Paulson, O B (2000) Reconstruction strategy for echo planar spectroscopy and its application to partially undersampled imaging. Magnetic Resonance in Medicine, 44 (3). pp. 412-7. ISSN 0740-3194
http://eprints.drcmr.dk/19/
oai:www.drcmr.dk:20
2010-04-02T00:05:24Z
7374617475733D707562
7375626A656374733D453035:45303578313936:4530357831393678383637:453035783139367838363778353139
7375626A656374733D473036:47303678353335
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
74797065733D61727469636C65
Optimal voxel size for measuring global gray and white matter proton metabolite concentrations using chemical shift imaging.
Hanson, L G
Adalsteinsson, E
Pfefferbaum, A
Spielman, D M
Metabolism
Magnetic Resonance Imaging
Magnetic Resonance Spectroscopy
Quantification of gray and white matter levels of spectroscopically visible metabolites can provide important insights into brain development and pathological conditions. Chemical shift imaging offers a gain in efficiency for estimation of global gray and white matter metabolite concentrations compared to single voxel methods. In the present study, the optimal voxel size is calculated from segmented human brain data and accompanying field maps. The optimal voxel size is found to be approximately 8 cc, but a wide range of values, 4-64 cc, can be chosen with little increase in estimated concentration error (<15%). Magn Reson Med 44:10-18, 2000.
Wiley InterScience
2000
Article
PeerReviewed
application/pdf
http://eprints.drcmr.dk/20/1/article3.pdf
http://dx.doi.org/10.1002/1522-2594(200007)44:1%3C10::AID-MRM3%3E3.0.CO;2-8
Hanson, L G and Adalsteinsson, E and Pfefferbaum, A and Spielman, D M (2000) Optimal voxel size for measuring global gray and white matter proton metabolite concentrations using chemical shift imaging. Magnetic Resonance in Medicine: MRM, 44 (1). pp. 10-8. ISSN 0740-3194
http://eprints.drcmr.dk/20/
oai:www.drcmr.dk:21
2010-04-02T08:24:07Z
7374617475733D707562
7375626A656374733D483031:48303178363731:4830317836373178373638:483031783637317837363878363338:48303178363731783736387836333878373231
7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
74797065733D61727469636C65
MR-skanning: Billeder fra den forbudte side af bølgelængdegrænsen
Hanson, Lars G.
Magnetic Resonance Imaging
Radio Waves
Magnetic Resonance Spectroscopy
Det er velkendt at almindelige optiske teknikker som mikroskopi og gennemlysning er bølgelængebegrænsede: På grund af lysets diffraktion ses ingen detaljer, der er mindre end bølgeængden af det anvendte lys. Ikke desto mindre er Magnetisk Resonans (MR) billeddannelse nu en udbredt skanningsmetode, der giver yderst detaljerede billeder af kroppens indre trods brug af bølgelængder i størrelsesorden meter. I 2002 blev en Nobelpris for klassisk MR billeddannelse givet til Paul Lauterbur og Sir Peter Mansfield. I de senere år har endnu en metode til at omgå bølgelængde-begrænsningen vundet stor indpas. Artiklen introducerer kernemagnetisk resonans (NMR) og de vigtigste billeddannelsesprincipper.
Niels Bohr Institute, University of Copenhagen
2006
Article
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/21/1/artikel.pdf
http://www.gamma.nbi.dk/
Hanson, Lars G. (2006) MR-skanning: Billeder fra den forbudte side af bølgelængdegrænsen. Gamma - tidsskrift for fysik (143). pp. 8-26. ISSN 0108-0954
http://eprints.drcmr.dk/21/
oai:www.drcmr.dk:22
2010-04-02T00:05:34Z
7374617475733D707562
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
7375626A656374733D4A3031:4A303178383937:4A30317838393778323830:4A3031783839377832383078353030:4A303178383937783238307835303078343830
7375626A656374733D493032:49303278393033:4930327839303378333032
74797065733D61727469636C65
Is Quantum Mechanics necessary for understanding Magnetic Resonance?
Hanson, Lars G.
Models, Educational
Magnetic Resonance Imaging
Medical Illustration
Magnetic Resonance Spectroscopy
Educational material introducing magnetic resonance typically contains sections on the underlying principles. Unfortunately the explanations given are often unnecessarily complicated or even wrong. Magnetic resonance is often presented as a phenomenon that necessitates a quantum mechanical explanation whereas it really is a classical effect, i.e. a consequence of the common sense expressed in classical mechanics. This insight is not new, but there have been few attempts to challenge common misleading explanations, so authors and educators are inadvertently keeping myths alive. As a result, new students' first encounters with magnetic resonance are often obscured by explanations that make the subject difficult to understand. Typical problems are addressed and alternative intuitive
explanations are provided.
