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

Table 1 Demographics n (%)

Population	Total (n = 400)	Group 1 (n = 200)	Group 2 (n = 200)
Age (yr), mean ± SD (range)	65.1 ± 11.1 (31-88)	63.6 ± 11.2 (38-87)	66.5 ± 10 (31-88)
Gender (M/F)	249/151	126/74	123/77
Symptoms
Typical angina	123 (30.8)	60 (30)	63 (31.5)
Atypical chest pain	204 (51)	101 (50.5)	105 (52.5)
Unstable angina	34 (8.5)	14 (7)	20 (10)
AMI	15 (3.8)	15 (7.5)	0 (0)
High risk asymptomatic	22 (5.5)	10 (5)	12 (8.3)
Cardiovascular risk factors
Hypertension	250 (62.5)	118 (59)	132 (66)
Dyslipidemia	202 (50.5)	92 (46)	110 (55)
Diabetes	58 (14.5)	30 (15)	28 (14)
Smoking	98 (24.5)	47 (23.5)	51 (25.5)
Family history	171 (42.8)	90 (45)	81 (40.5)
BMI (kg/m2), mean ± SD (range)	27.1 ± 3.9 (20-47)	26.7 ± 4.1 (20-47)	27.4 ± 3.8 (20-45)
RF/patient (mean ± SD)	2.1 ± 1.3	2.0 ± 1.2	2.2 ± 1.4
Calcium score (agatston score, mean ± SD)	336.7 ± 627.4	303.3 ± 628.8	370.2 ± 627.4
HR during CTCA (bpm), mean ± SD (range)	59.5 ± 7.3 (42-75)	59.5 ± 8.0 (43-75)	59.5 ± 6.5 (42-75)

AMI: Acute myocardial infarction; BMI: Body mass index; RF: Risk factors; CTCA: Computed tomography coronary angiography; HR: Heart rate; M/F: Male/female.

Table 2 General parameters (mean ± SD)

	Total	Group 1	Group 2	P-value
Global quality assessment	2.85 ± 0.34	2.83 ± 0.37	2.86 ± 0.31	0.425
Global vascular attenuation (HU)	370.6 ± 82.5	380.0 ± 65.2	353.5 ± 69.0	< 0.0001
Plaque attenuation (HU)	42.7 ± 23.5	48.3 ± 22.5	38.7 ± 21.4	< 0.0001
Lumen attenuation (HU)	344.1 ± 87.1	366.9 ± 85.1	327.4 ± 72.8	< 0.0001
Difference lumen vs plaque (HU)	301.4 ± 62.6	318.7 ± 88.9	289.2 ± 74.0	< 0.0001
Aortic attenuation (HU)	374.7 ± 67.4	380.1 ± 64.2	335.2 ± 70.6	< 0.0001
Aortic noise (HU)	26.4 ± 8.6	31.6 ± 8.3	21.2 ± 4.9	< 0.0001
RCA attenuation (HU)	372.3 ± 173.8	384.5 ± 76.5	336.7 ± 72.3	< 0.0001
LM attenuation (HU)	364.8 ± 70.6	375.3 ± 66.6	354.4 ± 73.1	0.003
Noise (HU)	23.3 ± 7.1	25.8 ± 6.5	18.0 ± 5.0	< 0.0001
S/N	18.7 ± 8.4	15.6 ± 4.7	21.2 ± 7.7	< 0.0001

HU: Hounsfield units; S/N: Signal to noise; RCA: Right coronary artery; LM: Left main; IQR: Inter-quartile range.

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.