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European Society of Radiology: Could you please give a detailed overview of when and for which diseases you use cardiac imaging?

Akira Kurata: For the general evaluation of cardiac structure and function, we usually combine symptoms, physical findings, history, and the results of an initial screening test (resting electrocardiography, and chest x-ray). It is recommended that cardiac imaging be considered for further evaluation in the following cases: (1) in patients with symptoms or conditions potentially related to cardiac aetiology including but not limited to chest symptoms, dyspnoea, palpitations, or an embolic event; or (2) prior test results or physical findings that raise concerns of cardiac disease or structural abnormality, including but not limited to the initial test, and cardiac biomarkers.

In particular, when regarding coronary artery disease (CAD), not only the pre-test probability (age, sex, symptom), but also coronary risk factors, and a positive or equivocal exercise electrocardiography test should be performed to determine the necessity of cardiac imaging. In the case of myocardial disease and heart failure, information from the personal and family history and systemic exploration can provide indications regarding the necessity for further evaluation using cardiac imaging.

For patients with congenital heart disease (CHD) or structural heart disease, it is important to know all the details, from global and regional three-dimensional (3D) anatomy to primary and comorbid cardiovascular deficits, including the therapies they have undergone. It is often valuable to integrate information on anatomy and haemodynamics.

ESR: Which modalities are usually used for what?

AK: Echocardiography (Echo) is the first-line modality in cardiac imaging, because of its non-invasiveness and easy accessibility. Echo allows global and regional assessment of anatomy, morphology, cardiac function, and haemodynamics (blood flow), as well as pre- and postoperative evaluation. The high spatial and temporal resolution enables us to assess cardiac functional parameters and the wall motion of the heart. Trans-mitral pulse-Doppler imaging for systolic and diastolic function, and colour-Doppler imaging for heart valve disease, can be routinely performed as a reference standard. In addition, echo is commonly used for CHD, while stress echo can be used for the assessment of myocardial ischaemia and viability in patients with CAD.

Cardiac computed tomography (CT) is one of the most recently developed diagnostic imaging modalities in cardiac imaging and has been used widely in clinical practice. It allows 3D volumetric imaging with high spatial resolution and can be used to visualise cardiac anatomy and morphology. The items of investigation include coronary arteries (calcium scoring, stenosis, and atherosclerotic plaque), non-coronary structures (cardiac chambers, myocardium, and cardiac valves), and surrounding structures. Recently, clinical applications of cardiac CT have been expanded to structural heart disease and CHD using low-dose protocols.

Cardiac magnetic resonance imaging (MR) can non-invasively assess the structure and function of the heart without radiation exposure. It uses multiple scan sequences as follows: cine-imaging (global and regional cardiac function), stress myocardial perfusion (myocardial ischaemia, for CAD), late gadolinium enhancement and T1 mapping (myocardial infarction and fibrosis, for CAD; cardiomyopathy; cardiac involvement of sarcoidosis or amyloidosis), T2 mapping (myocardial oedema, for acute myocardial infarction and myocarditis) and MR-angiography (for coronary artery and vascular diseases and CHD). By combining scan sequences, cardiac MR allows for comprehensive evaluations accounting for known or unknown cardiac diseases and is regarded as the reference standard in clinical practice due to its superiority in spatial and temporal resolution, and tissue characterisation ability.

Nuclear cardiology (NC) is a type of cardiac functional imaging that is based on single photon emission computed tomography (SPECT) and positron emission tomography (PET). By using radioactive tracers that label target molecules, it is possible to assess various parameters, such as myocardial perfusion, metabolism (fatty acid and glucose level), sympathetic nerve activity and inflammatory activity. Moreover, SPECT myocardial perfusion imaging has been established as a ‘gatekeeper’ for the management of CAD, and can be used for diagnosis of myocardial ischaemia and assessing viability, therapeutic decision-making, and prognosis. Further, [18F]-fluorodeoxyglucose PET is feasible for diagnostic purposes and for the assessment of therapeutic effects against inflammatory cardiac diseases, such as myocarditis and cardiac sarcoidosis.

ESR: What is the role of the radiologist within the ‘heart team’? How would you describe the cooperation between radiologists, cardiologists, and other physicians?

AK: Through cardiac imaging, radiologists can play a role in building strong cooperation among members of the ‘heart team’ (cardiologists, paediatricians, cardiovascular surgeons and radiologists). We radiologists provide information on cardiovascular anatomy and disease morphology that can be used for patient-tailored management from diagnosis to procedural planning, therapy, and assessment of prognosis. This cooperation is essential for treating patients with complex CAD requiring hybrid therapy with coronary artery bypass grafting and percutaneous coronary intervention, and for adolescent patients with CHD. Objective and standardised evaluations achieved through discussion among heart team members help us identify un-biased therapeutic strategies with better outcomes and enable us to assess new advanced diagnostic methods and therapeutic options.

