title: Comparison of self-gated and prospectively triggered fast low angle shot (FLASH) sequences for contrast-enhanced magnetic resonance imaging of the liver at 9.4 T in a rat model of colorectal cancer metastases.
abstract: OBJECTIVE
  The aim of this study was to compare a retrospectively self-gated fast low angle shot sequence (RSG-FLASH) with a prospectively triggered fast low angle shot sequence (PT-FLASH) using an external trigger device for dynamic contrast-enhanced magnetic resonance imaging of the liver at 9.4 T in a rat model of colorectal cancer metastases.
  
  
  METHODS
  In 10 rats with hepatic metastases, we acquired an axial RSG-FLASH sequence through the liver. A FLASH sequence with prospective triggering (PT-FLASH) using an external trigger device was acquired at the same location with the same imaging parameters. After intravenous injection of 0.2 mmol/kg body weight of Gd-DTPA, alternating acquisitions of both sequences were performed at 4 consecutive time points.Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and lesion enhancement were obtained for liver tumors and parenchyma. In addition, we assessed the total acquisition times of the different imaging approaches for each acquisition, including triggering and gating. Two independent readers performed a qualitative evaluation of each sequence. Statistical analyses included paired t tests and Wilcoxon matched pairs signed rank tests.
  
  
  RESULTS
  No statistically significant differences in SNR, CNR, or lesion enhancement were observed. Qualitative assessments of the sequences were comparable. However, acquisition times of PT-FLASH were significantly longer (mean [SD], 160.6 [25.7] seconds; P < 0.0001) and markedly variable (minimum, 120 seconds; maximum, 209 seconds), whereas the RSG-FLASH approach demonstrated a constant mean (SD) acquisition time of 59.0 (0) seconds.
  
  
  CONCLUSIONS
  The RSG-FLASH and PT-FLASH sequences do not differ qualitatively or quantitatively regarding SNR, CNR, and lesion enhancement for magnetic resonance imaging of the liver in the rats at 9.4 T. However, the variability of acquisition times for the PT-FLASH sequences is a major factor of inconsistency, and we therefore consider this approach as inappropriate for dynamic contrast-enhanced studies with multiple-measurement time points. In contrast, the RSG-FLASH sequence represents a fast, consistent, and reproducible technique suitable for contrast-agent kinetic studies in experimental small-animal imaging of the abdomen.
authors.affiliation: Clinic for Diagnostic and Interventional Radiology, Saarland University Medical Center, 66421 Homburg, Germany. drpeterfries@googlemail.com
authors.forename: Peter
authors.initials: P
authors.lastname: Fries
authors.forename: Roland
authors.initials: R
authors.lastname: Seidel
authors.forename: Andreas
authors.initials: A
authors.lastname: Müller
authors.forename: Kathrin
authors.initials: K
authors.lastname: Matthes
authors.forename: Gero
authors.initials: G
authors.lastname: Denda
authors.forename: Alexander
authors.initials: A
authors.lastname: Massmann
authors.forename: Michael D
authors.initials: MD
authors.lastname: Menger
authors.forename: Jens
authors.initials: J
authors.lastname: Sperling
authors.forename: John N
authors.initials: JN
authors.lastname: Morelli
authors.forename: Katrin
authors.initials: K
authors.lastname: Altmeyer
authors.forename: Günther
authors.initials: G
authors.lastname: Schneider
authors.forename: Arno
authors.initials: A
authors.lastname: Buecker
mesh_terms: D000465:Algorithms; D000818:Animals; D015179:Colorectal Neoplasms / Q000473:pathology*; D003287:Contrast Media; D004195:Disease Models, Animal; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008113:Liver Neoplasms / Q000473:pathology* / Q000556:secondary*; D008279:Magnetic Resonance Imaging; D051381:Rats; D015203:Reproducibility of Results; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA