1. QC in a Digital World John Aldrich PhD FCCPM Department of Radiology
Vancouver Coastal Health
University of British Columbia

2. Digital Imaging
Any sufficiently advanced technology is indistinguishable from magic… Arthur C Clarke 1961

3. Overview New paradigms Standards Image acquisition systems PACS
Radiography DR, CR
Fluoroscopy, Angiography DF CT US
PACS

4. New Paradigm Image Capture Image Storage Image Display
In electronic imaging the functional parts of conventional radiology have been separated:
Image Capture
Image Storage
Image Display

5. Imaging QC Principles Proactive QC rather than Reactive QC
Test tool/phantom
Standard imaging parameters/conditions
Scheduled testing (Daily/Weekly)
Defined and objective acceptance/rejection criteria
Patient replaces the phantom
Non-standard imaging parameters/conditions
Frequent testing (every patient)
Ill-defined and subjective acceptance/rejection criteria
The concept that I propose for the VCHA QC program is Proactive QC rather than Reactive QC.
(READ SLIDE INFO)
In my opinion, radiologists should not need to complain about image quality if the QC program is effective.

6. Quality Control (QC) Acceptance testing
New equipment
Conformance to manufacture’s specs/criteria
Routine performance evaluations
Specific tests performed at regular intervals
Consistency checks
Evaluate malfunctioning or out-of-spec equipment
Baseline value determination
Clinical use period
Next constancy testing
Data evaluation
Within the
established criteria
Remedy
First constancy testing
FAIL
PASS
There is a distinction between acceptance testing and regularly performed QC. Acceptance testing is performed to verify the manufacturers claims and to verify compliance with regulatory standards. Constancy tests are performed to determine whether the performance of a device has changed after its installation/acceptance. More specifically, a certain test is conducted at appropriate intervals to check the deviation of the current performance value from the reference performance value (baseline value).
If the measured performance value is within the predetermined acceptance deviation limit (established criteria), the device will be continuously used until the next test.
If the measured performance value is outside the acceptable range, an appropriate remedial action must be taken.

7. Digital System QC
Film
Developed
And
Fixed
Detector
Reading
Digital
Processing
Stored
PACS
Viewed
Display
QC of the digital systems is an additional requirement
– in addition to the usual x-ray performance tests

8. Health Canada - Quality Control
Safety Code 20A ( )
Recommended safety procedures for the installation, use and control of x-ray equipment. Mainly concerned with the x-ray output parameters of the equipment
Only film processor QC defined
Safety Code XX (due 2008)
Recommended safety procedures for the installation, use and control of x-ray equipment. Mainly concerned with the x-ray output parameters of the equipment
25% of the Code is concerned with QC of the digital imaging detector systems

9. Digital X-ray Systems Direct Radiography DR Computed Radiography CR
Formation of image without a secondary read-out device
Computed Radiography CR
Use of storage phosphor plate usually in a cassette-based system
Digital Fluoroscopy/Angiography DF
Image intensifier/video system replaced by digital plate.
Computed Tomography CT
Ultrasound US

10. DR, CR and DF – Extra QC
Routine QC interval will depend on system – not less than annually
Dose Calibration
Spatial Resolution
Low Contrast
Uniformity
Artifacts
Spatial Linearity
There are general QC tests that are performed on CR readers….Dose calibration, Resolution, Contrast, Uniformity, and Spatial Linearity.

11. Dose Calibration
Each system should be calibrated according to the manufacturers protocol, as they are all slightly different
General set-up
Arrange for defined dose at surface of cassette at 80 kVp
Expose and read image
Record Exposure Index
The image can also be used to check for uniformity, linearity and artifacts
Generally, this is the setup used for dose calibration.
Erase cassette, place at certain distance from tube, use specific technique, read the cassette after a standard amount of time and record the Exposure Index.

12. Image Quality
All CR and some DR/DF manufacturers have special Image Quality phantoms and automatic software to analyze image quality

13. Resolution and Contrast
Any high contrast resolution phantom can be used to provide comparative information
Low contrast resolution is one of the most difficult parameters to measure
There are several phantoms and measurement is subjective, so consistent technique is essential
A high contrast phantom can be used to ensure the information detail in an image remains constant over time. The phantom is placed on a cassette and exposed with a low technique.
After reading the cassette/IP, the image is sent to PACS and the point at which 50% of either lines, bars or mesh are resolvable is determined to be the resolution limit.
That should not change over the life of the equipment or between PM’s by more than +/- 20%.
The phantom we manufactured can be used for this purpose.

