Image Acquisition Chapter 8

Absorption

The xray photons removed from the xray beam as a result of the uptake of their energy of body tissues.

Attenuation

Reduction of the energy or number of photons in the primary xray beam after it interacts with anatomic tissue.

Coherent Scattering

An interaction that occurs with low energy xrays, typically below the diagnostic range. The incoming photons interact with the atom, causing it to be excited. The xray does not have energy but changes direction.

Compton Effect

Scattering that result from the loss of some energy of the incoming photon when it ejects an outer shell electron from a tissue atom. 

Compton Electron

the electron ejected from an atom during a Compton scattering effect

Contrast Resolution

Used to describe the ability of the imaging system to distinguish between small objects that attenuate the xray beam similarly in digital imaging. 

Differential Absorption

The difference between the xray photons that are absorbed photoelectrically versus those that penetrate the body.

Dynamic Range

the range of exposure intensities that an image receptor can respond to an require image data.

Exit Radiation

the attenuated ray beam leaves the patient and is composed of both transmitted and scattered radiation; also called remnant radiation

Fluoroscopy

the use of continous beam of xrays to create dynamic images of internal structures that can be viewed on a display monitor. 

Fog

unwanted exposure on the radiographic image that does not provide any diagnostic information.

Image Receptor

a device that recieves the radiation leaving the patient

Ionization

the removal of an electron from an atom

Latent Image

The invisible image that exists on the image receptor before it has been processed. 

Manifest Image

the visible radiographic image on the exposed detector after processing

Matrix

combination of rown and columns (array) of pixels that make up a digital image. 

Photoelectric effect

In the diagnostic range, the total absorption of the incident photon by ejecting an inner shell electron of a tissue atom. 

Photoelectron

the electron ejected from an atom during a photoelectric interaction

Pixel

picture element, the smallest component of the matrix, which is represented as a single brightnesslevel on a computer monitor. 

Pixel Bit Depth

also called number of bits, it affects the number of shades of gray available for image display 

remnant radiation

the attenuated xray beam leaving the patient is composed of both transmitted and scattered radiation, also called exit radiation

Scattering

incoming photons are not absorbed but instead lose energy during interactions with the atoms composing the tissue

Secondary Electron

the ejected electron resulting from the compton effect interaction, also called compton electron

Tissue Density

matter per unit volume or the comactness of the atomic particles composing the anatomic part

transmission

xray photons that pass through the body to expose the image receptor

Which of the following allows the greatest absorption/attenuation of the xray beam?

metal implants

To MAINTAIN exposure index, what should occur when kVp. is increased by 15%

mAs is decreased by 1/2

Only 1% of the original cathode electrons become the x-ray beam. What percentage of thecreated xray beam reaches the image receptor? 

5%

Based on the first lab, what is the expected outcome if mAs is doubled? 

EI increases by 2x

As patient size increases, total mAs needed to maintain EI will:

increase

Which of the following provides the ideal exposure index?

The EI should be the same whether AEC or manual techniques are used.

Which of the following allows the greatest transmission of the xray beam?

air

Which of the following should the technologist do FIRST if the EI is considerably higher than the acceptable range for the equipment? 

Decrease mAs

Increasing beam quality will ___ beam attenuation

decrease

Based on the first lab, what is the expected outcome if kVp is increased by 15%?

EI increases by 2x

Which of the following describes the process of radiographic image formation? 

differential absorption

X-rays can eject electrons from atoms. This is known as:

ionization

The x-ray interaction with anatomic tissue that is responsible for scattering is: 

compton

Which of the following will increase beam attenuation?

thicker anatomic part

factors that decrease x-ray absorption include:

increased xray beam quality

the range of exposure intensitites an image receptor can accurately detect defines:

dynamic range

Digital image quality is improved with:

larger matrix size

increaing the pixel bit depth will: 

increase contrast resolution

dynamic imaging of internal structures can be visualized with a/an: 

image intensifier and flat panel detector 

The process of differential absorption to form an image is the same for digital imaging and fluoroscopy?  TRUE OR FALSE

true

Milliamperage in the x-ray tube is the unit of measure describing

tube current

which of the following describes the x-ray tube current?

quantity of electron flow

which of the following statements describes the relationship between milliamperage and beam intensity? 

beam intensity is directly proportional to the mA

How is the x-ray beam changed when milliamperage is increased by a factor of 2? 

beam quantity increases by a factor of 2

Which of the following would double the quantity of photons in the x-ray beam?

double the exposure time, but do not change the milliamperage and double the milliamperage, but do not change the exposure time

which of the following statements describes the relationship between miliamperage and receptor exposure

receptor exposure is directly proportional to the millamperage

which of the following statements describes the relationship between millamperage and patient dose?

