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
External Project ID:NSC97-2314-B182-030-MY2
Status | Finished |
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Effective start/end date | 01/08/09 → 31/07/10 |
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