Technical Report AMI-MU-006:

Imaging Technologies: CT, MRI, X-Ray, Mammography

Authors: Michael Baran and Melissa Lemke, M.S.

Coordinating Editor: Melissa Lemke, M.S.

Location: Marquette University, Medical Device Accessibility & Usability Laboratory

Current Version & Key Contributors: 1.0 (March 2006, Baran)

Previous Version & Key Contributors: 0.1 (July 2003, Lemke)

Table of Contents

Executive Summary

People with disabilities require the same basic healthcare as all people and may even require this care more frequently. Unfortunately, people with disabilities often face barriers to medical care such as inaccessible facilities, inaccessible examination equipment and communication barriers (AARP, 2003). Thus, design development for accessible medical equipment has become an important area of research. Many companies are starting to make their technologies more accessible for people with various abilities and an important step to improving any technology requires an underlying knowledge of currently available options.

Imaging technologies are important for many applications in the health industry. Several imaging technologies will be discussed in this technical report including Computerized Tomography (CT), Magnetic Resonance Imaging (MRI), Mammography and x-ray. Accessibility features related to patient positioning and comfort are explored for each of the imaging technologies aforementioned. Because people with disabilities also work to provide healthcare to others, practitioner accessibility features related to patient positioning and ease of use are also presented.

Background

Imaging technologies are used as procedural and diagnostic tools in order to monitor and diagnose conditions of the various tissues within the body. CT scans are used to view the abdomen, pelvis, soft tissues, organs, bone, chest, and spine. To create the images, an x-ray emitting source within the device rotates around the human body creating a beam of x-rays sometimes as thin as a millimeter. These x-rays are received by sensors and later compiled into a complete image of a slice of the body (USFDA, 2002). The cross-sectional images of the soft tissues within the body are used to monitor and diagnose many circumstances.

MRI scans are used to produce detailed slices of the internal structures of the body that are stacked together to provide details of volumes of tissue. To create these images, an MRI creates both a magnetic field and radio waves. The human body will emit small signals in response to the radio waves, which are detected by the MRI coils (Mayo Clinic, 2005). When compiled together, the cross-sectional images can be compiled to create a three dimensional image of the human body. X-ray scans are also a very common way to diagnose different conditions of the human body. To create the images, an x-ray device emits a localized beam of radiation to the area of interest of the body. Depending on the density of the tissue, different parts of the body will absorb more or less of the x-rays. After the x-rays pass through the body, they are recorded onto film. Therefore bones, which do not allow much radiation to pass though, will appear white on the film, where as more radiation permeable tissue will appear translucent (Mayo Clinic, 2005).

Mammography is used to help screen for changes in the breast tissue over time so breast cancer can be detected before a woman may have any physical symptoms from the disease. A mammogram provides an x-ray image of the breast that often helps identify problem areas within the breast tissue, and an accurate examination can detect 85 to 90 percent of breast cancers in women over 50 and a tumor up to two years before a lump may be felt (USFDA, 1999). When a woman receives a mammogram, most often two standard views are taken of each breast, including a cranial-caudal view (CC) and a mediolateral-oblique view (MLO). The breast is flattened with compression paddles to spread the tissue into a relatively consistent thickness until the x-ray image is acquired. Modern equipment uses low levels of x-ray radiation with doses around 0.1 to 0.2 rad (radiation absorbed dose) per picture. Regular screening mammography procedures usually take around 20 minutes, but the compression only lasts a few seconds (MacEwan, 2003).

CT, MRI, x-ray, and mammography are often used as tools to screen for and diagnose a number of medical conditions, and it is important for these technologies to be available to people with disabilities. Some key factors to consider for accessible medical imaging include patient comfort and device reliability. Some disabilities may cause individuals to have difficulties with balance, posture, endurance, spasticity, or muscle weakness, which are factors that should be considered when developing imaging devices. Individuals also may have difficulties standing, so it would be helpful for imaging devices to allow an examination to be performed with the patient seated in a wheelchair, seated on an exam table, or lying down.

