The SCAR QA/QC Primer: CR, DR, displays and teleradiology

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Charles E. Willis, PhD, medical physicist with MD Anderson Cancer Center teamed up with MD Anderson's S. Jeff Shepard and John Romlein, clinical engineer with Xtria Healthcare Systems, to provide SCAR attendees with a comprehensive overview of quality control (QC) and quality assurance (QA) in the digital environment. Willis led with a discussion of QA in CR and DR, followed by Shepard's tips for selecting and maintaining displays. Finally, Romlein looked at QA issues from the teleradiology perspective.

QA in CR and DR

The first step in QA is to differentiate QA and QC, according to Willis. QA ensures maximum, consistent performance mandated by ACR standards and includes personnel and equipment; QC entails technical procedures that ensure a satisfactory product. In the digital environment, facilities need to consider the entire digital process, identify points where errors may occur and take action to avert and detect and correct errors. Willis walked participants through the process, identifying common errors throughout the DR/CR process.
The digital process begins when the patient arrives; identification and patient information such as allergies and pregnancy must be verified, and the tech must make sure the anatomy matches the request. The tech may err in the next step by misidentifying the patient to the imaging system, resulting in a broken studies or an orphan. The end-result is an unavailable image.
Procedures to remedy patient and exam identification errors include automated association such as a RIS interface, bar code scanner augmentation and DICOM worklist management. Willis cautioned that no remedy is perfect. For example, the DICOM worklist may not account for unscheduled exams or the tech may not notice if the bar code scanner does not catch a patient's medical record number.
The next round of potential errors occurs at the positioning level and includes mispositioning, movement, improper collimation and incorrect exam selection. QC should be performed at the acquisition device to identify positioning errors and complete repeat exams as necessary.

The next level of the QA plan involves reject/repeat analysis. Digital imaging sites need to develop a method for capturing rejected and repeated studies, collecting and analyzing the data, reporting results to management and staff, implementing training and sharing results with vendors.
Inadequate erasure of previous exams, artifacts, incorrect gain adjustment and inadequate correction of non-uniformity can occur as the image receptor captures the projection. Projection errors are generally detected at the acquisition station where they may be corrected; however, some errors necessitate a retake.
Willis stressed the importance of active QC countermeasures to avoid errors before they occur rather than correct them post-exam. Countermeasures include prophylactic erasure of all CR plates at the start of a shift, periodic checks of non-uniformity corrections, periodic gain recalibrations, periodic checks of phototimer calibration as well as cleaning, thorough acceptance testing and a comprehensive technique guide for techs.
Like in previous steps, the next phase of the digital process-rendering of the captured projection for viewing-is ripe for QA/QC. Potential problems include incorrect exposure field recognition, incorrect grayscale recognition and inappropriate histogram analysis-all errors that are typically corrected with a retake or re-processing. Willis noted that many digital vendors have incorporated methods for automating QC in the CR and DR solutions. For example, most systems provide an exposure indicator. "There is a documented tendency to overexpose CR and DR, but QC programs based on exposure indicators are successful," Willis said.
Vendors are increasingly integrating QC workstations into the acquisition device to further streamline digital workflow. Image processing can be modified at the QC workstation to correct for some errors. Other functions completed at the QC workstation include image rotation, annotations, demographic overlays and conjoining images.
A transmission failure may occur as the image is pushed to the archive; the study may be deleted from the local cache or information may be omitted from the transmitted image. Errors that may occur at the final step of image display for viewing include incorrect grayscale calibration, inadequate spatial resolution and incorrect or missing demographic information of annotations.
A variety of steps and procedures can be implemented to improve digital image quality; however, staff is key.  "[Hospitals and imaging centers] need to employ a team approach to QA," Willis recommended. "This includes the radiologist, radiology administrator, lead technologist, clinical engineer and medical physicist."

Selecting and maintaining a primary display system

MD Anderson's S. Jeff Shepard outlined considerations in display selection and implementation. The first consideration? LCDs vs. CRTs, Shepard explained. He discussed reliability studies indicating reliability issues, including loss of brightness, luminance and uniformity with CRTs with the average CRT life expectancy hovering in the 2.5 year range. LCDs have proven to be more reliable at numerous facilities including MD Anderson, University of California-Davis, Lehigh Valley Medical Center and Mayo Clinic and should be the display system of choice, Shepard said.
One of the primary LCD evaluation factors is resolution or display matrix size; 3 megapixels is adequate for general imaging, but mammography requires 5 or more megapixels. Vendors typically offer a few flavors of bit-depth or shades of gray; 8 or 10 are common options and 8 is adequate, he said. Off-axis contrast, which enables multiple viewers to see the same image, is another critical consideration. LCDs should conform to DICOM PS 3.14, which covers minimum and maximum luminance, calibration stability, self-calibration and calibration frequency. Displays should calibrate about once per second especially during warm-up, notes Shepard.
Most vendors offer remote management (or SNMP) with LCD displays. "SNMP allows the system administrators to view the status of monitors remotely and can reduce management costs," explained Shepard. As a facility selects and deploys new displays, it must develop security measures such as password ownership and management that prevent radiologists or others from changing displays parameters.
Beyond performance specifications, systems can be differentiated by the cost of ownership -- including terms and conditions of the sale and warranty. It's critical to understand vendors' different defective pixel specifications and security and SNMP approaches, Shepard said. At this point, the facility may opt to investigate off-the-shelf components; however, these devices are not suited to CR or DR and lack self-calibration and SNMP tools.
Key points to analyze on warranties include:
  • Minimum hours to failure
  • Backlight replacement policies
  • Artifact policies
  • Location and turnaround time for repairs
After the field is reduced to three to four vendors, Shepherd recommended that facilities solicit RFPs. During this phase, it's helpful to talk to sophisticated users of various systems and complete site visits to learn more about SNMP and reading room set-up. Shepard also recommended requesting a one month, on-site evaluation of the system to complete an initial acceptance test and analyze image viewing and SNMP functions. 
Once the facility purchases displays, QC entails acceptance testing, initial set-up and scheduled QC. Acceptance testing covers luminance response, chromacity, noise and diffuse and specular reflectance. The initial acceptance test is generally repeated annually; luminance is assessed on a monthly basis. Self-calibrating monitors do not require daily calibration; however stability should be ensured frequently during a test drive phase which can be gradually extended to one year.

QA for Teleradiology

Teleradiology is evolving and growing with multiple factors-consolidation of healthcare providers, digital imaging, nighthawk use and the EHR-fueling its growth. "QA and QC are not developing as fast as teleradiology," said John Romlein, clinical engineer with Xtria Healthcare Systems.
QA processes remain standard for both analog to digital and digital to digital teleradiology and should cover acquisition, digitization, manipulation, compression and store and forward. It should address both human and machine issues and progress through the workflow. Romlein identified printers and displays as two areas where errors can occur; both devices offer multiple ways to display the same dataset. Consequently, facilities need to implement task lists, output tests and establish and enforce minimum quality standards no matter where a device resides. A task allocation chart that lists all processes with connected systems and devices should define workflow and quality issues. The chart should assign various staff responsibility for identified quality issues; this includes required frequency as well as standards.