In vivo measurement of pulsewave velocity in small vessels using intravascular MR

Bolster, Bradley D.; Serfaty, Jean Michel; Atalar, Ergin

doi:10.1002/1522-2594(200101)45:1<53::aid-mrm1009>3.0.co;2-k

Cited by 12 publications

(9 citation statements)

References 27 publications

(30 reference statements)

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“…This device 11 has been shown to be useful for catheter tracking, and signal localization. [12][13][14][15][16] We have previously examined the transmit power distribution of the catheter antenna and have shown that the induced heating is highly localized near the device. 17 First, the SAR distribution of the transmitting rf coil was determined.…”

Section: Methodsmentioning

confidence: 99%

A Green's function approach to local rf heating in interventional MRI

Yeung

Atalar

2001

Medical Physics

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Current safety regulations for local radiofrequency (rf) heating, developed for externally positioned rf coils, may not be suitable for internal rf coils that are being increasingly used in interventional MRI. This work presents a two-step model for rf heating in an interventional MRI setting: (1) the spatial distribution of power in the sample from the rf pulse (Maxwell's equations); and (2) the transformation of that power to temperature change according to thermal conduction and tissue perfusion (tissue bioheat equation). The tissue bioheat equation is approximated as a linear, shift-invariant system in the case of local rf heating and is fully characterized by its Green's function. Expected temperature distributions are calculated by convolving (averaging) transmit coil specific absorption rate (SAR) distributions with the Green's function. When the input SAR distribution is relatively slowly varying in space, as is the case with excitation by external rf coils, the choice of averaging methods makes virtually no difference on the expected heating as measured by temperature change (deltaT). However, for highly localized SAR distributions, such as those encountered with internal coils in interventional MRI, the Green's function method predicts heating that is significantly different from the averaging method in current regulations. In our opinion, the Green's function method is a better predictor since it is based on a physiological model. The Green's function also elicits a time constant and scaling factor between SAR and deltaT that are both functions of the tissue perfusion rate. This emphasizes the critical importance of perfusion in the heating model. The assumptions made in this model are only valid for local rf heating and should not be applied to whole body heating.

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Section: Methodsmentioning

confidence: 99%

A Green's function approach to local rf heating in interventional MRI

Yeung

Atalar

2001

Medical Physics

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“…The authors hypothesized that the reduction of cerebral blood flow might be related to the impairment of the cerebral autoregulation, secondary to the degenerative disorder. The direct consequence would be a sequential ulterior reduction of blood pressure, due to dysregulation, which might accelerate the lowering of blood perfusion and therefore the underlying degenerative process (Guo et al 1996; Bolster et al 2001; Yamamoto et al 2001; Mehagnoul-Schipper et al 2002; Nilsson et al 2007). Lower systolic blood pressure was associated with cognitive decline and dementia.…”

Section: Hypotension and Dementiamentioning

confidence: 99%

Risk factors for vascular dementia: Hypotension as a key point

Moretti¹

2008

VHRM

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Physiologically, the cerebral autoregulation system allows maintenance of constant cerebral blood fl ow over a wide range of blood pressure. In old people, there is a progressive reshape of cerebral autoregulation from a sigmoid curve to a straight line. This implies that any abrupt change in blood pressure will result in a rapid and signifi cant change in cerebral blood fl ow. Hypertension has often been observed to be a risk factor for vascular dementia (VaD) and sometimes for Alzheimer disease although not always. Indeed, high blood pressure may accelerate cerebral white matter lesions, but white matter lesions have been found to be facilitated by excessive fall in blood pressure, including orthostatic dysregulation and postprandial hypotension. Many recent studies observed among other data, that there was a correlation between systolic pressure reduction and cognitive decline in women, which was not accounted for by other factors. Baseline blood pressure level was not signifi cantly related to cognitive decline with initial good cognition. Some researchers speculate that blood pressure reduction might be an early change of the dementing process. The most confounding factor is that low pressure by itself might be a predictor of death; nevertheless, the effect of low blood pressure on cognition is underestimated because of a survival bias. Another explanation is that clinically unrecognized vascular lesions in the brain or atherosclerosis are responsible for both cognitive decline and blood pressure reduction. We discuss the entire process, and try to defi ne a possible mechanism that is able to explain the dynamic by which hypotension might be related to dementia. Keywords: vascular dementia, hypotension, low blood pressure, alzheimer disease As longevity increases worldwide, age-related dementias are burgeoning. Age-related cerebral degenerative changes are coupled therefore with decreased perfusion, usually assumed to be secondary to decreased cerebral metabolic demands (Meyer et al 1999). During aging, the declines in cerebral tissue densities of the gray cortex (polio-araiosis) and of the white matter (leuko-araiosis) refl ect neuronal degenerative changes, which progress concurrently with cerebral perfusion declines.In particular, leuko-araiosis correlates with advancing age, cerebral atrophy, hypoperfusion of white matter, and cognitive impairments (Meyer et al 2000). Leuko-araiosis is detectable in 9%-19% of older 'normal' subjects, but is virtually always present in vascular dementia (VaD). Of special interest are the data emerging from the study of Meyer and colleagues (2000): normative subjects destined for later cognitive decline had excessive leuko-araiosis at study entry, suggesting leuko-araiosis is, by itself, a risk factor for cognitive decline.Thus, the researchers are trying to defi ne the passage between normality, the so-called leuko-araiosis age-related and the excess of the response to the vascular damage, confi guring the dementia, as a clinical syndrome. White matter injury m...

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“…An invasive technique, intravascular MRI, utilizes the signal-to-noise ratio (SNR) advantages of an intra-arterial catheter RF coil to gain access to the central arteries. Arterial wall stiffness is then directly assessed by imaging the central arterial pulse wave velocity locally (7).…”

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confidence: 99%

Vascular wall elasticity measurement by magnetic resonance imaging

Woodrum

Romano

Lerman

et al. 2006

Magnetic Resonance in Med

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The goal of this current study was to determine whether an MRI-based elastography (MRE) method can visualize and assess propagating mechanical waves within fluid-filled vessels and to investigate the feasibility of measuring the elastic properties of vessel walls and quantitatively assessing stenotic lesions by using MRE. The ability to measure the Young's modulus-wall thickness product was tested using a thin-walled latex vessel model. Also tested in vessel models was the ability to quantitate the degree of stenosis by measuring transmitted and reflected mechanical waves. This method was then applied to ex vivo porcine models and in vivo human arteries to further test its feasibility. The results provide preliminary evidence that MRE can be used to quantitatively assess the stiffness of blood vessels, and provide a non-morphologic method to measure stenosis. With further development, it is possible that the method can be implemented in vivo. Magn Reson Med 56: 593-600,

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In vivo measurement of pulsewave velocity in small vessels using intravascular MR

Cited by 12 publications

References 27 publications

A Green's function approach to local rf heating in interventional MRI

A Green's function approach to local rf heating in interventional MRI

Risk factors for vascular dementia: Hypotension as a key point

Vascular wall elasticity measurement by magnetic resonance imaging

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