CH. 8: Diagnostic Yield and Efficacy/Manipulation of Radiographic Equipment

general purpose of any medical imaging procedure

to provide accurate info about the patient's medical condition/disease

a physician has an array of procedures to choose from to help determine what is wrong with the patient; array of procedures such as

simple xray studies

sonograms

ct

mri

amount of clinically useful info on a diagnostic image

define diagnostic yield

what kinds of medical info that the image is going to show you regarding the pt's condition

diagnostic yield

These factors are considered in making what kind of a selection: radiation dose, risk to pt, pt medical cond, tolerance of procedure, costs/insurance coverage, timeliness

choosing one imaging modality procedure over another

in order to say "we are going to order this image" what has to outweigh what?

Diagnostic yield of information must outweigh the negative effects of the radiation; worth getting an image

the accuracy with which a diagnostic study reveals the patient's medical condition is called its...

diagnostic efficacy

efficacy vs yield

yield: amount of useful info

efficacy: accuracy of info

why is becoming as comfortable as possible with the maneuvering of the xray equipment early on important?

So you can concentrate on learning to master other imp skills like patient care, positioning, technique selection, image quality

all xray systems have the same basic design features:

t+s, c, t, g, cc, u I H

xray tube + support system

collimator assembly

xray table

xray generator

control console

upright image receptor holder devices

first step in mastering equipment manipulation is being able to what?

identify the generic components of a radiographic system

the design of a radiographic equipment allows the radiographer to position the...

xray tube and collimator assembly around the pt in any number of orientations

component of radiographic system that produces the xrays

xray tube

special type of glass that can withstand very high temps from the xray tube anode

pyrex glass

what is an insert?

xray tube

What is the xray tube "inserted" inside of?

tube housing

thinner portion of pyrex glass on the xray tube; called and function

window

-allows xrays/light to go through

the window of the xray tube is directed toward...

the patient

cathode vs anode

cath: negative electrode of the xray tube

anod: positive electrode of the xray tube

otc stands for and definition

Overhead Tube Crane

=mechanical support for suspending the xray tube/collimator assembly from the ceiling of the radiographic room allowing the radiographer to position it as needed over/around the patient

this is suspended from ceiling mounted rails

overhead tubecrane support OTC

electrical component that possesses polarity with a negative and positive terminal

diode

this causes the rapid acceleration of electrons to pass through the tube from cathode to anode; creating x radiation

kvp/potential difference

cathode filament is typically made of what material

tungsten

this is a tightly wound wire helix which is part of the cathode assembly

filament

Electrical current passes through the filament. When energy is enough to expel the electrons from the filament this is called

thermionic emission

why is tungsten used in the filament?

allows for higher temperature without the filament melting

this pushes out electrons produced by the electrical signal...

cathode assembly

which way do electrons move in current in a tube by means of anode/cathode

from cathode to anode

area on the rotating anode where the electrons from the cathode strike

target

made of tungsten; where radiation is produced; provides mechanical support for target

anode assembly

attached directly below the xray tube; beam limiting device

collimator assembly

what does the collimator light do?

shows us where the xrays are going to go

projects a high intensity light field on the pt which represents the area of xray field expsore

collimator assembly

what is a goniometer, where is it located? Way to remember!

angulation scale incorporated to indicate the degree of xray tube angle relative to the image receptor (built into collimator cover)

-gonio...how to make the angles go away/come back equals goiniometer

what else is built into collimator cover?

retractable tape measure for measuring the SID

the illuminated area of the what is representative of the xray field exposure area

collimator light

collimator lights generally get really hot so two things are done to help this

1. turns off after a preset time interval

2. Light Emitting Diode which lasts longer/does not get hot

what is the plexiglas shadow shield's purpose under the collimator?

to project a shadow of cross hairs marking the beam's central point

there can be additional lines on the plexiglas shadow under the collimator that indicate the position of exposure detectors...the exposure detectors are known as...Where located specifically

Automatic Exposure Control AEC

-located on the upright bucky assembly shown as three gray spots aka ionization chambers

this allows the xray unit to detect the size of the IR the radiographer is using and automatically collimates to a size not larger than the IR

pbl

positive beam limitation

three ways in which xray tables are classified:

1. tilting/nontilting

2. free-floating/stationary tabletop aka 4 way floating

3. adjustable/nonadjustable height

tilting tables are available in two types; describe/define

1. 90/90: tilts from horiz position to vertical position in either direction

2. 90-45: tilts to a complete vertical position in one direction and to a 45 degree tilt in the other direction

a receptor/cassette tray is often called what?

bucky tray

tabletops radiolucent/radiopaque??

radiolucent

tray holds cassette tightly in position and is centered to ----------axis of table..

longitudinal

the radiographic grid does what during exposure to blur out the lead grid lines:

oscillates

this is the workhorse of the total system

xray generator

consists of two main components:

1. electronics cabinet

2. operator console

the electrical interface btw the operator and the equipment

control console

all generator console designs must have these key features:

o/o, e f, s/s e, a/v e

turn system on/off

select xray exposure factors

initiate/terminate exposure

provide audible/visual indication of xray exposure

APR stands for/used for

Anatomically Programmed Radiography

-people buy it then program it select all required exposure types but a good tech looks at all the variations and don't just run autopilot

so what are the five generic controls a new student must learn on a console?

p, k, m, t, r/e

main power

kvp

mA

timer

rotor-exposure switch

the selection of these three things is collectively known as technique selection

kvp, ma, time

Necessary to make an exposure; also called "Prep", "Ready," or "Standby"; two functions: when activated it starts the rotating anode which creates the electrons and when held in the "on" position for a few seconds, it will indicate that the tube is ready for an exposure

rotor switch

Do not activate the ____ before you are completely ready to make an exposure; increases wear on both bearings and filament, shortening tube life

rotor

this indicates the amnt of current supplied to the xray tube

mAs

whats difference btw selecting singularly ma and s on console vs mas?

mAs mode will generate the highest allowable ma to achieve the shortest esposure times

device that begins the exposure

rotor exposure switch

according to federal regulations, the termination of the exposure must be indicated by two sense

audibly and visually

two steps of exposure sequence:

Rotor 1. anode spins at a high rate of speed; cathode filament heats to selected mA

Exposure 2. large potential difference (kVp) is applied across both electrical poles of xray tube, causing electrons to travel form cathode to anode at high speed, producing x radiation

what are the two distinct designs that xray tube support systems come in??

1. floor mounted tubestands

2. ceiling suspended Overhead Tube Cranes

floor mounted tubestands

found in clinical setting; consists of vert column that runs along a longitudinal rail mounted to the floor

OTC ceiling suspended systems

most sophisticated designs and standard of care in hospitals/large clinics

what does it mean for ceiling suspended systems to be ergonomically friendly and aesthetically pleasing?

erg: easy to move

aesth: not intimidating/looks pleasing to eye

if there is a setting exposure at the newer OTc tubehead, what still needs to be done somewhere else?

performing the exposure is still done behind the counter

three types of floor mounted tubestands compared to one type of OTC

1. floor only

2. floor and ceiling

3. floor and wall

OTC= ceiling

what are the basic movements of a typical diagnostic radiographic tube??

longitudinal, transverse, vertical, rotational around vertical axis, tube angulation

define detentes

-predetermined locking positions for the xray tube, table, and upright wall holder

-line up to the IR; stop at certain points