Wiley InterScience
2008-09-03
Article
PeerReviewed
application/pdf
http://eprints.drcmr.dk/22/1/article.pdf
image/jpeg
http://eprints.drcmr.dk/22/2/MagSpherical2crop.jpg
image/jpeg
http://eprints.drcmr.dk/22/3/MagPrecession2.jpg
image/jpeg
http://eprints.drcmr.dk/22/4/MagEquilib2.jpg
image/jpeg
http://eprints.drcmr.dk/22/5/MagRotated2.jpg
http://www3.interscience.wiley.com/journal/121394126/abstract
Hanson, Lars G. (2008) Is Quantum Mechanics necessary for understanding Magnetic Resonance? Concepts in Magnetic Resonance Part A, 32A (5). pp. 329-340. ISSN 1546-6086
http://eprints.drcmr.dk/22/
oai:www.drcmr.dk:28
2010-04-02T00:05:41Z
7374617475733D707562
7375626A656374733D493032:49303278393033
7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
7375626A656374733D4A3031:4A303178383937:4A30317838393778323830:4A3031783839377832383078353030:4A303178383937783238307835303078343830
74797065733D7465616368696E675F7265736F75726365
Introduktion til teknikken bag MR-skanning
Hanson, Lars G.
Teaching
Magnetic Resonance Imaging
Medical Illustration
Magnetic Resonance Spectroscopy
Man kan optage billeder med en MR-skanner uden at forstå princippet bag, men det kræver forståelse at opsøge de rette parametre og målemetoder, og at fortolke billeder og artefakter. Teksten her udgør en introduktion til teknikken bag magnetisk resonans (MR) skanning. Dele er møntet på begyndere med et minimum af teknisk baggrund, mens andre dele sigter lidt højere. Dette afspejler, at noterne er skrevet i forbindelse med undervisning af personer med blandet baggrund.
DRCMR homepage
2009-01-23
Teaching Resource
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/28/4/Intro.pdf
http://www.drcmr.dk/Intro.pdf
Hanson, Lars G. (2009) Introduktion til teknikken bag MR-skanning. [Teaching Resource]
http://eprints.drcmr.dk/28/
oai:www.drcmr.dk:33
2010-04-02T08:42:07Z
7374617475733D707562
7375626A656374733D493032:49303278393033
7375626A656374733D4A3031:4A303178383937:4A30317838393778323830:4A3031783839377832383078353030:4A303178383937783238307835303078343830
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
74797065733D7465616368696E675F7265736F75726365
Introduktion til teknikken bag MR-skanning
Hanson, Lars G.
Teaching
Magnetic Resonance Imaging
Medical Illustration
Magnetic Resonance Spectroscopy
Man kan optage billeder med en MR-skanner uden at forstå princippet bag, men det kræver forståelse at opsøge de rette parametre og målemetoder, og at fortolke billeder og artefakter. Teksten her udgør en introduktion til teknikken bag magnetisk resonans (MR) skanning. Dele er møntet på begyndere med et minimum af teknisk baggrund, mens andre dele sigter højere. Dette afspejler, at noterne er skrevet i forbindelse med undervisning af personer med blandet baggrund.
DRCMR homepage
2009-05-26
Teaching Resource
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/33/3/Intro.pdf
http://www.drcmr.dk/Intro.pdf
Hanson, Lars G. (2009) Introduktion til teknikken bag MR-skanning. [Teaching Resource]
http://eprints.drcmr.dk/33/
oai:www.drcmr.dk:37
2010-04-02T00:05:51Z
7374617475733D707562
7375626A656374733D4A3031:4A303178383937:4A30317838393778323830:4A3031783839377832383078353030:4A303178383937783238307835303078343830
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
7375626A656374733D493032:49303278393033
74797065733D7465616368696E675F7265736F75726365
Introduction to Magnetic Resonance Imaging Techniques
Hanson, Lars G.
Teaching
Magnetic Resonance Imaging
Medical Illustration
Magnetic Resonance Spectroscopy
It is quite possible to acquire images with an MR scanner without understanding the principles behind it, but choosing the best parameters and methods, and interpreting images and artifacts, requires understanding. This text serves as an introduction to magnetic resonance imaging techniques. It is aimed at beginners in possession of only a minimal level of technical expertise, yet it introduces aspects of MR that are typically considered technically challenging. The notes were written in connection with teaching of audiences with mixed backgrounds.
