Equip/Image - Digital Radiography (Unit 2-3)

Flat-Panel Detector (FPD) Digital Systems are also known as:

Digital Radiography (DR)

2 Types of Flat Panel Detectors

• Direct Conversion Detectors

• Indirect Conversion Detectors

Direct Conversion Detectors

Use a photoconductor, which is capable of converting x-rays into an electronic signal.

Indirect Conversion Detectors

Use a scintillator, which converts incoming x-ray photons to light.

Indirect Conversion has 2 steps:

1. Convert incoming x-ray photons to light first, which is accomplished through the use of a scintillator.

2. Convert light photons to an electronic signal using a photodetector.

Indirect DR systems include either a:

• Charged-coupled device (CCD)

• Amorphous silicon with a thin film transistor (TFT) array

Direct DR systems without a scintillation/light conversion step have a _______________.

Higher DQE

DQE (Detective Quantum Efficiency)

% of incoming x-ray photons that are detected and absorbed by the IR for transformation to the x-ray image.

High DQE

Detector uses x-rays efficiently to produce a detailed image with less radiation (most desirable).

Low DQE

Detector “wastes” x-rays and requires more dose to get the same clarity.

Direct conversion uses _____________________ and a TFT.

Amorphous Selenium

Both types of indirect detectors need a __________ to change the x-ray photons to light.

Scintillator

The main difference between TFT detectors and CCD in indirect DR is the way the light is converted to ______________.

An electrical signal

Scintillators emit light _____________ which can reduce spatial resolution.

Isotropically

Because the "glow" of light spreads out, the detector can't always tell precisely where each x-ray landed. This ____________ the image sharpness

Softens/decreases

Indirect TFT requires a scintillator such as ___________________, or _________________ to emit light. Which is more commonly used today?

• Cesium iodine (CsI)

• Gadolinium oxysulfide (GdOD)

• CsI

Once the light reaches the __________________ for detection, it is converted into electrical charges that are then deposited on a TFT.

Amorphous silicon (a-Si)

TFT collects the electric charges produced by either the selenium or silicon as an array or matrix of pixel-size ____________________.

Detector elements (DEL)

Detector Elements (DEL)

Receives exposure and collects signal. Smallest sensing unit in a digital x-ray detector.

Each DEL pixel is the same size and measures around _______, about the width of a human hair.

100-200 microns (μm)

DEL pixels and screen pixels are ______________.

Different

DEL pixel lives in the ___________ while screen pixels live in the _______________.

• Detector

• Display Monitor

TFTs act like buckets to _______________ electricity so the computer can make the picture.

Collect and move

The TFT acts like a ______. When open, the stored charge in the DEL flows out into the ____________. When closed, the charge _____________.

• Switch

• Readout electronics

• Stay put

Each pixel detector element (DEL) includes the ______________, the _____________, and the ________________.

• Sensing area

• Capacitor

• TFT

The _________ refers to the sensing area compared to the non-sensing electronics area.

Fill factor

______ is the fill factor used in modern DELs.

80/20

As fill factor % goes up, spatial resolution (sharpness) and contrast resolution (subtle differences in gray) will ___________.

Go up

Better resolution is achieved with a __________________ paired with a _________________.

• Smaller DEL size

• Greater fill factor

95% fill factor provides ________________________ than 75% fill factor.

More spatial resolution

Smaller DEL size of 100 µ (mammo) provides _____________________________.

More spatial resolution

Larger DEL size of 200μ (x-ray) provides _____ spatial resolution.

Less

CCD (Photodetector)

Sensor chip that is capable of converting visible light into an electric charge and storing it (no TFT involved).

The light produced (by a scintillator) from x-ray interactions must be optically coupled to the CCD sensor chip by ______ or _________.

• Lenses

• Fiber optics

Indirect TFT

• “Bucky Brigade”

• Detector itself collects the lgith and converts it to electrical charge right in each pixel

• More common system in diagnostic radiography.

Indirect CCD

• “Mini Camera”

• Light is sent to a separate “camera chip” to capture the signal.

• Older system - no common anymore

_______________________ may be used in place of the CCD as a photodetector.

CMOS (Complimentary Metal Oxide Semi-Conductors)

____ is slower, more expensive, and consumes more power but has better image quality and higher DQE.

CCD

_____ is faster, cheaper, and consumes less power but has lesser image quality and lower DQE.

CMOS

Direct Conversion Systems

Directly convert incoming x-ray photons to an electronic digital signal.

The photoconductor used in direct conversion systems is _________________.

Amorphous selenium (a-Se)

In a direct conversion system, ionization caused by the x-ray photons results in the selenium atoms _________ for collection.

Freeing electrons

Direct conversion is more common in ______ due to sharp detail capability.

Mammo

Image Acquisition

Both direct and indirect resulting data is the latent image that needs to be read out.

Processing

Only the exposed DELs are read. 2 Step process

• Pre-processing

• Post-Processing

The first step in DR processing is pre-processing, which _________________________.

Corrects for any faulty DELs

The second step in DR processing is post-processing, which _______________________ before it is displayed on the monitor.

