迭代重建技术的进展及其在冠状动脉CT血管成像中的应用

随着CT影像技术的不断发展及计算机性能的不断提高,传统CT影像重建算法——滤波反投影技术（FBP）受到明显制约,而迭代重建技术（IR）得以迅速发展并成功应用于临床。冠状动脉CT血管成像（CCTA）是CT影像检查的重要组成,IR技术在降低CCTA辐射剂量、减轻钙化斑块和冠状动脉支架伪影、提高粥样斑块显示等方面具有重要的临床价值,就IR技术的进展及其在CCTA中的应用予以综述。     

低剂量CT迭代重建技术及低浓度对比剂的应用进展

【摘要】CT技术的快速发展为临床带来极有益的诊断信息,但CT检查及对比剂的过度使用也使辐射风险加大,对比剂肾病及其它并发症日趋增多。如何在保证图像质量的前提下尽可能的降低辐射剂量、减少对比剂应用,成为近年来研究的热点。本文就降低CT扫描辐射剂量的技术及低浓度对比剂的应用进展进行综述。     

“双低”CT血管成像的应用现状

近年人们对CT辐射危害及对比剂肾病越来越重视,"双低"CT血管成像(CTA)技术逐步成为近年来研究的热点。所谓的"双低"CTA技术即同时采用低辐射剂量及低对比剂的CTA技术,使用该技术需在保证影像质量足够诊断的前提下降低CT检查时病人接受的辐射剂量及对比剂用量。就"双低"CTA常用的技术及其临床应用进展进行综述。     

多层螺旋CT评估左心室功能的应用进展

左心室功能评估对心脏疾病的诊断、风险分层、治疗及预后分析具有重要意义。心脏CT血管成像(CCTA)作为一种无创性成像技术,目前在心脏疾病的诊断中发挥着越来越重要的作用,它既可评估冠状动脉狭窄,也能获取左心室容积和功能方面的信息。64层及以上的多层螺旋CT(MSCT)可一站式评价冠状动脉和左心室功能,无需对比剂和辐射的重复暴露,心功能分析结果可重复性高,具有较高的临床应用价值。     

心血管CT新技术在缺血性心脏病中的应用进展

近年来, CT技术的发展极大地增加了从心脏CT中获得的信息量, 冠状动脉CT血管成像(CCTA)能够提供冠状动脉解剖和斑块特征信息, 其识别、描述和量化冠状动脉粥样硬化的能力可以对患者进行准确的风险分层并监测治疗效果。与此同时, CT功能成像新技术在心血管领域也得到了广泛的应用。新兴CT技术, 如基于CCTA的血流储备分数、CT心肌灌注成像、冠状动脉周围脂肪、CT心肌应变、基于碘对比剂延迟增强等可评估心肌缺血程度、心肌组织学特征及预后, 为缺血性心脏病(IHD)患者的诊疗提供重要依据。本文对心血管CT新技术在IHD中的应用进展进行综述。     

30mL碘对比剂、70kV管电压下前瞻性心电门控大螺距冠状动脉CT血管成像的初步可行性研究

正摘要目的评估 30 mL 碘对比剂 70 kV 管电压下前瞻性心电门控大螺距冠状动脉 CT 血管成像(CCTA)的可行性、影像质量及辐射剂量。方法本前瞻性研究共纳入 58 例体质     

冠状动脉CT血管成像剂量降低技术的应用现状和进展

冠状动脉CT血管成像(CCTA)的辐射剂量在“后64层CT”时代仍得到广泛关注,各种剂量降低技术得到进一步发展,使得高端机型CCTA的辐射剂量显著降低.熟练掌握并综合应用不同的剂量降低技术,有效地降低管球曝光强度、缩短曝光时间和减少曝光范围,能够实现病人接受辐射剂量的最小化.就有关CCTA剂量降低技术及新进展予以综述.     

