The Study Of MSCT For Coronary Artery Stenosis And Coronary Stent

Coronary artery disease (CAD) is one of the most severe disease which are harmful to our healthy. Recently, CAD has gradually increasing and younger trend owing to the improvement of living standard. So, it is very important for clinical doctor to detect, diagnosis and treat CAD. Currently, the selective coronary angiography (CAG) is the predominant method for detecting the coronary artery stenosis. Because this technique has limitation as a result of its invasive nature with a small, nevertheless not negligible, procedure-related mortality and morbidity rates and relatively high cost, attempts have been made to image the coronary artery with noninvasive methods. The introduction of multi-slice computed tomography (MSCT) in 1998 allowed for CT coronary angiography with a reasonable high spatial and temporal resolution. Promising results were reported for detection of coronary artery stenosis and followed-up of percutaneous transluminal coronary angioplasty (PTCA) and stenting. The temporal resolution of MSCT has been improved significantly because of the use of new techniques. At the same time, the application of the retrospective electrocardiogram (ECG) gated technique can reduce the movement of the heart and coronary artery and improve the image quality. MSCT with sub-second X-ray tube rotation scanner enables the generation of volume data sets, which cover the entire heart within a single breath hold. MSCT allows analyzing the data off-line and can select images with the least cardiac motion for image reconstruction. With MSCT, the entire cardiac phase can be obtained, and images in the end-systolic and end-diastolic phases can be selected for quantitive evaluation of cardiac function and wall motion. Previous study showed that there had good correlation between MSCT coronary angiography and CAG regarding the measurement of coronary artery inner diameters. The diagnostic accuracy of this noninvasive technique to detected coronary stenosis was good, particularly in the absence of extensive vascular calcification and in patients with low heart rate. It was useful to avoid invasive CAG examination for patients whose coronary artery was normal or light stenosis. PTCA and stenting is the main method for treatment of CAD. Stent replacement can reduce the coronary restenosis significantly because of avoiding the vessel remolding after balloon plasty. But stent itself can stimulate the hyperplasia of vascular smooth muscle cell. So in-stent stenosis (ISR) became another problem for the clinical doctor. Non-invasive methods for evaluating ISR become more and more important in recent years. MSCT with retrospective ECG-gated technique and segmented reconstruction method has proved to be valuable for non-invasive detection of obstructive CAD. The previous study showed that MSCT could evaluate the patency of coronary artery stents and ISR. Electron beam CT (EBCT) has gained clinical acceptance in noninvasive cardiac imaging and stent patency evaluation, but its spatial resolution in the z-axis is limited, which can affect the image quality of coronary artery and stents. Magnetic resonance angiography (MRA) has been demonstrated for evaluation of tantalum and copper-based alloy stent, and has the advantage of avoidance of radiation exposure and contrast medium. However, its limited spatial resolution and relatively long scan time restrict its application. In the first part of this study, the results of MSCT coronary angiography and CAG were compared to determine the feasibility and accuracy of MSCT for detecting proximal coronary artery stenosis in patients with CAD. At the same time the reason of dismatching for the results of MSCT and CAG was analyzed. In the second part, the coronary phantoms (CPs) were made to evaluate the effect of different scanning parameters of MSCT and different stent characteristics on the image quality of the stent in vitro. The measurements of inner stent diameters by MSCT were compared with results of intracoronary ultrasound (ICUS). In the third part, the coronary arterysegments with stent replacement were studied to detect the value of MSCT coronary angiography for coronary artery stents in patients with CAD in vivo. The results were compared with CAG and ICUS to discuss the application of MSCT in clinic. Part One: Clinical Evaluation of Coronary Artery Stenosis by Contrast-enhanced Multi-slice Helical CT Objective:. The purpose was to determine the feasibility and accuracy of multi-slice helical CT (MSCT) for detecting proximal coronary stenosis in patients with coronary artery disease (CAD). At the same time the reason of dismatching for the results of MSCT and CAG was analyzed. Methods: Thirty consecutive patients with CAD underwent contrast-enhanced MSCT (0.5sec/rotation, 0.5mm slice, Toshiba, Aquilion) and conventional selective coronary angiography (CAG) within one month. The MSCT data were acquired within a single breath-hold, and images were reconstructed by means of retrospective electrocardiographic gating. CAG was estimated using AHA reporting system (0%, 25%, 