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Influence of blood/tissue differences in contrast agent relaxivity on tracer based MR perfusion measurements
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Radiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Thoracic Surgery.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
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2015 (English)In: Magnetic Resonance Materials in Physics, Biology and Medicine, ISSN 0968-5243, E-ISSN 1352-8661, Vol. 28, no 2, 135-147 p.Article in journal (Refereed) Published
Abstract [en]

PURPOSE:

Perfusion assessment by monitoring the transport of a tracer bolus depends critically on conversion of signal intensity into tracer concentration. Two main assumptions are generally applied for this conversion; (1) contrast agent relaxivity is identical in blood and tissue, (2) change in signal intensity depends only on the primary relaxation effect. The purpose of the study was to assess the validity and influence of these assumptions.

MATERIALS AND METHODS:

Blood and cerebral tissue relaxivities r1, r2, and r2* for gadodiamide were measured in four pigs at 1.5 T. Gadolinium concentration was determined by inductively coupled plasma atomic emission spectroscopy. Influence of the relaxivities, secondary relaxation effects and choice of singular value decomposition (SVD) regularization threshold was studied by simulations.

RESULTS:

In vivo relaxivities relative to blood concentration [in s-1 mM-1 for blood, gray matter (GM), white matter (WM)] were for r1 (2.614 ± 1.061, 0.010 ± 0.001, 0.004 ± 0.002), r2 (5.088 ± 0.952, 0.091 ± 0.008, 0.059 ± 0.014), and r2* (13.292 ± 3.928, 1.696 ± 0.157, 0.910 ± 0.139). Although substantial, by a nonparametric test for paired samples, the differences were not statistically significant. The GM to WM blood volume ratio was estimated to 2.6 ± 0.9 by r1, 1.6 ± 0.3 by r2, and 1.9 ± 0.2 by r2*. Secondary relaxation was found to reduce the tissue blood flow, as did the SVD regularization threshold.

CONCLUSION:

Contrast agent relaxivity is not identical in blood and tissue leading to substantial errors. Further errors are introduced by secondary relaxation effects and the SVD regularization.

Place, publisher, year, edition, pages
2015. Vol. 28, no 2, 135-147 p.
Keyword [en]
MRI, relaxivity, contrast agent, perfusion
National Category
Radiology, Nuclear Medicine and Medical Imaging Analytical Chemistry
Research subject
Radiology; Medical Radiophysics
Identifiers
URN: urn:nbn:se:uu:diva-170528DOI: 10.1007/s10334-014-0452-5ISI: 000352149200004OAI: oai:DiVA.org:uu-170528DiVA: diva2:512718
Available from: 2012-03-28 Created: 2012-03-12 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Quantitative Tracer Based MRI Perfusion: Potentials and Limitations
Open this publication in new window or tab >>Quantitative Tracer Based MRI Perfusion: Potentials and Limitations
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tracer based MRI perfusion measurements is a clinically useful tool to assess regional distributions of tissue blood flow and volume. The method may be based on any of the three relaxation mechanisms T1, T1 and T2*, the latter denoted DSC-MRI being the most common. The primary aim of this work was to study the feasibility of obtaining quantitative estimates using these methods.

1) Feasibility of DSC-MRI for kidneys using an iron oxide based contrast agent and the influence of secondary relaxation effects on the results, part of a clinical phase II trial: The method proved feasible and the underestimation induced by secondary relaxation can be corrected for by using a double echo sequence.

2) Influence of blood flow rate on risk factors for developing cerebral ischemia during cardio pulmonary bypass, measurements in pig with gadolinium based DSC-MRI: The results indicated an ischemic threshold level at a blood flow rate of approximately 6 ml/kg/min.

3) The ability of gadolinium based DSC-MRI to detect changes in global blood flow, experimental measurements in pig and numerical simulations: The results support that DSC-MRI can discriminate between global flow levels in the same subject given that all other parameters are kept constant. The results also indicate that calculated perfusion values are highly sensitive to the arterial deconvolution procedure.

4) Influence of differences in blood/tissue relaxivity and secondary relaxation for a gadolinium based contrast agent, measurements in pig and numerical simulations: The blood/tissue relaxivity ratio is not unity and the situation is complicated by secondary relaxation effects. Deconvolution regularization appears to partly counteract the overestimation induced by difference in blood/tissue relaxivity for DSC-MRI.

In summary, the fundamental assumption of equal blood and tissue relaxivity is experimentally shown to be invalid and the influence of this discrepancy is substantial. Several factors contribute to measurement errors, a combination of these factors can incidentally lead to additive errors or error cancellation based on a variety of experimental and analysis conditions. Given that the differences in blood/tissue relaxivity cannot readily be accounted for in a clinical setting, absolute perfusion quantification by tracer based MRI remains challenging if not impossible.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 761
Keyword
MRI, Perfusion, Contrast agent, Relaxivity
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Radiology
Identifiers
urn:nbn:se:uu:diva-171901 (URN)978-91-554-8330-2 (ISBN)
Public defence
2012-05-16, Auditorium Minus, Museum Gustavianum, Akademigatan 3, Uppsala, 09:15 (Swedish)
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Supervisors
Available from: 2012-04-25 Created: 2012-03-29 Last updated: 2012-08-01Bibliographically approved

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Morell, ArvidLennmyr, FredrikJonsson, OveTovedal, ThomasPettersson, JeanBergquist, JonasThelin, StefanAhlström, HåkanBjørnerud, Atle

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Magnetic Resonance Materials in Physics, Biology and Medicine
Radiology, Nuclear Medicine and Medical ImagingAnalytical Chemistry

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