O's

Question 1

object

Answer 1

The thing or item being radiographed (i.e., patient or body part). Other names: subject, patient.

Question 2

object-film distance (OFD)

Answer 2

The distance between the patient and the film or image detector. In digital radiography, object-receptor distance.

Question 3

osteochondritis dissecans (OCD)

Answer 3

A developmental condition in which abnormal blood supply to epiphyseal bone disturbs endochondral ossification, resulting in thickening, softening, necrosis, and eventual collapse of cartilage.

Question 4

osteochondroma

Answer 4

A benign bony mass caused by abnormal location of physeal cartilage. Mass usually stops growing at skeletal maturity, but malignant transformation to chondrosarcoma or osteosarcoma can occur. Appears as an expansile, inhomogeneous, osseous mass extending awayfrom bone, typically with irregular borders and well-defined margins. Multiple osteochondroma is called osteochondromatosis or multiple cartilaginous exostoses.

Question 5

osteogenesis imperfecta

Answer 5

A rare, generalized condition caused by a defect in collagen production and resulting in fragile bones. May be confused with hyperparathyroidism

Question 6

osteolysis

Answer 6

An abnormal, localized area of active bone resorption caused by disease. The pattern of osteolysis reflects the aggressiveness of the disease process. A more aggressive disease process presents with less distinct bony margins, a longer zone of transition between normal and disease bone, and a more rapid rate of change on serial radiographs.

Question 7

osteoma

Answer 7

A rare, benign, slow-growing, osseous neoplasm that protrudes from the surface of a bone, usually on the skull.

Question 8

osteomalacia

Answer 8

Softening of bones due to faulty mineralization of available osteoid.

Question 9

osteomyelitis

Answer 9

Inflammation of bone; usually caused by an acute or chronic infection (e.g., bacterial, fungal, protozoal organisms). Technically, bone and medullary cavity.

Question 10

Osteopenia

Answer 10

Low bone density; decrease in bone mass (synonym for osteoporosis).

Question 11

osteopetrosis

Answer 11

Uncommon congenital disease leading to increased bone thickness and opacity. Other names: marble bone.

Question 12

osteophyte

Answer 12

A well-defined bony growth or bone spur projecting outward from a periarticular margin. Results from degeneration and mineralization of proliferating articular cartilage in non-weight-bearing areas. The common true sign of degenerative joint disease.

Question 13

osteoporosis

Answer 13

“Porous bones”; loss of bone mass resulting in decreased opacity of bone; may result from disuse or metabolic disease. Other names: bone atrophy.

Question 14

osteosclerosis (sclerosis)

Answer 14

Increased bone opacity; an area of bone with elevated density (more mineral is present in the bone). Radiographically more opaque.

Question 15

otic canalography

Answer 15

A radiographic contrast study of the external auditory canal.

Question 16

object-receptor distance (ORD)

Answer 16

The distance between the patient and the image detector or receptor.

Question 17

oblique radiograph

Answer 17

Animal or body part is slightly rotated from true lateral or true ventrodorsal/dorsoventral positioning to displace overlying structures from area of interest or to view a structure in profile. Oblique radiography may also be accomplished by changing the angle of the x-ray beam.

Question 18

OFA

Answer 18

Orthopedic Foundation for Animals, established in 1966.

Question 19

oligocephalic

Answer 19

Shape of skull in which nasal cavity is approximately equal in length to the cranium. Other names: mesaticephalic.

Question 20

opacity (radiopacity)

Answer 20

Characteristic of a material to block (attenuate or absorb) x-rays. The more opaque a material, the more x-rays are blocked and the whiter the material appears on a radiograph. One of five basic opacities is assigned to a material; gas, fat, soft tissue, bone, or metal. The inherent opacity of a material is related to its density (atomic number and degree of compaction). Overall opacity of a material relates to its thickness.

Question 21

opacity interface

Answer 21

The visible difference in shades of gray between two adjacent structures which allows them to be differentiated on a radiograph. Without opacity interfaces, a radiography would be homogenous, with no visible structures (see relative opacity). Opacity interfaces are affected by body condition (e.g., emaciation, immature age) and disease processes (e.g., effusion) and should not be confused with detail (affected by technical factors) or definition (refers to margination of a lesion).

Question 22

organic iodinated compounds

Answer 22

Positive contrast agents commonly used to study intravascular, intrathecal, intraarticular, and soft tissue structures. High atomic number and mass of iodine result in high opacity in these agents, which are available as ionic (hypertonic) and nonionic (isotonic) preparations.

Question 23

orthogonal radiographs

Answer 23

Radiographs made at right angles (perpendicular or 90 degrees) to each other. Radiographs are two-dimensional images of three-dimensional subjects and orthogonal projections are required for meaningful evaluation.

Question 24

ossification

Answer 24

The process of creating new bone by osteoblasts, usually in a cartilaginous or fibrous tissue matrix. Calcification occurs during ossification, but the reverse is not true.

Question 25

ossification center

Answer 25

A site of bone formation; primary centers of ossification develop in the diaphyses; secondary centers develop in the epiphyses and apophyses; and accessory centers form sesamoid bones.

Question 26

orthogonal

Answer 26

is the relation of two lines at right angles to one another (perpendicularity)

Lung lesions should be identified on at least 2 orthogonal rads.