Technical principles, benefits, challenges, and applications of photon counting computed tomography in coronary imaging: a narrative review.

Background and Objective: The introduction of photon-counting computed tomography (PCCT) represents the most recent groundbreaking advancement in clinical computed tomography (CT). PCCT has the potential to overcome the limitations of traditional CT and to provide new quantitative imaging information. This narrative review aims to summarize the technical principles, benefits, and challenges of PCCT and to provide a concise yet comprehensive summary of the applications of PCCT in the domain of coronary imaging. Methods: A review of PubMed, Scopus, and Google Scholar was performed until October 2023 by using relevant keywords. Articles in English were considered. Key Content and Findings: The main advantages of PCCT over traditional CT are enhanced spatial resolution, improved signal and contrast characteristics, diminished electronic noise and image artifacts, lower radiation exposure, and multi-energy capability with enhanced material discrimination. These key characteristics have made room for improved assessment of plaque volume and severity of stenosis, more precise assessment of coronary artery calcifications, also preserved in the case of a reduced radiation dose, improved assessment of plaque composition, possibility to provide details regarding the biological processes occurring within the plaque, enhanced quality and accuracy of coronary stent imaging, and improved radiomic analyses. Conclusions: PCCT can significantly impact diagnostic and clinical pathways and improve the management of patients with coronary artery diseases (CADs).

Photon-Counting Computed Tomography in Atherosclerotic Plaque Characterization.

Atherosclerotic plaque buildup in the coronary and carotid arteries is pivotal in the onset of acute myocardial infarctions or cerebrovascular events, leading to heightened levels of illness and death. Atherosclerosis is a complex and multistep disease, beginning with the deposition of low-density lipoproteins in the arterial intima and culminating in plaque rupture. Modern technology favors non-invasive imaging techniques to assess atherosclerotic plaque and offer insights beyond mere artery stenosis. Among these, computed tomography stands out for its widespread clinical adoption and is prized for its speed and accessibility. Nonetheless, some limitations persist. The introduction of photon-counting computed tomography (PCCT), with its multi-energy capabilities, enhanced spatial resolution, and superior soft tissue contrast with minimal electronic noise, brings significant advantages to carotid and coronary artery imaging, enabling a more comprehensive examination of atherosclerotic plaque composition. This narrative review aims to provide a comprehensive overview of the main concepts related to PCCT. Additionally, we aim to explore the existing literature on the clinical application of PCCT in assessing atherosclerotic plaque. Finally, we will examine the advantages and limitations of this recently introduced technology.

Spectral Photon-Counting Computed Tomography: Technical Principles and Applications in the Assessment of Cardiovascular Diseases.

Spectral Photon-Counting Computed Tomography (SPCCT) represents a groundbreaking advancement in X-ray imaging technology. The core innovation of SPCCT lies in its photon-counting detectors, which can count the exact number of incoming x-ray photons and individually measure their energy. The first part of this review summarizes the key elements of SPCCT technology, such as energy binning, energy weighting, and material decomposition. Its energy-discriminating ability represents the key to the increase in the contrast between different tissues, the elimination of the electronic noise, and the correction of beam-hardening artifacts. Material decomposition provides valuable insights into specific elements' composition, concentration, and distribution. The capability of SPCCT to operate in three or more energy regimes allows for the differentiation of several contrast agents, facilitating quantitative assessments of elements with specific energy thresholds within the diagnostic energy range. The second part of this review provides a brief overview of the applications of SPCCT in the assessment of various cardiovascular disease processes. SPCCT can support the study of myocardial blood perfusion and enable enhanced tissue characterization and the identification of contrast agents, in a manner that was previously unattainable.

Unsupervised machine learning for risk stratification and identification of relevant subgroups of ascending aorta dimensions using cardiac CT and clinical data.

