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Centennial Dissertation |
1
Department of Radiology, University of Chicago, MC 2026, 5841 S. Maryland
Ave., Chicago, IL 60637.
2
Department of Radiology, Beth Israel Medical Center, First Ave. and 16th St.,
New York, NY 10003.
3
Department of Pediatrics, University of Chicago, MC 4051, 5841 S. Maryland
Ave., Chicago, IL 60637.
Received May 24, 2000;
accepted after revision July 19, 2000.
Honoring Hollis E. Potter, MD and George W. Holmes, MD
Introduction
 Top Introduction Congenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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The role of the radiologist in cardiac diagnosis has changed dramatically since the 1960s and 1970s. In that era, radiologists were trained in many centers in the performance and interpretation of coronary arteriography using Melvin Judkins' new catheter technique [1]. As designed, the Judkins catheters lent themselves to adaptation of the Seldinger percutaneous transfemoral puncture. This avoided brachial arteriotomy, which required repair after the procedure [2]. Subsequently, cardiologists became competent in performing the Judkins technique. There were several reasons for this change, but self-referral played a significant role. An increase in the amount of cardiac surgery drove an increasing demand for coronary arteriography that radiology departments did not meet. Cardiologists recognized this demand, and after having initially been trained by radiologists, began to train other cardiologists to perform these procedures. Despite the role radiologists played in creating this technique, advancing the field, and developing new and more accurate imaging technology, radiologists were excluded from cardiac catheterization laboratories. Once radiologists were removed from the adult cardiac catheterization laboratory, the field of radiology withdrew from the investigation of the heart and the examination of patients with heart disease.
Remarkable advances have been made during the past three decades in the understanding, diagnosis, and treatment of heart disease. Traditionally, treatment of congenital and acquired heart disorders has been based on identifying morphologic changes or on clinical presentation. Radiography and cineangiography, the core of radiologic evaluation, were interpreted in terms of morphologic change and the instant physiologic aberration reflected in those changes. The rise of other cardiac imaging modalities, including nuclear medicine imaging and echocardiography, came about as a result of their ability not only to facilitate morphologic diagnosis, but also to allow quantification of morphologic changes and the resulting regional and global changes in cardiac function. Such quantitative information had significant value, providing the basis for risk stratification and objective assessment of the effects of medical or surgical treatment.
The development and growth of these quantitative techniques also marked a divide in the roles of radiologists and cardiologists in the treatment of patients with cardiac disease. The traditional interest of radiologists in morphologic diagnosis was no longer adequate for active participation in the treatment of patients with cardiac disease. Cardiologists were drawn to these newly available cardiac indexes as part of their routine clinical investigations and demanded their availability. To the extent that radiologists working in cardiac disease failed to perform those examinations that could provide needed data, they were replaced by cardiologists who were willing to do so. Hence, the contemporary approach of the clinical cardiologist, after taking the patient's history and performing a physical examination, is to obtain an ECG and institute an imaging algorithm, usually beginning with a chest radiograph. Depending on the clinical problem, echocardiography is the next most frequent study, performed for the purpose of quantifying regional and global cardiac function. Once the bailiwick of radiologists, these examinations are now performed by cardiologists. Further diagnostic testing, including left ventriculography, coronary arteriography, or nuclear medicine studies, which are performed for quantitative analysis, is now usually performed by cardiologists as well.
Advances in CT and MR imaging from which quantitative analysis of cardiac function can be determined allow acquisition of imaging data in radiology departments. The availability of these devices has brought a new excitement to the field of cardiac imaging, and radiologists are realizing that this has created new opportunities as well as concerns and challenges. The success of radiologists in maintaining a role in the treatment of patients with cardiovascular disease requires an understanding of the clinical problems of these patients and the ability to perform the appropriate imaging procedures.
Historically, radiologists have shown considerable interest and expertise in examining patients with congenital and acquired heart disease. In this review, we hope to show not only how newer modalities may expand the role of radiologists in this traditional endeavor, but also how conventional imaging methods have maintained radiology's involvement. First, we describe advances in the treatment of patients with congenital cardiac diseases and the role of cardiac imaging in treating many of these malformations using interventional procedures. New percutaneous interventional techniques continue to rely on imaging procedures to provide the basis for determining their indication, guiding the performance of the intervention, and assessing results. Although interventional techniques have evolved, the importance of radiologic imaging and the skill and experience of the radiologist in performing and interpreting these imaging studies remain crucial.
Next, we describe the resources available in radiology departments for the examination of patients with heart disease. Unenhanced chest radiography has generated renewed interest. Universally available, safe, inexpensive, and reproducible, chest radiography lies at the core of cardiac diagnosis. A snapshot of the heart, great arteries, and lungs, it is useful for excluding noncardiac causes of a patient's clinical problem, assessing cardiac chamber size and mass, and providing a rapid means of assessing the patient's physiologic status. Acquisition of faster CT images augmented by IV contrast enhancement and off-line three-dimensional reconstruction provide the means for visualizing intracardiac abnormalities and the basis for investigation into quantitative analysis of acquired data. MR imaging of the myocardium and coronary arteries is an exciting area of great potential for radiologists. These scanners produce images with high contrast and temporal resolution that appear to allow differentiation between normally functioning and dysfunctional myocardium; these scanners are operated in radiology departments.
We next address our understanding of the atherosclerotic process. Although many radiologists believe that they no longer play a role in the treatment of patients with heart disease, the ubiquitousness of this disease argues the opposite view. Our enhanced understanding of atherosclerotic plaque biology provides new avenues for the diagnosis and treatment of patients with this disease. In particular, we will discuss atherosclerotic coronary artery plaque formation and acute rupture, which will provide an understanding of why symptoms occur and explain the rationale behind the use of newer pharmacologic agents for therapy. Furthermore, we show the clinical problems that imaging studies may help to elucidate and describe how these modalities are faring in addressing these clinical issues.
Finally, this review addresses the means for reinforcing and increasing radiology's role in cardiac imaging. We emphasize the importance of research training and funding in addition to clinical training to support and maintain the viability of the specialty. This refers to the entire radiology community, not merely the subspecialty of cardiac imaging. Radiologists could learn a good deal from the cardiology community, which responded rapidly and effectively in the 1970s in obtaining grant funding from the National Institutes of Health and the American Heart Association. In that era, tremendous research funding became available for investigating heart disease; however, radiology departments failed to recognize the importance of research training for residents and fellows in this field.
Today few radiology residency training programs have cardiac imaging sections and even fewer have fellowship-trained faculty to teach this subspecialty. Cardiac radiology has therefore been allocated the least amount of supervised time in the residency curriculum. Radiologists have come to believe that cardiac radiology is not a viable radiology subspecialty and, consequently, have largely ignored it. Unfortunately, heart disease, particularly coronary artery occlusive disease, accounts for greater morbidity and mortality rates in adult patients 35-55 years old in the Western hemisphere than all other diseases combined, including cancer. Many noncardiac disorders mimic heart disease, and cardiologists often have limited skills and knowledge beyond their own specialty. Recognizing this fact, radiology organizations and leaders in academic radiology departments are now attempting to develop and expand training programs for radiology residents in this specialized area of medical imaging. This development is heartening because it suggests that previous advances and progress in cardiac imaging can be used as the basis on which the role of radiologists in cardiac imaging can build and expand to provide faster and more accurate diagnosis for patients with heart disease.
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Similarly, the growth in the number and range of percutaneous interventions in children and adults with congenital heart disease is related to accurate imaging of the lesions. The first therapeutic transcatheter intervention took place in 1953 when Rubio-Alvarez incised a stenotic pulmonary valve using a wire [3]. The era of interventional cardiology was born in 1966 when Rashkind and Miller described their balloon atrial septostomy [4]. Increasingly, the pediatric cardiac catheterization suite is used to perform therapeutic procedures or to obtain complementary morphologic data not readily available using noninvasive imaging techniques. Although modalities used by radiologists for primary morphologic diagnosis of patients with congenital heart disease are changing, the role of the radiologist in the area of MR imaging of these patients persists.
Pulmonary valve stenosis accounts for approximately 10% of the cases of congenital heart disease. Echocardiography is most commonly used to show the abnormal pulmonary valve and the morphologic sequelae of the lesion. Ballon pulmonary valvuloplasty [5] is indicated for any patient with a peak gradient greater than 40 mm Hg. Doppler examination may give a spuriously elevated valve gradient; the decision to dilate is often deferred until after direct measurement of the valve gradient is obtained in the catheterization laboratory. The procedure, performed with fluoroscopic guidance, is safe and effective and is the treatment of choice. Similarly, in patients with aortic valve stenosis, diagnosis is based on echocardiography findings. However, a valvular gradient obtained using the Doppler echo technique tends to overestimate values obtained at cardiac catheterization, so diagnostic catheterization is also often performed in these patients before an intervention. If the peak-to-peak systolic pressure gradient at catheterization is in excess of 65-70 mm Hg, then intervention is performed [6].
