| Summary: | 碩士 === 中原大學 === 生物醫學工程研究所 === 103 === Low dose lung computed tomography (CT) scan is ideal for lung cancer screening. Maintaining sensitivity of detecting lung nodule and reasonably reducing radiation dose is the rationale behind low dose lung CT scan. However, coronary calcification, sometimes evidently identified, cannot be accurately quantified in the setting of low dose lung CT scan. The purpose of this study was to explore the feasibility of deriving coronary calcium score from low dose lung CT scan and to establish a post-processing correction model accordingly.
This was a retrospective study conducted in a Northern healthcare institute with a sample size of 530 persons who simultaneous underwent low dose lung CT scan and standard CT scan for estimating Agatston coronary calcium score. For first part of the study, parameters in low dose lung CT scan image reconstruction were modified and the reconstructed new images were used for calculating coronary calcium score and calcium score ranking. Calcium score and calcium score ranking derived from low dose lung CT scan and standard CT scan were compared with its agreement reported. For second part of the study, the threshold CT value of coronary calcification was lowered from 130 to 90 Hounsfield Unit (HU) and calcium score was recalculated. The recalculated calcium score and calcium score ranking were compared with those by standard CT and its agreement was explored.
In first part of the study, age, gender and body mass index significantly correlated with coronary calcium score. Calcium score ranking derived from low dose CT scan and standard CT scan showed modest agreement - Kappa value 0.74 for overall and 0.89 for zero calcium score subgroup (comprising 78.6% of the overall sample size). Calcium score and its ranking showed good correlation between two CT scans with Pearson and Spearman correlation coefficient of 0.979 and 0.915, respectively. The average radiation absorbed dose in low dose lung CT scan reduced one third compared with standard CT scan. In second part of the study, the agreement and correlation of calcium score and calcium score ranking in low dose lung CT and standard CT were further improved with a Kappa value of 0.83, Pearson and Spearman correlation coefficient of 0.986 and 0.942, respectively. It is postulated that adjusting threshold CT value for coronary calcification to 90 HU may improve accuracy of calcium score and calcium score ranking in low dose lung CT scan.
Summing up, low dose lung CT scan combined with the proposed correction model may be feasible for estimating coronary calcium score in low-risk or asymptomatic subjects without risk factors for coronary artery disease. Reserving further work-ups such as standard CT scan for those with significant coronary calcification seen on low dose lung CT not only reduces radiation dose but also may be more time-saving and cost-effective.
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