Fig.1: Build up of an atherosclerotic plaque within the arterial wall

The heart is one of the critical organs in the human body. It is essential in order to feed the body's biological functions. The cardiac muscle itself is supplied by coronary arteries that branch off the aorta immediately after leaving the heart. Obviously, intact coronary vessels are vital for the proper functioning of the heart. Diseases affecting the heart include inflammatory heart disease, hypertensive heart disease, heart failure, valvular heart disease, and coronary heart disease (CHD) – the main cause of death in the industrialized world.

Coronary heart disease – Narrowing of coronary arteries

CHD is one of the most common cardiac diseases and is typically caused by atherosclerosis: plaque and fatty deposits build up on the artery walls, narrowing the vessels. This condition results in a reduced blood supply and thus a lack of oxygen for the heart muscle. CHD is a chronic disease progressing over years and decades and can remain asymptomatic for a long time. Some common symptoms are chest pain (angina pectoris), shortness of breath and (the most severe clinical manifestation) heart attack or myocardial infarction. Treatment options for CHD include medication and angioplasty with stenting and bypass surgery.

The main risk factors for the development of coronary heart disease include high blood pressure, diabetes and obesity, changes in the lipid metabolism, especially high cholesterol levels (hypercholesterolemia), smoking, genetic predisposition, stress, and insufficient physical exercise. The risk increases above the age of 40. Men are more often affected than women.

Diagnostic methods for detecting heart diseases

There is a broad range of diagnostic methods for identifying the various heart diseases. After a comprehensive anamnesis, measuring blood pressure, recording the heart's electrical activity (electrocardiogram, ECG), stress tests, and an analysis for certain enzymes, imaging techniques play a key role for a precise diagnosis. They include catheter-based coronary angiography, computed tomography angiography (CTA), echocardiography, magnetic resonance angiography (MRA), and nuclear scans. The method employed depends on the specific patient's condition, the physician's preferences, and the availability of the corresponding technologies.

When it comes to the diagnostic examination of expected coronary heart disease, preferences for certain methods may vary geographically. Whereas nuclear medicine (SPECT) plays an important role in the USA, echocardiography is still the method of choice in many other countries. However, we have seen changing trends in recent years. Following substantial innovations in computed tomography, the use of CT angiography has been showing rising growth rates. According to a survey conducted in the USA, cardiologists expect much more routine use of CT in cardiac indications in the coming years.

Coronary angiography in the diagnosis of coronary heart disease

Coronary angiography or arteriography is an invasive method involving a catheter. It is an x-ray examination of the blood vessels or chambers of the heart. A thin, flexible plastic tube (catheter) is inserted into a blood vessel in the upper thigh or arm. The tip of the tube is positioned either in the heart or at the beginning of the arteries supplying the heart, and a contrast medium is injected. This fluid is visible by X-ray, and the pictures obtained are called angiograms. Depending on what is revealed by angiography, additional catheter procedures such as a balloon angioplasty or stent placement may be performed immediately afterwards to open up a narrowed artery.

For a long time catheter-based coronary angiography has been the only means of visualizing the coronary arteries in vivo. It has the advantage that it enables immediate intervention when appropriate. However, interventional procedures are performed in only one third of angiography examinations. Due to the invasiveness of the method, coronary angiography is associated with certain risks, including heart attack, stroke, perforation of arteries, infections and blood clots. Although the incidence of such major adverse events is relatively low, this is a major disadvantage of the method. Angiography is an expensive procedure and takes time and the skill of highly trained physicians.

Fig.1: Dual Source CT delivers brilliant images of the heart (Courtesy of S. Achenbach, Germany)

Looking ahead – Non-invasive imaging techniques

Although angiography remains the gold standard for assessing coronary arteries and coronary blood flow when interventional procedures are expected, other imaging techniques are rapidly improving and expanding.

For instance, computed tomography angiography (CTA) is now being used to provide detailed images of the heart arteries, enabling a less invasive early detection of plaque formation. Coronary CTA involves the use of an X-ray contrast medium which is injected intravenously.

Spatial resolution has improved with each advance in multislice CT technology, and substantially improved image quality has been demonstrated in the latest scanner generations. CTA is minimally invasive, it is fast, it is widely available, and it produces brilliant images of the heart. Furthermore, CT angiography is very accurate in monitoring stents and bypasses.

The main advantages of CTA over MRA are wide availability, significantly better spatial resolution, and more consistent, shorter examinations with better patient adherence. It has been reported that the sensitivity and specificity of coronary MRA is generally lower than CTA.

Brilliant images of the heart with contrast-enhanced Dual Source Computed Tomography

A new era has begun in computed tomography with the availability of Dual Source Computed Tomography (DSCT). With its two x-ray sources and two 64-row detectors, it is twice as fast as previous high-end CT scanners. It provides brilliant images of the heart and its delicate coronary vessels. X-ray contrast media are essential for obtaining images in these cutting-edge applications.
DSCT provides high-resolution images of the coronary vessels at an incredible speed, which makes it possible to take perfect images even of a rapidly or irregularly beating heart – with a temporal resolution (“shutter speed”) of only 83 milliseconds and a total scan time of less than ten seconds. This is especially important in acute care, for example in patients with acute chest pain. In this situation it is important firmly establish the cause of the chest pain – be it a stenosis, a pulmonary embolism or an aortic dissection – as quickly as possible. Furthermore, DSCT traces narrowings and blockages even in the finer coronary vessels and can assess their severity with great precision.

Due to DSCT's enormous speed, patients do not have to take beta blockers order to improve image quality. This medication is usually given prior to a conventional multislice CT scan to slow the heart rate and thereby avoid movement artifacts in the images.

A non-ionic contrast medium is injected into an arm vein in all cardiac DSCT examinations. Only with the help of the contrast agent are the individual chambers of the heart and the coronary blood vessels clearly distinguishable from the surrounding tissue. In cooperation with Siemens Medical Solutions, Bayer HealthCare Pharmaceuticals has developed reliable and robust contrast-injection protocols for a wide range of DSCT applications to provide radiologists with reliable protocol recommendations for scanner use and optimized contrast-media injection parameters.