Peripheral pulmonic stenosis, which is usually associated with Alagille and Williams syndromes and congenital rubella infection, occurs in 30% of patients with tetralogy of Fallot and can develop after placement of systemic-to-pulmonary shunts or after the arterial switch procedure. The initial diagnosis may be made using echocardiography or may be inferred from the results of lung perfusion scanning if the obstruction is unilateral. Catheter pulmonary arteriography and newer MR imaging techniques are used to diagnose these conditions. Once the obstruction is localized, catheter-based balloon angioplasty or stent placement is indicated [7, 8]. In patients with coarctation of the aorta, MR imaging is used to characterize the narrow aortic segment and to reveal aortic collateral circulation. Although surgical repair is the primary therapy in these patients, balloon angioplasty has become accepted for treatment of children beyond the neonatal period, especially in cases of surgical failure. Many cardiac centers use stent implantation in older patients in whom percutaneous intervention is indicated [9].
In much the same way, diagnostic visualization of superior vena cava stenosis or other systemic venous obstruction, followed by percutaneous balloon angioplasty, has become an accepted method of treatment in these patients.
Atrial septal defects account for approximately 10% of all congenital heart disease. Transthoracic and transesophageal echocardiography have a high diagnostic value (Fig. 1A,1B,1C,1D) for such defects. The secundum type of atrial septal defect is amenable to catheter closure using umbrella-type devices. Since the first report by King and Mills [10], many devices have been evaluated in clinical trials. Perhaps the most widely used device is the Amplatzer septal occluder (AGA Medical, Golden Valley, MN) [11], which offers many advantages, including the ability to be retrieved and repositioned before release. This technique has a high rate of complete closure. Atrial septal defect closure is routinely performed in the catheterization laboratory with echocardiographic and fluoroscopic guidance. Surgical closure of muscular ventricular septal defects have a high risk of mortality and morbidity. Therefore, percutaneous catheter closure using a device is welcomed by surgeons and cardiologists. The procedure is usually performed with fluoroscopic guidance, although transesophageal echocardiographic guidance has been reported for anchoring the device across the ventricular septum [12].
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Percutaneous catheter closure of a persistent ductus arteriosus has become one of the most commonly performed procedures in the catheterization laboratory. For a small- to moderatesized ductus, the technique is easy and effective regardless of the device used. However, few devices can achieve complete closure in a large ductus. The Amplatzer duct occluder (AGA Medical) has recently been introduced with excellent clinical results [13]. The technique is not difficult, and most patients achieve complete resolution immediately after closure (Fig. 2A,2B) or on follow-up examination. In many patients with various forms of complex congenital heart disease, aortopulmonary collaterals augment pulmonary blood flow in right heart obstruction. Although these systemic-to-pulmonary artery collaterals increase pulmonary blood flow, they also increase the risk of pulmonary vascular occlusive disease and pulmonary hypertension. Surgical ligation of these collaterals can have some risk. Therefore, percutaneous catheter closure immediately before or after surgical correction of the underlying cardiac condition can be achieved with very little morbidity and a high success rate.
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Information obtained from chest radiographic images is provided in a convenient format with which all clinicians feel comfortable. Indeed, patients with known or suspected heart disease undergo routine frontal and lateral chest radiographs at most hospital and clinic visits to evaluate their clinical status. Cardiac chamber and great vessel size, shape, and position provide a wealth of information that facilitates the diagnosis of congenital and acquired heart disease. Before and after therapy, calcifications in the pericardium, myocardium, and coronary arteries help to confirm and elucidate the nature and severity of heart disease (Fig. 3A,3B).
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In addition, the chest radiograph is an excellent method for evaluating pulmonary hemodynamics, including the signs of pulmonary edema and heart failure, both of which may appear before physical signs can be detected. Furthermore, increased pulmonary blood flow caused by intra-and extracardiac shunts, venous anomalies such as arteriovenous fistulas, and evidence of pulmonary arterial hypertension can be diagnosed by a well-trained, experienced observer. Radiologists appreciate the significance of an observation that varies from normal findings. Radiology training in the physics of chest radiography provides a prism through which physiologic change can be differentiated from the effects of image acquisition and radiographic technique. In fact, the most significant limitation of chest radiography as a diagnostic tool is the experience and expertise of the individual interpreting the examination.
