| Background:Cardiovascular disease remains the leading cause of death,thus underscoring the need for earlier and accurate diagnosis.Coronary artery imaging by CT has historically been difficult.The small diameter of the coronary arteries necessitates high spatial resolution,whereas their perpetual and sometimes irregular motion demands high temporal resolution.The temporal resolution of a MDCT scanner is half the gantry rotation time when using the mono-segment reconstruction mode.Many investigators suggested thatβ-receptor antagonists for heart rate control should be administered before CT when the heart rate is more than 70 beats per minute(bpm).The temporal resolution of the coronary artery imaging by CT must be improved to acquire images without artifacts.A temporal resolution of better than 100ms independent of the heart rate is desirable for robust cardiac imaging in clinical routine.Many investigators recommend that multi-segment reconstruction approache should be applied when the heart rate is more than 70 beats per minute(bpm).At the same rotation speed,the temporal resolution of a MDCT scanner can be improved by splitting the half-scan data-sets into smaller segments,which are obtained from consecutive cardiac cycles. This multi-segment approach relies on the assumption that there is negligible variation in the position of the coronary arteries between each cardiac cycle.However,the temporal resolution with this approach strongly depends on the patient's heart rate and a stable and predictable heart motion.The dual source computed tomography(DSCT) is equipped with two X-ray tubes and two corresponding detectors.With its 83 ms temporal resolution of single segment reconstruction,high quality coronary artery CT angiography can be acquired without heart rate control.The studies about DSCT are restricted to the relationship between heart rate and image quality.However,there are few studies on the relationship between heart rate variability and accuracy of DSCT.The purpose of this study was to evaluate the effect of heart rate,heart rate variability on the image quality and the diagnostic accuracy of dual-source CT coronary angiography without heart rate control.Objective:To evaluate the effect of heart rate,heart rate variability on dual-source computed tomography(CT) image quality without heart rate control and to assess diagnostic accuracy of dual-source CT for coronary artery stenosis,by using invasive coronary angiography as the reference standard.MethodsWe have collected 134 patients(32 female patients,102 male patients;mean age,66.1±10.6 years;age range,37 - 87 years ) from June 2007 to October 2008.All patients have a high preptest probability of CAD and underwent DSCT coronary angiography and conventional coronary angiography(CAG) within two weeks. Patients were divided into two groups according to the average heart rate or the heart rate variability.There are ECG Data among the CT data of all patient.Exclusion criteria were as follows:post coronary artery stent placement,postoperative state of bypass grafts,bad breath-hold.No beta-blockers were administered prior to the scan. 1,Dual-Source CT ProtocolAll examinations were performed with a dual-source CT scanner(Somatom Definition ).Prior to acquisition of the topogram,patients received a single sublingual dose of 5 mg of nitroglycerin.No additionalβ-blockers were administered before CT.2,DSCT Data Reconstruction and PostprocessingAll images were reconstructed with retrospective ECG gating.A monosegment reconstruction algorithm consisting of the data from a quarter rotation of both detectors was used for image reconstruction.All images were transferred to an external workstation(Leonardo,Siemens Medical Solutions) equipped with cardiac postprocessing software(Syngo Circulation,Siemens).Postprocessing includes multiple planar reformation(MPR),thin-slab maximum intensity projection(thin-slab MIP) and volume rendering(VR).The coronary arteries were classified into 15 segments according to the scheme proposed by the American Heart Association.The right coronary artery(RCA) included segments 14,the left main coronary artery and left anterior descending coronary artery(LAD) included segments 5 10,and the left circumflex coronary artery (LCX) included segments 11 15.If present,the intermediate artery was designated segment 16.3,DSCT data analysisImages were analyzed and graded by two independent reviewers(each with experience in cardiovascular radiology ) blinded to mean heart rate and heart rate variability during scanning and using axial source images,multiplanar reformations, and thin-slab maximum intensity projections.The reviewers semiquantitatively assessed image quality and degree of motion artifacts on the 4-point scale as follows: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;and 4,not evaluative,doubling or discontinuity in the course of the segment preventing evaluation or vessel structures not differentiable.Scores 13 were considered