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Cardiovascular techniques and technology
Chapter 73
Cardiovascular techniques and technology Almir Badnjevića,b, Lejla Gurbeta Pokvića,b, Lemana Spahića a
Department of Genetics and Bioengineering, Faculty of Engineering and Natural Sciences, International Burch University, Sarajevo, Bosnia and Herzegovina, bMedical Device Inspection Laboratory Verlab Ltd., Sarajevo, Bosnia and Herzegovina
Cardiovascular diseases (CVD) cause an average of 17.7 million deaths each year (44% of NCD fatalities) making it one of the most deserving topics for research on prevention. CVD are a group of disorders of the heart and blood vessels which is the most significant cause of death globally. Despite the critical fatality rate 90% CVD can be prevented by taking necessary precautions. CVD has both health and social impacts. Long term treatments for CVD demand significant financial resources. This could cause poverty in low- and middle-income families. Widespread of CVD may ultimately cause a burden on the economies of the country. In countries where the medical and healthcare sector is not advanced, diagnosis of CVD could be late, which would result in patient conditions irreversibly worsen or even death. This could reduce the life expectancy levels in the country. There are three types of prevention mechanisms to prevent and reduce the impacts of a disease. Primary prevention refers to the steps taken by an individual to prevent the onset of the disease. This is achieved by maintaining a healthy lifestyle choice such as diet and exercise. Secondary prevention focuses on reducing the impact of the disease by early diagnosis prior to any critical and permanent damage. This facilitates avoiding life-threatening situations and long-term impairments from a disease. Tertiary prevention is used once long-term effects set in, by helping the patients to manage pain, increase life expectancy, and increase the quality of life. The secondary prevention of CVD includes diagnosis and prevention. The most critical step of secondary prevention is early diagnosis which allows medical professionals to provide required care for patients and improve the quality of life. This requires identifying risk factors, criticality of risk factors, and how the variation of these factors relates to CVD. Upon early diagnosis, patients could be directed to required treatments affording a higher quality of life. The main attraction of secondary prevention over tertiary prevention comes from 484
two factors. Factor one is the cost where the cost of secondary prevention is far less relative to tertiary prevention and secondly, its effects on the quality of life of the patient. Tertiary prevention involves major procedures that could cause discomfort to the patient as well as disrupt the daily activities, whereas secondary prevention focuses on less intense treatments which include drugs and lifestyle changes. Therefore, creating awareness of secondary prevention could create positive impacts on individual lives as well as on a macroeconomic level. Advancement in technology has benefited mankind in many different ways. Application of technology in the field of medicine has enabled researchers and doctors to treat their patients more effectively and efficiently. With the recent advancements in artificial intelligence and data mining, medical personnel have the ability to extend their ability from treatment to early prediction of diseases. Early prediction allows patients to receive appropriate medical attention before the disease worsens leading to further complications such as myocardial infarctions (MIs), muscle death of limbs, or even death. Receiving treatment at an early stage not only increases the life expectancy of patients but also improves the quality of life. This section will focus on different technological techniques used for prediction of CVD and their effectiveness in a more technological perspective. Data mining refers to the computational process analyzing large data sets and discovering patterns. In the context of medicine, data mining is processing large volumes of datasets created by medical professionals in order to uncover patterns which will aid in making patient-related decisions. This process is used mainly for two tasks, namely, descriptive and predictive tasks. Predictive tasks which are more applicable for disease prediction include uncovering hidden information and then extending these findings into the future in order to make predictions of future events using techniques such as artificial neural networks (ANNs) and Clinical Engineering Handbook. https://doi.org/10.1016/B978-0-12-813467-2.00074-2 Copyright © 2020 Elsevier Inc. All rights reserved.
Cardiovascular techniques and technology Chapter | 73 485
machine learning. Some common techniques of predictive analysis include regression and classification. Associative classification is a process which aims to identify relationships between variables. This allows researchers to create rules to interpret relationships between variables, which can solve classification problem uncertainty. Classifiers generate a wide range of rules using different approaches such as decision tree and Naive Bayes. Later a small high-quality subset of rules is selected using pruning techniques. Akhil Jabbar et al. have used associative classification and genetic algorithms to implement a system to predict heart diseases. In order to improve the accuracy of the classifier, they have incorporated informative attribute entered rule generation and hypothesis testing Z-statistics, which has resulted in an accuracy rate of 89% for predicting heart diseases (Akhil Jabbar et al., 2012). Prediction using classification analysis and regression trees. A research has been conducted to predict heart diseases by classifying phonocardiograms (a record of sounds and murmurs made by the heart) using regression trees and classification analysis. This aims to identify pathological murmurs in order to predict the onset of the disease process by involving three steps as follows. (1) Extracting and processing phonocardiogram signals in order to isolate heart sounds by removing noise. (2) Extracting features from the signals which are more critical in the classification process. (3) Generating a decision tree by splitting intermediate nodes into two child nodes with the objective of increasing the homogeneity of terminal nodes (Amiri and Armano, 2013). Disease prediction using Naive Bayes and Laplace smoothing. Another research associated with data mining where the researchers implemented a system to predict heart diseases using the Naive Bayes algorithm, which is used to create models that have predictive capabilities which have high dimensional inputs. This research focuses on 13 inputs in order to predict CVD: age, gender, chest pain type, fasting blood sugar, electrocardiogram (ECG), exercise-induced angina, slope, CA, thallium test, blood pressure, old peak, maximum heart rate achieved, and serum cholesterol. However, they have also implemented a mechanism to use six of the above inputs in order to arrive at predictions. The accuracy rates of two mechanisms are significantly different where six inputs generated an accuracy rate of 62% while 13 inputs generated 86% accuracy (Vincy Cherian, 2017). Heart disease prediction system (HDPS). A research conducted in Taiwan has produced a mechanism using an ANN for classification and 14 attributes as follows: gender, chest pain type, resting blood pressure, serum cholesterol, fasting blood sugar, ECG, maximum heart rate achieved, exercise-induced angina, old peak, slope, number of major blood vessels colored by fluoroscopy, and thal. The proposed network is a three-layer model with an input layer, hidden layer, and output layer. Each layer consists of 13, 6,
and 2 neurons, respectively. Each attribute is assigned with random weights at the beginning and is later revised during the training process in order to match the testing data set. This research has yielded an 80% accuracy rate in predicting heart diseases (DeFilippis, 2015). The past several decades have seen rapid and extensive changes in the practice of cardiology, especially in the innovation and utilization practices of imaging, interventional, and electrophysiology procedures. Enhanced radionuclide imaging techniques, the evolution of echocardiography, development of cardiac magnetic resonance (MR), and coronary computed tomography (CT) angiography techniques, as a well as drug-eluting stents and cardiovascular implantable electronic devices have revolutionized how patients are diagnosed and treated. Although these developments have resulted in direct patient benefits including improved survival and enhanced quality of life, there has been an accompanying increase in resource utilization and healthcare costs. Although declines in utilization of many cardiovascular procedures have been observed as of late, during the years preceding 2005, the growth rates were at times substantial as these technologies were adopted. The perceived high rate of growth of expenditures related to cardiovascular procedures has precipitated payers to initiate utilization constraints to markedly reduce spending and reimbursement. Various payer initiatives have created an onerous burden leading to costly administrative requirements, including physician profiling and prior authorization. These general programs are also, in part, driven by marked geographic variability in utilization, which underscores the need for further guidance regarding optimal patient selection for procedures. Professional efforts to better define quality have identified the importance of matching procedures and patients. In response to the imperative for improving the utilization of cardiovascular procedures in an efficient and contemporary fashion, the American College of Cardiology Foundation (ACCF), along with imaging subspecialty societies and other organizations, developed the first set of Appropriate Use Criteria (AUC) in 2005, focusing on indications for radionuclide imaging. A concurrent publication defined in some detail the methods involved in the construction of these criteria. During the ensuing 7 years, there have been numerous other AUC publications (Fig. 1) including revisions to several of the original criteria—that reflect the expansion of the AUC concept and advances within the specific disciplines, as well as met. The past several decades have seen rapid and extensive changes in the practice of cardiology, especially in the innovation and utilization practices of imaging, interventional, and electrophysiology procedures. Enhanced radionuclide imaging techniques, evolution of echocardiography, development of cardiac MR, and coronary CT angiography techniques, as a well as drugeluting stents and cardiovascular implantable electronic
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FIG. 1 Development of cardiovascular techniques.
d evices, have revolutionized how patients are diagnosed and treated. Although these developments have resulted in direct patient benefits including improved survival and enhanced quality of life, there has been an accompanying increase in resource utilization and healthcare costs. Although declines in utilization of many cardiovascular procedures have been observed as of late, during the years preceding 2005, the growth rates were at times substantial as these technologies were adopted. The perceived high rate of growth of expenditures related to cardiovascular procedures has precipitated payers to initiate utilization constraints to markedly reduce spending and reimbursement. Various payer initiatives have created an onerous burden leading to costly administrative requirements, including physician profiling and prior authorization. These general programs are also, in part, driven by marked geographic variability in utilization, which underscores the need for further guidance regarding optimal patient selection for procedures. Professional efforts to better define quality have identified the importance of matching procedures and patients.
Clinical indications As clinical indications or scenarios are developed, consistency, clarity, and utility are emphasized to support a foundation for meaningful evaluation. Whenever possible, indications are grouped under common headings. This
structured approach, when applied to cardiac imaging, commonly includes the construction of tables for patient diagnosis and risk assessment, current symptomatology, prior testing, previous revascularization, evaluation for a change in clinical status, and consideration of special clinical circumstances. At times, additional groups of scenarios may be included, such as the use of routine surveillance testing either early or late after a procedure or test. The AUC increasingly attempt to address such scenarios, recognizing that the clinical trial evidence base is often quite limited and, given the cost, may never be achievable in the current healthcare environment. AUC seeks to establish widespread consensus around the timeframes during which such testing is unlikely to yield important clinical information. Although initially it was felt that the AUC should not attempt to be all-inclusive but rather focus on common, real-world situations; external feedback regarding the early AUC documents highlighted gaps in indications or unclear clinical scenarios. The AUC Task Force responded to this feedback, by significant expansion and revision of the indications in subsequent documents. The ensuing applications of revised AUC are reflective of this expansion, noting that the added indications have markedly improved the utility of the documents. When possible, AUC now provides a hierarchy of indications to guide use of the AUC in a systematic fashion, tailored for each modality, and assist in applying a
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p articular clinical situation to one of the indications. This approach also greatly facilitates AUC evaluation and implementation, as it permits an ordered and reproducible way to apply AUC. Nuclear cardiology has an integral role in the noninvasive detection of coronary artery disease (CAD), assessment of myocardial viability, and stratification of risk. It imparts improved sensitivity and specificity over standard exercise stress testing. For example, the average sensitivity and specificity of single-photon emission computed tomography (SPECT) with technetium 99m have been reported to be 90% and 74%, respectively—though the exact performance characteristics depend on the prevalence of the disease in the population being studied. Nuclear imaging can provide functional and prognostic information that is quantifiable, reproducible, and readily obtainable in diverse patient populations. Diagnosis of CAD. Nuclear perfusion studies are performed to establish noninvasively the diagnosis of CAD in the following situations: history of stable angina; chest pain of unclear causation; unstable angina after stabilization; abnormal exercise test result without symptoms; risk stratification in the setting of multiple factors thought to confer a high likelihood of subclinical CAD; scheduled standard exercise testing in the setting of an abnormal e lectrocardiogram [ECG; due to left ventricular (LV) hypertrophy with associated repolarization changes, ST depression >1 mm, manifest preexcitation pattern on ECG, digoxin use, left bundle branch block, or ventricular-paced rhythm]; and previously nondiagnostic graded exercise test. (B) Assessment of the physiologic importance of known CAD. Perfusion imaging can assist in the determination of the functional significance of coronary stenosis that is in the “moderate-to-severe” (50%–70%) range on angiographic evaluation. It can, therefore, be useful to evaluate a specific coronary lesion before proceeding to percutaneous intervention. This remains an accepted indication for nuclear perfusion imaging, although its use for this purpose is being supplanted by other modalities that can assess the functional significance of coronary lesions at the time of angiography (e.g., fractional flow reserve). (C) Assessment after therapeutic intervention. In the past, perfusion imaging was often performed as a routine follow-up procedure after percutaneous intervention and coronary artery bypass grafting (CABG). More recent recommendations on appropriate use of this modality suggest that routine screening in asymptomatic patients who have been successfully revascularized by either method is not necessarily warranted, except in the evaluation of patients more than 5 years after CABG. On the other hand, radionuclide perfusion imaging is certainly appropriate in patients who have undergone prior revascularization and are presenting with recurrent symptoms consistent with coronary ischemia. (D) Risk stratification. With nuclear imaging, it is possible to stratify risk among patients with stable angina or
unstable angina, those who have had MI, and those about to undergo noncardiac operations. The most basic tool in nuclear imaging is the gamma or scintillation camera, which is used to detect gamma rays (i.e., X-ray photons) produced by the chosen radionuclide. Three types of gamma camera exist. (A) A single-crystal camera consists of one large sodium iodide crystal. Other essential elements of this camera include the collimator, a lead device that screens out the background or scattered photons, and the photomultiplier, an electronic processor that translates photon interactions with the crystal into electric energy. Electric signals from the photomultiplier are processed by the pulse height analyzer before reaching a final form. Only signals in a specified energy range are incorporated into the interpreted images. The range recognized by the pulse height analyzer is adjustable and is established on the basis of the radiopharmaceutical used. Digitalization of the single-crystal camera has greatly enhanced its performance. (B) A multicrystal camera works with an array of crystals with increased count detection capability. Because of the availability of an individual crystal to detect scintillation at any given time, this type of camera can be used to detect many more counts than can a single-crystal camera. (C) In the case of positron emission tomography (PET) scanning, a positron camera is a gamma camera used to detect the photon products of positron annihilation. Interaction between a positron and an electron causes annihilation, with the generation of two high-energy photons (511 keV) that travel in opposite directions. An array of multiple concentric rings of crystals constitute a positron camera. Each crystal is linked optically to multiple photomultipliers. The crystals are oriented in diametric pairs in such a way that each pair of crystals must be struck simultaneously by annihilation photons to record activity. Background interference and stray photon energy are automatically accounted for, and artifact is limited. Most positron cameras contain bismuth germanate for annihilation photon detection. Stress echocardiography (SE) is an effective method of evaluating for myocardial ischemia, based on the detection of stress-induced regional wall motion abnormalities (WMAs). Stressors include exercise, pharmacologic agents, and pacing. SE is used to screen for CAD, and it can help identify the coronary vessels involved. The accuracy of SE in the detection of significant coronary artery stenosis is 80%–90%, which is superior to that of exercise electrocardiographic testing and comparable to that of nuclear stress imaging. In patients with LV dysfunction and documented CAD, SE can differentiate viable myocardium from scarred myocardium, which may help predict whether LV function will improve after revascularization. As a diagnostic test for CAD, SE is safe and relatively inexpensive and can be rapidly performed by experienced hands. However, the interpretation of SE images remains primarily subjective and requires a considerable learning curve. SE can also
