Prospective-ECG Triggered High-pitch Spiral Scan Of Coronary CT Angiography In Patients With Atrial Fibrillation： Image Quality And Radiation Dose Using Reduced Tube Voltage And Iterative Reconstruction

Objective:(a) To compare image quality between iterative reconstruction (IR) andfiltered back projection (FBP) algorithm in high-pitch spiral scan of coronary CTangiography (CTA) in patients with atrial fibrillation.(b) To assess the image qualityand radiation dose of high-pitch spiral scan of coronary CTA using reduced tube voltageand IR in patients with atrial fibrillation, in comparison with CT using routine tubevoltage and FBP reconstruction.Methods:54consecutive patients with persistent atrial fibrillation underwent coronaryCTA using reduced tube voltage according to body mass index (BMI):(a)80kV forBMI <25kg/m2(group A1,27subjects),(b)100kV for BMI≥25kg/m2(group B1,27subjects). For comparison, the two sex-age-and BMI-matched groups using routinetube voltage were selected:(a)100kV for BMI <25kg/m2(group A2,27subjects),(b)120kV for BMI≥25kg/m2(group B2,27subjects). Coronary CTA usingprospective-ECG triggered high-pitch spiral scan mode was performed on a2ndgeneration dual source CT system. Acquisition parameters were as follows:2×64×0.6mm detector collimation,280ms gantry rotation time,3.4pitch and320mAs perrotation tube current time product. High-pitch spiral scan was prospectively triggered at60%of the R-R interval. Images were reconstructed with FBP and IR algorithm.Parameters for image reconstruction include a slice thickness of0.75mm, increment of0.7mm, and a medium soft convolution kernel (I26f for IR and B26f for FBP). Contrastmedium enhancement was achieved by injecting50-60ml of iodinated contrastmaterial and injected at5-6ml/s through an18-G intravenous antecubital catheter by using a dual-syringe injector. The image noise, signal-to-noise ratio (SNR) andcontrast-to-noise ratio (CNR) were compared respectively between IR and FBPreconstruction in each group. The image noise, SNR, CNR, image quality and radiationdose were compared respectively in each matched groups (A1and A2; B1and B2).Results:(a) In the each group, the image noise was significantly lower with IR thanwith FBP (P <0.01), and the SNR and CNR were significantly higher with IR than withFBP (P <0.01).(b) In patients with a BMI <25kg/m2, the CT attenuation of ascendingaorta was significantly higher with reduced tube voltage and IR (group A1) than withroutine tube voltage and FBP (group A2)(613.95±164.21HU vs.425.27±105.08HU,P <0.01). The image noise was significantly higher in group A1than in group A2(33.43±7.48HU vs.26.80±5.40HU P <0.01). There were no significant differences in SNR(18.40±6.19vs.15.48±5.27，P>0.05), CNR (14.52±5.84vs.11.80±4.59，P>0.05)and image quality scores (3.61±0.67vs.3.59±0.69，P>0.05) between two groups.The effective radiation dose of group A1was53.33%lower than that of group A2(0.42±0.04mSv vs.0.90±0.12mSv, P <0.01).(c) In patients with a BMI≥25kg/m2, theCT attenuation of ascending aorta was significantly higher with reduced tube voltageand IR (group B1) than with routine tube voltage and FBP (group B2)(404.73±76.60HU vs.335.03±37.74HU, P <0.01). The image noise was similar between two groups(22.78±4.23HU vs.22.53±3.61HU, P>0.05). The SNR and CNR were significantlyhigher in group B1than in group B2(16.49±2.98vs.14.36±3.05,12.66±2.88vs.10.32±2.55, P <0.01). There were no significant differences in image quality scoresbetween two groups (3.64±0.62vs.3.62±0.65, P>0.05). The effective radiation doseof group B1was41.45%lower than that of group B2(0.89±0.50mSv vs.1.52±0.11mSv, P <0.01).Conclusion:(a) In patients with atrial fibrillation, compared with FBP reconstruction,IR can reduce image noise and improve image quality in high-pitch spiral scan ofcoronary CTA using reduced tube voltage or routine tube voltage.(b) In atrialfibrillation patients with BMI <25kg/m2, high-pitch spiral scan of coronary CTA using80kV and IR can provide equivalent coronary quality, compared with CT using100kVand FBP reconstruction, that decreased approximately53%of the radiation dose. Theeffective radiation dose was lower than0.5mSv.(c) In atrial fibrillation patients withBMI≥25kg/m2, high-pitch spiral scan of coronary CTA using100kV and IR canprovide equivalent coronary quality, compared with CT using120kV and FBP reconstruction, that decreased approximately41%of the radiation dose. The effectiveradiation dose was lower than1mSv.