Components of Image Quality & Radiographic Artifacts Radiologic Technology A SPRING 2012

X-ray Exposure Factors Radiographic Density & Contrast Components of Image Quality Radiographic Artifacts

Review Primary radiation exits the tube Interacts with various densities in the body Photons may be absorbed Scattered Passed through without any interference to the cassette or image receptor (IR)

How well we can see something on the image

Image detail is affected by: Photographic properties and Geometric properties

Photographic Properties Contrast Density

X-ray Exposure Factors TECHNIQUE SELECTION: Radiographer selects the Kilovoltage peak (kVp) Milliamperage (mA) & time (s) Milliamperage x time = mAs (milliamperage multiplied by a set time measured in seconds)

Kilovoltage Peak kVp One kilovolt = 1000 volts The amount of voltage selected for the x-ray tube. Range 30 to 150 kVp kVp controls contrast

Milliamperage One milliampere (mA) = one thousandth of an ampere. The amount of current supplied to the x-ray tube How many x-rays will be produced Range 10 to 1200 mA

Time In seconds How long x-rays will be produced 0.001 to 6 seconds

Milliampere Seconds Technologists think in terms of mAs Calculated by mA x seconds Ex: 100mA X 0.2s = 20 mAs How many x-rays will be produced and for how long. Modern x-ray machines only allow control of mAs controls density

Factors Affecting Density Primary control factor mA Time (seconds) Influencing factors kVp Grids Beam restriction Body structures (size of pt, pathology Processing SID & OID Film Screen combinations

Primary Controlling Factor of Density mAs mA = AMOUNT of electrons sent across the tube combined with TIME (S) = mAs mAs controls DENSITY on radiograph primary function of mAs is DENSITY

Imagine this… If the mA station is changed from 200 to 400 mA, twice as many electrons will flow from the cathode to the anode. From 10 mA to 1000 mA = 100 x more mA controls how many electrons are coming at the target mAs is a combination of how many and for how long (seconds)

10 mA 1000 mA

Changing Mas – Changes Density + 25 % + 50 % mas

Influencing Factor on Density: kVp

15% kVp = doubling of exposure to the film  kVp more energy = more photons passing though tissue & striking the image 15% kVp = doubling of exposure to the film  15% kVp = halving of exposure to the film 15% rule will also change the contrast of the image because kV is the primary method of changing image contrast. Remember : 15% change ( ) KVP has the same effect as doubling or ½ the MAS on density 15% rule: 15% kVp = doubling of exposure to the film  15% kVp = halving of exposure to the film 15% rule will also change the contrast of the image because kV is the primary method of changing image contrast. Remember : 15% change ( ) KVP has the same effect as doubling or ½ the MAS on density

Change in kVp kVp controls the energy level of the electrons and subsequently the energy of the x-ray photons. A change from 72 kVp will produce x-rays with a lower energy than at 82 kVp Difference between a ball traveling 72 mph and 82 mph (how much energy did it take to throw the ball at the rates?)

+ 15% kvp - 15% kvp This will also influence the density on the image Increasing kVp = increase energy reaching the IR

Radiolucent vs. Radiopaque Radiolucent materials allow x-ray photons to pass through easily (soft tissue). Radiopaque materials are not easily penetrated by x-rays (bones)

Creating the Image Transmission Scatter Absorption no interaction Responsible for dark areas Scatter (grays) – produces no diagnostic info Absorption (photoelectric effect) Responsible for light areas

Images DENSITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH (mAs) CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES (kVp)

Why you see what you see… The films or images have different levels of density – different shades of gray X-rays show different features of the body in various shades of gray. The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass through The images are lighter in dense areas (like bones) that absorb more of the X-rays.

Image Production Primary Radiation – The beam of photons, B4 it interacts with the pt’s body. Remnant Radiation – The resulting beam that is able to exit from the patient. Scatter Radiation – Radiation that interacts with matter & only continues in a different direction – not useful for image production. Attenuation – Primary radiation that is changed (partially absorbed) as it travels through the pt. Primary Radiation – The beam of photons, B4 it interacts with the pt’s body. Remnant Radiation – The resulting beam that is able to exit from the patient. Scatter Radiation – Radiation that interacts with matter & only continues in a different direction – not useful for image production. Attenuation – Primary radiation that is changed (partially absorbed) as it travels through the pt.

