ARRT Limited Scope cheat sheet

Standard precautions apply to all patients: gloves for contact with blood, body fluids, mucous membranes, and nonintact skin; gown, mask, and eye protection when splash exposure is likely.

Patient identifiers must be verified with two independent identifiers (name plus date of birth or medical record number) before any examination or contrast administration.

Informed consent requires that the patient be told the procedure, its risks and benefits, and alternatives, and that consent be given voluntarily by a competent patient or legal guardian.

Medical asepsis reduces transmission of organisms; surgical asepsis (sterile technique) is required for any procedure that breaches skin or enters sterile body cavities.

Normal adult vital signs: oral temperature 36.1-37.8 C (97-100 F); pulse 60-100 beats/min; respirations 12-20/min; blood pressure approximately 120/80 mmHg.

Signs of an acute contrast reaction include urticaria, flushing, bronchospasm with wheezing, hypotension, and laryngeal edema; anaphylaxis is treated with epinephrine per protocol.

Lifting rule: keep the load close to the body, bend at the knees and hips rather than the waist, and avoid twisting the torso while bearing weight.

Fall prevention for a weak or unsteady patient includes a gait belt, locked stretcher or wheelchair wheels, and never leaving the patient unattended on an elevated surface.

ALARA: occupational dose is kept as low as reasonably achievable by limiting time, maximizing distance, and using appropriate shielding.

Inverse square law: intensity varies as 1/d squared, so doubling the distance from the source reduces exposure to one quarter.

Annual occupational effective dose limit is 50 mSv (5 rem); the lens of the eye limit is 150 mSv (15 rem); the extremity/skin limit is 500 mSv (50 rem).

Effective dose limits for the public are 1 mSv (0.1 rem) per year; the limit for an embryo-fetus of a declared pregnant worker is 0.5 mSv (0.05 rem) per month.

Primary protective barriers attenuate the useful beam; secondary barriers attenuate leakage and scatter radiation and require only about 1/1000 of the primary barrier thickness.

Lead shielding equivalent is 0.25 mm Pb for general diagnostic work and 0.5 mm Pb for fluoroscopy and higher-kVp procedures.

The x-ray tube housing must limit leakage radiation to no more than 100 mR per hour (about 1 mGy/h) at 1 meter from the focal spot at maximum rated technique.

Collimation to the smallest field that includes the anatomy reduces patient dose and scatter and improves image contrast by limiting Compton scatter reaching the receptor.

Occupational dosimeters are worn at collar level outside the lead apron; a second dosimeter at waist level under the apron is used during fluoroscopy to estimate fetal or effective dose.

Subject contrast is the difference in x-ray attenuation among tissue structures; radiographic (receptor) contrast is the visible difference in optical density or pixel value on the image.

Increasing kVp raises beam penetrability, lowers subject contrast (longer scale of contrast), and reduces patient dose for a given receptor exposure.

mAs controls the quantity of x-rays and is directly proportional to receptor exposure; doubling mAs doubles exposure if all else is constant.

The 15 percent rule: an increase of 15 percent in kVp approximately doubles receptor exposure, so mAs is halved to maintain exposure.

Milliampere-seconds and distance relate by the inverse square law; source-to-image distance changes require mAs compensation by the square of the distance ratio.

Geometric unsharpness increases with larger focal spot size, larger object-to-image receptor distance, and shorter source-to-image receptor distance.

Motion blur is controlled by short exposure times and patient instruction; it is independent of focal spot and distance factors.

Quantum mottle (noise) appears when too few photons reach the receptor; it is corrected by increasing mAs, not by increasing kVp alone.

Distortion includes magnification (object farther from receptor) and shape distortion from tube or part angulation; elongation results from tube angulation, foreshortening from part angulation.

PA chest: patient upright, chin elevated, shoulders rolled forward, 72-inch source-to-image distance, exposure at full inspiration with the beam centered at T7 (about 3-4 inches below the vertebra prominens).

Lateral chest: left lateral with arms elevated, 72-inch distance, exposure at full inspiration, beam centered at the midcoronal plane at the level of T7.

Chest evaluation: posterior ribs should appear roughly symmetric, the clavicles should be equidistant from the midline, and 9-10 posterior ribs should be visible above the diaphragm.

AP projection of the elbow shows the radial head, radial tuberosity, and capitulum in profile; the lateral projection requires 90 degrees of elbow flexion.

PA hand: palmar surface on the receptor, fingers separated, central ray perpendicular to the third metacarpophalangeal joint; the hand is the most commonly fractured body part.

AP knee: patient supine or seated with the knee flexed slightly, patella directed anteriorly, central ray angled 0-5 degrees cephalad to the mid-patella at the level of the joint space.

Cervical spine lateral: patient upright, chin elevated, shoulders depressed, 72-inch distance, beam centered at C4; C1 through C7 should be visible with the mandible clear of the upper vertebrae.

Lumbar spine AP: patient supine with hips and knees flexed to reduce lordosis, beam centered at L3 (about 2 inches above the iliac crests), collimated to include T12 through the sacrum.

Spine evaluation: intervertebral disk spaces should be open and even, spinous processes midline on AP projections, and vertebral end plates superimposed on lateral projections.

Skull PA (Caldwell): patient prone or upright with the orbitomeatal line perpendicular to the receptor, central ray angled 15 degrees caudad, exiting the nasion.

Skull lateral: patient with the interpupillary line perpendicular to the receptor and the midsagittal plane parallel to it, central ray 2 inches superior to the external auditory meatus.

Skull AP (Towne): central ray angled 30 degrees caudad to the orbitomeatal line, exiting the nasion, to project the occipital bone and foramen magnum.

Skull positioning lines: the orbitomeatal line passes from the outer canthus to the external auditory meatus; the infraorbitomeatal line passes from the infraorbital margin to the external auditory meatus.

Supine abdomen (KUB): patient supine, arms at the sides, beam centered at the level of the iliac crests, collimated to include the symphysis pubis through the diaphragm; exposure at end of expiration.

Abdomen evaluation: the psoas muscle margins, kidney outlines, and bowel gas pattern should be visible; the iliac crests should appear symmetric.

AP pelvis: patient supine with the midsagittal plane centered, feet internally rotated 15-20 degrees to place the femoral necks in profile, beam centered midway between the anterior superior iliac spines and the symphysis pubis.

Pelvis anatomy: the pelvic inlet (brim) is bounded by the sacral promontory, arcuate lines, pectineal lines, and pubic crests; the pelvic outlet is bounded by the coccyx, ischial tuberosities, and pubic arch.

Hip AP (unilateral): central ray perpendicular to the femoral neck, centered about 2 inches distal to the midpoint of a line between the anterior superior iliac spine and the pubic symphysis.