Radiology and Imaging

X-rays should be taken:

WEIGHT-BEARING

ANGLE AND BASE OF GAIT

Feet abducted 15°

Medial malleoli 2″ apart

STANDARD FOOT X-RAYS

A/P, Lat, MO

EXPOSURE FACTORS

Kilovoltage peak (kVp) is the component that controls the radiographic contrast or gray scale in the film. Increasing the kilovolts produces a more penetrating x-ray, with increased latitude, a shorter exposure time, and less x-ray tube heat. Increasing the kVp results in less exposure to the patient.

Milliamperage (mA) controls the quantity or amount of x-ray emitted from the x-ray tube and is the most important component controlling radiographic density. To reduce radiation exposure, decrease mA.

Distance: To achieve maximum fidelity (true size/shape of original object), the distance of the object to the film must be kept to a minimum. A small focal spot gives better detail.

RADIOGRAPHIC TERMINOLOGY

Compton effect: The Compton effect occurs when an x-ray photon
interacts with an outer shell electron. The Compton effect occurs mostly above 80 kVp. It causes less radiation to the patient and is detrimental to the image.

Grid: Composed of alternating strips of lead and aluminum spacers to control, by absorbing, scatter radiation

Collimation: A method of limiting the area of an x-ray beam, which by law cannot exceed the film size. A light beam from the collimator maps the area of the x-ray beam.

Photoelectric effect: Occurs at lower kVp when an x-ray photon collides with a lower shell electron. The electron is ejected, and another higher shell electron fills its space, releasing energy. The photoelectric effect is beneficial to the image, but results in greater absorption of radiation by the patient.

Orthoposer: The platform that enables weight-bearing images of the foot and ankle to be obtained. X-ray film or image receptors on the Orthoposer can lie flat or be placed vertically.

Hard x-rays: Hard x-rays are produced by increased kVp. They have a short wavelength, high frequency, and increased penetration and are less dangerous to the patient. Hard x-rays have higher energy, with photon energies above 5 to 10 kVp.

Soft x-rays: Soft x-rays are produced by decreased kVp. They have a long wavelength, low frequency, low penetration, and lower energy and are more dangerous to the patient.

Computed Radiography (CR) vs. Digital Radiography (DR)

CR radiography is taken in the usual way, but uses a reusable CR-specific cassette instead of standard x-ray film. The image on the cassette is then run through a CR reader, where the image is scanned into a digital format.

DR radiography transfers the x-ray directly into a digital signal.

Slow vs. Fast Speed Film

The larger the size of the AgBr crystals, the thicker the emulsion layer. The faster the film, the darker the image.

X-Ray Machine Requirements (Vary by State)

Dead-man type exposure switch with a 6-ft cord.

Machines <70 kVp do not need 1° or 2° barriers or special lead lined rooms (the majority of podiatric x-rays are taken below 70 kVp).

Lead aprons, gloves, and goggles are 0.25 mm thick; gonadal shields are 0.5 mm lead equivalent.

Relative Radiographic Densities

Cortex – Cancellous – Muscle – Nerve – Tendon – Ligament – SubQ – Fat – Air

Highest density——->——-Lowest density

PODIATRIC X-RAY VIEWS

Dorsoplantar (DP) or Anteroposterior (AP)

Central ray aimed at the second metatarsocuneiform joint

15° from vertical

When examining the foot for a foreign body, this view may be taken perpendicular for better spatial location.

Lateral

Medial side of foot against film

Central ray aimed at cuboid

Tube is angled 90° from vertical.

Non-Weight-bearing Medial Oblique (MO)

Center beam at 3rd metatarsocuneiform joint.

Angle the foot 45° with the medial side of the foot on the image receptor.

Non-Weight-bearing Lateral Oblique (LO)

Central ray aimed at 1st metatarsocuneiform joint

Angle the foot 45° with the lateral side of the foot on the image receptor.

Stress Lateral or Stress Dorsiflexion

Position patient for a lateral but then have patient flex knees and maximally dorsiflex ankle

Demonstrates any anterior ankle impingement (osseous equinus)

Plantar Axial

Head angled at 90° to the vertical

Aimed at the plantar aspect of the sesamoids

Good view of sesamoids and plantar aspect of metatarsal heads

Toes dorsiflexed against film and then raise heel

Positioning device may aid in taking this projection.

Harris-Beath (SKI-Jump)

Good for posterior and middle STJ coalitions

Patient stands on film with knees and ankles flexed 15° to 20°

First take a scout lateral film and determine the declination angle of posterior facet of STJ. Then take three views: one at the angle determined by the lateral film, one 10° above, and one 10° below.

Some advocate three arbitrary views at 35°, 40°, and 45°.

Calcaneal Axial

Central ray aimed at posterior aspect of calcaneus

Angle unit at 45°

Examines the calcaneus for fractures, abnormalities in shape, or internal fixation in major tarsal fusions

Good view for assessing the middle and posterior STJ facets

Isherwood

Three positions to fully visualize the STJ

Medial Oblique Position

Visualizes the anterior facet of the STJ

Foot is positioned the same as for a non-weight-bearing medial oblique x-ray.

Central ray aimed between the fibular malleolus and the cuboid

Medial Oblique Axial Position

Visualizes the middle facet of the STJ

Foot adducted 30° from image receptor

Dorsiflex and invert the foot using a sling

Central ray aimed between the fibular malleolus and the cuboid

Tube head angled 10° cephalad

Lateral Oblique Axial Position

Visualizes the posterior facet of the STJ

Foot abducted 30° from image receptor

Dorsiflex and evert the foot using a sling

Central ray between the tibial malleolus and navicular tuberosity

Tube head angled 10° cephalad

Stress Inversion (Talar Tilt)

Position the stress inversion view the same as an ankle AP view.

Examiner wears lead gloves.

Stabilize lower leg with one hand while forcefully inverting foot with other hand.

Performed following ankle inversion sprains, may need to anesthetize foot (common peroneal block) for pain relief and to relax foot.

Assess lateral ligamentous injury, specifically the ATF and CFL.

Positive is a test greater than 10° or if the talar tilt is 5° greater than the unaffected ankle.

Anterior Drawer or Push-Pull Stress

Patient supine or sitting with leg in lateral position. Stabilize leg with one hand and place an anterior dislocating force on the foot with the other hand.

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