In order for these imaging devices to be beneficial to healthcare, they need to be accessible to all people. However, it was determined in the RERC-AMI national consumer survey of individuals with all types of disabilities and diagnoses that the 2nd highest category of medical equipment rated at least moderately difficult to use was radiology equipment (68.0%) (Winters et al., in press). For patients with disabilities, inaccessible imaging equipment can be very imposing. If medical devices are not accessible to patients with disabilities, it may limit the desire or ability of these patients to seek proper healthcare examinations. As has been previously established, medical imaging procedures can be crucial and effective manners for diagnosis and possible prevention. Therefore, as technology allows for more defined and detailed images to be taken, significant consideration needs to be given to the manner in which a patient interacts with a medical device during an examination.

Another important aspect of accessible medical imaging surrounds the ease of use for and assistance available to practitioners or technicians during particular examinations. With complicated imaging technologies, especially, it is important for the controls to be simple and intuitive so the technician can focus on obtaining an accurate image and the patient and his or her comfort. It is also important for the technology to be easy to set up and perform accurately, so the technician can continue to assist the patient with their needs throughout the procedure.

Product Table

For an overiew and instructions on how to navigate within the product table click here.

Product Survey

The product table displays various models and characteristics of mammography, CT, MRI and x-ray devices. The imaging devices included within the table have at least one accessible feature to note. The table is organized with mammography, CT, MRI and x-ray devices grouped separately with the vertical columns displaying the following information, as applicable:

Product Evaluation

Mammography Products

New mammography units that are being developed feature more automated processes. This is mainly evident in the breast compression process. New devices feature compression paddles that respond to an individual’s breast density and automatically adjust the compression level accordingly. This feature not only leads to more efficient and higher quality imaging, it is also a positive feature for patients because it can lessen pain experienced during the procedure. Some automatic mammography units also have manual capabilities so healthcare providers can input some control over the examination. This may be crucial for specific imaging processes or to cater to different patients’ individual healthcare needs.

In a similar nature, automation is also impacting how the mammography unit uses radiation levels. As an example, the Alpha RT developed by GE Medical automatically adjusts imaging parameters so that better images can be acquired with less exposure. A similar feature is available with the MAMMOMAT 1000&3000 developed by Siemens. These devices have a feature called “Opdose,” which will also set optimum radiation dose levels based on an individual’s parameters. This automated imaging concept has been taken one step further with the addition of computer programs which aide healthcare providers in detecting health problems in the image. The Senographe 2000D developed by GE Medical includes a CAD program that can highlight problematic areas (e.g., lesions) to improve early breast cancer detection.

One other area of automation seen in some mammography devices is related to the placement of photocells in relation to the breast. The VectorPoint Photocell in GE Medical’s Alpha RT allows for placement of photocells under the densest areas of a patient’s breast. This feature can increase the efficiency of image acquisition as it can lessen the number of retakes needed during examinations, which is important for minimizing patient exposure to radiation.

As digital technology becomes more prevalent in imaging devices, including mammography units, the types of available imaging types become more diverse. Some mammography devices are capable of conducting full field scans. This type of digital imaging offers some advantages over the typical film screen mammography units as they can allow for multiple image views that may not be easily created with unidirectional breast compression. The benefits of digital imaging overall could lead to identifying issues within breast tissue that may have not been previously diagnosed. Two exemplary devices that feature this technology include the Senographe 2000D developed by GE and the Selenia developed by Hologic. These devices showcase a new method for mammography and what may become a standard as digital imaging technology improves.

The features previously described have implications for many patients who receive mammograms. In terms of accessibility to a mammography device, there are two important features that were found among some of the devices investigated. First, the adjustability of the height of the bucky on the mammography device is very important. While many patients may be able to have a mammogram while standing, many other patients (e.g., who use wheelchairs, who have limited strength or balance) cannot maintain a standing posture. Therefore, devices such as the MAMMOMAT 1000&300 and Senographe DMR, 700&800 are beneficial because of their vertical height adjustability.