Patient Body Size and Pathology

3 Different Body Habitus Hypersthenic Sthenic Hyposthenic Dr. Charman, Eric Guzman, Adam Guzman Thank you to the 3 men in my life !  DCharman

PATHOLOGY Pleural Effusion Excessive fluid in lung More dense than air

Pneumonia

Pneumothorax The right lung is almost completely collapsed; vascular shadows can not be seen in this area (arrow). Lung collapses No tissue in space Easy to penetrate with x-ray photons Pneumothorax

Lung Cancer

LUNG CANCER

Density and Images

Goal: Producing optimal radiographs DENSITY Could be caused by kVP or mAs. Too dark Too light

Controlling Factor of Contrast

Controlling Factor of Contrast Kilovolts to anode side – kVp Kilovolts controls how fast the electrons are sent across the tube kVp – controls CONTRAST on images

Producing optimal radiographs Contrast Scale Long scale short scale

Scale of Contrast? Which one is “better” How does the kVp affect these images?

Beam Restriction and Grids

Scatter Creates fog Lowers contrast (more grays) Increases as kV increases Field size increases Thickness of part increases

Effects of collimation (beam restriction) on scatter

Collimate to area of interest -reduces scatter and radiation dose to the patient

Grids A device with lead strips that is placed between the patient and the cassette Used on larger body parts to reduce the number of scattering photons from reaching the image

Basic Grid Construction Radiopaque lead strips Separated by radiolucent interspace material - Typically aluminum Allow primary radiation to reach the image receptor (IR) Absorb most scattered radiation Primary disadvantage of grid use Grid lines on film

GRIDS

Grid is placed between patient (behind table or upright bucky) & cassette

Grids absorb scatter – prevents it from reaching the image STOPS SCATTER

Contrast changes with the use of a grid Less scatter radiation – shorter scale = “better contrast” With Grid No Grid

GRIDS CAN LEAVE LINES ON THE IMAGE

GEOMETRIC Properties Recorded Detail DISTORTION Size distortion Magnification Shape distortion Elongation Foreshortening

RECORDED DETAIL

The degree of sharpness in an object’s borders and structural details. RECORDED DETAIL The degree of sharpness in an object’s borders and structural details. How “clear” the object looks on the radiograph

Recorded Detail The degree of sharpness in an object’s borders and structural details. Other names: -sharpness of detail -definition -resolution -degree of noise

RESOLUTION TEST TOOLS LINE PAIRS/ MM Depicts how well you can see the differences in structures More lines=more detail

Factors that affect Recorded Detail Geometric unsharpness OID SID SIZE SHAPE Motion unsharpness (blurring) Intensifying Screens Film Speed / Composition Film – Screen contact Kvp & Mas (density / visibility)

MOTION AKA Blurring

Motion Can be voluntary or involuntary Best controlled by short exposure times Use of careful instructions to the pt. Suspension of pt. respiration Immobilization devices

Decrease Motion Unsharpness Instruct patient not to move or breath Use Immobilization devices Use Short exposure times Lock equipment in place

Blurring of image due to patient movement during exposure.

Object Unsharpness Main problem is trying to image a 3-D object on a 2-D film. Human body is not straight edges and sharp angles. We must compensate for object unsharpness with factors we can control: focal spot size, SID & OID

SID Source to Image Distance The greater the source X-ray tube) to image (cassette) distance, the greater the image sharpness. Standard distance = 40 in. most exams Exception = Chest radiography 72 in.

The SID will influence magnification The SID will influence magnification. The farther away – the less magnified ↑SID ↓ MAGNIFICATION The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away – the less magnified ↑SID ↓ MAGNIFICATION

SID Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy” -On a radiograph called Penumbra Penumbra (fuzziness) obscures true border – umbra Farther the flashlight from object = sharper borders. Same with radiography.

