History of cardiovascular imaging procedures (as developed and/or applied in German cardiology)

The value of the four main imaging tools: radiology, magnetic resonance imaging, echocardiography and nuclear cardiology depends in the first place on physical properties which determine the spatial, temporal and density resolution and second on the conditions under which the relevant information can be obtained with respect to the diagnostic or therapeutic problem, the comfort of the investigation, the degree of invasivity and the expenses. For several decades radiology was the only available method that allowed a look into the body. Thereby, all relevant information about diseases amenable to any surgical or conservative therapy could be attained. Parallel to the progress of cardiovascular surgery, angiocardiography could provide the anatomic and functional characteristics of congenital and acquired heart diseases. The basic principles for the measurement of total heart size, volume and shape were established already before contrast injection--initially by hand--showed the internal architecture of the heart cavities and the circulatory system. With the invention of film changers, the fundamental knowledge about all kinds of malformations of the heart and vessels was gained. Further technical progress made the procedures faster by cineangiocardiography, more comfortable by simultaneous biplane operation and easier to handle by videotechniques, allowing electronic data processing, storage and retrieval in bright operating theaters. Computer technology favored flexible image processing which, like digital subtraction and functional angiocardiography, could reduce the amount of contrast material to be injected and thereby improve the compatibility, due to better nonionic contrast material and shorter study times. Finally, computer tomography with cross sectional, or spiral data collection enabled a dynamic three-dimensional reconstruction and visualization of the beating heart and to display selected information in 'measures and numbers'. Inspite all these successes, the 'stain' of invasivity remains. Strong competition arose first in echocardiography, which--after some pioneering activities in Germany in the late 1950s--flourished in the 1970s, after being reimported from the US. Most of the rapidly increasing number of ultrasound technologies--from M-mode, via various 2D linear and sector scanning procedures in combination with continuous, pulsed and/or color Doppler methods, new contrast-echo modalities and finally 3D volume scanning procedures--can be applied without any harm in all age groups and from each competent practitioner with comparably small and cheap equipment. Only oesophageal and intravascular approaches retain a touch of invasivity. Consequently not much room remains for other techniques except those, like MRI, which can differentiate tissue properties better and with higher resolution and give unlimited access to all intrathoracic organs noninvasively. Under these conditions the indications for nuclear cardiology are restricted to the small field of myocardial perfusion and metabolic studies, whereas transit time measurements and radionuclide ventriculography are practically obsolete.