Tomography derives from the Greek words "tomós" for editing and "gáphein" for writing. It is a radiological process for the three-dimensional imaging of organic structures. In order to achieve optimal diagnostics, the cooperation between Cardiology, Diagnostic Radiology and Intensive Care Medicine is indispensable.
The various tissue types and organs are clearly visible on the CT image thanks to the contrast graduation used. Computed tomography is an important tool for many medical issues, including heart disease.
Cardiac computed tomography makes sectional images of the cardiac anatomy and gives the cardiologist the opportunity to assess atherosclerotic processes in the coronary arteries. Cardiac constrictions can be proven or excluded, so that an invasive diagnosis by a cardiac catheter is dispensable. The physicians carry out the investigation by the electron beam tomography and the multi-line CT (multilayer spiral CT).
The main fields of application for this imaging diagnostic procedure are calcium score determination, CT angiography of the coronary vessels, CT angiography of bypass vessels, and aortic and pulmonary vein examinations. Cardiac computed tomography is also recommended in the case of symptoms that are directly related to the heart, such as acute chest pain without ECG change and currently occurring heart failure.
Computed tomography of the heart places high demands on both the medical profession and the technology. Cardiologists use the most advanced devices on the market, the "Second Generation Dual Score", in order to obtain optimal images in view of the natural motion of the heart. In these innovative scanners, two X-ray tubes rotate three times per second around the patient lying on their backs.
In less than half a second, the patient's heart is scanned and the electrical cardiosignal is recorded by means of an electrocardiogram (ECG). As a result, the scanner provides an image data set that shows a seemingly stationary heart, thereby eliminating artifacts due to cardiac motion. The calcium score is determined by a contrast-free CT scan used to detect or exclude and quantify a coronary calcification.
The diagnosed value is known in the jargon as Agatston Equivalent Score and gives an indication of the risk of heart attack. Based on these test results, cardiologists determine the therapeutic strategy for patients with cardiovascular risk factors. For evaluation, the physicians refer to the study of large groups of patients based nomograms (diagram). Patients are at increased risk if the critical limit set 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 imaging of the coronary arteries. To perform this examination, the patient is injected with an iodine-containing contrast agent via a peripheral venous indwelling catheter. This is usually placed on the back of the hand or in 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 catheterization (0.3 mm).
However, this method only replaces the cardiac catheterization in the case of certain questions. In contrast to calcium score determination, angiography shows complete vessel contouring, including soft plaque deposits, in addition to calcification (calcification in tissues). Through this imaging, cardiologists are able to exclude or recognize coronary stenosis with high accuracy.
By a three-dimensional processing of the data, the findings are additionally demonstrated plastically. Angiography of vessels assesses the cardiac situation of patients who have undergone a surgical bypass operation and, in contrast to angiography of the coronary vessels, records a greater distance of the thorax as the outlets of the "bypass vessels" are farther from the heart. Patients who are difficult to examine by cardiac catheterization or who are suspected of having premature closure are referred to this cardiac computed tomography of the "bypass vessels".
Further fields of application are the imaging diagnostics of pulmonary veins after stent implantation and ablation to eliminate atrial fibrillation. Furthermore, this innovative technology is used in the areas of coronary vein morphology (before CRT), pericardial diseases (pericarditis), myocardial function (heart muscle, heart wall), congenital heart disease and diseases of the aorta (main artery).
A follow-up of stents in the coronary vessels is possible. The image quality, however, depends on the location, size and metal type of the stent. Also for the regular follow-up examination of patients after a heart transplant a heart CT is meaningful. Cardiac computed tomography also accurately maps the heart valves. For patients who recommend catheter-based replacement of the aortic valve, the cardiologist may determine the correct prosthesis size prior to use by the CT scan.
The indication for cardiac computed tomography is due to the unavoidable X-ray radiation to make exactly.
Before the examination, the cardiologist checks the renal function of the patient (keratin values, eGFR). In patients taking metformhaltige drugs for diabetes mellitus (diabetes mellitus), an interaction with the contrast agents can not be excluded. The attending physician may need to temporarily stop the medication to prevent kidney damage. Prior to any X-ray examination, pregnancy and allergic reactions to the contrast media must be excluded.
Unlike the predecessor technology, the devices of the new generation guarantee reduced X-radiation. With this reduced risk, coronary CT is a recommended alternative to cardiac catheterization, 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 are the lack of possibility of direct intervention such as stent implantation and balloon dilation (balloon dilatation). Cardiologists are limited in the assessment of CT images in the case of severe calcification, cardiac arrhythmias and implanted stents. If indicated, private, but not the statutory health insurance companies take over the costs of this self-payer benefit.Tags: