Clinical Application Of 64 Multi-slice Spiral CT Coronary Angiography

Objective1.To explore the main influence factors on coronary artery image quality with 64 multi-slice spiral CT(MSCT).2.To study the value of 64 MSCT coronary angiography in diagnosis of coronary stenoses(≥50%)in patients with coronary heart disease(CHD),Compared with conventional angiography(CAG),and to evaluate the correlation of the plaque and the stenoses.3.To discuss the clinical application value of 64 MSCT in the diagnosis of congenital coronary artery anomalies.4.To evaluate the different individual adapted tube current selection method for obtaining consistent image noise and reducing radiation dose for patient population on 64-slice spiral CT coronary angiography(CTCA).Material and Method1.The influence factors on coronary artery image quality with 64 MSCT1.1 General material93 cases had 64 MSCT scan for coronary angiography.There were 64 male,29 female,and average age 57.30±9.12 years old.Clinical symptom included precordia complaint(n=48),history of CHD(n=25),and health examination (n=20).Subjects were ruled out by obvious irregularity of cardiac rhythm,worse breathing,unability to match the exam,heart failure,renal inadequacy and iodi hypersensitiveness.Every one had to have enhanced CT signed consent.1.2 Main instrument or equipmentRetrospective electrocardiogram(ECG)-gated coronary CT angiography was performed with GE Light Speed 64 VCT.ECG monitor with type of IVY 3150 was made in America.The type of two-bucket high pressure syringe made in America was LF CT 9000 and non-ion contrast medium with 350mgI/ml or 370mgI/ml were used.1.3 Examination technique and image processingScanning parameter:120 KV,650～680 mA,0.35 s/r,64×0.625 mm,FOV=25 cm,matrix=512×512,pitch=0.18～0.20,standard reestablish algorithm.Firstly,a timing bolus scan(TBS)was obtained at the level of the aortic root with the administration of 20ml non-ion iodic contrast medium(350mgI/ml or 370mgI/ml) followed by 20ml saline solution at 5ml/s.So transit time and optimun scanning time was able to decide.Subsequently,a bolus of 60～80 ml of contrast medium followed by 40ml of saline solution was injected at the same rate.The scanning range covered the heart from the level of tracheal bifurcation to the diaphragm.The total scanning time was about 6～8s.All of 93 cases,73 cases made a direct scan after breathholding and 20 cases done a scan after 5～8s breathholding.A dose of 12.5～25mg of a adrenergic blocking agent,metoprolol was administered orally before CT examination if the patient's heart rate was more than 75bpm.Different recombination algorithm were selected according to different heart rate,such as heart rate＜75bpm with mono-recombination or heart rate≥75 bpm with multi-recombination algorithm.AW4.2 postprocession workstation was used.Raw CT datas were firstly reconstructed at 75%R-R of the cardiac cycle.If the image qulity was not better, 45%reconstruction phase was needed.55%or 65%reconstruction phase was also required if artifact was still present.Different processes such as volume rendering (VR),multi-planar reformation(MPR),curved planar reformation(CPR)and maximum intensity projection(MIP)were used to assess for image quality combining cross section image.1.4 Coronary artery segmentTen coronary segments were analyzed in each patient according to the way of improvement.The right coronary artery(RCA)included proximal segment(R1), middle segment(R2),distal segment(R3).The left main artery(LM)diverged two main segements including of left anterior descending artery(LAD)and left circumflex artery(LCX).The LAD contained proximal segment(L1),middle segment (L2),distal segment(L3)and diagonal segment(L4).The LCX consisted of proximal segment(C1),distal segment(C2).1.5 Image quality evaluationThe image quality based on segment was assessed by rated as excellent,reduced but still diagnostic and non-diagnostic:no artifact,a sharp blood vessel with good continuous engorge;mild artifact,the vessel with no more smooth edge,but assessable;severe artifact,vague image,vessel discontinuation,less engorge, unassessable for the vessel by different reconstruction