Performance monitoring must be done on each digital radiography device. Performance testing and monitoring of digital display equipment should be maintained in accordance with the equipment manufacturer specifications, applicable industry guidelines, and state and federal regulations. In the absence of adequate manufacturer procedures, guidelines, or standards, the recommendations for the performance evaluation of display devices testing methods and frequencies contained in the AAPM Task Group 18 report, “Assessment of Display Performance for Medical Imaging Systems,” should be followed. It should be noted that CRT and LCD devices tend to have different characteristics and may not degrade in the same ways or at the same rates. The same holds true for color vs grayscale devices. Devices from different manufacturers may also degrade at different rates. In all cases, it is necessary to monitor the display parameters on a regular basis (at least once per month, possibly more frequently as the displays get older, because they tend to drift more with age.) Regular visual inspection also needs to be done on a monthly basis to check for dead pixels, which automatic quality assurance systems do not do.
As a minimum quality check for display devices, a test image, such as the SMPTE test pattern or the AAPM Task Group 18 pattern, should be captured, transmitted, archived, retrieved, and displayed at appropriate intervals, to test the overall operation of the system under normal operating conditions. As a spatial resolution test, at least 2.5 lp/mm resolution should be confirmed.
As a test of the display fidelity, SMPTE pattern data files should be sized to occupy the full area used to display images. The overall SMPTE image appearance should be inspected to ensure the absence of gross artifacts (eg, blurring or bleeding of bright display areas into dark areas or aliasing of spatial resolution patterns). All display monitors used for primary interpretation should be tested at least monthly. As a dynamic range test, both the 5% and the 95% areas should be seen as distinct from the respective adjacent 0% and 100% areas.
Compression
Data compression may be performed to facilitate transmission and storage. The type of medical image, modality, and the objective of the study will determine the degree of acceptable compression. Several methods, including both reversible and irreversible techniques (lossless and lossy are also common terms), may be used under the direction of a qualified physician or practitioner, with minimal if any reduction in clinical diagnostic image quality. If compression is used, algorithms accepted by the DICOM standard, including wavelet compression methods such as JPEG-2000, are generally recommended. The types and ratios of compression used for different imaging studies transmitted and stored by the system should be selected and periodically reviewed by the responsible physician to ensure appropriate clinical image quality. Regular bodies may require that the compression ratio be indicated on the compressed image. (See the ACR’s Practice Guideline for Electronic Medical Information Privacy and Security).
Transmission
The environment in which the studies are to be transmitted will determine the type and specifications of the transmission devices used. In all cases, for official interpretation, the digital data received at the receiving end of any transmission must have minimal, if any, loss of clinically significant information. The transmission system shall have adequate error-checking capability. (See the Practice Guideline for Electronic Medical Information Privacy and Security).
The DICOM Transmission and Storage Standard should be referred to for best practice implementation, especially the DICOM DX Image Information Object Definition. Optimally, all vendors should use the DX object.
Archiving and Retrieval
Digital imaging data management systems should provide storage capacity capable of complying with all facility, state, and federal regulations regarding medical record retention. Images stored at either a transmitting or receiving site should meet the jurisdictional requirements of the acquisition and transmitting site. Images interpreted off site need not be stored at the receiving facility, provided they are stored at the transmitting site. However, if the images are retained at the receiving site, the retention period of that jurisdiction must be met as well. The policy on record retention must be in writing.
Each examination data file must have an accurate corresponding patient and examination database record that includes patient name, identification number, accession number, examination date, type of examination, and facility at which the examination was performed. It is desirable that space be available for a brief clinical history. Prior examinations must be retrievable from archives in a time frame appropriate to the clinical needs of the facility and medical staff. Each facility should have policies and procedures for archiving digital image data equivalent to the policies for the protection of hard-copy storage media.
The exchange of imaging information should be conducted in accordance with the Integrating the Healthcare Enterprise initiative through the use of current standards by DICOM and Health Level 7.
Security
Medical images are subject to US privacy laws such as the Health Insurance Portability and Accountability Act of 1996 and applicable state privacy requirements. Digital image data management systems should provide network and software security protocols to protect the confidentiality of patients’ identification and imaging data as well as appropriate user accessibility and authentication. There should be measures to safeguard the data and to ensure data integrity against intentional or unintentional corruption. For teleradiology purposes, additional software and hardware devices such as virtual private networks may be required to maintain patient privacy. (See the ACR’s Practice Guideline for Electronic Medical Information Privacy and Security).
Reliability and Redundancy
For facilities practicing electronic radiology, quality patient care depends on the stability and reliability of the digital image data management system. Written policies and procedures must be in place to ensure the continuity of care at a level consistent with those for hard-copy imaging studies and medical records within a facility or institution. This should include internal redundancy systems, backup telecommunication links, and a disaster plan.