254: Unit 4 Fluoro / QC

fluoroscopy primary function

• provides real-time dynamic viewing of anatomic structures

  • motion of circulation

  • motion of internal structures

conventional fluoro

• less than 5 mA

• high patient dose

• long exposure time

• continuous exposure

ABC

automatic brightness control

other names for ABC

• ADC

• ABS

• AERC

ADC

automatic dose control 

ABS

automatic brightness stablization

image intensifier purpose

reduce patient dose by decreasing the amount of x ray photons needed for imaging purposes

image intensifier

• intercept the X-ray photons and convert them into visible light

  • amplify or intensify this light signal

• reduce patient dose by decreasing x ray photons needed

• contains cathode & anode

output phosphor

• a fluorescent screen

• receives the electrons from the photocathode

• absorbs electrons and emits light photons

• made a thin layer of silver activated zinc cadmium sulfate phosphor

anode

• positively charged end

• serves to attract the electrons emitted from the photocathode

• in front of the output phosphor

  • a hole in the center allows electrons to pass and interact with the output phosphor 

how do the electrons pass through to interact with the output phosophor? 

a hole in the center of the anode 

electrostatic lenses

• a series of negatively charged electrodes

• focuses and accelerates the electrons emitted from the photocathode toward the anode

• uses electrostatic repulsion

  • pushes the electron stream toward the middle 

input phosphor

• first element of the image intensifier

• scintillator screen

• absorbs X-ray photons and emits light

• constructed of cesium iodide crystals

flux gain

• energy gained during acceleration from the photocathode to the output phosphor

• light photons / x ray photons

flux gain equation

number of output light photons / number of input x ray photons

minifcation gain

• the concentration of photoelectrons from the input phosphor to the output phosphor

• (input screen)2 / (output screen)2

brightness gain

• the product of the flux gain and the minifcation gain

• product of X-ray photons coming in to how many light photons come out 

brightness gain equation 

minification gain (flux gain) 

multi-field image intensification purpose

magnify the image

multi-field image intensification

• increasing the voltage of the electrostatic lenses & uses a smaller input phosphor 

• brings focal spot closer to input phosphor and away from output phosphor 

  • magnifies the image sent to the output phosphor

magnification factor

ratio of diameters available to diameters used 

patient dose ____ when using magnification factor

increases

why does patient dose increase when using magnification factor? 

An image intensifier uses a smaller section of the input screen & systems ABC will increase the exposure to increase the exposure to keep the image bright 

advantages of magnification factor

• better spatial resolution

• better contrast resolution

disadvantage of magnification factor 

higher patient dose 

CCD advantages

• high spatial resolution

• high SNR

• high DQE

• no warm-up required

• no lag or blooming

• no spatial distortion

• no maintenance

• unlimited life

• unaffected by magnetic fields

• linear response

• lower patient radiation dose

FPIR

flat panel image receptor

Flat panel image receptor takes the place of 

the image intensifier 

Flat panel image receptor is made of

• cesium iodide (scintillator)

• amorphous silicon (photodetector)

Flat panel image receptor magnification

• done electronically 

• No increase in patient dose

Flat panel image receptor advantages

• distortion-free images

• constant image quality over the entire image

• improved contrast resolution over the entire image

• high DQE at all radiation dose levels

• rectangular image area coupled to a similar image monitor

multiple detector system 

• uses 3 TFT detectors 

• detectors switch between static and dynamic imaging

• The tube is below the patient

AERC

automatic exposure rate control

automatic brightness control

automatically adjust the kvp and mAs based on patient attenuation to maintain consistent brightness of contrast of the image 

single detector system 

• single TFT detector used for static and dynamic imaging 

• X-ray tube above the patient 

• allows for longer SIDs for a greater variety of exams 

• cost-effective

• can be used remotely by a radiologist 

digital fluoroscopy

• higher mA

• lower patient dose

• shorter exposure time

• pulsed exposure

intensification process

x rays → light → photon electrons → light

pulse progressive fluoroscopy 

• uses a high-power generator 

• Pulses the x ray production from the fluoro x ray tube synchonrously with the detector signal 

