(ROI) Keyboard controlled identification of a given area of an image for numerical analysis and the area of anatomy being scanned that is of particular importance in the image. This area can also be a volume, than called (VOI) volume of interest.
A ROI can be used for purposes such as calculation of pixel statistics. ROI measurements should be made with the smallest area and away from boarders and edges to avoid partial volume averaging.

X-rays contain a range of energies (polychromatic photons), the higher energies pass through the patient, the lower energies are absorbed or scattered by the body. Ideally, the x-ray beam should be monochromatic or composed of photons having the same energy. Strong filtration of the beam results in more uniformity. The more uniform the beam, the more accurate the attenuation values or CT numbers are for the scanned anatomical region.
There are two types of filtration utilized in CT:
Inherent tube filtration and filters made of aluminum or Teflon are utilized to shape the beam intensity by filtering out the undesirable x-rays with low energy. Filtration of the x-ray beam is usually done by the manufacturer prior to installation. The half value layer provides information about the energy characteristics of the x-ray beam. Too much filtration produces a loss of contrast in the x-ray image.
A mathematical filter such as a bone or soft tissue algorithm is included into the CT reconstruction process to enhance resolution of a particular anatomical region of interest.

A multiphase bone scintigraphy (bone scan) is a nuclear medical examination including blood flow images, immediate images, and delayed images.
The blood flow study is a dynamic sequence of planar images of the bone region of interest obtained during the injection of the radiopharmaceutical (radioactive tracer).
The immediate phase (blood pool or soft tissue study) include one or more static images of selected regions, obtained immediately after the blood flow phase within 10 min.
Delayed images (usually whole body) are usually acquired 2-5 hours after injection. Later (6-24 hour) delayed images result in a higher target to background ratio and may permit better evaluation of the pelvis if this was obscured by bladder activity on the routine images. This late imaging may be particularly helpful in patients with renal insufficiency or peripheral circulatory disorders and those with urinary retention.