Medical Imaging Displays Diagnostic Imaging and the Need for Conformance, Calibration QC & QA

By Harley Firth, Vice President—Healthcare, Richardson Electronics

The recipe for the selection, acquisition, delivery and installation of most diagnostic imaging workstation platforms often involves more ingredients than the best seven course meal. Fortunately, with the availability and affordability of 2D and 3D imaging software, high-end computing platforms and the vast array of sophisticated color and greyscale display systems to choose from, the main dish is rarely burnt and the “guests” are quite often pleased with the finished result placed in front of them.

In fact, today’s high quality imaging platforms are capable of consistently meeting the needs of the most demanding radiologists, clinical specialists and IT professionals—if the right hardware and software is chosen and implemented properly.

Healthcare facilities have become very good at choosing the right equipment for the critical task of diagnostic imaging; but oddly enough, one of the questions I am often asked by existing users is; “How do I ensure my workstations remain compliant to the diagnostic imaging performance recommendations of DICOM, ACR and AAPM TG18 ?” While many sites make their equipment selection based on very sound thinking and judgment, there seems to be a disconnect between the selection and implementation of these systems and the maintenance and guarantee of consistent performance.

The reason for this disconnect, in my opinion, is that the functions of Conformance, Calibration, and QC & QA of medical imaging display systems is not perceived by Healthcare Administrators and Diagnostic Imaging Departments as falling solely under the roles and responsibilities of only one department: Bio-Medical, Medical Physics, Radiology or IT. This “overlap” creates some confusion as to who is responsible for assuring diagnostic precision of the facility’s entire group of displays at all times. In the past, film printers were maintained by the Radiology or Bio-Medical Department. But with the introduction of more players in the game, this role seems to be up for debate. Unfortunately, it is a necessity; and something I feel needs to be addressed at a higher level within many facilities. After all, it is called “diagnostic imaging” for a reason. Clinicians and patients alike rely on the accurate interpretation of hundreds of thousands of images per day in the United States alone.

“Who” should be responsible within a facility for the functions of Conformance, Calibration, and QC & QA of medical imaging display platforms is not the issue. The American Association of Medical Physicists has clearly stated that the performance assessment of electronic display devices falls within their professional responsibilities. What is at issue, is the fact that at many sites medical physics is not being handed the role of medical imaging display QC & QA; and therefore, no one is taking care to ensure these systems consistently meet the standards necessary for diagnostic and clinical use. For those sites with a Medical Physics Department, this should be a priority. At facilities without a Medical Physics Department, someone needs to take ownership of this issue and put a plan in place. To that end, I have outlined my thoughts on this topic below.

First things first: In order to implement a Conformance, Calibration, and QC & QA plan, we need to be establish an understanding of how each of the functions below is going to be used to implement a comprehensive program throughout the facility or institution.

• Conformance – What are the conformance parameters (and associated margin of error) that each type of display system must meet? How critical are these parameters to the day-to-day performance of the system and the accuracy of the information/images presented to the radiologists?
  Conformance parameters should be based upon a strict set of guidelines (DICOM, ACR, AAPM TG18, etc…) and should include, as a minimum, the following:
  - Peak Brightness Stability
  - Black Level
  - DICOM Compliance (LUM Value and FIT Value)
  - Luminance Uniformity
  - Standard Image Assessment, etc
• Measurement – What measurements need to be taken in order to test for each of the above mentioned conformance parameters? What methodology will you use to ensure the accuracy, repeatability and soundness of each measurement?
• Data Collection – How will data be collected, logged and presented to the institution? Will data be collected in a manner that allows for historical analysis of performance and as a predictor of future failure? Who will manage the data? Who will be responsible for updating the data?
• Corrective Action – What are the corrective actions to be taken in the event of a failure of any of the conformance tests defined above?
  Corrective actions can be defined as any number of actions implemented to correct a display system’s failure of any of the conformance tests defined above or the actions taken to remove a system from use if its performance cannot be corrected on site.
• Calibration – How will deviations in the conformance parameters established above be corrected in order to ensure the system’s performance meets the requirements defined for acceptable use in diagnostic imaging? What tools (e.g., hardware and software) are available to calibrate the system’s performance? How will calibration be performed?
  Keep in mind that calibration is a correction and should only be used in the event of a conformance failure, or when a failure is predicted to occur before the next series of conformance tests.
• Quality Control – What frequency of conformance testing is necessary to ensure display system performance is maintained throughout the display system’s life?
  Certain tests will require more frequent testing, while others will not. Establishing the correct frequency for each conformance test is the key to limiting conformance failures.
• Quality Assurance – How will all of the above factors be used to ensure display performance consistently meets the expectations of the institution?
  Once conformance parameters have been established, measurement methodology determined, data collections rules defined, corrective action and calibration routines implemented and a frequency of testing put into place, the next step is to use all of these steps to assure medical imaging display performance meets expectation 100% of the time. Hence the term quality assurance. Very few sites have this kind of QA program in place.

