Presentation on theme: "RTEC 244 PROCESSING THE IMAGE SENSITOMETRY WEEK 12 - 2006."— Presentation transcript:
RTEC 244 PROCESSING THE IMAGE SENSITOMETRY WEEK
Safe Light 15 Watts Red filter Must be 3-6 feet from counter top or feed tray of processor Used to be amber or orange filter
DEVELOPER FIXER WASH DRY WATER - SOLVENT
AUTOMATIC PROCESSING CHEMICALS
What is in the Darkroom?
Darkrooms – Still Necessary? Darkrooms are necessary for manually fed processors And daylight processors. -Loading automatic (daylight) film processor magazines. Necessary for conducting certain quality control tests (daily sensitometric strip).To check consistency of processing
Darkrooms 4 Basic Functions Number 1 Function Storage –Unexposed film
Darkroom Contents Loading Bench Film Bin Film I.D. Printer Safelights Pass Box Light-tight Room Ample ventilation Warning Light outside room Lockable Door Wall Shielding if adjacent to x-ray room Walls painted with light color to reflect safelight
DARKROOM FUNCTION # 2 Purpose of Film Processing Change silver halide crystals from film emulsion (after exposure to x-ray or light photons) to black metallic silver. Latent image (invisible until processed) is developed into a Manifest image. Improper or careless processing can cause poor diagnostic quality.
Manual Feed Processor
TABLE TOP PROCESSOR
Function # 4: Film Identification Pt name Exam date & time Pt x-ray number Pt Birthday/DOB Rt or Lt marker Optional –Exam type –Dr. Name
FILM ID PRINTER In Daylight in Darkroom Cassette Flashed Film Flashed
WILL THIS WORK ????
Function # 3: Handling of Film
UNLOAD EXPOSED FILM
Basic Recommendations Now done by Processor Co. Follow mfg. recommendations: -strength of chemicals -temperature of chemicals -time requirements in each chemical Solutions should be replenished as necessary & changed regularly Solutions must be monitored (Daily QC strip).
CHEMICAL FOG strength of chemicals in DEVELOPER DILUTE – Under Processed (light films) OXIDIZED - over processed (films dark) temperature of chemicals Too Hot - films dark time requirements in each chemical Too long in tanks – films dark
Chemcial Fog diluted or contaminated chemisty
Strength of Chemisty can affect outcome radiograph
AUTOMATIC PROCESSING TRANSPORTATION SYSTEM DEVELOPER FIXER WASHER DRYER REPLENISHMENT SYSTEM
Processor Chemistry Overview Developer – converts latent image into manifest image Fixer – clear the film of unexposed, undeveloped silver bromide crystals, promotes archival quality Wash – rid the film of residual chemicals Dry - sets the film for handling
Developer Solution (6 Ingredients) 1.Reducing Agent: reduce exposed silver halide to black metallic silver -Hydroquinone (Blacks) SLOW -Phenidone (Grays) FAST (Metol or Elon) 2. Activator: softens gelatin, maintains alkaline pH (increase pH) -Sodium Carbonate
Developer Solution 3. Hardener: prevents damage to the film from over swelling of gelatin in automatic processors. -Gluteraldehyde 4. Preservative: Antioxidant that prevents oxidation of developer -Sodium Sulfite
Developer Solution 5. Restrainer: prevents chemical fog in new developer – antifogging agent -Potassium Bromide (In starter solution) 6. Solvent: dissolves & ionizes the developer chemicals -Water
Fixer Solution (5 Ingredients) 1.Clearing Agent: dissolves /removes undeveloped silver halide crystals -Ammonium Thiosulfate (Fixer retention – film turns brown if not washed off) 2.Activator: stops reduction, acidic pH ACETIC ACID
FIXER SOLUTION 3.Hardener: harden emulsion POTASSIUM ALUM (if films come out “sticky” this is depleted – it is not because of the dry not drying the films) 4. Preservative - maintains pH levels SODIUM SULFITE 5. Solvent: dissolves chemicals
Wash Rid the film of residual chemicals Residual chemicals on the film will discolor radiograph over time. Cold water processors are less efficient in removing chemicals – Warm water processors much better. Agitation during wash process is essential
