The Clinical Application Of "Double-low" Dose Coronary Computed Tomography Angiography In The Diagnosis Of Coronary Artery Disease

Part1To analysis the image quality of "double-low" dose coronary computed tomography angiographyAbstractObjectives Coronary CT angiography (CCTA) has been known to be one of the most sensitive noninvasive methods of detecting coronary artery diseases.However, the high radiation dose and contrast medium volume are harm to patients health.How to minimizing the radiation dose and contrast medium volume to protect patients and without affecting image quality to meet the needs of clinical diagnosis becomes very necessary to be solved. The most effective method to lower radiation dose of CCTA is lower tube voltage and using prospectively Electrocardiogram-Triggered.Further more, using lower tube voltage can increase the contast enhancement and thus potentially enabling a reduction of the volume of contrast medium, wihich can make it possible of "double-low" dose CCTA.The purpose of this study was to investigate the feasibility of lower volumes of contrast medium (CM) combined with low tube voltage in 256-slice prospectively coronary computed tomography angiography (CCTA) through analyzing the image quality.Methods Between March 2014 and January 2015, a total of 200 patients were considered for participation in this study. All CT examinations were performed with prospective ECG-gating using 256-slice multi-detector CT (Brilliance iCT, Philips). All patients were randomly divided into a routine-dose group (group A, n=100) and a "doule-low" dose group(group B, n=100).The age, heart rage,body weight and body mass index of the two groups had no significant difference. All patients with body mass index(BMI)≤30kg/m2; had no allergic reactions to iodinated contrast media; no serious damage of cardie and kidney function and no serious arrhythmia; no stent implantation and previous coronary artery bypass grafts; stable heart rate<70bpm, All the patients of group A were scanned with 120kVp and 150mAs,70ml contrast medium (CM,350mgI/ml) injected at a flow rate of 5ml/s,30mLof saline solution was chased at the same rate as CM, pre-determined signal attenuation threshold of 120 Hounsfield units (HU). All the patients of group B were scanned with 100kVp and 150mAs; lower CM (about 40-50ml,350mgI/ml) at 0.6-0.7 mL/kg determined by BW and BMI, CM flow rate was determined as dose of contrast medium divided by 10,30 mL of saline solution was chased at the same rate as CM, pre-determined signal attenuation threshold of 90 HU. The CT attenuation of the proximal, distal coronary artery segments and ascending aorta(AA) were measured in each patient, the image noise, signal-to-noise ratio(SNR) and contrast-to-noise(CNR) ratio of the AA were calculated.In addition, the CT value reduction in the most distal segments of the left anterior descending, circumflex and right coronary artery (LADp, LCXp, RCAp) compared to proximal point of each artery (LADd, LCXd, RCAd) were also calculated. Two radiologists assessed image quality of coronary arteries independently.Image quality of coronary segment were graded on a 4-point scale:1= blurred vascular contours, vascular discontinuous, severe motion artifacts and image noise in vessels such that the vascular situation could not be assede; 2=moderate motion artifacts and miage noise in vessels, no obvious wrong layer that did not affect the assesment; 3=clear vascular edges, slight image noise and motion artefacts; 4=no motion artifacts, very little noise and sharp vascular edges.Results The attenuation values of AA in group B were significantly higher than that of group A (p<0.0001). The image noise of AA was found to have significantly increase in group B (p<0.0001), but SNR, CNR of AA had no significant difference(p=0.3512, p=0.1855). The attenuation values of the proximal segments of each coronary arteries and the most distal point of RCX in group B were significantly higher than that of group A (P＜0.0001). The attenuation values of the most distal point of LAD and LCX had no significant difference (p-0.1024, p=0.3596). All the arteral segments of the two groups with the lower limits of the 95% confidence intervals for the mean attenuation values were found above the accepted lower limit of 300 HU. The CT value reduction in the most distal segments of the left anterior descending, circumflex were significant higer than right coronary artery (p<0.0001). The CT value reduction in LADd and LCXd of "double-low" dose group were significant higer than routine-dose group (p<0.0001). Althought the CT value reduction in RCAd of the two group have statistical difference, which has no obviously difference (p=0.0192).There was good interobserver agreement for image quality of the two radiologists (Kappa=0.82).There was no significant difference in the overall image quality of the coronary artery between the routine-dose group and "double-low" group (χ2=0.3821, p=0.9439)Conclusions In most patients,256-slice multi-detector prospectively CTCA performed with lower CM at 0.6-0.7 