Spatial Resolution

Spatial resolution

Ability of the imaging system to distinguish small, closely spaced objects as separate details

Penumbra

Fuzzy edge around a structure caused by geometric unsharpness

Penumbra and spatial resolution

Penumbra ↑ → blur ↑ → spatial resolution ↓

Motion and spatial resolution

Motion ↑ → blur ↑ → spatial resolution ↓

OID

Object-to-image distance; distance between the anatomy and the image receptor

OID and spatial resolution

OID ↑ → magnification ↑ → blur ↑ → spatial resolution ↓

Decreased OID

OID ↓ → magnification ↓ → spatial resolution ↑

SID

Source-to-image distance; distance from x-ray source to image receptor

SID and spatial resolution

SID ↑ → magnification ↓ → geometric blur ↓ → spatial resolution ↑

Decreased SID

SID ↓ → magnification ↑ → spatial resolution ↓

SOD

Source-to-object distance; distance from x-ray source to anatomy

SOD and spatial resolution

SOD ↑ → magnification ↓ → spatial resolution ↑

Decreased SOD

SOD ↓ → magnification ↑ → spatial resolution ↓

SID relationship

SID = SOD + OID

Focal spot size and spatial resolution

Focal spot size ↓ → geometric blur ↓ → spatial resolution ↑

Large focal spot

Produces more geometric blur and lower spatial resolution

Small focal spot

Produces less geometric blur and better spatial resolution

Best geometric setup for spatial resolution

Small focal spot + long SID + small OID + long SOD

Focal spot blur formula

Geometric blur = focal spot size × OID ÷ SOD

Focal spot blur relationship

Focal spot size ↑ or OID ↑ → blur ↑; SOD ↑ → blur ↓

Angulation and spatial resolution

Angulation can increase effective OID and distortion → spatial resolution ↓

DEL

Detector element; physical sensing element in the digital detector

DEL size and spatial resolution

DEL size ↓ → spatial resolution ↑

Pitch

Center-to-center distance between neighboring detector elements or pixels

Pitch and spatial resolution

Pitch ↓ → detector elements/pixels closer together → spatial resolution ↑

Fill factor

Percentage of each detector element that is actively sensitive to radiation

High fill factor

More active signal-collecting area in each detector element

Pixel

Smallest picture element in a digital image

Pixel size and spatial resolution

Pixel size ↓ → spatial resolution ↑

Matrix

Grid of pixels that makes up the digital image

Matrix and spatial resolution

Matrix ↑ with the same FOV → pixel size ↓ → spatial resolution ↑

Pixel size formula

Pixel size = FOV ÷ matrix

FOV and spatial resolution

FOV ↑ with the same matrix → pixel size ↑ → spatial resolution ↓

DEL vs pixel

DEL = physical detector element; pixel = digital image element

Image receptor matrix

Physical array of detector elements in the receptor

Digital image matrix

Grid of pixel values that makes up the stored digital image

Display monitor matrix

Grid of pixels on the monitor used to display the image

Display matrix and spatial resolution

Larger display matrix can improve the ability to display fine detail

Display pixel pitch

Smaller display pitch → pixels closer together → better displayed spatial resolution

General diagnostic monitor resolution

Approximately 3 MP minimum according to the course

Mammography monitor resolution

Approximately 5 MP minimum according to the course

SMPTE test pattern

Quality-control pattern used to evaluate monitor spatial resolution and grayscale display

Spatial resolution memory

Small focal spot + long SID + small OID + no motion = sharp image