In a similar fashion, adjustability can also play a key role in regards to rotation of the mammography imaging table and compression paddles. In the case of the MAMMOMAT 1000&3000 devices, a full 360-degree rotation of the unit? is possible. This is important when connected with a vertically adjustable unit as multiple positions of the device can be achieved relative to patients. Therefore, patients will be less likely to have to adapt to a stationary device. These MAMMOMAT models also feature a technology called “isocentric rotation,” which allows for consistent images to be captured irregardless of the angle of the mammography unit.

CT Products

For computerized tomography (CT) imaging, two important issues that are being stressed in new devices is examination times and dose levels. Many companies are stressing the efficiency of CT units by promoting shorter examination times due to better imaging technology. The eSpeed C300 developed by GE Medical allows for many examinations to occur during a single hold of breath. The higher quality imaging technology that allows for faster examination times is also translating into new CT applications, such as the case of the eSpeed CT unit which can be utilized for cardiac imaging.

Coupled with shorter examination times, another crucial aspect of CT examinations is control over radiation dose levels. In a similar fashion to technology previously described for mammography devices, CT technologies are also beginning to incorporate software calculated dose administration. The LightSpeed Pro developed by GE allows healthcare providers to administer and monitor radiation dose levels based on a three dimensional model that displays parameters on a patient by patient basis. This device also allows dose optimization for specific cardiac examinations as well. The Brilliance CT developed by Philips also features dose management through a feature called “DoseWise,” which automatically adjusts parameters for a given examination and patient.

During a CT exam, it may be necessary for the patient to hold their breath for a short period of time. Because most patients are left alone during the imaging process, it is necessary to provide a means for informing patients when to begin holding their breath and then again when they are finally able to breathe normally. GE Medical has developed a digital breath timer which features a simple cartoon animation notifying the patient when to hold their breath. This solution has multiple benefits including more efficient imaging acquisition and the digital animation allows for easy interpretation of instructions by a wide range of people.

Another important feature of the exam process is the size of the enclosure of the CT device. The LightSpeed RT developed by GE Medical features a larger radius gantry opening, which benefits both the patient and provider. For patients, a larger opening translates to a less claustrophobic environment and it also enables larger patients to feel more comfortable on the table. Also for the healthcare provider, additional space allows for easier patient positioning so that imaging efficiency increases.

In relation to positioning, another issue deals with keeping a patient stationary or positioned in a specific orientation during the examination process. For some patients with limited strength or mobility, maintaining a static position can become a problem. Therefore, some companies have devised positioning aides to help keep a patient more comfortable and assist in the imaging process. GE Medical, for example, has devised some patient positioning aides to work with the wider gantry opening of the LightSpeed RT. Positioning aides are also supported by Phillips’ Brilliance CT.

Related to accessibility, some CT devices have a few features that fulfill these requirements. The HiSpeed developed by GE offers a wider table which allows for higher patient security during the exam. It can also ease patient transfer onto the CT table. Some CT exam tables also have high weight limits of at least 400 lbs, such as the HiSpeed and Brillance CT. Finally, another important feature is the adjustability of the exam table itself. The Brilliance CT offers an exam table that can be adjusted vertically, which can allow for much easier transferring onto the examination table compared to fixed height tables.

X-Ray Products

Similar to other imaging devices previously mentioned, digital technology is also becoming prevalent in X-ray technologies (e.g., Exposcope 8000 developed by Xograph, CXDI series developed by Canon). Digital x-rays allow providers to view images on a computer screen shortly after the imaging procedure is completed. This is especially beneficial to healthcare providers because they can analyze images more quickly and therefore better assess if higher quality images need to be reacquired.

Issues surrounding patient-device orientations are being solved in a unique way for X-Ray devices. Many of these units are much smaller and redefine the examination process such that the X-ray devices orient to patients instead of the other way around. The Exposcope 8000 is mounted on a C-Arm bracket so it can more easily be rotated about 45 degrees around a patient. The CXDI series is completely portable and can be carried by hand much like a briefcase. These devices are small, lightweight, and thin, so there is greater flexibility in terms of imaging angles and patient positions.

