Radiology Final

pixels

Image composed of thousands of picture

elements

digit of pixel

derived from the intensity of radiation absorbed by the corresponding area on the sensor - give a number to describe grayscale

gray level of pixels

Pixel darkness - is proportional to digital value for display on monitor

Lower number = darker gray (radiolucent)

• 0 is black

high number = lighter shade of gray (radiopaque)

• 255 is white

x-ray exposure

X-rays directed through patient

remnant radiation

Pattern of radiation that exits patient after xays are scattered and absorbed

recorded on electronic sensor as altered pattern of electrons (voltage)

voltage

remnant radiation recorded on electronic sensor as altered pattern of electrons - more exposure = more voltage = radiolucent

*white has no voltage - amalgam - totally clear

Latent image

voltage pattern on sensor (pattern of electrons) - not seen until image is created

Steps in Image creation

1. Exposure: of sensor by remnant radiation

2. voltage: latent image

3. sampling: Analog-digital converter samples voltages in small discrete groups

4. quantization: ADC then assigns a number (digit) to

   each sampled area

5. Gray scale level: level of darkness ranging from black to clear,

   proportional to digital value

Photostimulable phosphor Plates (PSP plates)

thin and flexible like film

• put sensor in the scanner and expose to light (not connected to computer)

  • extra step delays appearance of image

*indirect digital radiography

Parts of PSP image plate

Base: back side with manufacturer and sensor size

Phosphor layer: europium doped barium fluorohalide layer

Protective coating: on the front with a for orientation

europium doped barium fluorohalide

makes up the phosphor layer in PSP film

• Europium ions added as imperfections

Europium ions

• added to phosphor plate as imperfections

• Exposure to x-rays excites Eu electrons to metastable state (F center) beyond the valence band

Number of electrons in the metastable state

proportional to x-ray exposure

PSP Exposure

X-rays excite Europium electrons to metastable state beyond valence band (the F center)

F center

Electrons sit in the F center during PSP exposure

• Number of electrons in the F center is

  proportional to x-ray exposure

PSP hard vs soft tissue imaging

Hard tissue: Lower exposure, fewer electrons

Soft tissue: Greater exposure, more electrons

scanning latent image steps

1. Plate with latent image is scanned by 600 nm (red) laser

2. Trapped Eu electrons released, emit light as they go back to valence band

3. Light converted to voltage

4. Voltage sampled and quantized (digitized) by ADC

5. Gray level: Each digital value given a degree of darkness

long term latent image

 Latent image will fade if not scanned quickly (more than 30 mintues)

⚫ Electrons leave the F center over time → visible image is very light

Latent image is erased after scanning

⚫ Sends any remaining electrons back to the valence band → White light floods the sensor after scanning

desktop vs laptop vs paper PSP visualizing

desktop is medical grade with superior spatial and contrast resplution for better image analysis

laptop has poorer spatial and contrast resolution

paper has poorer quality and contrast and less detail but better than transparent sheets (expensive printer)

When to use phosphor plates

Small mouth, mandibular tori (because they’re thinner and smaller)

Technical error

opperator error (sensor positioning, patient movement)

X-ray Criteria

Characteristics we need for a good-quality radiograph

X-ray retake

Technical error to the point where the criteria is not met

Evaluation symbols of x-ray

√ = No technical errors, criteria met, no retakes necessary

X = Radiograph has technical error that causes a failure to

meet criteria, retake required (error due to sensor/plate

placement/horizontal angulation/ vertical angulation/cone-cut)

? = One or more technical errors, but criteria met on film

itself or another, no retake required

S = Radiograph has no technical error, but criteria not met

due to pathologic or anatomic problems, retake required

PA distance behind 2nd and 3rd molars

6mm behind 2nd molar, 2mm behind 3rd molar

Digital vs PSP film radiation

PSP has more radiation

Technical error

operator error (positioning of sensor)

• not always an SNM - may be able to see issue on other xrays

Criteria

characteristics that must be present on the radiographs that makes the acceptable to use for dx

• if criteria is not met → re-exposure (must be documented)

check mark (x-ray)

no technical errors (Criteria met)

? (x-rays)

one or more technical errors (no retake)

X (x-rays)

technical error that fails to meet criteria (retake needed)

S (x-rays)

no technical error but criteria was not met (retake required)

• SNM

Premolar PAs bone visualization

2mm of bone around lamina dura/apex

Maxillary canine overlap

premolar can overlap slightly but lateral incisor must have open contact

Premolar bitewing

want distal caning, premolars and 1st molar

molar bitewing

2mm distal to last errupted tooth

Film placement error

move receptor/plate/sensor in the direction of the arrow

central ray error

Cone/positioning error causing a cone cut, move PID up/down, left/right according to the arrow

Vertical angulation error

Angulation error, fix by changing the steepness of the PID according to the arrow

Horizontal angle error

An issue leading to too much overlap, move the PID to increase or decrease the horizontal angle.

