NMR relaxation in tissues with weak magnetic inhomogeneities

Jensen, Jens Højgaard; Chandra, Ramesh

doi:10.1002/1522-2594(200007)44:1<144::aid-mrm21>3.0.co;2-o

Cited by 141 publications

(260 citation statements)

References 37 publications

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“…[12] and Eq. [16], the relaxation rates varied linearly with volume fraction. However, the dependence of B 0 ⅐ ⌬ on R * 2 and R 2 was quadratic only up to 3 T and then linear thereafter.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…It has been shown that the long time behavior of both the FID and CPMG signal decay is monoexponential in time (16). Hence, both signals were fit to exp(ϪAt) (where A denotes the relaxation parameter R* 2 or R 2 depending on the type of sequence) with Microcal Origin 5.0 (Microcal Software Inc., MA).…”

Section: Simulation Methodsmentioning

confidence: 99%

“…In addition, if the field variations are weak, it is possible to approximate Eq. [5] with the second moment as a function of time (15,16). In this case, Eq.…”

Section: Parameters Affecting the Rate Of Decay Of The Mr Signalmentioning

confidence: 99%

“…Equations [10], [12], [15], and [16] imply that the R* 2 , R 2 , *, and are linearly related to , but quadratically related to B 0 and ⌬ . When R 0 , , ⌬ , and B 0 remain fixed, the theory also predicts that R 2 and will initially increase with increase in 180 and then reach a plateau.…”

Section: Relation Between R* 2 and Pressurementioning

confidence: 99%

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On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

Dharmakumar

Plewes

Wright

2002

Magnetic Resonance in Med

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Recently, it has been suggested that gas encapsulated distensible microbubbles may serve as pressure probes in the MR field through the relationship between bubble size and 1/T 2 or 1/T* 2 . Currently, in vivo application of this technique is hindered by the ability of T 2 or T * 2 to detect pressure changes that are clinically relevant. This work identifies and characterizes, through numerical simulations, the set of parameters which optimize the ability of this technique to detect small pressure changes. Results show that when the bubbles do not interact magnetically, the T 2 -and T * 2 -based measurements of pressure are strongly influenced by the bubble size at atmospheric pressure, static magnetic field strength, magnitude of the susceptibility difference between the encapsulated gas and plasma, bubble volume fraction, and the refocusing interval.

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Section: Simulation Resultsmentioning

confidence: 99%

Section: Simulation Methodsmentioning

confidence: 99%

“…In addition, if the field variations are weak, it is possible to approximate Eq. [5] with the second moment as a function of time (15,16). In this case, Eq.…”

Section: Parameters Affecting the Rate Of Decay Of The Mr Signalmentioning

confidence: 99%

Section: Relation Between R* 2 and Pressurementioning

confidence: 99%

See 2 more Smart Citations

On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

Dharmakumar

Plewes

Wright

2002

Magnetic Resonance in Med

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“…Venous blood T 2 was obtained in vivo for each subject in both jugular veins (at the neck level, immediately above the facial vein drainage) using a magnetizationprepared segmented echo-planar imaging sequence (Chen and Pike, 2009;Stefanovic and Pike, 2004). From these T 2 measurements, venous oxygenation (Y) was estimated using the calibration relationship (T 2 dependence on blood oxygenation and Carr-Purcell-Meiboom-Gill (CPMG) refocusing interval) obtained by Chen and Pike (2009) based on in vitro whole human blood relaxometry (Chen and Pike, 2009) and the weak field-inhomogeneity diffusion model (Jensen and Chandra, 2001). Each oximetry measurement lasted 4.5 minutes.…”

Section: Methodsmentioning

confidence: 99%

Global Cerebral Oxidative Metabolism during Hypercapnia and Hypocapnia in Humans: Implications for BOLD fMRI

Chen

Pike

2010

J Cereb Blood Flow Metab

153

145

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The effect of carbon dioxide (CO 2 ) on cerebral metabolism is of tremendous interest to functional imaging. In particular, mild-to-moderate hypercapnia is routinely used in calibrated blood oxygenlevel dependent (BOLD)-functional magnetic resonance imaging (fMRI)-based quantification of cerebral oxidative metabolism changes (DCMRO 2 ), and relies on the assumption of a stable CMRO 2 during CO 2 challenges. However, this assumption has been challenged by certain animal studies, necessitating its verification in humans and under conditions customary to fMRI. We report, for the first time, on global DCMRO 2 measurements made noninvasively in humans during graded hypercapnia and hypocapnia. We used computerized end-tidal CO 2 modulation to minimize undesired concurrent changes in oxygen pressure, and our findings suggest that no significant change in global CMRO 2 is expected at the levels of end-tidal CO 2 changes customary to calibrated BOLD.

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Current Awareness

2000

NMR Biomed.

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NMR relaxation in tissues with weak magnetic inhomogeneities

Cited by 141 publications

References 37 publications

On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

On the parameters affecting the sensitivity of MR measures of pressure with microbubbles

Global Cerebral Oxidative Metabolism during Hypercapnia and Hypocapnia in Humans: Implications for BOLD fMRI

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