The potential of precision population health lies in its capacity to utilize robust patient data for customized prevention and care targeted at specific groups. Machine learning has the potential to automatically identify clinically relevant subgroups of individuals, considering heterogeneous data sources. This study aimed to assess whether unsupervised machine learning (UML) techniques could interpret different clinical data to uncover clinically significant subgroups of patients suspected of coronary artery disease and identify different ranges of aorta dimensions in the different identified subgroups. We employed a random forest-based cluster analysis, utilizing 14 variables from 1170 (717 men/453 women) participants. The unsupervised clustering approach successfully identified four distinct subgroups of individuals with specific clinical characteristics, and this allows us to interpret and assess different ranges of aorta dimensions for each cluster. By employing flexible UML algorithms, we can effectively process heterogeneous patient data and gain deeper insights into clinical interpretation and risk assessment.

About different localization of hypoattenuated lesions following transcatheter aortic valve replacement.

BACKGROUND: Subclinical leaflet thrombosis is diagnosed using multidetector computed tomography (MDCT) and is characterised by a meniscal-shaped hypoattenuated lesion of one or more leaflets. Transcatheter aortic self-expandable valves are commonly manufactured with pliable pericardium over a nitinol frame that forms leaflet and extra-leaflet components such as the valve skirt. Little is known about extra-leaflet hypoattenuated lesion localisation, including that at the anatomical sinus level. Thus, the main aim of this study was to describe leaflet and extra-leaflet (anatomic sinus and subvalvular level) hypoattenuated lesions following transcatheter aortic valve replacement with a self-expandable prosthesis. As a secondary aim, we sought to investigate predictors of hypoattenuated lesions. METHODS: Fifty patients underwent MDCT at the follow-up. RESULTS: At a follow-up of 12 months, hypoattenuated leaflet lesions with mild to severe restricted movement were detected in eight individuals (16%), anatomic sinus lesions were identified in nine patients (18%), with higher prevalence in the non-coronary sinus (16%), and subvalvular lesions with variable extension toward the valve inflow were diagnosed in eight patients (16%). In 4 patients (8%) the anatomic sinus thrombus was 'in overlap' with leaflet thrombus; in 3 patients (6%) was in continuity with subvalvular frame thrombus. Bicuspid valve was the only independent predictor associated with hypoattenuated lesions (adj OR 8.25 (95% CI: 1.38, 49.21), p = 0.02)). CONCLUSIONS: This study demonstrated that hypoattenuated lesions could be identified not only at the leaflet but also at the subvalvular and anatomic sinus levels. The clinical relevance of such lesions remains unclear.

Cardiovascular Applications of Photon-Counting CT Technology: A Revolutionary New Diagnostic Step.

Photon-counting computed tomography (PCCT) is an emerging technology that can potentially transform clinical CT imaging. After a brief description of the PCCT technology, this review summarizes its main advantages over conventional CT: improved spatial resolution, improved signal and contrast behavior, reduced electronic noise and artifacts, decreased radiation dose, and multi-energy capability with improved material discrimination. Moreover, by providing an overview of the existing literature, this review highlights how the PCCT benefits have been harnessed to enhance and broaden the diagnostic capabilities of CT for cardiovascular applications, including the detection of coronary artery calcifications, evaluation of coronary plaque extent and composition, evaluation of coronary stents, and assessment of myocardial tissue characteristics and perfusion.

Self-Expandable Prosthesis Valve Adaptation: Non-Uniform Expansion and Stent Frame Decoupling.

The incidence of non-uniform expansion in the context of the self-expandable transcatheter heart valve (THV) is little investigated, along with stent-frame decoupling, which is a form of stent adaptation, in which the lower part of the THV stent conforms to both the ellipticity of the left ventricle outflow tract and the native annulus while maintaining the higher part of the valve more circular. We analyzed post-implant multi-detector computed tomography scans in 50 patients. Prosthesis non-uniform expansion was assessed by computing the prosthesis eccentricity on 6 prespecified levels: (1) frame inflow, (2) native annulus, (3) leaflet inflow, (4) prosthesis waist, (5) leaflet outflow, and (6) frame outflow. Stent-frame decoupling was assessed by comparing the mean eccentricity on 6 different prosthesis levels. Implantation depth, leaflet expansion and alignment, and residual anatomic sinus area ratios were also calculated. Subclinical leaflet thrombosis was defined as hypoattenuated lesion of a meniscal shape. At a 12-month follow-up, non-uniform expansion was consistently detected at each valvular level. Highest eccentricity was measured at the native annulus level (eccentricity: 0.54 ±  0.12), while the lowest index at the frame outflow level (0.23 ± 0.11). Similar results were observed in the subgroup analyses of sizes 23, 26, 29, and 34. Eccentricity significantly decreased from the annulus level to the prosthesis frame outflow (p <0.001). Notably, the incidence of mild-to-severe subclinical leaflet thrombosis was relevant (16%). In conclusion, prosthesis non-uniform expansion and stent frame decoupling frequently occur after self-expandable THV replacement. The clinical and hemodynamic implications remain uncertain.

