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CT of the spine: Are plain spine radiographs necessary?
clinical Radiology (1990) 41, 317-320
CT of the Spine: Are Plain Spine Radiographs Necessary? B. M. TRESS and W. S. C. HARE
The University of Melbourne, Department of Radiology, Victoria, Australia
This study was designed to determine whether plain radiographs added any information of clinical significance to the information provided by CT (computed tomography) and its standard digital radiographs in 100 patients presenting for C T of the lumbar spine and 46 patients presenting for cervical spine CT. In only three (3%) of the lumbar studies and two (4.3%) of the cervical studies did the plain radiographs add diagnostic information. The added diagnostic information did not affect patient management in all cases with indications other than trauma. Good quality oblique cervical spine digital radiographs were obtained in 10 cases simply by moving the tube and detectors to the 45 ° arid 135 ° azimuths. The evidence from this study suggests that when a CT examination of lumbar or cervical spines is planned on a high resolution CT scanner for indications other than trauma, a conventional plain radiographic examination can be omitted in the first instance.
Computed tomographic scans performed by modern high resolution CT scanners are preceded by a computed digital radiograph generated by the scanner. The digital radiograph is primarily used for prescribing the exact levels and extent of subsequent scans. The diagnostic quality of the digital radiograph has progressively improved as high resolution CT scanners have been developed. It has always been considered that plain radiographs are mandatory in any radiological evaluation of the spine. The purpose of this study was to determine whether plain radiographs added any information of clinical significance to the information provided by the digital radiographs and CT studies in patients presenting for CT examinations of cervical and lumbar spines.
were performed routinely prior to the CT study (Fig. 1). These were not magnified, no oblique projections were performed and the normal windows for the digital radiograph (window width 500, window level 200-300) were not varied. All the scans and digital radiographs were performed upon a GE 9800 CT scanner. The indications for the CT studies are shown in Tables 1 and 2. The findings of the digital radiograph and the CT studies were separately tabulated by the staff radiologist on duty for CT at the time of the examination. The plain film series was then evaluated. The number of cases in which the plain film series provided the same information as the digital radiograph, more information than the digital radiograph and more information than the digital radiograph and CT study combined was noted. Oblique digital radiographs were obtained of 10 patients presenting for cervical spinal CT by simply moving the tube and detectors to the 45 ° and 135° azimuths (or positions). The images were enlarged for hard copying (Fig. 2). Contrast and density were varied using the window width and level controls to allow adequate demonstration of the lower cervical spine and cervico-dorsal junction (Fig. 3). RESULTS The digital radiograph alone provided as much diagnostic information as the lumbosacral spine series in 91% of cases. In 9% of cases the digital radiographs provided
MATERIALS AND METHODS The patient sample consisted of 100 consecutive patients who had plain lumbosacral spine radiography performed before presenting for lumbar spinal CT and 46 patients who had a cervical spine series before presenting for cervical spine CT. The majority of the cervical spine referrals were from private practice physicians outside the hospital. The lumbosacral spine series consisted of a minimum of two antero-posterior and two lateral spine radiographs, including the entire lumbar and sacral regions. The minimal cervical spine series consisted of an antero-posterior, lateral and two oblique plain radiographs. Antero-posterior and lateral digital radiographs Correspondence to: Professor B. M. Tress, The University of Melbourne, Department of Radiology, The Royal Melbourne Hospital, 3050 Victoria, Australia.
(a)
(b)
Fig. 1 - Patient with residual ependymoma after laminectomy at L3 and L4 levels. Lateral (a) and antero-posterior (b) digital radiographs, clearly demonstrating laminectomy and scalloped posterior margins of L3 and L4.