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be used to assess the severity of valvular disease, hypertrophic cardiomyopathy, and exercise-induced pulmonary hypertension. In addition, it provides important prognostic information after MI and prior to noncardiac surgery. All SE studies are conducted with exercise electrocardiographic testing and standard hemodynamic monitoring equipment. A SE software package on the echocardiographic machine is necessary to acquire digital images and to allow sideby-side comparison of prestress images with peak stress or postpeak stress images. Resuscitation equipment and a defibrillator should be readily available. Patients with LV dysfunction secondary to CAD have significant morbidity and mortality. Given the prognostic implications of poor ventricular function, it is imperative to identify any reversible myocardial dysfunction that may improve with revascularization. Assessment of myocardial viability is indicated in patients with CAD and resting LV dysfunction who are eligible for revascularization. Coronary angiograms provide information about anatomy and feasibility of revascularization but do not predict recovery of function. Resting echocardiography provides information regarding overall LV function and segmental WMAs but does not address recovery of function with revascularization techniques. Single-photon nuclear imaging techniques (single-photon emission computed tomography, SPECT), PET with a metabolic agent, dobutamine echocardiography, contrast echocardiography, and, more recently, delayed-enhancement magnetic resonance imaging (MRI) have been identified as techniques that can distinguish viable myocardium from nonviable myocardium. Each technique exploits a separate property of dysfunctional myocardium to determine the potential for recovery of function after revascularization. The test that is used often depends on the strengths and preference of each medical center, although an approach based on the individual patient would be preferable. (A) Singlephoton emission computed tomography. SPECT is the most common technique used in the United States to identify viable myocardium. This technique has been successful because thallium 201 and technetium 99m radiopharmaceuticals act as perfusion agents that are only taken up by viable tissue. The long half-lives of these agents allow for regional distribution, which makes them feasible to use in medical centers without a generator or cyclotron. In addition, stress SPECT protocols (exercise or pharmacologic) are frequently used to assess for ischemia, which makes this technique cost-effective in a busy clinical center. Routine studies also include gated imaging analyses that provide further information regarding LV function and wall motion assessment, which are important in the evaluation of viability. PET in conjunction with a metabolic agent, usually FDG, has been considered the gold standard for assessment of myocardial viability. PET uses positron-emitting isotopes capable of releasing two high-energy (511 keV) photons at
an angle of 180° from each other. The PET camera can detect these higher energy rays through coincidence counting. As a result, PET provides higher temporal and spatial resolution than SPECT, which translates into a higher quality image. Dobutamine echocardiography has proven to be a reliable predictor of recovery of function after myocardial revascularization. Cardiac MRI. Delayed-enhancement MRI using gadolinium-based agents given intravenously (0.2 mmol/kg) has been shown to reliably distinguish infarcted from viable myocardium. Unlike SPECT-based techniques, MRI poses no risk of ionizing radiation exposure. Cardiovascular magnetic resonance imaging (CMRI) has undergone rapid developments over the last two decades and is now an important imaging technique of the heart and great vessels. Advantages of CMRI include its large field of view, high spatial and temporal resolution, and ability to do tissue characterization. In contrast to nuclear imaging and cardiac computed tomography (CT), MRI does not involve exposure to ionizing radiation. Applications of CMRI include acquisition of anatomic-quality still and cine images of the heart and great vessels in multiple planes, precise measurement of cardiac chamber volume and function, assessment of myocardial perfusion and fibrosis, quantification of blood velocity and flow, and noninvasive magnetic resonance angiography (MRA). As CMRI is not a “pushbutton” technique, clear communication between the ordering physician and the imaging staff is important, indicating the reason for the CMRI examination so that adequate pulse sequences and imaging planes are obtained aiming to answer the desired clinical question. Spin echo. Spin-echo sequences are characterized by a refocusing RF pulse after delivery of the initial excitation pulse. Rapidly flowing blood appears dark, hence they are also known as “black-blood” sequences. Spin-echo sequences provide still images, which are typically used for anatomic delineation of the heart and great vessels owing to their excellent tissue contrast and high signal-to-noise ratio (SNR). They are relatively insensitive to magnetic field inhomogeneities and artifacts related to ferromagnetic objects such as sternal wires and prosthetic heart valves. Turbo spin echo is a newer technique that provides faster acquisition times than standard spin-echo does. The main disadvantage of spin-echo sequences is the relatively long time it takes to acquire an image, making them more susceptible to motion artifacts and unsuitable for cine imaging. Gradient echo. Gradient-echo sequences are characterized by the use of refocusing gradients after the delivery of the initial excitation pulse. Rapidly flowing blood appears bright, hence they are also known as “bright blood” sequences. Gradient echo is a fast imaging technique that is relatively insensitive to motion artifacts, making it ideal
