Plaque imaging with CT coronary angiography: Effect of intra-vascular attenuation on plaque type classification

Table 3 Plaque classification

Threshold	Type	Group 1		Group 2		P-value
		n (%)	Ratio (lipid/fibrous)	n (%)	Ratio (lipid/fibrous)
30 HU	Lipid rich	9 (1.9)	0.020	129 (20.0)	0.250	< 0.01
	Fibrous	459 (98.1)		515 (80.0)
50 HU	Lipid rich	151 (32.3)	0.476	467 (72.5)	2.638	< 0.01
	Fibrous	317 (67.7)		177 (27.5)
70 HU	Lipid rich	381 (81.4)	4.379	588 (91.3)	10.500	< 0.01
	Fibrous	87 (18.6)		56 (8.7)
	Total	468		644

The Table shows plaque classification in the two groups (Group 1 vs Group 2) depending on different attenuation thresholds [30 hounsfield units (HU), 50 HU and 70 HU]. The grey background is applied to threshold = 50 HU which represents the conventionally recognised threshold for plaque classification. Ratio represents the relative proportion of lipid rich vs fibrous plaques. The trend is significant towards a shift from fibrous to lipid rich plaques when thresholds are progressively increased in both groups (P < 0.05). However, the proportion of lipid rich plaques is consistently higher in Group 2 regardless of the threshold applied. As expected, the effect is slightly fading out with progressively higher thresholds.