Term explanation: partial volume effect

Partial volume effect and surrounding gap phenomenon

1. Partial volume effect: The value of each pixel on the CT image represents the average CT value of the entire corresponding unit tissue, which cannot

Truthfully reflect the CT values ??of various organizations within the unit. In CT scans, for lesions that are smaller than the slice thickness, the CT value is affected by the thickness of the slice. For lesions with a slice thickness, the CT value is affected by other tissues within the slice thickness. The measured CT value cannot represent the extent of the lesion. True CT value

For example, the CT value of small low-density lesions in high-density tissue is high; conversely, the CT value of small low-density lesions in low-density tissue is high. Density lesions have low CT values, a phenomenon called partial volume effect.

2. Peripheral gap phenomenon: refers to two adjacent structures with different densities perpendicular to the same scanning layer, and the CT values ????of their edges are also different. precise. The edge CT value of the one with high density is small, while the CT value of the edge of the low density one is large, and the edges of the intersection between the two structures are also unclear. This is caused by the overlapping of the scanning line beams when measuring the adjacent areas of the two structures. physical phenomena.