318
CLINICALRADIOLOGY
Table 1 - Indications for CT of lumbar spine
Indication
Number
Sciatica Claudication of cauda equina Back pain Probable metastases Trauma Osteomyelitis Total
(%)
54 17 10 9 7 3
54 17 10 9 7 3
100
100
Table 2 - Indications for CT of cervical spine
Indication
Number
(%)
Spondylotic cord compression Trauma Radiculopathy Other
19 13 11 3
42 28 24 6
Total
46
100
less information than the lumbosacral spine series, even in retrospect. These cases included lesions such as congenitally absent pedicle, laminectomy and pars defects. However, in only 3 % of cases did the digital radiographs and CT scans together fail to show abnormalities demonstrated by the lumbosacral spine radiographs (Tables 3 and 4). In one case the lumbar spine series showed that there were five lumbar type discs instead of six because hypoplastic ribs had not been detected on the digital radiograph. Single cases of slight retrolisthesis and spondylolisthesis were not detected by digital radiography and CT scan. In only 37% of cases did the routine digital radiograph provide as much diagnostic information as the cervical spine series. The majority of the abnormalities detected by the cervical spine series consisted of osteophytic encroachment on the lower cervical spinal canal or intervertebral foramina. However, in only two cases, or 4.3%, did the plain cervical spine series provide more diagnostic information than the digital radiograph and CT combined. In one case a lateral mass fracture was not detected by CT, but CT had demonstrated a prolapsed disc. In the other case of a patient with a fractured odontoid process, the CV series showed that there was considerable mobility at the fracture site. In none of the non-trauma cases in which the plain radiographs showed more diagnostic information than CT and digital radiography was patient management changed. In each of the 10 cases in which oblique digital radiographs were performed the intervertebral foramina as far as and including the cervico-thoracic junction were clearly demonstrated (Fig. 2). In addition variation of the window widths and levels frequently enabled the cervicodorsal junction to be demonstrated in the lateral projection (Fig. 3).
DISCUSSION CT of the lumbar spine is generally considered to be the examination of choice for the investigation of suspected disc prolapse (Raskin and Keating, 1982; Haughton et al.,
1982; Carrera et al., 1980) and spinal stenosis (Carrera et al., 1980; Epstein et al., 1977) and provides additional information in the evaluation of trauma (Brant-Zawadski et al., 1981), suspected metastases (Roub and Drayer, 1979) and osteomyelitis (Brant-Zawadski et al., 1983). In
patients with prolapsed intervertebral disc, plain radio. graphs may be normal, or show reduced disc spaces and osteophytes, but these are non-specific findings (Taveras and Wood, 1976). Plain radiography is notoriously inaccurate in the diagnosis of spinal stenosis (Gargano, !980). The radiation dose for a four film LSV series is of the order of 24 mGy maximum skin dose, 0.8 mGy mean active bone marrow dose and the dose to the gonads is approximately 2.18 mGy males and 7.21 mGy females (Whalen and Balter, 1984). The radiation dose from digital radiography is 1-2.5 mGy (General Electric, Milwaukee). Antero-posterior (A-P) and lateral digital radiographs are an integral part of the standard CT examination. Therefore, the radiation attributable to them is not additional to that of the CT scan procedure. If oblique digital radiographs are performed, the additional radiation is of the order of 2 mGy. The routine digital radiograph of the cervical spine was not as successful as that of the lumbar spine in determining abnormalities seen by plain radiography. This was due to the small size of cervical vertebrae relative to lumbar vertebrae, and to the inability of the patients in the supine position to depress their shoulders sufficiently to provide an adequate lateral digital radiograph of the lower cervical spine. In the present study the A-P and lateral digital radiographs were used for prescribing scan levels rather than for diagnosis and they were not enlarged in the hard copies. With minimal effort and time the quality of the digital radiography can be improved significantly. In fact all of the usual angulations used in conventional spinal plain radiography can be obtained automatically without moving the patient. These requirements, particularly in the cervical region, would be expected to overcome most of the deficiencies in digital radiography manifest in the present study. It