image analysis quiz one

Exposure index

indicates the amount of radiation reaching the image receptor

higher EI =

more receptor exposure

Deviation index

shows how far actual receptor exposure is from the target

if the DI is 0 then…

target exposure

if the DI is a positive number

= more receptor exposure

if the DI is negative then…

= less receptor exposure

s number

sensitivity number used on some systems (fuji); behaves inversely to exposure

higher S number =

less receptor exposure

dose creep

gradual increase in exposure over time because of automatic rescaling in digital systems to produce visually acceptable images even after exposures being higher than necessary

quantum noise

too few xray photons reach the IR. image will appear grainy, speckled, or sand like

raw data

digital values collected from the detector before the final display processing is applied

histogram

a graph of pixel gray shade values from the acquired image

VOI

image data that represent the anatomic structures of interest

Look up table (LUT)

the procedure specific ideal display reference used to rescale the image histogram

contrast

difference between adjacent brightness levels

subject contract

created by the patient by differential absorption before processing occurs

signal to noise ratio (SNR)

desired signal compared with undesired noise

contrast resolution

ability to distinguish subtle differences in gray shades

what is contrast resolution affected by?

subject contrast, noise, scatter, bit depth

spatial resolution

ability to visualize small structures and fine details

what is spatial resolution affected by?

motion, focal spot, OID

bit depth

determines how many digital gray values can be represented

five step problem solving:

SEE, IDENTIFY, CAUSE, CORRECT, DECIDE

how to treat trauma imaging?

adjust the tube, CR, receptor to match the patient to not force the injured patient into “textbook” position if unable

how to treat pediatric imaging?

use lower technical factors, precise collimation and short exposure time to reduce motion and radiation exposure

bariatric imaging

more tissue thickness increases attenuation and scatter and can reduce contrast resolution

additive patient condition

condition that increases tissue density/attenuation and often requires increased exposure

examples of additive condition

pneumonia, pleural effusion, ascites, pulmonary edema

destructive condition type

condition that decreases tissue density/attenuation and often requires decreased exposure

examples of destructive condition type

emphysema, pneumothorax, osteoporosis, osteolytic disease