- 作者：Daniel A. Henry ; MD ; FACR*
- 刊名：Critical Care Clinics
- 出版年：2000
- 出版时间：1 October 2000
- 年：2000
- 卷：16
- 期：4
- 页码：579-599
- 全文大小：1214 K
When one considers the advances in imaging over the last three or four decades of the 20th century, one has to marvel at the progress in diagnostic capability and the impact on patient care. Obviously the introduction and evolution of digital cross-sectional imaging with computed tomography (CT) and ultrasound, and later the introduction of magnetic resonance (MR) imaging, forever changed the landscape of diagnostic imaging. Interventional radiology advanced in lock step with imaging technology, introducing new and better devices and procedures; replacing major invasive therapies; accessing tissues with image-guided biopsy and drainage procedures; and occluding, recanalizing, or restructuring the vascular system with everything from inferior vena cava filters to aneurysm-occluding balloons. Nuclear medicine continued its march toward noninvasive functional evaluation with significant advances in nuclear cardiology, oncologic imaging, and positron emission tomography (PET). Conventional radiology evolved from analog images wet processed on standard radiographic film to digital data sets produced by laser scanning, dry processed or squeezed through wires and fiberoptic cables to computerized workstation displays. Computer-assisted interpretation of images has begun, and neural networks are being developed to guide decision making.
Most of these improvements in imaging, however, have not been ¡°in?the ICU, but portable imaging has brought services to the bedside in the ICU for conventional radiography, fluoroscopy, ultrasound, nuclear medicine, and most recently CT. Although some of the recent advances in imaging have been distant from the ICU environment, image availability in the ICU has become an electronic reality; it began with conventional images and then expanded to include the patient's imaging portfolio. These advances are based on the development of standardized image data sets; improvements in electronic networks, display stations, and bandwidth; and enhanced computer archiving and query/retrieve functions.
The impact of imaging on the ICU goes well beyond portability of available services. Patients entering ICUs frequently arrive from surgery or the emergency department or are transferred from a non-ICU care area. Certain clinical criteria must be met before ICU admission. Imaging facilitates the diagnostic and therapeutic decision-making process and assists in the evaluation of therapeutic efficacy and efficiency. In this role and integrated with other parameters, imaging provides patient-specific information that dramatically influences or supports the threshold for ICU admission, the tempo of care, the length of stay, and it is hoped, the quality of care. It is especially useful in the triage and assignment of patients to system-specific ICU environments such as neurosciences, coronary medical, medical respiratory, general surgery, shock/trauma, and so forth.
The immediate availability of high-quality, sophisticated imaging in the emergency department has promoted this clinical triage system, channeling certain classes of patients to system-specialized ICUs. A good example is the use of chest pain triage units in emergency departments across the country. These units screen patients with chest pain and admit them to coronary units for ¡°rule-in's?or reevaluate or discharge following a ¡°rule-out.?Cardiac nuclear medicine evaluations or cardiac MR imaging studies play a central role in screening these patients for admission, stratifying their risk if any, directing their further evaluation or therapy, and ultimately shortening their stay and possibly reducing cost.
The trauma patient can have several organ systems imaged and evaluated in the emergency department by means of conventional studies, ultrasound, CT, and in some cases, MR imaging, and then can be triaged to the appropriate ICU. More definitive clinical decisions can be made and the prioritization of therapy accomplished with more confidence based on findings on imaging studies. These steps are important for timely investigation and care and save considerable effort and personnel time in transporting and monitoring patients while they have various studies performed after admission.
Will the ICU continue in its relative isolation from imaging services? The emergency department has had dedicated or at least shared or relatively convenient imaging services for years. Will other critical care areas also have this advantage in the near future? Portable conventional imaging has been improved with portable computed radiography. This technology has converted portable radiography from analog images on plastic film to digital images on display stations, film, or both. Computed radiography has improved overall image quality and fostered transmission of conventional digital images to critical care and other areas by means of electronic networks and archives. Despite this significant advance, ICUs and other critical care areas remain relatively isolated especially from cross-sectional imaging. The exception to this is ultrasound, which is conveniently portable and very effective. Acuity of illness, monitoring requirements, clinical instability, limited personnel, and, of course, physical distance, are key obstacles.