MRI Products

One issue that is of major significance when discussing the MRI examination process is the prevention of claustrophobia. Many patients feel uneasy and uncomfortable within the confined spaces of an MRI device during the examination, thus many companies have strived to design open MRI devices. MRI scanners such as the Signa Profile developed by GE Medical have increased viewing area for the patient. In other words, the MRI coil is not as confining, allowing the patient to see more of the surrounding environment so they do not feel as confined as in other devices. One unique device developed by FONAR called the Upright MRI positions the MRI coils on either side of the patient allowing for the patient to sit or stand in the device with a complete open field of view from of the individual. For other devices with a more typical MRI coil design, such as the Signa CV/i 1.5T by GE Medical and the MRP-7000 developed by Hitachi, the coil opening is designed to be wide, allowing for increased patient comfort.

Along with wider patient openings for the MRI devices, there are other features which develop an increased sense of patient safety and comfort. The Signa Profile/i 0.2T and Signa Profile/o 0.2T developed by GE feature a patient call button and intercom for increased patient-provider communication during the imaging process. Also, both of these devices feature an incorporated seating area near the head of the device to allow a family member to sit with the patient during the procedure. The 0.7T Signa Open Speed, developed by GE, allows patients to control the environment within the MRI by adjusting the lighting and airflow. All of these features can lessen some patient anxieties and thus increase the quality and efficiency of an MR imaging procedure.

In order to increase the versatility of MRI examinations, many companies have developed individual coils for imaging specific body regions. These coils work with the larger MRI unit and offer more detailed images to be taken at localized areas of the body including: spine, neuro, extremity, and vascular imaging. Some coils are designed for improved radio wave reception only, while others can also generate a magnetic field. The coils overall can not only improve the quality of specific images, but also reduce some positioning issues that would be part of a normal examination.

Similar to CT images, positioning on an exam table for an MRI scan can be a challenge for some patients. To alleviate this issue, some device improvements have been made. The Signa Profile/i 0.2T and Signa Profile/o 0.2T, developed by GE Medical, feature a wider exam table. Some MRI exam tables also feature vertical adjustability so the table can be lowered or raised, depending upon patient preferences and abilities. This feature is a part of Hitachi’s AIRIS, AIRIS II and MRP-7000 and also a product feature of FONAR’s Upright MRI. Finally, the exam table should be able to support a wide range of patient weights, and the Altaire (Hitachi), AIRIS, AIRIS II, MRP-7000, and Virgo MRI (Millennium Technologies) advertise table supported weights of at least 400 pounds.

Once patients are on the imaging table, positioning their bodies into specific orientations on the table is the next step so that proper images can be acquired. The Signa SP/i 0.5T, Virgo MRI features alignment lights in the table so the patient has a visual reference with which to orient. Also, kinetic positioning aids are available for the Signa Profile/o 0.2T, AIRIS and AIRIS II for more intricate patient positioning needs.

Recommendations for R&D

Upon reviewing and compiling the information contained in this report, a few preliminary suggestions can be made for improving the accessibility of medical imaging devices.

Automation is very nice feature that is becoming more prevalent in medical devices. For all imaging devices, it is beneficial to have some automated detection of parameters of the patient to allow for minimal dose exposure and more efficient image acquisition. Automation can also be helpful for other types of imaging exams such as a mammography where the process of breast compression can be automated. This can lessen the chance of patients experiencing pain because the automation should compress the breast only as needed. Finally, automation of image analysis is also a significant improvement within this field. This feature can assist physicians with identifying problematic areas within an image. This being established, healthcare provider interaction is crucial for any type of imaging process, and therefore manual controls should still be an option.

Digital imaging is quickly becoming the industry norm, rather than the exception. This type of imaging has many benefits including quick image processing and easy data storage and transport. It is much more common to see physicians in hospitals now analyzing x-ray images via a computer screen rather than an actual piece of film. Some may argue that analog film still provides the best possible and highest quality images needed for detailed exams, yet as digital technology continues to improve throughout the next few years the convenience of digital imaging will become even more prevalent in the medical field.

