The following two Sagittal images of an artery were obtained with different transducers. What type of resolution is limiting visualization of the arterial lumen in the image on the left?

• A. Axial
• B. Lateral
• C. Temporal
• D. Slice thickness

Answer: (D)

The main idea here is elevational (slice-thickness) resolution. In ultrasound, there’s resolution not just along and across the beam, but also in the third dimension—the thickness of the ultrasound slice that the beam samples. If that slice is thick, echoes from the lumen mix with echoes from surrounding tissue within the same slice, causing partial volume averaging. That blurs the edges of the artery’s lumen and makes it harder to see clearly in the left image. A transducer with a thinner elevational dimension provides better slice-thickness resolution, yielding a crisper, more defined lumen. Axial resolution relates to along-the-beam detail, lateral to across-the-beam detail in the imaging plane, and temporal to frame rate; these aren’t the limiting factors for this vignette.