Feasibility And Clinical Application Of Low Dose DSCT Coronary Angiography

Part one:The clinical value of scan length adjustment using calcium scoring scan for low dose DSCT coronary angiography1Objective:To explore the clinical value of adjusting the scan length of CT coronary angiography with retrospective scan using calcium scoring images instead of the scout view with regard to radiation dose and image quality.2Materials and Methods:2.1. Study population:The imaging and clinical data of70consecutive symptomatic patients who were suspected of having coronary artery disease were studied from September to October2013. Only patients who had sinus rhythm and BMI≥25kg/m2, with65≤HR≤100bpm, heart rate variability≤10bpm were included. Excluded were patients with severe heart rate variability (n=5), who had a previous history of bypass surgery (n=3), respiratory adverse (n=2). Thus, our final study population comprised60patients, who were divided into two groups:group A (n=26) underwent retrospective scan using calcium scoring images, group B (n=34) was planned on the scout view.2.2CT scanning protocol:2.2.1Preparation for scanning: Strictly respiratory training was done before scanning. All patients received nitroglycerin sublingually three minutes before scanning. No oral or intravenous β-blockers were administered prior to scanning.2.2.2Equipment and Methods:Patients were scanned with use of a dual-source CT scanner (Somatom Definition; Siemens Medical Solutions). DSCT scan parameters were as follows: section thickness,0.75mm; detector collimation of32×0.625mm; the pitch varied between0.25for low HR and0.4for high HR; rotation time,330msec; medium-to-smooth convolution kernel, B26f. All patients underwent retrospective scan, the pitch was adapted to the heart rate, with standard ECG pulsing. The scan length of CT coronary angiography of group A (26patients) was planned on the axial images of the calcium scoring by identifying the origin of the left main artery and cardiac apex and adding1cm cranially and caudally. The scan range of CT coronary angiography of group B (34patients) was planned on the scout view by identifying from1cm below carina to just lcm below the diaphragm. A bolus of iodinated contrast material (Ultravist350; Bayer Schering Pharma), which varied between70and85mL depending on the expected scan time, was injected at a flow rate of5.0/5.5mL/sec in an antecubital vein, followed by a saline bolus chaser administered at the same rate. The start of CT data acquisition was controlled by bolus tracking. A region of interest was placed in the descending aorta, and image acquisition started6seconds after the signal attenuation reached the predefined threshold of90-180HU.2.3Reconstruction Methods:The reconstructions of image sequences were transferred to Syngo workstation with the heart post-processing software Circulation. The original image underwent volume rendering technique (VRT), curved planar reconstruction (CPR) maximum intensity projection (MIP) and so on. 2.4Radiation doseThe radiation dose of patients was assessed with volume CT dose index (CTDIvol), the dose length product (DLP) and the effective dose (ED). DLP and CTDIvol were noted from the scan protocol recorded with each CT examination, the effective dose of CT coronary angiography was derived from the product of the DLP and a conversion coefficient for the chest according to a method proposed by the European Working Group for Guidelines on Quality Criteria for Computed Tomography. The applied conversion coefficient [κ=0.014mSv/(mGy.cm)] was averaged between men and women using Monte Carlo simulations.2.5Statistical analysisSPSS software (SPSS13.0) was used for statistical testing. A p value of<0.05was considered statistically significant for all tests. Comparison between the two groups for age, body mass index, HR, HR variability, contrast agent load and rate was calculated by using the analysis of two sample t test, and comparison between the two groups for gender was calculated by using the chi-square test. The scan length, CTDIvol, DLP and ED between the two groups were analyzed by two sample t test. Spearman correlation analysis was used to assess the correlation between the scan length and the radiation dose.3Results:3.1Comparison of general informationAll calcium scoring and CT coronary angiography examinations were successfully performed without complications in all patients. We found no significant difference in general information (age, gender, BMI, HR, HR variability, contrast agent load and rate) between group A and group B. All images are diagnostic.3.2Comparison of radiation dose(1) CTDIvol:There was no significant difference in CTDIvol for group A (mean 47.22±5.36mGy) compared to group B (mean49.89±6.34mGy)(t=-1.724, p=0.90).(2) Scan length:The calcium scoring-derived scan length for the CT coronary angiography scan (10.67±0.89mm) was significantly smaller than the scout view-derived scan length (12.03±0.77mm)(t=-6.322, p<0.001).(3) DLP:Dose length product of CT coronary angiography using the calcium scoring-derived scan length(506.88±66.33)mGy.cm was significantly lower than that of CT coronary angiography using the scout view-derived scan length (636.79±91.18) mGy.cm (p<0.001)(4) Radiation dose:Radiation dose of CT coronary angiography using the calcium scoring-derived scan length (7.10±0.93)mSv was significantly lower than that of CT coronary angiography using the scout view-derived scan length (8.92±1.28)mSv (p<0.001) and corresponded to an average radiation dose reduction of20%.3.3Spearman correlation analysisScan length significantly correlated with DLP and radiation dose (r=0.804, p<0.001).4Conclusion:1. Adjustment of the scan length using the images from calcium scoring instead of the scout view is more feasible and accurate.2. Using the images from calcium scoring to determine the scan range of CT coronary angiography can effectively decrease the scan range and reduce the radiation dose significantly. Part two:Feasibility of prospective ECG gated scan and adaptive cardio sequence scan for low dose DSCT coronary angiography1Objective:The aim of this study was to evaluate image quality radiation dose of prospectively triggered vs retrospectively gated CTA in patients with low HR (≤65bpm), to investigate the feasibility and clinical application of prospective ECG-gated scan of dual-source