title: Investigation of the longitudinal relaxation rate of blood after gadobenate dimeglumine administration: sequence optimization, dynamic acquisition, and clinical impact for contrast-enhanced MR angiography of the carotid arteries.
abstract: OBJECTIVE
  To optimize the image acquisition parameters for improved steady-state (SS) contrast-enhanced magnetic resonance angiography (CE-MRA) of the carotid arteries with gadobenate dimeglumine.
  
  
  METHODS
  An inversion recovery fast low-angle shot (IR-FLASH) sequence for ultrafast determination of the longitudinal relaxation rate R1 was first optimized on phantoms and tested against a routine variable repetition time (TR) spin echo sequence used as reference standard. Different combinations of flip angle (FA, between 6 and 14 degrees) and inversion time (between 134 and 9000 milliseconds) were evaluated to achieve the best trade off between speed and accuracy. The optimized sequence was thereafter used in vivo in 5 subjects to determine the time evolution of blood R1 at 1.5 T after administration of gadobenate dimeglumine at 0.1 mmol/kg bodyweight. An optimal FA for angiographic measurement was thereafter derived from the Ernst equation based on experimental values of R1 previously determined in vivo. Finally, steady-state CE-MRA examinations were performed in 20 subjects to evaluate the improved contrast achieved after optimization of the FA for maximal blood signal enhancement.
  
  
  RESULTS
  An ultrafast IR-FLASH sequence with a flip angle of 8 degrees and a properly defined set of inversion time values was shown to give in vitro R1 determinations that were in good agreement with those obtained using a routine, time consuming, variable-TR spin echo sequence. The use of this ultrafast IR-FLASH sequence in vivo allowed the blood signal behavior in the carotid arteries after gadobenate dimeglumine administration to be monitored. Using this sequence, the R1 decreased from 8.7±0.96 s⁻¹ at 30 seconds after injection to 3.8±0.24 s⁻¹ at 10 minutes after injection. Based on these data for R1, the optimal FA for SS CE-MRA was calculated to be 18 degrees for a gradient echo acquisition protocol with TR=7.5 milliseconds, when gadobenate dimeglumine is used. Significantly higher blood signal to noise ratio was achieved on SS images acquired using a three-dimensional spoiled gradient echo sequence with a FA of 18 degrees than on corresponding images acquired with a FA of 35 degrees as used typically for intravascular blood pool contrast agents (52.5±8.3 vs. 29.5±6.0; P<0.05, Mann-Whitney U test).
  
  
  CONCLUSIONS
  Detailed experimental knowledge of the in vivo R1 behavior of blood after gadobenate dimeglumine injection and appropriate modification of the acquisition parameters enables improved signal intensity enhancement on steady-state CE-MRA of the carotid arteries.
authors: CRB-Bracco Imaging Spa, Colleretto Giacosa (TO), Italy. cristina.neira@bracco.com
authors: Cristina
authors: C
authors: Neira
authors: Michele
authors: M
authors: Anzidei
authors: Alessandro
authors: A
authors: Napoli
authors: Miles A
authors: MA
authors: Kirchin
authors: Beatrice
authors: B
authors: Cavallo Marincola
authors: Fulvio
authors: F
authors: Zaccagna
authors: Carlo
authors: C
authors: Catalano
authors: Roberto
authors: R
authors: Passariello
authors: Fabio
authors: F
authors: Tedoldi
mesh_terms: D000368:Aged; D000418:Albumins / Q000378:metabolism*; D002339:Carotid Arteries; D003287:Contrast Media / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography; D008297:Male; D008536:Meglumine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D008875:Middle Aged; D009942:Organometallic Compounds / Q000008:administration & dosage / Q000493:pharmacokinetics*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D000418:Albumins; D003287:Contrast Media; D009942:Organometallic Compounds; C064572:gadobenic acid; D008536:Meglumine