Physics Rad Tech Exam 2

Purpose of Automatic Brightness Control

to automatically adjust kVp, mA, filtration, and
pulse width to maintain a viewable image

Define Fluoroscopy

fluoroscopy is a type of x-ray imaging used to
obtain real-time images of the internal structures of a patient. (up to 30 images per second- “movies”)

Tyoes of image receptors used in fluoroscopy

image intensifier and flat pannel detector

in film-screen radiography, exposing the patient to an unnecessarily large radiation dose
will typically produce

an image that looks too dark

Using Rad. Tech. slang, what do we call an x-ray image receptor?

Bucky

What is II

Image Intensifier

The input phosphor of an image intensifier is made of what material?

Cesium-Iodide (CsI)

Light photons interact with a material and produce electrons by which part of the image
intensifier?

Photocathode

Flux gain formula

Fg = # of output / # of input

Compared to continuous fluoroscopy, what is the main advantage of pulsed fluoroscopy?

reduced dose to the patient

basic components of fluoroscopy

• X-Ray tube

• Surface for patient to lay on

• Image Receptor

• Display Device

What is flux gain

gain due to electron acceleration;
when electron energy is increased,
more photons are released when electrons strike
output screen—which causes the image to be brighter

Total gain formula

g= g_mg_f

Minification Gain

gm = area of input screen / area of output screen

Flux Gain formula

gf = number of output visible
light photons
divided by number of
input x-ray photons

In regards to the spatial resolution of conventional radiographic and CT images, which
images have better spatial resolution?

conventional radiographic images

In regards to the contrast resolution of conventional radiographic and CT images, which
images have better contrast resolution?

CT images

CT is good at distinguishing fat from other soft tissue because of the ____

decreased density of fat

indirect vs direct detection

• Direct detection: input produces the final result
  • Indirect detection: input produce something else, which eventually
  yields the final result.

EI

Exposure Index - a way of quantifying radiation exposure to the image receptor (NOT the patient.)

DI

Deviation Index- it measures how far off the exposure index for a given patient imaging exam is from the target value of the exposure index

This formula is what you need to keep the exposure at the image receptor constant

mAs1/GCF1 = mAs2/GCF2

kVp means what

peak X-ray tube voltage in kilovolts

mA

X-ray tube current in milliamperes

mAs

xray tube current in milliamperes times exposure time in seconds

primary effect of scatter

reduces contrast

How to find CT number

ct # = u-u(water)/u(water) * 1000