In this phantom image, two fluid-filled tubes are present. What type of resolution is being evaluated?

In this phantom image, two fluid-filled tubes are present. What type of resolution is being evaluated?

• A. Axial
• B. Lateral
• C. Contrast
• D. Elevational

Answer: (D)

The main idea here is how resolution in ultrasound is directional, with a distinct dimension for the slice thickness known as elevational resolution. When two fluid-filled tubes are arranged so their separation lies in the elevational direction (the thickness of the imaging slice, out of the plane of the image), being able to distinguish them shows how well the system resolves objects across that third dimension. Elevational resolution is determined by the beam’s thickness and the focusing in that out-of-plane direction, so a phantom with two tubes separated in that axis tests exactly that capability. If the tubes can be seen as two separate structures, the elevational resolution is sufficient; if they blur into one, elevational resolution is insufficient. This is different from axial resolution, which concerns separation along the depth of the beam, or lateral resolution, which concerns separation across the image plane within the same depth. Contrast resolution, meanwhile, is about distinguishing objects with similar brightness.

The main idea here is how resolution in ultrasound is directional, with a distinct dimension for the slice thickness known as elevational resolution. When two fluid-filled tubes are arranged so their separation lies in the elevational direction (the thickness of the imaging slice, out of the plane of the image), being able to distinguish them shows how well the system resolves objects across that third dimension. Elevational resolution is determined by the beam’s thickness and the focusing in that out-of-plane direction, so a phantom with two tubes separated in that axis tests exactly that capability.

If the tubes can be seen as two separate structures, the elevational resolution is sufficient; if they blur into one, elevational resolution is insufficient. This is different from axial resolution, which concerns separation along the depth of the beam, or lateral resolution, which concerns separation across the image plane within the same depth. Contrast resolution, meanwhile, is about distinguishing objects with similar brightness.