European Journal of Radiology, 14 (1992) Q 1992 Elsevier
EURRAD
Science Publishers
141-146
B.V. All rights reserved. 0720-048X/92/$05.00
141
00259
Technology assessment and diagnostic imaging H. David Banta Center for Medical Technology, TN0 Institute of Aging and Vascular Research, Leiden, The Netherlands
(Accepted
Key words: Technology
assessment,
radiology; Technology
6 November
assessment,
Introduction Societies all around the world are increasingly concerned about technology, including health care technology. As technology has become more pervasive, and its benefits and hazards more visible, governments have become more and more involved in attempts to influence technological change. [ 1,2]. One of those attempts has come to be known as technology assessment. In this paper, CT scanning and MRI scanning will be discussed to illustrate some aspects of health care technology assessment in the field of diagnostic imaging. What is technology assessment? Technology assessment is a comprehensive form of policy research that examines short- and long-term social consequences (for example, societal, economic, ethical, legal) of the application of technology [3,4]. The goal of technology assessment is to provide policy makers with information on policy alternatives, such as allocation of research and development funds, formulation of regulations, or development of legislation. Technology assessment, then, is action-oriented research whose aim is to change practices concerning technology [2]. Health care technology assessment, while a part of this broader field, also has differences. The first is based on the goal of health care: to improve health. Therefore, as it has developed, health benefits of technology has been the main focus of health care technology assessment, with increasing attention to financial costs over time. The main application of health care technology
Address for reprints: Prof. Dr. H. David Banta, CMT/TNO, Box 430, 2300 AD Leiden, The Netherlands.
P.O.
1991)
MRI; Magnetic resonance
imaging, technology
assessment
assessment has been to make specific decisions within specific policy areas, such as whether an insurance company will pay for a specific technology or a hospital will be given a license to provide a certain service. As the limitations of formal policies have become more and more apparent during the past decade, the field is also beginning to grapple with how to change clinical practice through information dissemination or other means. Efficacy (benefits) and safety are the basic starting points for evaluating the overall utility of a health care technology. Efficacy may be defined as the probability of benefit to individuals in a defined population from a health care technology applied for a given medical problem under ideal conditions of use [ 51. If a technology is not efficacious, it should not be used, and if its efficacy is unknown, statements about its overall value cannot be made. In addition, efficacy and safety data are needed to evaluate the cost-effectiveness of a technology. Neither the need for a technology nor its appropriate use can be established without good information on efficacy and safety. Another assessment problem concerns the appropriate number of any device, including any imaging device. Should there be one in every academic hospital? Should there be one in every casualty? Should every hospital have the device? Unfortunately, most original data is collected in university hospitals, and often has limited utility for answering questions related to nonuniversity hospitals. Technology assessment and policy making There are a variety of public policy mechanisms dealing with health care technology. Governments fund health-related research and development. Drugs are regulated for efficacy and safety. Medical devices are
142
sometimes regulated. Health planning mechanisms, such as licensing and regulation of facilities and technologies, have direct effects on health care institutions and technologies. And payment policy may be the most important determinant of technology use. Payment for health care services by sick funds and insurance companies means that people use technologies either free or at a small cost to themselves. This situation contributes to rapid and relatively uncontrolled proliferation of health care technology. Using technology assessment as an aid to decision making in these programs is a relatively new idea. Only in the area of drug regulation is evidence concerning the technology systematically collected and used as an important determinant of the decision. However, each policy mechanism, each regulation, each decision concerning payment and payment levels, could be improved by using the best available information on the technology [I]. The actual information needed varies from program to program. In the area of drug regulation, scientific evidence on safety and et& cacy is the main need; economic and social implications play relatively little part in the decisions. In regulation of facilities, efficacy and safety are important, but costs and efficiency are also key variables; cost-effectiveness analysis can be very helpful at this stage. In setting payment levels, the policy maker wants first to know that the technology works, and then would like to know how much it costs to provide the technology. Ideally, the payment level should be set rather close to the level of cost of providing the technology (in practice, the payment level is often set well above the cost of providing the technology, meaning that there is a large incentive to use the technology). One serious problem in using technology assessment as an aid to decision-making is that data from assessments is often not available when it is needed. Assessments are generally not done with strategic purposes in mind. Under an ideal model, all technologies would be tested for efficacy before they come into widespread use. They would then be tested in the emerging phase. In practice, that goal is only achieved in the area of drug regulation. Industry is required to produce the data on safety and efficacy. Otherwise, the testing of technologies for benefits by well-designed studies is done less often than desirable. This is shown by the lack of good information on the efficacy of specific technologies [5&l. Technology assessment and diagnostic imaging Diagnostic imaging has been subjected to intense scrutiny since the introduction of the CT scanner in
1972. At that time, relatively few assessment of diagnostic imaging had been done aside from assessments related to safety, especially in minimizing doses of ionizing radiation. Assessing diagnostic imaging was also seen as difficult from the beginning, because the impact of an image on health cannot be direct. The diagnosis must change therapy, and the therapy must be effective. These considerations led Fineberg et al. [7] to produce four (afterwards five) levels of evaluation for the efficacy of diagnostic imaging: (1) Technical evaluation: The technical output gives accurate information concerning the structure of the part of the body imaged; (2) Diagnostic accuracy: This output contains information that potentially improves the clinician’s ability to diagnose disease and assess the patient’s prognosisq; (3) Diagnostic impact: The information can alter plans for additional diagnostic tests, and (4) Therapeutic impact: The information can lead to changes in therapeutic plans for patients ; and Health impact: The end result may be improved (5) patient outcome. Prior to the mid-1970s, almost all assessments in the field of diagnostic imaging (or radiology) were at the first level. A few studies examined the diagnostic accuracy of specific imaging procedures by collecting data on their specificity and sensitivity. However, the field has developed rapidly since then, partially stimulated by demands from policy-makers and others for evidence of health impact, and a number of studies have been done assessing impact on diagnostic or therapeutic plans. It is now possible to develop decision rules for the use of diagnostic imaging in specific circumstances. For example, Harvard Medical School has published a useful book of such guidelines [8]. Technology assessment and CT scanning After its introduction in 1972, computed tomography (CT) scanning rapidly became the most visible technological advance in health care. As a complex, expensive device, it came to symbolize the problem of health care technology.’ The CT scanner is a device that uses X-rays, radiation sensors, a computer, and complex software to construct images of cross-sections of the body. A CT scanner that could only be used on the head was introduced to the international market in 1972 and began to diffuse rapidly into use. The Oflice of Technology Assessment (OTA) did one of its first health reports on this subject [9], using the Fineberg frame-
143
work to review the literature. The basic conclusion of the report was that “Well-designed studies of efficacy of CT scanners were not conducted before widespread diffusion occurred”. By the time of the report, 1978, it was known that CT scanners performed reliably and provided accurate diagnostic information. In addition, CT scanning was replacing other diagnostic tests, especially pneumoencephalography and cerebral arteriography. Little was known about how CT scanning affected the planning of therapy or patient health. The CT scanner was also an issue in Sweden. The first CT scanner was imported in Sweden in 1973. Swedish investigators carried out a cost-effectiveness analysis of CT scanning, based on its ability to replace other expensive diagnostic procedures. The study suggested that large hospitals could pay for a scanner out of replaced procedures [ lo]. Subsequently, large regional hospitals did buy CT scanners, but others were prudent. By May 1978, the United States had 4.8 scanners per million population, whereas Sweden had only 1.6 per million [ 111. In the United States, which had no effective planning mechanism, the OTA report had little impact on the situation with CT scanners. The scanner diffused very rapidly into practice. Another early experience with CT scanning was described from the United Kingdom [ 12,131. The Department of Health and Social Security (DHSS) was involved from an early stage in development of the CT scanner, since it provided prototype funds. The DHSS was quite restrictive toward purchases of the head scanner, and set up an explicit evaluation plan intended to guide policy. By 1978, the UK had 0.9 scanners per million population, compared to the 4.8 scanners in the United States. In the case of the body scanner, however, although the DH S S made a policy similar to that for the head scanner, scanners were taken up rapidly out of non-government funds, both endowment funds of institutions and private funds, such as those of donors. There were also explicit fund-raising drives by some hospitals [ 121. In the case of the body scanner, the strategy of restriction and assessment failed. One of the most interesting evaluations of CT scanning was developed by Fineberg et al. [ 71 and extended by Wittenberg and Fineberg [ 14,151. All physicians requesting a CT scan were asked to complete a questionnaire at the time of their request. The questionnaire asked three questions: (1) What diagnoses were considered, in probabilities? (2) What diagnostic tests would definitely be required and what tests would be required if no CT scanner were available? (3) What would the treatment plan be if the physician had no CT scanner available?. At the time of discharge of the patient, the physician was interviewed to ascertain
the diagnostic tests actually performed, treatments undertaken, and final diagnostic understanding of the case. In the lirst study [7] cranial CT was found to reduce other neurodiagnostic procedures by up to 73 y0 in the case of pneumoencephalograms, and lead to changes in therapy in 19% of cases. In later studies by Wittenberg and Fineberg [ 14,151 of body CT scanning, more extensive questionnaires were used. CT improved diagnostic understanding in 52% of patients, reassured the physician about previously planned therapy in 43 %, improved precision of previously planned treatment in 23x, and contributed to a change in therapy in 14% A number of other European countries developed standards for the number of CT scanners ‘needed’. The early standards were often based on information in the OTA report and the Swedish report. For example, in 1979 the French standard called for one CT scanner per million population [ 161. The standard in The Netherlands in 1979 called for 1 head scanner per 500,000 population [ 171. The case of the CT scanner has been visible in most countries of the world, including less developed countries. It has been a test of the new field. On the positive side, a number of useful reports and studies were carried out. The CT scanner probably has been studied more than any other health care technology. A number of countries did develop standards for the number of scanners that were effective in their planning programs. On the negative side, the CT scanner was seen as a prototype technology, whereas in fact it was one of the most expensive technologies in the medical marketplace. Lessons from the CT scanner did not readily transfer to other technologies. An important aspect of the CT scanner, however, was that it did demonstrate clearly that technology developing in one country, the United Kingdom in this case, could rapidly diffuse over the entire world. The result was that technology assessment was seen as having an important international dimension from its beginnings. Today, CT scanning is fully accepted as a fundamental diagnostic tool in many conditions. Its purchase is no longer regulated in the Netherlands Technology assessment and magnetic resonance imaging Magnetic resonance imaging (MRI), sometimes called nuclear magnetic resonance (NMR) is an imaging device that was introduced in the late 1970s and is now rapidly spreading into use as a diagnostic tool [ 18-221. NMR is projected to diffuse at a rapid rate through-out the world, with an increase in the market
144
