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Reflections |
1 From the Department of Radiology, University of California, San Francisco, Medical Center, 505 Parnassus Ave, Box 0628, Suite L308, San Francisco, CA 94143-0628. Received October 1, 1999; revision requested December 6; revision received March 29, 2000; accepted April 4. Address correspondence to the author (e-mail: charles.higgins@radiology.ucsf.edu).
ABSTRACT
The emergence of noninvasive imaging techniques for the definitive diagnosis and monitoring of cardiovascular disease has greatly altered cardiac imaging in the past 25 years. The practice of cardiac imaging in 1975 was centered on conventional radiography and angiography, but, in the past 2 decades, noninvasive techniques have substantially replaced catheterization and angiography. The reliance on echocardiography for the evaluation of many cardiac diseases had a profoundly negative influence on the role of the radiologist in cardiac imaging, since the exercise of this modality has been a nearly exclusive province of the cardiologist. However, in the past decade, magnetic resonance imaging has been gradually assuming more importance in cardiovascular diagnosis; with this increase in importance, the role of the radiologist has been reactivated. In 1975, fellowship training in cardiac imaging was frequently combined with training in angiography. Now, training may be more effective by combining cardiac and pulmonary imaging in a thoracic imaging fellowship, but cross-training with an associated subspeciality will be influenced by priorities and personnel in various departments.
Index terms: Angiocardiography, 50.1241, 50.1242 • Angiography, 50.1243, 50.1244 • Aorta, diseases, 562.1511, 94.14, 94.1971, 94.20, 94.30, 94.40, 94.72, 94.73, 94.74, 94.761, 94.78 • Heart, cardiomyopathy, 50.193 • Heart, CT, 50.1211 • Heart, diseases, 50.145, 50.151, 50.172, 50.175, 50.18, 50.19, 50.20, 50.70, 50.80 • Heart, ischemia, 50.1939 • Heart, MR, 50.12141 • Heart, US, 50.1298 • Heart, valves, 50.17 • Reflections
The definitive diagnosis of cardiovascular disease is now accomplished for the most part by using noninvasive imaging techniques. Several noninvasive cardiovascular imaging techniques have emerged during the past 25 years and have greatly altered the practice of cardiac imaging. My entrance into cardiac imaging was at a period of transition from the dominance of catheterization and angiography for diagnosis to the gradual increase in the importance of echocardiography, nuclear imaging, computed tomography (CT), and now magnetic resonance (MR) imaging. Indeed, during my fellowship in 1975, training and experience involved only radiography and angiography.
Although many changes have transpired in cardiovascular imaging in the past 25 years, it is important to recognize how reticent physicians are to change and how slowly new technologies were adapted for the complicated thoracic imaging conditions caused by the confounding effects of respiratory and cardiac motion. Echocardiography in a primitive form was introduced in the mid 1950s for the diagnosis of mitral stenosis and left-atrial tumors. It was not until the early 1970s that the use of echocardiography became widespread. Radionuclides for the evaluation of cardiac disease were shown to be feasible in the late 1940s but did not come into widespread clinical use until the early 1970s. The long persistent bias that existed toward the need for invasive techniques prior to surgery has disappeared so that now many patients undergo surgery without cardiac catheterization and angiography.
The noninvasive revolution in cardiovascular imaging has altered the diagnostic algorithm for all types of acquired and congenital cardiovascular disease. It is instructive to survey the diagnostic approach in circa 1975 compared with the current one in 2000.
THORACIC AORTIC DISEASE
Diagnostic imaging of thoracic aortic disease in the mid 1970s consisted of chest radiography and thoracic angiography. Thoracic aortography was the sole method for establishing the diagnoses of aneurysm and dissection. Surgeons required aortography before performing an operation in all patients. Some thoracic aortic diseases, such as aortic mural hematoma (dissection without internal rupture), were not yet recognized because conventional aortography provided depiction of only the lumen. One must certainly wonder how many negative aortograms in patients with dissectionlike chest pain were caused by intramural hematoma.
In the early 1980s, it became evident that contrast material–enhanced CT and MR imaging were superior to conventional angiography for the definitive diagnosis of thoracic aortic disease (Fig 1) (1,2). While surgeons were initially reluctant to follow this advice, they now nearly universally accept it, and conventional angiography is infrequently used for the preoperative evaluation of either acute or chronic thoracic aortic disease. Moreover, CT, MR imaging, and MR angiography are used routinely to monitor the status of the thoracic aorta after surgery for type A dissection and to monitor the dimensions of a thoracic aortic aneurysm to decide on the timing of surgical intervention (3). MR imaging is also used to monitor the status of the thoracic aorta in patients with Marfan syndrome and other inherited disorders with a propensity for the development of aneurysm and/or dissection (4). In recent years, transesophageal echocardiography has also been established as an accurate technique for the evaluation of acute aortic dissection (5).
