Distortion

Distortion

Is a misrepresentation of size or shape of the structures being examined

Size or shape distortion

Misrepresentation can be classified as either ... or ...

Film/screen radiography

Size distortion can only be magnified with ...

Magnification size distortion

is controlled by positioning the body part and tube to maximize SID while minimizing OID.

OID

Is the critical distance for magnification and resolution

20 inches or 50 cm

Reasonable SID as discussed in the 1918 "Extract from the United States Army X-ray manual"

1918 "Extract from the United States Army X-ray manual"

First recognized X-ray techniques book in the United States

25 in (63 cm) to 36 in (90 cm)

In 1928, "Modern X-ray Technic", Ed Jerman recommended SID distances from ... to ...

40 in (100 cm)

Glenn Files 1945 book "Medical Radiographic Technic" recommended an SID of ...

Shape distortion

is the misrepresentation by unequal magnification of the actual shape of the structure being examined

Elongation

projects the object so it appears to be longer than it really is

Foreshortening

projects the image so it appears shorter than it really is

Alignment

Shape distortion can be caused/avoided by careful ... of the central ray with the anatomical part and the image receptor

Central ray

- is the theoretical photon that exits from the exact center of the focal spot

- Ideally is intended to be projected perpendicular to both the anatomical part & the image receptor

Elongation

occurs when there is poor alignment of the tube and/or image receptor

Foreshortening

Occurs only when there is poor alignment of the part

Angulation

refers to the direction and degree the tube is moved from its normal position perpendicular to the image receptor

Longitudinal

The most common direction of the tube angle is ...

cephalad

Longitudinal angulation in which the tube is angled toward the patient's head

caudad

Longitudinal angulation in which the tube is angled toward the patient's feet.

roll

Radiographic tubes angled transversely

Degree

Is simply a method of describing the exact amount of angulation and is usually stated as the angle between the central ray and the image receptor plane from the standard reference point of perpendicularity