Optimizes image contrast, brightness, and detail

DR detectors have 2 general classifications:

• Portable detectors

• Integral detectors (built-in to bucky)

Most of today's FPDs are _________ and use TFTs with non-tethered wi-fi technology.

Portable

Some FPDs can withstand weights of _____.

500 lbs

The average cost of a FPD is ______.

$25k-50k

Which of the following are used as scintillors in Indirect DR systems? (select all that apply)

• Cesium Iodine

• Amorphous Silicon

• Amorphous Selenium

• Gadolinium Oxysulfide

• Cesium Iodine

• Gadolinium Oxysulfide

Which DR system uses amorphous selenium as a photoconductor?

Direct DR - TFT

Image Resolution is improved with selection of: (6)

• Smaller x-ray tube focal spots

• Shorter OIDs

• Longer SIDs

• Shorter exposure times with higher mA selections

• Grids (over 80 kVp)

• Tighter collimation

In digital imaging, kVp and contrast are ____________, and mAs does not affect ___________.

• Not directly related

• Image brightness

Final digital image quality is essentially a function of ___________.

Total exposure to the detector.

Higher ____ values are now recommended with digital detectors.

kVp

mAs exposures that are too low will result in ________________.

Quantum mottle/Noise

IR exposure changes should be at least __________ to produce a visible change.

25-33%

How should you change exposure factors for an additive condition?

5-15% increase in kVp

How should you change exposure factors for an destructive condition?

25-50% decrease in mAs

Fixed kVp Systems

Use an optimal kVp that is not changed and variable mAs.

Variable kVp Systems

Use an optimal mAs that is not changed and variabel kVp.

Both kVp systems will work, but ______________ are better suited for use with digital image receptors.

Fixed kVp systems

S# (Fuji, Konica, Phillips)

Range 150-250

• Higher = underexposed

• Lower = overexposed

EI# (Carestream, Siemens)

Range 1500-1800

• Higher = overexposed

• Lower = underexposed

Exposure Index (EI#)

Acutal exposure

Target EI (EIt)

Ideal exposure

Deviation Index (DI)

% deviation from target. DI value of 2 or more needs to be evaluated for a repeat.

Contrast/brightness is not an issue when evaluating an image because __________________ will fix it

Rescaling and LUT

What are the two most common issues found when evaluating an image?

• Poor positioning

• Noise

Because noise is a common issue in digital radiography, we tend to overcompensate with ________ and allow the computer to correct the image. This leads to ________.

• Higher mAs

• Dose creep

A DI of 3 is ____% too high and indicates _____________. Is a repeat warranted?

• 100

• Excessive overexposure

• Repeat only if there is burn-out.

A DI of -3 is ___% too low and indicates _____________. Is a repeat warranted?

• 50

• Excessive underexposure

• Repeat required due to excessive noise.

EIt-EI#= ___________

Deviation Value

Deviation Value/EIt= _________

% Deviation

Data Drop

Extreme overexposure in which DELs are overwhelmed with photon energy and become incapable of recognizing high-energy values.

Images with data drop will demonstrate _____ contrast.

Poor

Detector Saturation

Data-drop throughout an entire region of the detector and loss of diagnositc info or mimic of destructive pathology.

Digital Processing Latitude

Range of x-ray exposures that a digital detecor can capture and still produce a usable image.

A wide digital processing latitude means the system is ______ forgiving and makes it ______ to get a good image.

• More

• Easier

Benefits of increased latitude include the ability to image structures of ____________ without loss of visibility and increased ____________ in under or overexposure.

• Varying attenuation values

• Margin for error

Increased latitude maintains a useful __________.

Image brightness

Be wary of ______________, ___________________, and ______________with wide latitude systems.

• Underexposed quantum mottle

• Overexposed flattened saturation

• Dose creep

A deviation index value of 0.5 indicates:

Nearly optimum exposure.

In what situation are you most likely to see noise on your DR radiograph? (select all that apply)

• When you did not decrease technique for a smaller patient.

• When you did not increase technique for a larger patient.

• Underexposure

• Overexposure

• When you did not increase technique for a larger patient.

• Underexposure

Advantages of Digital X-Rays (3)

• Digital images can be manipulated without re-exposure to patients.

• Require less physical storage.

• Can be sent to remote locations.

Computer system consists of:

• Hardware

• Software

Hardware

Physical component of the computer; consists of input and output devices to allow info to be directed outside the computer.

Software

Set of instructions or program to operate the computer.

CPU (Central Processing Unit)

Primary control center of the computer which includes memory.

2 Types of Memory

• RAM (Random Access Memory)

• ROM (Read Only Memory)

RAM (Random Access Memory)

Volatile, losing info when computer is off.

ROM (Read Only Memory)

Hardwired to computer, stays in computer even when off.

Any given radiology facility may perform __________ examinations per year, requiring ______ of computer memory. Long-term storage may require ______.

• 150,000

• 3.2 TB

• 10-16 TB

Network

2 or more objects sharing resources and information.

Server

A centralized computer managing network resources; stores, sends, and receives data.

Informatics

The science of processing data for storage and retrieval; information science.

Clinical Informatics (BMI)

Utilizes data and information technology to deliver healthcare services.

Electronic Health Record (EMR)

Electronic medical records.