8 - Computed tomography

Summary

1. Regarding computed tomography (CT) number (CTn):

1. It represents the linear attenuation coefficient of each tissue

2. It is directly proportional to μ_water

3. It depends on kV, but not on filtration

4. It is between 20 and 30 for brain white matter

5. Air and water can be used for calibration of CTn

1. Regarding the partial volume effect:

1. A thin high-contrast object at an oblique angle is less visible

2. Because of the partial volume effect, a small high-contrast object that is smaller than the display pixel size is not visible

3. It reduces the visibility of low-contrast detail

4. It depends on the thickness of the tissue

5. It depends on the thickness of the transaxial slice

1. In CT:

1. The total number of detectors is around 500–1000 in each row

2. The gantry cannot tilt in the cranio-caudal direction

3. A bone algorithm improves the spatial resolution

4. The anode–cathode axis is perpendicular to the z-axis to reduce the heel effect

5. The main filter is usually 3 mm of aluminium

1. In CT geometry:

1. There are typically two focal spots and the smallest is 0.6 mm

2. The heating capacity is 0.4 MJ

3. The filter in first-generation scanners was copper to remove high-energy photons and aluminium for low-energy photons

4. Post-patient collimation is necessary in a multi-slice scanner to get an accurate thickness

5. […]