CCTA技术对冠状动脉狭窄及其钙化斑块的评估

冠状动脉CT血管成像（CCTA）是一种可无创检测冠状动脉粥样硬化性疾病的成像手段,已成为临床筛查及诊断冠心病的首要检查方法。但对于钙化严重的冠状动脉节段,CCTA的特异性及阳性预测值偏低,可导致病人过度治疗,因此限制了CCTA的临床应用。综述钙化斑块伪影对CCTA的影响,并就CCTA对冠状动脉狭窄准确评估的相关技术进展进行分析,以利于临床诊断中提高CCTA对冠状动脉狭窄率的评估。     

冠状动脉CT成像钙化斑块减影技术的临床应用

冠状动脉CT血管成像(CCTA)作为一种无创的冠状动脉成像方法,已经成为临床诊断冠心病的首选影像检查方法.由于钙化斑块往往会干扰CCTA对冠状动脉狭窄严重程度的评估,现临床上开发出一种新的冠状动脉成像技术方法——冠状动脉CT成像钙化斑块减影技术.通过去除钙化斑块对冠状动脉成像的干扰,从而对冠状动脉血管作出有效的评估.本文就这种新的影像技术方法的进展、原理及其在临床中的应用进行综述.     

双源CT超低管电压、低对比剂流率及容量冠状动脉CTA研究

目的探讨双源CT超低管电压、低对比剂流率及容量扫描方案行冠状动脉CT血管成像(coronary CT angiography, CCTA)的可行性。方法收集本院130例行CCTA检查的患者,体质量指数(BMI)≤25kg/m~2,分为2组,每组各65例。A组(实验组)扫描方案:固定管电压70kV,参考管电流500mAs;对比剂注射速率及容量分别为4.0ml/s、0.8ml/kg;B组(对照组)扫描方案:参考管电压120kV,参考管电流320mAs,对比剂注射速率及容量分别为5.0ml/s、1.0ml/kg。所有受检者均采用第二代双源CT进行扫描。测量右冠状动脉(RCA)开口、左冠状动脉主干(LM)开口、左冠状动脉前降支(LAD)近段、左冠状动脉回旋支(LCX)近段管腔内的CT值及图像噪声,并测量同层面胸壁下脂肪组织CT值及图像噪声,计算图像信噪比(SNR)及对比度噪声比(CNR);记录两组受检者的容积剂量指数(CTDIvol)、剂量长度乘积(DLP),计算有效辐射剂量(ED);比较两组受检者的年龄、性别、BMI、扫描时心率、实际管电流、图像质量及辐射剂量。结果两组受检者年龄、性别、BMI、扫描时心率及实际管电流无统计学差异;两组图像质量评分无统计学差异(P0.05)。A、B两组图像CT值、图像噪声、SNR及CNR均不具有统计学差异(P0.05)。A组有效辐射计量(0.69±0.25)mSv明显低于B组(2.42±1.18)mSv,且差异具有统计学意义(P0.05)。结论对于BMI≤25kg/m~2的受检者,70kV管电压结合双源CT前瞻性心电门控及迭代重建算法行CCTA检查,能够在得到满足临床诊断要求的图像质量的同时明显降低有效辐射剂量(ED1mSv),同时能降低对比剂流率和对比剂注射容量。     

CT低剂量技术在冠状动脉钙化积分检查中的应用现状与新进展

冠状动脉钙化积分(CACS)是无创性评估心血管风险分层及冠心病发生、发展和预后的一项重要指标,可以辅助临床治疗策略的选择制定。遵从辐射防护最优化原则(ALARA),可以采用直接方法(降低管电流、管电压,自动管电流调制技术)、间接方法(大螺距、迭代重建技术),以及直接在冠状动脉CT血管成像、双能CT虚拟平扫和非心电门控胸部CT平扫影像上测量CACS,从而降低该检查辐射剂量,并可准确、可重复地测量CACS,进行心血管风险分层。     

