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095 Plaque mapping based on contrast ratios permits identification of unstable coronary plaque and quantification of coronary atherosclerosis by coronary CT angiography
  1. D R Obaid1,
  2. P A Calvert1,
  3. M Goddard2,
  4. D Gopalan2,
  5. J H F Rudd1,
  6. M R Bennett1
  1. 1University of Cambridge, Cambridge, UK
  2. 2Papworth NHS Foundation Trust Hospital, Cambridge, UK


Background Previous attempts to characterise coronary components using CT have relied on fixed Hounsfield unit (HU) ranges which do not correct for the effect of inter-patient variation of contrast intensity on plaque attenuation. We examine the utility of using HU-ranges derived from contrast attenuation ratios.

Methods 57 patients underwent coronary CT and Virtual Histology IVUS examination. Attenuation was sampled in over 1000 plaque areas co-registered with VH-IVUS and compared to contrast attenuation to create contrast ratios for each plaque component. These ratios were used to create a colour map of the plaque based on the HU of its constituents and used to test: (A) Classification of plaque components against histology in 10 post-mortem human coronary arteries. (B) Quantification of plaque geometry and composition compared with VH-IVUS in 30 coronary segments. (C) Ability to differentiate 63 patients prospectively enrolled with either stable angina or acute coronary syndrome.

Results (A) CT contrast ratio defined HU-colour maps were created for the 10 post-mortem arteries which were then sectioned into eighty-seven 400 μm segments for histological analysis. The maps permitted detection of significant atherosclerosis with sensitivity-92% and specificity-90%, calcified-plaque with sensitivity-80% and specificity-88% and necrotic core sensitivity-55%, specificity-96%. If only necrotic core area >2 mm2 are considered (above the spatial resolution of CT) there is a significant improvement in sensitivity-75%. (B) Plaque-maps were created for 900 mm of coronary segments and co-registered with VH-IVUS. On average, CT overestimated total plaque area by 44%, vessel volume-33%, lumen-10%, necrotic core-140%, fibrous plaque-70% and calcified plaque-9%. However, correlation between CT and VH-IVUS was highly significant (p<0.001) for all measurements: vessel volume (r=0.86), lumen (r=0.74), necrotic core (r=0.47), fibrous plaque (r=0.74) and calcified plaque r=0.69). (C) Culprit lesions of 31 patients with stable angina and 32 with troponin-positive ACS underwent CT prior to PCI. Features discriminating acute from stable plaque detected using the plaque-maps include: micro-calcification-63% vs 35% (p=0.03), distinct necrotic core-56% vs 23% (p<0.01) (Abstract 095 figure 1) and positive vessel remodelling-68% vs 26% (p<0.001). The percentage of necrotic core (low attenuation plaque) was higher in acute plaques-54% vs 44% (p<0.01) while conversely the percentage of calcified plaque (high attenuation plaque) was lower-4% vs 15% (p<0.01). Intra-plaque contrast was more common 44% vs 6% (p<0.001) with high specificity for acute plaques (94%) and we feel it may represent visualisation of plaque rupture (Abstract 095 figure 1).

Abstract 095 Figure 1

(A) CT image of intra-plaque contrast with colour mapping. (B) Corresponding coronary angiogram. (C) IVUS reveals plaque rupture at this point.

Conclusion Plaque-mapping with contrast ratios allows plaque quantification and may assist diagnosis of acute plaque rupture.

  • CT
  • TCFA
  • dual energy

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