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MRI-based attenuation correction for PET/MRI using ultrashort echo time sequences

Vincent Keereman UGent, Yves Fierens, Tom Broux, Yves De Deene UGent, Max Lonneux and Stefaan Vandenberghe UGent (2010) JOURNAL OF NUCLEAR MEDICINE. 51(5). p.812-818
abstract
One of the challenges in PET/MRI is the derivation of an attenuation map to correct the PET image for attenuation. Different methods have been suggested for deriving the attenuation map from an MR image. Because the low signal intensity of cortical bone on images acquired with conventional MRI sequences makes it difficult to detect this tissue type, these methods rely on some sort of anatomic precondition to predict the attenuation map, raising the question of whether these methods will be usable in the clinic when patients may exhibit anatomic abnormalities. Methods: We propose the use of the transverse relaxation rate, derived from images acquired with an ultrashort echo time sequence to classify the voxels into 1 of 3 tissue classes (bone, soft tissue, or air), without making any assumptions on patient anatomy. Each voxel is assigned a linear attenuation coefficient corresponding to its tissue class. A reference CT scan is used to determine the voxel-by-voxel accuracy of the proposed method. The overall accuracy of the MRI-based attenuation correction is evaluated using a method that takes into account the nonlocal effects of attenuation correction. Results: As a proof of concept, the head of a pig was used as a phantom for imaging. The new method yielded a correct tissue classification in 90% of the voxels. Five human brain PET/CT and MRI datasets were also processed, yielding slightly worse voxel-by-voxel performance, compared to a CT-derived attenuation map. The PET datasets were reconstructed using the segmented MRI attenuation map derived with the new method, and the resulting images were compared with segmented CT-based attenuation correction. An average error of around 5% was found in the brain. Conclusion: The feasibility of using the transverse relaxation rate map derived from ultrashort echo time MR images for the estimation of the attenuation map was shown on phantom and clinical brain data. The results indicate that the new method, compared with CT-based attenuation correction, yields clinically acceptable errors. The proposed method does not make any assumptions about patient anatomy and could therefore also be used in cases in which anatomic abnormalities are present.
Please use this url to cite or link to this publication:
author
organization
year
type
journalArticle (original)
publication status
published
subject
keyword
MAGNETIC-RESONANCE, SCANNER, attenuation correction, PET/MRI, R2, UTE, TOMOGRAPHY, BRAIN, PET
journal title
JOURNAL OF NUCLEAR MEDICINE
J. Nucl. Med.
volume
51
issue
5
pages
812 - 818
Web of Science type
Article
Web of Science id
000277239000026
JCR category
RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING
JCR impact factor
7.022 (2010)
JCR rank
1/111 (2010)
JCR quartile
4 (2010)
ISSN
0161-5505
DOI
10.2967/jnumed.109.065425
language
English
UGent publication?
yes
classification
A1
copyright statement
I have transferred the copyright for this publication to the publisher
id
1165603
handle
http://hdl.handle.net/1854/LU-1165603
date created
2011-02-23 10:19:53
date last changed
2015-06-17 09:27:06
@article{1165603,
  abstract     = {One of the challenges in PET/MRI is the derivation of an attenuation map to correct the PET image for attenuation. Different methods have been suggested for deriving the attenuation map from an MR image. Because the low signal intensity of cortical bone on images acquired with conventional MRI sequences makes it difficult to detect this tissue type, these methods rely on some sort of anatomic precondition to predict the attenuation map, raising the question of whether these methods will be usable in the clinic when patients may exhibit anatomic abnormalities. Methods: We propose the use of the transverse relaxation rate, derived from images acquired with an ultrashort echo time sequence to classify the voxels into 1 of 3 tissue classes (bone, soft tissue, or air), without making any assumptions on patient anatomy. Each voxel is assigned a linear attenuation coefficient corresponding to its tissue class. A reference CT scan is used to determine the voxel-by-voxel accuracy of the proposed method. The overall accuracy of the MRI-based attenuation correction is evaluated using a method that takes into account the nonlocal effects of attenuation correction. Results: As a proof of concept, the head of a pig was used as a phantom for imaging. The new method yielded a correct tissue classification in 90\% of the voxels. Five human brain PET/CT and MRI datasets were also processed, yielding slightly worse voxel-by-voxel performance, compared to a CT-derived attenuation map. The PET datasets were reconstructed using the segmented MRI attenuation map derived with the new method, and the resulting images were compared with segmented CT-based attenuation correction. An average error of around 5\% was found in the brain. Conclusion: The feasibility of using the transverse relaxation rate map derived from ultrashort echo time MR images for the estimation of the attenuation map was shown on phantom and clinical brain data. The results indicate that the new method, compared with CT-based attenuation correction, yields clinically acceptable errors. The proposed method does not make any assumptions about patient anatomy and could therefore also be used in cases in which anatomic abnormalities are present.},
  author       = {Keereman, Vincent and Fierens, Yves and Broux, Tom and De Deene, Yves and Lonneux, Max and Vandenberghe, Stefaan},
  issn         = {0161-5505},
  journal      = {JOURNAL OF NUCLEAR MEDICINE},
  keyword      = {MAGNETIC-RESONANCE,SCANNER,attenuation correction,PET/MRI,R2,UTE,TOMOGRAPHY,BRAIN,PET},
  language     = {eng},
  number       = {5},
  pages        = {812--818},
  title        = {MRI-based attenuation correction for PET/MRI using ultrashort echo time sequences},
  url          = {http://dx.doi.org/10.2967/jnumed.109.065425},
  volume       = {51},
  year         = {2010},
}

Chicago
Keereman, Vincent, Yves Fierens, Tom Broux, Yves De Deene, Max Lonneux, and Stefaan Vandenberghe. 2010. “MRI-based Attenuation Correction for PET/MRI Using Ultrashort Echo Time Sequences.” Journal of Nuclear Medicine 51 (5): 812–818.
APA
Keereman, V., Fierens, Y., Broux, T., De Deene, Y., Lonneux, M., & Vandenberghe, S. (2010). MRI-based attenuation correction for PET/MRI using ultrashort echo time sequences. JOURNAL OF NUCLEAR MEDICINE, 51(5), 812–818.
Vancouver
1.
Keereman V, Fierens Y, Broux T, De Deene Y, Lonneux M, Vandenberghe S. MRI-based attenuation correction for PET/MRI using ultrashort echo time sequences. JOURNAL OF NUCLEAR MEDICINE. 2010;51(5):812–8.
MLA
Keereman, Vincent, Yves Fierens, Tom Broux, et al. “MRI-based Attenuation Correction for PET/MRI Using Ultrashort Echo Time Sequences.” JOURNAL OF NUCLEAR MEDICINE 51.5 (2010): 812–818. Print.