title: Effects of breath-hold and cardiac cycle on the MRI appearance of the aorta and inferior vena cava in t2 abdominal imaging.
abstract: OBJECTIVE
  The purpose of this article is to review the MR principles of blood signal and normal flow-related phenomena seen in the aorta and inferior vena cava (IVC) on T2-weighted images of the abdomen and to discuss the physiologic and physical basis of signal alterations with breath-hold imaging. We define time-of-flight (TOF) loss and list the factors that affect it; explain the physiologic effects of breath-hold imaging on both aortic and IVC waveforms and velocity; state which abdominal T2 imaging techniques are most susceptible to variable TOF effects and explain why based on physiologic effects and MR principles; and describe three trouble-shooting techniques to confirm that unexpected signal does not reflect pathology.
  
  
  CONCLUSIONS
  T2 images customarily result in TOF loss and dark blood signal. Abdominal MRI relies extensively on breath-hold imaging techniques that may alter markedly the flow velocity in normal vessels. This marked flow change results in signal heterogeneity and variable TOF loss especially with faster sequences filling k-space in shorter time frames. Breath-hold imaging decreases k-space fill time, and of the breath-hold T2 techniques, single-shot fast spin-echo decreases k-space fill time the most. Atypical blood signal during breath-hold imaging may mimic pathology, but abnormal findings can be verified by review of other sequences and planes of imaging.
authors.affiliation: Department of Radiology, Brooke Army Medical Center, 3851 Roger Brooke Drive, Ft. Sam Houston, TX 78234, USA. Christopher.Lisanti@amedd.army.mil
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lisanti
authors.forename: David B
authors.initials: DB
authors.lastname: Douglas
mesh_terms: D001011:Aorta / Q000502:physiology*; D001783:Blood Flow Velocity; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D012119:Respiration; D014682:Vena Cava, Inferior / Q000502:physiology*