Quantitative magnetic resonance imaging of human brain perfusion at 1.5 T using steady-state inversion of arterial water.

Roberts, D. A.; Detre, J.; Bolinger, Lizann; Insko, Erik K.; Leigh, Jr Js

doi:10.1073/pnas.91.1.33

Cited by 166 publications

(113 citation statements)

References 26 publications

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“…The constant of proportionality between B 1 2 and Gv is the adiabaticity factor, ␤ (Eq. [4]) (9). The optimum values of ␤ in the absence of relaxation are 1.50 (r ϭ 0.9999) and 1.53 (r ϭ 0.9999) in the human and animal models, respectively.…”

Section: B 1 and The Adiabatic Conditionmentioning

confidence: 95%

Velocity‐driven adiabatic fast passage for arterial spin labeling: Results from a computer model

Utting

Thomas

Gadian

et al. 2003

Magnetic Resonance in Med

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Velocity-driven adiabatic fast passage (AFP) is commonly employed for perfusion imaging by continuous arterial spin labeling (CASL). The degree of inversion of protons in blood determines the sensitivity of CASL to perfusion. For this study, a computer model of the modified Bloch equations was developed to establish the optimum conditions for velocity-driven AFP. Natural variations in blood velocity over the course of the cardiac cycle were found to result in significant variations in the degree of inversion. However, the mean degree of inversion was similar to that for blood moving at a constant velocity, equal to the time-averaged mean, at peak velocities and heart rates within normal ranges. A train of RF pulses instead of a continuous RF pulse for labeling was found to result in a highly nonlinear dependence of the degree of inversion on RF duty cycle. This may have serious implications for the quantification of perfusion.Magn The development of arterial spin labeling (ASL) MRI has made it possible to study microvascular blood flow completely noninvasively, offering a means of investigating tissue perfusion in numerous functional and pathological states. Much work has been performed to assess and improve the accuracy of perfusion values from ASL (1-3). However, its inherently low sensitivity remains one of the most significant limitations of the technique, and the labeling process is a key factor in determining the sensitivity.Velocity-driven adiabatic fast passage (AFP) was applied initially for MR angiography (4). It is now widely regarded as the preferred method for continuous ASL (CASL) because it provides a continuous supply of blood that is labeled by inversion. However, the degree of inversion is limited by several factors, including the amplitudes of the magnetic field gradient and radiofrequency (RF) pulse used for AFP; the velocity of blood, which varies in arteries over the course of the cardiac cycle; and the spin relaxation in blood. In addition, the duration of RF pulses is often limited by RF amplifiers, especially on some clinical scanners, and the relatively long pulse required for labeling in CASL experiments (2 or 3 s) must be divided into a series of short pulses. It has been assumed that the effectiveness of AFP is proportional to the duty cycle of the resulting train of RF pulses (2,5).A computer modeling approach was adopted for this study in order to investigate the influences of several parameters on velocity-driven AFP individually, in a controlled manner. The aims were to establish optimal RF pulse parameters, to determine the effect of pulsatile variations in the velocity of blood, and to study the dependence of the degree of inversion on the duty cycle of a discontinuous RF pulse during labeling. The modeling was performed with one set of parameters for imaging humans in a clinical scanner, and a second set of parameters for imaging rodents in a small-bore system for animals. THEORYTo invert moving spins by AFP, an RF pulse, B 1 , is applied in the presence of a magnetic field gr...

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Section: B 1 and The Adiabatic Conditionmentioning

confidence: 95%

Velocity‐driven adiabatic fast passage for arterial spin labeling: Results from a computer model

Utting

Thomas

Gadian

et al. 2003

Magnetic Resonance in Med

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“…Arterial spin labeling (ASL) involves acquiring images with and without inversion of water proton spins proximal to the area of interest, thereby allowing the measurement of cerebral blood flow (CBF) without requiring administration of an exogenous tracer (1)(2)(3). In order for the measurement to be quantitative, a kinetic model of the tag delivery process needs to be assumed and fit to the data to obtain the flow parameters.…”

mentioning

confidence: 99%

Modeling the effects of dispersion and pulsatility of blood flow in pulsed arterial spin labeling

