Image analysis Chapter 2 found

What is the purpose of the TFT?

Collects electrical charge produced in the DEL when remnant radiation strikes it

Uses cassette that can be placed in the Bucky or on the table to obtain a projection. Once upon has been exposed the body part is chosen in a menu at the work station

Computed radiography

What are the two types of digital imaging systems?

Computed radiography and direct-indirect digital radiography

A high SNR reaching the IR causes a loss in:

Contrast resolution

The degree of difference in brightness levels between adjacent tissues on a displayed image

Contrast resolution

What is the biggest obstacle when imaging obese patients?

Controlling scatter

How do cartilaginous spaces and epiphyseal plates in pediatric patients appear?

Darker shaded spaces or lines (may look similar to an irregular fracture or joint space to those not familiar with peds imaging)

True/False: exposure indicator is a measure of patient dose

False

True/false: masking should be used instead of collimation

False: masking does not decrease patient dose

What does the 15% rule indicate?

For every 15% change in kV exposure to the IR is adjusted by a factor of 2

When should the anode heel effect be taken into consideration?

For studies of the vertebral column and long bones

If contrast resolution is adequate, what should be adjusted to offset quantum noise?

mAs

What is the main controlling factor for exposure

mAs

What should be increased when imaging obese patients?

mAs and or kV

A mAs adjustment of ____ is needed when going from a 14x17 to a 10x12

35%

Where does the computer read the EI?

At the defined VOI (halfway between S1 and S2)

What are common causes of histogram analysis errors?

-part selection -central Ray centering -collimating -scatter radiation control -clearly defining the VOI (CR) -coverage of 30% (CR) -multiple projections on one IR (CR) -Background radiation fogging (CR)

Collimating should be witching ____ of the skin that prevents too much background data from being included

.5 inch

Collimation should be within _____ of the skin to prevent background data from being included in the exposure field.

0.5 inch

Digital radiography provides excellent contrast resolution because of the IRs ability to discern _____ difference in subject contrast

1%

All structures greater than ________ cm require the use of a grid

10

When OID increase causes significant scatter radiation to be diverted from the IR, the mAs should be increased by about ____ for every centimeter of OID to compensate and keep EI ideal.

10%

If a patient must be repeated because it does not demonstrate adequate contrast resolution of the VOI what should you use to demonstrate adequate subject contrast

15% rule and EI value

AEC backup timers should be set to ____% to ______% of expected manual exposure time when imaging obese patients.

150% to 200%

A mAs adjustment of ______ is needed when going from a 14x17 to a 8x10

50%

What is a lookup table?

An ideal histogram for every radiographic projection

Why must technical factors be increased for obese patients?

Because obese patients attenuate more of the beam

The maximum range of pixel values that a digital system can store

Bit depth

How is quantum noise decreased?

By increasing exposure to the IR

How is the histogram determined?

By total exposure that is used to create the

Increasing SID will _____________ IR exposure

Decrease

Uses a cassette less imaging capture system that is hard wired to image processing system and does not require the technologist to physically place the IR into the reader

Direct the-indirect radiography

How can overexposure be identified?

EI number, VOI demonstrates loss of contrast, over all graying due to excessive scatter

What happens when each DEL is sent to the computer for processing and manipulation?

Each DEL is given a a gray scale value

Any change in SID greater than 10% should be adjusted by using what formula?

Exposure maintenance formula

In computed radiography, what is applied to ensure that a histogram is generated correctly and that image is data is sharp?

Exposure recognition field algorithm

Greater gray shade differences goes with:

High contrast resolution

What is created after image data has been acquired?

Histogram

The midway point (VOI) is the median gray scale value which represents:

Ideal amount of x-Ray exposure at the detectors

Why is it important to select the correct body part in computed radiography?

To ensure the correct LUT is applied when image is rescaled

What formula is used to describe distance and intensity?

Inverse square law

Technical factor that determines the energy and penetrating ability of the x-Ray photons produced and is the controlling factor for differential absorption

Kilovolage (kV)

For cross table projections of the foot the projection of the beam performed are:

Lateromedial

Describe the process of image data acquisition in computed radiography.

Light is collected and converted to an electrical signal by the photomultiplier tube and then send to analog to digital converter to be digitized.

Obese patients have inherently ____ subject contrast.

Low

Lower gray shade differences

Low contrast resolution

Why might clothes show more on a peds image than an adults images,

Lower kV is used which may not be able to obscure clothing

Routine tabletop of the lateral foot performed the projection of the beam is

Mediolateral

What is the exposure maintenance formula?

New mAs / old mAs = new distance squared / old distance squared

What does the y axis of a histogram represent?

Number of pixels with those gray scale values

What happens to the original histogram data after an image is windowed and saved?

Original histogram data is lost

Where should masking be applied to an image?

Outside the exposure field

Photon exposure is higher than required to produce an acceptable projection and excessive dose was delivered to the patient

Overexposure

When should a grid be used for when doing images mobile?

Part thickness greater than 4 inches and more than 60 kV is used

For lateral images of the foot the CR should be ___________ to the IR

Perpendicular

In trauma imaging, why must the alignment of the CR and part be accurate?

To see joint spaces, see fracture lines, obtain specific anatomic relationships

What does the x axis of a histogram represent?

Pixel gray shade values

In direct/indirect radiography what does the image matrix contain?

Pixel size detector elements

What happens if the CR is not positioned perpendicular to the IR:

Projection may demonstrate elongation

The total quantity (intensity) of x-Ray photons that expose the patient and IR

Radiographic exposure

What are exposure indicators?

Readings that denote a out of radiation intensity (quantity of photons) that struck the IR

What is a common artifact on neonates?

Skin folds

Difference in radiation intensity in the remnant beam that demonstrates the degree of differential absorption resulting from the differing absorption characteristics of the body structures

Subject contrast

Pediatric imaging requires lower ________________.

Technical values

Which joint should be included in long bone imaging when both joints cannot be displayed?

The joint closest to the injury

What does a histogram represent?

The subject contrast in the remnant radiation

What do detector elements contain?

Thin-film transistors (TFT)

What reduces scatter radiation from reaching the IR?

Tight collimator, appropriate grid usage, lead sheet along the edge of the exposure field

In direct-indirect radiography, why must the technologist choose the correct exam from the workstation before the exposure is made?

To ensure the correct LUT is applied to the displayed image

True/False: subject contrast cannot be recovered or manipulated with post processing

True

What results when a portion of a chamber is exposed and the beam directly hits the chamber?

Underexposed resulting in quantum noise because the exposure terminated too quickly

What factors should be considered for obese patients?

Weight and body diameter

Allows user to change the average gray level (center gray shade on the dynamic range) increasing or decreasing the overall image brightness

Window level

Changes length of the dynamic range (total number of different gray shades)

Window width

Post processing manipulation of the images brightness and contrast to demonstrate the VOI more accurately

Windowing

What are ways to reduce scatter radiation from reaching the IR?

tight collimation, grid usage, lead sheet along the edge of the exposure field