DRY removes water, seals emulsion Hot Air
Transport System Components Feed Tray Rollers (Different Assemblies): 1. Entrance 2. Deep Racks 3. Turnaround 4. Crossover 5. Squeegee 6. Dryer Receiving Bin
Transport System (Rollers) Turnaround Entrance Deep Racks Crossover Squeegee Dryer Feed Tray
Replenishment System Main function: Keep solution tanks full and assure proper solution concentration. As film is introduced into processor, sensor initiates solution replenishment Right & wrong way to feed in film -Feed in along short edge Crosswise not lenghtwise (except 8x10) to not use up extra replensher
Transport System in Automatic Processors Conveys the film through different solutions (sections) by a series of rollers driven by gears, chains & sprockets. Done at a prescribed speed – determines length of time the film is in each solution
Temperature Regulation Main function: To control the temperature of each section of the processor. Developer – most important solution to regulate Usually between 92 degrees and 95 degrees Thermostatically controlled Water circulation helps to control temp – if water is not turned on – processor temp will rise
Recirculation System Provides agitation necessary for uniform solution concentration
Wash & Dryer Systems Wash: Provide thorough removal of chemical solutions from the film. -Archival film quality Dryer: Removes water from film by blowing warm, dry air - Between 120 degrees & 130 degrees F.
ARTIFACTS – An unwanted density on a film can appear as a dark or light mark on the film (image) Caused by: Improper: Handling, Processing or Storage
Artifact are undesirable an unwanted density on film is the term for markings or images that appear on the finished film that did not result from the attenuation of the x-ray beam passing through the patient. They may appear because of poor conditions related to the film, mishandling, or processing problems. Artifacts can cause an image to be misinterpreted, can make interpretation difficult or impossible (as in the images shown in the illustration), and may require a repeat procedure resulting in unnecessary additional patient exposure.
Different kinds of artifacts can occur, but virtually all can be prevented. Fog artifacts can be caused by high temperatures, bright light, high humidity, or ionizing radiation. Scratches or pressure on the film can cause white or dark areas. Poor contact between the screen and film can cause localized blurring or darker areas. Dirt on the screen or film can cause white spots. Damaged cassettes or screens can cause a range of artifacts, as can improperly functioning automatic processors. Shown in the illustration are films marred by a variety of artifacts. Only by following accepted and safe procedures for handling and storing film, and for processing exposed film, can artifacts be prevented.
ARTIFACTS AN UNWANTED DENSITY ON THE FILM
FIXER RETENTION (FIXER NOT WASHED OFF)
POOR SCREEN CONTACT
Blurring = Motion vs Poor screen contact
PATIENT ARTIFACT - JEWERLY
Crimping /cresent mark
Developer splashed on unprocessed film
Hypo (fixer) retention
Kink / cresent mark WHITE MARK – FILM BENT BEFORE EXPOSURE (SILVER SEPARATES) DARK MARK – FILM BENT AFTER EXPOSURE SILVER MOVES TOGETHER
ROLLER MARKS VS SCRATCHES ROLLER MARKS – USUALLY DARK PERPEDICULAR TO FILM TRAVEL – THE WAY THE FILM IS PLACED ON THE FEED TRAY SCRATCHES – LIGHT PARALLEL TO FILM TRAVEL
DIRT IN SCREEN – WHITE MARK
STATIC = LOW HUMIDITY
Careful Handling a must
PATHOLOGY NOT ARTIFACT
Silver Recovery About ½ of the film’s silver remains in the emulsion after exposure & processing. Other ½ (unexposed silver) is removed from the film during fixing process. Silver is toxic to public water supply – must have proper disposal.