interrogation time

time required for the generator to come on a produce the necessary kVp and mAse

extinction time

time required to shut the generator down in preperation for the next pulse

duty cycle

the fraction of time the x ray tube is energized

LIH

last image hold 

DSA

digital subtraction angiography

post processing

• window/level

• invert

• filtering edge enhancement

mobile fluoro (CR) minimum source to skin distance 

12” (30 cm) 

stationary fluoro minimum source to skin distance 

15” (38 cm) 

audible timer

5 mins

primary source of exposure for tech/ rad

the patient

lead apron & gloves

0.5 Pb/eq

bucky slot cover / protective curtain

0.25 mm / Pb eq

general purpose table top expsosure should not exceed

100 mGy_a/min

high level (IR) tabletop exposure should not exceed 

200 mGy_a/min

Quality Assurance

• deals with people

  • radiology reports

  • repeat rates

  • image QA

quality control

• deals with instrumentation & equipments

• equipments performance evaluations

QC step 1

acceptance testing

QC step 2

periodic monitoring

QC step 3

maintenance  and repair 

acceptance testing

• testing the new equipment once you receive it

• not done by the people who created the equipment

• done by a medical physicist

periodic monitoring

routine evaluation of the x ray producing or image processing equipment

maintenance and repair 

a dedicated analysis of each image to identify deficiencies and artifacts 

filtration

• tested annually

• greater than or equal to 2.5 mm Al

collimation

• semiannually

• plus / minus 2% SID

Focal spot size

• annually

• plus / minus 50%

Calibration of kVp

• annually

• plus/minus 10%

exposure timer accuracy 

• annually 

• plus/minus 5% with exposures greater than 10 ms 

exposure linearity

• annually

• plus/ minus 10% less than or equal to 10 ms

exposure reproducibility

• annually

• plus / minus 5%

primary test for effective FSS

slit camera 

Multiple Detectors in Room

• fluoroscopic

• upright imaging

• recumbent imaging

viewing systems

• LCD monitors (used more)

• Plasma monitors

AEC testing

• test the exposure readout using varying thicknesses of material (Al)

• no matter the thickness the receptor readout should be the same N

,

SMPTE pattern

• used for observing gross deviations in luminance 

• determines spatial resolution & contrast resolution 

DICOM

digital imaging and communication

GSDF

• gray scale display function

• allows medical images to be transferred at a DICOM standard to be displayed on any DICOM device with a consistent grayscale

• ensures images are displayed the same way on different monitors

TG18

• used to check for contrast and spatial resolution display quality on the radiologist's monitor

• evaluates for

  • geometric distortion

  • reflection

  • luminance

  • display resolution

  • display noise

ACR

recommends that all digital display devices utilize TG 18 patterns in formats that can be displayed on the digital monitor for evaluation  purpose

medical physicist

• test as appropriate

  • annually

  • post repair

  • acceptnace testing

• periodic review of the facility QC program

QC technologist

• routinely,l as established by the department QC program

• ability to acquire the TG 18 QC test pattern and use it on each digital display device regularly

staff technologist

• daily

• visually monitor workstations for indications of malfunction

geometric distortion

• lines in pattern should appear straight

• pincushion distortion

• barrel like distortion

display noise 

any high-frequency fluctuations or patterns that interfere with the detection of the true signal on

conventional

• continuous exposure

• Vidicon TV Camera Tube

• low mA

• higher patient dose

CCD took the place of _____

Vidicon TV Camera Tube

digital 

• post processing 

• ADC

• FPIR 

• CCD 

• pulsed exposure

• high mA

• low patient dose 

A

output phosphor

B

anode

C

electrostatic lenses

D

electrons

E

photocathode

F

input phosphor

G

glass envelope

H

focal point

at what stage of image intensified fluoroscopy is the number of photons the lowest

when entering the input phosphor