Gallichan

Jezzard

2008

Magnetic Resonance in Med

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Arterial spin labeling (ASL) is a method of using MRI to image cerebral perfusion. For the measurement to be calibrated, a model is required describing the kinetics of the flow of the inverted blood from the labeling region to the imaging region. It is common to assume plug-flow, but alternatives such as a Gaussian distribution of arrival times have also been suggested. In this study a physiologically based model for dispersion is developed and compared to existing models when fit to experimental data. The model is based on the assumption of parabolic flow in the major arteries, and also allows inclusion of cardiac pulsatility. It was found that fitting using the proposed model leads to higher perfusion estimates, with the difference becoming more pronounced in regions where the dispersion is greater. This suggests that current models may underestimate perfusion in these areas. However, fitting using the proposed model also leads to high uncertainties in parameter estimates due to non-orthogonality of the parameters. Effects due to pulsatility are expected to be observable, but when no cardiacgating is used the mean curve over several cardiac cycles is predicted to closely match the curve which assumes constant flow. Key words: pulsed arterial spin labeling; ASL; pulsatility; dispersionArterial spin labeling (ASL) involves acquiring images with and without inversion of water proton spins proximal to the area of interest, thereby allowing the measurement of cerebral blood flow (CBF) without requiring administration of an exogenous tracer (1-3). In order for the measurement to be quantitative, a kinetic model of the tag delivery process needs to be assumed and fit to the data to obtain the flow parameters. Buxton et al. (4) presented a general modeling framework for ASL which includes a tag delivery function that can be modeled to incorporate the dispersion of the tag between the tagging region and the imaging voxel. A common choice of tag delivery function model is 'plug-flow' (i.e., constant and without dispersion). However, it is known that blood flow in the major arteries is likely to be poorly approximated by simple plug-flow, as it is both highly pulsatile and has a time-varying nonuniform cross-sectional flowprofile (5). Indeed, Wu et al. (6) recently demonstrated experimentally that both flow dispersion and flow pulsatility have a significant effect on the ASL signal. They also presented a model to estimate the effect of the cardiac cycle on the ASL signal, but that model appears to implicitly assume plug-flow when calculating the variation in tag-volume. The dispersion is accounted for by assuming a Gaussian distribution of transit delays.Hrabe and Lewis (7) presented analytical forms of the kinetic model by assuming various tag delivery functions that included dispersion and concluded by advocating the assumption of a Gaussian distribution of tag arrival times at the imaging voxel. They justified this choice physiologically by assuming that the primary source of dispersion would be in vessels close to ...

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“…[52][53][54] The history of the development of the ASL MRI technique is summarized in Table 1. 43,44,49,50,[55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72] There are several potential advantages of using ASL techniques for the evaluation of tumor perfusion. First, because no intravenous contrast is administered, multiple measurements may be performed without accumulating tracer materials.…”

Section: Asl Mrimentioning

confidence: 99%

Magnetic resonance imaging as a biomarker in renal cell carcinoma

Pedrosa

Alsop

Rofsky

2009

Cancer

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The ability to noninvasively discriminate the most common types of renal cell carcinoma (RCC) based on their magnetic resonance imaging (MRI) appearances or their magnetic resonance phenotypes is achievable. Intracellular lipids, a histologic characteristic of the clear cell RCC, can be identified on chemical shift MRI. Intratumoral hemosiderin deposition, as observed histologically with papillary RCC, correlates to the low signal intensity on T2-weighted images. In addition to morphologic imaging features, the different subtypes of RCC have distinct patterns of enhancement on dynamic contrast-enhanced MRI. Clear cell tumors demonstrate much greater enhancement than papillary and chromophobe RCCs during the corticomedullary and nephrographic phases. The MRI technique arterial spin labeling (ASL) uses magnetic fields to label the water protons in arterial blood and measures blood flow into tissue; quantitative images of blood flow can be generated without exogenous contrast media. Multiple measurements of tumor perfusion may be repeated before and after a physiologic or drug challenge (ie, antiangiogenic therapy). In RCC xenografts and in patients with metastatic RCC, ASL MRI assessments can be used to monitor blood flow changes in response to antiangiogenic therapies. High blood flow on ASL MRI in RCC xenografts correlates with viable tumor at histopathologic analysis, whereas zones of absent or diminished signal correspond to necrosis. ASL MRI has the potential to serve as a biomarker for patients with metastatic RCC by offering a noninvasive measure of tumor blood flow changes accompanying antiangiogenic therapy. Cancer 2009;115(10 suppl):2334-45.

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Quantitative magnetic resonance imaging of human brain perfusion at 1.5 T using steady-state inversion of arterial water.

Cited by 166 publications

References 26 publications

Velocity‐driven adiabatic fast passage for arterial spin labeling: Results from a computer model

Velocity‐driven adiabatic fast passage for arterial spin labeling: Results from a computer model

Modeling the effects of dispersion and pulsatility of blood flow in pulsed arterial spin labeling

Magnetic resonance imaging as a biomarker in renal cell carcinoma

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