It seems inevitable that digital chest imaging using direct area detectors or computed radiography with phosphor plate methods will replace conventional X-ray analogue radiography and fluoroscopy systems. Temporal or energy subtraction should, therefore, become routine options in most modern radiology centers. In addition, computer-aided diagnosis will become commonplace for identifying disorders and for quantifying lesion shape, extent, and mass (thereby improving disease staging) and for measuring therapeutic effectiveness. Quantitative computer-aided diagnostic methods are available for evaluating heart disease and myocardial function.
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Single-slice CT was refined during the past two decades to provide faster acquisition and reconstruction times and to improve temporal and spatial resolution. The remarkably broad gray-scale density range of CT opened new vistas in diagnostic medicine. Blood pool contrast enhancement using IV-injected contrast media made the first CT images of the cardiac chambers possible and allowed differentiation of normal from infarcted myocardium [14]. CT can reveal left ventricular aneurysms (Fig. 4) and patency of coronary artery bypass grafts [15, 16]. CT also became a reliable technique for evaluating chronic aortic dissection [17]. Feasibility studies in patients with pulmonary embolism and myocardial infarction were conducted [18,19,20]. Pericardial disease can also be well shown using CT (Fig. 5). Prototype scanners explored ECG gating and showed the potential of CT for cardiac diagnosis [21, 22]. Millisecond electron beam CT extended these applications by measuring coronary artery calcification for risk stratification of disease. The feasibility and validation of myocardial and renal blood flow measurements were also performed [23,24,25]. However, studies in the United States, Europe, and Asia in patients with coronary artery lesions using electron beam CT indicate that stenoses can be seen and evaluated before and after angioplasty and surgery [26]. Contrast-enhanced CT reveals calcifications in the coronary arteries and arterial lumina (Fig. 6). The limited number of electron beam CT scanners and the lengthy period necessary for clinical trials have delayed the large-scale validation studies necessary for widespread acceptance of this technique.
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The advent of helical and, more recently, multidetector CT has changed several traditional clinical approaches to cardiovascular diagnosis [27]. However, CT angiography still has enormous potential in the new millennium. The widespread availability of rapid image acquisition has provided the basis for investigating direct imaging in real time of cardiac structures using CT. Application of thin-section image acquisitions to computerized three-dimensional reconstruction algorithms produces three-dimensional data sets from which images of the heart in any anatomic plane may be obtained. This enables radiologists with CT scanners to evaluate morphologic changes previously revealed only on echocardiography and, to some degree, on MR imaging. Naturally, cardiologists are interested in these new applications [28]; however, cardiologists tend to embrace new techniques only after careful validation. For example, there was a long period before angiocardiography, echocardiography, and nuclear medicine techniques were sufficiently refined, proven, and accepted by cardiologists for routine application. Nevertheless, the introduction and growth in availability and use of fast CT scanners should help stimulate radiologists to refocus their attention on heart disease.
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Early studies reported that edema, typically present in acute myocardial injury, appeared as a locus of increased signal intensity on ECG-gated spin-echo images [29, 30]. It was further shown that IV administration of gadopentetate dimeglumine and other chelates [31] would enhance the difference between infarcted and normal myocardium. Fat-saturated, contrast-enhanced, or unenhanced breath-hold gradient-reversal acquisition produces remarkable but limited images of the coronary tree. MR coronary arteriography is sensitive to motion artifacts resulting from patient breathing. Gating image acquisition to diaphragm position (representing phase of inspiration), termed the "navigator technique," improves image quality and sharpness [32]. This technique has been helpful in imaging the coronary arteries when applied to contrast-enhanced K-space—segmented two- and three-dimensional gradient-reversal acquisition because it increases the signal-to-noise ratio [33] (Fig. 9). Studies of the sensitivity and specificity of MR coronary arteriography reveal its limitations for clinical application [34]. However, MR imaging is an evolving technology. Intense investigation in areas of acquisition pulse sequences, high-gradient-strength imaging devices, and contrast enhancement techniques continues. Contrast enhancement may provide methods for differentiating infarcted from adjacent ischemic but viable, noninfarcted myocardium at risk. Normal myocardium exhibits signal enhancement on the first pass as a result of T1 shortening effects of the contrast agent, and reduced signal has been shown to correlate with regions of reduced perfusion [35]. Vasodilator (dobutamine or adenosine) stress cardiac MR imaging has the potential to evaluate subclinical disease and myocardial viability. Identification of ischemic as opposed to infarcted myocardium is crucial for making decisions concerning surgical or percutaneous interventional revascularization. Cine MR or gradient-echo imaging techniques as well as myocardial tagging (Fig. 10) continue to be studied.
