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hundreds of patients with pathological verification are needed to show a statistically significant difference. Size of the sample needed rapidly approaches 1000 as concern for the magnitude of false-positive and falsenegative errors becomes as important as concern for absolute accuracy.

THE INSITUTE of Medicine Report

A recent study of CT by the Institute of Medicine, sponsored by the Blue Cross Association, was designed to "review what is currently known about that matter [efficacy, cost and level of reimbursement, placement and implementation of CT scanners] and to develop a policy statement" with appropriate recommendations. 162 The study group found that information and recommendations on costs, levels of reimbursement, placement and implementation of CT scanners were relatively easy to determine. On the other hand, data on efficacy were at best fragmentary.

The committee consequently perceived CT as a diagnostic instrument of great promise, but one that had not been subjected to rigorous, controlled, prospective studies. Its primary findings were based on clinical studies reported in the current literature, which focused almost entirely on diagnostic accuracy as an end point. At the same time, it recognized the limitations of this end point as the sole criterion of efficacy. The committee expressed its ambivalence in a concluding statement:

...the committee can reach two different sets of conclusions about efficacy at the level of diagnostic impact. The first would be based on existing standards of clinical evidence evaluated by the expert judgment of leaders in the field.... The second type of evidence would require clinical trials meeting high standards of experimental design and statistical significance....

...The first standard would call for a finding of diagnostic efficacy for CT scanning in the head and for a number of indica tions in the body. The second standard would find the results still inconclusive. The logical policy conclusion based on the first standard would be to recommend reimbursement for those uses found efficacious. The conclusion based on the second standard would be that the procedures are still experimental and should be supported only in settings that are part of a clinical trial leading to more definitive evidence.......

The committee chose the first standard as the basis of its final recommendation and strongly endorsed reimbursement for CT scanning of both the head and body when appropriately used by installations acquired under a certificate of need.

The conclusions presumably reflected a compromise between the "producers" on the committee those using CT in day-to-day practice and the "consumer representatives" those viewing new technologies in relation to the rising cost of health care. Most observers would agree that the clinical evidence is sufficiently compelling to accept the critical role of cerebral CT in the detection and differential diagnosis of tumor, trauma and intracranial hemorrhage, abscess, stroke and hydrocephalus. In many intracranial conditions, such as cerebrovascular disease, the initial diagnostic method — the skull film —

Feb. 9, 1978

yields little diagnostic information. The radioisotope scan occupies the same screening echelon as CT, but is less commonly required when CT is available. Because of the lack of efficacy of skull films, CT is in effect a primary imaging approach to intracranial disease. With its high information yield, however, it may also represent the definitive diagnostic method.

In sharp contrast to brain CT, CT of the abdomen rarely occupies the primary diagnostic echelon. The major application of abdominal CT is in mass lesions suspected or detected: the location and volume; the texture, whether cystic or solid; the relation to other viscera; the presence of additional lesions; the depth of the lesion for biopsy; and the effect of therapy. Such imaging examinations as abdominal films, the gastrointestinal series, the barium enema, the gallbladder series and the intravenous urogram are generally used first for “screening" purposes and are then clarified by use of other examinations such as the intravenous cholangiogram, radionuclide studies,* ultrasound studies* and CT studies. Further definition and greater specificity may result from angiography and other invasive procedures. In body CT, "clinical trials meeting high standards of experimental design" remain to be performed to provide further evidence of efficacy and to place CT in perspective relative to competing imaging methods. 19

CONCLUSIONS

Computed tomography is an innovative contribution to medical diagnosis and represents the most important technical development in diagnostic radiology since the introduction of image amplification. CT of the brain is a primary diagnostic modality for disease of the central nervous system, the clinical usefulness of which has been widely demonstrated. Its information yield is sufficiently high so that it may obviate the need for secondary, more invasive diagnostic procedures. CT of the body is a second-level diagnostic approach to viscera and anatomic areas for which many effective imaging technics are already available. Its contribution to medical diagnosis beyond that of competing imaging technologies has not yet been fully established, perhaps partially because the latest advances in CT have not been fully documented in the literature. CT will probably have a major role, particularly in oncologic disease, but its incremental information gain is not yet defined.

