Cardiac Cat Scan - Research Paper Example

Conventional CT imaging, on the other hand, is an imaging modality with low temporal resolution: the heavy x-ray tube and the detector array must be moved very accurately in a circular pattern around the body. Therefore, dedicated scanner designs needed to be developed to increase acquisition speed. As Gilkeson, Ciancibello, and Multidetector (2003) point out, one further prerequisite cardiac CT imaging is to provide contiguous cross-sectional images of the heart with every displayed image to be of the same cardiac phase.

Otherwise, gaps may occur if adjacent images depict the heart in different phases of the cardiac cycle. Data acquisition must therefore be triggered by the patient's electrocardiogram (ECG) or, in case of continuous acquisition of x-ray data, image reconstruction must be synchronized to a function correlated to cardiac motion, such as the simultaneously recorded ECG called retrospective ECG gating. It is therefore possible to reconstruct cross-sectional images at any given instant in the cardiac cycle.

AS Mori, Endo, Tsunoo et al (2004) point out, this technique can be used to minimize motion artifacts by retrospectively selecting the cardiac phase with the fewest artifacts or to provide data sets during systole and diastole, which permits dynamic analysis of cardiac function. Apart from its intrinsic motion, the heart is subjected also to motion caused by breathing. To avoid artifacts, CT imaging of the complete heart has to be performed within one single breath-hold and CT scanners have to provide for sufficiently fast volume coverage.

In practice, image acquisition times of up to 35 seconds can be tolerated by a cooperative patient (Mori,et al). Image reconstruction algorithms that use projections covering less than 360 degrees are called partial scan reconstruction algorithms. In case of multidetector CT (MDCT), more advanced partial scan reconstruction algorithms are available that makes use of less than 180 degrees of tube rotation. To fill gaps and provide missing projection angles for reconstruction of an image at a given level, data are used that are acquired during a later heartbeat by another detector and assigned to the correct heart phase by means of the simultaneously recorded ECG.

Theoretically a better temporal resolution can be achieved by confining image reconstruction to shorter segments of the cardiac cycle. But the necessity to combine data from several successive heartbeats constitutes a disadvantage of this approach. As the heart may not return to exactly the same position from heartbeat to heartbeat, this may reduce image quality. Technology of cardiac CT continues to develop rapidly. One major development is to expand the number of detectors from 64 to 256. Thus, it is possible to visualize the entire volume of the heart in a single rotation, which can be performed during one heartbeat.

As opposed to previous scanner generations, this will decrease the length of the necessary breath-hold, decrease the amount of contrast agent necessary to achieve intravascular enhancement during the scan, and may be useful in patients with an inconstant heart rate or arrhythmias. Another new approach is the dual-source CT (DSCT) scanner. Two arrays of tubes and detectors are mounted orthogonally in a single gantry. It is therefore possible to obtain x-ray data in 180-degree projections by performing only a quarter-rotation of the gantry.

Temporal resolution is thus substantially higher than with