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VALVULAR HEART DISEASE
Valvular heart disease was evaluated and then monitored with chest radiography in the early and even mid 1970s. Preoperative assessment of patients with valvular heart disease relied entirely on cardiac catheterization and angiography.
In the late 1970s, M-mode and then two-dimensional echocardiography were increasingly used for the evaluation of valvular heart disease (6). The precision of echocardiography for this purpose was greatly improved with the introduction of Doppler and color flow mapping. In most patients, stenotic gradients and the approximate severity of regurgitation now are defined by using Doppler and color flow mapping without resorting to cardiac catheterization and angiography (6). Moreover, ventricular volumes, ejection fraction, and global contractile function can be monitored by using two-dimensional echocardiography to decide on the timing of surgery. Consequently, cardiac catheterization and conventional ventriculography are no longer necessary for the evaluation of valvular heart disease. Several technical developments and new applications of MR imaging indicate that this modality should have an effect on the diagnosis of valvular heart disease in the near future.
The role of the radiologist in 1975, the interpretation of chest radiographs and cardiac angiograms in patients with valvular heart disease, was important. Because echocardiography displaced these modalities in the past 2 decades and because radiologists do not usually participate in echocardiography, the role of the radiologist has greatly diminished in the diagnosis of valvular heart disease. However, the recognition of the capabilities of MR imaging should reactivate the role of the radiologist in the diagnosis of this disease. The capability of MR imaging for the evaluation of several aspects of this disease, including highly accurate quantification of ventricular volumes, mass, and function, has become evident (7,8). MR imaging can demonstrate valvular regurgitation (Fig 2). Moreover, velocity-encoded cine MR imaging has been shown to be the only noninvasive imaging method for quantifying the volume of aortic, mitral, and pulmonic regurgitation (Fig 3) (9).
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The approach in 1975 to the diagnosis of cardiomyopathies was similar to that described for valvular heart disease. Chest radiography was performed at periodic intervals for monitoring the severity of the disease and the response to therapy. The diagnosis of hypertrophic cardiomyopathy at this time became dependent on first M-mode and subsequently two-dimensional echocardiography (10). Cardiac and coronary angiography were performed to exclude coronary obstructive disease as the cause of dilated cardiomyopathy and to detect obstruction of the left-ventricular outlet region in hypertrophic cardiomyopathy.
By the early 1980s, the reliance on catheterization and angiography in patients with hypertrophic cardiomyopathy was altered by the increasing effectiveness of two-dimensional echocardiography and Doppler echocardiography (10). Coronary angiography has continued to be used to exclude ischemic heart disease as the cause of dilated cardiomyopathy. In recent years, MR imaging has been found to have some advantages for the assessment of the severity of and for the monitoring of cardiomyopathies (11).
As echocardiography increased in importance for the evaluation of cardiomyopathy, the role of the radiologist again diminished. Both echocardiography and MR imaging can provide the diagnostic information that in a previous era depended on cardiac catheterization and angiography (Fig 4). MR imaging in recent years has been recognized as the most accurate method for monitoring regression of left ventricular mass in response to therapy and for precisely defining the distribution of hypertrophy in the left ventricle (Fig 4c). It has also been shown to be the most precise and reproducible method for measuring ventricular volumes; this makes it an attractive technique for evaluating the response of dilated cardiomyopathies to new drugs (12). Consequently, the role of the cardiac radiologist can now be revived by the innovative application of MR imaging in the evaluation of cardiomyopathies.
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The evaluation of ischemic heart disease has consisted of the identification of the presence and extent of myocardial ischemia, the assessment of the severity of myocardial injury and complications of myocardial infarction, and the precise definition of the morphology of coronary arterial obstructive lesions. In 1975, the identification of the likely presence of myocardial ischemia was accomplished mostly with exercise electrocardiography and rest-exercise radionuclide imaging. At that time, the severity of pulmonary venous hypertension and pulmonary edema as portrayed on serial chest radiographs was considered an important surrogate of the severity of acute myocardial infarction. Complications of acute infarctions, such as acute mitral regurgitation associated with papillary muscle dysfunction or rupture, were initially evaluated with chest radiography followed by cardiac angiography.
