Contrast Agent Methods: Data Acquisition & Image Reconstruction
Ricardo Otazo1

1Center for Advanced Imaging, Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine

Synopsis

This lecture presents the main data acquisition and image reconstruction techniques for DCE-MRI and DSC-MRI, and discusses strengths, limitations and opportunities.

Objectives

  • Describe pulse sequences and parameters used for DCE and DSC MRI data acquisition
  • Study the application of acceleration techniques that exploit spatiotemporal correlations to DCE and DSC MRI

Introduction

The use of dynamic MRI techniques to track the passage of an external contrast agent has become an essential tool for tumor detection, characterization and treatment response. One significant strength is that quantitative information can be obtained using spatiotemporal data fitting with a pharmacokinetic model. Two of the most common methods are dynamic contrast enhanced MRI (DCE-MRI) and dynamic susceptibility contrast MRI (DSC-MRI). DCE-MRI acquires a series of T1-weighted images and is widely used for diagnosis of cancer (1). DSC-MRI methods use T2*-weighting to acquire dynamic information and are usually used for brain tumors (2). Both DCE and DSC require fast imaging to enable adequate combinations of temporal resolution to track the contrast agent passage, spatial resolution and volumetric coverage. The existence of a temporal dimension offers the great opportunity to apply compressed sensing techniques to exploit the inherent correlations among time points (3-5). This lecture presents a brief overview of pulse sequences and image reconstruction techniques of DCE-MRI and DCS-MRI. Special focus is given to accelerated imaging techniques that optimize the acquisition by exploiting spatiotemporal correlations.

Dynamic Contrast Enhanced (DCE) MRI

DCE-MRI exploits the relaxivity effect of the contrast agent and is usually performed with fast T1-weighted gradient echo pulse sequences. Standard gradient echo sequences can provide a moderate degree of T1-weighting, but pre-pulses such as saturation (90o) or inversion (180o) allow a significantly higher T1-weighting to be achieved (6). Significant improvements in temporal and spatial resolution, and motion robustness can be achieved using compressed sensing techniques (7-9). New trends in compressed sensing DCE-MRI are including the pharmacokinetic model in the reconstruction algorithm to directly estimate parameters from undersampled k-space data (10).

Dynamic Susceptibility Contrast (DSC) MRI

DSC-MRI exploits the susceptibility effect of the contrast agent and is usually performed with single-shot echo-planar imaging (EPI) pulse sequences, which are sensitive to T2* (due to long effective TE) and fast enough to track the passage of the contrast agent (6). The impact of compressed sensing in DSC-MRI is lower than in DCE-MRI, which is due in part to the challenges to randomly undersample EPI acquisitions. Other acceleration techniques, such as spatiotemporal parallel imaging with PEAK-GRAPPA (11) and simultaneous multislice (SMS) (12), are more promising to increase the performance of DSC-MRI.

Acknowledgements

Center for Advanced Imaging Innovation and Research, a National Institute for Biomedical Imaging and Bioengineering Biomedical Technology Resource Center (P41 EB017183)

References

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Proc. Intl. Soc. Mag. Reson. Med. 25 (2017)