2009-08-31
Teaching Resource
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/37/1/MRI_English_a4.pdf
application/pdf
http://eprints.drcmr.dk/37/2/MRI_English_letter.pdf
Hanson, Lars G. (2009) Introduction to Magnetic Resonance Imaging Techniques. [Teaching Resource]
http://eprints.drcmr.dk/37/
oai:www.drcmr.dk:39
2010-04-02T00:05:54Z
7374617475733D707562
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
7375626A656374733D493032:49303278393033
74797065733D636F6E666572656E63655F6974656D
The Bloch Simulator and Viewer - Free, interactive MRI visualisation
Hanson, Lars G.
Teaching
Magnetic Resonance Imaging
The Bloch Simulator is 3D graphical
software for visualising spin physics
and MRI techniques. It provides
demonstrations and exploration of
otherwise abstract concepts involved
in MRI. It is useful for students and
teachers alike and is available online
at no cost.
Phenomena such as precession, resonance,
excitation, inhomogeneity and
relaxation can be demonstrated. Likewise,
rotating frames, weightings,
spoilers, spin-echoes, simulated
echoes and more can be explored.
Finally, MR imaging concepts can be
demonstrated, e.g., how the similarity
between induced phase roll patterns
and the structures of the imaged
object is reflected in the MR signal.
2009-10-01
Conference or Workshop Item
PeerReviewed
application/pdf
http://eprints.drcmr.dk/39/1/Bloch_simulator_flyer_ESMRMB_2009.pdf
http://www.drcmr.dk/bloch
Hanson, Lars G. (2009) The Bloch Simulator and Viewer - Free, interactive MRI visualisation. In: Annual meeting of the European Society for Magnetic Resonance in Medicine and Biology, ESMRMB 2009, 1-3 Oct 2009, Belek, Turkey.
http://eprints.drcmr.dk/39/
oai:www.drcmr.dk:40
2010-04-02T00:05:55Z
7374617475733D707562
7375626A656374733D453031:45303178333730
7375626A656374733D4D3031:4D303178303630:4D30317830363078373033:4D3031783036307837303378353230
7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
7375626A656374733D453035:45303578313936:4530357831393678383637:453035783139367838363778353139
74797065733D61727469636C65
Motion correction of Single Voxel Spectroscopy by Independent Component Analysis applied to spectra from non-anesthetized pediatric subjects
de Nijs, Robin
Miranda, Maria J.
Hansen, Lars K
Hanson, Lars G.
Magnetic Resonance Spectroscopy
Infant, Newborn
Diagnostic Techniques and Procedures
Magnetic Resonance Spectroscopy
For Single Voxel Spectroscopy (SVS), the acquisition of the spectrum is typically repeated n times and then combined with a factor in order to improve the Signal-to-Noise Ratio (SNR). In practice the acquisitions are not only affected by random noise, but also by physiological motion and subject movements. Since the influence of physiological motion such as cardiac and respiratory motion on the data is limited, it can be compensated for without data-loss. Individual acquisitions hampered by subject movements on the other hand need to be rejected, if no correction or compensation is possible. If the individual acquisitions are stored, it is possible to identify and reject the motion-disturbed acquisitions before averaging.
Several automatic algorithms were investigated using a dataset of spectra from non-anesthetized infants with a gestational age of 40 weeks. Median filtering removed most subject movement artifacts, but at the cost of increased sensitivity to random noise. Neither Independent Component Analysis (ICA) nor outlier identification with multiple comparisons has this problem. These two algorithms are novel in this context. The peak height values of the metabolites were increased compared to the mean of all acquisitions for both methods, although primarily for the ICA method.
Wiley InterScience
2009-09-24
Article
PeerReviewed
application/pdf
http://eprints.drcmr.dk/40/1/Motion_rejection_01112009.pdf
de Nijs, Robin and Miranda, Maria J. and Hansen, Lars K and Hanson, Lars G. (2009) Motion correction of Single Voxel Spectroscopy by Independent Component Analysis applied to spectra from non-anesthetized pediatric subjects. Magnetic Resonance in Medicine, 62 (5). pp. 1147-1154. ISSN 0740-3194
http://eprints.drcmr.dk/40/
oai:www.drcmr.dk:41
2010-09-19T08:32:43Z
7374617475733D707562
7375626A656374733D453031:45303178333730:4530317833373078333530:453031783337307833353078353030
7375626A656374733D4A3031:4A303178383937
74797065733D61727469636C65
MR-skanning ved 7 tesla feltstyrke etableres i Danmark
Hanson, Lars G.