Trends in radiation protection in CT: Present and future status

With the introduction of modern multislice scanner generations, computed tomography (CT) has emerged as a useful tool for evaluation of the coronary arteries. A common application of coronary CT angiography (CCTA) is the examination of patients with intermediate pretest probability for obstructive coronary artery disease. Despite the widespread use of cardiac CT examinations in clinical practice, concern remains about the exposure to ionizing radiation and its potential hazards. Therefore, radiation dose and strategies for dose reduction have become an important focus of interest. Several smaller analyses have shown an effective radiation dose between 6.4 and 27.8 mSv for spiral CCTA image acquisition. The international Prospective Multicenter Study On RadiaTion Dose Estimates Of Cardiac CT AngIOgraphy I (PROTECTION I) study, the largest observational study on radiation dose estimates of cardiac CT so far, determined radiation dose estimates of CCTA, as well as the effect of different strategies to reduce dose in clinical practice. The median dose-length-product of 1965 CCTA examinations was 885 mGy × cm, which corresponds to a median estimated effective radiation dose of 12 mSv. However, a large variation in dose between study sites was observed, indicating a large potential to reduce dose for individual sites. Several dose-saving scanning techniques and algorithms have been developed. This article discusses these strategies as well as their effect on radiation dose and image quality. Because the contrast-enhanced CT angiography is the largest part of the total study dose, the following described strategies focus on radiation dose reduction for CCTA image acquisition.     

Impact of new technologies on dose reduction in CT

The introduction of slip ring technology enables helical CT scanning in the late 1980's and has rejuvenated CT's role in diagnostic imaging. Helical CT scanning has made possible whole body scanning in a single breath hold and computed tomography angiography (CTA) which has replaced invasive catheter based angiography in many cases because of its easy of operation and lesser risk to patients. However, a series of recent articles and accidents have heightened the concern of radiation risk from CT scanning. Undoubtedly, the radiation dose from CT studies, in particular, CCTA studies, are among the highest dose studies in diagnostic imaging. Nevertheless, CT has remained the workhorse of diagnostic imaging in emergent and non-emergent situations because of their ubiquitous presence in medical facilities from large academic to small regional hospitals and their round the clock accessibility due to their ease of use for both staff and patients as compared to MR scanners. The legitimate concern of radiation dose has sparked discussions on the risk vs benefit of CT scanning. It is recognized that newer CT applications, like CCTA and perfusion, will be severely curtailed unless radiation dose is reduced. This paper discusses the various hardware and software techniques developed to reduce radiation dose to patients in CT scanning. The current average effective dose of a CT study is ∼10 mSv, with the implementation of dose reduction techniques discussed herein; it is realistic to expect that the average effective dose may be decreased by 2-3 fold.     

Feasibility of prospectively ECG-triggered high-pitch coronary CT angiography with 30 mL iodinated contrast agent at 70 kVp: initial experience

Objectives

To evaluate the feasibility, image quality and radiation dose of prospectively ECG-triggered high-pitch coronary CT angiography (CCTA) with 30 mL contrast agent at 70 kVp.

Methods

Fifty-eight patients with suspected coronary artery disease, a body mass index (BMI) of less than 25 kg/m², sinus rhythm and a heart rate (HR) of less than 70 beats per minute (bpm) were prospectively enrolled in this study. Thirty mL of 370 mg I/mL iodinated contrast agent was administrated at a flow rate of 5 mL/s. All patients underwent prospectively ECG-triggered high-pitch CCTA on a second-generation dual-source CT system at 70 kVp using automated tube current modulation.

Results

Fifty-six patients (96.6 %) had diagnostic CCTA images and two patients (3.4 %) had one vessel with poor image quality each rated as non-diagnostic. No significant effects of HR, HR variability and BMI on CCTA image quality were observed (all P?>?0.05). Effective dose was 0.17?±?0.02 mSv and the size-specific dose estimate was 1.03?±?0.13 mGy.

Conclusion

Prospectively ECG-triggered high-pitch CCTA at 70 kVp with 30 mL of contrast agent can provide diagnostic image quality at a radiation dose of less than 0.2 mSv in patients with a BMI of less than 25 kg/m² and an HR of less than 70 bpm.