50%, 75%, 90%, 99%, 100%) by two cardiologists who were blinded to the results of MSCT. Curved MPR of MSCT was evaluated using the same system by a radiologist and a cardiologist who did not know the results of CAG. The segments with severe calcification or with stents implanted were eliminated when coronary stenosis were evaluated. The outcomes of the two kinds of examination methods were compared. Results: Seventy-eight percent (117/150) coronary segments were examined. Regarding CAG as the gold standard the overall sensitivity, specificity, and positive and negative prediction values in detecting stenotic lesions of ≥50% for assessable segment were 81.0% (17/21), 93.8% (90/96), 74.0% (17/23) and 95.7% (90/94), respectively. There were 86 segments (73.5%) matched and 31 segments (26.5%) mismatched between CAG and MSCT coronary angiography. The sensitivity, specificity, and positive and negative prediction values in detecting stenotic lesions of ≥75% for assessable segment were 91.7% (11/12), 99.0% (101/102), 73.3% (11/15) and96.2% (101/105), respectively. There were 112 segments (112/117, 95.7%) matched and 5 segments (5/117, 4.3%) mismatched between the results of CAG and MSCT coronary angiography. Conclusion: With a comparable result to CAG and a high sensitivity and specificity in detecting diameter stenosis of proximal coronary arteries, MSCT may be a promising and reliable noninvasive technique for diagnosis of CAD at routine clinical settings. Part Two: In Vitro Visualization of Coronary Artery Stents by Multi-slice CT Objective:PTCA and stenting is the main method for treatment of CAD. But stent itself can stimulate the hyperplasia of vascular smooth muscle cell. So in-stent stenosis (ISR) became another problem for the clinical doctor. The purpose of this study was to evaluate the effect of different scanning parameters of multi-slice helical CT (MSCT) and different stent characteristics on the image quality of the stent by comparing results of MSCT coronary angiography and CAG. And the measurements of inner stent diameters by MSCT were compared with results of ICUS to detect the measurement accuracy. Methods:The stents made of different materials were implanted into silicon tubes to make coronary phantoms (CPs). Stents were scanned by a 4-slice detector scanner. Heart rate was 54 bpm generated by self-made ECG signal generator. Rotation time was 500 ms, tube voltage 135KV and tube current 30mAs. Helical pitch (HP) was 0.8, and the field of view (FOV) 320mm. The long axis of the stent was placed perpendicularly to the direction of bed movement (z axis). With segmented reconstruction method, the raw data were reconstructed with 0.5 mm or 1.0 mm slice thickness and 0.2 mm reconstructed interval. FOV was 200mm, window level (WL) 100 HU and window width (WW) 800 HU. Short-axis multi planar reformation (MPR) images were generated from the reconstructed images at 2.0 mm intervals along the long axis of stent, and profile curves of short-axis images at two perpendicular directions were drawn to calculate the stent diameter. Theeffects of different stent material, stent diameter and reconstructed slice thickness on the image quality were evaluated, and measurements of inner stent diameters by MSCT were compared with results ICUS. Results:Tantalum stent could not be evaluated by MSCT and stainless steel stent over 3 mm inner diameter could be clearly visualized. The measurement of stent diameters filled with Omnipaque was significantly lower than filled with water (p<0.05) when scanned by MSCT. The lowest CT value of profile curves filled with water was lower than filled with Omnipaque (p<0.05). And the lowest CT value of 4 mm diameter stents was significantly lower than 3 mm diameter stents (p<0.05) either by water or by Omnipaque. For coronary stent visualization, 0.5 mm slice thickness was better than 1.0mm. The stent diameters measured by MSCT were significantly correlated with those measured by ICUS (r=0.85, P<0.05). Conclusion:MSCT can be used to evaluate the stent status, but the stent material, stent diameter, stent strut and reconstructed slice thickness should be considered.. Part Three: Clinical application of MSCT angiography for evaluating patency and restenosis of coronary stents Objective: The coronary artery segments with stent replacement were studied to detect the value of MSCT coronary angiography for coronary artery stents in patients with CAD in vivo. The results were compared with CAG and ICUS to discuss the application of MSCT in clinic. Methods: Sixteen CAD patients with implanted coronary artery stents (33 stents) were studied with MSCT coronary angiography to observe patency and restenosis of coronary stents. The diameter of stents were measured and compared with ICUS. Rotation time was 500 ms, tube voltage 135KV and tube current 140mAs. HP was 0.8-1.5, and the FOV was 360mm. The long axis of the stent was placed perpendicularly to the direction of bed movement (z axis). With segmented reconstruction method, the raw data were reconstructed at 70-77% R-R interval. Results: (1) Of 33 stents, 20 were patent, of which MSCT coronary...