RR: CR/DR/ Fluoroscopy/ Imaging Chart / Pre-Post Processing

CR Imaging Plate (PPCSLB)

1. protective layer

2. phosphor or active layer

3. conductive layer

4. support layer

5. reflective layer

6. backing layer

protective layer

• thin, tough, clear plastic that protects the active phosphor layer

• made of carbon fiber

phosphor (active) layer

• photostimulable phosphor

• barium haloflurohalid family

• ability to store & release energy

conductive layer

• ground the imaging plate from electrostatic charge

• increases spatial resolution by absorbing light

supoport layer

• semi- rigid material

• gives imaging plate strength

reflective layer

• sends light in a forward direction when released by the reader

• prevents unwanted light from affecting the unexposed latent image

backing layer

• soft polymer that protects the back of the cassette

• prevent unwanted background radiation from affecting the unexposed latent image

CR reading process

1. The imaging plate must be processed to release the latent image

2. inserted into the CR reader & imaging plate is removed (rollers)

3. latent image released from the phosphor (active) layer

4. CR red lasers scan information from the imaging plate using the rastar pattern

5. When red lasers hit the IP, the plate releases blue visible light

6. Light is captured by the photomultiplier tube to create the manifest image

7. IP is erased with a bright white light

latent image

• invisible image

• storage in phosphor (active) layer until activated

CR reading laser

• red helium neon laser light

• scans information off of the imaging plate in a rastar pattern

photomultiplier tube (PMT)

• captures light released from imaging plate

• creates manifest image

manifest image

• visible image

• created by photomultiplier tube

CR plate erasure

uses bright white light

what happens when the red laser hits the IP?

blue visible light is released from the plate

slow scan

moves the Imaging plate constantly yet slowly along the long axis of the IP

fast scan

the movement of the laser across the IP

ghost error

• double image

• second image partially outside collimated field

  • remnants of lead markers

• caused incomplete erasure of the imaging plate

• AKA: ghost image

• CR only

Digital Conversions

direct & indirect conversions

direct conversion

• semiconductor

• TFT

indirect conversion option #1

• scintillator

• fiber optics

• CCD

indirect conversion option #2

• scintillator

• photodiode

• TFT

semiconductor / photoconductor

• amorphous selenium

• x-rays → electrical signal

TFT (thin film transistor)

• collects the electrical signal released in direct & indirect conversions

• acts like a switch and sends over information

• matrix filled with DELs

scintillator

• cesium iodide (preferred) or gadolinium

• x-rays → light photons

fiber optics

• lenses

• attaches CCD to scintillator

CCD (charged couple device)

• optically coupled to each CCD sensor chip by lenses or fiber optics

• converts light photons → electrical signal

• collects electrical signal & sends to computer

• oldest indirect conversion system

photodiode

• amorphous silicon

• light → electrical signal

DEL

• detector element

• digital imaging

DEL size

The smaller the size, the more information is collected

• decrease in size = increase detail in the image

direct conversion

uses amorphous selenium

1. x rays interact with IR

2. x rays directly converted to electrical signal

indirect conversion

uses amorphous silicon

1. x rays interact with IR

2. x rays → light photons using a scintillator

3. light → electrical singal

cesium iodide

• formed into rods

• helps improve spatial resolution

• indirect conversion

TFT layer

• comprised of

  • matrix of DELs

  • Each DEL comprised of pixel

  • storage capacitor

  • switch

pixel

• picture element

• determined by the matrix size & FOV

• small = preferred

storage capacitor (TFT)

stores electrical charged produced by the capture element

TFT switch

releases electrical charge produces digital image

CMOS

• complementary metal oxide semiconductor

• developed by NASA

• less expensive than CCD

• convert light → electrical signal

DEL pitch

• distance between the detector elements

• measured from the center of one DEL to the center of the other DEL

decreased DEL pitch & size =

increased spatial resolution

DEL fill factor

• percentage of the pixel in an IR that is sensitive to the incoming x-ray beam

• 50-80%

higher fill factor =

higher spatial resolution

ADC (analog to digital converter)

• converts an electrical signal into a digital image

• using binary code (ones & zeros)

bit depth

• the number of shades of gray

• possible brightness levels that can be assigned to any individual pixel in the image

• 2^n

• higher = more information / image quality

quantization

• takes electrical signals & turns them into digital bits of information

  • assigns each pixel a number

  • each number has an assigned grayscale

  • occurs during ADC conversion

• specific brightness levels in the image

Detector quantum efficiency (DQE)

• how efficiently a system converts an input signal into a useful output image

• measures the quality of a digital image

• SNR

signal

actual radiographic image or useful information

noise

• mottle

• not useful information

• underexposed area

signal to noise ratio (SNR)

• effect of noise

• signal/noise

• more signal with less noise = higher quality image

• high SNR preferred

Does CR or DR have a higher DQE?