SILVER RECOVERY – Photography consumes approximately 30% of the worlds sliver - half of this is used in diagnostic imaging films 3 reasons for Diagnostic Imaging Department to use silver recovery: 1. Dwindling worldwide supply of silver 2. $$ cash for silver ( school’s processing services donated for silver recovery) (About 10% of the films cost is recovered through silver recover) 3. State and Federal pollution regulations One of the functions of the fixer solution is to remove the unexposed and undeveloped silver halide crystals from the film. These crystals are eliminated with the used fixer by the replenishment system. The dissolved silver averages about 50% of the silver that was originally on the film.
Three methods of recovery: 1. Metallic Replacement - Steel wool inside a canister collects the silver (most useful type of recovery for low volume processors) 2. Electrolytic - cells pass an electric current through a cylinder, causing silver to be plated onto the cathode cylinder of the unit. Silver is removed by scraping it off the cathode. (For medium to high volume) 3. Chemical Precipitation - (oldest form) Chemicals cause a separation of the silver form the fixer. The silver sinks to the bottom and forms a sludge where it can be removed. (This is the least desirable way - hazardous chemicals used with toxic fumes) ( Only used by very large institutions) SILVER RECOVERY FROM FILM:
Green film - contains most of the silver (should be separated from other film) this film is worth more than developed film Scrap Film & Archival Film - Silver can be removed by burning the film and removing silver from the ashes, or using chemical treatments. Usually paid on a price per pound of film
There are three types of silver recovery systems: metallic replacement units, electrolytic units, and chemical precipitation units. In metallic replacement units, the used fixer circulates through a tank in which iron molecules in steel screens break down and are replaced by metallic silver precipitates. This method is less efficient than other methods and is less commonly used. In electrolytic units, such as the one shown in the illustration, an electric current is passed through the fixer; ionized silver molecules in the fixer are attracted to, and form a plating on, the negatively- charged rotating cathode. Other units use a process of chemical precipitation in which other chemicals react with the silver in the fixer solution. Silver molecules are freed and precipitate out of the solution, falling to the bottom of the tank where they can be recovered from the silver sludge that forms.
silver recovery. A final consideration in film processing is silver recovery. This term is the process by which silver in the processing chemicals is reclaimed and recycled by a unit, such as the one shown in the illustration. This recycling is important for two reasons. Silver has economic value in its recycled form and helps recover some of the cost of the unexposed film, which is expensive, in part, because of the silver in it. Secondly, federal regulations require that heavy metals like silver be reclaimed from waste solutions before they are disposed of, to prevent pollution of the environment. Roughly half the silver in the film ends up dissolved in the fixer in the automatic processor. Different kinds of silver recovery units are used to process the used fixer to recover the silver.
First, the film is fed into the unit through a feed tray in a conventional unit or directly from the cassette in daylight systems. The film first enters the developer tank. The developer solution gives up electrons that neutralize the positively charged silver ions in the film in a process called reduction. The chemical in the developer solution responsible for this is called the reducing agent. Metallic silver builds up in visible black specks at the sensitivity specks. Other chemicals in the developer help control this process precisely and prevent overexposure. A hardener also prevents the film emulsion from becoming too soft or swollen during the processing. To obtain the best visible image, the development process depends on precise control of the concentration and temperature of the developer, as well as the length of time the film is in the developer. All these are controlled automatically by the film processor.
Why does x-ray film come out black? There are five possible reasons: The film is overexposured (exposures are too long or the setting is too high). The processing times are too long. The temperature is too warm. The film has been exposed to another light source. The safelight lens (filter) is cracked or damaged.