Now that we know the important steps involved (your facility may use different ones) the next task is answering the “How do we do that?” question. For that I suggest the following process:

• Thoroughly review DICOM Part 3.14 (DICOM Part 3.14 Hyperlink) and the ACR Technical Standard for Digital Image Data Management (ACR Technical Standard Hyperlink). These two documents contain a host of valuable information. They also provide some very good insight into not only what needs to be accomplished, but also why.
• Review the American Association of Physicists in Medicine (AAPM) Task Group 18 document on Assessment of Display Performance for Medical Imaging Systems, located at AAPM TG18 Hyperlink. This will become your bible as you move forward with your program. The AAPM has done a fantastic job in establishing the performance requirements and testing parameters for both diagnostic and clinical review systems. Their advice on the topic should not be overlooked.
  
  In addition, the AAPM TG18 document defines (1) who should be responsible for each of the tests they outline; (2) what tests should be performed for Acceptance testing, Annual QC testing, Quarterly QC, Monthly QC and Daily QC; and (3) that the acceptance and QC testing of a display system must be performed by individuals having appropriate technical and clinical competencies. These competencies are:
  - Acceptance Testing - Performed by Medical Physicists
  - Annual QC Testing - Performed by Medical Physicists
  - Quarterly QC - Other staff (Biomedical Engineers, Service Technicians, X-ray Technologists) trained/supervised by Medical Physicists
  - Monthly QC - Other staff (Biomedical Engineers, Service Technicians, X-ray Technologists) trained/supervised by Medical Physicists
  - Daily QC - Performed by User
• Collect any and all information available on the systems to be serviced. Be sure to include information from the manufacturers of the display systems and workstation platforms. This will include:
  - display types and serial numbers,
  - graphics card types and serial numbers,
  - graphics card driver name and revision number,
  - conformance and calibration software name and revision number,
  - workstation name,
  - specifications and location within the facility, and
  - any other information.
• Define the conformance parameters (and margin of error) you wish to employ in your program. Determine which tests/measurements can be performed via embedded software provided by your display manufacturer or reseller. Decide which will require front-of-screen manual testing with a hand held photometer (or the naked eye in the case of several qualitative tests).
• Develop the testing procedures needed to measure all of the conformance parameters. Many of these will be predefined; and, in most cases, you will not need to create a test procedure, but rather copy one that has been defined by the display manufacturer, AAPM or DICOM.
• Create a system of data collection (Excel, Access, etc…) and presentation. Many display systems already collect conformance testing data and store it directly on the host workstation or on a network server (if a networked display management tool or remote administration tool is used.) Moving this data from these locations is often quite simple and can be done by any savvy IT specialist.
• Define all of the corrective actions necessary in the event of a conformance failure. (Don’t forget that “remove from use” is a corrective action). This is very important – you must have a corrective action defined for each conformance failure; otherwise, if left unchecked, a faulty system could plague a radiologist or clinician, hamper their workflow, inhibit proper diagnosis and cost a facility thousands of dollars per day in down time and service issues.
• Ensure you have all of the measurement and calibration tools required for each type of system being serviced. You may need to purchase several different photometers, calibration software packages, etc. Testing half of your systems would be the same as only checking the air pressure in two of the tires of your car each time you get an oil change.
• Check your devices. Make sure your handheld light meters are annually calibrated to the NIST (National Institute of Standards and Technology) certification. NIST certified test facilities will supply a certificate of calibration that will start your QA traceability.
• Establish the frequency for each test. Some tests and measurements can be performed with a much higher frequency than others, as they will run independently on the workstation in the background or after hours. Those tests that require manual intervention will most likely be scheduled with lower frequency. There is no truer test of performance than having someone physically verify system performance, accuracy and efficiency with an NIST calibrated high-precision handheld photometer.
• Create a schedule of service. It must meet the capabilities of your equipment and your available manpower.
• Establish procedures to clean the front of screen of the displays with an appropriate cleaning solution. Cleanliness is often the key to excellent image quality and perception. Here is a test: Turn off your display and count the fingerprints on the screen. Now, imagine a radiologist using that display to make diagnoses and the possible errors these smudges could bring into play on a daily basis. Clean the front of the screen thoroughly and shut it off again. It should be fingerprint free. If not, rinse and repeat.
• Organize a cleaning schedule for the entire workstation. Don’t forget the workstation should be completely cleaned at least annually of all dust and grit. A clean system will perform better and last longer than a system that is allowed to gather dust until the screens and filters for the fans are completely clogged.
• Begin implementing service. Work towards a QA program that predicts future failure and allows you to ensure each display system is consistently operating at peak performance, and continuously meeting all of the available performance specifications.

Best Practice suggestions:

Calibrate and Conform Quarterly if the following is true:

• You are a facility that uses CRT technology.
• You have Liquid Crystal Displays that do not have backlight stabilization.

Conform Semi-Annually if the following is true:

• You have LCD displays with either backlight stabilization or front sensors installed.

Calibrate Annually if the following is true:

• You have LCD displays with either backlight stabilization or front sensors installed.