Table 1.

Characteristics of commonly used versions of time-of-flight MR angiography. These are spoiled gradient echo sequences acquired during breath-hold

Version	Characteristics
2-D or thin-slab 3-D sequential acquisitions	Short TR (5–10 ms), short TE (1–3 ms), flip angle >45°. Tracking saturation bands for selective imaging of pulmonary arteries or veins (mostly for sagittal acquisitions) can be used.
2-D interleaved acquisitions	Long TR (100–280 ms), short TE (1–3 ms), intermediate flip angles (25°–45°). No tracking saturation bands. Inflow effects on the arterial side can provide higher signal than veins.
2-D segmented k-space acquisition with electrocardiographic triggering	Short TR (5–10 ms), short TE (1–3 ms). Optimal inflow effect at peak systole allows higher signal-to-noise ratio and distinction against veins. Can be performed in a cine loop. Usually one thick slice per breath-hold is acquired.
Thick-slab 3-D acquisition	Short TR (5–10 ms), short TE (1–3 ms). Sagittal slab, one lung. Low flip angles or spatially variable RF (TONE, VUSE). Arteries can be seen with higher intensity as compared to veins.

TE echo time, TR repetition time, TONE tilt optimized non-saturated excitation, VUSE variable angle uniform signal excitation