The Computed tomography of the heart (CT) is an established diagnostic imaging system, which is becoming increasingly important in the field of coronary heart disease due to the use of high-resolution scanners.
Tomography is derived from the Greek words "tomós" for section and "gáphein" for writing. It is a radiological procedure for the three-dimensional imaging of organic structures. In order to achieve optimal diagnostics, the cooperation between cardiology, diagnostic radiology and internal intensive care medicine is essential.
What is computed tomography of the heart?
The different types of tissue and organs are clearly visible on the CT image thanks to the contrast gradation used. Computed tomography is an important instrument for many medical issues, including in the area of heart disease.
The cardiac computed tomography creates sectional images of the heart's anatomy and gives the cardiologist the opportunity to assess atherosclerotic processes in the coronary vessels. Coronary constrictions can be detected or excluded, so that invasive diagnostics using a cardiac catheter can be dispensed with. The doctors carry out the examination using electron beam tomography and multi-line CT (multi-slice spiral CT).
The main fields of application for this imaging diagnostic method are calcium score determination, CT angiography of the coronary vessels, CT angiography of bypass vessels and examinations of the aorta and pulmonary veins. Cardiac computed tomography is also recommended in the case of complaints that can be traced back directly to the heart, such as acute chest pain without an EKG change and currently occurring heart failure.
Function, effect & goals
Computed tomography of the heart places high demands on both medical professionals and technology. In order to obtain optimal images in view of the heart's own movement, the cardiologists use the most modern “Second Generation Dual Score” devices available on the market. In these innovative scanners, two X-ray tubes rotate three times per second around the patient lying on their back.
In less than half a second, the patient's heart is scanned and the electrical cardio signal is recorded using an electrocardiogram (EKG). As a result, the scanner delivers an image data set that shows an apparently standing heart, which excludes artifacts caused by the heart's movement. The calcium score is determined by a contrast agent-free CT examination, which serves to detect or exclude and quantify coronary calcification.
The diagnosed value is called the Agatston Equivalent Score in technical terms and gives an indication of the risk of heart attack. Based on these examination values, the cardiologists determine the therapy strategy for patients with cardiovascular risk factors. For the assessment, the doctors use nomograms (diagram) based on the examination of large patient groups. Patients are at an increased risk if the critical limit specified by the nomograms or the absolute value of 400 is exceeded. This high-risk constellation requires intensive therapy.
CT angiography (X-ray examination of the vessels) is a fast, high-resolution image of the coronary vessels. In order to carry out this examination, the patient is injected with an iodine-containing contrast medium via an indwelling peripheral venous catheter. This is usually placed on the back of the hand or in the crook of the elbow. To lower the heart rate, the patient takes a beta blocker before the examination. The breath hold phase is ten seconds. This non-invasive examination comes very close to the introduction of cardiac catheters, as the spatial resolution of the devices used, at 0.33 mm, comes very close to the value of the cardiac catheter examination (0.3 mm).
However, this method only replaces the cardiac catheter examination in the case of certain questions. In contrast to the calcium score determination, angiography shows not only the calcification (calcium deposits in tissue) but also the complete vessel contouring including soft plaque deposits. With this imaging, cardiologists are able to exclude or recognize coronary stenoses with high accuracy.
The findings are also vividly demonstrated through a three-dimensional processing of the data. Vascular angiography assesses the cardiac situation of patients who have undergone surgical bypass operation and, in contrast to coronary artery angiography, records a greater stretch of the thorax because the "bypass vessels" are located further away from the heart. Patients who are difficult to examine using a cardiac catheter or who are suspected of having premature occlusion are subjected to this cardiac computed tomography of the "bypass vessels".
Further areas of application are imaging diagnostics of the pulmonary veins after stent implantation and ablation to eliminate atrial fibrillation. This innovative technology is also used in the areas of coronary vein morphology (before a CRT), pericardial diseases (inflammation of the pericardium), myocardial function (heart muscle, heart wall), congenital heart diseases and diseases of the aorta (main artery).
A follow-up examination of stents in the coronary vessels is possible. The image quality, however, depends on the position, size and type of metal of the stent. A heart CT is also useful for regular follow-up examinations of patients after a heart transplant. Cardiac computed tomography also depicts the heart valves very precisely. For patients who recommend catheter-based replacement of the aortic valve, the cardiologist can use the CT scan to determine the correct size of the prosthesis before use.
Risks, side effects & dangers
The indication for cardiac computed tomography has to be made precisely because of the unfortunately unavoidable X-rays.
Before the examination, the cardiologist checks the patient's kidney function (keratin values, eGFR). In patients who take medication containing Metform for diabetes mellitus (diabetes), an interaction with the contrast media cannot be ruled out. The attending physician may have to temporarily stop the medication to prevent kidney damage. Pregnancy and an allergic reaction to the contrast agent must be excluded before each X-ray examination.
In contrast to the previous technology, the devices of the new generation guarantee reduced X-ray radiation. With this reduced risk, a coronary CT is a recommended alternative to cardiac catheter examinations, scintigraphy (nuclear medicine examination) and stress MRI for certain issues.
A major advantage of cardiac computed tomography is the non-existent risk of invasive surgery. Disadvantages show in the lack of the possibility of direct intervention such as stent implantation and balloon expansion (balloon dilatation). In the case of severe calcification, cardiac arrhythmias and implanted stents, the cardiologists are limited in their assessment of the CT images. If indicated, private, but not statutory, health insurance companies cover the costs of this self-payer service.
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