Development of Clinical MRI Methods for Assessment of Micro-Vessel Conditions of Brain Tumors

  • Liu, Ho-Ling (PI)
  • Hsu, Yuan-Yu (CoPI)
  • Wai, Yau-Yau (CoPI)

Project: National Science and Technology CouncilNational Science and Technology Council Academic Grants

Project Details

Abstract

Perfusion measurements using dynamic susceptibility contrast (DSC) MRI has been widely applied in clinical patients with brain tumors. Particularly, the cerebral blood volume (CBV) map is used to assess the tumor angiogenesis, which can be useful in differential diagnosis, biopsy guidance and treatment evaluation. In general clinical settings, a bolus injection of the Gd-based contrast agent is applied with dynamic T2- or T2*-weighted fast imaging. Then the CBV map can be calculated from the first-pass of the concentration time curve, assuming that the contrast medium stays in the vessels. However, in tumor vessels with disrupted blood-brain barrier (BBB), the contrast agent extravasation is often observed as additional T1 relaxation effects which can result in underestimated CBVs. In slightly leaky conditions, a pre-loading dose and/or a modeling of the T1 effect has been demonstrated to be capable of correcting the CBV errors. Besides, the mathematical modeling provided opportunities of assessing the permeability of tumor vessels. In very leaky conditions, however, the existing models could fail due to the T2 relaxation effects from the increased amount of contrast medium in the extravascular extracellular space (EES). In this proposal, we hypothesize that the contrast agents in the EES, including those from the pre-loading dose and the bolus leakage, could be modeled as a separate term in the residual function. And the first specific aim is to test whether the signal time curves measured from clinical patients can be fitted to such model and whether reliable permeability maps can be obtained from patients with various brain tumors. In addition to CBV and permeability, an important index of tumor micro-vessels is the mean vessel size. Based on the different relationships of T2 and T2* relaxivity with the vessel diameter, vessel size imaging (VSI) has been previously performed in both animals and human patients using an echo-planar image (EPI) sequence with both spin- and gradient-echoes. However, such sequence is not available in current clinical scanners and the spatial resolution and the echo time are limited by putting the two echoes together. In this proposal, we hypothesize that the dynamic T2- and T2*-weighted images can be obtained using a dual injection scheme with acceptable errors at 3T. The second specific aim is therefore to develop and optimize a clinical protocol with two bolus injections and to test whether the protocol can obtain reasonable vessel size measurement at high resolution. Imaging during one of the injections can be used for the above-mentioned CBV and permeability measurements. In summary, in two years, we propose to develop a set of clinical DSC MRI protocols that can generate useful and accurate information, including CBV, permeability and mean vessel size, for assessing micro-vessel conditions in patients with brain tumors.

Project IDs

Project ID:PC9801-2483
External Project ID:NSC97-2314-B182-030-MY2
StatusFinished
Effective start/end date01/08/0931/07/10

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