The identification of any disease process in the coronary artery is the main method to predict and prevent any cardiac mishaps. Different methods can be used to understand the topography and condition of the coronary arteries and their trees. This is especially useful in patients with increased heart beats, where concomitant dose of beta blockers can enhance the visualization of the coronary artery anatomy.
The introduction of sub millimeter techniques has widely improved this diagnostic procedure, and the use of different modalities such as curved planer, thin-slab and volumetric techniques largely enhance the final results of the diagnostics. These methods are especially useful to evaluate the status of the cardiac stents and bypass grafts in cardiac patients, and any pathological change that may be taking place in it. It can be a very helpful tool after cardiac surgeries to assess the patency of the various arteries such as the coronary and the internal mammary artery.
Similarly, any anomalies in the coronary tissue are also easily recognized. (White and Reed, 2004) Coronary artery stenosis can be very confidently predicted by the use of MDCTs especially the 64-slice MDCT variant. This method has been able to identify significant stenosis in smaller coronary artery segments as well as side branches. (Hoffman et al, 2006) CONTRAINDICATIONS FOR USE OF CT SCAN OF HEART CT scan in the heart is a relatively safe procedure and can be carried out with no side effects in a majority of the patients.
However, certain cases may not be the best candidates for the procedure. The most common of these are women who are pregnant, as the increased dose of radiation may be harmful for the child. In many of the cases, the use of iodine takes place as a contrast medium. Therefore, patient must be asked about history of allergy to shellfish, iodine, or any medications. Patients who are undergoing radiotherapy may not be ideal candidates for the procedure. CT heart is not an ideal procedure for those who are above 60 years of age, or have any kidney problems.
This is because the excretion of the contrast medium may be compromised in kidney patients. (History of Innovations, 2006) DIFFERENCE BETWEEN CONVENTIONAL AND CARDIAC CT SCANS: Cardiac CT scans are very different from CT scans of other systems and organs. This is due to the high resolution that is required. For this a 16-detector-row CT scanner is used. (Becker, 2003) The speed of the table is also reduced considerably to only 6mm/sec in order to gain more exposures and images.
The result is an increase in the number of radiographs which increases the resolution. The procedure therefore is of longer duration than other CT procedures. In many of the cases, concurrent ECG tracing is carried out so as to correlate the various cycles of cardiac contraction to the CT images. At the moment the detector rows available are in two forms, the 4-detector-rows and the 16-detector row. 16 detector rows are preferable due to the reduced scanning time, small increase in the dosage of radiation when compared to 4-detector-rows.
The image produced is clearer for 16 detector rows than with 4 detector rows, and even small structures such as the right coronary artery is better visualized with the 16 detector. (Becker, 2003) CONTRAST MEDIA IN THE CT OF HEART: The use of contrast media depends upon the type of procedure that is being carried out. For example there are two variations of the MDCT procedure. The first one, the calcium scoring CT is utilized without the use of contrasts and instead utilized the ECG gating.
However, CT angiography requires the use of contrast media, so that multiple cardiac phases are reproduced easily. (White and Reed, 2004) With the advent of faster CTs there is renewed emphasis on the use of contrasts for detection purposes. The technique for contrast is very specific and therefore requires it to be adequate, consistent and providing homogenous contrast in the entire coronary artery tree. Proper contrast is essential for two dimensional and three dimensional findings to take place.
The trick is to introduce an amount that simultaneously delineates the structure and allows identification of abnormalities and masses without obscuring it. This issue has been the biggest problem in the contrast CT scans for heart, and has resulted in false positive and false negative results in the past. The indications of this technique include CT coronary angiography techniques, contrast enhanced CT of coronary artery anomalies, by pass grafts and stents, and CAD detection. (Schoepf, 2004)