Acceptable evidence of the efficacy of CT and in particular of its marginal contribution to diagnosis, its effect on the cost of medical care, on short-term health outcomes and on long-term health outcomes is not available. Acquisition of such data requires careful prospective studies in which the contribution of CT is clearly related to that of competing methods and the impact of additional diagnostic information is documented.

*The sequence of ultrasound and radionuclide examinations may vary, and in many situations, in fact, they are used for "screening" purposes.

We are indebted to Mrs. Sally Edwards and Miss Katherine Arnoldi for assistance and to members of the Harvard Medical School-Peter Bent Brigham Hospital-Sidney Farber Cancer Institute Department of Radiology for help in conveying their perspective on the potential role of CT in diagnostic medicine.

REFERENCES

95. Stanley RJ, Sagel SS, Levitt RG: Computed tomography of the body. early trends in application and accuracy of the method. Am J Roentgenol 127:53-67, 1976

96. Sagel S, Stanley RJ, Evens RG: Early clinical experience with motionless whole-body computed tomography. Radiology 119:321-333, 1976 97. Muhm JR, Brown LR, Crowe JK: Detection of pulmonary nodules by computed tomography. Am J Roentgenol 128:267-270, 1977

98. Kreel L: Computerized tomography using the EMI general purpose scanner. Br J Radiol 50:2-14, 1977

99. Muhm JR, Brown LR, Crowe JK: Use of computed tomography in the detection of pulmonary nodules. Mayo Clin Proc 52:345-348, 1977 100. Schaner EG, Chang AE, Doppman JL, et al: Comparison of computed and conventional whole lung tomography in the detection of pulmonary metastases. J Comput Assist Tomogr 1:363, 1977

101. Alfidi RJ, Haaga J, Meaney TF, et al: Computed tomography of the thorax and abdomen: a preliminary report. Radiology 117:257-264, 1977

102 Kreel L: The EMI whole body scanner in the demonstration of lymph node enlargement. Clin Radiol 27:421-429, 1976

103. Hessel SJ, Adams DF, Judy PF, et al: Computed axial tomography of the ischemic heart. Radiology (in press)

104. Gray WR Jr, Parkey RW, Buja LM, et al: Computed tomography: in vitro evaluation of myocardial infarction. Radiology 122-511-513, 1977

105. Wittenberg J. Powell WJ Jr, Dinsmore RE, et al: Computerized tomography of ischemic myocardium: quantitation of extent and severity of edema in an in vitro canine model. Invest Radiol 12:215-223, 1977 106. Miller SW, Dinsmore RE, Wittenberg J, et al: Right and left ventricular volumes and wall measurements: determination by computed tomography in arrested canine hearts. Am J Roentgenol 129:257-261, 1977

107. Sagel SS, Weiss ES, Gillard R, et al: Gated computed tomography of the heart. Proceedings of the twenty-fourth annual meeting of the Association of University Radiologists, Kansas City, Missouri, 1977 108. Stephens DH, Sheedy PF II, Hattery RR, et al: Computed tomography of the liver. Am J Roentgenol 128:579-590, 1977 109. Levitt RG, Sagel SS, Stanley RJ, et al: Accuracy of computed tomography of the liver and biliary tract. Radiology 124:123-128, 1977 110. Alfidi RJ. Haaga JR, Havrilla TR, et al. Computed tomography of the liver. Am J Roentgenol 127:69-74, 1976

III. Bryan PJ, Dinn WM, Grossman ZD, et al: Correlation of computed tomography, gray scale ultrasonography, and radionuclide imaging of the liver in detecting space-occupying processes. Radiology 124:387393, 1977 112. Stanley R. Sagel S: Evaluation of the liver and pancreas with computed tomography: early results. Proceedings of the Conference on Computed Tomography in Radiology, St Louis, 1976, pp 79-85 113. Petasnick JP, Clark JW: Computed tomography of the abdomen: initial experience. Gastrointest Radiol 1:201-208, 1976 114. Allidi RJ: Computerized tomography of the gallbladder and biliary tract a preview, Roentgenology of the Gallbladder and Biliary Tract. Edited by B Felson. New York, Grune & Stratton, 1976 115. Kressel HY, Korobkin M, Goldberg HI, et al: The portal venous tree simulating dilated biliary ducts on computed tomography of the liver. J Comput Assist Tomogr 1:169-175, 1977