phase.The image quality based on every patient was defined by 5-point as follows: 5=all excellent image quality for all segments;4=only one segment with fine or diagnostic image quality;3=two segments with fine or diagnostic image quality; 2=equal or more than three segments with fine or diagnostic image quality;l=one or more than one segment with non-diagnostic.The overall quality for all images was assessed blinded and randomised by three experienced radiologists in a single consensus reading.Major people's opinion and negotiation for result may be used if opinion was on discrepancy.Patients were divided into 3 groups with heart rates:less than 65 bpm;between 65～75 bpm;more than 75 bpm.Three groups were also divided according to heart wave:less than 5 bpm; between 5～9 bpm;more than or equal 10 bpm.The CT value of main coronary segment(diameter≥2mm)was measured on primary cross section with ROI=6mm².1.6 Statistical analysisThe SPSS 13.0 software was applied in this study.Multiple variable Logistic regression was used to evaluate the influence factors on image quality.The spearman's and partial bivariate correlation were performed to analyze the different influence factors on image quality.The independent sample non-parameter test was applied to evalute the influence of heart rate,heart wave,reconstruction phase and breathholding on image quality.The independent sample t test was used to compare the mean datas.A P value of less than 0.05 was considered significant.2.The clinical application of 64 MSCT coronary angiography in patients with CHD2.1 General material50 cases with both 64 CTCA scan and CAG exam in one month for coronary angiography were retrospective analyzed.There were 41 male,9 female,and average age 57.25±11.50 years old.Of all patients,there were 38 cases with history of CHD, 22 cases with history of high blood pressure,and 11 cases with history of diabetes.2.2 Main instrument and methodThe method of CTCA was same as Part 1.CAG was performed with Siemens macro-type suspled C-arm and its matched workstation.Constrast medium was used with Omnipaque.The conventional cannula of arteria femoralis or arteria radialis was applied with Judkins,including 4～6 standard podition of left coronary artery(LCA)and 2～3 standard position of RCA.2.3 Stenoses assessment 15 coronary segments were analyzed in each patient according to the fractionation method recommended by America heart institution.The extent of coronary stenoses was assessed with international used eye measurement.Normal coronary artery was a smooth blood vessel,no atherosclerotic plaque,grade 3 with TIMI(thrombolysis in myocardial infarction).The stenosed extent of blood vessel diameter was ranked 4 groups:light stenoses,less than 50%; middle stenoses,50%～75%;weight stenoses,76%～99%;obstruction,blunting lumen of blood vessel and grade 0 with TIMI.The overall stenosed extent on 64 CTCA and CAG was respectively assessed blinded and randomised by two experienced radiologists in a single consensus reading.Negotiation for result may be used if opinion was on discrepancy.2.4 Plaque rankPlaque was ranked into 4 groups by current measurement of CT value:soft plaque,less than 60HU(partly negative value);fiber plaque,between 60～129HU; calcified plaque,more than 130 HU;mixed plaque,including calcifed and noncalcified component.2.5 Statistical analysisThe SPSS 13.0 software was applied in this study.The accurance,sensitivity(Se), specificity(Sp),positive predictive value(PPV),negative predictive value(NPV)were all calculated to evaluate the diagnosis of coronary stenoses(≥50%)on 64 CTCA. The matched-pair x² test,independent sample non-parameter test or Bonferroni mutiple comparison was applied to evalute the pairing data or ranked data.A P value of less than 0.05 was considered significant.3.The value of 64 MSCT in the diagnosis of coronary artery anomalies.3.1 General material64 MSCT coronary artery angiography datas of 1800 patients between February 2006 and December 2008 were analyzed retrospectively to find the coronary artery anomalies in 47 patients.There were 38 male,9 female,age from 37 to 72 years old, and average age 51.35±10.34 