2024-03-28T11:44:57Z
http://eprints.drcmr.dk/cgi/oai2
oai:www.drcmr.dk:40
2010-04-02T00:05:55Z
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http://eprints.drcmr.dk/40/
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/http://eprints.drcmr.dk/40/1/
oai:www.drcmr.dk:42
2010-12-02T11:47:36Z
7374617475733D756E707562
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7375626A656374733D453035:45303578313936:4530357831393678383637:453035783139367838363778353139
7375626A656374733D453031:45303178333730
7375626A656374733D4D3031:4D303178303630:4D30317830363078373033:4D3031783036307837303378353230
74797065733D746865736973
http://eprints.drcmr.dk/42/
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/http://eprints.drcmr.dk/42/1/