Final Quality

minimizes the risk of suboptimal images but can not prevent them entirely

repeat analysis, artifact analysis, analysis of accuracy, analysis of sensitivity, and analysis of specificity.

When repeats are kept to a minimum, departmental efficiency increases. Patient exam time is reduced and patient satisfaction is increased.

-Repeat analysis provides important data about equipment, departmental procedures, and the skill of the technologists.

The total repeat rate is found by dividing the total number or repeated films by the total number of films used for the time period in question.

•The causal repeat rate is the percentage of repeats from a specific cause. This is found by dividing the number of repeats from a specific cause by the total number of repeated films.

Departmental repeats rates should not exceed 4% to 6%.

Emulsion pickoff occurs when emulsion is removed from the film base. This occurs when films are stuck together during processing and then pulled apart afterward.

when emulsion that has been removed from previous films builds up on the rollers or becomes dissolved in the developer. It is then deposited on films. The primary cause for this is under replenishment of the developer or failure of the developer circulation system filter.

solution dripping on or running down a film. This can occur if the wash water is dirty or a film has jammed and must be removed from the processor before going through the dryer.

is an overdevelopment of the film that results in excessive base plus fog and Dmin on sensitometry films and excessive radiographic density on patient exams. Causes include increased developer temperature, time in developer, pH, or concentration of developer. It may also occur with over replenishment of developer solution.

are scratches on films made by bent, worn, damaged, or misaligned guideshoes. Guideshoe marks run parallel to the direction of film travel.

are artifacts that occur in relation to the circumference of a roller. They occur at regular intervals and run perpendicular to the direction of film travel.

appear as bands of increased density that occur perpendicular to film direction. Chatter is caused by inconsistent motion of the transport system, usually because the drive gears or drive chain slips

presence of stains that are either brown or greenish yellow. Brown stains on a film either indicate that the film was processed in oxidized developer or if the stain develops after years of storage, hyporetention may be the cause. A greenish yellow stain indicates the presence of silver halide crystals remaining in the film from incomplete fixation.

appear as fine grooves in the surface of the film. This is the result of excessive expansion and contraction of the film during processing due to uneven solution temperatures.

can be caused by uneven development of the image due to failure of the circulation system.

are stripes of decreased density from transport rollers being left in contact with the film, preventing development. These artifacts occur if power is lost while the film is in the developer solution, if the speed of the transport system is dramatically decreased, or if the film becomes stuck while in the developer.

appear as an increase in optical density due to liquid coming in contact with an unprocessed film.

appear as a series of dark stripes that match the grooves of the entrance rollers. This occurs if the rollers become wet. The combination of pressure and water marks the film. This may also occur if the tension of the entrance rollers is too great.

is a white, powdery residue that remains on the surface of films because of incomplete washing. Hyporetention can also result in brown dichotic stains with aging.

can be caused by excessive developer time, too high of a developer temperature, over replenishment, high pH, or excessive developer concentration

can be caused by developer temperature that is too low, not enough time spent in the developer, under replenishment, contamination of the developer with fixer, pH that is too low, or insufficient developer concentration.

are caused by the patient, tech, or the equipment during an exam.

a blurring of the image, resulting in a loss of recorded detail

expose the film and produce tree, crown, or smudge static.

are half moon shaped marks of increased density caused by bending the film before processing

Improper image brightness can occur in CR if an incorrect histogram is selected or improper collimation is used.

Heat blur is a blurring of the image that can occur when a CR cassette is exposed to intense heat before being processed by the CR reader.

Accuracy is a measure of the percentage of cases that are diagnosed correctly.

Sensitivity is a measure of the likelihood of obtaining a positive diagnosis in a patient who is actually positive for a disease. It is a measure of the true positives divided by the number of people actually positive for the disease (true positives plus false negatives).

Specificity is a measure of the likelihood of a patient obtaining a negative diagnosis when there is actually no disease present. It is a measure of the true negatives divided by the number or people actually negative for disease (true negatives plus false positives).

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Each vendor is required to supply phantoms capable of testing contrast scale, noise, slice thickness, spatial resolution for both high and low contrast objects, and a mean CT number for water.

• mandates that any nonhospital institution performing advanced diagnostic services such as CT must be accredited by January 2010 in order to
• receive Medicare reimbursement. (already passed)

if passed would provide similar requirements for hospitals as well.

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High contrast spatial resolution is described as the minimum distance between two objects that allows them to be seen as separate and distinct. The physicist may measure this is terms of point spread function and modulation transfer function. The technologist measures this by imaging a test object with a bar or hole pattern.

