Analysis of Calcium in Carotid Plaques With Agatston Scores for Appropriate Selection of Surgical Intervention
Background and Purpose— The aim of the study was to determine whether the Agatston calcium score might be applied as a useful tool for evaluation of carotid stenosis.
Methods— A total of 124 carotid bifurcations were examined with multidetector row CT. Calcium scores were determined according to the method described by Agatston et al.
Results— Agatston scores generally appear appropriate for evaluation of calcified plaques. Calcified lesions with bigger differences between mean and peak Hounsfield unit (HU) in single cases accounted for only 34.3% of those with volume scores under 500 mm3, whereas 81.3% (P<0.001) for those sized >500 mm3.
Conclusions— The Agatston calcium score is useful in evaluating carotid plaques with calcium. We recommend, however, individual analyses for quality (hardness) and quantity (volume) of each large calcified focus (>500 mm3) by multidetector row CT lesions in order to provide indications for surgical treatment of carotid stenosis, carotid endarterectomy or carotid artery stenting.
- Agatston calcium score
- carotid artery stenting
- carotid endarterectomy
- carotid plaque
- carotid stenosis
We previously found calcifications of carotid plaques depicted as similar calcification in multidetector row (MD) CT may include relatively soft calcifications of granular type.1 This would be expected to influence the result of carotid artery stenting (CAS), because hard calcification might sometimes prevent expansion of stents. There are cases of carotid stenosis that are recommended for surgical intervention according to the results of North American Symptomatic Carotid Endarterectomy (NASCET),2 Asymptomatic Carotid Atherosclerosis Study (ACAS) 3 or other randomized controlled studies in which carotid endarterectomy (CEA) should be avoided because of high risk conditions. If calcification proves to be large but relatively soft, we can preoperatively predict that there is a chance to apply CAS safely and effectively.
The Agatston calcium score4 has been regularly used for evaluating calcification of coronary arteries using helical CT or electron beam CT. Though carotid atherosclerotic disease often overlaps patient population and risk factors, only limited investigators have used this method with the focus on carotid calcification.5,6
The aim of the present study was to analyze calcification of individual carotid plaques regarding their quality (hardness) and quantity (volume) by MDCT and determine whether the Agatston calcium score might also be applied as a useful tool for evaluating plaques with calcification as in coronary artery diseases, especially for deciding indications for surgical treatment for carotid stenosis, whether CEA or CAS.
Patients and Methods
A total of 124 carotid bifurcations in 62 consecutive patients (mean age 70.6±6.4 years, male:female=53:9, symptomatic:asymptomatic=42:20) were examined by 16-row MDCT (IDT-16, Philips). Among all carotid bifurcations, surgical interventions were performed on 65 carotid arteries, 44 by CEA and 21 by CAS, including 3 restenosis cases. The ethics guidelines for clinical studies by the Japanese Health Labor and Welfare Ministry (2003) were strictly observed.
A continuous spiral CT scan and the reconstruction of the images were conducted with the precise protocol as described previously.7 Calcification of the carotid plaque was quantified using the specialized software implemented in the workstation (Aquarious, TeraRecon) with preoperative MDCT data. Calcium scores were determined according to the method described by Agatston et al,4 calculated as the products of the areas of calcified lesions and the weighted signal intensity scalars, dependent on the maximal Hounsfield unit (HU) value within the lesion (scalar=1 if 130 to 199, 2 if 200 to 299, 3 if 300 to 399, and 4 if 400 or greater). To differentiate calcification from intravascular contrast agent, a threshold of 420 HU was used in line with a previous study.6 Isotropically interpolated volume scores for calcium were calculated as the products of the numbers of voxels with attenuation >130 HU and the voxel volumes. Postoperative remained stenoses of carotids were also checked with maximum intensity projection or multiplanar reconstruction images of MDCT by the NASCET method.2 The Fisher exact probability test and the Mann–Whitney U test were used for comparison. P<0.01 was considered to be statistically significant.
In 124 carotid arteries, 83 plaques were found to have calcification areas >0.67 mm3, their Agatston calcium scores, volume scores, averaged and peaked HU ranging from 3.7 to 4274.2, 2.5 to 3205.7, 255.9 to 871.7 and 389 to 2075, respectively (Table⇓). In cases under 70 years old, averaged Agatston score, volume score and mean HU were 322.8, 239.5 and 597.7, whereas 570.0 (P=0.10), 427.2 (P=0.09) and 898.6 (P=0.002) in cases older than 70.
Figure 1 shows mean and peak HU in order of volume scores. Higher volume scores tended to have bigger difference between mean and peak HU in single cases.
Of all calcified plaques, 43.4% (36/83) had portions over 80% harder than the average for hardness. This was the case for only 34.3% (23/67) with a volume score under 500, whereas for scores higher than 500, 600 and 700, the percentage rose to 81.3 (P<0.001, 13/16), 90.0 (P<0.001, 9/10) and 100% (P<0.001, 7/7), respectively. Though cases were limited, the mean degrees of the postoperative remained stenoses of the cases for CAS were 7.5/2.2% (P=0.02) for the cases with a volume score over/under 500, whereas 0.65 (P=0.05)/0% (P<0.001) in CEA cases.
Generally, our results showed high Agatston scores for larger and harder masses (Figure 2A through 2D). However, some calcified lesions were found which had apparently hard and relatively soft parts in single calcifications. For example, in case 22, a 76-year-old man (Figure 2E through 2I), the Agatston and volume scores were 810.8 and 623.7, respectively. The lower part was relatively soft (433 in lateral and 693 HU in medial sides in maximum) and the upper part was hard (1302 HU). This case was assigned for CEA because no obstacle was found other than calcification in the plaque for surgical intervention. Diminishment of calcification and amelioration of the stenosis were observed on postoperative MDCT. In case 37, an 84-year-old woman (Figure 2J through 2S), the Agatston and volume scores were 672.4 and 504, respectively. The upper and the lower parts were relatively soft (878 and 695 HU in maximum) and the middle part was hard (1155 in lateral and 1222 in medial sides). CAS was selected because of her high age and severe heart disease. Relatively good improvement of the stenosis was observed on postoperative MDCT, though partial limitation of the expansion of the stent was noted in calcification. These cases illustrate the necessity for individual evaluation of calcification with large lesions.
Though cases were quite limited, the fact that the averaged degrees of the postoperative remained stenoses tended to be relatively higher in the CAS cases with volume scores over 500, which were likely to have portions over 80% harder than the average for hardness, may support the importance of analysis of plaques with large calcium deposits. Analysis of calcium is still important considering highly aged population of the disease. Even in our series, the high aged group over 70 years old tended to demonstrate higher Agatston, volume scores and mean HU (though not significant except HU).
In summary, the Agatston calcium score is useful for evaluating carotid plaques with calcium deposits. We recommend, however, individual analyses for quality (hardness) and quantity (volume) of each calcified focus on MDCT for large lesions (>500 mm3) to determine indications for surgical treatment for carotid stenosis, whether CEA or CAS.
The authors would like to thank Dr Mitsuhito Mase, Dr Noritaka Aihara and Dr Masao Nakatsuka for excellent performance of CAS. We also thank Dr Atsuo Masago, Dr Yotaro Takeuchi for assistance in collecting data and all our ward staff.
- Received April 12, 2007.
- Accepted May 1, 2007.