Multi-echo length and offset VARied saturation (MeLOVARS) method for improved CEST imaging

Research output: Contribution to journalArticlepeer-review


Purpose: The aim of this study was to develop a technique for rapid collection of chemical exchange saturation transfer images with the saturation varied to modulate signal loss transfer and enhance contrast. Methods: Multi-echo Length and Offset VARied Saturation (MeLOVARS) divides the saturation pulse of length Tsat into N = 3-8 submodules, each consisting of a saturation pulse with length of Tsat/N (∼0.3-1 s), one or more low flip-angle gradient-echo readout(s) and a flip back pulse. This results in N readouts with increasing saturation time from Tsat/N to Tsat without extra scan time. Results: For phantoms, eight images with Tsat incremented every 0.5 s from 0.5-4 s were collected simultaneously using MeLOVARS, which allows rapid determination of exchange rates for agent protons. For live mice bearing glioblastomas, the Z-spectra for five different Tsat values from 0.5 to 2.5 s were acquired in a time normally used for one Tsat. With the additional Tsat-dependence information, LOVARS phase maps were produced with a more clearly defined tumor boundary and an estimated 4.3-fold enhanced contrast-to-noise ratio (CNR). We also show that enhancing CNR is achievable by simply averaging the collected images or transforming them using the principal component analysis. Conclusions: MeLOVARS enables collection of multiple saturation-time-weighted images without extra time, producing a LOVARS phase map with increased CNR.

Original languageEnglish (US)
Pages (from-to)488-496
Number of pages9
JournalMagnetic resonance in medicine
Issue number2
StatePublished - Feb 1 2015


  • Brain tumor imaging
  • CEST
  • EPI
  • Length and offset VARied saturation (LOVARS)
  • Multi-echo LOVARS(MeLOVARS)

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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