• digital imaging (DR)

• direct DR = most efficient

  • no light conversion step

raw data

• exposure information prior to any processing algorithms

• converted into digital data using the ADC

grayscle

digital term for scale of contrast

how many values is 8 bits ?

256 possible values

how many values is 10 bits?

1024

histogram

• a graphical display of the pixel intensity distrubiton for a digital image

• frequency of recorded expsoure values

histogram analysis

• computer analyzes histogram using stored processing algorithms

• compares to a pre-established histogram specific to the part imaged

• values of interest

values of interest (VOI)

determines the range of the histogram data set that should be included in the digital image

Look Up table (LUT)

• a series of mathematical equations used for image processing

• allows grayscale values of the image to be remapped to improve image brightness or contrast

• specific to anatomic areas

• controls digital contrast

automatic rescaling

rescaling software with the abiity to produce images with consistent brightness & contrast

rescaling

• corrects the appearance of the image due to exposure errors

• computer modifies histogram to make it look how it should

dead pixel

• a pixel with a malfunction or sensor error

• able to be seen on tech panel

dead pixel correction

• software identifies dead pixels within the matrix & removes them from the image

• assigns a dead pixel a value based on the values of adjacent pixels

flat fielding

Dead pixels are removed from the matrix by masking the dead pixels

edge enhancement

• increases contrast along the edges of structures

• improves visibility of detail

• AKA: high pass filtering

halo artifact

• created by excessive edge enhancement

• white ring around image

equalization

soft tissue & bone are enhanced/equalized so all information within the region can be seen

smoothing

• AKA: low pass filtering/noise suppression

• used to mask quantum noise

• can cause a loss of spatial resolution

• cannot correct severe underexposure

windowing

• ability to alter the brightness & contrast of image

• post processing

window level

• adjust image brightness

• post processing

window width

• adjust image contrast & grayscale representation

• post processing

wide window width

• low contrast

• long scale

• more shades of gray

narrow window width

• high contrast

• short scale

• more black & white

high window level

high brightness = light image

low window level

low brightness = dark image

shuttering

• removes background or distracting light surrounding an image

• post processing

electronic cropping/masking

• electronic collimation

• should not be used in place of collimation

• post processing

image stitching

• used for scoliosis image

• connects two images into one

liquid crystal display monitors (LCD)

• displays digital images for interpretation

• QC test performed

luminance

• amount of light emitted from the display monitor

• important in low contrast structures

• measured in candela per square meter

monitor viewing angle

maximum angle at which display monitorq can be viewed with acceptable visual performance

quality of image & accuracy of interpretation depends on

• spatial resolution

• luminance

• contrast resolution

ambient lighting

• overall illumination of the room

• glare = too bright lighting

SMPTE pattern

• evaluates monitor for

  • luminance

  • resolution

  • noise

  • contrast

  • glare

photometer

• measures the luminance of the display monitor

• QC test

PACS

• picture archival and communication system

• allows users to acquire, transmit, store, recieve, & modify digital images taken in all modalites

archive

long term storage of images & documents

DICOM

• digital imaging & communications in medicine

• enables integration of scanners, servers, workstations, printers & network hardwarde from multiple manufactures

• handling, storing, printing, & transmitting of information

• teleradiology

HIS

• hospital information system

• patient information stored in the hospital database

• accessible to specific hospital group

RIS

• radiology information system

• radiology modality work list

• radiology orders

EMR

• electronic medical record

• digital patient chart

• medical history, diagnosis, medications, immunizations, allergies

• limited to the practice

EHR

• electronic health record

• infomration from various healthcare providers

Image Intensifier

• Fluoro / C-arm

• located above the patient

• X-rays photons exit patient → image intensifier

1. input phosphor

2. photocathode

3. electrostatic lenses

4. anode

5. output phosphor

6. CCD

7. ADC

8. digital image

input phoshpor

• cesium iodide

• takes the remnant beam from the patient

• converts x ray photons → light photons

photocathode

• light photons → electrical singal

• made of antimony compounds & cesium

electrostatic lenses / focusing lenses

focuses the electrons toward the anode

anode (image intensifier)

• donut-shaped with a hole in the middle

• accelerates the electrons to the output phosphor

• made of tungsten

output phosphor

• made of zinc cadmium sulfide

• electrical signal → light photons

photoemission

emitting electrons from light source

Flouro / C- arm

• X-ray photon goes through the patient

• remnant beam exit patient & enters image intensifier

• x ray tube under patient

• image intensifier above the patient

automatic brightness control (ABC)

• control kVp & mA in fluoroscopy

  • regulates depending on the part being imaged

• AKA: ABC or AERC

• image intensifier only

maximum mA station in fluoroscopy

5 mA