The Image Quality and Feasibility of Delayed Phase in Cardiac CT: Prospective ECG-Triggering Sequential Scan Versus Retrospective ECG-Gating Spiral Scan Using the Same Radiation Dose

心臟電腦斷層延遲相的影像品質和可行性分析：相同輻射劑量下前瞻性心電圖觸發順序掃描與回溯性心電圖門控螺旋掃描之比較

蔡瑋琳(Wei-Lin Tsai) ； 蔡依橙(I-Chen Tsai) ； 陳明至(Min-Chi Chen) ； 林保鐘(Pao-Chun Lin) ； 陳詩華(Si-Wa Chan) ； 何惠卿(Hui-Ching Ho) ； 廖婉君(Wan-Chun Liao) ； 陳啓昌(Clayton Chi-Chang Chen)

《中華放射線醫學雜誌》 34卷2期 (2009/06) Pp. 67-78

摘要

比較在相同輻射劑量下，以前瞻性心電圖觸發順序掃描（修改自鈣化分數掃描技術）與回溯性心電圖門控螺旋掃描，施作延遲相心臟電腦斷層之影像品質與可行性
自2007年三月到四月，以前瞻性心電圖觸發順序掃描技術施作所有延遲相之心臟電腦斷層。2007年五月到六月的患者則以回溯性心電圖門控螺旋掃描施作。輻射劑量皆經事先計算和設定以調整至相同等級。影像邊緣銳利度、層狀假影、射束硬化假影以grade 1（最差）到grade 5（最佳）作半定量分析，其中grade 1和grade 2定義為無法判讀。並以統計方法比較病患基本資料、影像雜訊、假影差異、掃描時間、以及輻射劑量。
排除已知有冠狀動脈或心肌疾病的病患後，兩種掃描方式各自有31名患者列入研究。前瞻性心電圖觸發順序掃描在影像雜訊和邊緣銳利度上表現較佳；回溯性心電圖門控螺旋掃描在層狀假影和射束硬化假影上表現較佳。若考慮是否可以判讀，則前瞻性心電圖觸發順序掃描組因嚴重層狀假影和射束硬化假影分別造成41.9%和85.5%的不可判讀比例；而螺旋掃描組則100%皆可判讀。
施作心臟電腦斷層延遲相時，若使用相同輻射劑量，則應使用回溯性心電圖門控螺旋掃描而非前瞻性心電圖觸發順序掃描。由於前瞻性心電圖觸發順序掃描會造成嚴重的層狀假影和射束硬化假影，在臨床使用上是不可行的。

並列摘要

To compare the image quality and interpretability of two delayed phase protocols of cardiac CT under the same low radiation dose: prospective ECG-triggering sequential scan (modified from the calcium score protocol) versus retrospective ECG-gating spiral scan with ECG-pulsing.
From March to April of 2007, in al l the patients referred for cardiac CT, prospective ECG-triggering sequential scan was used for the delayed phase. In May and June, retrospective ECG-gating spiral scan was used in all such patients. The radiation dose was pre-calculated to match the two protocols. The marginal sharpness, slab artifact and beam hardening artifact were graded 1 (worst) to 5 (best) semi-quantitatively for comparison. Grades 1 and 2 were considered uninterpretable. In addition, the demographic data of the patients, image noise, scan time, and radiation dose by dose-length-product were compared.
After excluding patients with known coronary artery disease or myocardial lesions, each group included 31 patients for comparison. The prospective ECG-triggering sequential scan rated good in less noise and better marginal sharpness, and the retrospective ECG-gating spiral scan rated good in less slab and beam hardening artifact. Considering the interpretability, in the sequential group, 41.9% and 85.5% of scans were uninterpretable due to severe slab and beam hardening artifact, respectively, whereas the spiral group reached 100% interpretability.
Conclusion: Under the similar low radiation dose, retrospective ECG-gating spiral scan with ECG-pulsing should be used instead of prospective ECG-triggering sequential scan (modified from the calcium score protocol) for delayed phase of cardiac CT. The sequential protocol is not clinically feasible due to severe slab and beam hardening artifact in a significant portion of patients.