M 3 & 4: Recording/PACs Flashcards
advantage of recording images and cine loops
can be used for future comparison and reference
importance of having a recording device
radiologist/cardiologist isnt always on site
needed for teleradiography (transmit images offsite for rad to see)
comparison
what was one of the most common ways of storing hard copy images
film
3 different types of film
transparency film (negative) - XRay polaroid film (positive) paper film
what was the most commonly used type of film
advantages and disadvantages
transparency film
PRO- several years of shelf life and infinite resolution
CON- storage space, ease of retrieval, cost
why was transparency film sometimes hard to retrieve
improper filing
or stored off site so you have to order it in each day
how is transparency film constructed
in layers w/ an acetate base topped w/ an emulsion layer that contains silver bromide crystals and a suspension of gelatin
how is the image formed w/ transparency film
light strikes the crystals to form the latent image and are converted to silver grains w/ chem processsing
how do we get the positive image/the image we want to see with a transparency film
we have to use the negative of the image we want to see
how does exposure to light effect the brightness/darkness of the image
more exposure increase activation of the sliver grains and the image becomes darker
more light = darker image, inversely related
what does film speed refer to
how fast the image darkens
film speed and contrast must be matched to what
the monitor that is used for exposure
when transparency film was processed manually, how long could it take to produce 1 film
1 hour
automatic processing of transparency film uses what 4 steps
advantages of automatic processing
development
fixing
washing
drying
PRO- faster, 1-2 minute per film
3 disadvantages of automatic processing of transparency film
- variations of density/contrast of processing
- chemical use which was expensive and bad for the environment
- time would be a disadvantages for todays standards
describe a multi-format camera
one of the most common devices used to expose transparency film… essentially a cathode ray tube that could fix images onto the film
advantages of multi-format camera
disadvantages
PRO- good gray scale
-could control exposure time and position by used a shutter and lens
CON- the CRTs curved screen which could distort the image
- high quality lens needed was expensive
- one camera per machine
- dust and movement a major issue
- could not expose film to the light
biggest disadvantage of the multi-format camera
one camera per machine
what does wet processing refer to
chemical processing in a dark room… the 4 steps of developing, fixing, washing, drying are done
which camera replaced the multi-format camera
laser camera
acronym for laser
light amplification by stimulated emission of radiation
advantages of the laser camera
- intensity and size of the beam are precisely controlled to improve contrast and detail resolution (lasers are ‘tighter’ and don’t bleed like light)
- biggest advantages was many machines/modalities could be accommodated by one camera
- didn’t have to worry about light exposure
how is the image produced w/ laser cameras
film contained a laser sensitive carbon layer that when activated by heat, causes the carbon to stick and the back can be peeled off (how we get grey scale)
w/ laser cameras, how does the amount of carbon affect darkness of the image
more carbon = darker
advantages of polaroid film
disadvantages
no special processing, inexpensive, quick and easy
poor spatial resolution
how was an image created w/ black and white, and colour, polaroid film
- black and white film worked w/ light exposure, creating white on the film using silver halide crystals
- colour have 3 layers, RGB that are activated w/ exposure
which printers have better quality images than video thermal printers
multi-formate and laser printers
describe how a video thermal printer works
a video signal is stored in the machines memory and transferred to a thermal printing mechanism….
….then the heat sensitive paper goes through the mechanism and the heat creates gray scale…. where the shade of grey corresponds to the amount of heat produced
w/ video thermal printers, how is the colour white produced
applying more heat
advantages of video thermal printers
disadvantages
- good contrast, image available immediately
- poor archival stability because the film would degrade if place by a heat source
the video thermal printer is similar to which other type of printer
colour video printer
describe how a colour video printer works
uses dye on paper, if no dye is applied, the paper is white…. to get black you mix RGB
con of colour video printers
time, printing black required a single pass of the paper for each colour to be applied
what were magnetic tape recorders used for
what cassette format did it use
to capture videos rather than still images
VHS or S-VHS (super VHS), which were played on VCRs
why was S-VHS preferred to VHS
better spatial resolution
describe how a magnetic tape recorders works
the tape contained magnetic dipoles that can be aligned in a magnetic field… the strength of the signal/magnetic field determines the alignment of the dipoles
how did playback work w/ magnetic tape recorders
the tape was passed by the ‘reader head’ and the changing magnetic field produced a video signal
can audio be included in magnetic tape recorders
yes, if so, you would have 1 head for the video and 1 head for the audio
spatial resolution of VHS and S-VHS
VHS: 240
S-VHS: 400
can S-VHS be played in a VHS machine
no.
compatibility issues, the VHS could only produce 240 scan lines, not the 400 S-VHS has
can S-VHS and VHS be played in an S-VHS machine
yes
do recordings on magnetic tape recorders degrade over time
yes, the magnet poles break down over time so you lose the image
describe magneto-optic disks (MO disc)
discs that combined 2 technologies - magnetics and optics
how do MO discs work
how are they read
a laser heats the disk past its Currie temp so that the magnetic crystals can be realigned when placed in a magnetic field…. then the disc it cooled to strengthen the bonds
a weaker laser scatters light off the disk and the intensity is registered to create the signal
advantages of MO discs
disadvantages
PRO: relatively large memory space, re-writable and not susceptible to magnetic damage
CON: lack of compatible drives, 30 seconds to load each image onto the disc
PACS acronym
picture archiving communication system
advantages of PACs
storage external viewing connection to other modalities wed access image quality, no degradation over time no processing time
describe how PACS works
the PACS system electronically transfers digital data from a machine to a workstation
disadvantages of PACs
- manufacturers used different programming and coding to digitize their images
- large investment initially
- additional staff needed due to complexity of equipment and maintenance/upkeep
- limited memory
why was DICOM created
what does it stand for
to create a universal standard for compressing images
Digital Imaging and Communications in Medicine
what is a stripchart recorder
a popular way to print M-mode information, included and CRT and cables that carry the image to the CRT where its exposed to ultraviolet sensitive paper, creating the image
which display devices where most commonly used in US before PACS
oscilloscope and CRTs/TV monitors
how many lines does a CRT have in total
how many fields
512 vertical lines…. formed by scanning two fields of 256 line each
how long does it take for the CRT to write each field across the screen
1/60 second each for a total of 1/30 seconds
3 controls affecting display
brightness
contrast
focus
Does the multiformate camera need wet processing
Yes, after exposure it needs wet processing in a dark room
