Cohort study of Western Australia computed tomography utilisation patterns and their policy implications

Background: Computed tomography (CT) scanning is a relatively high radiation dose diagnostic imaging modality with increasing concerns about radiation exposure burden at the population level in scientific literature. This study examined the epidemiology of adult CT utilisation in Western Australia (WA) in both the public hospital and private practice settings, and the policy implications. Methods: Retrospective cohort design using aggregate adult CT data from WA public hospitals and Medical Benefits Schedule (MBS) (mid-2006 to mid-2012). CT scanning trends by sex, age, provider setting and anatomical areas were explored using crude CT scanning rates, age-standardised CT scanning rates and Poisson regression modelling. Results: From mid-2006 to mid-2012 the WA adult CT scanning rate was 129 scans per 1,000 person-years (PY). Females were consistently scanned at a higher rate than males. Patients over 65 years presented the highest scanning rates (over 300 scans per 1,000 PY). Private practice accounted for 73% of adult CT scans, comprising the majority in every anatomical area. In the private setting females predominately held higher age-standardised CT scanning rates than males. This trend reversed in the public hospital setting. Patients over 85 years in the public hospital setting were the most likely age group CT scanned in nine of ten anatomical areas. Patients in the private practice setting aged 85+ years were relatively less prominent across every anatomical area, and the least likely age group scanned in facial bones and multiple areas CT scans.Conclusion: In comparison to the public hospital setting, the MBS subsidised private sector tended to service females and relatively younger patients with a more diverse range of anatomical areas, constituting the majority of CT scans performed in WA. Patient risk and subsequent burden is greater for females, lower ages and some anatomical areas. In the context of a national health system, Australia has various avenues to monitor radiation exposure levels, improve physician training and modify funding mechanisms to ensure individual and population medical radiation exposure is as low as reasonably achievable

The effect of iterative model reconstruction on coronary artery calcium quantification

Coronary artery calcium (CAC) scoring with computed tomography (CT) is an established tool for quantifying calcified atherosclerotic plaque burden. Despite the widespread use of novel image reconstruction techniques in CT, the effect of iterative model reconstruction on CAC score remains unclear. We sought to assess the impact of iterative model based reconstruction (IMR) on coronary artery calcium quantification as compared to the standard filtered back projection (FBP) algorithm and hybrid iterative reconstruction (HIR). In addition, we aimed to simulate the impact of iterative reconstruction techniques on calcium scoring based risk stratification of a larger asymptomatic population. We studied 63 individuals who underwent CAC scoring. Images were reconstructed with FBP, HIR and IMR and CAC scores were measured. We estimated the cardiovascular risk reclassification rate of IMR versus HIR and FBP in a larger asymptomatic population (n = 504). The median CAC scores were 147.7 (IQR 9.6-582.9), 107.0 (IQR 5.9-526.6) and 115.1 (IQR 9.3-508.3) for FBP, HIR and IMR, respectively. The HIR and IMR resulted in lower CAC scores as compared to FBP (both p < 0.001), however there was no difference between HIR and IMR (p = 0.855). The CAC score decreased by 7.2 % in HIR and 7.3 % in IMR as compared to FBP, resulting in a risk reclassification rate of 2.4 % for both HIR and IMR. The utilization of IMR for CAC scoring reduces the measured calcium quantity. However, the CAC score based risk stratification demonstrated modest reclassification in IMR and HIR versus FBP

Non-invasive and invasive imaging of vulnerable coronary plaque

Vulnerable plaque is characterized by a large necrotic core and an overlying thin fibrous cap. Non-invasive imaging modalities such as computed tomography angiography (CTA) and magnetic resonance imaging (MRI) allow for the assessment of morphological plaque characteristics, while positron emission tomography (PET) enables the detection of metabolic activity within the atherosclerotic lesions. Invasive imaging modalities such as intravascular ultrasound (IVUS), optical-coherence tomography (OCT), and intravascular MRI (IV-MRI) display plaques at a high spatial resolution. Near-infrared spectroscopy (NIRS) allows for the detection of chemical components of atherosclerotic plaques. In this review, we describe state-of-the-art non-invasive and invasive imaging modalities and stress the combination of their advantages to identify vulnerable plaque features

