Journal of Digital Imaging

, Volume 26, Issue 1, pp 38–52 | Cite as

ACR–AAPM–SIIM Technical Standard for Electronic Practice of Medical Imaging

  • James T. Norweck
  • J. Anthony Seibert
  • Katherine P. Andriole
  • David A. Clunie
  • Bruce H. Curran
  • Michael J. Flynn
  • Elizabeth Krupinski
  • Ralph P. Lieto
  • Donald J. Peck
  • Tariq A. Mian
  • Margaret Wyatt
Article

Preamble

These guidelines are an educational tool designed to assist practitioners in providing appropriate radiologic and radiation oncology care for patients. They are not inflexible rules or requirements of practice and are not intended, nor should they be used, to establish a legal standard of care. For these reasons and those set forth below, the American College of Radiology cautions against the use of these guidelines in litigation in which the clinical decisions of a practitioner are called into question.

The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by the physician or medical physicist in light of all the circumstances presented. Thus, an approach that differs from the guidelines, standing alone, does not necessarily imply that the approach was below the standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set forth in the guidelines when, in the reasonable judgment of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources, or advances in knowledge or technology subsequent to publication of the guidelines. However, a practitioner who employs an approach substantially different from these guidelines is advised to document in the patient record information sufficient to explain the approach taken.

The practice of medicine involves not only the science, but also the art of dealing with the prevention, diagnosis, alleviation, and treatment of disease. The variety and complexity of human conditions make it impossible to always reach the most appropriate diagnosis or to predict with certainty a particular response to treatment.

Therefore, it should be recognized that adherence to these guidelines will not assure an accurate diagnosis or a successful outcome. All that should be expected is that the practitioner will follow a reasonable course of action based on current knowledge, available resources, and the needs of the patient to deliver effective and safe medical care. The sole purpose of these guidelines is to assist practitioners in achieving this objective.

Introduction

This technical standard has been revised by the American College of Radiology (ACR), the American Association of Physicists in Medicine (AAPM), and the Society for Imaging Informatics in Medicine (SIIM).

For the purpose of this technical standard, the images referred to are those that diagnostic radiologists would normally interpret, including transmission projection and cross-sectional X-ray images, ionizing radiation emission images, and images from ultrasound and magnetic resonance modalities. Research, nonhuman and visible light images (such as dermatologic, histopathologic, or endoscopic images) are out of scope, though many of the same principles are applicable.

Increasingly, medical imaging and patient information are being managed using digital data during acquisition, transmission, storage, display, interpretation, and consultation. The management of these data during each of these operations may have an impact on the quality of patient care.

This technical standard is applicable to any system of digital image data management, from a single-modality or single-use system to a complete picture archiving and communication system (PACS) to the electronic transmission of patient medical images from one location to another for the purposes of interpretation and/or consultation.

It defines goals, qualifications of personnel, equipment guidelines, specifications of data manipulation and management, and quality control and quality improvement procedures for the use of digital image data that should result in high-quality radiological care. A glossary of commonly used terminology (Appendix A) and a reference list are included.

In all cases for which an ACR practice guideline or technical standard exists for the modality being used or the specific examination being performed, that practice guideline or technical standard will continue to apply when digital image data management systems are used.

Digital mammography is outside the scope of this document. For further information, see the ACR–AAPM–SIIM Practice Guideline for Determinants of Image Quality in Digital Mammography.

The goals of the electronic practice of medical imaging include, but are not limited to:
  1. 1.

    Initial acquisition or generation and recording of accurately labeled and identified image data.

     
  2. 2.

    Transmission of data to an appropriate storage medium from which it can be retrieved for display for formal interpretation, review, and consultation.

     
  3. 3.

    Retrieval of data from available prior imaging studies to be displayed for comparison with a current study.

     
  4. 4.

    Transmission of data to remote sites for consultation, review, or formal interpretation.

     
  5. 5.

    Appropriate compression of image data to facilitate transmission or storage, without loss of clinically significant information.

     
  6. 6.
    Archiving of data to maintain accurate patient medical records in a form that:
    1. (a)

      May be retrieved in a timely fashion

       
    2. (b)

      Meets applicable facility, state, and federal regulations

       
    3. (c)

      Maintains patient confidentiality

       
     
  7. 7.

    Promoting efficiency and quality improvement.

     
  8. 8.

    Providing interpreted images to referring providers.

     
  9. 9.

    Supporting telemedicine by making medical image consultations available in medical facilities without on-site medical imaging support.

     
  10. 10.

    Providing supervision of off-site imaging studies.

     
  11. 11.
    Providing timely availability of medical images, image consultation, and image interpretation by:
    1. (a)

      Facilitating medical image interpretations in on-call situations

       
    2. (b)

      Providing subspecialty support as needed.

       
     
  12. 12.

    Enhancing educational opportunities for practicing radiologists.

     
  13. 13.

    Minimizing the occurrence of poor image quality.

     

Appropriate database management procedures applicable to all of the above should be in place.

Qualifications and Responsibilities of Personnel

Qualified personnel trained in the examination to be performed must perform the imaging examination at the transmitting site. In all cases this means a physician, a licensed and/or registered radiologic technologist, a radiation therapist, a nuclear medicine technologist, or a sonographer. The technologist, radiation therapist, or sonographer must be under the supervision of a qualified licensed physician. It is desirable to have a qualified medical physicist and an imaging informatics professional as a consultant.

Physician

  1. 1.

    Physicians using the image data management system for official interpretation1 should understand the basic technology of image acquisition, transmission, manipulation, retrieval, and display, including the strengths, weaknesses, and limitations in the use of the image viewing equipment. Where appropriate, the interpreting physician must be familiar with the principles of radiation protection, the hazards of radiation exposure to both patients and radiological personnel, and patient and personnel monitoring requirements. The physician performing the official interpretation must be responsible for the quality of the images being reviewed and understand the elements of quality control of digital image management systems.2

     
  2. 2.

    The physician must demonstrate qualifications as delineated in the appropriate ACR practice guideline or technical standard for the particular diagnostic modality being interpreted.

     
  3. 3.

    The physician should have a working knowledge of those portions of the digital image chain from acquisition to display that affect image quality and potential artifact production.

     

Qualified Medical Physicist

A qualified medical physicist is an individual who is competent to practice independently one or more of the subfields in medical physics. The American College of Radiology considers certification, continuing education, and experience in the appropriate subfield(s) to demonstrate that an individual is competent to practice one or more of the subfields in medical physics and to be a qualified medical physicist. The ACR strongly recommends that the individual be certified in the appropriate subfield(s) by the American Board of Radiology, the Canadian College of Physics in Medicine, or by the American Board of Medical Physics.

The appropriate subfields of medical physics for this standard are therapeutic medical physics, diagnostic medical physics, and nuclear medical physics. (Previous medical physics certification categories including radiological physics, therapeutic radiological physics, medical nuclear physics, diagnostic radiological physics, and diagnostic imaging physics are also acceptable.)

A qualified medical physicist should meet the ACR Practice Guideline for Continuing Medical Education (ACR Resolution 17, 1996—revised in 2012, Resolution 42) and should include continuing education in radiation dosimetry, radiation protection, and equipment performance.

Registered Radiologist Assistant

A registered radiologist assistant is an advanced level radiographer who is certified and registered as a radiologist assistant by the American Registry of Radiologic Technologists after having successfully completed an advanced academic program encompassing an ACR/American Society of Radiologic Technologists (ASRT) radiologist assistant curriculum and a radiologist-directed clinical preceptorship. Under radiologist supervision, the radiologist assistant may perform patient assessment, patient management, and selected examinations as delineated in the Joint Policy Statement of the ACR and the ASRT titled “Radiologist Assistant: Roles and Responsibilities” and as allowed by state law. The radiologist assistant transmits to the supervising radiologists those observations that have a bearing on diagnosis. Performance of diagnostic interpretations remains outside the scope of practice of the radiologist assistant (ACR Resolution 34, adopted in 2006).

Radiologic Technologist

The technologist must:
  1. 1.

    Be certified by the appropriate registry and/or possess unrestricted state licensure.

     
  2. 2.

    Meet the qualification requirements of any existing ACR practice guideline or technical standard for acquisition of a particular examination.

     
  3. 3.
    Be trained to properly operate those portions of the image data management system with which he or she must routinely interact. This training should include as appropriate:
    1. (a)

      Image acquisition technology

       
    2. (b)

      Image processing protocols

       
    3. (c)

      Proper selection of examination specific options

       
    4. (d)

      Image evaluation

       
    5. (e)

      Radiation dose indicators

       
     

Imaging Informatics Professional

The imaging informatics professional should be qualified to assess problems and provide input to solutions, to initiate repairs, and to coordinate system-wide maintenance programs that will assure sustainable high image quality and system functioning. The responsibilities and experience of an imaging informatics professional include:

Maintenance of the network for all informatics systems, e.g., radiology information system, PACS, speech recognition systems, computer servers, and desktops.
  1. 1.

    Maintenance of the integrity of system databases to ensure continuous and accurate operation of the informatics systems.

     
  2. 2.

    Coordination of the interaction/functionality of all data entry and management systems with the necessary radiology applications, programs and databases.

     
  3. 3.

    Knowledge of computer systems using common operating systems (Windows, Unix/Linux, Mac), data communications standards and equipment, network protocols, database management, internet protocols, and systems analysis methods and design.

     

A qualified imaging informatics professional is an individual who is competent to practice independently in the areas of informatics listed above and discussed in the section on informatics workflow. He or she should have a minimum of a bachelor’s degree in computer science or equivalent, and continuing education and experience in imaging informatics to demonstrate that an individual is competent to practice as an Imaging Informatics Professional. Certification through the American Board of Imaging Informatics can be used as validation of an individual’s qualification as a qualified imaging informatics professional.

Equipment Specifications

Specifications for equipment used in digital image data management will vary depending on the application and the individual facility’s needs; but in all cases, it should provide image quality and availability appropriate to the clinical needs whether that need be official interpretation or secondary review.

Compliance with the Digital Imaging and Communications in Medicine (DICOM) standard, the Integrating the Healthcare Enterprise (IHE) Radiology Technical Framework, and where applicable the IHE-Radiation Oncology Technical Framework (IHE-RO) is strongly recommended for all new equipment acquisitions, and consideration of periodic upgrades incorporating the expanding features of that standard should be part of the ongoing quality control program.

Acquisition or Digitization

Initial image acquisition should be performed in accordance with the appropriate ACR modality or examination practice guideline or technical standard.
  1. 1.

    Direct image capture

    The image dataset acquired by the digital modality in the full spatial resolution (image matrix size) and pixel bit depth should be transferred to the image management system. It is recommended that the DICOM standard be used.

     
  2. 2.

    Scanned radiographic films

    Films from prior patient studies may be digitized using modern film scanning systems. When used, the pixel pitch of the scanner should be small enough to capture the limiting resolution of the film. For general purpose radiographic films, a pitch of less than 200 μm (2.5 cycles/mm limiting resolution) should be used. For high-resolution film or mammography, a pitch of less than 100 μm (5.0 cycles/mm limiting resolution) should be used. The scanner should be capable of recording film optical densities up to at least 3.2 for general purpose radiographs and 4.0 for high-resolution radiographs and mammograms. The digitization should have at least 12 bits of precision (0–4,095) and produce either DICOM presentation values or values proportional to film density. In general, photographic cameras should not be used to digitize films because of inherent distortion and optical artifacts.

