Measurement of tumor vascular volume and mean microvascular random flow velocity magnitude by dynamic GD‐DTPA‐Albumin enhanced and diffusion‐weighted MRI

Abstract

Tumor vascular volume fraction and the magnitude of the mean microvascular random flow velocity were measured in an animal tumor model by combining dynamic Gd-DTPA-albumin enhanced MRI and diffusion-weighted MRI in conjunction with a compartmental modeling analysis. The vascular volume fraction maps were obtained from the dynamic Gd-DTPA-albumin enhanced MRI measurement. It was found that the vascular volume fraction for Walker 256 tumor was higher within the outgrowing rim and decreased towards the central region. The average value obtained from five animals was 0.062 +/- 0.009 ml/g. By using the vascular volume fraction from the Gd-DTPA-albumin enhanced MRI measurement, maps of the magnitude of the mean microvascular random flow velocity were obtained from the diffusion-weighted MRI measurements with the compartmental modeling analysis. The relative extravascular and intravascular contributions to the diffusion-weighted MRI signal were determined for three tissue groups with different Gd-DTPA-albumin enhancement characteristics, and the flow and molecular diffusion-induced attenuation factors for the intravascular compartment were also compared. The mean microvascular random flow velocity magnitude maps were obtained with an average value of 0.67 +/- 0.06 mm/s.

Intravoxel partially coherent motion technique: Characterization of the anisotropy of skeletal muscle microvasculature

“…Eddy currentcompensated stimulated echo diffusion is preferable than twice-refocused spin-echo diffusion protocol for muscle DTI with a b-value of 500-700 s/mm 2 (42), but further work is needed to investigate which echo preparation has higher SNR for the IVIM acquisition, where a train of b-values is acquired. Some of the technical issues related to the high SNR requirement of the presented method might be overcome by employing macromolecular contrast agents (43), by optimizing the employed diffusion encoding scheme, or by focusing on tissues with higher vascular volume fraction than the skeletal muscle at rest (myocardium, liver (44), or kidney).…”

Variability of Renal Apparent Diffusion Coefficients: Limitations of the Monoexponential Model for Diffusion Quantification

“…When analyzed with a biexponential model, IVIM effects provide useful sensitivity to perfusion that is modifi ed in disease states. Extensive human ( 27,28 ) and animal ( 29,30 ) IVIM imaging has been devoted to assessing cerebral microcirculation, and animal model tumors, with pathologically abundant vascularity, have also provided an ideal target for the technique ( 31 ). However, if ignored because of the use of a monoexponential model, IVIM effects can distort the measurement of the ADC.…”

Assessment of regional cerebral blood flow by dynamic susceptibility contrast MRI using different deconvolution techniques

“…The concentration was calculated using Eq. [1], where S 0 was calculated as the mean signal of five images taken from the beginning of the series (after signal steady-state). The AIFs were used for rCBF assessment using different approaches.…”

“…In tumor applications, blood-flow measurements are of obvious interest in, for example, tumor characterization, assessment of prognosis, and monitoring of cancer therapy. Studies exploring the combination of diffusion and perfusion MRI in cancer applications are sparse at this point (1)(2)(3), but might become increasingly useful in the future. In acute ischemic stroke, the combination of diffusion and perfusion MRI is likely to become a powerful diagnostic tool in, for example, the prediction of stroke outcome (4 -6).…”