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for cine imaging. However, it has less tissue contrast and increased susceptibility to magnetic field inhomogeneities and ferromagnetic-related artifacts than spin-echo imaging but less than balanced steady-state free precession (B-SSFP). A variety of gradient-echo sequences are widely used in CMRI for cine imaging, myocardial perfusion and scar assessment, coronary imaging, and MRA. Cine imaging. The most widely used pulse sequence for cine imaging is a gradient-echo sequence called B-SSFP, which is characterized by high SNR, high image contrast between blood and myocardium, and low sensitivity to motion artifact. However, B-SSFP is relatively insensitive to blood flow and, therefore, can be suboptimal for imaging of valve dysfunction or intracardiac shunts, which can usually be better illustrated using other gradient-echo pulse sequences, such as echo-planar imaging or phase velocity mapping. In addition B-SSFP is also more susceptible to magnetic field inhomogeneities which can be problematic in patients with mechanical valves or other cardiac implants. Myocardial tagging. RF pulses can be applied before the excitation pulse to generate dark saturation lines or grids on cine images, which are then tagged to the myocardium and further used to assess myocardial deformation. The tags can be used to help qualitatively assess myocardial motion and pericardial tethering or to quantitatively measure myocardial strain. Perfusion imaging. Very fast gradient-echo sequences are used for dynamic imaging of LV myocardial perfusion during the first pass of a gadolinium contrast agent during rest and stress states. Fast gradient-echo techniques are commonly used, such as a fast low-angle shot or B-SSFP with a prepulse to null or darken the myocardium. Normally perfused myocardium shows an increase in signal intensity due to gadolinium contrast, whereas abnormally perfused areas remain dark or hypoperfused. Delayed imaging. Delayed hyperenhancement imaging for myocardial scar or fibrosis is performed 10–30 min after injection of gadolinium contrast using gradient-echo sequences with an inversion recovery prepulse to a null signal from the myocardium. Areas of myocardial scar or fibrosis have a larger extracellular space with a greater accumulation and slower washout of gadolinium and, therefore, appear bright compared with dark, normal myocardium on delayed imaging. Phase-contrast velocity mapping. The phase difference in the spin of protons in moving blood compared with nonmoving protons within a magnetic gradient is called the “spin phase shift” and is proportional to the velocity of the moving protons. A phase-encoded image is constructed, with the gray level of each pixel coded for velocity. Phasecontrast velocity mapping could be considered analogous to pulse wave Doppler echocardiography. It can be used to measure blood velocity and hence quantify cardiac output, shunts, and valve dysfunction. There are, however,
limitations, given that the accuracy of this method is highly dependent on factors such as flow pattern, flow velocity, size, and tortuosity of the vessel. Flow-related signal loss can be a result of the loss of phase coherence that can occur in cases of significant flow acceleration and even in higher orders of motion present in complex flow patterns. Magnetic resonance angiography. MRA of the great vessels typically involves a 3D fast gradient-echo acquisition after injection of gadolinium contrast. The image resolution is typically 2 × 2 × 3 mm, making MRA an excellent option for imaging of large to intermediate size arteries, but less optimal for imaging of smaller vessels. Parallel imaging. A number of parallel imaging techniques make use of multiple receiving body coils to acquire extra data after each excitation pulse. This helps to decrease the imaging time and improve temporal resolution, but at the small relative cost of a decrease in the SNR. Cardiovascular computed tomography (CT) has continued to rapidly evolve over the past decade, gaining new and expanded indications for noninvasive assessment of the heart, great vessels, and peripheral vasculature. Technological improvements, including increasing numbers of detectors, improved temporal and spatial resolution, and advanced postprocessing, have broadened the clinical utility of this imaging modality. Advanced multidetector computed tomography (MDCT) scanners and new scanning protocols have significantly reduced radiation and contrast dosages. Numerous considerations are involved in the proper selection of cardiovascular CT protocols, and skilled operators are required to plan and interpret these examinations. MDCT involves using an X-ray tube mounted opposite multiple detector rows on a gantry, which is then rotated around the patient at a rapid rate (220–400 ms/rotation). The patient is moved at either a fixed or variable speed, or pitch, through the scanner. An increasing number of detectors allows for an increased z-axis (cranial-caudal) coverage, permitting faster scans with improved image quality due to less cardiac and respiratory motion artifact. Temporal resolution is improved by faster gantry rotation, the use of two X-ray tubes and detector arrays mounted at 90° angles to each other (dual-source MDCT), and special reconstruction techniques. Dual-source/dual-energy scanners provide substantial improvements by utilizing dual-source MDCT technology as well as dual-energy sources to improve temporal resolution and decrease scatter. The fastest scanners provide a temporal resolution of 83–105 ms. Spatial resolution is largely determined by detector architecture (typically 0.4 mm isotropic resolution), although thicker slices (1–5 mm) can be acquired to reduce radiation dose according to the study indication. MDCT can be used for both cardiac and noncardiac studies, and it is now the most widely used type of CT hardware for cardiac imaging.
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Electron beam computed tomography (EBCT), although rarely used today, was specifically developed for cardiac imaging. It involves the use of a rapidly oscillating electron beam reflected onto a stationary tungsten target. Because there is no mechanical motion within the gantry, EBCT is capable of very high temporal resolution (50–100 ms). EBCT was used primarily for the quantitative detection of coronary artery calcification (CAC).
References Akhil Jabbar, M., Deekshatulu, B.L., Chandra, P., 2012. Heart disease prediction system using associative Classification and genetic algorithm. In: Proceedings of the International Conference on Emerging Trends in Electrical, Electronics and Communication Technologies-ICECIT. Springer. Amiri, A.M., Armano, G., 2013. Early diagnosis of heart disease using classification and regression trees. In: Proceedings of the 2013 International Joint Conference on Neural Networks, IJCNN 2013, USA. DeFilippis, A.P., 2015. Analysis of calibration and discrimination among multiple cardiovascular risk scores in a modern multiethnic cohort. Ann. Intern. Med. 162 (4), 266–275. https://doi.org/10.7326/M14-1281. Vincy Cherian, B.M., 2017. Heart disease prediction using Naive Bayes algorithm and Laplace smoothing technique. Int. J. Comput. Sci. Trends Technol. 5, 68–73.
Further reading Alić, B., Gurbeta, L., Osmanovic, A., Badnjević, A., 2017. Machine learning techniques for classification of diabetes and cardiovascular diseases. In: 2017 6th Mediterranean Conference on Embedded Computing (MECO), Bar, Montenegro, pp. 1–4. https://doi.org/10.1109/ MECO.2017.7977152. Badnjevic-Cengic, A., Kovacevic, P., Dragic, S., Momcicevic, D., Badnjevic, A., Gurbeta, L., Hasanefendic, B., 2015. Serum nitric oxide levels in patients with acute myocardial infarction with ST elevation (STEMI). Respiron J. 5 (1–2), 6–8. Griffin, B.P., Ovid Technologies, I., Callahan, T.D., Menon, V., Wu, W.M., Cauthen, C.A., Dunn, J.M., 2013. Manual of Cardiovascular Medicine, fourth ed. LWW, Philadelphia. Hendel, R.C., Patel, M.R., Allen, J.M., Min, J.K., Shaw, L.J., Wolk, M.J., et al., 2013. Appropriate use of cardiovascular technology: 2013 ACCF appropriate use criteria methodology update: a report of the American College of Cardiology Foundation appropriate use criteria task force. J. Am. Coll. Cardiol. 61 (12), 1305–1317. Karunathilake, S.P., Ganegoda, G.U., 2018. Secondary prevention of cardiovascular diseases and application of technology for early diagnosis. Biomed. Res. Int. 2018, 1–9. Magjarević, R., Badnjević, A., 2018. Inspection and testing of electrocardiographs (ECG) devices. In: Badnjević, A., Cifrek, M., Magjarević, R., Džemić, Z. (Eds.), Inspection of Medical Devices. Series in Biomedical Engineering, Springer, Singapore.
