STrategically Acquired Gradient Echo (STAGE) imaging, part I: Creating enhanced T1 contrast and standardized susceptibility weighted imaging and quantitative susceptibility mapping

Magn Reson Imaging. 2018 Feb;46:130-139. doi: 10.1016/j.mri.2017.10.005. Epub 2017 Oct 19.

Abstract

Purpose: To provide whole brain grey matter (GM) to white matter (WM) contrast enhanced T1W (T1WE) images, multi-echo quantitative susceptibility mapping (QSM), proton density (PD) weighted images, T1 maps, PD maps, susceptibility weighted imaging (SWI), and R2* maps with minimal misregistration in scanning times <5min.

Methods: Strategically acquired gradient echo (STAGE) imaging includes two fully flow compensated double echo gradient echo acquisitions with a resolution of 0.67×1.33×2.0mm3 acquired in 5min for 64 slices. Ten subjects were recruited and scanned at 3 Tesla. The optimum pair of flip angles (6° and 24° with TR=25ms at 3T) were used for both T1 mapping with radio frequency (RF) transmit field correction and creating enhanced GM/WM contrast (the T1WE). The proposed T1WE image was created from a combination of the proton density weighted (6°, PDW) and T1W (24°) images and corrected for RF transmit field variations. Prior to the QSM calculation, a multi-echo phase unwrapping strategy was implemented using the unwrapped short echo to unwrap the longer echo to speed up computation. R2* maps were used to mask deep grey matter and veins during the iterative QSM calculation. A weighted-average sum of susceptibility maps was generated to increase the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR).

Results: The proposed T1WE image has a significantly improved CNR both for WM to deep GM and WM to cortical GM compared to the acquired T1W image (the first echo of 24° scan) and the T1MPRAGE image. The weighted-average susceptibility maps have 80±26%, 55±22%, 108±33% SNR increases across the ten subjects compared to the single echo result of 17.5ms for the putamen, caudate nucleus, and globus pallidus, respectively.

Conclusions: STAGE imaging offers the potential to create a standardized brain imaging protocol providing four pieces of quantitative tissue property information and multiple types of qualitative information in just 5min.

Keywords: Quantitative susceptibility mapping (QSM); Susceptibility weighted imaging (SWI); T1 mapping; T1 weighted (T1W) imaging.

MeSH terms

  • Adult
  • Brain / diagnostic imaging
  • Brain Mapping / methods*
  • Caudate Nucleus / diagnostic imaging
  • Computer Simulation
  • Contrast Media / chemistry
  • Female
  • Globus Pallidus / diagnostic imaging
  • Gray Matter / diagnostic imaging*
  • Humans
  • Image Processing, Computer-Assisted
  • Magnetic Resonance Imaging / methods*
  • Male
  • Models, Statistical
  • Neurodegenerative Diseases / diagnostic imaging
  • Protons
  • Putamen / diagnostic imaging
  • Signal-To-Noise Ratio
  • White Matter / diagnostic imaging*

Substances

  • Contrast Media
  • Protons