Dual-Source Photon-Counting Computed Tomography-Part III: Clinical Overview of Vascular Applications beyond Cardiac and Neuro Imaging.

Photon-counting computed tomography (PCCT) is an emerging technology that is expected to radically change clinical CT imaging. PCCT offers several advantages over conventional CT, which can be combined to improve and expand the diagnostic possibilities of CT angiography. After a brief description of the PCCT technology and its main advantages we will discuss the new opportunities brought about by PCCT in the field of vascular imaging, while addressing promising future clinical scenarios.

Epicardial and thoracic subcutaneous fat texture analysis in patients undergoing cardiac CT.

Introduction: The aim of our study was to evaluate the feasibility of texture analysis of epicardial fat (EF) and thoracic subcutaneous fat (TSF) in patients undergoing cardiac CT (CCT). Materials and methods: We compared a consecutive population of 30 patients with BMI ≤25 kg/m2 (Group A, 60.6 ± 13.7 years) with a control population of 30 patients with BMI >25 kg/m2 (Group B, 63.3 ± 11 years). A dedicated computer application for quantification of EF and a texture analysis application for the study of EF and TSF were employed. Results: The volume of EF was higher in group B (mean 116.1 cm3 vs. 86.3 cm3, p = 0.014), despite no differences were found neither in terms of mean density (-69.5 ± 5 HU vs. -68 ± 5 HU, p = 0.28), nor in terms of quartiles distribution (Q1, p = 0.83; Q2, p = 0.22, Q3, p = 0.83, Q4, p = 0.34). The discriminating parameters of the histogram class were mean (p = 0.02), 0,1st (p = 0.001), 10th (p = 0.002), and 50th percentiles (p = 0.02). DifVarnc was the discriminating parameter of the co-occurrence matrix class (p = 0.007).The TSF thickness was 15 ± 6 mm in group A and 19.5 ± 5 mm in group B (p = 0.003). The TSF had a mean density of -97 ± 19 HU in group A and -95.8 ± 19 HU in group B (p = 0.75). The discriminating parameters of texture analysis were 10th (p = 0.03), 50th (p = 0.01), 90th percentiles (p = 0.04), S(0,1)SumAverg (p = 0.02), S(1,-1)SumOfSqs (p = 0.02), S(3,0)Contrast (p = 0.03), S(3,0)SumAverg (p = 0.02), S(4,0)SumAverg (p = 0.04), Horzl_RLNonUni (p = 0.02), and Vertl_LngREmph (p = 0.0005). Conclusions: Texture analysis provides distinctive radiomic parameters of EF and TSF. EF and TSF had different radiomic features as the BMI varies.

Intravenous Contrast Material for Cardiac Computed Tomography: Results From the Open-label Multicenter, Multivendor Italian Registry of Contrast Material Use in Cardiac Computed Tomography.