OID Object to Image Distance The closer the object to the film, the sharper the detail. OID , penumbra , sharpness  OID , penumbra , sharpness  Structures located deep in the body, radiographer must know how to position to get the object closest to the film. The closer the object to the film, the sharper the detail. OID , penumbra , sharpness  OID , penumbra , sharpness  Structures located deep in the body, radiographer must know how to position to get the object closest to the film. *See page 74 in your book

The position of the structure in the body will influence how magnified it will be seen on the image The farther away – the more magnified

Distortion Misrepresentation of the true size or shape of an object MAGNIFICATION size distortion TRUE DISTORTION shape distortion

MAGNIFICATION TUBE CLOSE TO THE PART (SID) PART FAR FROM THE CASSETTE (OID)

Demonstrates increased OID which increases magnification

http://www. coursewareobjects. com/objects/mroimaging_v1/mod04i/0416a http://www.coursewareobjects.com/objects/mroimaging_v1/mod04i/0416a.htm

Size Distortion & OID If source is kept constant, OID will affect magnification As OID , magnification  The farther the object is from the film, the more magnification

Which side is more magnified?

In terms of recorded detail and magnification the best image is produced with a small OID & large SID

Minimal magnification small OID Magnification - large OID

Size Distortion & SID Major influences: SID & OID As SID , magnification  Standardized SID’s allow radiologist to assume certain amt. of magnification factors are present Must note deviations from standard SID Major influences: SID & OID As SID , magnification  Standardized SID’s allow radiologist to assume certain amt. of magnification factors are present Must note deviations from standard SID

40” SID VS 72” SID

SHAPE DISTORTION Elongation and Foreshortening

Shape Distortion Misrepresentation of the shape of an object Controlled by alignment of the beam, part (object), & image receptor Influences: Central ray angulation & body part rotation

A = good B & C = shape distortion (elongation of part)

D & E = shape distortion (foreshortening of part)

Image Distortion When the part to be imaged – does not lay parallel with the IR (cassette) If the Central Ray is not perpendicular to the part CR should be at right angle with the cassette

Central Ray Angulation Body parts are not always 90 degrees from one another Central ray angulation is used to demonstrate certain details that can be hidden by superimposed body parts. Body part rotation or obliquing the body can also help visualize superimposed anatomy.

Central Ray Radiation beam diverges from the tube in a pyramid shape. Photons in the center travel along a straight line – central ray Photons along the beam’s periphery travel at an angle When central ray in angled, image shape is distorted.

Elongation Foreshortened Normal

Distortion (x-ray beam not centered over object & film) Distortion (object & film not parallel)

Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.

Focal Spot Size Smaller x-ray beam width will produce a sharper image. Fine detail = small focal spot (i.e. small bones) General radiography uses large focal spot Beam from penlight size flashlight vs. flood light beam

ANODE ANODE

THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

FOCAL SPOT ANGLE SMALLER ANGLE – SMALLER BEAM AT PATIENT

ARTIFACTS: AN UNWANTED DENSITY ON THE FILM http://www.xray2000.co.uk/

Artifacts - Types Processing Artifacts Exposure Artifacts Handling & Storage Artifacts

Processing Artifacts Emulsion pickoff Chemical fog Guide-shoe marks Water marks Chemical spots Guide-shoe & roller scratches

Developer Spots

Water spot

Discolored film due to hypo (fixer) retention. Chemicals not washed off – over time will turn film brown

Scratch marks from rollers in automatic processor.

Exposure Artifacts Motion Improper patient position Wrong screen-film match Poor film/screen contact Double exposure Warped cassette Improper grid position

Artifact

Blurred image due to patient motion

PATIENT ARTIFACT - JEWERLY

Handling & Storage Artifacts Light fog Radiation fog Static Kink marks Scratches Dirty cassettes

Crimping /cresent mark

2 exposures made on top of each other – Double Exposure 2 exposures made on top of each other – from poor handling of cassettes

Static electricity

Dirt on screen mimicking a foreign object.

Scratch marks from improper handling.

Light fog

Kink mark or nail pressure mark

cast

POOR SCREEN CONTACT

Patient motion

motion

Double exposure Child

Poor screen contact

Double exposure

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? Is it motion or double exposure

Pt clothing

Hip replacement

2 chest tubes in the patient

Patient swallowed batteries What size are they?

PATHOLOGY NOT ARTIFACT

Name & cause of this?

scratches

Digital image Mis- Registration error

Roller marks from film stuck – then pulled from processor

Hardware In cervical spine

Dust in imaging plate can cause white marks on image Both in film/screen and computed radiography

E E G MONITOR

What do you See? 2 exposures

Evaluating Images What do you think?

See anything wrong with this image?

Contrast? What influences this? (kVp in f/s)

Collimation – reducing the size of beam helps to improve the image, and reduce the dose to the patient

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