Tech, Positioning, Special Imaging Flashcards
What part of the x-ray machine PRODUCES x-ray?
The tube comprised of a glass envelope, exit window, cathode (- small and large filaments with focusing cup) and anode (+ target plate slanted 12o)
What is the housing of the tube made of?
Lead-lined steel or aluminum and contains oil
When to use small vs large filaments?
Small: smaller targets, longer exposure time, more penumbra
Large: larger objects, shorter exposure time, less penumbra
Characteristic radiation aka Hard x-rays:
10-15% of beam and doesn’t contribute to formation of image
Bremsstrahlung radiation aka Braking radiation AKA soft x-rays:
85-90% of x-ray beam and creates image
Deflected x-rays create?
Filmfog
Compton effect:
interacts with matter causing ionizing radiation which may damage tissues with lots of H+ (fat)
How does a grid help with the Compton effect?
Reduces scatter radiation that reaches the film
Photoelectric effect:
X-rays completely absorbed by patient and has no effect on film
Radiographic noise:
Unwanted radiographic densities that obstruct viewing of structural details on film
Artifact:
Caused by objects in or on patient like necklaces, rubber bands, implanted medical devices or caused by damage to film emulsion
Three types of mottle:
Quantum: variation in density of uniformly exposed film from random spatial distribution of x-ray quanta absorbed in screen
Structure
Film graininess
Ways to reduce scatter radiation:
Reduce beam size, increasing kVp, decreasing field size (collimation, grid, air-gap),
Thermionic emissions:
Boiling off of electrons from heated filament, current is mA increasing current current increase temperature increases number of electrons generated
Rectifier:
Converts AC to DC voltage measured in kVp and affects speed of electrons
Port filters:
made of aluminum and decrease amount of radiation patient is exposed to and decrease the amount of tissue damage
Collimator:
Device made of two layers of metal laid at right angles narrows field size to reduce pt exposure dose, scatter and improves quality of film
Lead shields
Prevent x-rays from passing through organs like gonads, thyroid, etc
Increasing the mA brings what filament into play? Decreasing?
Large filament
Small filament - sharper image
Good and best grid ratios?
12: 1
6: 1
Put in order: grid, film, pt
Pt, grid, film
Intensifying screen:
Made of small phosphorus crystals, two of them on either side of film, crystals fluoresce and expose film, large crystals increase light and small ones increase detail
Silver halide crystals:
embedded in emulsion layer of gelatin in film plastic which is sensitive to light emitted by screens and x-rays
Six processing steps of film:
- Pre-wet - allow chemicals to penetrate emulsion uniformly
- Develop: in solution for 5 seconds so silver halide crystals reduce to black metallic silver raising temperature 1o will decrease developing time by 20%
- Stop bath: water + acetic acid for 30s to stop action of developer
- Fix: solution for 10 minutes, stops development, hardens film, sodium thiosulfite and reclaim silver from old films
- Wash: removes developer and fixer, prevent brown film
- Dry
Density:
Overall blackness of film
Directly proportional to kVp and mA (1o)
Contrast:
Differences in shades of gray in film and indirectly related to kVp (low contrast high kVP, high contrat, low kVp)
Detail:
How clear structures are visualized
How would you increase detail?
Increae FFD, decrease OFD or kVp
FFD of 40” vs 72”
40: more radiation, penumbra, magnification and less detail
72: less radiation, penumbra, magnification, and more detail
Inverse square law:
radiation intensity is inversely related to square of FFD
50/15 rule:
50% decrease in mAs is equivalent to a 15% increase in kVp
16:20% rule:
Decrease kVp by 16% you have to double mAs or it will halve the film density
If you increase kVp 20% you have to decrease mAs by half or you will double the film density
Increasing kVp will:
increase film exposure, scatter radiation, fog and decrease contrast
Increasing mAs will:
increase film exposure and darken film
Anode heel effect:
Cathode should be closer to larger or fatter part of the object
Bergonie-Tribondeau law:
Radiosensitivity of tissue is directly proportional to the rate at which the tissue multiples
What are radiosensitive tissues?
Gonads, bone marrow, lymphoid tissue, colon, lungs
What are radioresistant tissue?
Brain, spinal cord, thyroid, muscle
HVL:
High value laser, thickness of a material needed to attenuate intensity of the x-ray by 50%
Rem:
Roentgen equivalent in man; unit of ionizing radiation
Sievert:
Unit of ionizing radiation absorbed dose equivalent to 100 Rems
Millisievert:
1000th of a Sievert [10^-3 SV]
RAD:
Radiation absorbed dose
RBE:
Relative biological effectiveness
What to do if a film is underexposed? Overexposed?
Increase mAs
Decrease mAs
What films are taken at 72”?
Cervicals: lateral, obliques, flexion, extension
Chest: P-A, lateral
Lateral sternum
Full spine AP and later
What film are PA?
Skull, mandible, chest, wrist, tunnel, patella
Which films are inhale and hold?
PA, lateral chest (not if pneumothorax)
AP full spine
AP and lateral thoracic spine
When should grids be used?
Body parts >12cm to reduce scatter radiation with at least 70 kVp
Which films have caudal tube tilts?
Cervical anterior oblique
Lateral lumbar
AP coccyx
Y-scapular
Holmblad is also known as?
Intercondylar and Tunnel
The sunrise view of the knee is also known as?
Tangenital
The abduction view of the shoulder is also known as?
