Radiology Physics & Safety Flashcards
Radiology physics
- X-rays are part of the electromagnetic spectrum, which also includes radio waves, microwaves, infrared, visible light, UV, and gamma rays
- The difference between these rays is the amount of energy, frequency and wavelength
Wavelength
Defined as the distance between two similar points on two successive waves
Frequency
Can be defined as the number of waves that pass a given point per unit time
- The sorter the wavelength, the higher the frequency
- X-rays have very short frequency and high energy
X-ray production
- Fast moving electrons are released from x-ray tube
- The tube contains a heated tungsten filament and a cathode
- The electrons slam into a metal object (the anode)
- 99% of the electrons produce thermal energy in this process, only 1% actually produce x-rays
Energy difference and transfer
- The energy difference going from cathode to anode is measured in kilivolts (kV)
- When the electrons strike the target, the energy is transfered in the form of kinetic energy (KE=1/2mv^2) where m = mass and v = velocity
Image formation
Factors controlled by operator:
- mA, which idicates number of electrons that reach the anode (high mA = dark film, low mA = light film)
- kV, which indicates the penetrating power of the electrons
- Distance from x-ray tube
“Soft x-rays”
- Lower voltage = decreased speed of electrons
- Lower speed electrons = longer wavelength x-rays
- Decreased penetrating power
Produced by decreased kVp, have long wavelength, low frequency, low penetration and are more dangerous to the patient
“Hard x-rays”
- Increased voltage = increased speed of electrons
- High speed electrons = shorter wavelength x-rays
- Increased penetrating power
Produced by increased kVp, have shorter wavelength, higher frequency, increased penetration and are less dangerous to the patient
Intensifying screens
Intensifying screens, which are within the film cassette, convert the energy of the x-ray beam into visible light
After the image is intensified, a fluorescent image is produced and recorded on photosensitive film
Roentgen
International unit of quantity of radiation exposure
Ionization of air by radiation
Radiation absorbed dose (rad)
Unit of absorbed dose by the patient
1 RAD = 100 ERGS of energy per gram of tissue
Roentgen equivalent man (rem)
Unit of biological exposure in man
Equivalence between roentgen, rad and rem
1 roentgen = 1 rad = 1 rem
Curie (Ci)
Unit to measure radioactivity
Lethal dose
The dose of radiation that will result in death within 30 days in 50% of people
300 rad in a human
Radiation effects of gonads
10 rads = delayed menstruation/decreased spermatozoa
200 rads = temporary sterility
500 rads = permanent sterility
Fetal dose of radiation
10 rads
- Spontaneous abortion rate increases by 0.1%
- Congenital abnormalities increase by 1%
- Malignant disease increases
Leakage radiation
All radiation from within the x-ray tube housing except the useful beam
Scatter radiation
Radiation that, during the passage through matter, has deviated in a direction beyond the image plane
Radiation protection ALARA concept
“As low as reasonably achievable”
- A principle to protect occupational exposure to radiation
- Three basic principles: time, distance and shielding
Time, distance, shielding
- Radiation directly proportional to time exposed to radiation
- Reduced radiation by keeping greater distance
- Shielding your body from radiation via protective equiptment
Structural barriers
- Walls and doors
- Control-booth barrier
Control booth barriers
Must be at least 7 feet tall from floor and be permanently secured
Primary protective barrier
A wall that lies directly perpendicular to un-deflected line of travel of x-ray beams and its purpose is to prevent direct or un-scattered radiation from reaching the public
Secondary protective barrier
Protects the personnel/public against secondary radiation that may leak or scatter, essentially, it is any wall or barrier that is never struck by the primary x-ray beam
Accessory protective equiptment
Lead impregnated vinyl
- Aprons
- Gloves
- Thyroid and neck shields
Protective eye glasses to shield lens of eye
Protective maternity apparel to protect pregnant radiologists and radiographers
Limiting x-rays
Avoiding repeated x-rays, which diminishes unnecessary exposure
Collimating (restricting) and filtrating x-ray beam
Limits the amount of low-energy photons that interact with the patient’s body and the amount of scattered radiation that enters the room
Compton effect
Scatter radiation caused by interaction with outer shell electrons
It causes less radiation exposure to the patient and is detrimental to the image
Collimators
Light beam that shows where the x-ray beam will project
Photoelectric effect
The absorbed radiation involving interaction with the inner electron shell
It is beneficial to the image and increases the exposure to the patient - increases at lower kVp
Orthoposer
The elevated lead lined base of the x-ray unit which the patient stands on during the x-ray
Relative densities
HIGH density - Cortical bone - Cancellous bone - Muscle - Nerve - Tendon - Ligament - Subcutaneous tissue - Fat - Air LOW density
AP image
- Aimed at lateral portion of navicular
- 15 degrees from vertical
Lateral image
- Medial side of foot against film
- Central ray aimed at cuboid
- Tube angled 90 degrees from vertical
Medial oblique image
- Center beam at lateral (3rd) cuneifom)
- Angle unit 45 degrees from vertical
Lateral oblique image
- Central ray aimed at navicular
- Center beam at 45 degrees from vertical
Stress lateral or stress dorsiflexion image
- Flex knees and maximally dorsiflex ankle
- Demonstrates any anterior ankle impingement (osseous equinus)
Plantar axial image (sesamoid axial)
- Head angled at 90 degrees to vertical
- Aimed at plantar aspect of sesamoids
- Good view of sesamoids and plantar aspect of metatarsal heads
- Toes dorsiflexed against film and then raise heel
Harris Beath (ski-jump)
- Good for posterior or middle STJ coalitions
- Angle unit 45 degrees
- Patient stands on film with knees and ankles flexed 15-20 degrees
- Take 3 views: 35, 40 and 45 degrees
Calcaneal axial
- Central ray aimed at posterior aspect of calcaneus
- Angle unit at 45 degrees
- Examines calcaneus for fracture, abnormalities in shape or internal fixation in major tarsal fusion
Stress inversion (talar tilt) image
- Patient supine or sitting in chair, internally rotate foot 15 degrees while stabilizing leg
- Central ray focused at ankle joint
- Performed after ankle inversion sprains
- May need to anesthetize foot for pain relief and relaxation
- Assesses for lateral ligamentous injury
- Positive if talar tilt is greater than 4 degrees of inversion
Anterior drawer test
Positive test is greater than 2 mm excursion of the talus out of the ankle mortise
Ankle mortise image
- Leg internally rotated 15 degrees, placing malleoli in a plane parallel to the film
- Better view of tib fib articulation
- X-ray head set at 90 degrees to vertical
- Aimed at center of ankle joint
- Articular relationship between trochlea of talux and tibial plafond
- Space between lateral malleolus and talus
Accessory bones
12 to know in the foot…
Os vesalianum
5th metatarsal styloid process
Os trigonum
Lateral tubercle of posterior process of talus
Os peroneum
In peroneus longus as it courses under cuboid
Os sustentaculum tali
Sustentaculum tali
Os calcaneus secondaris
Anterior process of calcaneus
Os tibiale externum
In tibialis posterior tendon at medial aspect of navicular, AKA accessory navicular
Os intercuneiform
Intermediate cuneiform
Os intermetatarsum
Between bases of 1 and 2
Os talonavicular dorsale
Dorsal TN joint
Fabella
Sesamoid bone in teh lateral head of gastroc muscle (behind knee)