size of 90% per year, almost a doubling. One reason this rapid diffusion is a concern is because of the high cost of MRI units, more than 2 million guilders for the least expensive device. MRI produces images of cross-sections of, the human body similar to those produced by computed tomography (CT) scanning [23]. There are important differences, however. A CT scanner depicts the X-ray opacity of structure of the body. MRI images depict the density or even the chemical environment of hydrogen atoms [24]. These properties of parts of the body are not necessarily correlated. MRI has several advantages. It gives a high contrast sensitivity in its images. It does not employ ionizing radiation as CT scanning and other imaging methods do. It is not necessary to inject potentially toxic contrast agents, as is often done with CT scanning (although contrast agents are being used more and more frequently with MRI scanning). MRI allows choice of different imaging planes without moving the patient; CT scanning can only produce an image of one plane at a time, and some planes are not possible. Finally, images can be obtained from areas of the body where CT scanning fails to produce clear images. It may be that an MRI scan can replace many diagnostic laboratory tests in the future [25]. Despite this great potential, a technology must be assessed in reality. One can ask such questions as these: Is present MRI an advance in imaging technology as compared with (say) CT scanning? Does it produce useful information at a reasonable cost? Does it produce diagnostic information not otherwise available? Technology assessment and MRI imaging MRI imaging has been repeatedly assessed since its introduction. One of the early reports was done by the Dutch Health Council (Gezondheidsraad) [ 181. It has been assessed by several groups in the US [20,23, 25-261 and has also been formally assessed in the Nordic countries [27], in Australia [28] and in Switzerland by means of a consensus conference [29]. There is widespread agreement that MRI is a reliable diagnostic device that produces information that can be quite useful at times. Its potential advantages over other modalities such as CT scanning include: MRI is able to distinguish between various normal and abnormal tissues. Blood flow, circulation of the cerebrospinal fluid and the contraction and relaxation of organs can be assessed. Since the compact bone emits no signal, tissues surrounded by bone (e.g. the contents of the posterior cranial fossa and of the vertebral canal) can
be represented without disturbance by artifacts [29]. MRI also has the advantage of easy selection of planes, which is particularly useful when imaging the spine and spinal canal. Thus, despite the fact that MRI images contain artifacts that can be confusing and that require expertise to interpret, MRI can be said to produce information that is useful for the diagnostic process. However, this is not sufficient for answering practical questions such as the following: Which patients should be scanned with MRI, and which with other diagnostic modalities (in other words, where does MRI have real advantages in making diagnosis). Which conditions that can be diagnosed by MRI can also be effectively treated? What is the place of MRI in relation to other diagnostic imagsuch as CT, nuclear medicine, ing modalities ultrasound, and conventional X-ray. For example, a literature review published in 1988 [ 301 found that 54 evaluations did poorly when rated by commonly-accepted scientific standards such as use of a ‘gold standard’ comparison of blinded readers of the images (the expert doing the reading did not know the status of the patient). Only one article had a prospective design. Also, over the period examined, there was no improvement in quality of research over time. Kent et al. pointed to a continuing problem in later articles [31,32]. A recent review done by the author shows no change in this situation. The most thorough literature review was by Kent et al. [ 3 11. The literature showed that MRI is probably superior to computed tomography, its main competitor, for detection and characterization of posterior fossa (brain) lesions and spinal cord myelopathies, imaging in multiple sclerosis, detecting lesions in patients with refractory partial seizures, and detailed display for guiding complex therapy, as for brain tumors. In other diseases, the efficacy of MRI was found to be similar to computed tomography. In fact, the best designed study, carried out in a heterogenous group of patients in neuroradiology, studied in a matched pair design, found that sensitivity and specificity of CT scanning were somewhat better than that of MRI [33]. More recent literature does not contain articles refuting these conclusions. As for diagnostic or therapeutic impact, little information is available. For diagnostic purposes, brain imaging is by far the most frequent use of MRI. For example, Bradley [ 341 found that more than 65% of scans were of the brain, and between 10 and 20% of the spine. MRI does not appear to have replaced other modalities such as CT scanning in the brain except that it is used preferentially in suspected posterior fossa tumors. In a prospective randomized study in patients
145
with suspected posterior fossa tumors, Teasdale et al. [ 351 found that in groups of about 500 patients each, 93 of those who had CT first were referred subsequently for MRL, whereas only 28 of those who had MRI first were then referred for a CT scan. In the spinal cord, two studies have examined the relative accuracy of MRI in relation to myelography and computed tomography [36,37]. The studies found that MRI and CT were roughly equivalent in terms of true positive results, but that both were superior to myelography. Several studies have indicated that MRI may replace CT scanning and myelography in scanning of the spine [36,38]. Peddecord et al. [39] found that MRI gradually replaced both CT scanning and myelography. In their study, the percentage of physicians ordering myelography prior to MRI dropped from 15 % to zero during the 2 year period of their study. This could be significant, since myelography is a risky procedure. Another area where MRI could be quite useful is in imaging joints. A common problem is torn or damaged menisci (cartilages) of the knee. The standard diagnostic procedure is either arthroscopy by scope or arthogram, an X-ray procedure. Both are invasive, in that the scope must be inserted into the joint or a contrast material must be injected. MRI is noninvasive. Crues et al. [40] found that, for more serious meniscal tears, the false-negative rate of MRI was 6 %, a figure comparing favorably with the alternatives. Manco and Berlow [41] reported similar findings. However, the advantage of arthroscopy is that a therapeutic procedure can be done if an abnormality is found. One study has been carried out in Norway, using the Wittenberg/Fineberg method [ 421. The investigators found that 33% of patients had their main diagnosis changed by MRI scanning. Plans for surgery changed in 20% of the patients, and plans for radiotherapy changed in 8% of patients. Costs of MRI The capital cost of an MRI scanner varies greatly, depending particularly on the strength of the magnets. A basic unit costs at least 2 million guilders. Evens [43] reported survey results that found that operating an MRI facility in the United States cost US$840,000 a year. Bradley [ 341 reported that the costs of operating two MRI facilities varied from US$841,000 to US$1,115,000 per year. It is worth noting that only about one-third of this operating cost is accounted for by the capital investment in the MRI scanner. Other expenses include space, personnel, equipment and maintenance. The cost per scan in Bradley’s two centers was between US$370 and
US$550, and the fee for the scan was US$500. The costs apparently do not include the payment to the physician. Bradley [ 341 comments on the possibility that costs will be offset by replacement of other diagnostic procedures, particularly myelography. Invasive diagnostic procedures such as myelography must be done with a hospitalization of at least one day, whereas MRI can be done on an out-patient basis. The author made rough estimates of the number of cases of specific disease problems in the Netherlands that might be imaged with MRI. Important disease problems and number of cases include: Brain tumors 850 Tumors of the spinal cord 70 Multiple sclerosis 400 Herniated nucleus pulposis 22000 Torn meniscus 3735 It can readily be seen that the potential for MRI scanning in terms of numbers is with herniated nucleus pulposis (‘herniated disk’) and torn meniscus. Otherwise, the national demand for MRI scanning can readily be met by existing units in university hospitals. Discussion Diagnostic imaging makes up about 5% of the national health expenditure in industrialized countries. This 5% is highly visible, and diagnostic imaging has been perhaps more subject to regulation than any other area of medicine. This scrutiny will continue. In The Netherlands, as in most industrialized countries, hospital budgets are now tightly constrained. This means that each new purchase must compete with other alternatives. It is probably a frequent occurrence that imaging departments must choose between several possible purchases. Thus, technology assessment may become more useful at the hospital level than at the national policy level. The main problem with the field of technology assessment remains the poor quality of primary data. Technology assessment reports are usually based on syntheses of available scientific information, with an input of judgment and clinical experience. Without good data, the usefulness of the field will be limited. References 1 Banta HD, Behney CJ. Policy formulation and technology assessment. Milbank Memorial Fund Quaterly/Health and Society 1981; 59: 445-479. 2 Banta HD, Behney CJ, Willems JS. Toward rational technology in medicine. New York: Springer, 1981. 3 Ofice ofTechnology Assessment. Development of medical tech-
146 nology: opportunities for assessment. Washington, DC: US Government Printing Office, 1976. 4 Office of Technology Assessment. Strategies for medical technology assessment. Washington, DC: US Government Printing Office, 1982. 5 Office of Technology Assessment. Assessing the efficacy and safety of medical technologies. Washington, DC: US Government Printing Office, 1978. 6 Institute of Medicine. Assessing medical technologies. Washington, DC: National Academy Press, 1985. 7 Fineberg HV, Bauman R, Sosman M. Computerized cranial tomography. Effect on diagnostic and therapeutic plans. JAMA 1917; 238: 224-221. 8 McNeil B, Abrams H eds. Brigham and Women’s Hospital handbook of diagnostic imaging. Boston: Little, Brown and Company, 1986. 9 Office of Technology Assessment. Policy implications of the computed tomography (CT) scanner. Washington, DC: US Government Printing Office, 1978. 10 Jonsson, E. Studies in health economics. Stockholm: The Economic Research Institute, Stockholm School of Economics, 1980. 11 Gaensler EHL, JHL, Jonsson E, Neuhauser D. Controlling medical technology in Sweden. In: Banta D, Kemp K eds. The management of health care technology in nine countries. New York: Springer Publishing Company, 1982: 167-192. 12 Stocking B. The image and the reality: a case study of the impacts of medical technology. London: Nuffteld Provincial Hospitals Trust, 1978. 13 Stocking B. The management of medical technology in the United Kingdom. In: Banta D, Kemp K, eds. The management of health care technology in nine countries. New York: Springer, 1982; 10-27. 14 Wittenberg J, Fineberg HV, Black EB, Kirkpatrick RH, Schaffer DL, Ikeda MK, Ferruci JT. Clinical efficacy of computed body tomography. AJR 1978; 131: 5-14. 15 Wittenberg J, Fineberg HV, Ferruci JT, Simeone JF, Mueller PR, Van Sonnenberg E, Kirkpatrick RH. Clinical efficacy of computed body tomography, II. AJR 1980; 134: 111 l-1120. 16 Fuhrer R. Policy for medical technology in France. In: Banta D, Kemp K, eds. The management of health care technology in nine countries. New York: Springer, 1982: 100-126. 17 Groot LMJ. Medical technology in the health care system of the Netherlands. In: Banta D, Kemp K, eds. The management of health care technology in nine countries. New York: Springer, 1982: 150-166. 18 Gezondheidsraad. NMR - vorming en opleiding. Den Haag. 13 July 1985. 19 Luiten AL. The birth and development of an innovation: the case of magnetic resonance imaging. In: FFH Rutten, SJ Reiser eds. The economics of medical technology. Berlin: Springer-Verlag, 1988; 99-108. 20 National Center for Health Services Research and Health Care Technology Assessment. Magnetic resonance imaging. Health Technology Assessment Reports, No 13. Rockville, MD: US Public Health Service, 1985. 21 Steinberg EP, Sisk JE. Locke KE. The diffusion of magnetic resonance imagers in the United States and worldwide. Int J Technol Assessm Health Care 1985; 1: 499-514. 22 Wing WS, Tsurude JS, Kortinan KE, Bradley WG. Practical MRI. Rockville, MD: Aspen, 1987. 23 Offtce of Technology Assessment. Nuclear magnetic resonance imaging technology, a clinical industrial, and policy analysis.
Health Technology Case Study 27. Washington, DC: US Government Printing Office, 1984. 24 Iezzoni LI, Grad D, Mostowitz MA. Magnetic resonance imaging: overview of the technology and medical applications. Int J Technol Assessm Health Care 1985: 1: 481-498. 25 ECRI. The third revolution in radiology: diagnostic imaging, digital radiography, NMR and PETT. Issues in Health Care Technology 9.1, 198 1. 26 Abrams H, Berne A, Dodd Get al. Magnetic resonance imaging. National Institutes ofHealth consensus development conference statement. Washington, DC: US Government Printing Offtce, 1987. 27 NEMT. The Collaborating Centre for Assessment of Medical Technology in the Nordic Countries. Magnetic resonance imaging in the Nordic countries. Stockholm: Spri, 1987. NEMT Report No. l/87. 28 National Health Technology Advisory Panel. Consensus statement on clinical efficacy of MRI imaging. Canberra: Australian Institute of Health, 1991. 29 Swiss Institute fo Public Health and Hospitals. Final report of the MRI-Consensus-Conference. Berne, 25-26 April 1989. 30 Cooper LS, Chalmers TC, McCally M, Berrier J, Sacks HS. The poor quality of early evaluations of magnetic resonance imaging. JAMA 1988; 259: 3277-3280. 3 1 Kent DL, Larson EB. Magnetic resonance imaging of the brain and spine. Is clinical efficacy established after the first decade. Ann Intern Med 1988; 108: 402-424. 32 Kent DL. Clinical efficacy of MR needs rigorous study. Diagn Imag 1990; 161: 69-71. 33 Hat&ton V, Rimm A, Sobocinski K et al. A blinded clinical comparison of MR imaging and CT in neuroradiology. Radiology 1986; 160: 751-755. 34 Bradley WG. Comparing costs and efficacy of MRL. AJR 1986; 146: 1307-1310. 35 Teasdale GM et al. Comparison of MRI and CT in suspected lesions in the posterior fossa. BMJ 1989; 299: 349-355. 36 Medic M, Masaryk R, Boumphrey F, Goormastic M, Bell G. Lumbar herniated disk disease and canal stenosis: prospective evaluation by surface coil MR, CT and myelography. Amer J Neuroradiol 1986; 7: 709-717. 37 Medic M, Masaryk R, Mulopulos G, Bundschuh C, Han J, Bolhman H. Cervical radiculopathy: prospective evaluation with surface coil MR imaging, CT with metrizamide, and metrizamide myelography. Radiology 1986; 161: 753-759. 38 Berkelbach van D, Sprenkel J, Mauser H et al. MRI in neurosurgical diagnosis and management of craniocervical junction and cervical spine pathology. Clin Nemo1 Neurosurgery 1986; 84: 245-251. 39 Peddecord KM, Janon EA, Robins JM. Substitution of magnetic resonance imaging for computed tomography. Int J Technol Assessm Health Care 1988; 4: 573-591. 40 Crues J, Mink J, Levy T, Lotysch M, Stoller D. Meniscal tears of the knee: accuracy of magnetic resonance imaging. Radiology 1987; 164: 445-448. 41 Manco L, Berlow M. Meniscal tears - comparison of arthrography, CT and MRI. Crit Rev Diagn Imaging 1989; 29: 151-179. 42 Piene H, Heggestad T, Skolbekken JA, Nilsen G. Medical consequences of MRI diagnosis. Presented at the 1990 meeting of the International Society for Technology Assessment in Health Care, Houston, May 21-23, 1990. 43 Evens R. Economic costs of nuclear magnetic resonance imaging. J Comput Assist Tomogr 1984; 3: 200-203.
