Intravascular susceptibility agent effects on tissue transverse relaxation rates in vivo

Johnson, Kevin; Tao, Jing; Kennan, Richard P.; Gore, John C.

doi:10.1002/1522-2594(200012)44:6<909::aid-mrm12>3.3.co;2-l

Cited by 5 publications

(15 citation statements)

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supporting

confidence: 81%

“…The integration over d in Eq. [3] performs the averaging over the isotropically distributed population of vessels. In a similar way this expression should be averaged for a given distribution of vessel radii (11).…”

Section: Analytical Description Of Relaxation In Extravascular Spacementioning

confidence: 99%

“…The transverse relaxation in blood doped with contrast agents has been investigated in a number of studies (3,6,9,10). The tracer-induced increase in the relaxation in blood was found to differ from that in organs (3,6) and to depend nonlinearly on the concentration of contrast agent (3,6,9,10).The results summarized above justify a dependence of the transverse relaxation effect of contrast agent on the host tissue, a finding that has implications for dynamic susceptibility contrast perfusion measurements (7,8). In particular, this effect explains a significant overestimation of cerebral blood flow found in noise-free simulations (11).…”

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confidence: 99%

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Theoretical model of intravascular paramagnetic tracers effect on tissue relaxation

Kjølby

Østergaard

Kiselev

2006

Magnetic Resonance in Med

123

163

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It is a fundamental problem of quantitative contrast-enhanced MRI to measure the concentration of contrast agent or tracer. In contrast to CT and PET, the concentration of tracers in MRI is measured indirectly via their relaxation effect. This raises the problem of converting the relaxation into the concentration. There are several experimental studies of the transverse relaxation effect of various contrast agents. The results indicate that this relaxation effect has a broad variation between different organs beyond the expected dependence on the magnetic field and the type of contrast agent used.Mørkenborg et al. (1) and Pedersen et al. (2) measured the transverse relaxation effect of gadolinium in the kidney cortex in animal models. They found a significant difference between the relaxation in tissue and that in blood plasma at field strengths of 1.5 (1) and 7 T (2). The measurements in kidney cannot serve as a model for the measurements in the brain, in which case gadoliniumbased chelates do not leave the blood pool.Transverse relaxation of a intravascular contrast agent was studied in rat organs by Johnson et al. (3) at 1.5 T. Dysprosium-loaded red blood cells served as a tracer. The relaxation effect was linear and varied significantly between organs when represented as a function of tissue concentration of the contrast agent. This difference was attributed to different microvascular architecture. This finding agrees with the theoretical conclusion about the dependence between the geometry of microscopic susceptibility-induced magnetic field and the resulting transverse relaxation (4,5).One more comparison of the transverse relaxation effect between organs was performed by Bjørnerud et al. (6) who investigated the relaxation of nanoparticles of iron oxide at 1.5 T in pig renal cortex and muscle. The increase in the relaxation rate due to the contrast agent was studied as a function of its concentration in blood. They found a 16-fold difference in the relaxivity of the contrast agent. This value can hardly be explained by the difference in the blood volume between two organs, thus supporting indirectly the finding by Johnson et al. (3).In dynamic susceptibility contrast-based perfusion measurements, blood serves as a reference for the calculation of perfusion parameters (7,8). The transverse relaxation in blood doped with contrast agents has been investigated in a number of studies (3,6,9,10). The tracer-induced increase in the relaxation in blood was found to differ from that in organs (3,6) and to depend nonlinearly on the concentration of contrast agent (3,6,9,10).The results summarized above justify a dependence of the transverse relaxation effect of contrast agent on the host tissue, a finding that has implications for dynamic susceptibility contrast perfusion measurements (7,8). In particular, this effect explains a significant overestimation of cerebral blood flow found in noise-free simulations (11). The theory of transverse relaxation in biologic tissue is required for a better understanding of the ...

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supporting

confidence: 81%

Section: Analytical Description Of Relaxation In Extravascular Spacementioning

confidence: 99%

mentioning

confidence: 99%

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Theoretical model of intravascular paramagnetic tracers effect on tissue relaxation

Kjølby

Østergaard

Kiselev

2006

Magnetic Resonance in Med

123

163

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“…As the spatial distribution of blood vessels differs among normal, infracted, and ischemic myocardial fibers, the relaxation effects of a given concentration of agent also vary (8). The proportionality between relaxation rate change and susceptibility agent concentration can be expressed as follows: where R 2* = 1/ T 2 * and c agent refers to the concentration of contrast agent per unit volume of tissue (9). Baseline R 2* values are strongly influenced by shimming effects, so that their absolute values have limited meaning; but it is possible to detect a change in these values with intravascular contrast concentration, using the target prior to contrast as control.…”

Section: Discussionmentioning

confidence: 99%

Novel double contrast MRI technique for intramyocardial detection of percutaneously transplanted autologous cells