     
  3. 3.

    Video digitizer acquisitions

    Traditional fluoroscopy systems have used video recording cameras to acquire images from the output phosphor of an image intensifier. Recordings may be of individual spot exposures, pulsed fluoroscopic sequences, or continuous fluoroscopic frames. Analog video cameras produce a time-varying voltage signal corresponding to a raster scan of the image. Analog to digital conversion systems are used to convert these signals to digital images formatted according to the DICOM standard. These systems are susceptible to degraded quality due to analog signal noise, timing, and drift. When used, the image quality should be closely monitored. In general, the use of digital recording cameras with image intensifiers or direct digital fluoroscopy panels is preferred.

     
  4. 4.
    General requirements
    1. (a)

      At the time of patient imaging, the imaging modality must have capabilities for capturing demographic as well as imaging information such as accession number, patient name, identification number, date and time of examination, name of facility or institution, type of examination, patient or anatomic part orientation (e.g., right, left, superior, inferior), amount and method of data compression, and total number of images acquired in the study. (In some cases, the total number of images may not be known if the modality sends images as they are acquired.) This information must be associated with the images when transmitted with a modality-specific information object descriptor. These fields should be formatted according to the DICOM standard. It is desirable to obtain this information using the DICOM modality work list services that communicate the correct information electronically.

       
    2. (b)

      The ability to capture the patient date of birth, sex, indications for the examination, and a brief patient history is desirable.

       
     

Compression

Compression may be defined as mathematically reversible (lossless) or irreversible (lossy). Reversible compression may always be used, since by definition there is no impact on the image. Irreversible compression may be used to reduce transmission time or storage space only if the quality of the result is sufficient to reliably perform the clinical task. The type of body part, the modality, and the objective of the study will determine the amount of compression that can be tolerated.

The term diagnostically acceptable irreversible compression (DAIC) refers to mathematically irreversible compression that does not affect a particular diagnostic task [1]. DAIC may be used under the direction of a qualified physician with no reduction in clinical diagnostic performance by either the primary image interpreter or decision makers reviewing the images.

The ACR and this technical standard make no general statement on the type or amount of compression that is appropriate to any particular modality, disease, or clinical application to achieve the diagnostically acceptable goal. The scientific literature and other national guidelines may assist the responsible physician in choosing appropriate types and amounts of compression, weighing the risk of degraded performance against the benefits of reduced storage space or transmission time. The type and amount of compression applied to different imaging studies transmitted and stored by the system should be initially selected and periodically reviewed by the responsible physician to ensure appropriate clinical image quality, always considering that it may be difficult to evaluate the impact on observer performance objectively and reliably [2].

If reversible or irreversible compression is used, only algorithms defined by the DICOM standard such as Joint Photographic Experts Group (JPEG), JPEG-LS, JPEG-2000, or MPEG should be used, since images encoded with proprietary and nonstandard compression schemes reduce interoperability, and decompression followed by recompression with a different irreversible scheme (such as during migration of data) will result in significant image quality degradation [1]. The DICOM standard does not recommend or approve any particular compression scheme for any particular modality, image type, or clinical application.

The US Food and Drug Administration (FDA) requires that when an image is displayed, it be labeled with a message stating if irreversible compression has been applied and with approximately what compression ratio [3]. In addition, the name or type of compression scheme used (for standard schemes such as JPEG, JPEG 2000, etc.) should also be displayed, since this affects the interpretation of the impact of the compression. The DICOM standard defines specific fields for the encoding of this information, and its persistence even after the image has been decompressed.

The FDA does not allow irreversible compression of digital mammograms for retention, transmission, or final interpretation, though irreversibly compressed images may be used for images from prior studies [4]. For other modalities, the FDA does not restrict the use of compression, but it does require manufacturers of devices that use irreversible compression to submit data on the impact of the compression on quantitative metrics of image quality (such as peak signal-to-noise ratio) [3]. Since it is known that such simple metrics do not correlate well with human observer assessment of quality or performance for diagnostic tasks [5], the claim of the manufacturer that irreversible compression is satisfactory may not be sufficient and the burden remains on the responsible physician to assure that the image quality is sufficient to achieve a diagnostically acceptable goal.

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 no loss of clinically significant information. The transmission system should have a bandwidth commensurate with expected volumes in the ability to deliver images in a timely fashion. The transmission system must have adequate error-checking capability. Only the appropriate modality-specific DICOM service-object pair classes should be used for transmission and storage.

Display

The consistent presentation of images on workstations is essential for electronic imaging operations. Images seen by technologists during acquisition, by radiologists during interpretation, and by physicians as a part of patient care should have similar appearance. The spatial and contrast resolution of images displayed for interpretation is particularly important. The presentation of images is influenced by workstation software, graphic controllers, and display devices.
  1. 1.
    Workstation characteristics
    1. (a)

      Graphic bit depth: The operating systems of most workstations manage images with red, green, and blue channels having 8 bits (256 values). The number of available gray levels where the red, green, and blue values are equal is thus 256. Systems with increased bit depth such as 30 bit graphics with 10 bits per channel require support from the operating system, workstation software, graphic card, and monitor. While subtle differences between 8- and 10-bit systems can be demonstrated using test patterns, no evidence has been found to date that diagnostic interpretations are affected by the use of higher than 8-bit systems.

