The Clinical Application On Low Tube Voltage For Coronary Imaging By 256 Slice ICT

PartⅠ Radiation dose analysis of low tube voltage coronary artery imagingby 256 slice iCTObjective Through study of low tube voltage (100KVp) prospective ECG gated coronary artery imaging by 256 slice iCT for the clinical suspected patients with coronary heart disease, calculated the radiation dose, which was compared with that of 120KVp prospective ECG gated coronary artery imaging and 100KVp retrospective ECG gated coronary imaging. And then analyzed the clinical value and significance oflow tube voltage prospective ECG gated coronary artery imaging by 256 slice iCT in reducing radiation dose.Materials and methods1. Clinical dataCollected 106 patients with coronary artery imaging by 256 slice iCT in our hospital from August 2015 to January 2016, whose body mass index (BMI)were 18-25kg/m2.Group 1:40 cases of prospective ECG gated coronary artery imaging,100KV tube voltage,, male 26 cases, female 14 cases, age 38-83 years old, the average age (58±11) years old, heart rate range of 42-74 per minute, the average heart rate(61±6) per minute. Exclusion criteria:serious arrhythmia, heart rate greater than 75 times per minute, acute heart failure and severe damage of liver and kidney function, and couldn’t cope with the breath,iodine contrast agent allergy, coronary artery calcification severely, after coronary stented.Group 2:28 cases of prospective ECG gated coronary artery imaging,120KV tube voltage, male 18 cases, female 10 cases, age 37-80 years old, the average age (58 ±11) years old, heart rate range of 51-74 per minute, the average heart rate(61 ±7) per minute. Exclusion criteria:the same as Group 1.Group 3:38 cases of retrospective ECG gated coronary artery imaging,100KV tube voltage, male 24 cases, female 14 cases, age 37-81 years old, the average age (60 ± 9) years old, heart rate range of 51-89 per minute, the average heart rate(68 ±9) per minute. Exclusion criteria:the same as Group 1.2. Scanning equipmentUsing 256 slice spiral (Philips Brilliance iCT) scanner, post processing workstation(Philips EWB 4.01), double tube high pressure syringe(Stellant), non-ionic iodine contrast agent dianbile (370mgI/ml).3. Scanning methodsSupine position on the back, scanning direction from the head to the foot, Scan range from tracheal carina to the diaphragmatic surface of the heart. Scanning conditions:Group 1, prospective ECG gated scanning,100KV tube voltage,250mA tube current,Scanning layer thickness 0.90mm, layer spacing 0.45mm, ball tube rotation time 0.27s, pitch 0.164, matrix 512 x 512,128mm x 0.625mm detector, width 8cm,Recombination phase at 78%.Interest region (ROI) was set at the ascending aorta, threshold 150HU. Artificial intelligence triggered scanning, pre-injected saline 20ml, flow rate 5.0 ml/s, contrast agent volume 65-70ml, flow rate5.0ml/s. After the injection of contrast agent, injected 50ml saline to flush pipe, flow rate 4.5 ml/S. Group 2, prospective ECG gated scanning,120KV tube voltage, the rest was the same as Group 1. Group 3, retrospective ECG gated scanning,100KV tube voltage,850mA tube current,pitch0.164. The rest was the same as Group 1,40%,45%,75% phase were priority for reorganization. IDose4 iterative reconstruction algorithm was adopted in each group.4. Image post processingUsing Philips EWB 4.01 workstation, multi-planar reconstruction (MPR), maximum intensity projection (MIP), volume rendering (VR), recombinant (CPR) curve and surface shaded display (SSD) etc. were performed for coronal artery images.5. Radiation dose calculationDetailedly recorded each patient’s volume computed tomography dose index (CTDIvol), dose length product (DLP) which were generated automatically by computer, and calculated effective dose (ED, ED=DLP×K, K for conversion factor: chest 0.0140).6. Statistical methodsUsing the SPSS 20 statistical software, all data were expressed by mean plus or minus standard deviation. p<0.05, The difference has statistically significant.Results1. Group 1:40 cases of 100KVpprospective ECG gated coronary artery imaging group. The CTDIvol value was (28.74±3.23) mGy, DLP (205.18±32.24) mGy·cm, ED (2.87±0.45) mSv.2. Group 2:28 cases of 120KVP prospectiveECG gated coronary artery imaging group. The CTDIvol value was (50.24±7.18) mGy, DLP (312.99±62.84) mGy·cm, ED (4.38±0.87) mSv.3. Group 3:38 cases of 100KVP retrospective ECG gated coronary artery imaging group. The CTDIvol value was (43.35±4.49) mGy, DLP (626.20±90.70) mGy·cm, ED(8.76±1.27)mSv.4. Compared Group 1 with group 2, and group 1 withgroup 3, BMI value and age didn’t statistically have significant difference between both. The differences of CTDIvol, DLP and ED were statistically significant between group 1 and group 2, and between group 1 and group 3 (P< 0.05).ConclusionCompared 100KVp prospective ECG gated coronary artery imaging with 120KVp prospectiveECG gated coronary artery imaging and 100KVp prospective ECG gated coronary artery imaging, the radiation dosage of low tube voltage (100KVp) coronary artery imagingreduced significantly.Part Ⅱ Image quality analysis of low tube voltage coronary artery imagingby 256 slice iCTObjective Through study of low tube voltage (100KVp) prospective ECG gated coronary artery imaging by 256 slice iCTfor the clinical suspected patients with coronary heart disease, analyzed