The molecular structure of some iodinated contrast agents makes them suitable for the computer-tomographic examination of the biliary tract. Organic iodine compounds increase the attenuation of x-rays and the contrast between body tissues containing iodine and those tissues that do not contain iodine. The degree of opacification is directly proportional to the concentration and volume of the iodinated contrast agent (the total amount of iodine).
Biliary contrast agents can be taken orally, for example calcium iopodate, or intravenous meglumine iotroxate. The contrast media are excreted by the liver and concentrate in the gallbladder after passing the intrahepatic biliary tree and cystic duct.
Oral biliary contrast agents usually opacify the gallbladder after a few hours. If the gallbladder is removed, an intravenous cholegraphic agent is required and gallbladder CT can start 60 minutes after the beginning of contrast medium infusion.
The main limitation of the use of biliary contrast agents is the high rate of allergic reactions and of renal or hepatic toxicity. Caused by the potential for systemic toxicity with intravenous cholangiography, ultrasonography should be the preferred method for evaluation of the gallbladder and the bile ducts.

A biopsy is a procedure in which tissue samples are collected. This can be done with a needle, which is inserted into the abnormal area.
An example is the needle breast biopsy. Needle biopsies are usually guided by different imaging techniques like ultrasound, computed tomography, or magnetic resonance imaging. Stereotactic-assisted breast biopsies use computer maps to guide the needle. The location of the breast lump is provided from digital mammograms taken from two angles.
The cells can be removed and examined under a microscope to determine whether the abnormality is cancerous.

See also CT Guided Biopsy.

The basic unit of information.
Definition: The smallest unit of information in the storage on a computer. Eight bits are grouped together to form one byte, additional start and stop bit.
Larger units are
kilobyte (kB) = 1 000 bytes (computer storage 1024 bytes)
megabyte (MB) = 1 000 kB (computer storage 1024 kB)

See also Bit Range, Binary System, Decimation, Digitization, Sampling Rate and Picture Archiving and Communication System.

A bone scan or bone scintigraphy is used to in evaluate diseases of the skeletal system. Scintigraphic whole body bone imaging is a highly sensitive method to show changes in bone metabolism. Increased metabolic activity is seen as a hot spot.
The study requires the injection of a 99mTc-labeled radiopharmaceutical (most commonly methylene diphosphonate (MDP), hydroxymethylene diphosphonate (HMDP) or hydroxyethylene diphosphonate (HDP)). The activity administered for bone scanning is around 500 MBq (300-1100 MBq, 8-30 mCi), depending on age and weight of the patient. After 2-5 hours, the emitted gamma rays are detected by gamma cameras. The produced planar images include anterior and posterior views of the skeleton.
Multiphase bone scintigraphy is used to differentiate a bone process from tissue pathology. In some cases additional SPECT imaging is helpful to better characterize the presence, location and extent of disease.

(Radioactive Seed Implantation Therapy) Brachytherapy is a type of radiation therapy in which a sealed source (encapsulated radionuclide) is placed inside the patient as close as possible to the area being treated. The brachytherapy source delivers usually gamma or beta radiation at a distance up to a few centimeters either by surface, intracavitary or interstitial application.

See also Low Dose Rate, Cryotherapy, RF Thermal Ablation and Prostate Ultrasound.