       
    2. (b)

      Liquid crystal display (LCD) technology: Nearly all workstation displays now use LCD panels. Their discrete pixels offer excellent resolution without distortion. The flat panel surfaces are able to absorb ambient light to minimize reflections and glare. However, lower cost units using twisted nematic (TN) pixel structures severely alter image brightness, contrast, and color in relation to viewing angle. TN devices should not be used. Several advanced pixel structures are now available to provide improved viewing angle performance (vertical alignment, in-plane switching, and dual domain structures). The viewing angle characteristics of any LCD device should be evaluated using contrast transfer test patterns prior to purchase.

       
    3. (c)

      Graphic interface: LCD devices are inherently digital with an internal buffer storing the data for each pixel in the rows and columns of the device. The interface between the graphic controller and the LCD device should transfer the image data using a digital format such as DVI-D (either single-link or dual-link) or display port. For optimal resolution, the graphic controller device driver should always be set to the native rows and columns of the LCD device. An analog video interface signal such as VGA or DVI-A is not recommended since the digital to analog conversion in the graphic controller and the analog to digital conversion in the LCD device can introduce image degradation.

       
    4. (d)

      Image presentation size: The rows and columns of the displayed image are typically different than the rows and columns of the acquired image. The application software working in conjunction with the graphic controller interpolates from the acquired image data to get the displayed image data.

      For optimal image resolution, the interpolation of each displayed pixel, whether up- or down-sampling, should consider more than the closest four acquired pixel values. Cubic spline and cubic polynomial interpolation algorithms are commonly used for high quality interpolation with the graphic controller providing acceleration so that images are presented with negligible delay. When down-sampling noisy images, the extended region considered in the interpolation also helps reduce noise in the presentation.

       
    5. (e)
      Presentation support features: The application software used to select and present images studies should provide features to allow rapid and easy review or interpretation of a study.
      • 1. Hanging protocols that address the selection of image series and display format should be flexible and tailored to user preferences with proper labeling and orientation of images.

      • 2. Fast and easy navigation between new and old studies should be feasible.

      • 3. Accurately associating the patient and study demographic information with the images of the study performed is essential.

      • 4. Window and level adjustment tools must be available since the full dynamic range of most images cannot be displayed on most digital devices. Preset window/level settings (e.g., bone or lung windows using set lookup table (LUT) transformations) are recommended to increase the speed of user interaction with the display device.

      • 5. Zoom (magnification) and pan functions capable of meeting guidelines for display at the originally acquired spatial resolutions (i.e., direct presentation of acquired pixels on the display pixels) are essential so that the display monitor does not limit the intrinsic spatial resolution of the image. For some applications, the ability to present an image with anatomic structure having true size relative to the acquisition is important.

      • 6. Rotating or flipping the images must preserve the correct patient orientation labels.

      • 7. Calculating and displaying accurate linear measurements and pixel value determinations in values appropriate for the modality (e.g., Hounsfield units for CT images) are necessary, if those data are available and can be calibrated to the acquisition device.

      • 8. Prior application of irreversible compression ratio, processing, or cropping on the image and/or overlay should be indicated.

      • 9. Clinically relevant technical parameters should be accessible with overlay information on the display or with capabilities to view the DICOM header content.

       
    6. (f)
      Ergonomic factors
      • 1. Adequate air flow, optimal temperature, and humidity control should be maintained in reading areas.

      • 2. Viewing conditions should be optimized to minimize eye fatigue by controlling reading room lighting to eliminate reflections on the monitor and lowering the ambient lighting level as much as is feasible without turning the lighting off completely (20–40 lx is recommended in the work space environment) [5]. Brighter ambient lighting may be tolerable or even desirable so long as conformance with AAPM Task Group 18 specifications is maintained. [6].

      • 3. Noise from computer equipment and other devices should be minimized.

      • 4. Proper chairs with lumbar support and adjustable height controls (including armrests) are recommended to avoid injuries and excessive fatigue.

      • 5. The workstation table should be height adjustable, and the keyboard, mouse, and monitors should be designed to maximize comfort and efficiency. The display devices should be placed to maintain the viewers at an arm’s length from the display (i.e., about 2/3 m or 60 cm).

      • 6. Dictation tools, internet access, and other reference tools should be readily accessible and easy to use during image interpretation.

      • 7. Guidelines on the maximum number of acceptable pixel defects is specified by ISO 9241 as a function of display class [7]. Documentation of allowed pixel defects should be provided by the display manufacturer. Displays should be evaluated for significant pixel defects initially and periodically (at least annually is recommended).

       
     
  2. 2.
    Display characteristics
    1. (a)

      Luminance response

      The brightness and contrast of grayscale medical images result from the luminance in relation to the image gray level values [8].
      • 1. Ambient luminance (Lamb): When the power to the display device is off, the display surface will still show some brightness due to diffusely reflected room lighting. This is called the ambient luminance. The ambient luminance should be less than one fourth of the luminance of the darkest gray level.

      • 2. Minimum luminance (Lmin): Since the contrast response of the adapted human visual system is poor in very dark regions, the luminance of the lowest gray value, Lmin, should not be extremely low. The minimum luminance including a component from ambient lighting, Lmin = Lmin + Lamb, should be at least 1.0 cd/m2 for diagnostic interpretation and 0.8 cd/m2 for other uses.

      • 3. Maximum luminance (Lmax): The perceived contrast characteristics of an image depend on the ratio of the luminance for the maximum gray value (Lmax) to Lmin. This is the luminance ratio (LR), which is not the same as the contrast ratio often reported by monitor manufacturers. Ideally, all display devices in a facility should have the same LR so that the presentation is consistent for all viewers of a study.

      • 4. The LR must be large for good image contrast; however, an excessively large LR will exceed the range of the adapted human visual system. A LR of 350, which is equivalent to a film OD range from 0.20 to 2.75, is effective. For acceptable contrast, LR should always be greater than 250.

