Recommendations on Standards for the Design of Medical Diagnostic Equipment for Adults with Disabilities, Advisory Committee Final Report

4. Perspectives of Equipment Types
4.3 Diagnostic Imaging Equipment

The diagnostic imaging equipment covered by this subcommittee had an extraordinary breadth and depth of its diversity of design, configurations, and principles of operation. This is the direct result of enormous variety of diagnostic tasks, clinical indications, and patient populations this equipment has been designed to serve both in a general manner as well as configurations that are highly optimized to provide optimized results for a particular clinical need.

The types of equipment covered and evaluated by the imaging subcommittee include:

• Computed Tomography (CT)

• Magnetic Resonance (MR)

• Nuclear Medicine (Scintigraphy & Single Photon Emission Computed Tomography) (NM)

• Positron Emission Tomography (PET)

• X-Ray Fluoroscopy

• X-Ray Radiography

• X-Ray Interventional

• X-Ray Mobiles

• X-Ray C-arms

• Dual-energy X-ray Absorptiometry (DXA)

• X-Ray Mammography Biopsy Tables

• PET/CT Combined Systems

• NM/CT Combined Systems

• PET/MR Combined System

These represent all virtually all diagnostic imaging systems except conventional Mammographic systems which were addressed by their own subcommittee and Ultrasound systems that due to their portability do not fall under the scope of these proposed standards.

This equipment consist mostly of large capital equipment, uses ionizing radiation (or a very strong magnetic field) to produce the images, has many years of service life, and represents significant investment to the facility. This equipment is also primarily permanently mounted in a fixed installation that special room siting design needs to be performed for. This special siting is the result of a variety of factors that include shielding of ionizing radiation or magnetic fields and specialized high power capacity electrical service. These systems do not have patient “operable parts” (i.e. the patient does not activate, deactivate, or adjust the equipment).

This equipment are all prescription use only devices, meaning that one must have a physician’s order before a person may receive an exam. The devices all must be operated by a trained and qualified technologist, who must be present during the exam to aid all patients onto the table, explain the exam process, and aid in properly positioning the patient.

This equipment represents US Food and Drug Administration (FDA) Class II medical devices that need pre-market notification to FDA (510(k) clearance) prior to being placed on the market. They must be design and manufactured under the Quality System Regulations for medical devices, 21CFR820, that includes design controls and good manufacturing practices. They must be tested and certified by an OSHA credentialed Nationally Recognized Testing Laboratory to demonstrate that they meet the basic safety and essential performance required by IEC60601-1 as well as the applicable IEC 60601-1 series of collateral and particular standards. The devices that produce X-rays must also be certified to FDA to meet the applicable performance standards for radiation safety found in 21CFRSubchapter J. The design process must conform include risk-management in accordance with ISO 14971. Radioactive Sources and Radiopharmaceuticals used for PET and NM are also regulated by the Nuclear Regulatory Commission.

A diagnostic imaging device’s the transfer surface (table) is both imaged through and also positions the patient during the imaging process, hence it plays in integral role in the diagnostic exam and is critical to achieving accurate diagnostic results and controlling radiation exposure to the patient. This, along with the mechanical, electrical, and physics aspects and needs of diagnostic imaging equipment create for a wide variety of designs and some inherent limitations to table (transfer surface) design possibilities.

The following is a rough grouping of diagnostic imaging devices that was used to help evaluate the criteria:

Equipment with bores: CT, PET, PET/CT, NM, NM/CT - Here the table plays an integral part in achieving the sub-mm dynamic positioning accuracy needed during the scan.
MR - This shares same aspects as equipment with bores, but has special considerations due to the very strong magnetic field.
DXA - This equipment necessitates positioning the x-ray source under the patient in a fixed, known geometry for diagnostic effectiveness and radiation dose concerns.
Conventional XR and Fluoroscopy - This equipment has rectangular, radio-translucent tables that may translate in both directions in the horizontal plane.
Mobile XR - These systems can be moved to the patient and can utilize detachable detectors that often can be placed behind the patient anatomy to be imaged without significant patient movement.
Interventional XR - This type of equipment, such as that used in cath labs and C-arms, has virtually all patients under some form of sedation prior to transfer, and is used in an invasive “interventional-like” procedure after initial diagnostic findings.
Prone breast biopsy tables - This unique design needs to accommodate room for the physician underneath the patient, patients may have some form of sedation, and is used in an invasive “interventional-like” procedure after initial diagnostic findings.

Diagnostic imaging tables mostly fall into two main groupings. One group is those tables used with “equipment with bores”, such as CT, MR, and NM systems. These tables tend to be long and relatively narrow in order to move the patient into and fit through the bore. They are typically rated for patients in excess of 400 lbs. They are capable of adjusting with the high precision (sub millimeter) accuracy needed for accurate diagnostic information both vertically for both patient loading and unloading procedures, and horizontally in one direction (into the bore).

