Imaging QA Test 2

every radiographic image must include
(Can be in the DICOM Header):

Required by law:

Patient name

Patient DOB

Date of Exam

Location of Exam

Rt or Lt Marker

NOT required by law:

MR #

Tech’s ID (initials, etc…)

EI Number

Referring Physician

Reading Radiologist

Common Errors:

Wrong Patient -- may have x-rayed the correct pt, but sent under the wrong ID

Wrong Body Part -- sent under the wrong body part... the wrong accession # = Hard for the physician to locate

Wrong Side -- Wrong Marker, but correct side OR wrong accession # for bilateral examinations

Wrong annotation -- upright vs. supine; PA vs. AP

Receptor Exposure

the amount of radiation striking the receptor

Mottle

Saturation– soft tissues eliminated

Patient and technical factors need consideration

S#s and EI#s are brand specific and will not be assessed on the ARRT exam

Processing Errors

Histogram analysis

•Values of interest

•Rescaling – modifying image to what the computer thinks it should look like

•LUTs – processed with the right amount of brightness and contrast

•Correct Collimation is crucial – lowest exposure regions of a histogram can represent collimated borders

•Asymmetrical collimation causes problems in CR because CR is processed looking for 2 or 4 borders

ARTIFACTS

any part of an image that does not accurately represent the anatomic structures present within the subject being evaluated

damage

Receptor physical damage to the receptor

•Hyperdense artifacts

•DR dexel malfunctions (Dead dels)

Pixel Malfunctions –malfunctions with the screen

•Dead or damaged pixels

•Located in the exact same location every image

Dexel Drop-Out Effects

In DR systems, dead detector elements (dexels) can fail =    not produce a gray square = broken

Entire rows or columns of dexels can also drop out due to electronic failure

•Mild – moderate issues are compensated for

•Many rows (severe), the detector plate will need to be replaced

The most common way to correct these is using a software kernel in which the values of the 8 pixels surrounding a dead pixel are averaged, then this value is inserted into the dead pixels

STEPS:

•SUM eight surrounding pixels

•

•AVERAGE these values

•

•INSERT result into centered pixel

Data Clipping

•If the dynamic range or bit depth of a digital processing system is too limited, it is possible for data clipping to occur when either brightness or contrast are adjusted

•

•The dynamic range of the software, supported by the bit depth of the computer hardware, must extend sufficiently above and below typical input values to allow for all probable adjustments to the image

•

•Would restrict the amount of data shared to the Radiologist and therefore limit their windowing ability

Aliasing (Moire Artifact)

•An interference pattern

•A  false presentation of artefactual lines

•One way is to overlap two similar patterns of alternating, periodic structures, especially high contrast structures, such as grid lines from two overlapping grids

aliasing 

•In CR processing, an electronic version called “aliasing” is much more likely to occur IF:

  A stationary grid is used, and the grid lines run parallel to the scanning lines of the CR reader

•

•If the frequency of the of the grid lines is close to the scanning frequency of the CR reader, and they run parallel to each other, the artifact may occur

•Older grids often have a frequency of 40-50 lines/cm

•To prevent aliasing artifacts:

•Use high-frequency grids at >50 lines per cm (expensive)

•Use new multi-hole grids

•Use Short-Dimension (SD) grids positioned such that the grid lines run perpendicular to the CR scanning lines

long dimension vs short dimension

lead strips run parallel vs perpendicular

17 in vs 14 inches

ALIGNMENT ISSUES

•For CR, exposure indicator errors are likely unless at least 30 percent of imaging plate is exposed

üTherefore, for tightly-collimated views of digits, it is recommended that two or three views be taken on one imaging plate

üUse at least 1/3rd of the CR Plate for an exposure

  (CR IRs come in different sizes!)

NOTE:

Because they scan the receptor plate in sections, DR systems are not subject this 30 percent rule for plate coverage

BILATERAL PROJECTIONS

When “manual” technique is used, CR systems generally have no difficulty processing bilateral views without processing errors

However, when AEC (automatic exposure control) is used, special care must be taken to activate the two side detector cells and ensure that the anatomy is positioned directly over the energized cells, to avoid early shut-off and unacceptable mottle

Artifacts:CR

Dust, aging phosphors, ghosting, scratches

Laser jitters = wavy appearance

Laser obstruction

Radiation Fog

Ghost Images

•CR only issue

•Incomplete erasure of the CR receptor

Backscatter

Backscatter artifacts are more likely to appear in situations with more scatter (ie, with large patients or wide-open collimation) or if the x-ray beam is not fully intercepted by the detector

---------

If projections of detector electronics are visible on a patient image, options for a repeated image include using tighter collimation (decreasing the field of view), verifying good imaging geometry, or placing additional shielding behind the detector, such as a lead apron or plate to block the backscatter from striking the detector.

A GREAT TECHNOLOGIST ALWAYS
follows these 8 CRITERIA for digital radiographs:

1. Brightness:

All pixel brightness levels within the anatomy of interest should be neither completely white   nor pitch black, but should possess a long a broad range from very light to very   dark gray

  “SEE THROUGH” that area

2. Contrast and Gray Scale:

Should be such that the number of   details present in the image is maximized, and  there is sufficient visual differentiation between adjacent details

3. Signal-to-Noise Ratio:

must be achieved in every image, by:

  A. Increasing the signal reaching the image receptor

  B. Decreasing the electronic noise, scatter radiation, and all other forms   of noise (Artifacts) reaching the image receptor

To ensure adequate penetration of the signal,  sufficiently HIGH kVp must be used

4. Spatial Resolution (Sharpness of Detail):

should be apparent in electronic images:

•At least 8 LP/mm for static images

•At least 6 LP/mm for digital fluoroscopy

•Dependent upon:

1)Geometrical factors in the original projection

2)Digital processing

3)Vertical and horizontal resolution of the display monitor

4)Zoom (magnification) level

 5. Artifacts:

      of all kinds must be absent

6. Shape Distortion:

must be minimized, such that accurate representation of the anatomy of interest is achieved

•Dependent entirely upon geometry of original projection

7. Geometric Magnification (Size Distortion):

of the original image should generally be minimized

•Strictly controlled by the SID/SOD ratio and related positioning

•Long SID; Short OID

•

8. Display Magnification:

of the digital image should not be so extreme that the image becomes pixelywhere individual

pixels become apparent and sharpness of details is lost

•controlled by display screen size, matrix size, and field of view

Effects on Contrast REVIEW:

Procedural factors