PURPOSE: The Italian Registry of Contrast Material use in Cardiac Computed Tomography (iRCM-CCT) is a multicenter, multivendor, observational study on the use of contrast media (CM) in patients undergoing cardiac computed tomography (CCT). The aim of iRCM-CCT is to assess image quality and safety profile of intravenous CM compounds. MATERIALS AND METHODS: iRCM-CCT enrolled 1842 consecutive patients undergoing CCT (≥50 per site) at 20 cluster sites with the indication of suspected coronary artery disease. Demographic characteristics, CCT, and CM protocols, clinical indications, safety markers, radiation dose reports, qualitative (ie, poor vascular enhancement) and quantitative (ie, HU attenuation values) image parameters were recorded. A centralized coordinating center collected and assessed all image parameters. RESULTS: The cohort included 891 men and 951 women (age: 63±14 y, body mass index: 26±4 kg/m2) studied with ≥64 detector rows computed tomography scanners and different iodinated intravenous CM protocols and compounds (iodixanol, iopamidol, iohexol, iobitridol, iopromide, and iomeprol). The following vascular attenuation was reported: 504±147 HU in the aorta, 451±146 HU in the right coronary artery, 474±146 HU in the left main, 451±146 HU in the left anterior descending artery, and 441±149 HU in the circumflex artery. In 4% of cases the image quality was not satisfactory due to poor enhancement. The following adverse reactions to CM were recorded: 6 (0.3%) extravasations and 17 (0.9%) reactions (11 mild, 4 moderate, 2 severe). CONCLUSIONS: In a multicenter registry on CM use during CCT the prevalence of CM-related adverse reactions was very low. The appropriate use of CM is a major determinant of image quality.

Aortic valve and vascular calcium score in pre-TAVI CT: correlation with early post-procedural complications.

PURPOSE: The aim of our study was to evaluate the prevalence of early complications after Transcatheter Aortic Valve Implantation (TAVI) and their correlation with the Calcium Score (CS) of the aortic valve, aorta and ilio-femoral arteries derived from pre-procedural computed tomography (CT). MATERIALS AND METHODS: We retrospectively reviewed 226 patients (100 males, mean age 79.4 ± 6.7 years) undergoing 64-slice CT for pre-TAVI evaluation from January 2018 to April 2021. The population was divided into CS quartiles. RESULTS: Overall, 173 patients underwent TAVI procedure, of whom 61% presented paravalvular leak after the procedure, 28% presented bleeding or vascular complications, 25% presented atrioventricular block, and 8% developed acute kidney injury. The prevalence of paravalvular leak and vascular complications was higher in the upper CS quartiles for aortic valve and ilio-femoral arteries. CONCLUSIONS: Aortic valve and vascular CS could help to predict post-TAVI early complications.

Cardiac Magnetic Resonance with Delayed Enhancement of the Right Ventricle in patients with Left Ventricle primary involvement: diagnosis and evaluation of functional parameters.

Cardiac Magnetic Resonance (CMR) allows an accurate Right Ventricle (RV) assessment that could be of great relevance in diseases causing inflammation or fibrosis. The aim of this study was to evaluate the concomitant involvement of the RV in patients with delayed enhancement (DE) of the Left Ventricle (LV-DE) using CMR. We retrospectively enrolled 95 (male n. 66; age 55±18years; BMI 26±5kg/m2) consecutive patients with LV-DE who underwent a CMR (Achieva 1.5 T, Philips) for different indications: post-ischemic dilated cardiopathy (PDM), hypertrophic cardiomyopathy (HCM), myocardial infarction (MI), myocarditis/pericarditis (MP) and congenital heart disease (CD). We assessed the presence and extension of DE and functional parameters such as ventricular end-diastolic (EDV), end-systolic volumes (ESV) and ejection fraction (EF) of both LV and RV. Prevalence of RV-DE was 30.5% (29/95): 75% (3/4) for CD, 44% (4/9) for PDM, 36% (17/47) for MI, 27.8% (5/18) for MP and 0% (0/17) for HCM. LV-EF and RV-EF were 53±15mL and 51±13mL, respectively, for patients without RV-DE (RV-DE-), and 40±19 mL and 42±15 mL, respectively, for patients with RV-DE (RV-DE+) (p<0.05), while LV-EDV and LV-ESV were 80±28 mL and 40±26 mL, respectively, for RV-DE- and 100±45 mL and 65±49 mL, respectively, for RV-DE+ (p<0.05). The prevalence of RV-DE in patients with LV primary involvement is not negligible and it is found mainly in patients with CD and PDM and then in patients with MI and MP. It is more often associated with LV-EF and RV-EF reduction and increase in LV volumes.

