Spatial Resolution (Chapter 28)

Spatial resolution

The degree of geometric sharpness or accuracy of the structural lines actually recorded in the radiographic image (definition, sharpness, resolution, spatial resolution, or detail)

IR exposure levels and contrast can be ______ and you can still have good recorded detail

Unacceptable

What is resolution or detail measured in for film?

Line pairs per millimeter (lp/mm)

How many line pairs per millimeter can the human eye see?

5 lp/mm

What is the term for recorded detail in digital?

Spatial resolution

Spatial resolution is primarily controlled by?

• matrix size

• pixel size

• grayscale bit depth

Lack of sharp definition is caused by unacceptable levels of _______

Penumbra

What are the units used to measure spatial resolution?

• PSF

• LSF

• spatial frequency

• MTF

• noise

PSF stands for?

Point spread function

LSF stands for?

Line spread function

MTF stands for?

Modulation transfer function

Quantum noise

Lack of sufficient incoming data for processing

PSF, line spread function and edge spread function all express the ______ of an image

Boundaries

PSF measures ______ and is determined by a sequence of mathematical measurements

Penumbra

What is beam divergence?

Photons have point source and then diverge outwards like a cone shape

Umbra

Distinctly sharp are of shadow

Penumbra

Imperfect, unsharp shadow surrounding the umbra

Describe spatial frequency

High spatial frequency represents a high-frequency signal that is capable of imaging smaller objects

What type of wavelength does high-frequency have?

Short

What type of wavelength does low-frequency have?

Long

Closer wavelengths = ______ line pairs

Closer

Modulation transfer function (MTF) measures the ________ of an image compared to the original object

Accuracy

Modulation transfer function is used on a scale of?

0-1

Fidelity

Trueness of the image

MTF of 0 represents?

No signal, therefore no image

MTF of 1 represents?

A signal of such high fidelity that it records the image perfectly

As spatial frequency of object _______ (smaller the object), the MTF _______

Increases, decreases

What are the types of noise?

• system noise

• ambient noise

• quantum noise

As noise level increases=

More complex algorithms are needed to fix the image

If noise limits are reached, then _____ of the image occurs

Degradation

What is signal to noise ratio (SNR)?

Measures signal strength relative to total noise

What is contrast to noise ratio (CNR)?

Ratio of the difference of signal intensities of two regions of interest to imaging noise

High CNR values are not possible without _____ SNR values

High

If you do not have high CNR and SNR values, it results in?

Blotchy or mottled image

How is quantum mottle resolved?

Only by increasing the # of incoming signals = increase in mAs

What is digital sampling (NYGUIST Criterion)?

Digital imaging requires that spatial resolution frequency signal be samples twice from each cycle

What is the Nyguist criterion?

A processing algorithm that averages the incoming analog data by using the distance between the DELs (to ensure no data is missed)

What is the Nyguist criterion considered?

Signal averaging

_____ sampling frequency rate _____ image fidelity

Higher, increase

What are the factors affecting spatial resolution?

• OID

• SID

• focal spot size

• film

• intensifying screens

• film/screen contract

• motion

• part thickness

The ______ the OID, the _____ the detail

Smaller, greater

The _____ the SID, the _____ the detail

Greater, greater

Why is social spot size a major controller of spatial resolution?

Because it controls penumbra

The ____ the focal spot, the ____ the penumbra, the _____ the detail

Smaller, less, greater

What can penumbra also mean in CR?

Edge gradient

______ penumbra means _____ detail

More, less

What is the formula for measuring penumbra or geometric unsharpness?

P= Focal spot size x OID/ SOD

The thicker the body part, the _____ produced, therefore _____ recorded detail

More, less

Primary factors affecting spatial resolution in digital systems are?

• Geometric properties

• Image processing system

PSP (or CR), and indirect DR intensifying screen with CCD detector have spatial resolution limitations similar to?

Film/screen intensifying-phosphor systems

The major factors in digital affecting spatial resolution are?

• the intensifying-screen (phosphor size, layer thickness, and concentrations)

• scanning system

Indirect DR with silicon/scintillator/TFT system has limitations due to the:

Fill factor

What is the fill factor?

The quantity of photons that can be registered within a single detector

_____ fill factor= _____ resolution

High, higher

Processing between system elements (more parts to go through)= ______ resolution

Lower

The major factor that limits both silicon and selenium digital systems is the size of the _________

Detector element (DEL)

Direct DR (or selenium detectors) _____ be made as small as silicon detectors

Cannot

With digital radiography, processing sets limits on recored detail depending on:

• acquisition and display matrix

• pixel pitch

• grayscale bit-depth (corresponds to x-, y-, and z-axes)

Using an intensifying screen = _____ resolution

Less

The faster the screen speed = ______ resolution

Less

The screen speed depends on:

• phosphor size

• phosphor layer thickness

• phosphor concentration

When the phosphor size increases, what effect does it have on resolution?

Decreases

When the phosphor size increases, what effect does it have on patient dose?

Decrease

When the phosphor size increases, what effect does it have on IR exposure?

Increase

When the phosphor size decreases, what effect does it have on resolution?

Increase

When the phosphor size decreases, what effect does it have on patient dose?

Increase

When the phosphor size decreases, what effect does it have on IR exposure?

Decrease

When the layer thickness increases, what effect does it have on resolution?

Decrease

When the layer thickness increases, what effect does it have on patient dose?

Decrease

When the layer thickness increases, what effect does it have on IR exposure?

Increase

When the layer thickness decreases, what effect does it have on resolution?

Increase

When the layer thickness decreases, what effect does it have on patient dose?

Increase

When the layer thickness decreases, what effect does it have on IR exposure?

Decrease

When phosphor concentration increases, what effect does it have on resolution?

Increase

When phosphor concentration increases, what effect does it have on patient dose?

Decrease

When phosphor concentration increases, what effect does it have on IR exposure?

Increase

When phosphor concentration decreases, what effect does it have on resolution?

Decrease

When phosphor concentration decreases, what effect does it have on patient dose?

Increase

When phosphor concentration decreases, what effect does it have on IR exposure?

Decrease

Motion is a very _____ cause of loss of sharpness/resolution

Common

What are the types of motion?

• voluntary

• involuntary

• equipment

What is voluntary motion?

Motion is that under the direct control of the patient

What is the best way to minimize voluntary motion?

Communication

What is involuntary motion?

Motion not under the conscious control of the patient

What are examples of involuntary motion?

Heartbeat, peristalsis, tremors

What is the best way to control involuntary motion?

Exposure time and immobilization

What is equipment motion?

Movement or vibration of the cassette, Bucky tray, grid, or tube

Tomography

A procedure that utilizes motion to blur out unwanted images