radiology Flashcards
name the order of the rays
radio, micro, infrared, vl, UV, xrays, gamma (most dangerous)
focal spot
- located on the anode
- area on target where focusing cup directs electrons from filament. Sharpness of radiograph increases as size of this spot decreases (can be done by dec angulation)
why is tungsten the best
- high atomicc number, high melting point, thermal conductivity, low vapor pressure
bensons line focus principle
- smaller the anode tilt, the smaller the effective focal spot
cathode
- in mA, contains the filament
anode
- positive
- kV, contains focal spot and tungsten target
mA determines
number of e made, increasing this will increase quantity of xray beams
kVp
(kVp is for AC, KvC is for DC which is better)
determines energy of the xrays produced
- increases the quality of the xray
filtration
reduces intensity, increases the mean energy so less rad to patient
target object distance
- increase it means increased image sharpness!!
photoelectric absorption
- the scatter ray that interacts with matter to form the image
particulate radiation
alpha, beta, cathode
compton scatter
- most interaction, cause of scatter
coherent scatter
least common scatter
attenuation
absorption of individual photons in the beam by atoms in tissues or photons being scattered
beam hardening
- increase mean energy and decrease intensity
cell cycle and radiosensitivity
- less radiosensitive in g1, least in s phase, most in g2 and m phase
chromosome aberration
occurs when rad before DNA synth
chromatid abberation
after dna synth rad
what cells are rad resistant and which are most
- fully differentiated cells
- lymph ccells are MOST
where does most radiation come from
radon and ct scan
best radiographic practice
- usse E/F speed film
- rare earth screen for films
- use CBCT for region of interest
personal protection
stand more than 6 ft away, use backscatter shield
- use long cone head
- stand at 90 to 135 degrees from central beam
collimators
rectangular is 66% less area than round!
parallelling technique
- sensor is parallel to central axis
- longer object film distance (16”)
- pros: teeth are accurate, minimal distortion, less rad
- disadvL sensor is big, longer distance may mean higher mag and lower sharpness
bisecting angle
- beam is perp to an imaginary bisector of the angle formed by long axis of tooth and long axis of the film
- pros: easy to place, shorter cone
- disadv: hard to see film, film can bend, not dimensionally accurate
X ray is
invisible beam or photon of energy
Image receptor is
material on which the image is created. (COD/CMOSS?)
Intraoral detectors:
the thing that take the image (sensor or film)
Radiograph
is ANY kind of radiographic image (resultant image)
Visualization of films
done by air technique (of films to see them)
machine parts
has power supply
Control panel
Tube head (surrounded by oil)
Radiolucent
dark image
Lec 1, slide 15
parts of X-ray tube head
characteristic radiation
X-rays are produced by a certain photon energy called characteristic radiation. This is done by filtration (only takes short wavelength) by aluminum filter (must be 1.5 mm for 70 kVp, and 2.5 for over). This means less radiation to patient
Inherent filtration:
done by glass wall of tube, insulating oil, barrier surrounding the oil (done by natural materials)
Factors affecting image quality:
decrease kV, filter thickness, ambient light, collimator size, target, detector distance (NOT target object), focal spot size ALL increase radiographic contrast
radioactive decay
Radiation is released during radioactive decay (more high rate of decay is more radioactivity)
particulate radiation
alpha, beta and cathode rays
Deterministic effects
response is proportional to dose (but there are thresholds where no symptoms show). Effect the immediate area of radiation
- not caused by diagnostic
Stochastic effects
probability of change is dose dependent. Long term ie cancer
- caused by diagnostic
- no threshold so its all or nothing
- higher dose is more frequent effect
Direct radiation effect:
biological molecule is ionized by energy of photon (if done in s phase, it is propagated!)
