title: Measurement of caval blood flow with MRI during respiratory maneuvers: implications for vascular contrast opacification on pulmonary CT angiographic studies.
abstract: OBJECTIVE
  Transient interruption of the contrast bolus has been described as a physiologic artifact that can sometimes result in poor opacification of the pulmonary arteries on pulmonary CT angiographic studies. To better understand the mechanism underlying this artifact, we used velocity-encoded cine MRI to measure flow in the inferior vena cava (IVC) and superior vena cava (SVC) during respiratory maneuvers.
  
  
  METHODS
  Quantitative measurements of SVC and IVC flow per R-R interval were performed on 10 healthy volunteers (six men, four women; median age, 30 years; range, 25-55 years) with a retrospectively ECG-gated velocity-encoded gradient-echo cine sequence on a 1.5-T MRI unit with axial slices at the level of the diaphragm and just below the azygous vein confluence during free breathing, continuous inspiration, breath-hold at end inspiration, Valsalva maneuver, and breath-hold at end expiration.
  
  
  RESULTS
  Median flow during free breathing was 38.9 mL in the SVC and 74.3 mL in the IVC, during continuous inspiration was 43.9 mL in the SVC and 113.7 mL in the IVC, during breath-hold at end inspiration was 31.0 mL in the SVC and 56.1 mL in the IVC, during a Valsalva maneuver was 28.9 mL in the SVC and 53.9 mL in the IVC, and during breath-hold at end expiration was 35.3 mL in the SVC and 61.2 mL in the IVC.
  
  
  CONCLUSIONS
  MRI measurements showed a significant increase in caval flow during inspiration and a greater relative increase in blood flow in the IVC than in the SVC. For thoracic CT performed with IV contrast enhancement, deep inspiration before scanning leads to a large influx of IVC blood that does not contain contrast medium and dilutes the contrast bolus, causing poor vascular opacification. Avoiding initial inspiration before scanning is suggested as a way to limit the transient interruption of the contrast bolus artifact.
authors.affiliation: Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL 32224, USA. rskuzo@hotmail.com
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Kuzo
authors.forename: Robert A
authors.initials: RA
authors.lastname: Pooley
authors.forename: Julia E
authors.initials: JE
authors.lastname: Crook
authors.forename: Michael G
authors.initials: MG
authors.lastname: Heckman
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Gerber
mesh_terms: D000328:Adult; D016477:Artifacts; D001783:Blood Flow Velocity / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011651:Pulmonary Artery / Q000000981:diagnostic imaging* / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology*; D011859:Radiography; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D012680:Sensitivity and Specificity; D014684:Venae Cavae / Q000033:anatomy & histology / Q000502:physiology*