In the early 1970s, the introduction of successful coronary revascularization surgery provided an impetus for the growth of selective coronary arteriography. The procedure has remained the cornerstone for coronary arterial surgical procedures. Early after its introduction, coronary arteriography was reserved for patients with sufficient symptoms to consider revascularization surgery; now it is used earlier in the course of ischemic heart disease, as angioplasty and stent placement have become alternative or temporizing therapies for coronary obstructive lesions. Cardiac radiologists conducted the seminal investigations on the development and early clinical use of coronary arteriography (13–16). An early elegant and comprehensive monograph that describes coronary arteriographic anatomy and disease was published by Sven Paulin in 1964 (16).
Two distinct approaches for coronary arteriography emerged in the late 1960s: the Judkin and Sones techniques. Mason Sones, a cardiologist working at the Cleveland Clinic, attracted cardiologists to his technique of using a brachial arteriotomy for introducing flexible but not preformed catheters (17). Mel Judkins, a radiologist at the University of Oregon and then Loma Linda University, designed a technique of introducing preformed catheters into the femoral artery by means of the Seldinger technique (13). This was the approach taught to radiologists in the 1970s that because of its simplicity and reliability emerged as the standard method used by both radiologists and cardiologists by the early 1980s.
During my fellowship training in circa 1975, approximately 80% of my daily work involved the performance of selective coronary arteriography and other cardiac angiographic procedures. During the 1st several years of my practice, the performance of coronary arteriography and the interpretation of coronary arteriograms were the major tasks occupying my clinical time.
Now, 25 years later, echocardiography has become the most frequently applied test in ischemic heart disease. It is used to evaluate global and regional ventricular function after acute infarction. It has become competitive with stress-rest nuclear perfusion studies for the identification and estimation of the severity of myocardial ischemia. The detection of regional myocardial dysfunction provoked by drugs, such as dobutamine, is being applied both to determine the presence of hemodynamically significant coronary artery disease and to demonstrate residual viability (inotropic reserve) in putatively stunned and hibernating myocardium (18).
Currently, the heavy reliance on echocardiography as a noninvasive imaging technique for ischemic heart disease has greatly diminished the role of the radiologist. Moreover, radiologists now have little role in selective coronary arteriography.
Now, at the beginning of the 21st century, MR imaging and electron-beam CT are being recognized as important new techniques in the evaluation of ischemic heart disease. My colleagues and others have pursued research on the potential applications of these tomographic techniques in patients with ischemic heart disease for the past 15 years (19).
The applications of MR imaging and electron-beam CT in ischemic heart disease are now becoming important components of our clinical practice. MR imaging is being used to evaluate the anatomy, function, perfusion, and tissue characterization in patients with ischemic heart disease. Several research groups are predicting an important future role for coronary MR angiography, although the only clear clinical use at the current time is for the demonstration of coronary arterial anomalies.
Electron-beam CT is being used clinically with increasing frequency for estimating the burden of coronary arteriosclerosis by measuring the mass of calcification in the coronary arteries (20). Contrast-enhanced electron-beam CT is also being pursued by our own (21) and other (22) groups for noninvasive coronary angiography (Fig 5). The further development and refinement of MR imaging, MR angiography, and electron-beam CT for application in ischemic heart disease has the promise of reinvigorating the role of the radiologist in cardiovascular diagnosis.
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Congenital heart disease was being treated surgically with reasonable success in the mid 1970s. Consequently, management depended on the precise definition of the pathoanatomy required for preoperative planning. At that time, cardiac catheterization and angiography were essential for this purpose. The chest radiograph was used to give some insight into pulmonary vascularity and the presence and severity of pulmonary edema. My and my colleagues’ routine was to evaluate the chest radiograph and physical findings with the pediatric cardiologists on the day preceding catheterization or on the morning on which catheterization was to be performed. Subsequently, I and my colleagues participated in the catheterization procedure and provided contemporaneous assessment of the angiograms.
The diagnostic approach to congenital heart disease had altered considerably by 1980 and has continued on a noninvasive line since then. At the current time, the pathoanatomy is usually defined by using echocardiography. Hemodynamics and ventricular contractile function are estimated with Doppler and two-dimensional echocardiography. Thoracic radiography remains important for preoperative monitoring of pulmonary vascularity and heart size and for early postoperative monitoring of the lungs and indwelling catheters and tubes.
