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In order to take the best possible view of the part of the body being radiographed, the patient, film, and x-ray tube must be positioned in the most favorable alignment possible. There are special terms used by radiologists to designate the position of the body to be examined. Some of the x-ray terms describing the position of the x-ray beam are

1. AP view (anteroposterior). In this view, the patient is usually supine (lying on the back), and the x-ray tube is aimed from above at the anterior. The film lies underneath the patient. The AP view may also be taken with the patient in the upright position.

2. PA view (posteroanterior). In this view, the patient is upright with her or his back to the x-ray machine and the film to the chest. The x-ray machine is aimed horizontally at a distance of about 6 feet from the film.

3. Lateral view. In this view, the x-ray beam passes from one side of the body toward the opposite side. In taking a right lateral view, the right side of the body is held closely against the x-ray film and the x-ray beam passes from the left to the right through the body.

4. Oblique view. In this view, the x-ray tube is positioned at an angle from the perpendicular plane. Oblique views are used to show regions that would be hidden and superimposed in routine AP and PA views.

The following terms are used to describe the position of the patient or part of the body in the x-ray examination;

Abduction	Moving the part of the body away from the midline of the body or away from the body.
Adduction	Moving the part of the body toward the midline of the body or toward the body.
Eversion	Turing outward
Extension	Lengthening or straightening a flexed limb.
Flexion	Bending a part of the body.
Inversion	Turing inward
Lateral decubitus	Lying down on the side with the x-ray beam horizontally positioned; sometimes called cross-table lateral.
Prone	Lying
Recumbent	Lying down (may be prone or supine).
Supine	Lying on the back (face up).

Nuclear Medicine

A. Radioactivity and Radionuclides

The emission of energy in the form of particles or rays coming from the interior of a substance is called radioactivity. A radionuclide (or radioisotope) is a substance that gives off high-energy particles or rays as it disintegrates. Radionuclides are produced in either a nuclear reactor or a charged-particle accelerator (cyclotron) or by irradiating stable substances, causing disruption and instability. Half-life is the time required for a radioactive substance (radionuclide) to lose half of its radioactivity by disintegration. Knowledge of a radionuclide�s half-life is important in determining how long the radioactive substance will emit radioactivity when in the body. The half life must be long enough to allow for diagnostic imaging but as short as possible to minimize patient exposure to radiation. Technetium-99m (99m Tc), with a half-life of 6 hours, is an ideal radionuclide and is used most frequently in diagnostic imaging.

Radionuclides emit three types of radioactivity:

� Alpha particles,

� Beta particles,

� Gamma rays (They have greater penetrating ability than alpha and beta particles, and more ionizing power, are especially useful to physicians to both the diagnosis and the treatment of disease.)

B. Nuclear medicine Tests in Vitro and Vivo Procedures

Nuclear medical physicians use two types of tests in the diagnosis of disease;

� in vitro (in the test tube) procedures

� in vivo (in the body) procedures.

In vivo procedures involve analysis of blood and urine specimens using radioactive chemicals. For example, a radioimmunoassay (RIA) is an in vitro procedure that combines the use of radioactive chemicals and antibodies to detect hormones and drugs in a patient�s blood. The test allows the detection of minute amounts of drug. RIA is used to monitor the amount of digitalis a drug used to treat heart disease, in a patient�s bloodstream and can detect hypothyroidism in new born infants.