RADT 102 EXAM #2 - FLUOROSCOPY

Static means …

not moving

Dynamic means …

moving

What is the HISTORY of FLUOROSCOPY

• thomas edison discovered in 1896

• screen (zinc-cadmium sulfide) placed over patient’s body in x-ray beam

• radiologist looked directly at screen

• in 1950, image intensifiers were developed (intensified the light of the image)

• before that, they would wear red goggles 30 minutes before the exam to see better

Describe CONES (eyes)

• central

• less sensitive to low light (threshold of 100 lux)

• will respond to bright light

• daylight vision (phototopic vision)

• perceives COLOR, differences in brightness

• perceives fine detail

• utilized in fluoroscopy

Describe RODS (eyes)

• periphery

• sensitive to low light

• used in night vision (scotopic vision)

• dims objects seen better peripherally

• color blind

• do not perceive detail

Fluoro is viewed at the same level of brightness as radiographs which is ______

100 - 1000 lux

Fluoro x-ray tube operate at _____ mA, why so low?

0.5 to 5 mA

• there is longer exposure time, so you make the mA shorter

KVP is dependent on body section and changes based on section to see everything at a good brightness throughout the body

True

What systems MAINTAIN BRIGHTNESS?

• ABC (subset of AEC/AERC)

• ABS

• AGC

• all control, stabilization, gain control

• makes sure that the brightness stays the same

A FIXED tube may be mounted no closer than ______ inches or ______ cm to patient

• 15

• 38

A MOBILE (c-arm) tube may be brought no closer than ____ inches or ____ cm to patient

• 12

• 30

There is LESS radiation if tube is _______

under the table

State the SEQUENCE of FLUOROSCOPY

• beam exits the patient (remnant radiation)

• hits the INPUT PHOSPHOR (cesium iodide CsI tightly packed needles … great spatial resolution)

  • converts X-RAYS to VISIBLE LIGHT

• hits PHOTOCATHODE (cesium and antimony)

  • emits ELECTRONS when struck by LIGHT (turns the light into electrons)

• the potential difference within the image intensifier tube is a constant 25,000 volts

• electrons are accelerated to ANODE

  • anode is circular plate with hole for electrons to go through

  • there are lenses to force the electrons together and push them towards and out the anode

• electrons hits OUTPUT PHOSPHOR (zinc cadmium sulfide) with high kinetic energy producing an increased amount of light

Each photoelectron at the OUTPUT PHOSPHOR, has ______ more ______ ______

50-75, light, photons

What is the purpose of ELECTROSTATIC LENSES

• electrons must be focused for accurate image pattern

• these accelerate and focus the electron beam

OLD SCHOOL - light was emitted from output phosphor and then …..

was transmitted as an analog signal via a TV tube called plumbicon/vidicon

NOW - light is emitted from output phosphor and then …

is captured by a CCD or a flat panel system is used

If the DIAMETER of the INPUT PHOSPHOR DECREASES, the overall BRIGHTNESS of the OUTPUT PHOSPHOR _______

decreases

• not a good thing

DESCRIBE flux gain

comparing the # of x-rays coming in and the # of light photons coming out

• ratio of number of light photons at the output phosphor to the number of x-rays at the input phosphor

• # of output light photon / # of input x-ray photons

• represents how bright it would be coming out

DESCRIBE minification gain

comparing a change of activated diameter of the input phosphor to the fixed diameter of the output phosphor

• ratio of the square of the diameter of the input phosphor the square of the diameter of the output phosphor OR

• # of electrons produced at large input screen squared, compressed into the area of small output screen squared

DESCRIBE brightness gain

minification gain x flux gain

• increases illumination level of an image

• ratio of the intensity of the illumination to the output phosphor to the radiation intensity at the input phosphor

• when too low, ABC/AGC/ABS/AERC kick in to fix the brightness

• brightness gain of 5000-30,000

When flux, minification, and brightness gain DECREASE, magnification _____, mAs ____, and pt exposure ______

increases, increases, increases

Describe CONVERSION FACTORS

• ratio of intensity of illumination at the output phosphor (measured in Candela per meter squared) to the radiation intensity at the input phosphor (mGya per sec)

• (Cd/m squared) / (mGya / s)

What is MULTIFIELD IMAGE INTENSIFICATION

• allows focal point change to reduce field of view and magnify the image

• multifield = the different diameters of input phosphor

Most popular MULTIFIELD IMAGE INTENSIFIER is _______

25/17/12

• others are 23/15/10

DESCRIBE multifield image intensification

• NUMERIC dimensions refer to the INPUT phosphor (25/17)

• SMALLER dimension (25/17) result in MAGNIFIED images

• at 25 - all photoelectrons are accelerated to output phosphor

• smaller dimension - voltage of focusing lenses is increased

• electron focal spot moves away from the output

• only the electrons from the center of input strike the output

If the diameter is REDUCES to magnify the image, how does that impact flux, minification and ultimately brightness?

reduces flux, reduces minification, brightness goes down

• increases pt exposure because the ABC increases the mAs to get the right brightness

What are the PROS of using a SMALLER DIMENSION

• only central region of input is used

• spatial resolution is better (kinda like the umbra)