mL/kg (about 40-50ml) and lower tube voltage can provide good image quality equal to the routine-dose group and can also reduce the radiation dose and iodine intake.Part 2Diagnostic accuracy of "double-low"dose coronary CT angiography in patients with suspected coronary artery diseaseAbstractObjective Coronary CT angioguaphy (CCTA) has been used extensively in the evaluation of coronary disease (CAD) due to its high diagnostic accuracy and non-invasiveness.However, the higer radiation dose and contrast medium intake of CCTA is of clinical concern.In order to reduce the ionizing radiation damage and contrast-reduced nephropathy (CIN), we should reduce the radiation dose and contrast medium intake.For these reason, a large number of studies on "double-low" (low radiation dose and low contrast medium volume) dose CCTA scanning techniques have recently been conducted.Most of the studies focus on the image quality of "double-low" dose CCTA, but rare of its accuracy in the diagnosis of coronary artery disease.However, dose the "double-low" dose CCTA can be used as a routine examination in clinical application mainly due to the diagnostic accuracy of coronary artery disease.So, it is important to evaluate the diagnostic value of coronary artery disease using "double-low" dose CCTA.The purpose of this study was to evaluate the feasibility of "double-low" dose CCTA through comparing and analyzing its diagnostic value of coronary artery disease.Methods 88 patients of coronary CTA underwent Digital silhouette angiography (DSA) examination, including routine-dose group (group C, n=46) and "double-low" dose group (group C, n=42).All DS A examination were performed within 2 weeks of coronary CTA.A cardiovascular radiologist with 5 years experience assessed the luminal narrowing severity as a percentage of the vessel diameter by visual estimations of transverse sections as well as curved multiplanar reformats for all available segments on a dedicated workstation (Extended Brilliance Work-space).The DSA result was evaluated by another experienced reader who was blind to the CCTA results but acknowledged clinical history. With DSA coronary examination considered as the "gold standard", CAD was defined as a luminal narrowing of>50%.The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of coronary CTA were calculated on segment-, vessel-and patient-based levels.The differents in diagnostic performance between the two groups were tested.Non-evaluable segments and the segments that had a minimal diameter of< 1.5mm were excluded from per-segment analysis.A vessel and a patient were considered to be diseased if a luminal narrowing of>50% was found in at least one coronary segment.Results The sensitivity, specificity, PPV,NPV and accuracy were 93.2%,96%,84.6%, 98.4%,95.5%(segment-based),92.8%,88.7%,83.1%,95.3%,90.2%(vessel-based), 97.3%,77.8%,94.7%,87.5%,93.5%(patient-based) of group C. The sensitivity, specificity, PPV, NPV and accuracy were 93.3%,95.5%,83.1%,98.4%,95.1% (segment-based),91.2%,90.1%,82.5%,95.2%,90.5%(vessel-based),97%, 70%,91.4%,87.5%,90.5%(patient-based) of group D.There were no significant differents of the diagnostic value between the two groups (segment-based:χ2=0.1201, p=0.7289; vessel-based:χ2=0-0067,p=0.9346; patient-based:χ2=0-2702, p=0.6032).Diagnostic image quality was found in 626 segments of routine-dose group.In the segment-based analysis, coronary CTA disdiagnosed 28 segments; 8 segments failed to show the presence of significant stenosis (false negative) and 20 segments were incorrectly diagnosed as having significant narrowing (false positive).The cause of incorrect diagnosis were dense calcification in 18 segments and motion artifacts in 6 segments. Two segments in the middle part of the LCX were misdiagnosed as stenosis (false positive) because of the poor vascular filling. One segment in the ministry of the starting of RCA were misdiagnosed as stenosis (false positive) because of the transient spasm. Another segment in the mistry of the starting of posterior descending artery failed to show the presence of significant stenosis (false negative) because of the narrow scope is small. Diagnostic image quality was found in 551 segments of "double-low" dose group.In the segment-based analysis, coronary CTA disdiagnosed 27 segments; 7 segments failed to show the presence of significant stenosis (false negative) and 20 segments were incorrectly diagnosed as having significant narrowing (false positive).The cause of incorrect diagnosis were dense calcification in 17 segments and motion artifacts in 5 segments.4 segments were misdiagnosed as stenosis (false positive) because of the poor vascular filling. Additionally, one segment of the first diagonal branch(D1)was misdiagnosed as stenosis (false positive) because of compression caused by the crossing-over of the cardiac vein.Conclusin "Double-low" dose coronary CTA can provide high diagnostic sensitivity, specificity and accuracy for detection of coronary heart disease, which is equal to routine dose group and can be widely applied in clinical.