X-ray film scanner Turns an analog image into an electronic image See Ch. 43
Digital – Reverse Image
RT 244 REVIEW CASSETTES / FILM AND INTENSIFYING SCREENS
FILM SIZES 14 X X X 12 8 X 10
Film Sizes Standard “inches”: 8” x 10” 10” x 12” 11” x 14” 14” x 17” Metric: 18cm x 24cm 24cm x 30cm 30cm x 35cm 35cm x 43cm
X-Ray Film Film is a media that makes a permanent record of the image. Image recorded on film is caused by exposure to energy: -X-ray energy converted to light energy -Image before processing = Latent image -Made visible by chemical processing
X-ray Film cont’d Radiographic film is/was most common image receptor Two parts: 1. Base 2. Emulsion
Film Construction Made of a polyester plastic Must be clear, strong, consistent thickness Tinted pale blue or blue-gray (reduces eye strain) Photographic emulsion can be on one side or both sides of base (single emulsion / double emulsion) Protective overcoat layered on top of emulsion
FILM COMPOSTION SINGLE OR DOUBLE EMULSION COATED ON A BASE EMULSION : GELATIN WITH SILVER HALIDE CRYSTALS BASE: SUPPORT POLYESTER
Film Emulsion Made of mixture of gelatin & silver halide crystals (fluorine, chlorine, bromine, & iodine) Most x-ray film emulsions made of : silver bromide (90%) silver iodide (10%) Photographically active layer – activated by light & radiation to create image
X-Ray Film Cross Section
Film Characteristics Size of silver halide crystals & emulsion thickness determine speed of film and degree of resolution Larger crystals / thicker crystal layer =Faster response, less detail, less exposure (chest x-ray) Finer crystals / thinner crystal layer =Slower response, greater detail, more exposure (extremity)
FIRST “FILM” GLASS PLATES WW 1 CELLULOSE ACETATE HIGHLY FLAMMABLE EASILY TORN RESPONSIBLE FOR MANY FIRES IN HOSPITAL BASEMENTS
X-ray Film Sensitivity Light X-rays Gamma Rays Gases Fumes Heat Moisture Pressure Static Electricity Age So what happens??
FILM FOG!!!! Unintended uniform optical density on a radiograph because of x-rays, light, or chemical contamination that reduces contrast.
Film Storage Clean, dry location 40 degrees – 60 degrees Fahrenheit Away from chemical fumes Safe from radiation exposure Standing on edge Expiration date clearly visible
FILM BIN - STORAGE
Spectral Sensitivity Film is designed to be sensitive to the color of light emitted by the intensifying screens. Blue LIGHT– Conventional Calcium Tungstate screen Green, Yellow-Green LIGHT – Rare Earth screen
Cassettes Cassettes serve 3 important functions: 1.Protect film from exposure to light 2.Protect film from bending and scratching during use. 3.Contain intensifying screens, keeps film in close contact to screen during exposure.
CASSETTE or FILM HOLDER The CASSETTE is used to hold the film during examinations. It consist of front and back intensifying screens, and has a lead (Pb) backing. The cassette is light tight
Cassette Features - Front Exposure side of cassette is the “front”. Has the ID blocker (patient identification) Made of radiolucent material – easily penetrated by x-rays, lightweight metal alloy or plastic material made of resin. Intensifying screen mounted to inside of front.
Cassette Features - Back Back made of metal or plastic Inside back is a layer of lead foil – prevents backscatter that could fog the film Inside foil layer is a layer of padding – maintains good film/screen contact Back intensifying screen mounted on padding
Intensifying Screens Flat surface coated with fluorescent crystals called phosphors that glow, giving off light when exposed to x- rays.
Intensifying Screens Direct x-ray exposure to film requires 25 to 400 times more radiation than film/screen. Two advantages to using intensifying screens: 1.Reduce patient exposure 2.Increase x-ray tube life
Screen Construction Polyester plastic base – support layer Phosphor layer – active layer Reflective layer – increases screen efficiency by redirecting light headed in other directions Protective coating
Phosphor Layer Active layer – x-ray photons converted to light photons *Photoelectric Effect Type must correlate with film: -Calcium Tungstate = blue to purple light -Rare Earth = green & ultraviolet light NAMES 3 ?
Rare Earth Screens Gadolinium Lanthanum Yttrium Found in low abundance in nature
Intensifying Screen & Film Cross Section
Screen Speed Efficiency of a screen in converting x-rays to light is Screen Speed.