Baby arm
The caldwell view is for what anatomy?
Frontal sinus
The towne view is for what anatomy?
Foramen magnum
The water view is for what anatomy?
Maxillary sinus
The lateral skull view is for what anatomy?
Sella turcica
The apical lordotic view is for what anatomy?
Pancoast tumor
The Sunrise view is for what anatomy?
Apical view of the patella and intercondylar groove
Cervical anterior oblique tube tilt, central ray focus?
150 caudal
C4; RAO shows R intervertebral foramina
Cervical posterior oblique tube tilt, central ray focus?
15o cephalad
C4; RPO shows L intervertebral foramina
AP Lower cervical tube tilt, central ray focus?
15o cephalad
C4
Lateral lumbosacral tube tilt?
5o caudal
AP coccyx tube tilt, central ray focus?
10o caudal
1” superior to symphysis pubis
PA lumbosacral spot tube tilt, central ray focus?
30o cephalad
L5 spinous process
AP sacrum tube tilt, central ray focus?
15o cephalad
1/2 btw ASIS and symphysis pubis
AP Foot and medial oblique tube tilt, central ray focus?
10o cephalad
Base of 3rd metatarsal
Axial patella tube tilt?
10-20o cephalad
Lateral and AP knee? tube tilt, central ray focus?
5o cephalad
Center of joint and inferior pole of patella
APOM tube tilt, central ray focus?
5o cephalad
Through the uvula of the soft palate
CT (Computerized Tomography)
Conventional X-radiation measured in Hounsfield unit produces reconstructed axial images with a thin fan-shaped x-ray beam (rotate around pt in 180o arc in serial or spiral fashion) producing slices 1-10mm thick, image tends to be grainy
Pros to CT:
Contrast resolution 95X better than conventional radiography, can make 3D images of any part of the body, good for intraspinal and intracranial masses, bleeding, spinal canal stenosis, abdominal masses, bony structures, lung pathology, disc
Cons to CT:
Excludes very large patients, pregnant people, induce sense of claustraphobia, increased exposure to ionizing radiation
MRI:
Large magnetic field (30,000X >than Earth’s magnetic field) to generate radio frequency waves measured in Tesla units and measures how much H+ reacts to magnetic and radio waves
T1 for fatty tissues as white - gadolinium contrast
T2 for water as white
Pros to MRI:
No radiation, good for spinal cord and brain pathology, disc lesions, solid organ pathology, mets, demyelinating CNS disorders, musculotendinous disorders
Cons to MRI:
claustraphobia, no large patients, contraindicated for pacemakers and defibrillators, intracranial aneurysm, surgical clips, cochlear implants, neurostimulators
Radionuclide Bone Imaging (Bone scan, Bone Scintigraphy):
Use radioactive pharmaceuticals (technetium 99, indium 111 labeled WBCs) injected into patient and gamma camera to create the images, radioactive material is taken up by osteoblastic tissue (SI, AC, SC joints, kidney, tips of scap, frontal parasagittal regions of the skull, costochondral joints, occult fx, AVN,PE, blastic mets, osteomyelitis)
Diagnostic Ultrasound:
High frequency sound waves to investigate suspected vascular diseases (AAA, carotid/vertebral A disease, pregnancy, ovarian disease, cholelisthiasis)
fMRI
Measuring brain activity by detecting changes inblood oxygenation (hemoglobin contains iron can be magnetized) and more active areas of the brain require more oxygen resulting in change in density of the magnetic signal
For pt’s suffering from depression, schizophrenia, fibromyalgia
PET
Measure regional cerebral BF using radioactively labeled tracer glucose molecules since most tumors preferentially use glycolytic pathway for energy there’s a greater concentration of radioactive glucose in malignant tissues (Warburg effect)
SPECT
Injection of radionuclide into blood stream and pictures are taken w/gamma camera
When do you use a barium swallow?
Visualize
ALARA:
Radiation exposure should be kept AS LOW AS REASONABLY ACHIEVABLE
10 day rule:
Limit exposure to radiation to 10 day period following onset of menses in a female
American College of Radiology Practice Guidelines for the performance of Spine Radiography in Children and Adults (2007):
Evaluation of: pain or limitation of motion, spinal trauma (symptomatic or in at risk patients), previous surgery, suspected malignancy, congenital anomalies, previously detected spinal abnormality, alignment abnormalities including scoliosis and kyphosis, shoulder or arm pain from suspected cervical radiculopathy, occipital headache, pain radiating around the chest wall, pain radiating into buttock/hip/groin, compression fracture
Canadian C-spine rules:
Radiographs if after trauma
High risk factors such as older than age 65, work with dangerous mechanisms or paresthesia in extremities
Presence of midline cervical spine tenderness or delayed onset neck pain
Unable to actively rotate the neck beyond 45o
NEXUS rules:
No x-ray needed if present after hx of injury to neck:
No posterior cervical spine tenderness, evidence of intoxication, focal neurological damage, painful distracting injury
Normal level of alertness
Ottawa knee rules:
X-rays recommended if hx of trauma to knee and:
>55 years, isolated tenderness of patella, tenderness at head of fibula, inability to flex to 90o inability to take more than 4 steps immediately and in office
Ottawa ankle rules:
> 55 years, inability to take more than 4 steps immediately and in office, local tenderness at talus, navicular, cuboid, 5th met or posterior/crest of either malleolus
