Intro to X-Ray Production, Density, Contrast, and Detail

Question 1

what is radiology?

Answer 1

a clinical tool to determine:
1. presence or absence of disease
2. specific disease recognition and/or localization
3. progression of disease
4. evaluation of therapeutic success or failure

Question 2

what is ionizing radiation?

Answer 2

radiation with sufficient energy (>15eV) to cause an atom or molecule that reacts with it to lost an electron; is hazardous to health because produces free radicals and DNA damage

exhibited by x-rays and gamma rays

Question 3

describe the steps of x-ray production

Answer 3

production occurs through conversion of energy within particulate radiation (electrons) to electromagnetic energy (x-rays); this process occurs within the x-ray tube

1. electrons produced at the negative end of the x-ray tube (anode)
2. high voltage applied between the negative (cathode) and positive (anode)
3. high speed electrons collide with the metal anode and x-rays are produced

Question 4

describe cathode, anode, and the 2 types of anodes

Answer 4

cathode: negatively charged portion of the x-ray beam; controlled in units of mA (milliamperes) or mAs (milliampere seconds), correlating to the number of electrons produce

anode: the positively charged portion of the x-ray beam; only 1% of the electrons that hit it produce radiation! the rest produce heat; controlled in units of kVp (kilovoltage peak applied across the tube), the quality of the electrons)

2 types of anodes:
stationary: cheaper, lower voltage, easily overheated, short lasting
rotating: better dissipates the heat, long lasting, higher voltage currents, more expensive

Question 5

describe kVp

Answer 5

1. kilovoltage peak applied across the x-ray beam; average x-ray beam is only 1/3 to 1/2 the kVp because the beam includes many other energy x-rays
2. increasing kVp increases the intensity and the energy of the beam but LOWERS contrast
3. kVp is the only prime exposure variable that can change the energy of the beam

Question 6

why is it not always a good idea to increase kVp?

Answer 6

because increasing kVp lowers contrast, meaning that you will not be able to distinguish shades of grey as clearly, which you need to be able to differentiate between organs

Question 7

describe mAs

Answer 7

1. milliamperes per second, determine the size of the electron cloud produced (quantity of electrons)
2. used to quantify the amount of radiation produced; higher mAs produce more electrons boiled off the filament and then more x-ray photons will be produced

Question 8

contrast increasing mAs to increasing kVp

Answer 8

increase mA (tube current) increases the amount of electrons and the NUMBER of x-rays

increasing kVp increases electron energy and the ENERGY of the x-ray

Question 9

what is the heel effect?

Answer 9

1. some x-rays are absorbed by the anode, so the x-rays closer to the anode are less intense, while the x-rays on the cathode side are more intense
2. use this in your favor while obtaining x-rays by positioning the THICKER portion of the patient TOWARD the cathode!! (aka the head) because you need more x-rays to go through a thicker body part

Question 10

what are the 3 fates of x-rays?

Answer 10

1. absorbed by imaging plate: do no generate any helpful info for the image (absorbed = white)
2. pass through an object: will yield various shades of grey to the image; the denser the object, the closer to white; the less dense the object, the closer to black
3. scatter: refracted after interacting with a body part; this is what you must wear PPE to protect against; not as high energy as the direct beam, but still high enough to cause some damage

Question 11

describe attenuation of the x-ray beam

Answer 11

reduction in intensity of the primary beam as it travels through an object/patient by either absorption or scatter (more matter more scatter!!)

Question 12

describe what could cause:
too white, too dark, high contrast, and low contrast images

Answer 12

too white: underexposed, mA too low (white body parts in a tan line were underexposed to the sun; bathing suit line was too high to let you tan in that spot)
too dark: overexposed: mA too high
high contrast: low kVp; fewer shades of grey, easier to differentiate black and white
low contrast: high kVp; more shades of grey (because 50 shades of grey is a low quality book)

thorax already has high contrast, so need a low contrast technique to balance it out

abdomen already has low contrast, so need a high contrast technique to balance it out