| Popis: |
Imaging techniques have improved dramatically over the past decade. Small structures, such as lymph nodes with a diameter of 10 mm or more, are routinely detected with scanners that offer a spatial resolution up to 0.30 mm or 14 line pairs per cm (volume resolution up to 0.12 mm3) and a contrast resolution up to 2.2 mmxliscernable with 3 Hounsfield units (HU) and 20 y. Scan exposure times play an important role in the depiction of small structures in and around moving organs, such as in the thorax. Third generation CT scanners allow us scan exposure times of less than 3 s, but motion is still a major problem with a time resolution of 2 s, resulting in inconsistencies of the view data. The obvious way to reduce motion artifacts is to employ a shorter scan time. In many third generation scanners, the application of shorter scan times is possible, but at the cost of the acquisition of considerably fewer data, resulting in sharply diminished spatial and contrast resolution. |