EURRAD
Science Publishers
141-146
B.V. All rights reserved. 0720-048X/92/$05.00
141
00259
Technology assessment and diagnostic imaging H. David Banta Center for Medical Technology, TN0 Institute of Aging and Vascular Research, Leiden, The Netherlands
(Accepted
Key words: Technology
assessment,
radiology; Technology
6 November
assessment,
Introduction Societies all around the world are increasingly concerned about technology, including health care technology. As technology has become more pervasive, and its benefits and hazards more visible, governments have become more and more involved in attempts to influence technological change. [ 1,2]. One of those attempts has come to be known as technology assessment. In this paper, CT scanning and MRI scanning will be discussed to illustrate some aspects of health care technology assessment in the field of diagnostic imaging. What is technology assessment? Technology assessment is a comprehensive form of policy research that examines short- and long-term social consequences (for example, societal, economic, ethical, legal) of the application of technology [3,4]. The goal of technology assessment is to provide policy makers with information on policy alternatives, such as allocation of research and development funds, formulation of regulations, or development of legislation. Technology assessment, then, is action-oriented research whose aim is to change practices concerning technology [2]. Health care technology assessment, while a part of this broader field, also has differences. The first is based on the goal of health care: to improve health. Therefore, as it has developed, health benefits of technology has been the main focus of health care technology assessment, with increasing attention to financial costs over time. The main application of health care technology
Address for reprints: Prof. Dr. H. David Banta, CMT/TNO, Box 430, 2300 AD Leiden, The Netherlands.
P.O.
1991)
MRI; Magnetic resonance
imaging, technology
assessment
assessment has been to make specific decisions within specific policy areas, such as whether an insurance company will pay for a specific technology or a hospital will be given a license to provide a certain service. As the limitations of formal policies have become more and more apparent during the past decade, the field is also beginning to grapple with how to change clinical practice through information dissemination or other means. Efficacy (benefits) and safety are the basic starting points for evaluating the overall utility of a health care technology. Efficacy may be defined as the probability of benefit to individuals in a defined population from a health care technology applied for a given medical problem under ideal conditions of use [ 51. If a technology is not efficacious, it should not be used, and if its efficacy is unknown, statements about its overall value cannot be made. In addition, efficacy and safety data are needed to evaluate the cost-effectiveness of a technology. Neither the need for a technology nor its appropriate use can be established without good information on efficacy and safety. Another assessment problem concerns the appropriate number of any device, including any imaging device. Should there be one in every academic hospital? Should there be one in every casualty? Should every hospital have the device? Unfortunately, most original data is collected in university hospitals, and often has limited utility for answering questions related to nonuniversity hospitals. Technology assessment and policy making There are a variety of public policy mechanisms dealing with health care technology. Governments fund health-related research and development. Drugs are regulated for efficacy and safety. Medical devices are
142
sometimes regulated. Health planning mechanisms, such as licensing and regulation of facilities and technologies, have direct effects on health care institutions and technologies. And payment policy may be the most important determinant of technology use. Payment for health care services by sick funds and insurance companies means that people use technologies either free or at a small cost to themselves. This situation contributes to rapid and relatively uncontrolled proliferation of health care technology. Using technology assessment as an aid to decision making in these programs is a relatively new idea. Only in the area of drug regulation is evidence concerning the technology systematically collected and used as an important determinant of the decision. However, each policy mechanism, each regulation, each decision concerning payment and payment levels, could be improved by using the best available information on the technology [I]. The actual information needed varies from program to program. In the area of drug regulation, scientific evidence on safety and et& cacy is the main need; economic and social implications play relatively little part in the decisions. In regulation of facilities, efficacy and safety are important, but costs and efficiency are also key variables; cost-effectiveness analysis can be very helpful at this stage. In setting payment levels, the policy maker wants first to know that the technology works, and then would like to know how much it costs to provide the technology. Ideally, the payment level should be set rather close to the level of cost of providing the technology (in practice, the payment level is often set well above the cost of providing the technology, meaning that there is a large incentive to use the technology). One serious problem in using technology assessment as an aid to decision-making is that data from assessments is often not available when it is needed. Assessments are generally not done with strategic purposes in mind. Under an ideal model, all technologies would be tested for efficacy before they come into widespread use. They would then be tested in the emerging phase. In practice, that goal is only achieved in the area of drug regulation. Industry is required to produce the data on safety and efficacy. Otherwise, the testing of technologies for benefits by well-designed studies is done less often than desirable. This is shown by the lack of good information on the efficacy of specific technologies [5&l. Technology assessment and diagnostic imaging Diagnostic imaging has been subjected to intense scrutiny since the introduction of the CT scanner in
1972. At that time, relatively few assessment of diagnostic imaging had been done aside from assessments related to safety, especially in minimizing doses of ionizing radiation. Assessing diagnostic imaging was also seen as difficult from the beginning, because the impact of an image on health cannot be direct. The diagnosis must change therapy, and the therapy must be effective. These considerations led Fineberg et al. [7] to produce four (afterwards five) levels of evaluation for the efficacy of diagnostic imaging: (1) Technical evaluation: The technical output gives accurate information concerning the structure of the part of the body imaged; (2) Diagnostic accuracy: This output contains information that potentially improves the clinician’s ability to diagnose disease and assess the patient’s prognosisq; (3) Diagnostic impact: The information can alter plans for additional diagnostic tests, and (4) Therapeutic impact: The information can lead to changes in therapeutic plans for patients ; and Health impact: The end result may be improved (5) patient outcome. Prior to the mid-1970s, almost all assessments in the field of diagnostic imaging (or radiology) were at the first level. A few studies examined the diagnostic accuracy of specific imaging procedures by collecting data on their specificity and sensitivity. However, the field has developed rapidly since then, partially stimulated by demands from policy-makers and others for evidence of health impact, and a number of studies have been done assessing impact on diagnostic or therapeutic plans. It is now possible to develop decision rules for the use of diagnostic imaging in specific circumstances. For example, Harvard Medical School has published a useful book of such guidelines [8]. Technology assessment and CT scanning After its introduction in 1972, computed tomography (CT) scanning rapidly became the most visible technological advance in health care. As a complex, expensive device, it came to symbolize the problem of health care technology.’ The CT scanner is a device that uses X-rays, radiation sensors, a computer, and complex software to construct images of cross-sections of the body. A CT scanner that could only be used on the head was introduced to the international market in 1972 and began to diffuse rapidly into use. The Oflice of Technology Assessment (OTA) did one of its first health reports on this subject [9], using the Fineberg frame-
143
work to review the literature. The basic conclusion of the report was that “Well-designed studies of efficacy of CT scanners were not conducted before widespread diffusion occurred”. By the time of the report, 1978, it was known that CT scanners performed reliably and provided accurate diagnostic information. In addition, CT scanning was replacing other diagnostic tests, especially pneumoencephalography and cerebral arteriography. Little was known about how CT scanning affected the planning of therapy or patient health. The CT scanner was also an issue in Sweden. The first CT scanner was imported in Sweden in 1973. Swedish investigators carried out a cost-effectiveness analysis of CT scanning, based on its ability to replace other expensive diagnostic procedures. The study suggested that large hospitals could pay for a scanner out of replaced procedures [ lo]. Subsequently, large regional hospitals did buy CT scanners, but others were prudent. By May 1978, the United States had 4.8 scanners per million population, whereas Sweden had only 1.6 per million [ 111. In the United States, which had no effective planning mechanism, the OTA report had little impact on the situation with CT scanners. The scanner diffused very rapidly into practice. Another early experience with CT scanning was described from the United Kingdom [ 12,131. The Department of Health and Social Security (DHSS) was involved from an early stage in development of the CT scanner, since it provided prototype funds. The DHSS was quite restrictive toward purchases of the head scanner, and set up an explicit evaluation plan intended to guide policy. By 1978, the UK had 0.9 scanners per million population, compared to the 4.8 scanners in the United States. In the case of the body scanner, however, although the DH S S made a policy similar to that for the head scanner, scanners were taken up rapidly out of non-government funds, both endowment funds of institutions and private funds, such as those of donors. There were also explicit fund-raising drives by some hospitals [ 121. In the case of the body scanner, the strategy of restriction and assessment failed. One of the most interesting evaluations of CT scanning was developed by Fineberg et al. [ 71 and extended by Wittenberg and Fineberg [ 14,151. All physicians requesting a CT scan were asked to complete a questionnaire at the time of their request. The questionnaire asked three questions: (1) What diagnoses were considered, in probabilities? (2) What diagnostic tests would definitely be required and what tests would be required if no CT scanner were available? (3) What would the treatment plan be if the physician had no CT scanner available?. At the time of discharge of the patient, the physician was interviewed to ascertain
the diagnostic tests actually performed, treatments undertaken, and final diagnostic understanding of the case. In the lirst study [7] cranial CT was found to reduce other neurodiagnostic procedures by up to 73 y0 in the case of pneumoencephalograms, and lead to changes in therapy in 19% of cases. In later studies by Wittenberg and Fineberg [ 14,151 of body CT scanning, more extensive questionnaires were used. CT improved diagnostic understanding in 52% of patients, reassured the physician about previously planned therapy in 43 %, improved precision of previously planned treatment in 23x, and contributed to a change in therapy in 14% A number of other European countries developed standards for the number of CT scanners ‘needed’. The early standards were often based on information in the OTA report and the Swedish report. For example, in 1979 the French standard called for one CT scanner per million population [ 161. The standard in The Netherlands in 1979 called for 1 head scanner per 500,000 population [ 171. The case of the CT scanner has been visible in most countries of the world, including less developed countries. It has been a test of the new field. On the positive side, a number of useful reports and studies were carried out. The CT scanner probably has been studied more than any other health care technology. A number of countries did develop standards for the number of scanners that were effective in their planning programs. On the negative side, the CT scanner was seen as a prototype technology, whereas in fact it was one of the most expensive technologies in the medical marketplace. Lessons from the CT scanner did not readily transfer to other technologies. An important aspect of the CT scanner, however, was that it did demonstrate clearly that technology developing in one country, the United Kingdom in this case, could rapidly diffuse over the entire world. The result was that technology assessment was seen as having an important international dimension from its beginnings. Today, CT scanning is fully accepted as a fundamental diagnostic tool in many conditions. Its purchase is no longer regulated in the Netherlands Technology assessment and magnetic resonance imaging Magnetic resonance imaging (MRI), sometimes called nuclear magnetic resonance (NMR) is an imaging device that was introduced in the late 1970s and is now rapidly spreading into use as a diagnostic tool [ 18-221. NMR is projected to diffuse at a rapid rate through-out the world, with an increase in the market
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size of 90% per year, almost a doubling. One reason this rapid diffusion is a concern is because of the high cost of MRI units, more than 2 million guilders for the least expensive device. MRI produces images of cross-sections of, the human body similar to those produced by computed tomography (CT) scanning [23]. There are important differences, however. A CT scanner depicts the X-ray opacity of structure of the body. MRI images depict the density or even the chemical environment of hydrogen atoms [24]. These properties of parts of the body are not necessarily correlated. MRI has several advantages. It gives a high contrast sensitivity in its images. It does not employ ionizing radiation as CT scanning and other imaging methods do. It is not necessary to inject potentially toxic contrast agents, as is often done with CT scanning (although contrast agents are being used more and more frequently with MRI scanning). MRI allows choice of different imaging planes without moving the patient; CT scanning can only produce an image of one plane at a time, and some planes are not possible. Finally, images can be obtained from