MSCT, the new imaging modality for non-invasive visualisation of the coronary arteries, is still in its early phases of clinical evaluation The newer CT scanners have improved rotation. speed and are capable of performing several rotations in a second. Scans are usually gated to the ECG trace. Frequently, a test image is taken to determine the location of the heart and the best scan settings, following which a scan for the calcium score can be performed. Of note, diabetic patients have a higher likelihood of coronary calcification, rendering MSCT coronary angiography less likely to be conclusive in some cases.
CT angiography is obtained using an injection of 80-20 cc dye. Data acquisition takes 5-25 seconds, during which a breath-hold is required. Image reconstruction takes place at a later time point. The medical community is investigating the place of MSCT in the cardiovascular imaging arsenal. Both the 16-slice and 64-slice CT scanners are associated with substantial ionising radiation doses (6.5-10.5mSv). Nevertheless, this dose is favourably comparable to other frequently used, non-invasive procedures, such as myocardial nuclear imaging scans ( Table 1 ).
Of note, treadmill stress tests and nuclear scans provide functional data while angiography and MSCT angiography provide anatomical data. Nuclear scans and MSCT are non-invasive and allow only diagnosis, with no therapeutic options. Heart catheterisation is an invasive diagnostic procedure that has the advantage of also being therapeutic. The diagnostic portion of this imaging modality has a lower radiation exposure than current non-invasive diagnostic imaging modalities, such as a nuclear stress test and MSCT.[4,5,6,7,8,9]
In general, coronary interventions use more radiation, depending on the complexity and length of the procedure. Invasive angiography may cause deterministic radiation effects (e.g. erythema, hair loss, skin ulcers) in very rare cases.[12,13] Yet, such procedures improve symptoms and may also be lifesaving and, thus, the risks associated with the radiation are usually of secondary consideration. There are also non-radiation risks associated with the investigations, such as allergy due to contrast agents and the fact that false positive results may lead to additional tests.
Br J Cardiol. 2007;14(5):289-292. © 2007 Medinews (Cardiology) Limited
Cite this: Radiation During Cardiovascular Imaging - Medscape - Nov 01, 2007.