For patient positioning, there are a few possible solutions to lessen this issue. First, in the case of a CT scan or MRI, wide openings are a positive feature. This allows for the patient to become more comfortable during the exam, which can also translate to a more efficient exam overall. The Upright MRI developed by FONAR is a perfect example of this. Not only does its design create a wide and open interface for patients, but it also allows patients to be in many positions during the procedure, including an upright posture. One issue that needs to be considered, is the image quality of open MRI’s. The coils of an open MRI are designed differently than would be found in a traditional system. This can result in different properties of the generated magnetic field, resulting in a loss of image quality. For another beneficial feature, if an exam table is required it should also be wide and adjustable. The extra width is essential for patient comfort during a possible transfer and later positioning on the table. Also, vertical adjustability is essential for allowing easier independent patient transfers onto the device. For example, if patients need to transfer from a wheelchair onto an exam table, it is much easier to transfer onto the table when it is below the height of the chair. Likewise, when patients need to transfer off of the table back into their wheelchair it is ideal to adjust the table height slightly above that of the wheelchair seat. Finally, positioning aides are great features because they can help keep patients physically stable during an exam as well as increase their comfort by offering support to necessary areas of the body while a certain position is maintained.

During the examination process, communication between the patient and healthcare provider should always be easy and available. Therefore, the use of intercom systems or call buttons is a plus. Also, the use of easy to comprehend graphical interfaces, such as the digital breath timers seen in some MRI devices, are beneficial because a wide range of patients can understand the instructions needed for a proper examination. Both of theses features can also bolster patient safety and sense of security. Furthermore, incorporating redundant audio, visual, and tactile cues is ideal for increasing access for individuals with visual and hearing disabilities.
While not applicable for all devices, portability is a great idea for some. Not only does portability work in a pragmatic sense for hospital staff, but more importantly in regards to accessibility it allows the device to orient to the patient and not the other way around. If an X-ray device is small enough, it can be place in multiple positions relative to the patient, without any movement by the patient. This is especially beneficial for patients with limited mobility.

Also an additional feature that could be applied to many devices would be hand rails. These would offer the patient additional support in many instances including during transport and the examination. In terms of a CT, or MRI device, handrails on the exam table could also offer an extra sense of safety for patients who may not feel comfortable on a narrow table. The hand rails could provide the patient with an improved sense of spatial orientation, which could calm the patients positioning fears during an examination.

Acknowledgement

This work is supported by the Rehabilitation Engineering Research Center on Accessible Medical Instrumentation, funded by the National Institute on Disability and Rehabilitation Research, U.S. Department of Education Grant #H133E020729. All opinions are those of the authors.

References

  1. American Association of Retired Persons. Beyond 50 2003: A report to the Nation on Independent Living and Disability. 2003.
  2. MacEwan, Becky. Personal interview. August 1, 2003.
  3. Mayo Clinic. “MRI: Viewing the body's hidden structure.” 2005a. http://www.mayoclinic.com/health/mri/SM00035
  4. Mayo Clinic. “X-Ray.” 2005b. http://www.mayoclinic.com/health/x-ray/FL00064
  5. U.S Food and Drug Administration. “FDA Sets Higher Standard for Mammography” http://www.fda.gov/fdac/features/1999/199_mamm.html
  6. U.S. Food and Drug Administration. “What is Computed Tomography?” 2002 http://www.fda.gov/cdrh/ct/what.html
  7. Winters, J.M.W., Story, M.F., Barnekow, K., Kailes, J.I., Premo, B., Schwier, E., Danturthi, R.S., and Winters, J.M. (in press). Results of a National Survey on Accessibility of Medical Instrumentation for Consumers. In J.M. Winters & M.F. Story (Eds.), Accessibility and Usability Considerations for Medical Instrumentation. Boca Raton, FL: CRC Press.