Recently, a battery-powered, portable CT device has become available for ICU use. Obviously, this device represents a significant advancement for critical care areas including operating rooms. Imaging flexibility remains an issue when compared with stationary subsecond spiral multidetector CT scanners and their image acquisition capabilities. CT technology and certainly MR imaging are still developing, and recent efforts have been directed primarily at improving image quality and speed of acquisition. CT, portable or otherwise, provides significantly more information than conventional studies in many instances; however, the specific applications of CT are still being explored and then utility substantiated for the ICU population. The absolute necessity of the CT information and the increasing number of clinical circumstances that are materially impacted may drive the process. These outcome data coupled with additional miniaturization of components may further support and even expand portable CT services. Assuming this effort continues, the resulting acquisition hardware, even reduced in size, would be substantial. Entering an ICU, getting off and on elevators with this equipment, and roaming the halls of health care facilities with this delicate technology seem a remote wish but obviously not an impossibility.
The development of computer and software technology will drive CT and MR imaging to new vistas in both functional and morphologic imaging and, as long as that process continues, those goals will dominate future applications development, especially for MR imaging. Most MR imaging units available today weight thousands of pounds and are linked to multiple computer cabinets in environmentally controlled rooms. There are smaller, organ-specific MR imaging units available or under development, but their focus is narrow and they are not portable. Image quality remains a challenge.
Perhaps research and development should focus on the design of the health care facility and the equipment to transport patients safely. As mentioned earlier, the critical care mission of the emergency department has been supported by either dedicated or conveniently available imaging equipment. Many emergency departments are built adjacent to radiology departments to share services with non-emergency department patients. This proximity relationship is based on the concept that radiology departments need to be centralized service centers. With the transition to digital imaging, archiving, and networking, radiology departments need no longer be isolated units. In the past and currently, radiology departments have been built around central services of film processing and supply, film file libraries, interpretation areas, and radiation safety considerations. With networking of interpretation stations, digital processing, and digital film archives, remote image acquisition will become the norm. CT and MR imaging scanners and other digital imaging equipment could thus be more strategically located in areas of high use based on the needs of the clinical population. Pods of digital imaging equipment could be central to a floor of critical care units or part of the unit. Design would have to consider personnel, radiation safety, maintenance, environmental requirements, and electronic support. Electronic imaging should reduce or remove the redundancy of radiology supporting services and requirements. Inpatient and outpatient services would have to be evaluated carefully and perhaps totally divided, but market-driven expectations of outpatient imaging services and the increasing demands of inpatient services have essentially separated these groups. It seems appropriate that the advances in digital imaging technology should promote a reconsideration of the traditional design of health care facilities.
Bed design and transportation of patients is another area of potential improvement. Perhaps ICU beds should be designed not to be just mobile, but to travel. Just as some beds rotate and others accept a film cassette or are designed for C-arm fluoroscopy, why can't an ICU bed be designed to dock with a CT scanner? At one point, there were emergency department stretchers that offered motorized assistance to elevate patients and move them on and off radiographic tables. The patient aperture of the CT scanner would have to be enlarged, but if an ICU bed docked with a scanner, patients could conceivably move through the device, undergoing a very rapid examination, and never leave their beds. This technique may not be portable CT in the ICU but these remedies would address some of the current challenges of moving a monitored ICU patient for a cross-sectional imaging study.
In addition to the ambitions to directly support critical care with portable imaging services and image accessibility, a substantial effort is being made to push the envelope in all areas of diagnostic imaging. The next few years will see an extension of current technology and the investigation and implementation of new imaging applications. Computer advances will be a significant catalyst, but the insight and vision of clinical, laboratory, and industry investigators are the substrate. The following is a survey of future advances that will be of interest to critical care in the applicable radiologic subspecialties.