Bontrager Chapter 1 part 2 imaging principles

What controls the energy of the penetrating beam?

kV

What controls the quantity or number of the x-rays?

mA

What controls the duration of exposure?

Time; expressed in s (seconds)

For patient protection use a ________________ kV with a ___________ mAs.

high, low

Spatial resolution

sharpness/detail in the image

What is the greatest deterrent of spatial resolution?

Motion

The 2 types of motion that interfere with spatial resolution?

voluntary and involuntary

Lack of sharpness is termed

unsharpness or blur

unsharp edges in an image are called

penumbra

What are the sharp edges of an object referred to in an image?

Umbra

Spatial resolution is measured in

lines per pair per millimeter (lp/mm)

The greater the lp/mm the

higher the spatial resolution

Voluntary motion is seen on an image as generalized

blurring of linked structures

How can voluntary motion be controlled?

Patient cooperation

4 helpful ways decrease voluntary motion

- controlled breathing

-immobilization devices

-communication

-high mA short time

Can involuntary motion be controlled by the Pt?

no.

How is involuntary motion displayed on an image?

localized unsharpness or blurring

What can we use do reduce visualization of involuntary motion?

Short exposure time

What size focal spot size is needed for increase spatial resolution?

Small

In order to increase spatial resolution the SID needs to be

large

Decreasing the OID increases the spatial resolution of the image. True/False

True

For high spatial resolution you need to have a ________________ matrix and small ______________________ size.

large, small pixel

Use the smallest ________________ to increase spatial resolution.

IR

For the highest degree of spatial resolution exposure time should be

short

Distortion refers to a misrepresentation of an objects ______________ or _______________.

size, shape

There will always be distortion due to the OID and beam divergence. However, the least amount of distortion is at the __________________________.

Central ray

Another name for size distortion is

magnification

Magnification can be caused by a ________________ SID and a __________________ OID.

Short, long

For the least amount of size distortion use the largest SID at a minimum ____________ and the _____________ OID

40", smallest

Two forms of shape distortion are

elongation and foreshortening

What shape distortion is caused by angling the CR/Tube?

elongation

Angling of a part of the patients body can cause what on an image?

Foreshortening

Angling the IR causes

elongation

For the least amount of SHAPE distortion, keep the CR __________ to the IR, keep the part __________ to the IR

perpendicular, parallel

What device is used to limit scatter from hitting the IR that increases patient dose but improves spatial resolution?

Grid

Grid cutoff is seen as a loss of x-rays on all or portions of the image. What are the 4 grid errors called?

1. off-center grid

2. off-level grid

3. off-focus grid

4. upside-down grid

What is the most common grid error?

off-level

The anode heel effect causes the intensity of the beam to be greater on the _____________ side than the __________ side.

cathode, anode

The beam intensity can be reduced up to how much due to anode heel effect?

a reduction of up to 45%

Because of the anode heel effect, When performing a radiograph of a part with thinner to thicker anatomy you should place the thicker part towards the ___________________ and the thinner towards the ________________.

cathode, anode

Compensating filters are used to "even out" uneven part thickness, sometimes these are made of plastic but they are usually made out of

aluminum

3 types of compensating filters

wedge, trough, boomerang

Images viewed on a monitor are referred to as

soft copies

Digital images are a numeric representation of the __________________________ intensities that are transmitted through the patient.

x-ray

Each 2-dimentional image is formed by a ______________ with numerous ______________

matrix, pixels

The systematic application of highly complex mathematical formulas is called

algorithms

Digital has a ___________________ dynamic range compared to cassette based imaging.

higher

The 6 factors of digital image quality

1. Brightness

2. Contrast Resolution

3. Spatial Resolution

4. Distortion

5. Exposure indicator

6. Noise

The intensity of light that represents the individual pixels in the image on the monitor is called the

brightness

Brightness is controlled by preprocessing software algorithms called

LUTs (Look up tables)

Brightness levels are adjusted by the

window level

The ability of an imaging system to distinguish between similar tissues is called and the difference of brightness between light and dark areas on an image

contrast resolution

Contrast resolution is controlled by the preprocessing algorithms (LUTs) and are adjusted by the

window width

The range of shades of gray in one pixel, determined by the manufacturer is

bit depth

The ____________ the bit depth the ____________ the contrast resolution

greater, greater

Since DR is very sensitive to scatter, what 3 things can help with contrast resolution

