Three tissue layers called tunicae, or coats, surround the lumen of an artery. The adventitia (outer coat) is the outermost layer of an arterial wall and is composed of connective tissue containing elastic fibers and another layer of protein called the external basement membrane. Smooth muscle cells comprise the tunica media, or middle coat. The muscle cells contract or relax to constrict or dilate the artery.

See also Coronary Angiogram, Angiography, Angioplasty, and Cardiac Catheterization.

Adverse reactions on contrast agents are rare, but like all other pharmaceuticals, contrast media are not completely without side effects.
Adverse effects to contrast media include allergic symptoms, anaphylactoid reactions, chemotoxic reactions, idiosyncratic reactions, contrast-induced nephropathy, iodide-induced hyperthyroidism and local tissue damage. An adverse reaction can be related to dose, the toxicity, and the physio-chemical properties of the contrast agent, for example osmolality, viscosity, and hydrophilicity.
Side effects such as a metallic taste in the mouth, generalized warmth or flushing, nausea and vomiting, increase with rapid flow and large volume of the injected agent. Although venous tolerance is usually good, there have been reports of sensation like burning, stinging or numbness and of venospasm.

Characterization of adverse reactions include:

The aerosol method uses technetium-labeled DTPA crushed by an atomizer into small particles. This aerosol inhales the patient during the aerosol ventilation scintigraphy to study airways disease.

An aerosol ventilation scintigraphy is a nuclear medical imaging procedure that records the distribution of an inhaled radioactive aerosol within the bronchopulmonary system.
Aerosol ventilation in the gamma camera section does not constitute a significant radiation hazard to personnel. Patient compliance is an important factor to minimizing the dose. Clear instructions and practice are a vital part of the diagnostic imaging procedure.

See also Lung Scintigraphy, Aerosol Method, Gas Ventilation Scintigraphy and Inhalation Scintigraphy.

Air KERMA (Kinetic Energy Released per unit MAss of air) measures the amount of radiation energy in air, unit is J/kg. This include the initial kinetic energy of the primary ionizing particles such as photoelectrons, Compton electrons, positron//negatron pairs from photon radiation, and scattered nuclei from fast neutrons, when for example air is irradiated by an x-ray beam. J/kg (gray) is also the unit of the radiation quantity 'Absorbed Dose'.