areas of the body where CT scanning fails to produce clear images. It may be that an MRI scan can replace many diagnostic laboratory tests in the future [25]. Despite this great potential, a technology must be assessed in reality. One can ask such questions as these: Is present MRI an advance in imaging technology as compared with (say) CT scanning? Does it produce useful information at a reasonable cost? Does it produce diagnostic information not otherwise available? Technology assessment and MRI imaging MRI imaging has been repeatedly assessed since its introduction. One of the early reports was done by the Dutch Health Council (Gezondheidsraad) [ 181. It has been assessed by several groups in the US [20,23, 25-261 and has also been formally assessed in the Nordic countries [27], in Australia [28] and in Switzerland by means of a consensus conference [29]. There is widespread agreement that MRI is a reliable diagnostic device that produces information that can be quite useful at times. Its potential advantages over other modalities such as CT scanning include: MRI is able to distinguish between various normal and abnormal tissues. Blood flow, circulation of the cerebrospinal fluid and the contraction and relaxation of organs can be assessed. Since the compact bone emits no signal, tissues surrounded by bone (e.g. the contents of the posterior cranial fossa and of the vertebral canal) can
be represented without disturbance by artifacts [29]. MRI also has the advantage of easy selection of planes, which is particularly useful when imaging the spine and spinal canal. Thus, despite the fact that MRI images contain artifacts that can be confusing and that require expertise to interpret, MRI can be said to produce information that is useful for the diagnostic process. However, this is not sufficient for answering practical questions such as the following: Which patients should be scanned with MRI, and which with other diagnostic modalities (in other words, where does MRI have real advantages in making diagnosis). Which conditions that can be diagnosed by MRI can also be effectively treated? What is the place of MRI in relation to other diagnostic imagsuch as CT, nuclear medicine, ing modalities ultrasound, and conventional X-ray. For example, a literature review published in 1988 [ 301 found that 54 evaluations did poorly when rated by commonly-accepted scientific standards such as use of a ‘gold standard’ comparison of blinded readers of the images (the expert doing the reading did not know the status of the patient). Only one article had a prospective design. Also, over the period examined, there was no improvement in quality of research over time. Kent et al. pointed to a continuing problem in later articles [31,32]. A recent review done by the author shows no change in this situation. The most thorough literature review was by Kent et al. [ 3 11. The literature showed that MRI is probably superior to computed tomography, its main competitor, for detection and characterization of posterior fossa (brain) lesions and spinal cord myelopathies, imaging in multiple sclerosis, detecting lesions in patients with refractory partial seizures, and detailed display for guiding complex therapy, as for brain tumors. In other diseases, the efficacy of MRI was found to be similar to computed tomography. In fact, the best designed study, carried out in a heterogenous group of patients in neuroradiology, studied in a matched pair design, found that sensitivity and specificity of CT scanning were somewhat better than that of MRI [33]. More recent literature does not contain articles refuting these conclusions. As for diagnostic or therapeutic impact, little information is available. For diagnostic purposes, brain imaging is by far the most frequent use of MRI. For example, Bradley [ 341 found that more than 65% of scans were of the brain, and between 10 and 20% of the spine. MRI does not appear to have replaced other modalities such as CT scanning in the brain except that it is used preferentially in suspected posterior fossa tumors. In a prospective randomized study in patients
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with suspected posterior fossa tumors, Teasdale et al. [ 351 found that in groups of about 500 patients each, 93 of those who had CT first were referred subsequently for MRL, whereas only 28 of those who had MRI first were then referred for a CT scan. In the spinal cord, two studies have examined the relative accuracy of MRI in relation to myelography and computed tomography [36,37]. The studies found that MRI and CT were roughly equivalent in terms of true positive results, but that both were superior to myelography. Several studies have indicated that MRI may replace CT scanning and myelography in scanning of the spine [36,38]. Peddecord et al. [39] found that MRI gradually replaced both CT scanning and myelography. In their study, the percentage of physicians ordering myelography prior to MRI dropped from 15 % to zero during the 2 year period of their study. This could be significant, since myelography is a risky procedure. Another area where MRI could be quite useful is in imaging joints. A common problem is torn or damaged menisci (cartilages) of the knee. The standard diagnostic procedure is either arthroscopy by scope or arthogram, an X-ray procedure. Both are invasive, in that the scope must be inserted into the joint or a contrast material must be injected. MRI is noninvasive. Crues et al. [40] found that, for more serious meniscal tears, the false-negative rate of MRI was 6 %, a figure comparing favorably with the alternatives. Manco and Berlow [41] reported similar findings. However, the advantage of arthroscopy is that a therapeutic procedure can be done if an abnormality is found. One study has been carried out in Norway, using the Wittenberg/Fineberg method [ 421. The investigators found that 33% of patients had their main diagnosis changed by MRI scanning. Plans for surgery changed in 20% of the patients, and plans for radiotherapy changed in 8% of patients. Costs of MRI The capital cost of an MRI scanner varies greatly, depending particularly on the strength of the magnets. A basic unit costs at least 2 million guilders. Evens [43] reported survey results that found that operating an MRI facility in the United States cost US$840,000 a year. Bradley [ 341 reported that the costs of operating two MRI facilities varied from US$841,000 to US$1,115,000 per year. It is worth noting that only about one-third of this operating cost is accounted for by the capital investment in the MRI scanner. Other expenses include space, personnel, equipment and maintenance. The cost per scan in Bradley’s two centers was between US$370 and