      • 5. The Lmax of diagnostic monitors used for interpretation should be at least 350 cd/m2 with an Lmin of 1.0 cd/m2. For the interpretation of mammograms, Lmax should be at least 420 cd/m2 with an Lmin of 1.2 cd/m2. The monitors used for other purposes should have an Lmax of at least 250 cd/m2 with an Lmin of 0.8 cd/m2. For brighter monitors, Lmin, should be proportionately larger to maintain the same LR.

      • 6. Luminance versus gray level: In addition to having similar LR, the luminance of intermediate gray values between Lmin and Lmax should follow the same response function for all monitors in a facility. It is recommended that the DICOM grayscale display function (GSDF) be used to set the intermediate gray values.

      • 7. Calibration: The luminance response, LR and GSDF, of some medical and professional graphics monitors can be selected using the monitor on screen display controls. Other medical/professional devices require software from the monitor manufacturer to load LUTs to the monitor that set the luminance of each gray level. For business class monitors used by technologists and clinical care staff, the calibration can be achieved by loading a LUT to the driver of the graphic control card.

      • 8. Quality control: All display devices should be periodically checked to verify that the luminance response is correct. Basic verification can be done using a visual test pattern designed for evaluating contrast response. Advanced tests, done on an annual or quarterly basis, measure the luminance in relation to gray value and evaluate the contrast. The contrast response of monitors used for diagnostic interpretation should be within 10 % of the GSDF over the full LR. For other uses, the contrast response should be within 20 % of the GSDF over the full LR.

      • 9. White point: The color characteristics of a display with respect to the presented color space are not considered in this technical standard. However, the white point associated with presentation of grayscale images is important for medical imaging systems. It is recommended that monitors be set to a white point corresponding to the CIE daylight standard D65 white point. This corresponds to a color temperature of about 6,500 °F.

       
    2. b.

      Pixel pitch and display size

      The spacing of pixel structures, referred to as the pixel pitch, determines how much detail can be presented. The size of the active display region, in combination with pixel pitch, determines the number of pixels in the display device. While it has been common to classify monitors based on the number of pixels (i.e., 1, 2, 3, or 5 megapixel), it is recommended that the pixel pitch and display size be used when considering the capabilities of a particular device.
      • 1. Pixel pitch: The pixel pitch of a monitor determines the maximum spatial frequency that can be presented in an image. Using the sampling theorem, the maximum spatial frequency that can be described by digital signals with a constant pitch, P in millimeter, is 1/(2P) cycles/mm. It is desirable to have the pixel pitch sufficiently small so as to present all of the spatial frequencies that the human visual system can perceive. At an arm’s length viewing distance (2/3 m, 60 cm), the eye can perceive displayed spatial frequencies up to a maximum of 2.5 cycles/mm.

        For monitors used in diagnostic interpretation, it is recommended that the pixel pitch be about 0.200 mm and not larger than 0.210 mm. For this pixel pitch, individual pixels and their substructure are not visible and images have continuous tone appearance. No advantage is derived from using a smaller pixel pitch since higher spatial frequencies are not perceived.

        For the presentation of images with acquired detector element size different from the pixel pitch, zoom and pan display features should be used rather than moving closer to a display. Since the human visual system has maximum contrast sensitivity at about 0.5 cycles/mm, image zoom with interpolation can often reveal subtle detail not seen at true size.

        Monitors used by technologists and clinical care staff are often not viewed at a desk, and the viewing distance is larger than for diagnostic interpretation. For these monitors, a pixel pitch of 0.250 mm (not larger than 0.300 mm) is appropriate.

      • 2. Display size: When interpreting images, the attention of the viewer is not limited to the center of the display but extends to the edges as well via peripheral vision. Good visualization of the full scene is achieved when the diagonal display distance is about 80 % of the viewing distance. At 2/3 m, this corresponds to a diagonal size of 53 cm (21 in.). Monitors with a pixel array size of 1,500 × 2,000 and a pixel pitch of 0.210 will have a diagonal size of 52.5 cm.

        An aspect ratio, width to height, of 3:4 or 4:5 is well suited for the presentation of radiographic images. Such a portrait presentation requires image rotation from the graphic controller. However, the displays currently being manufactured typically have a wide format, 16:9 or 16:10. These can be used similar to a dual monitor workstation if the application software can present images in two regions with 8:9 or 8:10 aspect ratio.

       
     

Archiving, Retention, and Retrieval

  1. 1.

    Digital imaging data management systems must provide storage capacity capable of complying with all facility, state, and federal regulations regarding medical record retention. Images stored by either a transmitting or receiving site should meet the jurisdictional requirements of both the transmitting and receiving site. Images interpreted off site need not be stored at the receiving facility provided they are stored at the transmitting site or its designee. 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 should be in writing.

     
  2. 2.

    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.

     
  3. 3.

    Current and prior examinations must be retrievable in a time frame appropriate to the clinical needs of the facility and medical staff.

     
  4. 4.

    Each facility should have policies and procedures for archiving and storage of digital image data equivalent to the policies that exist for the protection of hardcopy storage media to preserve imaging records.

     
  5. 5.

    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 continuity of care at a level consistent with those for hard-copy imaging studies and medical records within a facility or institution. They should include internal redundancy systems, backup telecommunication links, disaster recovery, and business continuity plan.

     

Image Sharing

  1. 1.