Indirect radiation effect
ionization of water occurs, producing free radicals that create change (radiolysis 2/3 of effects: SEE SLIDES 23-25 of lec 2)
MOST radiosensitive
sperm, erythroblast, lymph organs, bone marrow, intestine, mucous membrane
Intermediate radiosensitivity
growing bone, salivary glands, kidney, liver
low radiosensitivity
optic lens, muscle and neurons
exposure
quantity of radiation incident on something expressed in Roentgen
- 1 c/Kg is 3870 R
dose absorbed
There is dose absorbed (what u give patient) in rad
dose equiv
biological damage produced by the radiation in rem
Sievert
1 Sv = 100 rems)
Kerma
kinetic energy released in matter
Effective dose
can’t be calculated easily! (Ht is sum of organ dose and Wt is weighting factors, eon is E = Ht x Wt)
Natural background radiation
3600 mSv per year. (10 per day)
Stochastic exposure limit
50 mSv. Deterministic is shown to cause cancer so 150 for the eye, and 500 for the skin (occupation)
Public exposure limit:
5 mSv but NOW it is 1 per year. 15 for eye and 50 for skin
How to reduce exposure (kvc, ma and distance limits)
nly take radiograph when needed, use fast image rreceptors, source to image receptor distance WILL not be less than 20 cm and SHOULD not be less than 40 cm, rectangular collimation, filtration with 1.5 mm aliuminum for 70 kVp, lead apron and thyroid collar (always visible in clinic), kVc should be 60-65 and mA should be 3.7-3.8, clinic should have shielding by walls
collimation for posterior pa and bitewing
horizontal
anterior pa and verticcal bitewing collimation
vertical
peri apical
apex of tooth and 2 mm beyond apex
bitewing
maxilla, mandible with crown, alveolar crest, 1/3 roots of each jaw, inter proximal contacts
occlusal
not used too often. Get more area in mouth. Shows the top part
unexposed receptor
image looks white and clear
overexposed
image is dark or highly dense
underexposed
image is light or low in density
how to find where a lesion is
SLOB
- if you move the same direction as the shift of the PID, the object is LINGUAL
If it moves opposite, it is buccal
Crooks tube
filament heats up, electrons release (thermionic emission)
Form electron cloud at cathode (- charge, 10v so lower power)
Voltage to anode creates a high potential difference (65-80 kvolts) and electrons bombard the anode (+)
Electrons interact with tungsten
Electrons get converted to x-ray photons as they decelerate
Angulation directs rays to filter and stream out (only short ones)
coolidge tube
- the “cool” new one
- rotating anode to stop burnout
Copper ring with oil chamber
Two circuits with step up and step down transformer
Evacuated glass
**power is used to heat filament and create voltage potential difference
cathode
filament made of tungsten
Focusing cup
- charge concave reflector (charge repels electrons) - cathode? Made of molybdenum
Anode
tungsten in copper stem (dissipates heat from tungsten). Converts kinetic energy of electrons into x rays. Only 1% works!
dose
effect is proprtional to dose
dose rate
exposure at high dose rate kills more cells per unit dose since less time to repair lethal damage
Oxygen enhancement ratio:
how much oxygen is needed to kill same amount of cells( usually less time). See the whole radical thing
LET
linear energy transfer where low let is for X-rays and high let is for slower, more damaging stuff. Impart more energy
Radiation caries:
type 1 is widespread superficial, type 2 is in cementum and dentin (most common - where teeth meet), type 3 is whole crown is dark
Xerostomia
since salivary glands are in path of radiation
Gamma ray therapy
they put a mouthguard inside
Osteoradionecrosis
soft tissue dies, then infection spreads to bone
**wait 20 days after removing tooth to irradiate. Treated with hyperbaric oxygen therapy
pano advantages
ADV: broad coverage, low radiation, easy, comfy, quick, good for patient education
pano disadv
magnification is unequal so measurement not good, lower res, image errors ()ghost, real, double), needs good patient pos, must be read well,
positioning for pano
the light must be at half of face, and one must be at the canine. Patient needs to bite on block, rest chin, Tongue must be on hard palate
- frankfort plane parallel to ground
- jaw in focal trough where image is most clear
too far in front of bite block
image is wide
bite block is too into the mouth
vertical stretch
poor light alignment pano
magnification of one side of mouth
xray face turned down
shows teeth smile going up
xray face turned up
smile goes down
double image
what you want, but shown twice. This is because there is a diamond shape in middle of mouth (tongue area) that is exposed twice, so centre structures (hard palate, cervical spine, hyoid bone and airway)
ghost image
the image is always on the side that the structure is on (so left jaw bone will be on left side of paper or “right” side of image) this is for mandible, cervical spine ALWAYS superior to real image and blurry!
- hard palate and hyoid bone are REAL double images that also produce ghost images
calcified lymph node
bottom of jaw wayyy under
Tonsilloliths
when the corners have this radiopacity underneath
Carotid artery calcification
(can see stent on R and L side)
other pathology
Impacted third molars or teeth
- trauma fracture
Pathoses
a bunch of white stuff and bone pattern has changed
digital image and pixels
image is pixels, and each one has a unique location. More pixels is more image. Smaller size pixel, smaller details can be shown. Pixels form the matrix
1 byte
8 bits
Digital vs film:
digital requires less exposure, sensor is more sensitive, 50-90% less exposure time than film!