116 Havrilla TR, Haaga JR, Alfidi RJ, et al. Computed tomography and obstructive biliary disease. Am J Roentgenol 128:765-768, 1977 117. Taylor KJW, Rosenfield AT: Grey-scale ultrasonography in the dif ferential diagnosis of jaundice. Arch Surg 112:820-825, 1977 118. Bartrum RJ Jr, Crow HC, Foote SR: Ultrasonic and radiographic cholescystography. N Engl J Med 296:538-541, 1977

119. Hanga JR, Alfidi RJ, Zelch MG, et al: Computed tomography of the pancreas. Radiology 120:559-595, 1976

120. Haaga JR, Alfidi RJ, Macintyre WJ, et al: CT longitudinal scan. Am J Roentgenol 127:1059-1060, 1976

121. Wiggans G, Schein PS, MacDonald JS, et al: Computerised axial tomography for diagnosis of pancreatic cancer. Lancet 2.233-235, 1976 122. Stanley RJ, Sagel SS, Levitt RG: Computed tomographic evaluation of the pancreas. Radiology 124:715-722, 1977

123. Huuga JR, Alfidi RJ, Havrilla TR, et al: Definitive role of CT scan. ning of the pancreas; the second year's experience. Radiology 124:723730, 1977

124. Sheedy PF II, Stephens DII, Hattery RR, et al: Computed tomogra phy in the evaluation of patients with suspected carcinoma of the pancreas. Radiology 124:731-737, 1977

124a. Barkin J, Vining D, Miale A Jr, et al. Computerized tomography, diagnostic ultrasound, and radionuclide scanning: comparison of efficacy in diagnosis of pancreatic carcinoma. JAMA 238 2040-2042, 1977 125. DiMagno EP, Malagelada J-R, Taylor WF, et al: A prospective comparison of current diagnostic tests for pancreatic cancer. N Engl J Med 297:737-742, 1977 126. Haaga JR, Alfidi RJ, Havrilla TR, et al: CT detection and aspiration of abdominal abscesses. Am J Roentgenol 128:465-474, 1977 127. Cooperman AM, Haaga J, Alfidi R, et al: Computed tomography: a valuable aid to the abdominal surgeon. Am J Surg 133:121-126, 1977 128. Reich NE, Seidelmann FE: Computed tomography of the total body. II. The abnormal scan. J Am Osteopath Assoc 75:651-657, 1976 129. Sagel SS, Stanley RJ, Levitt RG, et al: Computed tomography of the kidney. Radiology 124:359-370, 1977

130. Stephens DH, Hattery RR, Sheedy PF II: Computed tomography to the abdomen: carly experience with the EMI body scanner. Radiology 119:331-335, 1976

131. Mitty HA: Computerized tomography, sonography and angiography in the evaluation of adrenal tumors, Proceedings of the fourth annual meeting of the Society of Cardiovascular Radiology, Los Angeles, California, 1977

132. Haaga JR, Zelch MG, Alfidi RJ, et al: CT-guided antegrade pyelography and percutaneous nephrostomy. Am J Roentgenol 128:621-624, 1977

133. Redman HC, Glatstein E, Castellino RA, et al: Computed tomography as an adjunct in the staging of Hodgkin's disease and non-Hodgkin's lymphomas. Radiology 124:381-385, 1977

133a. Breiman RS, Castellino RA, Harrell GS, et al: CT-pathologic correlations in Hodgkin's disease and non-Hodgkin's lymphoma. Radiology 126:159-166, 1978

134. Harrell GS: Computed tomography in Hodgkin's disease and nonHodgkin's lymphoma. Med Imag 2:31-32, 1977

135. Schaner EG, Head GL, Doppman JL, et al: Computed tomography in the diagnosis, staging, and management of abdominal lymphoma. J Comput Assist Tomogr 1:176-180, 1977

136. Boldt DW, Reilly BJ: Computed tomography of abdominal mass lesions in children: initial experience. Radiology 124:371-378, 1977 137. Whalen JP, Watson RC: The potential role of computerized tomogra phy in bone diseases, Proceedings of the Conference on Computerized Tomography in Radiology, St Louis, 1976, pp 25-28 138. Weinstein MA, Rothner AD, Duchesneau P, et al: Computed tomography in diastematomyelia. Radiology 118.609-611, 1975 139. Grossman ZD, Wistow BW, Wallinga HA, et al: Recognition of vertebral abnormalities in computed tomography of the chest and abdomen. Radiology 121:369-373, 1976