Key points

? Prospectively ECG-triggered high-pitch CCTA at 70 kVp/30 mL contrast agent is feasible. ? Diagnostic image quality can be obtained at a radiation dose of less than 0.2 mSv. ? This protocol is suitable for normal-weight patients with slow heart rate.     

Liver metastases from colorectal carcinoma: detection with continuous CT angiography.

A diagnostic approach to assess liver metastases from colorectal carcinoma was prospectively evaluated in 30 patients with and without metastases on the basis of findings at conventional computed tomography (CT). With the technique, termed continuous CT angiography (CCTA), CT data were continuously sampled for 24 seconds at the same section level after initiation of a 3-second injection of 10-20 mL of contrast medium in the common hepatic artery. The procedure was repeated for each contiguous section level of the liver. Findings at preoperative ultrasound (US), conventional CT, and CCTA were compared with those at intraoperative US and surgical exploration as the standard of reference. Forty-four liver metastases were identified in 16 patients, and 14 patients had no metastases. CCTA had a sensitivity of 98% (43 lesions identified) and higher accuracy (81% [54 of 67 diagnoses]) than US and conventional CT. The data indicate that CCTA can supplement information obtained with conventional imaging techniques in patients who must undergo hepatic surgery because of metastases from colorectal carcinoma.     

Coronary computed tomography angiography using prospective electrocardiography-gated axial scans with 64-detector computed tomography: evaluation of stair-step artifacts and padding time

Purpose  

We compared stair-step artifacts and radiation dose between prospective electrocardiography (ECG)-gated coronary computed tomography angiography (prospective CCTA) and retrospective CCTA using 64-detector CT and determined the optimal padding time (PT) for prospective CCTA.     

Cardiac-CT with the newest CT scanners: An incoming screening tool for competitive athletes?

Competitive athletes of all skill levels are at risk of sudden cardiac death (SCD) due to certain heart conditions. Prior to engagement in high-intensity athletics, it is necessary to screen for these conditions in order to prevent sudden cardiac death. Cardiac-CT angiography (CCTA) is a reliable tool to rule out the leading causes of SCD by providing an exceptional overview of vascular and cardiac morphology. This allows CCTA to be a powerful resource in identifying cardiac anomalies in selected patients (i.e. unclear symptoms or findings at ECG or echocardiography) as well as to exclude significant coronary artery disease (CAD). With the advancement of technology over the last few years, the latest generations of computed tomography (CT) scanners provide better image quality at lower radiation exposures. With the amount of radiation exposure per scan now reaching the sub-millisievert range, the number of CT examinations it is supposed to increase greatly, also in the athlete's population. It is thus necessary for radiologists to have a clear understanding of how to make and interpret a CCTA examination so that these studies may be performed in a responsible and radiation conscious manner especially when used in the younger populations. Our work aims to illustrate the main radiological findings of CCTAs and highlight their clinical impact with some case studies. We also briefly describe critical features of state-of-the-art CT scanners that optimize different acquisitions to obtain the best quality at the lowest possible dose.     

Adequate image quality with reduced radiation dose in prospectively triggered coronary CTA compared with retrospective techniques

The goal of our study was to compare a prospective triggering (PT) CT technique with retrospectively gated (RG) CT techniques in coronary computed tomographic angiograms (CCTA) with respect to image quality and radiation dose. Sixty consecutive patients were enrolled. CCTAs using the RG technique were obtained with a dual-source 64-slice CT system in 40 patients, using ECG-triggered tube current modulation, with either a broad pulsing window at 30–80% of the RR interval (group RGb, 20 patients, heart rate > 70 bpm) or a small pulsing window at 70% (group RGs, 20 patients, heart rate < 70 bpm). The other 20 patients underwent CCTA using the PT technique on a 128-slice CT system (group PT, heart rate < 70 bpm). All images were evaluated by two observers for quality on a three-point scale, with 1 being excellent and 3 being insufficient. The effective radiation dose was calculated for each patient. The average image quality score was 1.5 ± 0.6 for PT, 1.35 ± 0.5 for RGs and 1.65 ± 0.5 for RGb. The mean effective dose for RGb was 9 ± 4 mSv, for RGs 7 ± 3 mSv and for PT 3 ± 1 mSv. This represents a 57% dose reduction for PT compared with RGs and a 67% dose reduction for PT compared with RGb. In conclusion, in selected patients CCTA with the PT technique offers adequate image quality with a significantly lower radiation dose compared with CCTA using RG techniques. None of the authors have financial or other kinds of interests that might pose a conflict of interest in connection with this article.     