MR imaging is being increasingly applied in the diagnosis of morphologic and functional features of congenital heart disease in both patients who have not undergone an operation and patients who have undergone an operation (23,24). It provides as definitive a depiction of the morphology of congenital heart disease as that provided by cardiac angiography (Fig 6). It will grow to be a very important modality for monitoring the conditions of patients after surgical correction (Fig 6). For instance, I and my colleagues now use MR imaging to monitor right-ventricular volumes and to quantify the volume of pulmonic regurgitation in patients after correction of tetralogy of Fallot, as proposed a few years ago by Rebergen, de Roos, and colleagues (25).
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Indeed, the main role of catheterization and angiography today is to guide transcatheter interventional procedures (26). The future of the diagnosis and therapy of congenital heart disease may eventually involve dual-modality laboratories that employ both MR imaging and conventional angiographic facilities with a pedestaled bed on tracks, which would permit seamless transport between the two imaging modalities (Fig 7).
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Cardiovascular imaging has always occupied a watershed area between radiology and cardiology. While cardiac and coronary angiography were conceived and developed by radiologists, the role of the radiologist in the performances of cardiac catheterization and coronary angiography has essentially ceased in North America. The role of the radiologist has been further diminished by the increasing importance of echocardiography. Consequently, the imperatives for training have substantially changed.
My fellowship training in 1975 consisted of performing catheterization for cardiac and vascular angiography, including coronary angiography. During the early years after training, cardiac and vascular angiography were the major components of my clinical activity. Now, my and my colleagues’ work in cardiac imaging involves the performance of MR imaging and CT and the interpretation of the resultant studies. Cardiac imaging in radiology departments, if it exists at all, is now usually performed by a person with major chores in addition to cardiac imaging.
At the current time, a logical combination of clinical duties seems to be pulmonary and cardiovascular imaging. Consequently, I now try to guide my fellows through training in thoracic imaging with about 40%–50% of the clinical time devoted to conventional radiography, CT, MR imaging, and angiography of the cardiovascular system. Because we are fortunate to have been awarded a National Institutes of Health training grant in cardiovascular imaging research for the past 15 years, my trainees also have had the opportunity to pursue research training for 1 or more years. In other departments, other combinations of specialties may fit better, such as cardiovascular imaging along with interventional radiology. However, the practicality of a busy interventional practice frequently leaves little time for an individual to devote to the monitoring of cardiac MR imaging and the interpretation of cardiac MR imaging studies.
FUTURE
The future of cardiac imaging is critically dependent on three factors. The first factor is the amalgamation of cardiac imaging with thoracic imaging and the training of new thoracic imaging specialists with equal capabilities for cardiac and pulmonary imaging. Alternatively, vascular specialists might be trained in cardiac imaging to promote equal commitment and to foster cardiac and vascular imaging in their departments.
The second factor is the increase in the use of MR imaging for the evaluation of cardiac and vascular diseases. In the past few years, there has clearly been an increasing recognition of the value of MR imaging in cardiac disease and of MR angiography in vascular disease.
The third factor is the maintenance of cardiac MR imaging within the realm of radiology. MR imaging, especially for cardiac imaging, remains a technically challenging modality for which the training and experience of radiologists is optimal. On the other hand, cardiologists usually have extensive understanding of the functional aspect of cardiovascular diseases. Consequently, the most effective clinical use of MR imaging in cardiac diagnosis may in many settings be augmented by cooperative interaction with cardiologic imaging specialists. Dedicated cardiac MR imaging units might in some settings be most effectively operated with the sharing of financial and clinical obligations by radiology and cardiology.
REFERENCES
This article has been cited by other articles:
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  A. Miguel-Dasit, L. Marti-Bonmati, P. Sanfeliu, and R. Aleixandre Cardiac MR Imaging: Balanced Publication by Radiologists and Cardiologists Radiology, February 1, 2007; 242(2): 410 - 416. [Abstract] [Full Text] [PDF]
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 F. M. Vogt, C. U. Herborn, P. Hunold, T. C. Lauenstein, T. Schroder, J. F. Debatin, and J. Barkhausen HASTE MRI Versus Chest Radiography in the Detection of Pulmonary Nodules: Comparison with MDCT Am. J. Roentgenol., July 1, 2004; 183(1): 71 - 78. [Abstract] [Full Text] [PDF]
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M. E. Spieth and C. B. Higgins Evaluation of Ischemic Heart Disease * Dr Higgins responds: Radiology, October 1, 2002; 225(1): 310 - 311. [Full Text] [PDF]
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