title: Contrast-enhanced magnetic resonance angiography: first-pass arterial enhancement as a function of gadolinium-chelate concentration, and the saline chaser volume and injection rate.
abstract: OBJECTIVE
  To evaluate the effect of the contrast medium (CM) concentration and the saline chaser volume and injection rate on first-pass aortic enhancement characteristics in contrast-enhanced magnetic resonance angiography using a physiologic flow phantom.
  
  
  METHODS
  Imaging was performed on a 3.0-T magnetic resonance system (MAGNETOM Trio, Siemens Healthcare Solutions, Inc, Erlangen, Germany) using a 2-dimensional fast low angle shot T1-weighted sequence (repetition time, 500 milliseconds; echo time, 1.23 milliseconds; flip angle, 8 degrees; 1 frame/s × 60 seconds). The following CM concentrations injected at 2 mL/s were used with 3 different contrast agents (gadolinium [Gd]-BOPTA, Gd-HP-DO3A, Gd-DTPA): 20 mL of undiluted CM (100%) and 80%, 40%, 20%, 10%, 5%, and 2.5% of the full amount, all diluted in saline to a volume of 20 mL to ensure equal bolus volume. The CM was followed by saline chasers of 20 to 60 mL injected at 2 mL/s and 6 mL/s. Aortic signal intensity (SI) was measured, and normalized SI versus time (SI/Tn) curves were generated. The maximal SI (SI(max)), bolus length, and areas under the SI/Tn curve were calculated.
  
  
  RESULTS
  Decreasing the CM concentration from 100% to 40% resulted in a decrease of SI(max) to 86.1% (mean). Further decreasing the CM concentration to 2.5% decreased SI(max) to 5.1% (mean). Altering the saline chaser volume had no significant effect on SI(max). Increasing the saline chaser injection rate had little effect (mean increase, 2.2%) on SI(max) when using ≥40% of CM. There was a larger effect (mean increase, 19.6%) when ≤20% of CM were used. Bolus time length was significantly shorter (P < 0.001), and area under the SI/T(n) curve was significantly smaller (P < 0.01) for the CM protocols followed by a saline chaser injected at 6 mL/s compared with a saline chaser injected at 2 mL/s.
  
  
  CONCLUSIONS
  With 40% of CM and a fast saline chaser, SImax close to that with undiluted CM can be achieved. An increased saline chaser injection rate has a more pronounced effect on aortic enhancement characteristics at lower CM concentrations than at higher CM concentrations.
authors.affiliation: Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Daniela B
authors.initials: DB
authors.lastname: Husarik
authors.forename: Mustafa R
authors.initials: MR
authors.lastname: Bashir
authors.forename: Paul W
authors.initials: PW
authors.lastname: Weber
authors.forename: Eli B
authors.initials: EB
authors.lastname: Nichols
authors.forename: Laurens E
authors.initials: LE
authors.lastname: Howle
authors.forename: Elmar M
authors.initials: EM
authors.lastname: Merkle
authors.forename: Rendon C
authors.initials: RC
authors.lastname: Nelson
mesh_terms: D001011:Aorta / Q000033:anatomy & histology* / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D002614:Chelating Agents / Q000008:administration & dosage; D003287:Contrast Media / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D005682:Gadolinium / Q000008:administration & dosage*; D006801:Humans; D007269:Injections, Intra-Arterial; D018810:Magnetic Resonance Angiography / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012965:Sodium Chloride / Q000008:administration & dosage*
chemical_list: D002614:Chelating Agents; D003287:Contrast Media; D012965:Sodium Chloride; D005682:Gadolinium