Cardiovascular techniques and technology Almir Badnjevića,b, Lejla Gurbeta Pokvića,b, Lemana Spahića a
Department of Genetics and Bioengineering, Faculty of Engineering and Natural Sciences, International Burch University, Sarajevo, Bosnia and Herzegovina, bMedical Device Inspection Laboratory Verlab Ltd., Sarajevo, Bosnia and Herzegovina
Cardiovascular diseases (CVD) cause an average of 17.7 million deaths each year (44% of NCD fatalities) making it one of the most deserving topics for research on prevention. CVD are a group of disorders of the heart and blood vessels which is the most significant cause of death globally. Despite the critical fatality rate 90% CVD can be prevented by taking necessary precautions. CVD has both health and social impacts. Long term treatments for CVD demand significant financial resources. This could cause poverty in low- and middle-income families. Widespread of CVD may ultimately cause a burden on the economies of the country. In countries where the medical and healthcare sector is not advanced, diagnosis of CVD could be late, which would result in patient conditions irreversibly worsen or even death. This could reduce the life expectancy levels in the country. There are three types of prevention mechanisms to prevent and reduce the impacts of a disease. Primary prevention refers to the steps taken by an individual to prevent the onset of the disease. This is achieved by maintaining a healthy lifestyle choice such as diet and exercise. Secondary prevention focuses on reducing the impact of the disease by early diagnosis prior to any critical and permanent damage. This facilitates avoiding life-threatening situations and long-term impairments from a disease. Tertiary prevention is used once long-term effects set in, by helping the patients to manage pain, increase life expectancy, and increase the quality of life. The secondary prevention of CVD includes diagnosis and prevention. The most critical step of secondary prevention is early diagnosis which allows medical professionals to provide required care for patients and improve the quality of life. This requires identifying risk factors, criticality of risk factors, and how the variation of these factors relates to CVD. Upon early diagnosis, patients could be directed to required treatments affording a higher quality of life. The main attraction of secondary prevention over tertiary prevention comes from 484
two factors. Factor one is the cost where the cost of secondary prevention is far less relative to tertiary prevention and secondly, its effects on the quality of life of the patient. Tertiary prevention involves major procedures that could cause discomfort to the patient as well as disrupt the daily activities, whereas secondary prevention focuses on less intense treatments which include drugs and lifestyle changes. Therefore, creating awareness of secondary prevention could create positive impacts on individual lives as well as on a macroeconomic level. Advancement in technology has benefited mankind in many different ways. Application of technology in the field of medicine has enabled researchers and doctors to treat their patients more effectively and efficiently. With the recent advancements in artificial intelligence and data mining, medical personnel have the ability to extend their ability from treatment to early prediction of diseases. Early prediction allows patients to receive appropriate medical attention before the disease worsens leading to further complications such as myocardial infarctions (MIs), muscle death of limbs, or even death. Receiving treatment at an early stage not only increases the life expectancy of patients but also improves the quality of life. This section will focus on different technological techniques used for prediction of CVD and their effectiveness in a more technological perspective. Data mining refers to the computational process analyzing large data sets and discovering patterns. In the context of medicine, data mining is processing large volumes of datasets created by medical professionals in order to uncover patterns which will aid in making patient-related decisions. This process is used mainly for two tasks, namely, descriptive and predictive tasks. Predictive tasks which are more applicable for disease prediction include uncovering hidden information and then extending these findings into the future in order to make predictions of future events using techniques such as artificial neural networks (ANNs) and Clinical Engineering Handbook. https://doi.org/10.1016/B978-0-12-813467-2.00074-2 Copyright © 2020 Elsevier Inc. All rights reserved.
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machine learning. Some common techniques of predictive analysis include regression and classification. Associative classification is a process which aims to identify relationships between variables. This allows researchers to create rules to interpret relationships between variables, which can solve classification problem uncertainty. Classifiers generate a wide range of rules using different approaches such as decision tree and Naive Bayes. Later a small high-quality subset of rules is selected using pruning techniques. Akhil Jabbar et al. have used associative classification and genetic algorithms to implement a system to predict heart diseases. In order to improve the accuracy of the classifier, they have incorporated informative attribute entered rule generation and hypothesis testing Z-statistics, which has resulted in an accuracy rate of 89% for predicting heart diseases (Akhil Jabbar et al., 2012). Prediction using classification analysis and regression trees. A research has been conducted to predict heart diseases by classifying phonocardiograms (a record of sounds and murmurs made by the heart) using regression trees and classification analysis. This aims to identify pathological murmurs in order to predict the onset of the disease process by involving three steps as follows. (1) Extracting and processing phonocardiogram signals in order to isolate heart sounds by removing noise. (2) Extracting features from the signals which are more critical in the classification process. (3) Generating a decision tree by splitting intermediate nodes into two child nodes with the objective of increasing the homogeneity of terminal nodes (Amiri and Armano, 2013). Disease prediction using Naive Bayes and Laplace smoothing. Another research associated with data mining where the researchers implemented a system to predict heart diseases using the Naive Bayes algorithm, which is used to create models that have predictive capabilities which have high dimensional inputs. This research focuses on 13 inputs in order to predict CVD: age, gender, chest pain type, fasting blood sugar, electrocardiogram (ECG), exercise-induced angina, slope, CA, thallium test, blood pressure, old peak, maximum heart rate achieved, and serum cholesterol. However, they have also implemented a mechanism to use six of the above inputs in order to arrive at predictions. The accuracy rates of two mechanisms are significantly different where six inputs generated an accuracy rate of 62% while 13 inputs generated 86% accuracy (Vincy Cherian, 2017). Heart disease prediction system (HDPS). A research conducted in Taiwan has produced a mechanism using an ANN for classification and 14 attributes as follows: gender, chest pain type, resting blood pressure, serum cholesterol, fasting blood sugar, ECG, maximum heart rate achieved, exercise-induced angina, old peak, slope, number of major blood vessels colored by fluoroscopy, and thal. The proposed network is a three-layer model with an input layer, hidden layer, and output layer. Each layer consists of 13, 6,
and 2 neurons, respectively. Each attribute is assigned with random weights at the beginning and is later revised during the training process in order to match the testing data set. This research has yielded an 80% accuracy rate in predicting heart diseases (DeFilippis, 2015). The past several decades have seen rapid and extensive changes in the practice of cardiology, especially in the innovation and utilization practices of imaging, interventional, and electrophysiology procedures. Enhanced radionuclide imaging techniques, the evolution of echocardiography, development of cardiac magnetic resonance (MR), and coronary computed tomography (CT) angiography techniques, as a well as drug-eluting stents and cardiovascular implantable electronic devices have revolutionized how patients are diagnosed and treated. Although these developments have resulted in direct patient benefits including improved survival and enhanced quality of life, there has been an accompanying increase in resource utilization and healthcare costs. Although declines in utilization of many cardiovascular procedures have been observed as of late, during the years preceding 2005, the growth rates were at times substantial as these technologies were adopted. The perceived high rate of growth of expenditures related to cardiovascular procedures has precipitated payers to initiate utilization constraints to markedly reduce spending and reimbursement. Various payer initiatives have created an onerous burden leading to costly administrative requirements, including physician profiling and prior authorization. These general programs are also, in part, driven by marked geographic variability in utilization, which underscores the need for further guidance regarding optimal patient selection for procedures. Professional efforts to better define quality have identified the importance of matching procedures and patients. In response to the imperative for improving the utilization of cardiovascular procedures in an efficient and contemporary fashion, the American College of Cardiology Foundation (ACCF), along with imaging subspecialty societies and other organizations, developed the first set of Appropriate Use Criteria (AUC) in 2005, focusing on indications for radionuclide imaging. A concurrent publication defined in some detail the methods involved in the construction of these criteria. During the ensuing 7 years, there have been numerous other AUC publications (Fig. 1) including revisions to several of the original criteria—that reflect the expansion of the AUC concept and advances within the specific disciplines, as well as met. The past several decades have seen rapid and extensive changes in the practice of cardiology, especially in the innovation and utilization practices of imaging, interventional, and electrophysiology procedures. Enhanced radionuclide imaging techniques, evolution of echocardiography, development of cardiac MR, and coronary CT angiography techniques, as a well as drugeluting stents and cardiovascular implantable electronic
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FIG. 1 Development of cardiovascular techniques.
d evices, have revolutionized how patients are diagnosed and treated. Although these developments have resulted in direct patient benefits including improved survival and enhanced quality of life, there has been an accompanying increase in resource utilization and healthcare costs. Although declines in utilization of many cardiovascular procedures have been observed as of late, during the years preceding 2005, the growth rates were at times substantial as these technologies were adopted. The perceived high rate of growth of expenditures related to cardiovascular procedures has precipitated payers to initiate utilization constraints to markedly reduce spending and reimbursement. Various payer initiatives have created an onerous burden leading to costly administrative requirements, including physician profiling and prior authorization. These general programs are also, in part, driven by marked geographic variability in utilization, which underscores the need for further guidance regarding optimal patient selection for procedures. Professional efforts to better define quality have identified the importance of matching procedures and patients.
Clinical indications As clinical indications or scenarios are developed, consistency, clarity, and utility are emphasized to support a foundation for meaningful evaluation. Whenever possible, indications are grouped under common headings. This
structured approach, when applied to cardiac imaging, commonly includes the construction of tables for patient diagnosis and risk assessment, current symptomatology, prior testing, previous revascularization, evaluation for a change in clinical status, and consideration of special clinical circumstances. At times, additional groups of scenarios may be included, such as the use of routine surveillance testing either early or late after a procedure or test. The AUC increasingly attempt to address such scenarios, recognizing that the clinical trial evidence base is often quite limited and, given the cost, may never be achievable in the current healthcare environment. AUC seeks to establish widespread consensus around the timeframes during which such testing is unlikely to yield important clinical information. Although initially it was felt that the AUC should not attempt to be all-inclusive but rather focus on common, real-world situations; external feedback regarding the early AUC documents highlighted gaps in indications or unclear clinical scenarios. The AUC Task Force responded to this feedback, by significant expansion and revision of the indications in subsequent documents. The ensuing applications of revised AUC are reflective of this expansion, noting that the added indications have markedly improved the utility of the documents. When possible, AUC now provides a hierarchy of indications to guide use of the AUC in a systematic fashion, tailored for each modality, and assist in applying a
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p articular clinical situation to one of the indications. This approach also greatly facilitates AUC evaluation and implementation, as it permits an ordered and reproducible way to apply AUC. Nuclear cardiology has an integral role in the noninvasive detection of coronary artery disease (CAD), assessment of myocardial viability, and stratification of risk. It imparts improved sensitivity and specificity over standard exercise stress testing. For example, the average sensitivity and specificity of single-photon emission computed tomography (SPECT) with technetium 99m have been reported to be 90% and 74%, respectively—though the exact performance characteristics depend on the prevalence of the disease in the population being studied. Nuclear imaging can provide functional and prognostic information that is quantifiable, reproducible, and readily obtainable in diverse patient populations. Diagnosis of CAD. Nuclear perfusion studies are performed to establish noninvasively the diagnosis of CAD in the following situations: history of stable angina; chest pain of unclear causation; unstable angina after stabilization; abnormal exercise test result without symptoms; risk stratification in the setting of multiple factors thought to confer a high likelihood of subclinical CAD; scheduled standard exercise testing in the setting of an abnormal e lectrocardiogram [ECG; due to left ventricular (LV) hypertrophy with associated repolarization changes, ST depression >1 mm, manifest preexcitation pattern on ECG, digoxin use, left bundle branch block, or ventricular-paced rhythm]; and previously nondiagnostic graded exercise test. (B) Assessment of the physiologic importance of known CAD. Perfusion imaging can assist in the determination of the functional significance of coronary stenosis that is in the “moderate-to-severe” (50%–70%) range on angiographic evaluation. It can, therefore, be useful to evaluate a specific coronary lesion before proceeding to percutaneous intervention. This remains an accepted indication for nuclear perfusion imaging, although its use for this purpose is being supplanted by other modalities that can assess the functional significance of coronary lesions at the time of angiography (e.g., fractional flow reserve). (C) Assessment after therapeutic intervention. In the past, perfusion imaging was often performed as a routine follow-up procedure after percutaneous intervention and coronary artery bypass grafting (CABG). More recent recommendations on appropriate use of this modality suggest that routine screening in asymptomatic patients who have been successfully revascularized by either method is not necessarily warranted, except in the evaluation of patients more than 5 years after CABG. On the other hand, radionuclide perfusion imaging is certainly appropriate in patients who have undergone prior revascularization and are presenting with recurrent symptoms consistent with coronary ischemia. (D) Risk stratification. With nuclear imaging, it is possible to stratify risk among patients with stable angina or
unstable angina, those who have had MI, and those about to undergo noncardiac operations. The most basic tool in nuclear imaging is the gamma or scintillation camera, which is used to detect gamma rays (i.e., X-ray photons) produced by the chosen radionuclide. Three types of gamma camera exist. (A) A single-crystal camera consists of one large sodium iodide crystal. Other essential elements of this camera include the collimator, a lead device that screens out the background or scattered photons, and the photomultiplier, an electronic processor that translates photon interactions with the crystal into electric energy. Electric signals from the photomultiplier are processed by the pulse height analyzer before reaching a final form. Only signals in a specified energy range are incorporated into the interpreted images. The range recognized by the pulse height analyzer is adjustable and is established on the basis of the radiopharmaceutical used. Digitalization of the single-crystal camera has greatly enhanced its performance. (B) A multicrystal camera works with an array of crystals with increased count detection capability. Because of the availability of an individual crystal to detect scintillation at any given time, this type of camera can be used to detect many more counts than can a single-crystal camera. (C) In the case of positron emission tomography (PET) scanning, a positron camera is a gamma camera used to detect the photon products of positron annihilation. Interaction between a positron and an electron causes annihilation, with the generation of two high-energy photons (511 keV) that travel in opposite directions. An array of multiple concentric rings of crystals constitute a positron camera. Each crystal is linked optically to multiple photomultipliers. The crystals are oriented in diametric pairs in such a way that each pair of crystals must be struck simultaneously by annihilation photons to record activity. Background interference and stray photon energy are automatically accounted for, and artifact is limited. Most positron cameras contain bismuth germanate for annihilation photon detection. Stress echocardiography (SE) is an effective method of evaluating for myocardial ischemia, based on the detection of stress-induced regional wall motion abnormalities (WMAs). Stressors include exercise, pharmacologic agents, and pacing. SE is used to screen for CAD, and it can help identify the coronary vessels involved. The accuracy of SE in the detection of significant coronary artery stenosis is 80%–90%, which is superior to that of exercise electrocardiographic testing and comparable to that of nuclear stress imaging. In patients with LV dysfunction and documented CAD, SE can differentiate viable myocardium from scarred myocardium, which may help predict whether LV function will improve after revascularization. As a diagnostic test for CAD, SE is safe and relatively inexpensive and can be rapidly performed by experienced hands. However, the interpretation of SE images remains primarily subjective and requires a considerable learning curve. SE can also
