Radiology: X-Rays and Electromagnetic Spectrum

Radiology Introduction

• Radiology uses imaging for diagnoses and treatment guidance.
• Diagnostic imaging includes radiographs, ultrasound, CT scans, MRI, and nuclear medicine.

X-Rays

• X-rays are a form of radiation that transfer energy or energetic particles.
• Ionizing radiation has enough energy to cause electrons to leave an atom, thus creating ions.

Properties of X-Rays or Photons

• Travels at the speed of light.
• Cannot be refracted or reflected like light.
• No electrical charge and remain unaffected by magnetic or electrical fields.
• Travels in a straight line.
• Can penetrate matter to some degree.
• Can cause fluorescence.
• Can interact with photogenic emulsion.
• Can cause ionization.
• Cannot be felt.
• Invisible.

Electromagnetic Spectrum

• Electromagnetic spectrum spans from radio waves(low frequency, long wavelength) to gamma rays (high frequency, short wavelength).

Hazards of Radiation

• Sufficient energy can be transferred to living tissue, creating ions within the tissues.
• Molecular structure and cell changes can occur.
• Loss of cell function or abnormal cell function is possible.
• Genetic or somatic abnormalities may arise, including mutations, cataracts, leukemia/cancer, and or death.

Hazards of Radiation: Cell Sensitivity

• Most sensitive cells are that have a high division rate.
• Gonads and embryonic tissue are highly sensitive.
• Damaged sperm and eggs can carry on defects to future generations.
• Radiation exposure during the 1st trimester can cause embryonic death, congenital abnormalities, or growth defects.

Shielding

• Use personal shielding like lead or lead-equivalent impregnated clothing to protect from radiation.
• Includes gloves and aprons - 0.5 mm Pb equivalent
• Thyroid shields range from 0.25 mm to 0.5 mm Pb equivalent.
• Eye glasses - 0.75 mm Pb equivalent
• Use structural shielding such as screens and lead-impregnated doors and walls.

Image Formation

• Black areas on an image indicate all x-rays hit the receiver (digital plate or cassette and film).
• White areas indicate all x-rays have been absorbed by the patient.
• Various shades of gray indicate partial absorption by the patient, with some x-rays hitting the receiver.

Radiopacities

• Radiopacity refers to the relative inability of structures to be penetrated by x-rays. Metals with high atomic numbers prevent x-ray penetration.
• Radiolucency describes substances of low atomic number that allow x-rays to penetrate them, leaving darkened images. Air is the most radiolucent substance on a radiograph.
• Opacities are not tied to specific structures and thickness plays a role in how tissues appear.

X-Ray Machine

• The x-ray machine consists of an x-ray housing and tube, collimator, table, grid and imaging plate/cassette.

Naming Radiographic Views

• Radiographic views are named for the direction of the primary beam, starting with point of entry, followed by the point of exit.
• Ventrodorsal view of the thorax is when the patient is in dorsal recumbency, the beam enters the ventral portion and exits via the dorsum.
• Right lateral view of the thorax is when the patient is right lateral recumbency and the beam enters the left side and exits the right side. The true name is Left to right lateral view.

Viewing Radiographs

• Lateral radiographs should be viewed with the cranial portion pointing to the viewer's left.
• Ventrodorsal/dorsoventral views should be viewed with the head pointing upwards and the left side of the patient on the viewer's right.
• Limbs should be viewed with the proximal portion facing upwards, the distal portion facing the floor, and the cranial/dorsal portion facing the viewer's left.

The Views

• Radiographs are named by the direction through which the photons transverse the patient.

Cases

• "Roxy” is a 6-month old intact mixed breed female vomiting several times throughout the day and eating from the fruit trees in the yard.
• “Ally” is a 2-year-old spayed female DSH that presents to the clinic with a history of limping on the right forelimb for 2 days because of suspected trauma.