Cardiac Imaging Tests

Standard imaging tests include. Echocardiography chest x-ray computed tomography (CT) MRI Various radionuclide techniques The standard CT and -MRT can only be used limited because the heart beats constant, but faster CT and MRI techniques can provide useful cardiac images. Sometimes patient is given a drug (eg. As a ?-blocker) to slow the heart rate during imaging. When ECG gating the image recording (or reconstruction) is synchronized with the ECG (ECG gating) and information from a plurality of cardiac cycles provided that can be used to produce individual images of selected time points in the cardiac cycle. CT gating, which uses the ECG to trigger the X-ray in the desired region of the heart cycle, exposes the patient to less irradiation than gating, the information simply reconstructed only from the desired portion of the cardiac cycle (gated reconstruction) and does not interrupt the X-ray , Chest x-ray Chest x-ray images are often the first step in cardiac diagnosis makes sense. Posteroanterior and lateral views provide a broad overview of atrial and ventricular size and shape as well as the pulmonary vessels, but additional tests are almost always necessary to cardiac structure and shape to characterize precisely. CT The spiral CT can be used for evaluation of pericarditis, congenital heart disease (v. A. Abnormal arteriovenous connections), diseases of the large vessels (eg. As aortic aneurysm, aortic dissection), cardiac tumors, acute pulmonary embolism, chronic pulmonary thromboembolic diseases and arrhythmogenic right ventricular dysplasia be used. However, CT requires contrast agents, whereby the use may be limited in patients with renal insufficiency. Electron beam CT, formerly called ultrafast CT or cine-CT, uses, in contrast to conventional CT no moving X-ray source and destination. Instead, the direction of the X-ray beam is passed through a magnetic field and detected by a series of stationary detectors. Since mechanical movement is not necessary, the images can be acquired in a split second (and recorded at a particular point in the cardiac cycle). The electron beam CT is primarily used for the detection and quantification of coronary calcification, an early sign of atherosclerosis. However, the spatial resolution is poor and the apparatus can not be used for non-cardiac diseases, which recent standard CT techniques are preferably used for the cardiac use. Multidetector CT (MDCT) with ?64 detectors has a very fast scan time. Some advanced machines can produce an image of a single heartbeat, although the typical acquisition time is 30 seconds. Dual Source CT uses two X-ray sources and two multi-detector rows which reduces the scan time in half at a single portal. Both procedures seem to be able to coronary calcification and the flow limiting (d.. H> 50% stenosis) to identify coronary obstructions. Typically, an i.v. Contrast agents are used, although non-invasive scans can detect Koronararterienkalkbildung. MDCT is currently used mainly in patients with indeterminate stress imaging test results as a non-invasive alternative to coronary angiography. The primary advantage of MDCT seems to be the exclusion of clinically significant coronary artery disease in patients who have a low or intermediate risk of coronary heart disease. Also, the radiation dose can be significant, about 15 mSv (compared to 0.1 mSv at a chest x-ray absorption and 7 mSv at coronary angiography), newer imaging protocols can reduce the exposure to 5 to 10 mSv .. The presence of calcified plaques high density produces image artifacts, that interfere with the interpretation. MRT The standard MRI is useful to examine the regions around the heart, especially the mediastinum and (to investigate such. As to aneurysms, dissections and stenoses) the large vessels. With an ECG-triggered data gain, the image resolution can approach the CT or echocardiography, clearly determine the Myokardwanddicke and movement, determine the chamber volume, intraluminal tumors or thrombi and flap openings. Sequential MRI -Untersuchungen after injection of a paramagnetic contrast agent (gadolinium Diethylenetriaminpentaessigsäure [Gd-DTPA]) provide a higher resolution in myocardial blood flow measurements than is the case with the radionuclide imaging. MRI is usually regarded as the most accurate and reliable measure of ventricular volumes and ejection fraction. However, patients may develop nephrogenic systemic fibrosis with impaired renal function after use of gadolinium contrast agent, a potentially life-threatening disease. Contrast agents are used in MRI, 3-dimensional information on infarct size and -lokation can obtained and blood flow velocities are measured in the heart chambers. MRI can detect the tissue vitality, by the contractile response to inotropic stimulation is observed with dobutamine or by use of a contrast agent (eg., Gd-DTPA, which is not taken up by cells with intact cell membrane). MRI distinguishes a myocardial scar of inflammation with edema. In patients with Marfan syndrome MRI measurements of the expansion of the aorta ascending accurate than echocardiographic measurements. MR angiography (MRA) is used to determine the interest blood volume (for example, blood vessels in the chest or abdomen.); all blood flows can be determined simultaneously. The MRA can be used for detection of aneurysms, stenosis or occlusion of Kardotiden, of the coronary arteries, the renal arteries or peripheral arteries. The use of this technique for the detection of deep vein thrombosis is currently under investigation. Positron Emission Tomography (PET) PET can show myocardial perfusion and metabolism and is sometimes used to myocardial viability or myocardial perfusion after an ambiguous single-photon emission CT (SPECT) – to assess the study or at very obese patients. Perfusion agents are radioactive nuclides that are used to entering the amount of blood flow in a particular region to pursue and are therefore useful in the unmasking of Myokardperfusionsdefiziten that are undetectable at rest. These are carbon-11 (11C) CO2, oxygen-15 (15O-) water, nitrogen-13 (13N-) of ammonia, and rubidium-82 (82Rb). Only 82Rb does not require a cyclotron on site. Metabolic means are radioactive analogues of normal biological substances which are absorbed and metabolized by the cells. These include: fluorine-18 (18F) -labeled performed deoxyglucose. 11C-acetate FDG demonstrates the increase of glucose metabolism under ischemic conditions and may differ in this way, ischemic but still viable myocardium of scar tissue. The sensitivity is higher than that of myocardial perfusion imaging. Thus, the FDG imaging may be helpful in selecting patients for revascularization and avoiding this process, if only scar tissue is present. These benefits could justify the higher cost of PET. The half-life of 18F is long enough (110 minutes), so FDG often does not have to be produced locally. Techniques that make it possible to combine the FDG imaging with conventional SPECT cameras could make this imaging method widely available. FDG was also used to detect (infected pacemaker wires, aortic vasculitis, cardiac sarcoidosis z. B.) inflammatory cardiovascular diseases. The uptake of carbon-11 acetate seems to reflect all of the oxygen metabolism of cardiomyocytes. The recording does not depend on potentially variable parameters such as blood glucose levels, which can affect the FDG distribution. The 11C-acetic imaging can better predict the postinterventional recovery of myocardial function than FDG imaging. However, since the half-life is 20 minutes has to be produced locally 11C in a cyclotron.

Health Life Media Team

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