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be used to assess the severity of valvular disease, hypertrophic cardiomyopathy, and exercise-induced pulmonary hypertension. In addition, it provides important prognostic information after MI and prior to noncardiac surgery. All SE studies are conducted with exercise electrocardiographic testing and standard hemodynamic monitoring equipment. A SE software package on the echocardiographic machine is necessary to acquire digital images and to allow sideby-side comparison of prestress images with peak stress or postpeak stress images. Resuscitation equipment and a defibrillator should be readily available. Patients with LV dysfunction secondary to CAD have significant morbidity and mortality. Given the prognostic implications of poor ventricular function, it is imperative to identify any reversible myocardial dysfunction that may improve with revascularization. Assessment of myocardial viability is indicated in patients with CAD and resting LV dysfunction who are eligible for revascularization. Coronary angiograms provide information about anatomy and feasibility of revascularization but do not predict recovery of function. Resting echocardiography provides information regarding overall LV function and segmental WMAs but does not address recovery of function with revascularization techniques. Single-photon nuclear imaging techniques (single-photon emission computed tomography, SPECT), PET with a metabolic agent, dobutamine echocardiography, contrast echocardiography, and, more recently, delayed-enhancement magnetic resonance imaging (MRI) have been identified as techniques that can distinguish viable myocardium from nonviable myocardium. Each technique exploits a separate property of dysfunctional myocardium to determine the potential for recovery of function after revascularization. The test that is used often depends on the strengths and preference of each medical center, although an approach based on the individual patient would be preferable. (A) Singlephoton emission computed tomography. SPECT is the most common technique used in the United States to identify viable myocardium. This technique has been successful because thallium 201 and technetium 99m radiopharmaceuticals act as perfusion agents that are only taken up by viable tissue. The long half-lives of these agents allow for regional distribution, which makes them feasible to use in medical centers without a generator or cyclotron. In addition, stress SPECT protocols (exercise or pharmacologic) are frequently used to assess for ischemia, which makes this technique cost-effective in a busy clinical center. Routine studies also include gated imaging analyses that provide further information regarding LV function and wall motion assessment, which are important in the evaluation of viability. PET in conjunction with a metabolic agent, usually FDG, has been considered the gold standard for assessment of myocardial viability. PET uses positron-emitting isotopes capable of releasing two high-energy (511 keV) photons at
an angle of 180° from each other. The PET camera can detect these higher energy rays through coincidence counting. As a result, PET provides higher temporal and spatial resolution than SPECT, which translates into a higher quality image. Dobutamine echocardiography has proven to be a reliable predictor of recovery of function after myocardial revascularization. Cardiac MRI. Delayed-enhancement MRI using gadolinium-based agents given intravenously (0.2 mmol/kg) has been shown to reliably distinguish infarcted from viable myocardium. Unlike SPECT-based techniques, MRI poses no risk of ionizing radiation exposure. Cardiovascular magnetic resonance imaging (CMRI) has undergone rapid developments over the last two decades and is now an important imaging technique of the heart and great vessels. Advantages of CMRI include its large field of view, high spatial and temporal resolution, and ability to do tissue characterization. In contrast to nuclear imaging and cardiac computed tomography (CT), MRI does not involve exposure to ionizing radiation. Applications of CMRI include acquisition of anatomic-quality still and cine images of the heart and great vessels in multiple planes, precise measurement of cardiac chamber volume and function, assessment of myocardial perfusion and fibrosis, quantification of blood velocity and flow, and noninvasive magnetic resonance angiography (MRA). As CMRI is not a “pushbutton” technique, clear communication between the ordering physician and the imaging staff is important, indicating the reason for the CMRI examination so that adequate pulse sequences and imaging planes are obtained aiming to answer the desired clinical question. Spin echo. Spin-echo sequences are characterized by a refocusing RF pulse after delivery of the initial excitation pulse. Rapidly flowing blood appears dark, hence they are also known as “black-blood” sequences. Spin-echo sequences provide still images, which are typically used for anatomic delineation of the heart and great vessels owing to their excellent tissue contrast and high signal-to-noise ratio (SNR). They are relatively insensitive to magnetic field inhomogeneities and artifacts related to ferromagnetic objects such as sternal wires and prosthetic heart valves. Turbo spin echo is a newer technique that provides faster acquisition times than standard spin-echo does. The main disadvantage of spin-echo sequences is the relatively long time it takes to acquire an image, making them more susceptible to motion artifacts and unsuitable for cine imaging. Gradient echo. Gradient-echo sequences are characterized by the use of refocusing gradients after the delivery of the initial excitation pulse. Rapidly flowing blood appears bright, hence they are also known as “bright blood” sequences. Gradient echo is a fast imaging technique that is relatively insensitive to motion artifacts, making it ideal