The other group is those tables used on X-Ray system. These too are typically rated for patients in excess of 400 lbs, but are wider than those used with equipment with bores and in many cases are able to move horizontally in two directions. The may not be designed to adjust vertically, but some are designed to rotate to place the patient in a more vertical position needed for specific diagnostic exam needs. Tables for DXA equipment present a noteworthy uniqueness because for both diagnostic and mechanical reasons, they are fixed and do not adjust in any direction.

It must be noted that for patient support devices must meet applicable safety factors as delineated in IEC 60601-1. These factors typically range from 4x to 8x. This means a patient table labeled to support a 500 lb patient must actually be designed and tested at up to 4000 lbs. This has significant implications for adjustable height table design as many design loose mechanical advantage as they go lower.

Many X-Ray systems have imaging components such as X-Ray tubes, high voltage generators, and/or detectors located under the table (transfer surface). The fact that the tables used for diagnostic imaging equipment must not only support large weights, precisely position and image, and potentially accommodate imaging components make redesign of imaging tables challenging at best, but perhaps in some cases infeasible. In all cases, due to the complexity of the equipment and the regulatory requirements, a redesign of an imaging system or its table would require a multi-year process.

One type of equipment stood out as unique are systems used for interventional and biopsy procedures. Both interventional procedures and biopsies are technically considered “diagnostic” because they can provide diagnostic information. These systems however, frequently require all patients to under some form of sedation prior to transfer. Because of the use of sedation, their invasiveness, and that these exams are a secondary follow-up to a primary diagnostic finding, they seem more related treatment and hence the subcommittee and the full advisory committee believes they should be considered out of scope for these standards and hence exempted.

For those systems that will be subject to the new standards, there are certain constraints and performance considerations:

• Must maintain same degree of diagnostic performance for all patients.

• Huge variation of clinical applications and patient needs.

• Technical and diagnostic constraints.

• Must maintain accessibility for all patients and patient conditions.

• Must maintain health care professional access to patient and patient support equipment.

• Must maintain infection control constraints.

• Must continue to adhere to FDA and international standards.

• There is not a one-size-fits-all solution.

All current diagnostic imaging equipment does not meet a minimum transfer height of 17 inches, however some equipment with bore tables do currently meet 19 inches. However, with equipment redesign there are some that may (e.g. CT), but most will encounter a significant technical or diagnostic barrier if the actual transfer surface (table) must be altered. Creative and alternative solutions are needed to increase independent transfer for maximum adoption by facilities (e.g. “accessibility packages”).

The subcommittee believes alternate criteria or “accessibility packages”, to strive for equivalent facilitation, will be needed to best improve independent access in the most meaningful way while adhering to the above constraints and considerations. Accessibility Packages would include accessory components, ancillary equipment, and/or siting design requirements. Accessibility packages may be able a timely, cost effective solution that may also be able to be applied to existing equipment to increase accessibility.

Section 201(h) of the Federal Food Drug & Cosmetic Act includes accessories with the definition of a medical device, and the IEC 60601-1 international standard for medical electrical equipment also identifies that medical electrical equipment includes those accessories that are necessary to enable the normal use of the equipment which includes facilitation of its use.

Section 5 of this report contains some figures of conceptual ideas for accessibility accessories.

Patient Positions during Diagnostic Imaging

The vast majority of diagnostic imaging exams are conducted while the patient is lying on the table; hence the focus of the subcommittee was for the proposed standards in Section M301. However, given the enormous diversity of imaging equipment needed to achieve the broad range of diagnostic objectives Sections M302, Diagnostic Equipment used by Patients in Seated Position; M303, Diagnostic Equipment used by Patients Seated in a Wheelchair; and M304, Diagnostic Equipment used by Patients in Standing Position were considered and are noted in this report.

There are some Nuclear Medicine systems that have a unique design for convenience where the system’s table can pivot out of the way to allow a scan while a patient seated (in a chair or wheelchair). However, given the clinical input from the radiologist that presented to the advisory committee, an equivalent diagnostic exam, in all cases may be obtained while a patient is on the table. As such both the subcommittee and the full advisory committee agreed that for these types of Nuclear Medicine systems, only the M301 criteria should be applied.

Some specialized MR and possibly other modality devices designed and used for extremity scans may not be provided with a table. In such cases the patient chair should comply with the conclusions of the tables and chairs subcommittee to the extent practical while still meeting the diagnostic needs.

Some X-Rays exams are performed with a wall stand in use where the patient is asked to stand. In these situations M304 would apply. However it is likely that the standing supports may need to be an accessory or a mounting in the room. Additionally, given that these supports may also need to serve the diagnostic purpose of a positioning aid some of the dimensions proposed in M305.3 may need to be adjusted in order to maintain diagnostic efficacy.