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Manufacturers of radiographic equipment recognize the potential of MR imaging for cardiac applications. Future advances in clinical applications of 32P MR spectroscopy and the development of dedicated cardiac imaging systems with higher gradient strength and faster gradient switching will continue to be seen. Radiologists must have the ability to image the peripheral vascular tree, heart, and coronary arteries and to understand the relevance of abnormal findings so that they are prepared to provide the technical expertise in what may become one of the primary technologies for examining patients with cardiovascular disease [36].
Pathophysiology of Atherosclerosis
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Atherosclerosis has been recognized for more than a century, but its relevant pathophysiology has only recently been identified by means of modern cellular and molecular biology techniques [38,39,40,41,42,43,44]. Endothelial damage has been attributed to bacterial infection, notably Chlamydia pneumoniae, which is common in the general population and is responsible for 10% of community-acquired pneumonia. Infection is typically mild or asymptomatic [45]. Serologic testing has shown a relationship with heart disease, but various studies show conflicting data, and the discussion continues. Nevertheless, the organism has been cultured from atherosclerotic arteries [46, 47].
Plaque Formation and Progression
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Arterial Thrombosis and Myocardial Infarction
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Morphology of an atherosclerotic plaque is characterized by a fibrous cap covered by endothelium, shielding the plaque from the circulation. As long as the fibrous cap remains intact, the disease progresses slowly and results in progressive narrowing of the coronary arteries and angina pectoris. However, some plaques develop progressive thinning followed by rupture of the fibrous cap, which exposes tissue factor and other extracellular matrix components to circulating platelets and coagulation factors, with subsequent thrombus formation. Events responsible for progressive thinning of the fibrous cap are not completely understood but appear to be the result of an intense local inflammatory process. Autopsy specimens have shown the presence of inflammation, especially at the "shoulder" region of atherosclerotic plaques, which is the most frequent site of rupture, composed of a large number of macrophages, T lymphocytes, and mast cells. Macrophages produce metalloproteinases, which degrade collagen. Peripheral metalloproteinase levels are elevated in patients with unstable coronary syndromes. Mast cells are also found in large numbers in atherosclerotic plaques and are in an activated state when the plaques rupture. Mast cells contain a variety of mediators, including proteases (chymase and tryptase), that can cleave metalloproteinases to their active forms that are capable of digesting collagen [48].
Plaque rupture is confined to plaques with a large lipid core. Vulnerability to plaque rupture is associated with a thin cap. Erosion and rupture produce thrombi, which vary widely in size. Variably sized clumps of platelets, which may be up to several hundred microns in diameter, are periodically swept downstream from these plaques and may occlude small arteries and arterioles in the myocardium.
The pathology of unstable angina is that of a nonoccluding thrombus. Angina at rest may be caused by bursts of platelet emboli or spasm at the site of injury in an epicardial artery. Intermittent growth of the thrombus can occlude the vessel, which may reopen by natural lysis. Blood flow is also important in determining the fate of the thrombus. As a result of these causes, unstable angina can last for hours or days. Occlusive thrombosis may develop rapidly in a major coronary artery, or it could evolve over days. Once a thrombus partially or completely occludes an artery, it may propagate downstream into its branches. The time infarction occurs after thrombosis will depend on hemodynamic and other factors. Radiolabeled fibrinogen has been given to patients presenting with angina at hospital admission who subsequently died from infarction. These studies revealed that the isotope was found only on new thrombus in the distal tail region after infarction had occurred; the thrombus that formed over the plaque rupture site was not radiolabeled [48].
Sudden and complete occlusion of a coronary artery results in transmural myocardial infarction. Myocardial necrosis is uniform as a result of sudden and complete vessel occlusion for at least a few hours. In contrast, in patients with unstable angina, residual antegrade blood flow or collateral flow around the arterial obstruction preserves the subepicardium. In the latter group of patients, histologic examination reveals numerous small areas of necrosis, which vary greatly in age.
