The Influence of Noise on Bold-Mediated Vessel Size Imaging Analysis Methods

Abstract

Vessel size imaging (VSI) is a magnetic resonance imaging (MRI) technique that aims to provide quantitative measurements of tissue microvasculature. An emerging variation of this technique uses the blood oxygenation level-dependent (BOLD) effect as the source of the imaging contrast. Gas challenges have the advantage over contrast injection techniques in that they are noninvasive and easily repeatable because of the fast washout of the contrast. However, initial results from BOLD-VSI studies are somewhat contradictory, with substantially different estimates of the mean vessel radius. Owing to BOLD-VSI being an emerging technique, there is not yet a standard processing methodology, and different techniques have been used to calculate the mean vessel radius and reject uncertain estimates. In addition, the acquisition methodology and signal modeling vary from group to group. Owing to these differences, it is difficult to determine the source of this variation. Here we use computer modeling to assess the impact of noise on the accuracy and precision of different BOLD-VSI calculations. Our results show both potential overestimates and underestimates of the mean vessel radius, which is confirmed with a validation study at 3T.

Advances in translational imaging of the microcirculation

“…217 The off-label use of the MR contrast agent Ferumoxytol has also been explored recently as an alternative to gadolinium-based VSI in patients with an array of diseases 218 such as acute ischemia 219 and those with advanced metastatic disease outside the brain. 220 Recently, BOLD-based VSI 189 was used to increase the microvascular specificity of fMRI. 221 There are numerous technical considerations regarding image acquisition, tracer kinetic modeling, image processing, and data interpretation that need to be borne in mind when employing DSC 206 and DCE 205 MRI protocols.…”

Gas-free calibrated fMRI with a correction for vessel-size sensitivity

“…The simulations above were repeated on networks populated by two different distributions of vessel radii, referred to here as the Lauwers (Lauwers et al, 2008) and Frechet (Germuska et al, 2013) distributions, and shown in Fig. 4.…”

“…For the vessel-size distributions, the Lauwers distribution was obtained using the parameters for the complete vessel network in (Lauwers et al, 2008) with the radii ranging from 3.0-40 µm. The Frechet distribution was implemented in MATLAB using the gevrnd function with the input parameters µ = 10.1 µm, σ = 5.8, and k = 0.41 taken from (Germuska et al, 2013) and with the radii ranging from 2.5-60 µm.…”

Vessel calibre—a potential MRI biomarker of tumour response in clinical trials

“…83,94 Thus, the current clinical hardware and imaging protocols limit the traditional VSI estimate to vessel radii considered larger than ‘very small’ (>2 µm) but smaller than ‘very large’ (<50 µm). 94,101,102 The range of vessel calibres that can be acceptably defined using BOLD-VSI is probably even narrower because of the inherent small changes in magnetic susceptibility during activation of the target tissue. 94 …”

“…86 BOLD-VSI analyses based on gas challenges is also influenced by vasodilation. 101 Increased cerebral vasodilation and flow is observed for hypercapnia (abnormally elevated CO 2 concentrations in the blood), whereas the opposite effect is seen in hypocapnia (low blood CO 2 levels); 112 however, the effects of gas-induced vasodilation on blood volume and, therefore, BOLD-VSI are not fully understood, 101 although venous volume fractions seem to be relatively unaffected by vasodilation. 113 …”