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Influence of blood/tissue differences in contrast agent relaxivity on tracer based MR perfusion measurements
Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi.
Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Anestesiologi och intensivvård.
Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Thoraxkirurgi.
Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Anestesiologi och intensivvård.
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2015 (Engelska)Ingår i: Magnetic Resonance Materials in Physics, Biology and Medicine, ISSN 0968-5243, E-ISSN 1352-8661, Vol. 28, nr 2, s. 135-147Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
2015. Vol. 28, nr 2, s. 135-147
Nyckelord [en]
MRI, relaxivity, contrast agent, perfusion
Nationell ämneskategori
Radiologi och bildbehandling Analytisk kemi
Forskningsämne
Radiologi; Medicinsk radiofysik
Identifikatorer
URN: urn:nbn:se:uu:diva-170528DOI: 10.1007/s10334-014-0452-5ISI: 000352149200004OAI: oai:DiVA.org:uu-170528DiVA, id: diva2:512718
Tillgänglig från: 2012-03-28 Skapad: 2012-03-12 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
Ingår i avhandling
1. Quantitative Tracer Based MRI Perfusion: Potentials and Limitations
Öppna denna publikation i ny flik eller fönster >>Quantitative Tracer Based MRI Perfusion: Potentials and Limitations
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2012. s. 67
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 761
Nyckelord
MRI, Perfusion, Contrast agent, Relaxivity
Nationell ämneskategori
Radiologi och bildbehandling
Forskningsämne
Radiologi
Identifikatorer
urn:nbn:se:uu:diva-171901 (URN)978-91-554-8330-2 (ISBN)
Disputation
2012-05-16, Auditorium Minus, Museum Gustavianum, Akademigatan 3, Uppsala, 09:15 (Svenska)
Opponent
Handledare
Tillgänglig från: 2012-04-25 Skapad: 2012-03-29 Senast uppdaterad: 2012-08-01Bibliografiskt granskad

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

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Morell, ArvidLennmyr, FredrikJonsson, OveTovedal, ThomasPettersson, JeanBergquist, JonasThelin, StefanAhlström, HåkanBjørnerud, Atle
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RadiologiAnestesiologi och intensivvårdThoraxkirurgiAnalytisk kemi
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Magnetic Resonance Materials in Physics, Biology and Medicine
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