Myocardial Perfusion Imaging. Dual-Energy Approaches

The evaluation of patients presenting with symptoms sug- gestive of myocardial ischemia is one of the most common and challenging scenarios clinicians face. Despite consider- able advances in treatment, more than 50% of acute myocar- dial infarctions (AMI) resulting in death occur in patients before undergoing cardiac catheterization. Thus, risk stratifi- cation plays a central role in averting major adverse cardiac events [1]. The current WHO rating attributes more than 25% of deaths worldwide to cardiovascular disease (CVD). Despite a decreasing trend in the last decade, CVD is the leading cause of death in the United States and worldwide. On average there is approximately one CVD-related death every 40 s, resulting in the death of over 2000 Americans each day. The estimated direct and indirect cost of CVD in 2015 was $320.1 billion and is projected to be$918 billion by 2030. According to the current appropriate use criteria, coro- nary CT angiography (CCTA) is a robust imaging technique that provides a noninvasive, morphological assessment of the coronary arteries which can accurately depict coronary anatomy and atherosclerotic plaque burden. Thanks to its power to exclude significant coronary artery stenosis in patients with low and intermediate coronary artery disease (CAD) risk profiles, CCTA has become an integral part of the noninvasive diagnostic workup for the anatomic evaluation of the coronary arteries in patients with suspected CAD. A growing body of evidence has validated CCTA as the noninvasive imaging technique with the high- est sensitivity and specificity in detecting CAD, with a pooled sensitivity and specificity of 98% and 89%, respectively. These results compare favorably with alterna- tive noninvasive imaging tests, where SPECT reaches sensitivities and specificities of 88% and 61%, PET of 84% and 81%, and cardiac magnetic resonance imaging (CMR) of 89% and 76%, respectively. Although CCTA remains a morphological technique that can accurately depict coronary anatomy and atherosclerotic plaque burden, it is hampered by several limitations in the assessment of the hemodynamic significant coronary stenosis. The FAME and COURAGE trials, two major studies validating the impact of functional tests in coronary revascu- larization, have shown that the hemodynamic relevance of coronary stenosis is not adequately predicted by purely ana- tomical tests. Additionally, without functional data, ICA and CCTA can only provide limited correlation with myocardial perfusion defects. As revascularization should be guided by information on the state of myocardial perfusion, increasing efforts aim at determining the functional relevance of lesions by CCTA. Thus, noninvasive evaluation of patients with suspected CAD has started to shift focus from morphological CAD assessment to a complex, comprehensive mor- phological and functional evaluation. Furthermore, patient evaluation, management, and prognostication are more reli- able and effective when morphological and functional assess- ments are used in concert. Multiple CT techniques have the potential to provide a functional analysis. Some of these techniques are based on post-processing analysis of CCTA dataset and are focused on the direct assessment of coronary stenosis significance, such as CCTA-derived fractional flow reserve (CT-FFR) and transluminal attenuation gradient (TAG). CT-FFR relies on principles of computational fluid dynamics to calculate the ratio between the maximum coronary flow in the presence of a coronary stenosis and the hypothetical maximum coronary flow in absence of stenosis. Despite excellent results in terms of diagnostic accuracy, the only CT-FFR software that has been granted FDA approval to date requires complex offsite analysis. TAG represents the contrast attenuation gradient along the course of a coronary artery. The reliability of this technique is often hampered by extensive coronary cal- cifications or temporal inhomogeneity due to the acquisition window covering multiple heartbeats. The correlation between coronary density and the corresponding aortic attenuation at the same axial slice, formally known as CCO (corrected coronary opacification), has been proposed as a method to achieve more robust results. However, TAG and CCO have inferior diagnostic performance when compared to other functional tests. Other techniques based on CT data are focused on direct assessment of myocardial ischemia. Due to recent advance- ments in CT technology, in fact, in addition to its role in assessing coronary morphology and left ventricular function, CCTA has been utilized in the evaluation of a third aspect in the diagnostic algorithm of ischemic heart disease – myocardial perfusion. Computed tomography myocardial perfusion imaging (CTMPI) offers the possibility to directly detect the presence of perfusion defects in the myocardium following the administration of pharmacological stressing agent. Providing diagnostic information for each of these three cor- nerstones of ischemic heart disease workup, this emerging technology has the potential to become the stand-alone method for the evaluation of patients with suspected CAD using a single imaging modality and within a single imaging session