The pulmonary perfusion scintigraphy records the distribution of pulmonary arterial blood flow. The most common indication for lung scintigraphy is the detection of pulmonary embolism. The most widely used radiopharmaceuticals are technetium-99m MAA (macroaggregates of albumin) or 99mTc-HAM. Other radiopharmaceuticals include sulphur colloid macroaggregated albumin, radioactive albumin microspheres and albumin labeled with I-131, or I-113m.
Perfusion imaging of the bronchopulmonary system is based on the principle of capillary blockade. The perfusion study is accomplished by injecting 40 to 160 MBq (1-4 mCi) of the radiopharmaceutical and during repeated deep inhalation. The aggregates are extracted during their first pass through the lung, thus imaging can begin immediately. Pulmonary perfusion scintigraphy is particularly useful in combination with gas ventilation scintigraphy and aerosol ventilation scintigraphy.

See also Inhalation Scintigraphy.

Reflux is the backward flow of fluids.

Single-head contrast media injectors ('contrast only') have been first developed in the 1970s. The construction consists of a syringe with the contrast medium inserted into the injector head and a plunger to deliver the contrast medium from the syringe via tubing connected to the patient.
Injectors used in cath lab angiography are often single-head injectors using one syringe.
Angiography contrast delivery systems inject contrast agent into arteries, where air embolisms can present a serious risk. For that reason, cath lab pressure injectors should have air embolism detectors, warning of bubbles in the line before they reach a patient. Air embolisms are not a major issue for CT scans, due to the venous access any small bubbles injected into a vein are expelled through the lungs. Procedures in the interventional suite need low, variable flow rate injections.

See also Contrast Media Injector, Dual-Head CT Power Injector, CT Power Injector, Multi-Head Contrast Media Injector, Syringeless CT Power Injector.

Viscosity is measured in centipoise (cP). The viscosity of water at 20° C is approximately 1 cP. Viscosity depends on temperature, size and shape of the dissolved particle.
The viscosity of contrast agents is an important factor in diagnostic imaging procedures like angiography and other studies where the injection rate can be of critical importance. Warming the contrast agent to body temperature may achieve higher flow rates. Contrast media are approximately twice as viscous at 20° C as at body temperature.

(W) The SI unit of power.
Definition: 1 watt is equal to a power rate of one joule of work per second of time or in electrical terms it is the power produced by a current of one ampere flowing through an electric potential of one volt.
Power is the rate at which work is done, or the rate at which energy is expended and is used both in mechanics and in electricity.
The unit is named for James Watt, a British engineer.