140. Reich NE, Seidelmann FE, Tubbs RR, et al: Determination of bone mineral content using CT scanning. Am J Roentgenol 127:593-594, 1976

141. Isherwood I, Rutherford RA, Pullan BR, et al: Bone-mineral estimation by computer-assisted transverse axial tomography. Lancet 2:712715, 1976

142. Rüegsegger P, Elsasser U, Anliker M, et al: Quantification of bone mineralization using computed tomography. Radiology 121:93-97,

1976

143. Carter BL, Kahn PC, Wolpert SM, et al: Unusual pelvic masses; a comparison of computed tomographic scanning and ultrasonography. Radiology 121:383-390, 1976

144. Alfidi RJ, Macintyre WJ, Meaney TF, et al. Experimental studies to determine the application of CAT scanning to the human body. Am J Roentgenol 124:199-207, 1976

145. Reese DF, Carney JA, Gisvold JJ, et al: Computerized reconstructive tomography applied to breast pathology. Am J Roentgenol 126:406412, 1976

146. Gisvold JJ, Karsell PR, Reese DF, et al. Clinical evaluation of computerized tomographic mammography. Mayo Clin Proc 52:181-185, 1977

147. Shapiro S, Strax P, Venet L: Periodic breast cancer screening in reducing mortality from breast cancer. JAMA 215:1777-1785, 1971 148. Reese DF, Gisvold J, Kaivell P, et al: Computerized breast tomogra phy, Proceedings of the American College of Radiology Conference, 1976

149. Gomes MN: ACTA scanning in the diagnosis of abdominal aortic aneurysms. Comput Tomogr 1:51-61, 1977

150. Axelbaum SP. Schellinger D. Gomes MN, et al: Computer tomographic evaluation of aortic aneurysms. Am J Roentgenol 127.75-78, 1976

151. Twigg HL, Axelbaum SP. Schellinger D: Computerized body tomog raphy with the ACTA scanner. JAMA 234:314-317, 1975

152. Haaga JR, Alfidi RJ: Precise biopsy localization by computed tomography. Radiology 118:603-607, 1976

153. Holm H, Pedersen JF, Kristensen JK, et al: Ultrasonically guided

318

percutaneous puncture. Radiol Clin North Am 13:493-504, 1975 154. McAfee JG: Complications of abdominal aortography and arteriography, Angiography. Third edition. Edited by HL Abrams. Boston, Little, Brown, 1971, pp 717-728

155. Jelden GL, Chernak ES, Rodriguez-Antunez A, et al: Further progress in CT scanning and computerized radiation therapy treatment planning. Am J Roentgenol 127:179-185, 1976

156. Wittenberg J, Fineberg HV, Ikeda MK, et al: The influence of computed body tomography on medical decision making: a pilot project. J Comput Assist Tomogr 1:361-362, 1977

157. Goitein M, Wittenberg J, Ferrucci J, et al: Prospective study of the value of CT scanning in radiation therapy treatment planning. J Comput Assist Tomogr 1:372, 1977

157a. Stewart JR, Simpson LD: Computed tomography and the quality of radiation therapy. Am J Roentgenol 129:943-944, 1977

Feb. 9, 1978

158. McNeil BJ, Collins JJ Jr, Adelstein SJ: Rationale for seeking occult metastases in patients with bronchogenic carcinoma. Surg Gynecol Obstet 144:389-393, 1977

159. Bishop JE: Maker of computerized x-ray scanners says they sharply cut diagnostic costs. Wall Street Journal, July 26, 1977

159a. Gempel PA, Harris GH, Evens RG: Comparative Cost Analysis: Computed tomography vs. alternative diagnostic procedures, 19771980. Cambridge, Massachusetts, Arthur D Little, Inc, 1977 160. Swets JA: The relative operating characteristic in psychology. Science 182:990-1000, 1973

161. McNeil BJ, Weber E, Harrison D, et al: Use of signal detection theory in examining the results of a contrast examination: a case study using the lymphangiogram. Radiology 123.613-617, 1977 162. Institute of Medicine: Computed Tomographic Scanning. Washington, DC, National Academy of Sciences, 1977