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for cine imaging. However, it has less tissue contrast and increased susceptibility to magnetic field inhomogeneities and ferromagnetic-related artifacts than spin-echo imaging but less than balanced steady-state free precession (B-SSFP). A variety of gradient-echo sequences are widely used in CMRI for cine imaging, myocardial perfusion and scar assessment, coronary imaging, and MRA. Cine imaging. The most widely used pulse sequence for cine imaging is a gradient-echo sequence called B-SSFP, which is characterized by high SNR, high image contrast between blood and myocardium, and low sensitivity to motion artifact. However, B-SSFP is relatively insensitive to blood flow and, therefore, can be suboptimal for imaging of valve dysfunction or intracardiac shunts, which can usually be better illustrated using other gradient-echo pulse sequences, such as echo-planar imaging or phase velocity mapping. In addition B-SSFP is also more susceptible to magnetic field inhomogeneities which can be problematic in patients with mechanical valves or other cardiac implants. Myocardial tagging. RF pulses can be applied before the excitation pulse to generate dark saturation lines or grids on cine images, which are then tagged to the myocardium and further used to assess myocardial deformation. The tags can be used to help qualitatively assess myocardial motion and pericardial tethering or to quantitatively measure myocardial strain. Perfusion imaging. Very fast gradient-echo sequences are used for dynamic imaging of LV myocardial perfusion during the first pass of a gadolinium contrast agent during rest and stress states. Fast gradient-echo techniques are commonly used, such as a fast low-angle shot or B-SSFP with a prepulse to null or darken the myocardium. Normally perfused myocardium shows an increase in signal intensity due to gadolinium contrast, whereas abnormally perfused areas remain dark or hypoperfused. Delayed imaging. Delayed hyperenhancement imaging for myocardial scar or fibrosis is performed 10–30 min after injection of gadolinium contrast using gradient-echo sequences with an inversion recovery prepulse to a null signal from the myocardium. Areas of myocardial scar or fibrosis have a larger extracellular space with a greater accumulation and slower washout of gadolinium and, therefore, appear bright compared with dark, normal myocardium on delayed imaging. Phase-contrast velocity mapping. The phase difference in the spin of protons in moving blood compared with nonmoving protons within a magnetic gradient is called the “spin phase shift” and is proportional to the velocity of the moving protons. A phase-encoded image is constructed, with the gray level of each pixel coded for velocity. Phasecontrast velocity mapping could be considered analogous to pulse wave Doppler echocardiography. It can be used to measure blood velocity and hence quantify cardiac output, shunts, and valve dysfunction. There are, however,
limitations, given that the accuracy of this method is highly dependent on factors such as flow pattern, flow velocity, size, and tortuosity of the vessel. Flow-related signal loss can be a result of the loss of phase coherence that can occur in cases of significant flow acceleration and even in higher orders of motion present in complex flow patterns. Magnetic resonance angiography. MRA of the great vessels typically involves a 3D fast gradient-echo acquisition after injection of gadolinium contrast. The image resolution is typically 2 × 2 × 3 mm, making MRA an excellent option for imaging of large to intermediate size arteries, but less optimal for imaging of smaller vessels. Parallel imaging. A number of parallel imaging techniques make use of multiple receiving body coils to acquire extra data after each excitation pulse. This helps to decrease the imaging time and improve temporal resolution, but at the small relative cost of a decrease in the SNR. Cardiovascular computed tomography (CT) has continued to rapidly evolve over the past decade, gaining new and expanded indications for noninvasive assessment of the heart, great vessels, and peripheral vasculature. Technological improvements, including increasing numbers of detectors, improved temporal and spatial resolution, and advanced postprocessing, have broadened the clinical utility of this imaging modality. Advanced multidetector computed tomography (MDCT) scanners and new scanning protocols have significantly reduced radiation and contrast dosages. Numerous considerations are involved in the proper selection of cardiovascular CT protocols, and skilled operators are required to plan and interpret these examinations. MDCT involves using an X-ray tube mounted opposite multiple detector rows on a gantry, which is then rotated around the patient at a rapid rate (220–400 ms/rotation). The patient is moved at either a fixed or variable speed, or pitch, through the scanner. An increasing number of detectors allows for an increased z-axis (cranial-caudal) coverage, permitting faster scans with improved image quality due to less cardiac and respiratory motion artifact. Temporal resolution is improved by faster gantry rotation, the use of two X-ray tubes and detector arrays mounted at 90° angles to each other (dual-source MDCT), and special reconstruction techniques. Dual-source/dual-energy scanners provide substantial improvements by utilizing dual-source MDCT technology as well as dual-energy sources to improve temporal resolution and decrease scatter. The fastest scanners provide a temporal resolution of 83–105 ms. Spatial resolution is largely determined by detector architecture (typically 0.4 mm isotropic resolution), although thicker slices (1–5 mm) can be acquired to reduce radiation dose according to the study indication. MDCT can be used for both cardiac and noncardiac studies, and it is now the most widely used type of CT hardware for cardiac imaging.
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Electron beam computed tomography (EBCT), although rarely used today, was specifically developed for cardiac imaging. It involves the use of a rapidly oscillating electron beam reflected onto a stationary tungsten target. Because there is no mechanical motion within the gantry, EBCT is capable of very high temporal resolution (50–100 ms). EBCT was used primarily for the quantitative detection of coronary artery calcification (CAC).
References Akhil Jabbar, M., Deekshatulu, B.L., Chandra, P., 2012. Heart disease prediction system using associative Classification and genetic algorithm. In: Proceedings of the International Conference on Emerging Trends in Electrical, Electronics and Communication Technologies-ICECIT. Springer. Amiri, A.M., Armano, G., 2013. Early diagnosis of heart disease using classification and regression trees. In: Proceedings of the 2013 International Joint Conference on Neural Networks, IJCNN 2013, USA. DeFilippis, A.P., 2015. Analysis of calibration and discrimination among multiple cardiovascular risk scores in a modern multiethnic cohort. Ann. Intern. Med. 162 (4), 266–275. https://doi.org/10.7326/M14-1281. Vincy Cherian, B.M., 2017. Heart disease prediction using Naive Bayes algorithm and Laplace smoothing technique. Int. J. Comput. Sci. Trends Technol. 5, 68–73.
Further reading Alić, B., Gurbeta, L., Osmanovic, A., Badnjević, A., 2017. Machine learning techniques for classification of diabetes and cardiovascular diseases. In: 2017 6th Mediterranean Conference on Embedded Computing (MECO), Bar, Montenegro, pp. 1–4. https://doi.org/10.1109/ MECO.2017.7977152. Badnjevic-Cengic, A., Kovacevic, P., Dragic, S., Momcicevic, D., Badnjevic, A., Gurbeta, L., Hasanefendic, B., 2015. Serum nitric oxide levels in patients with acute myocardial infarction with ST elevation (STEMI). Respiron J. 5 (1–2), 6–8. Griffin, B.P., Ovid Technologies, I., Callahan, T.D., Menon, V., Wu, W.M., Cauthen, C.A., Dunn, J.M., 2013. Manual of Cardiovascular Medicine, fourth ed. LWW, Philadelphia. Hendel, R.C., Patel, M.R., Allen, J.M., Min, J.K., Shaw, L.J., Wolk, M.J., et al., 2013. Appropriate use of cardiovascular technology: 2013 ACCF appropriate use criteria methodology update: a report of the American College of Cardiology Foundation appropriate use criteria task force. J. Am. Coll. Cardiol. 61 (12), 1305–1317. Karunathilake, S.P., Ganegoda, G.U., 2018. Secondary prevention of cardiovascular diseases and application of technology for early diagnosis. Biomed. Res. Int. 2018, 1–9. Magjarević, R., Badnjević, A., 2018. Inspection and testing of electrocardiographs (ECG) devices. In: Badnjević, A., Cifrek, M., Magjarević, R., Džemić, Z. (Eds.), Inspection of Medical Devices. Series in Biomedical Engineering, Springer, Singapore.