diagnostic.In case of disagreement between reviewers,consensus interpretation was appended.Vessel diameters were measured by cardiac postprocessing software(Syngo Circulation,Siemens) three times and the average value was chosen.The haemodynamically significant stenoses was defined as luminal diameter narrowing≥50%.4,Conventional Coronary AngiographyCAG was performed according to standard techniques and at least two views in different planes were obtained for each coronary artery.One experienced observer blinded to the clinical data(name,age,result of CTA,and so on ) evaluated all angiograms with regard to the presence(diameter reduction≥50%) or absence of significant stenoses.Results:1,Image Quality of Coronary Artery SegmentsA total of 1,751 coronary segments in 134 patients were evaluated.We obtained motion artifact free images(score 1) of 51.4%(899/1,751) of the coronary segments. Minor artifacts(score 2) were found on images of 41.5%(727/1,751) of the segments and moderate artifacts(score 3) on images of 6.5%(114/1,751 ) of the segments.Severe artifacts(score 4) rendering image quality nondiagnostic were involved 0.6%(11/1,751) of the segments.Not-evaluative image quality was found in segment 2(n = 1 ),segment4(n=1),segment 7(n=2),segment8(n=1),segment 12(n=1),segment13(n=2) and segment15(n=3).2,Effect of Mean Heart Rate on Image QualityAll patients were subdivided into mean heart rates of <70 bpm and≥70 bpm. The image quality score of segment 5,segment 12,segment 14 and segment 16 was not statistically significantly different between two groups.There were statistically significantly differencen in other segments(p < 0.05 ).3,Effect of Heart Rate Variability on Image QualityAll patients were subdivided into heart rate variability of <8 bpm and≥8 bpm. The image quality score was not statistically significantly different in any segment between two groups(P > 0.05 ).4,Effect of Mean Heart Rate on Diagnostic AccuracyIn patients with mean heart rate≥70 bpm,the sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of RCA was 94.1%,97.7%,82.1%,99.3%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of LM and LAD was 100%,98.7%,91.9%,100%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of CX was 84.6%,98.7%,73.3%,99.4%,respectively.Overall sensitivity was 96.2%,specificity was 98.4%,positive predictive value was 86.2%,and negative predictive value was 99.6%.In patients with mean heart rate < 70 bpm,the sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of RCA was 94.4%,96.6%,85.0%,99.4%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of LM and LAD was 100%,99.1%,93.9%,100%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of CX was 100%,99.5%,92.9%,100%,respectively.Overall sensitivity was 98.4%,specificity was 99.0%,positive predictive value was 91.0%,and negative predictive value was 99.8%. The sensitivity,specificity,and positive and negative predictive values was not statistically significantly different between two groups(P>0.05 ).5,Effect of Heart Rate Variability on Diagnostic AccuracyIn patients with heart rate variability≥8 bpm,the sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of RCA was 91.4%,97.8%,84.2%,98.9%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of LM and LAD was 100%,98.6%,90.9%,100%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of CX was 100%,99.0%,83.3%,100%,respectively.Overall sensitivity was 97.0%,specificity was 98.5%,positive predictive value was 87.4%,and negative predictive value was 99.7%.In patients with heart rate variability < 8 bpm,the sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of RCA was 100%,98.0%,81.0%,100%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of LM and LAD was 100%,99.2%,95.0%,100%,respectively.The sensitivity,specificity,and positive and negative predictive values of DSCT coronary angiography for the detection of significant stenoses of CX was 81.8%,99.0%,81.8%,99.0%,respectively.Overall sensitivity was 97.0%,specificity was 98.8%,positive predictive value was 88.9%,and negative predictive value was 99.7%.The sensitivity,specificity,and positive and negative predictive values was not statistically significantly different between two groups(P> 0.05 ).The sensitivity,specificity,positive and negative predictive value of all patients for dual-source CT coronary angiography were 97.0%,98.6%,88.0%,99.7%,respectively. Conclusion:The overall image quality of dual-source CT coronary angiography is sufficient for diagnosis within a wide range of mean heart rates due to the improvement in temporal resolution to 83ms.At the same time,absolute phase reconstruction method provids diagnostic images within a wide range of variability of heart rates.In Patients with High Heart Rate or arhythmia,dual-source CT coronary angiography provides a high diagnostic accuracy for the diagnosis or exclusion of significant coronary stenosis as compared with the reference standard CAG.
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