14. Digital Radiography QC
Many DR systems require more frequent calibration of the uniformity eg every month
Flat field measurement (uniform copper plate)
Uniformity correction
Noise
Artifacts
Contrast-detail and resolution phantom

15. Special Requirements for CR QC
In film screen systems the film is changed for every image
With CR the IP is read up to 10,000 times
Almost all plates suffer from wear artifacts
If you are suspicious about an artifact take an image using the same plate and no patient
Make sure there is a QC program to detect wear before you detect it clinically
Hammerstrom et al
J Digital Imaging :226

16. Observations Let’s begin with Agfa IPs.
On this clinical image, there appears to be two artifacts that are prominent and two others along the edges that are less obvious. But, there are more artifacts visible. In fact about 12 more. When the flat-field image is examined it is apparent that the small white line densities in the clinical image are not due to patient anatomy but are in fact artifacts caused by scratches on the phosphor surface. It is interesting to note that the two prominent artifacts do not appear on the flat-field radiograph and may be artifacts caused by something on or in the patient. The scratches were all visible visually.

17. Observations Let’s begin with Agfa IPs.
On this clinical image, there appears to be two artifacts that are prominent and two others along the edges that are less obvious. But, there are more artifacts visible. In fact about 12 more. When the flat-field image is examined it is apparent that the small white line densities in the clinical image are not due to patient anatomy but are in fact artifacts caused by scratches on the phosphor surface. It is interesting to note that the two prominent artifacts do not appear on the flat-field radiograph and may be artifacts caused by something on or in the patient. The scratches were all visible visually.

18. Observations
Sharp particulates embedded in the felt lining under a plastic clip etched phosphor surface to create density on radiograph
Not enough pressure beside plastic clip to cause 2nd wear mark to effect radiograph
Like the Agfa IPs, those from Fuji are also vulnerable to etching from sharp particulates embedded in the felt-like material that lines the cassettes. In this case, the phosphor has been etched by particulates in two adjacent areas but only the area under the same plastic clip shown in the last slide has been damaged enough to become radiographically significant.
Also, the phosphor is white and not orange as it appears in this photograph. The brightness and contrast have been altered a little to better visualize the damage.

19. Observations Yellowing of phosphor Virox
Artifacts observed around the periphery of Fuji flat-field radiographs was most often caused by yellowing of the phosphor. Yellowing is caused when the physical integrity of the IP edge is compromised and moisture oxidizes the halides in the phosphor. For example from iodine to iodate.
Yellowing of phosphor
Virox

20. Observations Scratches Dust Lastly, we will look at Kodak IPs.
The phosphor surface of several large IPs were observed to have a slightly darker hue along one edge and it wasn’t until the phosphor surface was gently wiped with a gloved fingertip that it became apparent that the hue was really a dusting of very fine aluminum particulates. The magnified areas in the radiograph show the areas where the dust was removed from the phosphor surface.
Scratches were also apparent both radiographically and visually and were most often found in this location on large IPs and were oriented in the direction of IP travel.

21. CR QC Recommendations Quality Control (QC) - perform monthly
Inspection – cassette and IP
Visual
Radiographic
CR Cassette cleaning
CR IP cleaning
Benefits
Fewer image artifacts and repeated exposures
Increased life cycle of cassettes, IPs, and readers
Compliance with vendor warranties
I would strongly encourage anyone using CR to perform regular quality control on your CR cassettes and imaging plates. Look at them, radiograph them, and clean them on a regular basis.
The primary goal of such a program is to reduce the number of artifacts visualized and the number of repeats performed. Other benefits include an increased life cycle of your CR equipment and compliance with vendor warranties.

22. Consistency Checks Weekly/daily Simple phantom to test reproducibility
To use if there seems to be a problem

23. Vancouver Phantom
This phantom we have developed for routine constancy QC of digital systems
Field collimation
Standard operating conditions
Resolution
Contrast
For those who do not have phantoms this phantom we are developing would be a start
Low contrast circles
High contrast mesh

24. Orthopaedic Measurements
A set of devices has been prototyped and tested at the GLDHCC Radiology office to use with OrthoView templating software. When a marker of known size is included at the same plane as the proximal femur in an x-ray image, the image can be resized by the Orthoview software to match the size of prosthetic templates included with the software. An early prototype included a 25.4 mm washer (from Home Depot) embedded in a plexiglass disk.
Eventually a set of three devices: a 27 cm disk, a 5 cm disk and a baton, all made of ABS plastic with an embedded 25 mm copper disk, were designed and manufactured.
The baton is used by allowing the patient to hold the baton and press the end containing the copper disk against their hip.
Preferably, the 27 cm disk is used. First the tech ensure the 25 mm copper disk (located under the white insert) is in the plane of the proximal femur. A marking at the 12 o’clock position on the disk indicates the distance the copper disk is from the table. A mental note is made of this number and the disk is then moved between the patient’s legs. If the disk moves before the exposure is made, the tech simply needs to reposition the disk so the same number is again at the 12 o’clock position.
A small 5 cm disk can be used in a similar manner for extremity joint imaging.