    Each facility should have a mechanism for image sharing on physical media, including CD, DVD, and USB media, and should be able to export and import data compliant with the IHE Portable Data for Imaging (PDI) profile [9, 10]. PDI requires that DICOM images be recorded in a standard manner, and also permits additional “web content,” such as in the form of prerendered JPEG images. Even if a facility has a means of sharing images over a network, standard physical media is required for those recipients not able to use the network. Physical media containing proprietary formatted images should not be used. Physical media may contain an executable viewer. If present, an embedded viewer should be capable of displaying the standard DICOM PDI images, and not depend on the presence of proprietary formats [9]. Each facility should comply with the recommendation of the American Medical Association Expert Panel on Medical Imaging, which put forward the following statement that embodies the standard the medical imaging community must achieve: “All medical imaging data distributed should be a complete set of images of diagnostic quality in compliance with IHE-PDI.” The panel further stated that “this standard will engender safe, timely, appropriate, effective, and efficient care; mitigate delayed care and confusion; enhance care coordination and communication across settings of care; decrease waste and costs; and, importantly, improve patient and physician satisfaction with the medical imaging process.” The statement was signed by the American Medical Association, the American Association of Neurological Surgeons, the Congress of Neurological Surgeons, the American Academy of Neurology, the American College of Radiology, the American Academy of Orthopedic Surgeons, and the American College of Cardiology.

     
  2. 2.

    Each facility should have a mechanism for secure image sharing over the Internet. The network exchange of imaging information should be conducted in accordance with the IHE Cross Document Sharing (XDS.b) profile (and XDS-I.b for imaging objects) [10]. Depending on the needs of the recipient, the images exchanged may be of original diagnostic quality, in which case DICOM PS 3.10 images are required, or may be prewindowed and prerendered. Every facility should have a mechanism for providing both a full set of diagnostic quality DICOM images and a subset of prerendered images of the appropriate quality for this purpose, consistent with the AMA’s recommendations for the analogous exchange on physical media.

     
  3. 3.

    Each facility should have a mechanism for importing images and associated information in standard DICOM form from physical media and from the Internet, with reconciliation of foreign identifiers, accession numbers and procedure descriptions or codes, such that they do not collide with local identifiers. Each facility should make it possible to display such foreign images with the same fidelity and side by side in the same user interface as locally acquired images. This allows for better patient care and fewer unnecessarily repeated studies (hence avoiding the cost, inconvenience, and safety risk from contrast and radiation of repeating a study). The importation should be performed in accordance with the IHE Import Reconciliation Workflow profile.

     

Security, Privacy, Reliability, and Redundancy

See the ACR–SIIM Practice Guideline for Electronic Medical Information Privacy and Security.

Informatics Infrastructures and Workflow Processes

Electronic practice of diagnostic radiology involves a number of processes that should be coordinated by systems using the DICOM, HL7, IHE, and IHE-RO informatics standards to ensure that information associated with the imaging study and patient record is accurate, that errors are minimized, and that the processes are efficient. These include:
  • Patient demographic data should be obtained on admission (registration), rather than repeatedly reentered at each step of the workflow.

  • The appropriate modality and modality-specific imaging protocol should be selected during scheduling.

  • The demographic and scheduling information should be communicated electronically to the modality in a standard form.

  • Complete and consistent demographic data should be transferred across all systems.

  • Relevant data about the acquisition should be included in the electronic radiology report (preferably in an automated and structured manner).

  • Relevant data about the acquisition should be made available for correct coding of the examination for billing, tracking and quality control.

  • Relevant observations by the technical staff and interpreting radiologist should be retained and distributed in a standard form.

The DICOM and HL7 [11, 12] standards provide the building blocks for such an infrastructure, and the IHE Radiology Technical Framework [9] defines profiles for using those standards to implement the required processes.

Some of the processes associated with diagnostic radiology workflow and the standards that should be used are given below.
  1. 1.

    Ordering and scheduling of procedures, performance of the acquisition, and transfer of images and associated information to the PACS should be in compliance with the IHE Scheduled Workflow (SWF) profile. This profile establishes the continuity and integrity of basic departmental imaging data, specifies transactions that maintain the consistency of patient and ordering information, provides the scheduling and imaging acquisition procedures steps, and makes it possible to determine whether images and other evidence objects associated with a particular performed procedure step have been stored (archived) and are available to enable subsequent workflow steps, such as reporting. The SWF profile may also provide central coordination of the completion of processing and reporting steps as well as notification of appointments to the placer of the order.

     
  2. 2.

    Correction of incorrect identification used during acquisition should be performed in compliance with the IHE Patient Information Reconciliation (PIR) profile. PIR extends the SWF profile by providing the means to match with the patient’s record, images, diagnostic reports, and other evidence objects acquired for a misidentified or unidentified patient (for example, during a trauma case).

     
  3. 3.

    In selecting a procedure, the ordering physician should be assisted by an appropriateness criteria or decision support system.

     
  4. 4.
    Standard terminology and codes for ordering should be used, including:
    1. (a)

      Systematized Nomenclature of Medicine—Clinical Terms (see http://www.ihtsdo.org/snomed-ct).

       
    2. (b)

      RadLex—Lexicon for Uniform Indexing and Retrieval of Radiology Information Resources (see http://www.radlex.org).

       
    3. (c)

      Logical Observation Identifiers Names and Codes

       
     
  5. 5.

    Each facility should use a standard set of predefined image acquisition protocols. Many image acquisition systems (e.g., CT, MRI, NM) have complex protocols that need to be defined by the radiologist prior to the acquisition. The appropriate protocol needs to take into consideration the order information (e.g., history, patient type), modality capabilities, and the technologist knowledge of the equipment/protocol. By requiring the definition of the appropriate protocol prior to the acquisition, the examination can be optimized to use the lowest radiation dose sufficient to achieve the necessary image quality and the parameters matched to the equipment and clinical needs of the patient. Evolving standards are being defined by professional organizations to optimize the use of radiation dose for a particular indication, for example in CT scanning [13]. Using standard codes, such as those defined by the RadLex PlayBook [14], the choice of protocol should be communicated to the acquisition modality using the IHE Assisted Protocol Setting option to the SWF profile [9].

     
  6. 6.