CT coronary angiography.The aim of this study was to evaluate image quality radiation dose of adaptive cardio sequence scan vs retrospectively gated CTA in patients with moderate and high HR (>65bpm), to investigate the feasibility and clinical application of adaptive cardio sequence scan of dual-source CT coronary angiography2Materials and Methods:2.1Patient populationFrom June to September2013we screened255patients who were scheduled to undergo invasive coronary angiography because they were suspected of having coronary artery disease. They were divided into two groups:group A underwent prospective scan, group B underwent retrospective scan. The two groups were further subdivided into low heart rate group (HR≤65bpm) and high heart rate group (65<HR≤90bpm), recorded as A1(n=51), A2(n=89), B1(n=26), B2(n=89), respectively. Group A1preceded with prospective ECG gated scan; group A2performed with adaptive cardio sequence scan; group B1and B2underwent retrospective scan.2.2Dual-source CT scan protocol2.2.1Preparation for scanningStrictly respiratory training was done before scanning. All patients received nitroglycerin sublingually three minutes before scanning. No oral or intravenous β-blockers were administered prior to scanning.2.2.2Equipment and Methods Patients were scanned with use of a dual-source CT scanner (Somatom Definition; Siemens Medical Solutions). DSCT scan parameters were as follows: section thickness,0.75mm; detector collimation of32×0.625mm; the pitch varied between0.2and0.5; rotation time,330msec; medium-to-smooth convolution kernel, B26f. All of them applied ACTM (automatic current tube modulation) technique. Patients with a body mass index (BMI)≥25kg/m2were examined with a tube voltage of120kV, whereas BMI<25kg/m2were examined with100kV. For Group A1, the center of the data acquisition window was set at70%of the RR-interval. For group A2, with65HR≤75bpm,70%of R-R interval was used, with HR>75bpm,40%of R-R interval was chosen. ECG pulsing was used in all retrospectively ECG-gated CTCA protocols, as previously recommended:with mean heart rates below60bpm, full tube current was applied from60%to70%, at61-69bpm from60%to80%, at70-79bpm from55%to80%, and with heart rates above79bpm from30%to80%of the RR-interval.2.3Reconstruction Methods and Image evaluation:The reconstructions of image sequences were transferred to Syngo workstation with the heart post-processing software Circulation. The original image underwent volume rendering technique (VRT), curved planar reconstruction (CPR) maximum intensity projection (MIP) and so on. Coronary segments were classified according to a15-segment modified American Heart Association classification. The image quality was evaluated by two experienced radiologists with a four-point Likert scale:1=excellent, no motion artifacts, clear delineation of the segment;2=good, minor artifacts, mild blurring of the segment;3=adequate, moderate artifacts, moderate blurring without structure discontinuity allowing the exclusion of significant stenoses but being limited for nonstenotic noncalcified plaques; and4=nonevaluable, doubling or discontinuity in the course of the segment preventing diagnostic evaluation. Scores1-3were considered diagnostic.2.4Radiation doseThe radiation dose of patients was assessed with volume CT dose index (CTDIvol), the dose length product (DLP) and the effective dose (ED). DLP and CTDIvol were noted from the scan protocol recorded with each CT examination, the effective dose of CT coronary angiography was derived from the product of the DLP and a conversion coefficient for the chest according to a method proposed by the European Working Group for Guidelines on Quality Criteria for Computed Tomography. The applied conversion coefficient [κ=0.014mSv/(mGy.cm)] was averaged between men and women using Monte Carlo simulations.2.5Statistical analysisSPSS software (SPSS13.0) was used for statistical testing. A p value of<0.05was considered statistically significant for all tests. Comparison between the two groups for age, body mass index, HR, HR variability, contrast agent load and rate was calculated by using the analysis of two sample t test, and comparison between the two groups for sex was calculated by using the chi-square test. Wilcoxon two-sample test was used to assess image quality of coronary artery between the two groups. The CTDIvol, DLP and ED between the two groups were analyzed by two sample t test.3Results:3.1Comparison of general informationThere was no significant difference in general information (age, gender, BMI, HR, HR variability, contrast agent load and rate) was detected in A1and B1(p>0.05), A2and B2(p>0.05).3.2Comparison of image quality(1) There was no significant difference in image quality for group A1(1.17±0.30) compared to group B1(1.20±0.42)(p=0.726). (2) No statistical differences in images scores was detected in A2(1.26±0.35) and B2(1.27±0.44)(p=0.079).3.3Comparison of radiation dose(1) Effective doses of prospective scan (Group Aland A2) and retrospective scan (Group Bland B2) were (3.03±1.29) mSv and (5.28±1.49) mSv, respectively (t=-9.720, p<0.001), showing that prospective scan reduced radiation dose obviously compared with that of retrospective scan.(2) Compared to protocols with retrospective ECG-gating (ED:4.99±2.36mSv), the prospective ECG-triggering (ED:2.62±0.85mSv) reduces the effective dose to40%. Radiation dose of CT coronary angiography using prospective ECG-triggering scan was significantly lower than that of CT coronary angiography using retrospective ECG-gating (t=-6.434, p<0.001) in patients with HR≤65bpm.(3) Compared to protocols with retrospective ECG-gating (ED:5.36±2.54mSv), the prospective ECG-triggering (ED:3.26±1.43mSv) reduces the effective dose to50%. Radiation dose of CT coronary angiography using prospective ECG-triggering scan was significantly lower than that of CT coronary angiography using retrospective ECG-gating (t=6.779, p<0.001) in patients with65<HR≤90bpm.4Conclusion:Using prospective ECG gated scan and adaptive cardio sequence scan, assessable image quality of coronary artery can be acquired with dual source CT (heart rate<90bpm), and radiation dose can be obviously reduced. The physicians and technicians should adopt suitable techniques in order to ensure that patients undergoing the procedure will receive a radiation dose as low as reasonably achievable.