25. QC in CT - Daily In-air calibration of scanner every 24 hours
These are the suggested tests which should be made routinely. I have divided them into three areas – mechanical, image quality and dose.
These tests should also be performed in the order shown.
In-air calibration of scanner every 24 hours
Adjusts sensitivity of all detectors
Important to do this – build into schedule.

26. QC Frequency
It is suggested that all of the tests be carried out on at least an annual basis. Noise and uniformity and CT number linearity should be measured on a weekly basis.

27. QC Phantoms ACR CT Accreditation Phantom (RMI) Scanner QC phantoms
Alignment, noise, uniformity, CT number, resolution, MTF, low contrast, image slice width
Scanner QC phantoms
GE: noise, uniformity, resolution, MTF, low contrast
Siemens: noise, uniformity, MTF
What phantoms are available, and which ones should be used?
The first of these is the American College of Radiology (ACR) Phantom which is an integral part of the new ACR CT Accreditation Program. This phantom can measure all the image quality parameters.
Secondly, the phantoms provided with the CT scanners may also be used for many of the tests.
Lastly, the acrylic phantom will be necessary if you wish to measure CTDIw, but as we will see other measurements may be adequate to monitor dose.

28. Ultrasound QC - Phantom
The phantom includes nylon filaments spaced at regular vertical and horizontal distances, anechoic cysts, grey scale targets, axial resolution targets and dead zone target groups.

29. Cracked/Dead Elements
US Probe Test Report
A report is generated after testing a probe with the FirstCall 2000 device. This is the last of three pages and shows the pulse waveform and frequency spectrum results of three elements across the array…the center element and two near but not at each edge.
The first two pages show the results of the frequency, capacitance, 20dB pulse width, frequency, and fractional bandwidth tests. The x-axes show the performance of individual elements and if all is functioning properly, each element should be performing similarly to its neighbour. This probe is functioning optimally.
Cracked/Dead Elements

30. Ultrasound QC – Clinical
6 dead elements – right image
Slight shadowing in the middle of the image
Discernable loss of signal amplitude
The same probes used in the previous slide were also tested clinically with great care taken to replicate the imaging parameters. Again the image on the left was taken with the good probe and the one on the right with the probe with six dead elements in the centre of the array.
The malfunctioning probe produced an image with slight shadowing in the middle of the image with a discernable loss of signal amplitude.

31. Optimization of Displays
Clean the surface of the display
With the display OFF look at reflections on the surface of the display such as lamps, windows, white coats and name tags. Reduce these artifacts as much as possible
Display the SMPTE test pattern
Ensure you can see the 5% and 95% grey scales

32. Radiology Workstation Contrast
Aldrich JE et al. J Digital Imaging 2005;18:

33. Calibration of Displays
Software generates grayscale levels
Photometer measures the luminance output at each level and adjusts video card output to obtain a perceptually linear gradation between grayscale levels
Calibrates display to DICOM standard
To calibrate the displays, a photometer is held against the display surface while software generates gray-scale intervals from black to white. The luminance at each gray-scale level is measured by the photometer and adjustments are made to the video card output to obtain a perceptually linear gradation between gray-scale levels.
I calibrate approximately 180 primary and secondary displays in the VCHA. Primary displays at LGH and STS are calibrated by a Rad. Service engineer whose office is at LGH.
181

34. Primary PACS Displays
Primary reporting workstations should be used in custom-built reporting areas with low reflecting surfaces, ergonomically-designed chairs, recessed pot lighting with dimmer controls and climate control.
Our primary reporting stations are calibrated for luminance and contrast ratio every three months.

35. Secondary PACS Displays
In contrast, the secondary displays are used under a range of conditions, often with the possibility of distracting reflections and high ambient lighting.
The secondary displays are checked normally only on installation
Calibration factors can often be changed by the user.
Location:
Operating Rooms
Emergency Rooms
3D Processing workstations
(Offices, wards, home)

36. The Imaging Chain
Detector
Reading
Digital
Processing
Stored
PACS
Viewed
Display
Image are used to follow disease processes so it important that the whole digital chain is linear
Linearity should be checked after changes to software/hardware in any component

37. The only perfect science
The Future
The only perfect science
is hindsight