years old.Clinical symptom included occasional chest pain or distress(n=29),clinical diagnosis of CHD or angina(n=5),and health examination(n=13).7 cases of coronary atherosclerosis were revealed using 64 MSCT,including 4 cases of clinical coronary stenosis(≥50%).Two cases had CAG exam in half past one month after 64 MSCT coronary angiography.One case had 64 CTCA scan because of no detecting coronary gab on CAG.3.2 Main instrument and methodThe method of CTCA and CAG was same as Part 2.4.The way of low dose scanning on fixed noise level in 64 MSCT cardiac imaging4.1 General materialTotal 60 cases were divided into two groups in this study.Firstly,30 cases as fixed-mA group were retrospectively analyzed with CTCA exam from Nov to Dec in 2008.Among them,there were 22 male,8 female,and average age 49.10±9.04 years old.Sequently,30 cases of individual-mA group were prospectively studied on CTCA scan from Jan to Feb in 2009.Among them,there were 24 male,6 female,and average age 49.73±9.92 years old.The patients were ruled out because of bearing premature,worse breathing,heart failure,renal inadequacy and iodi hypersensitiveness. All subjects must keep heart rate≤70 bpm and heart wave＜5 bpm.4.2 Main instrument or equipment:same as Part 1.4.3 Examination technique and image processingRetrospective study:We firstly analyzed 30 patients underwent CTCA using 64 MSCT with standard scan protocol(TBS:120KV,80mA,5mm thick,standard reestablish algorithm;CA:120KV,680mA,0.35s/r,64×0.625 mm,pitch=0.18, standard reestablish algorithm)to establish the relationship between SD_TB,BMI and SD_CA.An excel table was established to predict the required mA to achieve a desired SD₀ for patient with single SD_TB.The image noise was measured for each patient using the average of three consecutive slices in the ascending aorta with region of interest(ROI)cursor of 1 cm×1 cm.Prospective study:We then scanned 30 patients with individual SD_TB-adapted mA from the table to evaluate the robustness and practicability of this method.We did not use other dose reduction techniques in this study.The way of SD mesurement was same as fixed mA group.CT dose index volume(CTDIvol)and effective dose (ED)were recorded.The other examination technique and image processing were same as Part 1.4.4 Image noise and quality evaluationThe overall quality for all images was assessed blinded and randomised by two experienced radiologists in a single consensus reading based on a five point grading scale as follows:5=clear delineation of small structures,distinct anatomic detail and sharp vessel;4=clear anatomic detail with mild increase in image noise;3=distinct increase in image noise with still unaffected diagnostic image quality;2=obscured anatomic detail due to deterioration in image quality,extensive blurring and distinct increase in image noise leading to unsure diagnosis or even resulting in an insufficient evaluation of diagnosis;and l=non-diagnostic.4.5 Statistical analysisThe SPSS 13.0 software was applied in this study.The Pearson's bivariate correlation was used to analyze the relationship of the SD_TB,BMI and SD_CA,and to establish a equation of linear regression.The Spearman rank correlation was applied to evalute the relationship of SD_CAand image quality analysis.The mean datas was presented with(?)±S pattern.The independent sample t test was used to compare the values of the two groups and statistical difference was granted as P value＜0.05. Results1.The influence factors on coronary artery image quality with 64 MSCT1.1 Of 730 segments,the rate of segment used to estimate was 93.7%(684/730).1.2 Heart rate and heart wave were the main influence factors on coronary artery image quality.The relationship of them showed negative correlation,with heart rate closer to image quality(r=-0.422,P=0.000),and then the heart wave(r=-0.257, P=0.015).The better image quality was obtained when the heart rate was≤75 bmp, the heart fluctuation was＜10 bmp.1.3 87.5%cases of all only selected 65%～75%reconstruction phase to get better image quality if the heart rate was≤75 bpm.When the heart rate was＞75bpm, 45%～55%reconstruction phase was reselected by 47.1%cases of all.The selected reconstruction phase of different heart rate groups had a statistical significance (Z=-2.841,P=0.004).1.4 The CT Attenuation values of the main coronary segment on the heart rate≤75bpm group were higher by 50HU than the heart rate＞75 bpm group.Only CT value of the LM in two groups had a statistical significance(t=2.394,P=0.028),but all satisfied clinical diagnosis.1.5 The excellent rate of image quality on the scan after 5⁸s breathholding is higher than the direct scan after breathholding(Z=-2.571,P=0.01),but the rate as excellent and reduced but still diagnostic of the two groups had no significant difference(Z=-0.956,P=0.339).2.The clinical application of 64 MSCT coronary angiography in patients with CHD2.1 Total 683 segments of 50 patients were able to evaluate on 64 CTCA.The plaque and stenoses were detected in 153 segments of coronary arteries.2.2 The distribution and extent of 63 coronary arterial segments stenoses(≥50%)revealed by 64 CTCA were correlated exactly with CAG in 75 coronary arterial segment stenoses.The coincidence rate was 84.0%.The diagnosis value of coronary arterial segments or branches on 64 CTCA had little difference,and the Se,Sp,PPV, NPV and accuracy were 84.0%,97.9%,81.8%,98.2%,96.5%or 87.5%,95.1%, 87.5%,95.1%,93.0%respectively.2.3 The different stenosed extent resulted from the different coronary plaque (X²=30.00,P=0.000).Calcified plaque always caused mild lumen diameter stenoses. However,the mixed plaque aways leaded to serious lumen diameter stenoses.The distribution of stenoses caused by noncalcified plaque was no specificity,and had a same appearance on CAG.The distribution of stenoses between calcified and noncalcified plaque or between calcified and mixed plaque had significant difference (P=0.000).3.The value of 64 MSCT in the diagnosis of coronary artery anomalies.In consecutive 1800 patients,64 MSCT identified 47 patients by 2.6%with an anomalous coronary artery.Anomalous origin of coronary artery contained 32 cases, including LCA or RCA origin from supra-sinus(n=12),multi-orifice(n=7),RCA origin from left coronary artery sinus or sinus crista(n=10),LCA origin from the proximal segment of RCA(n=1),LCX origin from right coronary sinus(n=1)or the first diagonal artery(n=1).The others were absence of LCX(n=1),single LCA(n=2), and myocardial bridge(n=12).4.The way of low dose scanning on fixed noise level in 64 MSCT cardiac imaging4.1 The relationship of SD_TB(x)and SD_CA(y)was closer(r=0.867)to be able to establish a equation of linear regression in the fixed mA group: y=1.747x+1.920(adjusted R²=0.736)4.2 The relationship of SD_CAand image quality analysis showed negative correlation (r=-0.412,P=0.024).A cardic image noise level(SD₀)of 28 HU was found to be adequate for clinical diagnosis purpose based on the image quality analysis. 4.3 The formula to predict the needed mA(z)for obtaining consistent image noise (SD₀)was to established on the base of SD_TB(x): z={(1.747x+1.920)/28}²Ã—680 mA.4.4 The t test indicated that the individual mA group for adapting mA method produced much smaller radiation dose for CTDIvol(t=7.038,P=0.000)and ED (t=7.038,P=0.000)than the fixed mA group.And the mean reduced dose rate was 10.64%,15.03%respectively.However,the image quality analysis between the two groups showed no significant difference(t=0.530,P=0.598).Conclusion1.Heart rate and heart wave are the main influence factors on coronary artery image quality with 64 MSCT.Strictly trainning for breathholding,controlling the heart rate and heart wave,selecting optimal reconstruction phase can elevate the image quality of CTCA.2.64 MSCT has a higher specificity and accuracy in diagnosis of CHD and can be acted as effective screening method.But it also has some limit.3.64 MSCT is a safe,noninvasive,accurate method for screening and diagnosis of congenital coronary artery anomalies,and also a direction for catheter approach on CAG or treatment.4.The use of individual adapted mA selection method is robust and practical to obtain consistent image quality for different patients and may provide dose reduction for smaller patients compared to the use of fixed mA.