Screen Speed Greater efficiency = less exposure = faster -Standard screen speed class of screen speed is twice as fast Speeds for routine work: 200 – 800 Speeds for high detail:
Objectives Calculate speed points, speed exposure points and relative speeds from D log E curves Calculate gamma, gradient point, average gradient and latitude from D log E curves
Objectives Analyze D log E curves to determine speed, contrast and latitude relationships Discuss the relationships between speed, contrast and latitude
Sensitometry Measures the response of film to exposure and processing
Sensitometric Equipment Penetrometer or sensitometer –Used to create a uniform set of densities on a film Densitometer –Provides measurement of light transmitted through film –Measures optical density
Penetrometer Stepwedge Used to monitor x-ray equipment Also used to monitor film/screen combinations Not recommended for processor monitoring
Sensitometer Uses a controlled light source –Produces same amount of light each time it is triggered
Sensitometer Available in 11- or 21- step versions –21 step version increases density by a factor of the square root of 2 (1.41) for each step
Densitometer Uniform light source and an optical sensor Calibration control allows for easy calibration
Optical Density Numbers Formula: –OD=log 10 I o /I t If 100% of the light is transmitted through the film, it has an OD of 0 If none of the light transmits through film the OD is 4
Opacity Ability of a film to stop light transmission Formula: –I o /I t
The D Log E Curve Describes relationship between density and exposure This is done through sensitometry
The D Log E Curve AKA –Sensitometric curve –Characteristic curve –Hurter and Driffield (H & D) curve Sensitometry’s roots lie in analysis of photographic film
The Sensitometric Curve Plots OD vs. LRE Log relative exposure Allows large range of exposure displayed in a few numbers
Densitometer Reads on a scale of 0-4 –0 meaning that all light is transmitted –4 meaning that no light transmits through the film Typical diagnostic densities range between 0.25 to 2.5
Parts of the Curve Base + fog Toe-D min –Where the density becomes light Straight line portion –Used to demonstrate the relationship to the film’s exposure vs. the density transmitted
Parts of the Curve Shoulder-D max –Where the density becomes dark
Film Properties Base density –Inherent in a piece of film due to dyes etc. –Value is usually 0.1 OD Fog Density –Inadvertent exposure during storage handling etc. –Fog density should not exceed 0.2 OD
Base + Fog Cannot separate base and fog density measurements Typical range of OD for Base + fog –0.18 to 0.23 –Should not exceed 0.25
Toe D min Controlled by phenidone –Fast acting reducing agent in developer –Produces gray tones on film
Straight Line Portion Area of curve between toe and shoulder Contains range of useful densities –Typically 0.25 – 2.5 or 3.0
Shoulder D max Controlled by hydroquinone –Slow acting reducing agent in developer –Produces blacks in image
Reversal or Solarization Once a film has been exposed to D max, it will begin to lose density after further exposure Duplication film has been solarized
Film Characteristics Resolution Speed Contrast Latitude
Resolution Ability to accurately image an object AKA –Detail –Sharpness –Definition –Resolving power
Resolution Inversely related to size of silver halide crystals
Speed Ability of an IR to respond to low exposure measures its sensitivity or speed Speed index –Specified by base + fog
Speed Faster film will have a curve closer to y-axis of graph
Speed Film sensitivity is affected by: –Size of silver halide crystals –Number of sensitivity specks –Thickness of the emulsion All of the above are directly related to film speed
Speed Affected by processing –Immersion time –Solution temperature –Chemical activity
Contrast Contrast is controlled by hydroquinone –Hydroquinone establishes the shoulder –Thus, it affects slope of the straight line portion of curve
Film Contrast and Curve Film contrast is defined by straight line portion of the characteristic curve –Gamma slope of straight line
Film Contrast and Curve As the line becomes more vertical the contrast gets higher
Average Gradient Used to identify contrast of a film by manufacturers Slope of line that is drawn between –0.25 above base and fog density
Average Gradient Slope of line that is drawn between –And 2.0 above base and fog density Higher the average gradient, the higher the contrast
Latitude The lower the slope (the more horizontal the line) the wider the latitude
Latitude Low scale of contrast in film –More latitude –Margin of error higher