In our hospital, we have a monthly joint conference of the heart team, including radiographers/radiological technologists, for clinical practice and research, where we can effectively discuss in-hospital collaborative research.

ESR: Radiographers/radiological technologists are also part of the team. When and how do you interact with them?

AK: Radiographers or radiological technologists are the experts who control cardiac imaging examinations, especially with regard to image quality, radiation dose management, and clinical workflow. We radiologists initially develop basic scan protocols together with them and often consult them on individual disease-specific or patient-tailored testing goals and protocols before examination.

Radiographers conduct not only cardiovascular CT but also other cardiac imaging tests, from data acquisition to image reconstruction, a series of procedures that are directly related to image quality and clinical outcomes. We provide them with image-based feedback in daily practice. We encourage them to attend in-hospital, local, and domestic conferences, and hands-on courses in cardiac imaging to update their knowledge. Professor Mochizuki, the Chairman of the Department of Radiology, constantly promotes this.

ESR: Please describe your regular working environment (hospital, private practice). Does cardiac imaging take up all, most, or only part of your regular work schedule? How many radiologists are dedicated to cardiac imaging in your team?

AK: I personally work for the Department of Radiology as a cardiac radiologist. I am engaged in cardiac and non-cardiac nuclear imaging, cardiovascular CT and secondary interpretation of cardiovascular CT during my regular work schedule. Five regular staff radiologists and four junior radiologists (concurrent with their PhD courses) are dedicated to cardiac imaging (CT, MR and nuclear imaging). I believe that the abundance of talented colleagues may be one of the strengths of the heart team.

In the affiliated hospital and private clinic, I perform image interpretation of cardiovascular CT and outpatient care, as a cardiologist.

ESR: Do you have direct contact with patients and if yes, what is the nature of that contact?

AK: I have direct contact with patients to some extent. Most of the contact occurs when monitoring daily examinations or clinical research protocols. After confirming the identity of the patient and the purposes and details of the examination with the radiology residents or doctors in charge, we try to gently communicate with patients, providing procedural or explanation and necessary clarifications.

ESR: If you had the means: what would you change in education, training and daily practice in cardiac imaging?

AK: I have close communication with residents and graduate students involved with cardiac imaging in daily practice – every evening – and clinical research – once every two weeks.

Cardiac CT is widely available in our affiliated hospitals. We have discussed the necessity of systematically updating the knowledge of cardiac CT not only for our graduate students but also for the radiology residents and radiological technologists.

I am currently involved with two cardiac CT courses. One is a regional lecture-based cardiac CT course (EHIME CT Hands-on) that is held once a year at our university hospital in collaboration with affiliated hospitals. We share basic knowledge; scan protocols; workflow, including image quality and radiation dosage; and standardised reporting guidelines. The other is a cardiac CT course (Sakurabashi Hands-on) that is endorsed by the Society of Cardiac Computed Tomography (SCCT) Japan regional committee educational working group, which is held four times a year in Osaka. This CT course has a six-year history and provides basic knowledge and systematic case reading, wet-lab simulation and/or 3D printing experience. These approaches aim to help the participants understand 3D cardiac imaging. I have also served as a lecturer and have come to understand that communication and sharing knowledge is extremely important.

ESR: What are the most recent advances in cardiac imaging and what significance do they have for improving healthcare?

AK: 3D echo has been rapidly developing, and real-time 3D volume echo of the heart, which can be acquired in just a single heartbeat using wide fully sampled matrix probes, has recently become available. This technique is very promising for the image-guided catheter interventional therapy required in the case of structural heart disease. The high sampling rate allows myocardial strain imaging, and the recently introduced image fusion of coronary CT angiography (CTA) and 3D echo myocardial strain imaging will aid in the assessment of CAD.

Considerable progress has been made in CT functional/physiological imaging for CAD. One approach is coronary CTA-derived fractional flow reserve (CT-FFR) analysis using computational flow dynamics, which was introduced in 2011 and has become a gamechanger in cardiac CT. Several CT vendors and research groups are also developing related algorithms and computational methods for use in clinical research. The other approach is stress CT perfusion imaging. Several single-centre studies and multicentre trials have shown that stress CT perfusion is not inferior to SPECT and cardiac MR for detecting myocardial ischaemia and haemodynamically significant coronary artery stenosis.