    Each facility should store annotations made by staff on images in a standard form as defined by DICOM in presentation states, structured reports or structure sets. The IHE Consistent Presentation of Images profile specifies the use of DICOM presentation states. It also requires that displays be calibrated according to the DICOM GSDF for the purpose of approaching consistency of perceived grayscale contrast on different displays and in different viewing environments (see also “Equipment Specifications” section). The IHE Simple Image and Numeric Report specifies the use of the DICOM Structured Report to store a simple structure consisting of a title, an observation context, and one or more sections, each with a heading, observation context, text, image references, and coded measurements. Its use facilitates searches and serves as the input to the formal diagnostic report, thus avoiding re-entry of information.

     

Documentation

Physicians officially interpreting examinations3 using digital image data management systems should render reports in accordance with the ACR Practice Guideline for Communication of Diagnostic Imaging Findings.

If reports are incorporated into the data management system, they should be retrievable with the same conditions of timeliness and security as those for the imaging data.

Licensing, Credentialing, and Liability

The interpreting physician is responsible for the quality of the images being reviewed.4 Physicians who provide the official interpretation of images transmitted by teleradiology should be familiar with the licensure requirements for providing radiologic or telemedicine service at both the transmitting and receiving sites and obtain licensure as appropriate. Physicians practicing teleradiology should conduct their practice in a manner consistent with the bylaws, rules, and regulations for patient care at the transmitting and receiving site jurisdictions. Regulations should not restrict the ability of radiologists to provide second opinion consultations when requested in a jurisdiction where the consulting radiologist is not licensed. When interpreting images from a hospital, physicians should be credentialed and obtain appropriate privileges at that institution. Physicians providing domestic and international teleradiology services should consult with their professional liability carrier to ensure coverage in both the sending and receiving sites (state or jurisdiction). The malpractice insurance coverage and claims jurisdiction should be determined by those contracting to receive teleradiology services. Some states may require specific patient consent for telemedicine consultation. Disclosing the use of international telemedicine to the patient and referring physician should be considered if patient confidentiality is not assured by the international provider. Physicians providing emergency interpretations should be immediately available for consultation. For non-emergent interpretations, the physician should be available for consultation or have a method to communicate and authenticate his or her findings.

Images stored at either site should meet the jurisdictional requirements of the transmitting site. Images interpreted off site need not be stored at the receiving facility, provided they are stored at the transmitting site. However, if images are retained at the receiving site, the retention period of that jurisdiction should be met as well. The policy on record retention should be in writing.

Radiation Safety in Imaging

Radiologists, medical physicists, radiologic technologists, and all supervising physicians have a responsibility to minimize radiation dose to individual patients, to staff, and to society as a whole, while maintaining the necessary diagnostic image quality. This concept is known as “as low as reasonably achievable (ALARA).”

Facilities, in consultation with the medical physicist, should have in place and should adhere to policies and procedures, in accordance with ALARA, to vary examination protocols to take into account patient body habitus, such as height and/or weight, body mass index or lateral width. The dose reduction devices that are available on imaging equipment should be active; if not; manual techniques should be used to moderate the exposure while maintaining the necessary diagnostic image quality. Periodically, radiation exposures should be measured and patient radiation doses estimated by a medical physicist in accordance with the appropriate ACR Technical Standard. (ACR Resolution 17, adopted in 2006—revised in 2009, Resolution 11)

Exposures to patients from digital X-ray equipment (including projection radiography, fluoroscopy, angiography, and CT) should be recorded digitally by the modality in a standard form (such as the DICOM Radiation Dose Structured Report [RDSR]) and transmitted and monitored using the IHE Radiation Exposure Monitoring (REM) profile. Facilities should also contribute deidentified digital records of patient radiation exposure to the appropriate dose index registry (such as the ACR’s Dose Index Registry component of the National Radiology Data Registry), for the purpose of establishing, maintaining, and comparing facility performance against national Diagnostic Reference Levels. Facilities that have legacy technology not supporting standards such as DICOM RDSR and IHE REM should employ tools using techniques such as Optical Character Recognition to extract the numeric exposure information from modality manufacturer’s dose screens, or other mechanisms, where possible.

Quality Control and Improvement, Safety, Infection Control, and Patient Education

Policies and procedures related to quality, patient education, infection control, and safety should be developed and implemented in accordance with the ACR Policy on Quality Control and Improvement, Safety, Infection Control, and Patient Education appearing under the heading Position Statement on QC & Improvement, Safety, Infection Control, and Patient Education on the ACR web site (http://www.acr.org/guidelines).

Any facility using a digital image data management system must have documented policies and procedures for monitoring and evaluating the effective management, safety, and proper performance of acquisition, digitization, processing, compression, transmission, display, archiving, and retrieval functions of the system. The quality control program should be designed to maximize the quality and accessibility of diagnostic information.
  1. 1.

    Performance testing and monitoring of official or primary interpretation display devices should be performed in accordance with any relevant ACR modality accreditation program quality control manual recommendations, 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 AAPM Task Group 18: Assessment of Display Performance for Medical Imaging Systems [15] should be followed.

     
  2. 2.

    As a minimum quality check for acquisition workstation and secondary display devices, a test image such as the AAPM TG18-QC test pattern should be captured, transmitted, archived, retrieved, and displayed at appropriate intervals to test the overall operation of the system under conditions that simulate its normal operation. As a spatial resolution test, at least 2.5 lp/mm, resolutions should be confirmed for official interpretation. As a test of the display fidelity, TG18-QC pattern data files sized to occupy the full area used to display images on the monitor should be displayed. The overall SMPTE image appearance should be inspected to assure the absence of gross artifacts (e.g., 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.

     
  3. 3.

    Hardcopy imager accuracy and stability testing should also be performed and documented.

