digital imaging chaacteristic (slide notes)

spring 2025-2026

xray beams start as ,, to become digital images, they must be converted to ,, digital systems do this using

xray beams start as ANALOG SIGNALS

to become digital images, they must be converted to NUMBERS

ADC (analog-to-digital conversion)

two steps turn an analog signal into a digital image

sampling

quantization

sampling measures the ,, quantization assigns a

sampling measures the analog signal at small , regular intervals

quantization assigns a numerical value (BINARY) to each sample

a digital img is made of tiny squares called ,, each pixel has a ___ ___ that becomes a shade of gray ,, pixels arranges in rows and columns form a ,, DEL is a

a digital img is made of tiny squares called PIXELS

each pixel has a NUMERICAL VALUE that becomes a shade of gray

pixels arranges in rows and columns form a MATRIC

DEL is a detector element

bit depth is,, bit depth determines ,, example of bit depth (8-bit =…) ,, higher bit depth = …

bit depth is how much info each pixel can store

bit depth determines how many gray shades the system can display

8-bit = 256

higher bit depth = better contrast resolution but larger file size

the systems ability to show very small exposure differences is

higher contrast resolution = …

contrast resolution
higher contrast resolution = better soft-tissue visibility

matrix is the grid of ,, common size of matrix is ___x___ or ____x____ ,, bigger matrix = more pixels = better …

matrix is the grid of pixels

common size of matrix is 512×512 or 1024×1024

big mat = more pix = better

FOV = …

FOV controlled by (2)

larger FOV = shows more …

FOV = how much anatomy is included in img

FOV controlled by detector size + distance

pixel size is determined by the (2)

smaller FOV = smaller pixels = better …

changing matrix or FOV changes pixel size, but

pixel size is determined by the FOV + matrix

smaller FOV = smaller pixels = better resolution

changing matrix or FOV changes pixel size, but NOT EACH OTHER

spatial frequency measures ___

higher spatial frequency = ability to see ____ ___

spatial frequency depend on … (3)

spatial frequency measures detail

higher spatial frequency = ability to see smaller structures

spatial frequency depend on pixel size , matrix, FOV

air kerma measures how much …

units of air kerma is ___ aka (…)

air kerma measures how much rai

units of air kerma is gray (Gy)

KTSD stands for

KTSD is a

is used for …

KTSD stands standardized radiation exposure

KTSD is a standardized exposure for the IR

is used for equipment calibration

KIND standes for

the ___ exposure to the IR for a specific image

derived from

KIND stands for indicated equivalent air kerma

the ACTUAL exposure to the IR for a specific image

derived from pixel values

KTGT stans for

what is it

set by the

KTGT stands for target equivalent air kerma

ideal exposure for each exam type + view

set by the manufacturer

di is the difference btwn ___ and ____

difference btwn KIND and KTGT

the final displayed img depends on (3)

brightess

contrast res

spatial res

2 photographic properties reveal detail

receptor exposure

contrast

brightness is

not the same as

brightness is luminance of the monitor

not the same as the old film

long scale is

short scale is

subject contrast is

image contrast

long scale is many shades of gray LOW CONT

short scale is few shades of grey HIGH CONT

subject contrast is PAT TISS CONT

image contrast ADJUSTING BY PROCESS

subject cont comes from

tissues interact w/ (4)

subject cont comes from character

tissues interact w/

• attenuation

• absorption

• penetration

• scatter

primary beam is coming out of the tube b4 …

creates no …

primary beam is coming out of the tube b4 hitting the patient

creates no scatter

remnant beam exits the …

carries …

also contains some …

remnant beam exits the patient and reaches the IR

carries image-forming info

also contains some scatter

attenuation is

absorption is

attenuation is partail absorption + scattering of x-rays

absorption is x-ray completely stopped

4 categories of bone absorbers

bone

muscle

fat

air

dynamic range is the total range of exposures a ...

too low =

too high =

bigg dynamic range = more gray = better …

dynamic range is the total range of exposures a detector can capture

too low = mottle

too high = saturation

bigg dynamic range = more gray = better contrast res

exposure latitude is the range of exposures within dynamic range that produce …

wider latitude =

exposure latitude is the range of exposures within dynamic range that produce acceptable images

wider latitude = more flexible

3 types of noise

system noise

ambient noise

quantum noise

system noise is

ambient noise is

quantum noise is

system noise is electronics

ambient noise is background radiation

quantum noise is too few photons

high snr = better image but …

noise decreases …

high snr = better image but high dose

noise decreases contrast and fine details

DQE stands for

DWE measures how efficiently the…

higher DQE =

perfect DQE =

depends on

DQE stands for detective quantum efficiency

DWE measures how efficiently the the detector conv x-rays to img

higher DQE = low dose-good img quality

perfect DQE = 1.0

depends on MTF (sharpness)

MTF stands for …

high MTF =

as spatial frequncy increases , MTF …

MTF stands for …

high MTF =

as spatial frequncy increases , MTF modulation transfer function