Quantitative assessment of atherosclerotic plaque,recent progress and current limitations

An important advantage of computed tomography coronary angiography (CCTA) is its ability to visualize the presence and severity of atherosclerotic plaque, rather than just assessing coronary artery stenoses. Until recently, assessment of plaque subtypes on CCTA relied on visual assessment of the extent of calcified/non-calcified plaque, or visually identifying high-risk plaque characteristics. Recent software developments facilitate the quantitative assessment of plaque volume or burden on CCTA, and the identification of subtypes of plaque based on their attenuation density. These techniques have shown promise in single and multicenter studies, demonstrating that the amount and type of plaque are associated with subsequent cardiac events. However, there are a number of limitations to the application of these techniques, including the limitations imposed by the spatial resolution of current CT scanners, challenges from variations between reconstruction algorithms, and the additional time to perform these assessments. At present, these are a valuable research technique, but not yet part of routine clinical practice. Future advances that improve CT resolution, standardize acquisition techniques and reconstruction algorithms and automate image analysis will improve the clinical utility of these techniques. This review will discuss the technical aspects of quantitative plaque analysis and present pro and con arguments for the routine use of quantitative plaque analysis on CCTA.     

Coronary CT angiography with iterative reconstruction in early triage of patients with acute chest pain

Background

Patients who present to the emergency department (ED) complaining of acute chest pain are of clinical concern because a small percentage will have acute coronary syndrome (ACS). The American College of Cardiology (ACC) and the American Heart Association (AHA) recommend hospitalization for patients with a low-to-intermediate risk of ACS who have initial negative ECG and enzyme test results. A negative coronary CT angiography (CCTA) during the triage has a very high negative predictive value for ruling out ACS decreasing the length of hospital stay. Recent techniques e.g. ASiR in CCTA should be used to decrease the radiation dose as low as possible.

Objective

The aim of this study is to evaluate the role of low radiation dose CCTA with ASiR in triage of low-risk patients with acute chest pain in emergency department. A negative CCTA early in the workup may enable a shorter length of stay.

Subjects and methods

We studied 54 selected patients (55.6% men; mean age 48 ± 6 years) with chest pain who were awaiting hospital admission to rule out ACS despite the absence of diagnostic ECG changes and normal cardiac enzymes on ED presentation. Patients underwent CCTA before hospital admission. Afterward, patients received standard clinical care (SCC). ER physicians involved in the patient’s care were blinded to the results of CCTA. An expert panel established the presence or absence of ACS based on AHA guidelines. The CCTA images were evaluated for the presence of significant coronary artery stenosis (diameter reduction >50%) and were used to make a triage decision.

Results

Four patients (7.4%) with chest pain had at least one significant coronary stenosis on CCTA (sensitivity 100%, specificity 96%, accuracy 96.3%, positive predictive value (PPV) 66.7% and negative predictive value (NPV) 100%). Significant coronary stenosis was excluded in 48 of the 54 patients by CCTA (88.9%), potentially saving about 71.6% of unnecessary hospital admission hours.

Conclusion

CCTA based detection of significant coronary stenosis has potential role to decrease the length of hospital stay , without reducing appropriate patient care, in low risk patients with acute chest pain. CCTA should be done with lowest radiation possible using recent techniques.