Atherosclerotic changes in the heart appear identical to those found in other vascular beds; however, plaques in the carotid, femoral, and iliac arteries and those in the aorta are much larger. They may be 2 cm in length or more and may undergo both erosion and rupture. Because these vessels are much larger, occlusion is rare. After rupture, the contents of the plaque wash away and an ulcer crater may form. This crater is covered by a layer of platelets and may be the source of emboli (e.g., to the brain from the carotid artery).
Clinical Manifestations of Acute Coronary Syndromes
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Other Types of Acquired Heart Disease
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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The cell was once considered primarily a metabolic unit, whereas now it is more appropriate to regard it as a signal processing unit. Accordingly, molecular cardiologists have developed methods to introduce genes directly into cells in the heart and vascular tree. For example, restenosis can be reduced by preventing the uncontrolled accumulation of smooth muscle cells after angioplasty. Modified adenoviruses can be used as vectors to deliver genes engineered to inhibit cell division of smooth muscle cells. Such molecular "cytostatins" may be used to suppress one or more molecular signals required for cells to divide. Other gene therapy techniques stimulate angiogenesis and arteriogenesis in ischemic zones.
The human genome will soon be sequenced so that the primary encoding protein structure of every cell will become known and available. The field of molecular cardiology is still in its infancy, but the funding opportunities and potential for making important discoveries are profound. Radiologists with a few notable exceptions are, at best, only spectators in this panorama, yet they are heavily involved in vascular imaging, which will certainly play an important role in the molecular biology revolution [52]. Radiologists must recognize the crucial need to train our residents and fellows in this field and other new areas of imaging science [53].
New technologies continue to become available for imaging, including MR microscopy, light source imaging, and imaging using infrared and monochromatic radiation. The brightness of synchrotron radiation from the accumulation ring of accelerated positrons or electrons is much greater than that from a conventional X-ray source. High-resolution contrast-enhanced images can be obtained with fluorescent screens using a high-definition television camera. Studies are in progress at synchrotron sites in Germany, Japan, and the United States [54].
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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Selecting the most appropriate imaging modality, avoiding duplicate studies, and showing improved patient outcome based on cost-effective diagnostic and therapeutic algorithms are being demanded of radiologists. However, it is considerably more difficult to show the value of diagnostic studies in patient outcome research than it is for therapeutic procedures. Nevertheless, this is an important area for radiology.
It has been estimated that more than $100 billion is spent in the United States annually on heart disease, much of which is for reimbursing diagnostic imaging studies. Indeed, a group of the 10 most common CPT-4 (Current Procedural Terminology [55]) codes are for cardiac procedures and account for 32% of all Medicare part B imaging costs [56]. Reimbursement from echocardiography alone, which is the most common procedure (15%), was twice that of all MR imaging studies (7.4%), including neuroradiology procedures [56]. These values place the frequency and dollar value of cardiac imaging and its importance to society as a whole into perspective. Furthermore, there continues to be increased utilization and self-referrals of patients by cardiologists.
Nuclear medicine is an important clinical and research area that does not attract sufficient new radiology specialists. This is unfortunate, because the field offers outstanding opportunities as new methods continue to emerge [57, 58]. Targeting contrast media to cellular elements to explore the pathophysiology of disease is only one example of the types of applications and potential of the field [59].
Considerably more funding is available today for imaging research than there was in the past. Furthermore, many millions of new research dollars are available for molecular biology research studies of vascular disease. These are compelling arguments for radiologists to become more interested and involved in this area and more active in the cardiac imaging field [60]. The radiologist's window of opportunity lies in the potential of CT and MR imaging to replace more invasive diagnostic methods and to improve the management of patients with cardiovascular disease [61, 62].
Because radiologists are responsible for the whole installed base of CT and MR imaging scanners, they are well positioned to reenter the exciting and rewarding field of cardiac imaging [63].
The next 3 years will determine if the major radiology societies and the American Board of Radiology are successful in persuading the radiology community to respond to this challenge, which requires that radiologists recognize the implications and become personally involved. Training sufficient numbers of new radiologists in cardiac imaging will be a critical challenge, but the rewards will be worthwhile. Radiology leadership, however, must show their commitment to this initiative. The tragic alternative for radiologists may be that most vascular radiology intervention—not merely cardiac imaging—will be performed exclusively by members of other specialties.
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TopIntroductionCongenital Heart DiseaseChest RadiographyCT of the HeartCardiac MR ImagingPathophysiology of...Plaque Formation and ProgressionArterial Thrombosis and...Clinical Manifestations of Acute...Other Types of Acquired...Molecular BiologySummaryReferences |
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