Quality Control

HIGH QUALITY FILMS

  REPRODUCES ANATOMICAL IMAGE EXACTLY FILM HAS:     CORRECT TECHNICAL FACTORS NO MOTION NO ARTIFACTS PROCESSED CORRECTLY

RESOLUTION

   ABLE TO VISUALLY SEPARATE OBJECTS BONE VS. TISSUE-- IE: SPATIAL RESOLUTION  CR VS CONVENTIONAL FILM DIFFERENCES BETWEEN DIFFERENT TISSUES-- IE: CONTRAST RESOLUTION  CR VS. CONVENTIONAL FILM

NOISE

   FILM GRAININESS (INHERENT) SIZE OF FILM CRYSTALS STRUCTURE MOTTLE (INHERENT), PHOSPHOR IN SCREEN QUANTUM MOTTLE

QUANTUM MOTTLE

   LOW NUMBER OF X-RAY PHOTONS INTERACTING WITH SCREEN. INSUFFICIENT AMOUNT OF PHOTONS STRIKING INTENSIFYING SCREEN CAUSING AN INSUFFICIENT LIGHT TO EMIT FROM PHOSPHOR CRYSTALS.

How do we adjust technique for this?

CR and Quantum Mottle

SPEED

  FILM’S ABILITY TO RESPOND TO X-RAY EXPOSURE IF FILM “

A”

RECORDS MORE DENSITY

SOONER

THAN FILM “

B”,

WHICH FILM HAS A HIGHER SPEED?

SENSITOMETRY

 MEASUREMENT OF SENSITIVITY TO LIGHT AND THE FILM’S RESPONSE TO CHANGES IN TECHNIQUE AND PROCESSING.

DENSITOMETRY

 MEASUREMENT OF THE DENSITY OF THE FILM BASED ON THE PERCENTAGE OF LIGHT TRANSMITTED THROUGH THE FILM.

ANATOMY OF A CHARACTERISTIC (H & D CURVE)

OVERHEADS!!!!!!!

RECIPROCITY LAW

  OD REMAINS THE SAME NO MATTER THE LENGTH OF EXPOSURE 100 mA X 1 sec = 100 mAs ↓↓ 200 mA X .5 sec= 100mAs ↓↓ 400 mA X .25 sec =100mAs →→ same OD 500 mA X .2 sec = 100mAs ↑↑ 

Applicable to direct screen exposures

RECIPROCITY LAW FAILURE

     FILM/SCREEN RADIOGRAPHY EXPOSURE TIMES LESS THAT 10 MILLISECONDS EXPOSURE TIMES GREATER THAN 5 SECONDS INTERVENTIONAL STUDIES MAMMOGRAPHY

RADIOGRAPHIC CONTRAST

IMAGE RECEPTOR CONTRAST PLUS SUBJECT CONTRAST

IMAGE RECEPTOR CONTRAST

   Formerly known as film contrast. Why the change in name?

Inherent to film Affected by processing

SUBJECT CONTRAST

   SIZE SHAPE X-RAY ATTENUATION OF THE ANATOMY AND ENERGY OF BEAM

REVIEW

   L ATITUDE (REMEMBER THIS IN REFERENCE TO THE FILM) W I D E LATITUDE = LOOOOONNNNG GRAY AKA LOW OR LONG SCALE CONTRAST NARROW LATITUDE = SHORT SCALE =HIGH CONTRAST

WIDE LATITUDE FILM, BECAUSE OF LONG GRAY SCALE ALLOWS AS MUCH AT 15% ERROR BY RADIOLGRAPHER

MAGNIFICATION FACTORS

  MOST IMAGES ARE LARGER ON RADIOGRAPH THEN IN ACTUALITY DUE TO SID AND SOD!

FOR EVERY 1” INCREASE IN OID, SID MUST BE INCREASED BY 7” TO COMPENSATE FOR MAGNIFICATION

SID AND SOD?

 SID: SOURCE TO IMAGE DISTANCE  SOD: SOURCE TO OBJECT DISTANCE  MAG. FACTOR IMAGE SIZE OR SID OBJECT SIZE SOD TO FIND SOD SUBTRACT THE OID FROM THE SID

 IF YOU COULD MEASURE A HEART AND IT MEASURED 12.5 CM BUT ON THE RADIOGRAPH IT MEASURED 14.7 CM, THE MAGNIFICATION FACTOR WOULD BE CALCULATED AS 14.7 DIVIDED BY 12.5 WHICH EQUALS A MAGNIFICATION FACTOR OF 1.17.

WAYS TO DECREASE MAGNIFICATION

    IF OID IS INCREASED? INCREASE SID!

CHEST LATERAL AND OBLIQUE C-SPINE

DISTORTION

  

Foreshortening



Object at an angle and CR is perpendicular to the part that is angled-trauma elbow Spatial



Tube is angled to separate body parts



Clavicle Elongation

 

object is parallel but tube is angled sigmoid

FOG LEVEL/CONTRAST AND THE PROCESSOR

   As time extends in the developing process the fog level____(toe of the characteristic curve) and the contrast____ increases decreases

90 seconds is the optimal developer time

 A variation of 5 seconds either way can affect quality of film.

Developer temperature

   As the temperature increases the fog level______ increases optimum temperature is usually 90 degrees F.

SUBJECT CONTRAST

   Review: Rad. Contrast=film contrast plus subject contrast film contrast is controlled latitude of film, and processing factors

Subject contrast

    Patient (Size) Tissue (KUB) Atomic # ( higher produces high contrast) object shape

MOTION

  PATIENT TUBE MOVEMENT  TOMOGRAPHY

MOTION

  LARGE SID = LESS FOCAL SPOT BLUR SMALL SID = MORE FOCAL SPOT BLUR

FOCAL SPOT BLUR

KVP

   GIVES ELECTRONS ENERGY TO HIT THE ANODE HIGH AMOUNT OF KINECTIC ENERGY IN AN ELECTRON PRODUCES A HIGHLY ENERGIZED X-RAY PHOTON BETTER PENETRATION=LOTS OF GRAYS

KVP

   LOW KVP PRODUCES A BLACK AND WHITE IMAGE. TO PRODUCE AN ADEQUATE OD MUST USE HIGHER MAS HIGHER MAS MEANS MORE EXPOSURE TO THE PATIENT

HIGH KVP HIGH MAS

     +Greater margin of error +Reduction in patient dose +Wider latitude -increase scatter -increase fog     +Higher OD +Lower Rad noise -increased pt. Exposure -less margin of error

The Radiographer controls

      kVp mAs focal spot size distance added filtration screen speed

REMEMBER

   200 mA increased to 300mA is a 50% increase in electrons being produced As mA increases, time must decrease to maintain same density Distance Maintenance formula--New Sid over Old Sid Squared

REMEMBER

     Small mA station uses smaller focal spot smaller focal spot = more detail Inherent = .5 mm additional 2 mm of aluminum between housing and collimator collimator adds 1 mm