Abstract
Dynamic measurements of T1 shortening (dynamic contrast enhanced—DCE) as well as of T2* shortening (dynamic susceptibility contrast—DSC) as two separate measurement strategies are widely used to quantitatively describe tumor perfusion and vascularity. Dual-echo approaches allow for the simultaneous assessment of both effects. The extension to multi-echo sequences should inhere the advantage of improved signal-to-noise ratios and more precise sampling of the T2* decay. The aim of our study is to investigate, if an extension of the dual-echo approach to the multi-echo approach allows for more stable quantitative determination of pharmacokinetic parameters in brain tumors. This study applies a multi-echo approach to obtain different estimations of a vascular input function and analyzes various combinations of vascular input functions and pharmacokinetic models. Perfusion measurements were performed with 52 consecutive patients with different brain tumors using a 10-echo gradient echo sequence. Our findings show that the extension to multi-echo sequences leads to an 11%-improvement of the Contrast-to-Noise ratio. Compared to other combinations, an application of Extended Tofts model using the T2*-related venous output function or an output function estimated in the tumor tissue enables the most reliable determination of perfusion parameters, reducing the reproducibility range by a factor of 1.2 to 10 for Ktrans and of 1.2 to 5.5 in the case of rBV calculation. Determination of Ktrans within repeated measurements within about 3 days results as most stable, if AIF from tumor pixels is used as vascular input function, meaning that the scatter is reduced by a factor of 1.2 compared to the next best VIF and by a factor of 10 compared to the worst of the tested approaches. In addition, this study shows that signal decomposition into two components with different Larmor frequencies might provide additional information concerning tissue composition of brain tumors.
Highlights
Dynamic contrast enhanced (DCE) magnetic resonance imaging and dynamic susceptibility contrast (DSC) magnetic resonance imaging are widely used techniques for the assessment of tumor perfusion and tumor vascularity
Determination of Ktrans within repeated measurements within about 3 days results as most stable, if Arterial Input Function (AIF) from tumor pixels is used as vascular input function, meaning that the scatter is reduced by a factor of 1.2 compared to the best VIF and by a factor of 10 compared to the worst of the tested approaches
The multi-echo approach results in a significant better contrast-to-noise ratio (CNR) of the calculated R2* (t ) and S0(t) compared to the dual-echo approach
Summary
Dynamic contrast enhanced (DCE) magnetic resonance imaging and dynamic susceptibility contrast (DSC) magnetic resonance imaging are widely used techniques for the assessment of tumor perfusion and tumor vascularity. Since the diffusion of CM into the interstitial space is much slower compared to the passage of a CM bolus through the capillaries, T1-related dynamic measurements can be performed with a temporal resolution of about 45 seconds to 3 minutes [3] [4]. For this reason, spin echo or gradient echo volume sequences with short echo times (TE) can be used to minimize the influence of T2* changes. Long repetition times (TR) assure minimal influence of T1 shortening
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