• lower noise, higher contrast resolution

What are the CONS of using a SMALLER DIMENSION

• minification gain is reduced = dimmer image

• to compensate must increase mA

• increases pt dose

What does a BEAM SPLITTING MIRROR do

splits the beam to be sent to additional recording devices

What is an ABS sensor

bumps up mA to maintain brightness

Why is it easy to convert a conventional fluoro unit to a digital one?

there is already a system to take light and digitize it

DESCRIBE digital fluoro

• image acquisition is FASTER

• can post process

• has TWO monitors

• operates in radiographic mode

  • MA station is around 400 in flat panel mode

  • time isn’t longer as the process isn’t as long so the patient dose will be lower

Describe PULSED PROGRESSIVE FLUOROSCOPY

• generator can be switched on and off rapidly

• broken into different time frames

  • interrogation / extinction

• each must have times of less than 1 ms

What is INTERROGATION TIME (pulsed progressive fluoroscopy)

tube switched on and meets selected levels of kVp and mA

What is EXTINCTION TIME (pulsed progressive fluoroscopy)

time required for the tube to be switched off

• duty cycle - time tube is energized

Describe FLAT PANEL IMAGE RECEPTORS (FPIR)

• they are beginning to replace CCD’s

• made of CESIUM IODIDE pixel detectors

• lighter, smaller than image intensifiers

• improvement to image as the SPATIAL RESOLUTION is uniform and distortion free

• HIGH DQE

• improved contrast

What is the SEQUENCE of a CCD

• x-ray interacts with scintillation material

• sent to capacitors which convert light into electrical charge

• charge sent to ADC

Describe a CCD

• structure is a silicon chip

• made of cesium iodide (structured phosphor reducing light spread)

• lenses or fiber optics focus light onto chip

• used in fluoro, c-arms for trauma biopsy

Describe BINNING

allows charges from adjacent pixels to be combined on the sensor before the charge is read out through the amplifier, the dominant noise source on a CCD

• this results in faster readout speeds and improved signal to noise ratios with reduced spatial resolution

• WITH BINNING →

  • combines charges as they drop into readout

  • instead of 4 pixels, there are two

  • LESS things being read out on amplifiers = LESS noise

  • QUICKER process

• WITHOUT BINNING →

  • MORE NOISE

  • MORE SPATIAL RESOLUTION, but COMPROMISED due to increased noise

  • SLOWER process

Describe CMOS

• Complementary metal oxide semiconductor

• highly efficient and inexpensive

• more susceptible to noise so lower quality, lower resolution and lower sensitivity as compared to CCD

• converts light into electrons, stored in capacitors within the pixel then to ADC

List COMPARISONS between CCD and CMOS

• CMOS sensors are more susceptible to noise

• light sensitivity of a CMOS chip is lower than a CCD

• CMOS uses very little power compared to CCD

• CMOSs are inexpensive compared to CCD sensors

• CMOS chips are intended for shorter period and have lower quality, lower resolutions, lower sensitivity

• pixel fill factor is greater with CCDs than CMOSs

What are the ADVANTAGES of a CCD

• relatively inexpensive compared to a TFT flat panel system

• they are modular, making them easy to repair, replace and upgrade

What is a DISADVANTAGE of a CCD

CCDs result in demagnification, which requires for pixels to reduce in size, reducing DQE

Image intensifiers receive the _______, convert it to ______ and increases the ______ ______ 5000-30,000 times

remnant x-ray beam, light, light intensity

RED

the 25 intensifier (25/17/12)

ORANGE

the 17 intensifier (25/17/12)

YELLOW

the 12 intensifier (25/17/12)

• converges before the focal point, almost like increased OID

• the converging of electrons is farther away from output phosphor which causes the increased magnification

BLACK

moves the table (control button)

GRAY

tilts the table (control button)

PINK

fluoro button (control button)

PURPLE

capturing a signal image (control button)

GREEN

collimation (control button)

RED (image intensifier tube)

focal point

ORANGE (image intensifier tube)

glass envelope

YELLOW (image intensifier tube)

input phosphor

GREEN (image intensifier tube)

photocathode

BLUE (image intensifier tube)

electrons

PURPLE (image intensifier tube)

electrostatic lenses

PINK (image intensifier tube)

anode

BLACK (image intensifier tube)

output phosphor

What is the GREATER DENSITY formula?

mAs x kVp squared / SID squared x grid conversion factor

How do you turn VOLTS into KILOVOLTS

/1000

What is the INPUT PHOSPHOR made out of?

cesium iodide (CsI)

What is the OUTPUT PHOSPHOR made out of?

zinc-cadmium sulfide

What is the PHOTOCATHODE made out of?

thin metal layer composed of cesium and antimony compounds

ELECTROSTATIC LENSES aka ….

focusing lenses

1 x-ray: _____ photons

3000

Pulse progressive fluoro also avoids _____ _______

thermal overloading

List the ADVANTAGES of a CCD device

• HIGH spatial resolution

• HIGH SNR

• HIGH DQE

• no warm-up required

• NO spatial distortion

• NO maintenance

• unlimited life

• UNAFFECTED by magnetic fields

• linear response

• LOWER patient radiation dose

List the ADVANTAGES of a FLAT-PANEL IMAGE RECEPTOR (over a CCD)

• distortion free images

• constant image quality over the entire image

• improved contrast resolution over entire image

• HIGH DQE at all radiation dose levels

• rectangular image area couples to similar image monitor

• UNAFFECTED by external magnetic fields