ECG is one of the popular methods for reconstruction of the images received from the CT scan of the heart. ECG as mentioned can work either prospectively or retrospectively for the reconstruction technique. However, the methods are limited in cases where a pacemaker is present in the patient, as it is the pacemaker that directs the contraction of the heart. Other problems include the inability to record premature ventricular contraction. (United States Patent 6721386, 2004)
Any improvement in the image reconstruction will require the adjustment and removal of the problems mentioned above. The new techniques utilize both ECG signaling and input as well as the input of mechanical motion signals. By correlating these two sets of variables, a correct reproduction of the various phases of the cardiac cycle can be established. (United States Patent 6721386, 2004) In order to make this intervention successful, the apparatus required will comprise of three components.
These include the imaging device, the ECG monitor and a cardiac motion sensor. Each instrument has a certain function to fulfill. The radiation imaging device will obtain the CT images of the patient. The ECG equipment will record the cardiac data of the patient and the motion sensor will detect cardiac data associated with mechanical motion of a cardiac region of the subject. The computer and the software then synchronize and compare the information from the three sources and compiles to give a final result.
This method is ideal for 3 D visualization of the heart, and in identifying the topography of the associated vasculature. Calcifications are easily diagnosed through this process, and therefore this system has applicability in cardiac scoring of the patients. This process is also good in procedures such as contrast angiographies, and is able to give detailed account of any abnormalities in the cardiac function due to the present of the ECG as well as the motion sensors. (United States Patent 6721386, 2004)
PROBLEMS AND POTENTIAL ERRORS IN EVALUATING CARDIAC CT RESULTS; There are many factors of the procedure that must be clear in the mind of the operator and the physician before evaluating the cardiac ct results and findings. The type of image evaluated is the first and foremost issue. Experts claim that the best image evaluations are carried out by the original axial images obtained, and therefore, must be given priority over other images and angles. This is especially so in the cases of coronary artery stenosis evaluation.
The multiplaner reformatted or MPR images should then be used as an aid to the axial images to reach diagnosis. The identification of any plaques in the lumen should then be confirmed using long axis views which would give a cross sectional image of the area. This improves the diagnosis of the findings considerably. The visualization of the stents may not be optimal in the CT angiographies. This is due to the high density of the stents, coupled with beam hardening artifacts from the stent struts.
Understanding anatomy of the coronary veins is important to identify any variations and not to mistake them with any pathology. Identification of artifacts such as motion, misalignment and slab artifacts is essential for proper identification of any cardiac pathology. Other artifacts may include blooming artifacts, beam hardening artifacts and respiratory artifacts. (Hoffman et al, 2006) These artifacts can be outlined as those that are pertaining to the patient, those that are procedure related and finally those that are reconstruction related.
Among the patient related factors obesity is a main issue in CT scanning. Those patients who have weights above 80 kgs or those who have large breast may have artifacts in their imaging. Since this procedure requires the patient to hold their breath for 8 to 10 seconds, failure to do so may result in faulty results. Motion relation artifacts can be eliminated by calming the patient and removing anxiety. The present of metal due to bypass surgery can also lead to streak artifacts in the results. (Telkar, 2007)
Procedure related errors may be due to improper placement of the electrodes, improper or poor contact and poor planning of the procedure. The use of contrasts in the procedure can lead to two types of artifacts, known as the streak and the slab artifacts respectively. (Telkar, 2007) The reconstruction related artifacts can be due to high or variable heart rates. There are many methods employed to remove or minimize these artifacts. Multisector reconstructions are a good way to minimize artifacts. ECG traces can be manipulated by placing the syncs in the correct position or inserting extra syncs. (Telkar, 2007)