the image quality, and compared with the 120KVp prospective ECG gated coronary artery imaging and 100KVpretrospective ECG gated coronary artery imaging, then estimated the feasibility of low tube voltage ECG gated coronary artery imaging by 256 slice iCT.Materials and methods1. Clinical data, scanning equipment and scanning methods were all the same with the part1.2. Image quality evaluation methodsSubjective image quality evaluation:a double blind method was adopted to score the reconstructed images from 2 experienced cardiovascular imaging diagnosis doctors. Assessment criteria were divided into 4 grades,4 points (vascular continuity and clear edge, good brightness, no step shaped artifact),3 points (vascular continuity, good brightness,vascular edge blur, Slight vessels artifact in the axial scanning),2 points (step shapedvessels artifact, vascular edge blur, but not affect the diagnosis),1 points (vascular discontinuity, severe step shaped vessels artifact, could’t distinguish between blood vessels and surrounding tissues). Greater than or equal to 2 points to reach the diagnostic requirements.Objective image quality evaluation:axial images were chosen to measure 3 times, and took its average. (1) CT value measurement of the aortic root lumen (1 level before left coronary sinus appeared), ROI of about 100 mm 2. CT value measurement of the major thoracic muscle in the same level with aortic root, ROI of about 20 mm2. According to the following formula, signal to noise ratio (SNR) and contrast to noise ratio (CNR)were calculated, SNR equaled mean aortic root lumen CT value divided noise within the lumen of the blood vessel, CNR equaledmean aortic root lumen CT value minusmajor pectoralis average CT value and then divided major pectoralis SD.(2) CT value measurement of left main (LM), left anterior descending (LAD), the left circumflex artery (LCX) andproximal right coronary artery lumen (RCA) (away from the vessel export within 1 cm, ROI of about 2 mm2).3. Image post processingUsing Philips EWB 4.01 workstation, multiplanar reconstruction (MPR), maximum intensity projection (MIP), volume rendering (VR), recombinant (CPR) curve and surface shaded display (SSD) etc. were performed for coronal artery images.4. Statistical methodsUsing the SPSS 20 statistical software, all data were expressed by mean plus or minus standard deviation. p<0.05, The difference has statistically significant.Results1. Patients’ age, BMI index between the three groups didn’t have statistically significant difference (p>0.05)。2. Subjective image quality evaluation:compared group 2 with group 1 and compared group 3 with group 1, the differences were not statistically significant (P< 0.05).3. Objective coronary artery image quality evaluationGroup 1:aortic root mean CT value (511±66) HU, left main (LM) (509±61) HU, left anterior descending branch (LAD) (504±69) HU, the left circumflex artery (LCX) (508±86) HU, the right coronary artery (RCA) (520±105) HU; noise (SD) (39.55±8.40), signal to noise ratio (SNR) (13.45±2.98), contrast to noise ratio (CNR) (21.17±5.41).Group 2:aortic root mean CT value (410±56) HU, left main (LM) (425±73) HU, left anterior descending branch (LAD) (401±53) HU, the left circumflex artery (LCX) (409±69) HU, the right coronary artery (RCA) (420±76) HU; noise (SD) (27.01±5.80), signal to noise ratio (SNR) (15.97±4.47), contrast to noise ratio (CNR) (19.78±4.55).Group 3:aortic root mean CT value (580±83) HU, left main (LM) (581±86) HU, left anterior descending branch (LAD) (579±87) HU, the left circumflex artery (LCX) (557±103) HU, the right coronary artery (RCA) (580±104) HU; noise (SD) (32.74±8.60), signal to noise ratio (SNR) (18.68±4.81), contrast to noise ratio (CNR) (27.05±6.73).(1) compared group 1 with group 2, CT value of the former’s aortic root, left main, left anterior descending, left circumflex branch and proximalright coronary artery lumenwere higher than that of,the latter, and the difference was statistically significant (P< 0.05). (2)Compared group 1 with group 3, CT value of the former’s aortic root, left main, left anterior descending, left circumflex branch and proximalright coronary artery lumenwere lower than that of the latter, and the difference was statistically significant (P< 0.05).4. Image noise (SD), signal to noise ratio (SNR), and contrast to signal to noise ratio (CNR):(1) Compared group 1 with group 2, image noise (SD) of the group 1 was higher than that of the group 2, the difference had statistical significance (P< 0.05). Signal to noise ratio (SNR) of the group 1 were lower than that ofthe group 2, the difference had statistical significance (P< 0.05).(2)Compared group 1 with group 3, image noise (SD) of the group 1 was higher than that of the group 3,the difference had statistical significance (P< 0.05). Signal to noise ratio (SNR) and contrast to noise ratio (CNR) of the group 1 were lower than that of the group 3, the difference had statistical significance (P< 0.05).ConclusionCompared prospective 100KVp ECG gated coronary artery imaging with 120KVp prospective ECG gated coronary artery imaging and 100KVp retrospective ECG gated coronary artery imaging, its noise(SD) was higher, the signal to noise ratio (SNR) were lower.But its subjective image quality evaluation is no significant difference, can meet the requirement for clinical diagnosis.