Appropriateness criteria for the use of cardiac computed tomography, SIC-SIRM part 2: acute chest pain evaluation; stent and coronary artery bypass graft patency evaluation; planning of coronary revascularization and transcatheter valve procedures; cardiomyopathies, electrophysiological applications, cardiac masses, cardio-oncology and pericardial diseases evaluation.

In the past 20 years, cardiac computed tomography (CCT) has become a pivotal technique for the noninvasive diagnostic workup of coronary and cardiac diseases. Continuous technical and methodological improvements, combined with fast growing scientific evidence, have progressively expanded the clinical role of CCT. Randomized clinical trials documented the value of CCT in increasing the cost-effectiveness of the management of patients with acute chest pain presenting in the emergency department, also during the pandemic. Beyond the evaluation of stents and surgical graft patency, the anatomical and functional coronary imaging have the potential to guide treatment decision-making and planning for complex left main and three-vessel coronary disease. Furthermore, there has been an increasing demand to use CCT for preinterventional planning in minimally invasive procedures, such as transcatheter valve implantation and mitral valve repair. Yet, the use of CCT as a roadmap for tailored electrophysiological procedures has gained increasing importance to assure maximum success. In the meantime, innovations and advanced postprocessing tools have generated new potential applications of CCT from the simple coronary anatomy to the complete assessment of structural, functional and pathophysiological biomarkers of cardiac disease. In this complex and revolutionary scenario, it is urgently needed to provide an updated guide for the appropriate use of CCT in different clinical settings. This manuscript, endorsed by the Italian Society of Cardiology (SIC) and the Italian Society of Medical and Interventional Radiology (SIRM), represents the second of two consensus documents collecting the expert opinion of cardiologists and radiologists about current appropriate use of CCT.

Focal hepatic intrinsically hyperattenuating lesions at unenhanced CT: Not always calcifications.

Due to the growing use of CT, there has been an increase in the frequency of detecting focal liver lesions. Intrinsically hyperattenuating hepatic lesions or pseudolesions are not uncommon at unenhanced CT. Hyperattenuating hepatic lesions can be divided into non-calcified and calcified. Causes of intrinsic hyperattenuation include hemorrhage, thrombosis, and calcifications. Focal liver lesions can show hyperattenuation on unenhanced CT in case of severe liver steatosis. Recognition of etiologies associated with hyperattenuation on unenhanced CT can help the radiologist in characterizing focal liver lesions and pseudolesions. In this paper, we describe the spectrum of intrinsically hyperattenuating focal liver lesions and pseudolesions at unenhanced CT.

Whole-Body Magnetic Resonance Imaging: Current Role in Patients with Lymphoma.

Imaging of lymphoma is based on the use of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) and/or contrast-enhanced CT, but concerns have been raised regarding radiation exposure related to imaging scans in patients with cancer, and its association with increased risk of secondary tumors in patients with lymphoma has been established. To date, lymphoproliferative disorders are among the most common indications to perform whole-body magnetic resonance imaging (MRI). Whole-body MRI is superior to contrast-enhanced CT for staging the disease, also being less dependent on histology if compared to 18F-FDG-PET/CT. As well, it does not require exposure to ionizing radiation and could be used for the surveillance of lymphoma. The current role of whole-body MRI in the diagnostic workup in lymphoma is examined in the present review along with the diagnostic performance in staging, response assessment and surveillance of different lymphoma subtypes.

SIRM-SIC appropriateness criteria for the use of Cardiac Computed Tomography. Part 1: Congenital heart diseases, primary prevention, risk assessment before surgery, suspected CAD in symptomatic patients, plaque and epicardial adipose tissue characterization, and functional assessment of stenosis.

In the past 20 years, Cardiac Computed Tomography (CCT) has become a pivotal technique for the noninvasive diagnostic work-up of coronary and cardiac diseases. Continuous technical and methodological improvements, combined with fast growing scientific evidence, have progressively expanded the clinical role of CCT. Recent large multicenter randomized clinical trials documented the high prognostic value of CCT and its capability to increase the cost-effectiveness of the management of patients with suspected CAD. In the meantime, CCT, initially perceived as a simple non-invasive technique for studying coronary anatomy, has transformed into a multiparametric "one-stop-shop" approach able to investigate the heart in a comprehensive way, including functional, structural and pathophysiological biomarkers. In this complex and revolutionary scenario, it is urgently needed to provide an updated guide for the appropriate use of CCT in different clinical settings. This manuscript, endorsed by the Italian Society of Medical and Interventional Radiology (SIRM) and by the Italian Society of Cardiology (SIC), represents the first of two consensus documents collecting the expert opinion of Radiologists and Cardiologists about current appropriate use of CCT.