Baklanov

deMuinck

Thompson

et al. 2004

Magnetic Resonance in Med

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Bone marrow cells (BMC) labeled with iron particles can be injected into the heart and detected with MRI. Improvement in conspicuity of labelled cells would be advantageous. This study examined if double contrast with iron oxide and Gd-DTPA enhances cell MRI after transvascular transplantation in myocardial infarction. Ten pigs with week-old myocardial infarction had transvascular peri-infarct delivery of microspheres alone (Group I, n ‫؍‬ 3) or mixed with iron-labeled BMCs (Group II, n ‫؍‬ 7). Gradient-echo MRI before and 1 min after systemic Gd-DTPA administration produced regions of interest with hypoenhancement that were compared to contralateral regions for contrast-to-noise (CNR) and signal-to-noise (SNR) ratios. All hearts were harvested for gross and microscopic analysis. Areas of focal hypoenhancement corresponding to the BMCs were detected in the myocardium in Group II. Early after administration of Gd-DTPA CNR increased from 17.58 ؎ 8.5 to 27.25 ؎ 15.8 (P < 0.05) and SNR from 24.87 ؎ 9.6 to 35.08 ؎ 15.5 (P < 0.05). There was no hypoenhancement in Group I. Tissue examination confirmed presence of iron-containing cells and microspheres in corresponding segments of the heart. The distribution of microspheres was similar between the groups. Double contrast with cellular iron and Gd-DTPA in surrounding myocardium resulted in improved cell localization by MRI. Magn

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“…First, the concentration of contrast agent (in both the tissue and the AIF) is assumed to be linearly proportional to the change in relaxation time T2 and T2*. 14,28 This proportionality constant has been shown to be tissue dependent 33 and therefore is likely to vary also with pathology. Second, deconvolution of Equation 1 provides information about the product of k⅐CBF.…”

Section: Assumption 2: Tissue Characteristicsmentioning

confidence: 99%

Quantification of Perfusion Using Bolus Tracking Magnetic Resonance Imaging in Stroke

Calamante

Gadian

Connelly

2002

Stroke

260

242

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Background-MR techniques have been very powerful in providing indicators of tissue perfusion, particularly in studies of cerebral ischemia. There is considerable interest in performing absolute perfusion measurements, with the aim of improving the characterization of tissue "at risk" of stroke. However, some important caveats relating to absolute measurements need to be taken into account. The purpose of this article is to discuss some of the issues involved and the potential implications for absolute cerebral blood flow measurements in clinical use. Summary of Comment-In bolus tracking MRI, deconvolution of the concentration-time course can in theory provide accurate quantification. However, there are several important assumptions in the tracer kinetic model used, some of which may be invalid in cerebral ischemia. These can introduce significant errors in perfusion quantification. Conclusions-Although we believe that bolus tracking MRI is a powerful technique for the evaluation of perfusion in cerebral ischemia, interpretation of perfusion maps requires caution; this is particularly true when absolute quantification is attempted. Work is currently under way in a number of centers to address these problems, and with appropriate modeling they may be overcome in the future. In the interim, we believe that it is necessary for users of bolus tracking perfusion data to be aware of the current technical limitations if they are to avoid misinterpretation or overinterpretation of their findings. Key Words: cerebral blood flow Ⅲ cerebral ischemia Ⅲ contrast media Ⅲ magnetic resonance imaging Ⅲ perfusion Ⅲ stroke T he term perfusion normally refers to the delivery of blood at the level of the capillaries, where exchange of oxygen and nutrients between blood and tissue takes place. When quantified, perfusion is measured in units of milliliters per 100 g per minute. MR techniques have been very powerful in providing indicators of tissue perfusion in the brain in the former, nonquantitative sense; indeed, they have been shown to contribute important new information not accessible by any other MR technique to date. One of the major applications has been in the assessment and management of patients with acute stroke, with numerous recent reports demonstrating the key role of perfusion MRI, mostly in combination with diffusion MRI since the latter is believed to provide an early marker of cytotoxic edema (see Reference 1 for a recent review).Many of the recent perfusion MRI studies have been concerned with predicting the eventual infarct volume in patients who have suffered an ischemic insult, with a major aim of selecting the most appropriate patients for possible therapeutic intervention. A large number of these studies have shown a regional mismatch between diffusion abnormality and perfusion deficit (eg, References 2-4), while others have shown the presence of perfusion abnormalities even in the absence of any abnormality on structural or diffusion MRI. [5][6][7] Although these areas of mismatch are generally believed to be...

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Intravascular susceptibility agent effects on tissue transverse relaxation rates in vivo

Cited by 5 publications

References 0 publications

Theoretical model of intravascular paramagnetic tracers effect on tissue relaxation

Theoretical model of intravascular paramagnetic tracers effect on tissue relaxation

Novel double contrast MRI technique for intramyocardial detection of percutaneously transplanted autologous cells

Quantification of Perfusion Using Bolus Tracking Magnetic Resonance Imaging in Stroke

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