Double exposure error

PSP plate error where the sensor was exposed twice, causing errors in the image

Processing/Scanning error

error in PSP plates when they are placed too close in the scanner and they overlap/connect

VBW

vertical bite wing recommended due to low bone level due to bone loss

“a” on PSP plates

towards the apex on anteriors

towards the occlusal for posteriors

CRE

central ray error

SLOB rule

if the object is lingual it shifts in the same direction

If the object is buccal it shifts in the opposite direction

Hand washing for infection corntol

lather for 20 seconds, rinse for 10 seconds and repeat, dry hands and turn off faucet with towel

• before putting on gloves and after removing gloves

Infection control with PSP plates

place and seal in plastic packet (lay out on butcher paper)

• using clean hands after decontaminating plate with a caviwipe

Preparing to take a radiograph

• have patient remove and hold on to oral appliances

• place lead apron and thyroid collar without gloves on

Positioning PSP plate in bite block

blue side towards PID, writting away from opperator

Protocol for a dropped sensor

1. remove gloves and pick up sensor

2. open packet and drop sensor on shelf

3. wash hands then place sensor in a new plastic barrier

4. return to opperatory and put on new gloves

What can we touch with gloves in the opperatory

the patient and anything with plastic wrap/covering

• touching locations without plastic leads to cross contamination and technical error

Transporting cup of complete x-rays

use new gloves or overgloves to bring the cup to the dark scanning room, open each packet (can wipe before to remove saliva) and drop into the transfer box WITHOUT TOUCHING THE SENSOR (no saliva can be on it either), then remove gloves and carry to scanner

Scanning PSP x-rays

pick up sensor by the edges from transfer box with clean bare hands and place into the scanner, blue side facing scanner, words facing the operator

• green light must be on before scanning

pick up erased sensors with bare hands after they fall out of the scanner (can be reused)

most radiopaque tissue in the body

enamel

cementum

similar to dentin - attaches to PDL

PDL Space

radiolucent line outside of roots with soft tissue that anchors tooth to roots into alveolar process

*widening indicates inflammation

double PDL

seen if root has two convexities (maxillary posterior teeth

lamina dura

hard bone outside the PDL (radiopaque)

dental follicle

CT surrounding the developing tooth producing cememtum, PDL and part of the alveolar bone

• thin uniform radiolucency around the unerupted tooth

Dental Papilla

delicate CT that forms dental pulp (seen with dental follicle in xrays)

Nutrient canals

inside alveolar process carrying neurovascular tissue to bone and teeth (radiolucent)

• mostly seen in anterior mandible

trabecular bone

thin interlacing radiopaque plates and rods interspersed between rods between cortical plates of tooth roots (loss indicates ds)

• maxilla: thin and numerous (granular pattern)

• mandible: fewer (step latter appearance)

*more numerous where cortical plates are thin (maxilla and anterior mandible)

*not as many where cortical plates are thick (posterior mandible)

bone marrow

in alveolar trabecullae

Cortical bone

forms lamellar bone - outside of maxilla and mandible (margin

• smooth and sharp internal margin

incisive foramen

roof of mouth behind #8 and #9 opening of nasopalatine canals

• oval, round or heart shaped (nasal spine super imposed)

median palatine suture

line connecting the right and left maxilla between 8 and 9

incisive canals

from floor of nasal cavities to palate

• carry nasopalatine vessels and nerve to anterior palate

  • edges are hyperosotic

nasal fossae

air cavities superior to oral cavity (radiolucencies overlying anterior teeth)

• anterior wall of nasal fossa

• nasal septum

• inferior turbinate bone (concha)

Anterior Wall of Nasal Fossa

pirifiorm apetiure - bilaterally densely radiopaque below nasal fossae (nose opening)

Nasal septum

Vomer, perpendicular plate of ethmoid, cartilage (vertical, irregular radiopacity between nasal fossae)

inferior turbinate bone (concha)

attached to lateral wall of nasal fossa

anterior nasal spine

subjacent to midline 1.5-2 mm above alveolar process

Soft Tissue of nose

superimposed over maxillary anterior teeth and nasal fossae (faintly radiopaque) - nose tip and ala

lateral fossa

depression over the lateral incisor root

Lining of maxillary sinuses

mucoperiostium - filled with air

inverted Y

radiolucency over roots of posterior teeth/canines

pneumatization

the maxillary sinus extends down into a space where there is a missing maxillary tooth

Maxillary Sinus Septa

some sinuses have vertical walls in the sinus cavity and run from inferior sinus to the floor of the orbit

nasolabial fold

line of contact from corner of the nose to the corner of the lip. (fatty tissue of the cheek)

zygomatic process of the maxilla

extension of the maxilla - supported by the buttress