US$550, and the fee for the scan was US$500. The costs apparently do not include the payment to the physician. Bradley [ 341 comments on the possibility that costs will be offset by replacement of other diagnostic procedures, particularly myelography. Invasive diagnostic procedures such as myelography must be done with a hospitalization of at least one day, whereas MRI can be done on an out-patient basis. The author made rough estimates of the number of cases of specific disease problems in the Netherlands that might be imaged with MRI. Important disease problems and number of cases include: Brain tumors 850 Tumors of the spinal cord 70 Multiple sclerosis 400 Herniated nucleus pulposis 22000 Torn meniscus 3735 It can readily be seen that the potential for MRI scanning in terms of numbers is with herniated nucleus pulposis (‘herniated disk’) and torn meniscus. Otherwise, the national demand for MRI scanning can readily be met by existing units in university hospitals. Discussion Diagnostic imaging makes up about 5% of the national health expenditure in industrialized countries. This 5% is highly visible, and diagnostic imaging has been perhaps more subject to regulation than any other area of medicine. This scrutiny will continue. In The Netherlands, as in most industrialized countries, hospital budgets are now tightly constrained. This means that each new purchase must compete with other alternatives. It is probably a frequent occurrence that imaging departments must choose between several possible purchases. Thus, technology assessment may become more useful at the hospital level than at the national policy level. The main problem with the field of technology assessment remains the poor quality of primary data. Technology assessment reports are usually based on syntheses of available scientific information, with an input of judgment and clinical experience. Without good data, the usefulness of the field will be limited. References 1 Banta HD, Behney CJ. Policy formulation and technology assessment. Milbank Memorial Fund Quaterly/Health and Society 1981; 59: 445-479. 2 Banta HD, Behney CJ, Willems JS. Toward rational technology in medicine. New York: Springer, 1981. 3 Ofice ofTechnology Assessment. Development of medical tech-
146 nology: opportunities for assessment. Washington, DC: US Government Printing Office, 1976. 4 Office of Technology Assessment. Strategies for medical technology assessment. Washington, DC: US Government Printing Office, 1982. 5 Office of Technology Assessment. Assessing the efficacy and safety of medical technologies. Washington, DC: US Government Printing Office, 1978. 6 Institute of Medicine. Assessing medical technologies. Washington, DC: National Academy Press, 1985. 7 Fineberg HV, Bauman R, Sosman M. Computerized cranial tomography. Effect on diagnostic and therapeutic plans. JAMA 1917; 238: 224-221. 8 McNeil B, Abrams H eds. Brigham and Women’s Hospital handbook of diagnostic imaging. Boston: Little, Brown and Company, 1986. 9 Office of Technology Assessment. Policy implications of the computed tomography (CT) scanner. Washington, DC: US Government Printing Office, 1978. 10 Jonsson, E. Studies in health economics. Stockholm: The Economic Research Institute, Stockholm School of Economics, 1980. 11 Gaensler EHL, JHL, Jonsson E, Neuhauser D. Controlling medical technology in Sweden. In: Banta D, Kemp K eds. The management of health care technology in nine countries. New York: Springer Publishing Company, 1982: 167-192. 12 Stocking B. The image and the reality: a case study of the impacts of medical technology. London: Nuffteld Provincial Hospitals Trust, 1978. 13 Stocking B. The management of medical technology in the United Kingdom. In: Banta D, Kemp K, eds. The management of health care technology in nine countries. New York: Springer, 1982; 10-27. 14 Wittenberg J, Fineberg HV, Black EB, Kirkpatrick RH, Schaffer DL, Ikeda MK, Ferruci JT. Clinical efficacy of computed body tomography. AJR 1978; 131: 5-14. 15 Wittenberg J, Fineberg HV, Ferruci JT, Simeone JF, Mueller PR, Van Sonnenberg E, Kirkpatrick RH. Clinical efficacy of computed body tomography, II. AJR 1980; 134: 111 l-1120. 16 Fuhrer R. Policy for medical technology in France. In: Banta D, Kemp K, eds. The management of health care technology in nine countries. New York: Springer, 1982: 100-126. 17 Groot LMJ. Medical technology in the health care system of the Netherlands. In: Banta D, Kemp K, eds. The management of health care technology in nine countries. New York: Springer, 1982: 150-166. 18 Gezondheidsraad. NMR - vorming en opleiding. Den Haag. 13 July 1985. 19 Luiten AL. The birth and development of an innovation: the case of magnetic resonance imaging. In: FFH Rutten, SJ Reiser eds. The economics of medical technology. Berlin: Springer-Verlag, 1988; 99-108. 20 National Center for Health Services Research and Health Care Technology Assessment. Magnetic resonance imaging. Health Technology Assessment Reports, No 13. Rockville, MD: US Public Health Service, 1985. 21 Steinberg EP, Sisk JE. Locke KE. The diffusion of magnetic resonance imagers in the United States and worldwide. Int J Technol Assessm Health Care 1985; 1: 499-514. 22 Wing WS, Tsurude JS, Kortinan KE, Bradley WG. Practical MRI. Rockville, MD: Aspen, 1987. 23 Offtce of Technology Assessment. Nuclear magnetic resonance imaging technology, a clinical industrial, and policy analysis.
Health Technology Case Study 27. Washington, DC: US Government Printing Office, 1984. 24 Iezzoni LI, Grad D, Mostowitz MA. Magnetic resonance imaging: overview of the technology and medical applications. Int J Technol Assessm Health Care 1985: 1: 481-498. 25 ECRI. The third revolution in radiology: diagnostic imaging, digital radiography, NMR and PETT. Issues in Health Care Technology 9.1, 198 1. 26 Abrams H, Berne A, Dodd Get al. Magnetic resonance imaging. National Institutes ofHealth consensus development conference statement. Washington, DC: US Government Printing Offtce, 1987. 27 NEMT. The Collaborating Centre for Assessment of Medical Technology in the Nordic Countries. Magnetic resonance imaging in the Nordic countries. Stockholm: Spri, 1987. NEMT Report No. l/87. 28 National Health Technology Advisory Panel. Consensus statement on clinical efficacy of MRI imaging. Canberra: Australian Institute of Health, 1991. 29 Swiss Institute fo Public Health and Hospitals. Final report of the MRI-Consensus-Conference. Berne, 25-26 April 1989. 30 Cooper LS, Chalmers TC, McCally M, Berrier J, Sacks HS. The poor quality of early evaluations of magnetic resonance imaging. JAMA 1988; 259: 3277-3280. 3 1 Kent DL, Larson EB. Magnetic resonance imaging of the brain and spine. Is clinical efficacy established after the first decade. Ann Intern Med 1988; 108: 402-424. 32 Kent DL. Clinical efficacy of MR needs rigorous study. Diagn Imag 1990; 161: 69-71. 33 Hat&ton V, Rimm A, Sobocinski K et al. A blinded clinical comparison of MR imaging and CT in neuroradiology. Radiology 1986; 160: 751-755. 34 Bradley WG. Comparing costs and efficacy of MRL. AJR 1986; 146: 1307-1310. 35 Teasdale GM et al. Comparison of MRI and CT in suspected lesions in the posterior fossa. BMJ 1989; 299: 349-355. 36 Medic M, Masaryk R, Boumphrey F, Goormastic M, Bell G. Lumbar herniated disk disease and canal stenosis: prospective evaluation by surface coil MR, CT and myelography. Amer J Neuroradiol 1986; 7: 709-717. 37 Medic M, Masaryk R, Mulopulos G, Bundschuh C, Han J, Bolhman H. Cervical radiculopathy: prospective evaluation with surface coil MR imaging, CT with metrizamide, and metrizamide myelography. Radiology 1986; 161: 753-759. 38 Berkelbach van D, Sprenkel J, Mauser H et al. MRI in neurosurgical diagnosis and management of craniocervical junction and cervical spine pathology. Clin Nemo1 Neurosurgery 1986; 84: 245-251. 39 Peddecord KM, Janon EA, Robins JM. Substitution of magnetic resonance imaging for computed tomography. Int J Technol Assessm Health Care 1988; 4: 573-591. 40 Crues J, Mink J, Levy T, Lotysch M, Stoller D. Meniscal tears of the knee: accuracy of magnetic resonance imaging. Radiology 1987; 164: 445-448. 41 Manco L, Berlow M. Meniscal tears - comparison of arthrography, CT and MRI. Crit Rev Diagn Imaging 1989; 29: 151-179. 42 Piene H, Heggestad T, Skolbekken JA, Nilsen G. Medical consequences of MRI diagnosis. Presented at the 1990 meeting of the International Society for Technology Assessment in Health Care, Houston, May 21-23, 1990. 43 Evens R. Economic costs of nuclear magnetic resonance imaging. J Comput Assist Tomogr 1984; 3: 200-203.