patient dose is directly proportional to the milliamperage

increasing millamperage result in which of the following?

increased beam quantity

to reduce a patients dose by half, what must be done to the millamperage if all other factors are held constant? 

reduce mA by 1/2

x-rays taken using 200 milliamperes at 0.50 sec and result in 0.10 mgy of patient exposure. Assuming that all other factors remain constant, which mA settings would result in a pateint exposure of 0.20 mGy

400 mA

Exposure time is the amount of time that

electrons are flowing through the xray tube

what is a unit of measure for exposure time?

seconds

What is the unit of measure for tube current?

milliamperage

what property of the xray beam is influenced by changes to the mAs

intensity

Exposure made using 100 mA and 0.05 sec. How will the beam intensity change if the exposure is repeated using 200 mA and 0.025 sec

beam intensity remains the same

and exposure made using 100 mA and 0.05 sec. How will the patient dose change it exposure is repeated using to 200 mA and 0.025 sec? 

patient dose will remain the same

which of the following is an important benefit of using a short exposure time?

decrease motion blur

Which of the following exposure settings will produce a radiograph with the least amount of motion blur? 

420 mA and 0.001 sec

A radiograph required on a non compliant patient demonstrates appropriate exposure but significant motion blur. If the original technique was 100 mA and 0.5 sec, what new technique will decrease motion artifact while maintaining the same total exposure?

500 mA and 0.1 sec

The default technique for a lateral projection of the thoracic spine is 400 mA, 0.1 sec, 80 kVp, and 40 SID. How should the technologist modify this technique to blur the ribs, and increase the visibility of the spine while maintaining the same receptor exposure? 

decrease mA and increase exposure time

kVp iin the x-ray tube is the unit of measurement describing

tube potential 

which prime exposure factor controls the energy of the x-ray beam

kVp 

Which of the following statements describes the relationship between kVp and x-ray energy

maximum x-ray energy is numerically equal to the kVp

kVp influences which 3 characteristics of the xray beam

quantity, quality, penetrability

an xray exposure is made using 320 mA, 0.2 sec, 96 kVp, and SID of 60 inches. What is the maximum energy of xray photons in the beam? 

96 kEv

Which statement describes the relationship between kVp and beam intensity?

beam intensity is directly proportional to the square of the kVp

A radiograph acquired at 60 kVp results in an under exposed image. What new kVp setting will double the receptor exposure?

69 kVp

A radiograph acquired 100 kVp results in an underexposed image. What new kVp setting will double the receptor exposure?

115 kVp

When using a fixed technique, an increase in kVp will cause patient dose to?

increase

when using a fixed technique, a decrease in kvp will cause patient dose to?

decrease

SID is defined as the distance from the

anode focal spot to the image receptor

What characteristic of the xray beam is influenced by changes to the SID

intensity

When the distance from xray sourcce increases, the beam intensity will

decrease

When the distance from the xray source decreases, the beam intensity will

increases

When the distance from the xray source decreases, patient dose will

increase

When the distance from the xray source increases, the patient dose will

decrease

What term describes the geometry of the xray beam? 

divergent-spreading apart and becoming less concentrated through space

which statement describes the relationship between the SID and receptor exposre

receptor exposure is inversely proportional to the square of the SID

A radiograph required at 40 inches results and a receptor exposure of 10 mGy. What is the new receptor exposure if the radiograph is acquired with the same technical factors and 72 inches

3.1 mGy

A radiographic technique chart recommends 4 mAs and 68 kVp at 72 inches for a certain procedure. How will the receptor exposure be affected if the radiograph is performed using the recommended exposure technique but at 60 inches

receptor exposure wi

What is the positive side of th

Which of the following would result in the highest attenuation of the xray beam?

spine

Which of the following would result in highest transmission

lungs

which does not affect absorption

image receptor

the majority of photons produced in the xray tube are a result of which interactions

brems 

The majority of photons absorbed by the patient are a result of what interaction

photoelectric

Which occurs in patient issue and produces a photon with enough energy to leave the patient

compton

xray are generally attenuated at a rate of

50% per 4-5 cm of tissue thickness

Which atomic number and element will absorb the most photons: 

56 barium

The xray beam prior to entering the patient is called primary beam

primary beam

less than 5% of the primary beam interacting with the patient reaches the IR

true

The ability of the IR system to detect xray photons is known as 

dynamic range

Which of the following has the smallest pixel size

256 × 256

Where is the grid located?

between the patient and IR

larger bit depth=

more gray in the image