Low contrast resolution is the ability of a CT system to demonstrate subtle differences in tissue densities.

Low contrast resolution is expressed as either the smallest diameter of an object with a specific contrast that can be detected or the smallest difference in attenuation that can be identified for an object of a specific diameter.

A phantom consisting of rows of holes of varying sizes filled with a liquid that has a CT number different from the surrounding plastic is image

Noise represents the portion of the CT image that contains no useful information.

It is defined as the random variation of CT numbers about a mean value when an image of a uniform object is obtained.

CT numbers represent the attenuation values of different structures within the body according to their atomic number and physical density.

The CT numbers are assigned a shade of gray corresponding with the attenuation value. For example, the CT number for air is -1000 HU and 0 HU for water. Tissues with densities greater than water have positive CT numbers and those with densities less than water have negative CT numbers.Water is there ference material used because it constitutes 90% of soft tissue mass and is reproducible and easy to obtain.

• The slice thickness in CT is determined by the collimators.
• Measurements of slice thickness are determined with a phantom that includes a ramp, spiral, or step wedge in the test objects. The test objects have known measurements and provide a standard with which to compare the scanner.

Patient dose varies with slice thickness, kVp, and mAs.

While no maximum dose limits per patient exam are specified, dose should be kept within 10% of manufacturer specifications.

mandates that any nonhospital institution performing advanced diagnostic services such as MRI must be accredited by January 2010 in order to receive Medicare reimbursement.

if passed would provide similar requirements for hospitals as well.

• Center frequency or resonance frequency is the radiofrequency that matches the static magnetic field.
• The value for center frequency should be recorded daily.
• Most manufacturers provide an automated way to determine the resonance frequency.
• A change in the center frequency indicates that there is a change in the strength of the magnetic field.

• High contrast resolution is the MR system’s ability to resolve small objects.
• A phantom consisting of pegs, bars, rods, or holes of known sizes is imaged.

• Low contrast resolution is a measure of the system’s ability to differentiate between adjacent tissues having minimal differences in signal intensities.
• A phantom containing objects of varying size and contrast is used for this test.

the homogeneity of a system’s magnetic field is an indication of the quality or uniformity of its field.

Poor homogeneity can result in poor image quality and artifacts.

Changes in homogeneity can be due to ferromagnetic objects located within the bore of the magnet and external ferromagnetic structures that may be in the neighboring magnetic field.

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Interslice RF interference tests can be used to determine how close slices can be before adjacent slices interfere with each other.

that all spaces over 5 gauss have appropriate warning signs.

(Mammography Quality standards Act) to standardize mammography quality throughout the U.S.

must be kept at a facility for either 10 years if the patient never returns for another exam or 5 years if the patient returns regularly

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digital has lower spatial resolution than film/screen

digital has higher contrast resolution than film/scree

its objective is to minimize artifacts on films by maintaining the cleanest darkroom possible.

it is done in terms of screen cleanliness and lack of artifacts on the films

• -mid-density and density difference should be within +-.1 of operating level ( if its outside these but within +-.15 films can still be processed that day)
• -base plus fog should be +-.03OD, no films can be processed
• -developer temp should be +-.5 degrees

objective is to assure that cassettes and screens are free of dust and dirt which cause artifacts.

is determined by the presence of artifacts on the film by using a screen cleaner and wiping with camel hair brush or spraying canned air

both the mammo machin and the automatic processor (all components of imaging chain)

assure that optimal contact is maintained between the intensifying screen and the film in each cassette

putting acrylic sheet on top of compression paddle and bring it to the tube. use manual tech. and view film on a viewbox, look for poor film contact

eliminate trapped air

compression should be between 25 and 45lbs in both the manual and powered mode.

quarterly or at least when 250 patient exams have been completed in low volume clinic

viewbox surfaces cleaned with window cleaner to remove all strau marks. All making equipment is checked. Illumination level is checked.

evaluates the radiologists ability to detect cancer on the mammo films, done by comparing the interpretation of the film to a pathology report.

by taking 3 exposure each of 3 different phantom thicknesses. for ea. phantom thickness, exposures are made using the lowest average and highest kVp clinically used in facility. FOr a given kVp the mAs should increase as the phantom thickness increases.

resolution can be effected

• using phantom and dosimeter placed in bucky, compression applied and exposure made. Dosimeter reading and mAs readout are recorded for each exposure.
• -Average glandular dose is calculated using HVL

to simulate the breast

if outside and miss breast tissue we can possibly miss cancer

assesed for the presence of artifacts (grids, collimators, compression device, breast support tray, processor artifact)

ensures that the unit produces a consistent, uniform beam that has enough energy to produce a quality image.