Abstract
BackgroundStandard MRI has been used for high-grade gliomas detection, albeit with limited success as it does not provide sufficient specificity and sensitivity to detect complex tumor structure. Therefore targeted contrast agents based on iron oxide, that shorten mostly T2 relaxation time, have been recently applied. However pulse sequences for molecular imaging in animal models of gliomas have not been yet fully studied. The aim of this study was therefore to compare contrast-to-noise ratio (CNR) and explain its origin using spin-echo (SE), gradient echo (GE), GE with flow compensation (GEFC) as well as susceptibility weighted imaging (SWI) in T2 and T2* contrast-enhanced molecular MRI of glioma.MethodsA mouse model was used. U87MGdEGFRvIII cells (U87MG), derived from a human tumor, were injected intracerebrally. A 9.4 T MRI system was used and MR imaging was performed on the 10 day after the inoculation of the tumor. The CNR was measured prior, 20 min, 2 hrs and 24 hrs post intravenous tail administration of glioma targeted paramagnetic nanoparticles (NPs) using SE, SWI, GE and GEFC pulse sequences.ResultsThe results showed significant differences in CNR among all pulse sequences prior injection. GEFC provided higher CNR post contrast agent injection when compared to GE and SE. Post injection CNR was the highest with SWI and significantly different from any other pulse sequence.ConclusionsMolecular MR imaging using targeted contrast agents can enhance the detection of glioma cells at 9.4 T if the optimal pulse sequence is used. Hence, the use of flow compensated pulse sequences, beside SWI, should to be considered in the molecular imaging studies.
Highlights
Standard MRI has been used for high-grade gliomas detection, albeit with limited success as it does not provide sufficient specificity and sensitivity to detect complex tumor structure
The goal of our studies was to optimize contrast-to-noise ratio (CNR) using spin echo (SE), gradient echo (GE) and gradient echo with flow compensation (GEFC) in contrast-enhanced molecular MRI at 9.4 T
An in vivo model was used for evaluating CNR of antibody-targeted iron nanoparticles in transplanted glioma using a range of pulse sequences to assess the vascular density of the tumor
Summary
Standard MRI has been used for high-grade gliomas detection, albeit with limited success as it does not provide sufficient specificity and sensitivity to detect complex tumor structure. The aim of this study was to compare contrast-to-noise ratio (CNR) and explain its origin using spin-echo (SE), gradient echo (GE), GE with flow compensation (GEFC) as well as susceptibility weighted imaging (SWI) in T2 and T2* contrast-enhanced molecular MRI of glioma. One. While the impact of the size and composition of targeted contrast agents on MR properties have been studied using standard pulse sequences, optimization of pulse sequences for molecular imaging in animal models of gliomas have not been yet fully characterized. [13]), data post processing [14] or ordered phase encoding [15] these methods do not address spin dephasing between excitation pulses and data acquisition due to fluid flows To overcome these MR sequence shortfalls, we applied a pulse sequence that uses flow compensating gradients, known as gradient moment nulling (GMN) [16,17,18]. An in vivo model was used for evaluating CNR of antibody-targeted iron nanoparticles in transplanted glioma using a range of pulse sequences to assess the vascular density of the tumor
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