Magnetic Resonance Imaging
Technology
Igennem længere tid har en bred kreds
af forskere og klinikere på hospitaler
og universiteter [1] forsøgt at rejse de
nødvendige midler til at etablere ultrahøjfelts
MR-skanning i Danmark. I juni
2010 udløstes jubel, da “the John and
Birthe Meyer Foundation” meget generøst
bevilgede 38,6 Mkr til indkøb af en
human MR-skanner med en feltstyrke
på 7 tesla. Dette svarer til cirka 140
tusind gange jordens magnetfelt hvilket
mere end fordobler hospitalernes
hidtil kraftigste felter. Bevillingen supplerede
offentlig støtte på 27,4 Mkr fra
Forsknings- og Innovationsstyrelsens
infrastrukturmidler, og dermed er den
nødvendige kapital til etablering af en
7T facilitet ved MR-forskningscentret på
Hvidovre Hospital tilvejebragt. Ultimo
2011 kan brugere af MR-skanning i
Danmark se frem til væsentligt forbedrede
undersøgelser på en række områder,
og nye typer målinger, som ikke
er mulige ved lavere felt. Med fokus på
tekniske forhold beskrives her de unikke
muligheder og udfordringer, som skanning
ved 7T feltstyrke afstedkommer.
Der tages udgangspunkt i en kort generel
beskrivelse af MR.
Scanpublisher A/S
2010-08
Article
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/41/1/7T_Hanson_MTI_p20_n4_2010.pdf
http://www.e-pages.dk/scanpub/202/
Hanson, Lars G. (2010) MR-skanning ved 7 tesla feltstyrke etableres i Danmark. MTI - Medicinsk Teknologi & Informatik, 7 (4). pp. 20-22. ISSN 1901-4465
http://eprints.drcmr.dk/41/
oai:www.drcmr.dk:42
2010-12-02T11:47:36Z
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7375626A656374733D483031:48303178363731:4830317836373178353739:483031783637317835373978363331
7375626A656374733D453035:45303578313936:4530357831393678383637:453035783139367838363778353139
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7375626A656374733D4D3031:4D303178303630:4D30317830363078373033:4D3031783036307837303378353230
74797065733D746865736973
Corrections in clinical Magnetic Resonance Spectroscopy and SPECT: Motion correction in MR spectroscopy, downscatter correction in SPECT
de Nijs, Robin
Diagnostic Techniques and Procedures
Magnetic Resonance Spectroscopy
Magnetic Resonance Spectroscopy
Infant, Newborn
The quality of medical scanner data is often compromised by several mechanisms. This can be caused by both the subject to be measured and the scanning principles themselves. In this PhD project the problem of subject motion was addressed for Single Voxel MR Spectroscopy in a cohort study of preterm infants. In Iodine-123 SPECT the problem of downscatter was addressed. This thesis is based on two papers. Paper I deals with the problem of motion in Single Voxel Spectroscopy. Two novel methods for the identification of outliers in the set of repeated measurements were implemented and compared to the known mean and median filtering. The data comes from non-anesthetized preterm infants, where motion during scanning is a common problem. Both the novel outlier identification and the independent component analysis (ICA) perform satisfactory and better than the common mean and median filtering. ICA performed best in the sense that it recovered most of the lost peak height in the spectra. The ICA motion correction algorithm described in paper I and in this thesis was applied to a quantitative analysis of the Single Voxel Spectroscopy data from the cohort study of preterm infants. This analysis revealed that differences between term and preterm infants are not to be found in the concentrations of Lactate (caused by inflammation or hypoxia-ischemia) and/or NAA (caused by hypoxia-ischemia) as hypothesized before the cohort study. Instead choline levels were decreased in the preterm infants, which might indicate a detrimental effect of the extra-uterine environment on brain development. Paper II describes a method to correct for downscatter in low count Iodine-123 SPECT with a broad energy window above the normal imaging window. Both spatial dependency and weight factors were measured. As expected, the implicitly assumed weight factor of one for energy windows with equal width is slightly too low, due the presence of a backscatter peak in the energy spectrum coming from high-energy photons. The effect on the contrast was tested in 10 subjects and revealed a 20% increase in the specific binding ratio of the striatum due to downscatter correction. This makes the difference between healthy subjects and patients more profound. Downscatter in Iodine-123 SPECT is not the only deteriorating mechanism. Normal scatter compromises the images quality as well. Since scatter correction of SPECT-images also can be performed by the subtraction of an energy window, a method was developed to perform scatter and downscatter correction simultaneously. A phantom study has been performed, where the in paper II described downscatter correction was extended with scatter correction. This new combined correction was compared to the known Triple Energy Window (TEW) correction method. Results were satisfying and indicate that TEW is more correct from the physics point of view, while the in paper II described method extended with scatter correction gives reasonable results, but is far less noise sensitive than TEW.
