Intro to Radiographic Image Quality (RADS 342)

Largest controlling factor of contrast

Algorithm (what exam we pick on the comp.)

Radiographic Image Quality

how close or exact the representation of an anatomic structure is to the recorded image (does the image look like the body and how it sits in the pt.)

Radiographic Quality cannot be...

measured only described

Two major divisions of radiographic quality

Geometric Factors (sharpness of details) & Photographic Factors (visibility of details)

Two Subdivisions of Geometric Factors

Spatial Resolution & Distortion

Two Subdivisions of Photographic Factors

Image Receptor Exposure (IRE) or Brightness & Contrast

Resolution

the ability to visually detect separate objects on an image (can you see separate objects individually)

Spatial Resolution

the ability of an imaging system to resolve a small object that contrasts the background

-the sharpness of the structural edges recorded in the image or the bone vs soft tissue interface

The smaller the pixel size... (spatial resolution)

the greater the spatial resolution

Largest driver for Spatial Resolution is...

Pixel Size

lack of spatial resolution is

blur or unsharpness

Spatial resolution is measured in

line pairs per millimeter (lp/mm)

Spatial Fequency/ Line Pairs are used to...

quantify how small of an object can be recorded with accuracy & clarity

The higher the lp/mm... (spatial resolution)

the better the spatial resolution/quality

distortion

a misrepresentation of the size or shape of the structures recorded in the radiographic image

size distortion (magnification)

the enlargement of the recorded image as compared to the actual size of the structure

-can never have none of this and can never minify a bone/anatomy

Shape distortion or True distortion

misrepresentation of the shape (elongated or foreshortened) of the structure recorded as compared to actual shape of the structure

Size distortion is what kind of issue?

distance issue as a shorter SID or more OID leads to magnification of the part and for this it's equal parts of magnification across the entire bone

Shape distortion is what kind of issue?

angulation issue of the CR, part, or IR, for this its unequal magnification from angling, one part will be closer or farther causing this distortion

Image Receptor Exposure

the amount of radiation striking the image receptor, exposure is increased when the source is increased

Brightness

a measurement of the luminance of a monitor calibrated in units of candela (cd) per square meter, cd/m^2 or nit

Brightness is always just a function of the...

monitor/ computer, can only be changed here

Contrast

the visible different between any two selected areas of brightness levels whiting the displayed image

Most important factor in radiographic quality?

contrast

What modality is contrast most important for?

Mammography

Grayscale (scale of contrast)

refers to the number of brightness levels (gray shades) visible on an image

dynamic range

the number of gray shades that an imaging system can reproduce and can be represented by each pixel in CR/DR

Long Scale

term used when slight differences between gray shades are present (LOW CONTRAST) but the total number of gray shades are increased

-more grays

Short Scale

the term used when considerable or major differences between gray shades are present (HIGH CONTRAST) but the total number of gray shades is reduced

-more black & white

kVp and contrast relationship

inversely proportional

-high kVp - low contrast (long scale)

-low kVp - high contrast (short scale)

the dynamic range for CR/DR compared to film imaging is...

much larger, went from 30 shades of gray to more than 65000 shades of gray

Radiographic contrast

variations in brightness on the image

Image receptor contrast

the fixed characteristic of the receptor, no amount of kVp changes will change what the computer doesn't let us

Contrast resolution

the ability to image similar tissues and being able to resolve information on an image

-changes based on the machine that's used

contrast resolution is limited by...

the quantization (number of bits per pixel) of the analog-to digital converter

exposure latitude

the range of exposure factors that will produce quality images at appropriate patient doses, sometimes referred to as the margin of error

subject contrast

the magnitude of the signal difference in the remnant beam (exiting beam) as a result of the different absorption characteristics of the tissues and structures making up that part

subject contrast is dependent on...

the cellular makeup of the pt. (fat, bone, muscle) as they will all attenuate differently on an x-ray

Noise

the undesirable differences in the brightness levels of the image as it destroys contrast resolution and comes from too little mAs

Quantum Mottle

principal contributor to radiographic noise referring to the randomness with which a low number of x-ray photons interact with the image receptor

-coming from too little exposure to produce a diagnostic image