Tube Exposure Factors Math Technique Contrast and Density RTA 2011 WK 5 FINAL Tube Exposure Factors Math Technique Contrast and Density

X-ray Properties

X-Ray Properties Are highly penetrating, invisible rays which are a form of electromagnetic radiation. Are electrically neutral and therefore not affected by either electric or magnetic fields

X-Ray Properties Can be produced over a wide variety of energies and wavelengths (polyenergetic & heterogeneous). Release very small amounts of heat upon passing through matter.

X-Ray Properties Travel in straight lines. Travel at the speed of light in a vacuum. Can ionize matter.

X-Ray Properties Cause fluorescence of certain crystals. Cannot be focused by a lens. Affects photographic film.

X-Ray Properties Produce chemical and biological changes in matter through ionization and excitation. Produce secondary and scatter radiation.

Artistic Talent

Artistic Talent

Your artistic talent…..

Your artistic talent….. Your signature

What is Technique? Exposure factors under the control of the radiographer at the control panel mAs (mA x s) Milliamperage seconds kVp

How does it affect our image?

The Control Console Where tech sets technical factors B. _____ C. ____________ Only a ________________ individual is authorized to energize the console The control console is device that allows the technologist to set technical factors (mAs & kVp) and to make an exposure. Only a legally licensed individual is authorized to energize the console.

Control panel AKA Control Console

Producing optimal radiographs

PRIME FACTORS mAs kVp Distance (SID) Exposure factors under the control of the radiographer. Consists of the 3 prime factors It will make a difference as to whether the image is optimal or not.

DENSITY DENSITY THE AMOUNT OF _________“DARKNESS” ON THE RADIOGRAPH Usually in response to_________________ Described as a comparison of light going __ and light coming ____

_________________ on a radiograph DENSITY _________________ on a radiograph or of a certain part of the image Results from: the _______of radiation that reaches a particular area of the ______________

Anatomic Density vs. Optical Density ________________ Pathology or condition that _________ the atomic number of that body part Will appear as a ___________ in optical density on the film Optical density The level of darkening we SEE on the film

Inversely Proportional Atomic number (z#) increases _______________ Atomic number (z#) decreases

Variables that Affect Density Patient size Tissue composition mAs kVp Source image receptor distance (SID) Beam modification Image receptor Processing

Variables that Affect Density Patient size Tissue composition mAs kVp Source image receptor distance (SID) Beam modification Image receptor Processing

______ is the PRIMARY controlling factor of density

mAs __________ Also called: number of x-ray photons in the beam x-ray output Intensity

Milliamperage mA One milliampere is equal to one thousandth of an ampere. The amount of current supplied to the x-ray tube Range 10 to 1200 mA Tube current is equal to the number of electrons flowing from the cathode to the anode per unit time

Time In seconds How long x-rays will be produced 0.001 to 6 seconds

mAs mA X s = mAs

mAs Reciprocity 100 mA x 1/4 = 25 mAs 200 mA x 1/8 = 25 mAs

What changes to mAs are needed for human eye to detect?

mAs DOUBLED = DENSITY DOUBLED

DENSITY directly proportional to mAs + 25%mAS = 25% increase in density +50% mAs = 50% increase in density

Math Problems

CONTRAST THE DIFFERENCES BETWEEN: Blacks Whites Dark gray Light gray The differences between adjacent densities. It gives us the various shades of grays on the IR.

Contrast Comparison of all densities on image _________________ Gray tones from darkest to the lightest gray

Short scale of Contrast _________________ Greater distance between densities

Long Scale of Contrast ______________ ______________M Less distance between densities

Kilovoltage Peak (kVp) Is the _______________________ of contrast _____________ ability of photons Manipulates radiographic contrast Strength or ______________ of photons Maximum ___________ energy Ranges from 0-peak Heterogeneous or polyenergetic

Beam Attenuation AKA absorption Different parts of body attenuate differently The difference in attenuation is the basis for contrast High kVp Penetrates more easily Causes more grays Low scale of contrast Low kVp Decreases penetration Causes more black-white High scale of contrast

Optimal kVp Is there such a concept? YES and NO Depends on the body part The anatomic area of interest More energy is needed to penetrate through bony tissue (high z #) than soft tissue (low z #)

15% Rule 15% kVp = doubling of exposure to the image receptor  15% kVp = halving of exposure to the image receptor 15% rule will always change the contrast of the image because kV is the primary method of changing image contrast. Remember : 15% change ( ) KVP has the same effect as doubling or ½ the MAS on density

+ 15% kvp - 15% kvp

Three things can happen… When x-rays interact with patient: (1) the x-ray photon is __________ (2) the x-ray photon is __________ (3) the x-ray photon is __________ When x-rays pass through a patient's body, three things can happen: (1) the x-ray photon is transmitted, passing through the body, interacting with the film, and producing a dark area on the film; (2) the x-ray photon is absorbed in an area of greater tissue density, producing lighter areas on the film; and (3) the x-ray photon is scattered and reaches the film causing an overall gray fog.

Film Screen _____________ Too ______ too much x-ray photons reached the image receptor Could be from too much mAs or too much kVp too ______ Too little x-ray photons reached the image receptor Could be from too little mAs or too little kVp Overexposed Referring to a radiograph that is too dark because too much x-radiation reached the image receptor Underexposed Referring to a radiograph that is too light because too little x-radiation reached the image receptor

X-Ray Machine Purpose: provide a specific current (mA) & voltage (kV) to the x-ray tube convert electrical energy to electromagnetic energy (x rays) in a controlled manner control the energy of the x-ray photons control the number of photons

kVp & mAs kVp = mAs quality of beam intensity of how much tissue it can penetrate mAs the amount (quantity) of photons time the beam is left on

kVp = energy mAs = amount QUALITY vs. QUANTITY

Source to Image Receptor Distance SID -controlled and manipulated in the x-ray room

Intensity of the beam As distance _______: intensity ________ Inverse relation

Inverse square law Farther the distance of the x-ray tube to the IR Photons have less chance of getting to IR Due to divergent beam

How does distance affect IR exposure? Increased distance: decreased exposure ________________ Decreased distance: increased exposure Inversely proportional to the square of the distance Intensity is ¼ of original Intensity increases to 4 x’s the original exposure

INVERSE SQUARE LAW Used for RADIATION PROTECTION When you change your distance from the “radiation source” The intensity of radiation will be reduced by a square of the distance MOVING AWAY FROM THE SOURCE INCREASED – CLOSER TO SOURCE

DISTANCE Distance from the radiation source should be kept as great as possible

Application of inverse square law principles can yield significant reductions in patient and operator radiation exposure.

INTENSITY IS SPREAD OUT…

Inverse Square Law Formula Distance #2 - Squared Intensity #1 Distance #1 - Squared Intensity #2

How the current gets to the TUBE

Current from the outlet

Generator+ Transformers (where the power comes from)