An MRI perfusion model incorporating nonequilibrium exchange between vascular and extravascular compartments

To evaluate the sensitivity of the intravoxel incoherent motion (IVIM) technique to changes in cerebral blood flow, we made measurements of IVIM parameters in rat brain under conditions of altered arterial pCO2. The arterial pCO2 was varied over a range which would be expected to change cerebral blood flow from roughly 50 to 500 ml/(100 g.min). The IVIM measurements were made with suppression of extravascular water signal. The parameters f' (the apparent fraction of spins which have "fast" pseudodiffusion), D1* (the "fast-pseudodiffusion") coefficient), and D2* (the "slow-pseudodiffusion" coefficient) all showed statistically significant positive linear correlations with arterial pCO2. These results suggest that the IVIM method, when used with suppression of extravascular water signal, is sensitive to changes in blood flow.

Section: Discussionmentioning

confidence: 99%

An evaluation of the sensitivity of the intravoxel incoherent motion (IVIM) method of blood flow measurement to changes in cerebral blood flow

Neil

Bosch

Ackerman

1994

The capillary network: a link between ivim and classical perfusion

D¹,

Turner²

1992

372

378

MR measurements based on motion encoding gradients, such as intravoxel incoherent motion imaging, could provide, in principle, information on flowing blood volume and blood velocity. This note shows that, in addition, the knowledge of the capillary network organization may provide a link between these measurements and those obtained by conventional and MR perfusion techniques based on tracer uptake by tissues.

Inversion recovery EPI of bolus transit in rat myocardium using intravascular and extravascular gadolinium‐based MR contrast media: Dose effects on peak signal enhancement

Wendland

Saeed

et al. 1994

Inversion recovery gradient recalled echo planar imaging (TI/TR/TE = 700/2000/10 ms) was used to dynamically monitor the first pass of an intravascular (GdDOTA-polylysine) and an extravascular (GdDTPA-BMA) contrast agent through normal rat myocardium. It was found that myocardial enhancement increased with dose of the intravascular agent to a limiting value of approximately 50% of fully relaxed intensity, consistent with enhancement of 40% of myocardial water content during the first pass. Larger doses produced no further increase in peak response. On the other hand, the extravascular agent caused incrementally increased enhancement throughout the dose range examined to a final value of 68 +/- 2% of fully relaxed intensity. The profile of dose dependence for both agents was inconsistent with monoexponential T1 relaxation. It was concluded that: (a) compartmentalization of myocardial water combined with restricted myocardial water diffusion limits the peak response during bolus transit; (b) extraction of the extravascular agent during transit elevates the peak response over that obtained from agent confined to the vascular volume; and (c) models that assume simple monoexponential T1 relaxation to derive time-density curves do not adequately describe the relationship between changes in signal intensity, R1 and contrast concentration.