2009-08
Thesis
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/42/1/phd221_rdn.pdf
de Nijs, Robin (2009) Corrections in clinical Magnetic Resonance Spectroscopy and SPECT: Motion correction in MR spectroscopy, downscatter correction in SPECT. PhD thesis, Technical University of Denmark.
http://eprints.drcmr.dk/42/
oai:www.drcmr.dk:46
2012-06-21T22:49:49Z
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An active learning approach to education in MRI technology for the biomedical engineering curriculum
Hanson, Lars G.
Magnetic Resonance Imaging
Teaching
It is challenging to give students an intuitive understanding of the basic magnetic resonance phenomenon and a sample of the many MRI techniques. Whereas compact mathematical descriptions of MRI techniques can be made, students are typically left with no intuitive understanding unless the common sense expressed in the math is in focus. Unfortunately, the nuclear dynamics happen in four dimensions, and are therefore not well suited for illustration on blackboard. 3D movies are more appropriate, but they do not encourage active learning. The typical solution employed by educators is hand waving (literally), since arm motions can to a limited extent be used to illustrate nuclear dynamics. Many students find this confusing, however, and students who do not grasp the meaning during lectures, are left in a bad position. For this reason, educational software was developed over the last decade (the Bloch Simulator). It is freely available and can be run directly from the software homepage that also links to YouTube software presentations aimed at educators and students who have already gotten a first introduction to MRI concepts. The software is mainly aimed at educators for interactive demonstration of MRI techniques but can also be used for student exercises which may significantly improve the understanding of MRI concepts. The presentation demonstrates software made for the first few minutes of MRI education but focuses mostly on the educational value of the more advanced Bloch Simulator. It is explored how, and to what extent, active learning based on the software may improve student understanding. An interactive teaching session on advanced topics (pulse types, the Fourier relationship, selectivity) was evaluated using pre- and post-lecture anonymous questionnaires. These are challenging and significant subjects, and it was hypothesized that the approach may improve student understanding considerably. Though rigorous testing of the benefit over traditional teaching was not within the scope of the project, indications of improved skills were found, and the student satisfaction was excellent.
2012-06-20
Conference or Workshop Item
PeerReviewed
application/pdf
http://eprints.drcmr.dk/46/1/HansonALE2012.pdf
Hanson, Lars G. (2012) An active learning approach to education in MRI technology for the biomedical engineering curriculum. In: 11th Active Learning in Engineering Education workshop (ALE 2012), June 20th-22nd, 2012, Copenhagen, Denmark.
http://eprints.drcmr.dk/46/
oai:www.drcmr.dk:47
2012-09-09T09:57:27Z
7374617475733D707562
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74797065733D636F6E666572656E63655F6974656D
MRI safety in practice: The EU directive on work in electromagnetic fields – practical
and clinical aspects
Hanson, Lars G.
Magnetic Resonance Imaging
The current paper addresses the practical consequences of the EU directive 2004/40/EC
passed in 2004 concerning protection of workers from electromagnetic fields (EMF). These
consequences were evaluated in detail only after the directive was passed, and they were
found to be severe. Consequently, the directive has not yet been implemented fully in the EU
member state's legislation, and a revision is expected before this happens in October 2013,
the latest. The revised directive is expected to be based on revised recommendations of
the International Commission on Non-Ionizing Radiation Protection (ICNIRP), and may in
other ways limit the detrimental consequences for MRI, but this is uncertain. Hence the
presented summary of consequences is based mainly on the current directive, representing a
realistic worst-case scenario, except for a static field limit that will likely be introduced in a
revised directive. An estimated 5-8% of current examinations will be severely affected. The
inadvertent effects include reduced access to interventional MRI, and to procedures involving
personnel in the scanner rooms during scanning, e.g paediatric examinations, and scanning
conducted under anaesthesia. Other consequences are increased use of alternative imaging
modalities including X-ray based techniques, hindered development of improved MRI
techniques, and general consequences of increased complexity and cost.
2012-09
Conference or Workshop Item
NonPeerReviewed
application/pdf
http://eprints.drcmr.dk/47/1/ISMRM_safety_Hanson_2012.pdf
application/pdf
http://eprints.drcmr.dk/47/4/ISMRMsafety2012Hanson.pdf
Hanson, Lars G. (2012) MRI safety in practice: The EU directive on work in electromagnetic fields – practical and clinical aspects. In: ISMRM Safety Workshop 2012, 5-8 Sep 2012, Lund, Sweden.
http://eprints.drcmr.dk/47/