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Effects of Breath-Hold and Cardiac Cycle on the MRI Appearance of the Aorta and Inferior Vena Cava in T2 Abdominal Imaging

¹ Department of Radiology, Brooke Army Medical Center, 3851 Roger Brooke Dr., No. 3600, Ft. Sam Houston, TX 78234.
² David Grant Medical Center, Travis AFB, CA.

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.

CONCLUSION. 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.

Keywords: abdominal imaging • aorta • cardiac imaging • breath-hold imaging • hemodynamics • inferior vena cava • MRI

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