The compressed sensing technique is one of the most recent advances in cardiac MR. Conventional MR cine-imaging was relatively time-consuming, but compressed sensing, combining sparse data sampling and iterative reconstruction, allows for a drastic reduction in the acquisition time of a cardiac MR examination without compromising on accurate quantitative evaluation of cardiac function. This technique is expected to be applicable to other sequences for various types of evaluation in cardiac MR.

Since the introduction of image fusion techniques such as SPECT/CT or PET/CT, the ultrafast gamma camera system has become one of the most important advances in NC imaging. This multiple stationary semiconductor detector system can generate a 3D volumetric image of the heart that can be acquired simultaneously by all the detectors. The system can directly convert radiation to electric signals and provide high energy and spatial resolution, which allow significant reduction of the acquisition time (approximately 3–5 minutes for one scan). In addition to these advantages, this system is also promising for simultaneous acquisition of dual-isotope tracers, dynamic SPECT, radiation dose reduction, and so on.

ESR: In what ways has the specialty changed since you started? And where do you see the most important developments in the next ten years?

AK: In the last two decades, SPECT myocardial perfusion imaging has been already established as a non-invasive ‘gatekeeper’ in the management of CAD. With rapid technological advances in multidetector-row CT, cardiac CT has rapidly become available in clinical practice, as coronary CTA to assess coronary artery stenosis and atherosclerotic plaque. Due to numerous distinguished multicentre studies and individual daily practice, morphological assessment capability and clinical value of cardiac CT is well known in the fields of CAD, and congenital and structural heart disease.

Qualitative complimentary use – or image fusion of coronary CTA – and NC imaging both help in the assessment of CAD. However, quantification and functional imaging have been required for the patient or disease severity-tailored management that has been developed in recent years; for instance, myocardial strain imaging in echo, and tissue characterisation of the myocardium in cardiac MR, and stress CT perfusion and CT-FFR in cardiac CT.

In the next ten years, I imagine that not only quantification as mentioned above, but also the integration of image data and practical use of 3D cardiac imaging (3D printing, and virtual and augmented reality) will become more important.

ESR: Is artificial intelligence already having an impact on cardiac imaging and how do you see that developing in the future?

AK: I am not well versed in the subject of artificial intelligence (AI), but I expect AI to have a great impact on cardiac imaging and clinical cardiology. We learn the basics from the text and guidelines and manage clinical practice utilising various patient information, such as symptoms, laboratory and imaging data for diagnosis and therapeutic management of their cardiovascular disease. I imagine that AI can help us in all of these processes.

With regard to the large thin-slice volumetric data and various imaging parameters, AI can not only reduce diagnostic errors and bias but also quantitatively assess the images as data, using image recognition and registration, and play an important role in powerful and automated sustainable computerised digital processing for clinical practice and studies, such as machine-learning based CT-FFR computation.

When all of the image data are integrated with the non-imaged data such as a patient’s electronic medical records, laboratory data, and genetic data, AI can help us by providing more precise diagnoses and recommendations regarding therapeutic management using personalised medicine. Nevertheless, I believe that the significance of image quality as the input will be increasing in the AI era, even in cardiac imaging.

Dr. Akira Kurata is a cardiac radiologist and associate professor in the radiology department at Ehime Graduate School of Medicine, Toon, Ehime, in Japan. He trained in the university hospital and affiliated hospitals in cardiology and entered the Ehime Graduate School of Medicine in 2002. In collaborative research with cardiology and radiology, he reported the clinical feasibility of stress CT perfusion for the assessment of myocardial ischaemia using multidetector-row CT in 2005. He has been an active researcher in cardiac imaging, with a special interest in cardiac CT. Since he moved to the radiology department in 2008, under Professor Mochizuki’s supervision, he and his colleagues reported various clinical applications of stress CT perfusion (static and dynamic CT perfusion, dual-energy imaging, and late iodine enhancement). Ehime University Hospital became a leading centre in the CT perfusion community in Japan. Dr. Kurata worked at Erasmus University Medical Centre Rotterdam, the Netherlands, as a visiting professor in 2012–2014, and was involved in several research projects with Dr. Koen Nieman (Stanford University at present). Dr. Kurata’s interests in cardiac CT are diverse, including CT perfusion, CT-FFR, coronary artery territory mapping, and 3D printing. Dr. Kurata is an active speaker, having given more than 30 invited lectures and held more than 60 presentations at national and international meetings. He is the author of eleven book chapters. He has served as faculty for the Society of Cardiovascular Computed Tomography Japan international regional committee since 2012; as International Liaison for the Asian Society of Cardiovascular Imaging; as deputy secretary for the Japanese Society of Cardiovascular 3D-modeling for medical 3D printing since 2015; and as a collaborator in the working group of Guidelines for Chronic Coronary Artery Lesions of the Japanese Circulation Society since 2018 (JCS 2019).

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