Film is familiar, less expensive initially but slowly adds up, needs chem processing, film needs to be stored so security issue too
Digital is 80% less rad, expensive, but quicker, used in patient education, no chemicals, easy to read, can email it, very secure
analog to digital conversion (ADC)
- conversion from voltage to digital numbers. each detector corresponds to a pixel in the image
Cmos receptor:
rigid device with layers. The X-ray scintillator is most important since it creates visible light image to be captured by CMOS
- the chip is less expensive than CCD
ccd vs cmos
CMOS each component generates its own charge that is added up, while CCD move it from pixel to pixel and convert to voltage at the end
Direct digital (CMOS and CCD):adv/disadv
- sensor is exposed and transmits to computer
ADV: good resolution, less exposure, fast since image comes out instant, lower cost, efficient
DISADV: set up is expensive, quality is less, sensor is thick, infection control since can’t clean sensor, legal issues because of security
- intra and extraoral
Images are stored by
Digital Imaging and Communication in Medicine (DICOM) standards, for all imaging (can see them all over the world)
Indirect digital
expose receptor than must process it to see image
Storage phosphor: reusable imaging plate, scanner, less rapid than digital. Coated with phosphor instead of sensor (PSP plate). The laser is red, then the photodiode that is read is blue light
- can also be taking a picture of a film
Fluoresce
glows in light
phospho
glows even after light
standard film
blue light emitting
rare earth film
green
films must be
used in pairs with screen since double sided
canthomeatal plane
ear to eye
ala-tragus plane
Ear to nose
Frankfort horizontal plane
Top ear to eye
sagittal plane
Half face
axial plane
Top and bottom half face
posterior anterior ceph:
canthomeatal line at 10 degrees with film (nose on film)
Occipitomental
(waters): chin on receptor (Canthomeatal line at 37 degrees to film). Good for sinus pathology!
Reverse Townes
canthomeatal line at negative 30 to film (forehead to film, jaw open)
Townes:
jaw open, back of head on receptor (the image right is patient right!)
SMV or submentovertex:
chin up and back of head on receptor (canthomeatal plane is parallel to film
Lateral ceph
side head on receptor. This is uneven mag of left and right sides
Double space arthrogram
for jaw disk thinng??
Ct scan has 3 views,
coronal (front), sagittal (patient right), axial (looking up from toes to nose)
MRI
where bone is black and tissue is white
why do a pano
- evaluation of dentition and TMJ
- examine lesions
0 pos of impacted teeth - trauma
- check up of permanent dentition
- can’t do intraoral
how much dose for a bitewing with PSP or F speed film
5 microSV, 0.6 day
full mouth using PSP for F speed film
5 days 40 micro SV
full mouth with CCD sensor
20 micro SV, 2.5 days
pano dosage
20 micro Sv, 2.5 days
where to stand when xray if you must
90 to 135 degrees of beam (by patient ears)
object film distance
- stay small so image is not magnified
source film distance
long so less magnification
CCD stands for
charged coupled device
- most common
CMOS stands for
complementary metal oxide semiconductor
PSP stands for
photostimulable phosphor plate
make sure to also review kendra’s study guide for FMS pictures
GO DO IT
1 gray = how many rad
100
1 sV = how many rems
100
diagnostic radiation
- low dose and long term
therapeutic radiation
high dose, short and long term
radiolysis
- usually forms water or h2 with free radical
- OR can use water to generate h20+ (if photon takes e)
or h20- if electron gets added to water
h20+ and water make
h20+ and OH- (hydroxyl free radical)
h- and oxygen make
h02- superoxide radical
2 h20- make
hydrogen peroxide, h202
worst and best film to use
worst is D film with round collimator
- best is F speed with rectangular collimator
receptors used for paralleling technique
- size 1 for anterior, vertial direction
- size 2 for posterior, horizontal direction
bitewings indications
- proximal margins of restorations
- perio disease
- when teeth are in contact, history of smooth surface caries
angulation erros
forshortening (teeth look short) from excessive vertical angulation
- elongation from insufficient vert angulation
- pan beam has negative vertical angulation so lingual objects are higher and buccal are lower
multistep image capture process
each detector corresponds to a pixel
- x rays are absorbed in scintillator (captures the x ray and turns it to light)
- light is transmitted to CMOS that produce electrical charge within each pixel
- voltage is proportional to number of photons which is converted to a digitized value and processed by computer
full mouth PSP or F speed with round collimator
400 mSv, 48 days
full mouth with CCD sensor round collimator
100 mSv, 12 days