1. correct grids

2. close collimation

3. optimal kV

The numeric value that is representative of the dose of exposure the IR has received is known as the

exposure indicator (EI)

Although the image outside of the EI may appear good on tech monitor, the superior resolution and brightness of this monitor can show image correctly

the Radiologist Primary monitor

The ___________ the bit depth, the ________________ the dynamic range equivalates to a higher contrast resolution

higher, higher

Fuji, Phillips, and Konica use an inverse exposure index termed S number and the exposure numbers are

inversely related

Carestream (kodak) (EI) and Afga (LgM) have a numerical system associated with the exposure index ranging from 1900-2300 (CR) and have what type of relationship with amounts

direct relationship

The deviation index ranges from -3 to +3 with a target exposure of -0.5 to +0.5. A positive DI indicates ______________________ while a negative DI indicates ___________________.

overexposure, underexposure

A DI of +1 indicates what percentage of overexposure

25%

A DI of -1 indicates what percentage of underexposure

20%

A random disturbance the obscures or reduces clarity showing as graininess on an image is referred to as

Noise

SNR (signal-to-noise ratio) is the ratio of signal (x-rays) and noise (random disturbance) that strike the

IR

A high SNR is desirable and a low SNR is

undesirable

Changing or enhancing the electronic image for the purpose of improving its diagnostic quality is called

post processing

Window width is used to adjust

contrast

Window level is used to control brightness. True/False

True

What is used in postprocessing to reduce noise on the image?

Smoothing

What alters the pixel values to the edge of structures to make them more prominent known as?

Edge enhancements

What makes low brightness brighter and high brightness less dark across an image?

equalization

What is used in angiography to remove background structures around contrast filled vessels?

Subtraction

When light and dark pixels are reversed it is known as

image reversal

text that is added to images for anatomical labeling or descriptive purposes is known as

annotation

Picture Archiving and Communication System (PACS)

An integrated computer system that obtains, stores, retrieves, and displays digital images (in healthcare, radiological images)

Techs radiation dose is monitored by what device worn at the collar

OSL (optically stimulated luminescence dosimeter)

Should the OSL be worn inside or outside of the lead apron during fluoroscopy?

outside

Pregnant techs wear a fetal dosimeter at the waist level __________________ a lead apron.

under

Pregnant Techs are limited to .5 mSv a month for a total gestational dose of

10 mSv

Occupational (unpregnant) workers have a dose limitation of 50 mSv annually and a lifetime limit of 10mSv x ___________?

age

Due to ALARA holding should be avoided by

Occupationally exposed workers, pregnant and under 18 individuals. Instead opt for family members or non occupational employees when available

Patient Radiation Protection

minimize repeats by using correct filtration, collimation, and shielding, projections and techniques

The main cause for repeats is

miscommunication

Learn anatomy and structures that must be included on an image to avoid

clipping

Any tubes operating over 70 kV requires a minimum total filtration of 2.5mm al/eq. What effect does filtering have on the primary beam?

it increases the quality by removing low energy photons

What reduces patient dose, reduces scatter hitting IR, and has a light field that appears smaller than it is due to reduced SOD?

Collimation

What automatically adjusts the light field to the size of the IR when bucky is closed?

Positive Beam Limitation

Positive Beam Limitation (PBL) was required on all units from ____________ to _____________, however, it is no longer required.

1974, 1993

Limitation of the light field to only the area of interest, insuring to include a border on all 4 sides of the IR is known as the

Collimation Rule

Correct collimation leads to less tissue being irradiated which produces less scatter thereby reducing

patient dose

Shields for radiosensitive organs such as gonads, breasts, and eyes must have a minimum thickness of

0.25 pb/eq

Gonadal shielding occurs when within 2" of the PB reducing the gonad dose by __________________ if the gonads occur within the PB.

50-90%

What type of shields are attached to the collimator and do not touch patient?

Shadow

Contact shields are more common than __________________ shields

shadow

Male gonad shields are placed ______________ to the pubis symphysis, while female gonad shields extend from _____________ to slightly above the pubic symphysis.

distally, ASIS(anterior superior iliac spine)

If patient is pregnant consult with Radiologist prior to imaging, imply careful ____________ and ________________. Patient must be informed of risks and waiver may be needed depending on department.

Collimation, shielding

The 10-day since _________________ is no longer valid.

LMP (last menstrual period)

Dose is reduced when using AEC by increasing

kV