     
  4. 4.

    The view box luminance should be sufficient to meet the diagnostic needs of the imaging procedure and applicable industry standards and/or recommendations should be followed when available.

     

The use of digital imaging and digital image data management systems does not reduce the responsibilities for managing and supervising radiologic examinations. Locations and physicians providing remote imaging services should participate in a documented ongoing quality assurance program at least equivalent to that of the originating facility. Summaries of the quality control monitoring should be provided to the originating facility

Footnotes

  1. 1.

    The ACR Medical Legal Committee defines official interpretation as that written report (and any supplements or amendments thereto) that attach to the patient’s permanent record. In healthcare facilities with a privilege delineation system, such a written report is prepared only by a qualified physician who has been granted specific delineated clinical privileges for that purpose by the facility’s governing body upon the recommendation of the medical staff.

  2. 2.

    The ACR Rules of Ethics state: “It is proper for a diagnostic radiologist to provide a consultative opinion on radiographs and other images regardless of their origin. A diagnostic radiologist should regularly interpret radiographs and other images only when the radiologist reasonably participates in the quality of medical imaging, utilization review, and matters of policy which affect the quality of patient care.”

  3. 3.

    The ACR Medical Legal Committee defines official interpretation as that written report (and any supplements or amendments thereto) that attach to the patient’s permanent record. In health care facilities with a privilege delineation system, such a written report is prepared only by a qualified physician who has been granted specific delineated clinical privileges for that purpose by the facility’s governing body upon the recommendation of the medical staff.

  4. 4.

    The ACR Rules of Ethics state: “it is proper for a diagnostic radiologist to provide a consultative opinion on radiographs and other images regardless of their origin. A diagnostic radiologist should regularly interpret radiographs and other images only when the radiologist reasonably participates in the quality of medical imaging, utilization review, and matters of policy which affect the quality of patient care.”

Notes

Acknowledgments

This guideline was revised according to the process described under the heading The Process for Developing ACR Practice Guidelines and Technical Standards on the ACR web site (http://www.acr.org/guidelines) by the Guidelines and Standards Committee of the Commission on Medical Physics in collaboration with the AAPM and the SIIM.

Collaborative Committee—members represent their societies in the initial and final revision of this guideline

ACR

James T. Norweck, MS, Co-Chair

David A. Clunie, MB, BS

Ralph P. Lieto, MS

AAPM

Bruce H. Curran, MS, ME

Michael J. Flynn, PhD

Donald J. Peck, PhD

SIIM

J. Anthony Seibert, PhD, FACR, Co-Chair

Katherine P. Andriole, PhD

Elizabeth Krupinski, PhD

ACR Guidelines and Standards Committee—Medical Physics—ACR Committee responsible for sponsoring the draft through the process.

Tariq A. Mian, PhD, FACR, Chair

Maxwell R. Amurao, PhD, MS

Chee-Wai Cheng, PhD

Laurence E. Court, PhD

Richard A. Geise, PhD, FACR

Nicholas J. Hangiandreou, PhD

Bruce E. Hasselquist, PhD

Ralph P. Lieto, MS

Jeffrey P. Limmer, MSc

Janelle Lira Park, MD

Doug Pfeiffer, MS

Christopher J. Watchman, PhD

Gerald A. White, Jr., MS, FACR

John W. Winston, MS

James Hevezi, PhD, FACR, Chair, Commission

Comments Reconciliation Committee

Arun Krishnaraj, MD, MPH, CSC Co-Chair

Christopher G. Ullrich, MD, FACR, CSC Co-Chair

Katherine P. Andriole, PhD

Kimberly E. Applegate, MD, MS, FACR

David A. Clunie, MB, BS

Bruce H. Curran, MS, ME

Howard B. Fleishon, MD, MMM, FACR

Michael J. Flynn, PhD

James M. Hevezi, PhD, FACR

Elizabeth Krupinski, PhD

Paul A. Larson, MD, FACR

Ralph P. Lieto, MS

James T. Norweck, MS

Tariq A. Mian, PhD, FACR

Debra L. Monticciolo, MD, FACR

Donald J. Peck, PhD

J. Anthony Seibert, PhD, FACR

Julie K. Timins, MD, FACR

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Copyright information

© Society for Imaging Informatics in Medicine and American College of Radiology 2012

Authors and Affiliations

  • James T. Norweck
    • 1
  • J. Anthony Seibert
    • 2
  • Katherine P. Andriole
    • 3
  • David A. Clunie
    • 4
  • Bruce H. Curran
    • 5
  • Michael J. Flynn
    • 6
  • Elizabeth Krupinski
    • 7
  • Ralph P. Lieto
    • 8
  • Donald J. Peck
    • 9
  • Tariq A. Mian
    • 10
  • Margaret Wyatt
    • 12
  1. 1.Radiology Inc.HuntingtonUSA
  2. 2.Department of ImagingUniversity of California Davis health SystemSacramentoUSA
  3. 3.Department of Radiology, Brigham and Women’s HospitalHarvard Medical SchoolBostonUSA
  4. 4.Comview CorporationTarrytownUSA
  5. 5.Department of Radiation OncologyRhode Island HospitalProvidenceUSA
  6. 6.Department of RadiologyHenry Ford Health SystemsDetroitUSA
  7. 7.Department of Medical ImagingUniversity of ArizonaTucsonUSA
  8. 8.Radiation Safety OfficeSt. Joseph Mercy Health SystemAnn ArborUSA
  9. 9.Department of RadiologyHenry Ford Health SystemDetroitUSA
  10. 10.Medical Radiation Physics, IncScottsdaleUSA
  11. 11.DeLandUSA
  12. 12.Guidelines and Standards DevelopmentAmerican College of RadiologyRestonUSA

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