Computed tomography (CT) is an imaging technique that has revolutionized medical imaging. It is widely available, fast, and provides a detailed view of the internal organs and structures. Helical CT is most common, but conventional, axial, step-and-shoot CT is used for thin section high-resolution CT scanning of the lungs, coronary artery calcification scoring, and prospective ECG-gated coronary CT angiography.
●The principal components of a CT scanner are the x-ray tube and a diametrically opposed array of detectors. The x-ray tube generates an x-ray beam as it rotates around the patient and the detectors concurrently record the radiation that traverses the body. The acquired data are digitized and then reconstructed into axial images.
●CT is superior to conventional radiography because of its exquisite contrast resolution and its lack of superimposition of anatomic structures.
●Helical CT is superior to conventional, step-and-shoot, axial CT because it is faster and it minimizes respiratory misregistration and motion artifacts. In addition, helical CT can enable the performance of CT angiography with subsequent reformation of high quality multiplanar two-dimensional and three-dimensional images.
●Several of the parameters used in CT are set by the operator. These include the collimation of the beam and reconstructed section thickness, pitch, the field of view, the duration of the helix, the reconstruction interval, and the reconstruction algorithm or kernel. Operators must also be familiar with proper breathing instructions and protocols for the injection of intravenous contrast material.
●Multislice helical CT is a major technical advancement in helical CT scanning. It has many advantages over conventional single slice helical CT. However, its major drawback is its higher effective radiation dose.