ECG-gated multislice Computed Tomography angiography as a comprehensive non-invasive imaging tool in patient with aortic coarctation.

We describe a case of a 52 year-old-woman with aortic coarctation demonstrated by means of 40-slice MSCT angiography. Based on the information extracted from MSCT it was possible to display the anatomical configuration of the disease, the thoraco-abdominal collateral pathways. The best therapeutic approach was established on the basis of MSCT findings. MSCT is a reliable and comprehensive tool for the assessment of adult patients with aortic coarctation.

Assessment of EVAR Complications using CIRSE Complication Classification System in the UK Tertiary Referral Centre: A ∼6-Year Retrospective Analysis (2014-2019).

PURPOSE: To retrospectively analyse complications in endovascular aortic repair (EVAR) interventions and evaluate if the CIRSE (Cardiovascular and Interventional Radiological Society of Europe) complication classification system is appropriate as a standardized classification tool for EVAR patients. MATERIALS AND METHODS: Demographic, procedural and complication data in 719 consecutive patients undergoing EVAR at one institution from January 2014 to October 2019 were retrospectively reviewed. Data (imaging reports, procedural reports, nurse notes, discharge summary reports) were collected consulting the electronic patient record system (EPR) of the hospital and cleaned and stored in a Microsoft Excel database. All the procedures were analysed in consensus by two interventional radiology consultants and a resident radiologist and if an intra- , peri- or post-procedural complication occurred, a grade (1-6) was assigned using the CIRSE grading complication classification system. RESULTS: Twenty-five patients were excluded from the analysis because of invalid or incomplete data. The final population was made up of 694 patients (mean age 75,4 y.o., 616 male/78 female, min age 23 y.o., max age 97 y.o.). Complications emerged in 211 patients (30,4% of cases, 22 female/189 male). The number of patients with CIRSE grade I, II, III, IV, V and VI complications was 36 (17%), 17 (8%), 121 (57,3%), 15 (7,1%), 3 (1,4%), 19 (9%). Nineteen (2,6%) patients succumbed after EVAR. Thirty-four complications (16,1%) were related to vascular access. CONCLUSION: The CIRSE complication classification system represents a broadly applicable and feasible approach to evaluate the severity of complications in patients following EVAR. However, some deficit may be considered relevant and as starting standing-point for future improvements.

Imaging the COVID-19: a practical guide.

The Coronavirus Disease 2019 (COVID-19) represents the first medical catastrophe of the new millennium. Although imaging is not a screening test for COVID-19, it plays a crucial role in evaluation and follow-up of COVID-19 patients. In this paper, we will review typical and atypical imaging findings of COVID-19.

Coronary CT angiography: a guide to examination, interpretation, and clinical indications.

INTRODUCTION: The introduction of Cardiac Computed Tomography (CCT) has changed the paradigm in the field of diagnostic cardiovascular medicine. CCT is the primary tool in the assessment of suspected Coronary Artery Disease (CAD) and should be followed by functional assessment when needed to stratify disease and to plan potential interventional or surgical therapy. AREAS COVERED: We provided the current state of the knowledge on the main aspects of technique of examination, image interpretation and clinical indications. We have focused our attention on the basic routine applications and activities. EXPERT OPINION: The primary role of CCT in suspected CAD will progressively become the standard approach. In general, any situation in which anatomy of the heart and thoracic vessels/structures is mandatory must be approached using CT first, whenever possible. The quantity and quality of information that can be provided by CCT is big and the operators should learn how to deal with this information. On the other hand, CCT is only apparently a straightforward and simple examination. It is actually the most complex diagnostic procedure that can be performed on CT and requires highly skilled operators and state-of-art-technology.