should also be noted that because the digital radiographs and CT scans were evaluated before the plain film series in every case, this study is biased in favour of the plain film series. The inability of the A-P and lateral digital radiographs in the present study to demonstrate the lower cervical vertebrae adequately is probably not of importance in those patients presenting with a clinical diagnosis of cervical spondylosis. In a prospective, blinded trial the degree of spondylosis in patients presenting with a clinical diagnosis of cervical spondylosis when compared with an age and sex matched control group presenting for barium swallow was similar, with no statistically significant difference in degree of spondylosis between the two groups (Hellen et al., 1983). The CT scans in our study much more accurately depicted the dimensions of the spinal canal and the intervertebral foramina than did plain radiography, a CT feature previously noted by Roub and Drayer (1979). We also confirmed that high resolution cervical spinal CT can differentiate between soft disc herniation and spondylotic nerve root compression in patients presenting with cervical radiculopathy (Daniels et al., 1984). This potentially can dictate in which patients discectomy via the anterior approach (Cloward's procedure) should be performed and in which cases foraminotomy will suffice. In our small cervical spine series, no surgery was considered necessary. However,
CT OF THE SPINE
plain CT is of little use in the evaluation of cervical rnyelopathy due to spondylotic compression or multiple disc prolapses as scans through the lower cervical spine are often degraded by artefacts derived from the inclusion of the shoulders in the field of view. Myelography or magnetic resonance imaging (MRI) are more appropriate in this clinical context. In this study the number of patients referred from private practice clinicians for evaluation of presumed spondylotic cord compression reflected lack of consultation and indicated the need for more direct advice by the radiologist as to the limitations of a plain CT examination. Even though cervical and lumbar spine X-rays showed some abnormalities not demonstrated by CT and its standard digital radiograph, management of the nontrauma cases was not altered by the extra diagnostic information. This may in part reflect some inappropriate indications for radiological examination. The radiation dose from plain radiographs of the cervical spine is of the order of 6.4 mGy maximum skin dose and 0.08 mGy to the bone marrow (Whalen and Baiter, 1984). The geometry of third generation scanners is particularly conducive to the production of high quality digital radiographs, in that all the detectors are utilised in the production of the image. Only that portion of the 360 ° detector ring subtended by the fan beam of fourth generation scanners contributes to the digital radiograph, with resultant degradation of spatial resolution and increased noise. The cost of conventional plain cervical and lumbosacral radiography adds a significant financial burden to that of the CT scan. Moloney and Rogers (1979) found that it was the 'small ticket' radiological examinations rather than CT which contributed far more to the cost of radiological examinations in the United States. The evidence from this study suggests that when a CT
319
(b)
(c) Fig. 2 Cervical digital radiographs. (a) Antero-posterior. (b) Lateral. (c) 45 °. Oblique, clearly demonstrating intervertebral foramina.
(a)
examination of lumbar or cervical spines is planned on a high resolution CT scanner for most indications other than trauma, a conventional plain examination can be omitted in the first instance. In adopting this policy radiologists are encouraged to optimise the quality of the initial digital radiography ('scout views') by obtaining oblique views and refining the hard copy display by magnification and optimal window setting.
CLINICAL RADIOLOGY
320
Table 3 - Lumbosacral spine radiograph findings not detected by CT and digital radiographs
Finding
Number
% of tOtal
Transitional thoraclumbar vertebra Slight retrolisthesis Slight spondylolisthesis
1 1 1
1 1 1
Total
3
3
Table 4 - Cervical spine radiograph findings not detected by CT and digital radiography
Findings
Number
% of Total
Lateral mass fracture Mobility at odontoid fracture site
1 1
2.15 2.14
Total
2
4.3
References
(a)
(b) Fig. 3 - Lateral cervical computed radiographs. (a) Standard window width and level. (b) Increased window level to demonstrate cervicothoracic junction.
Brant-Zawadski, M, Burke, VD & Jeffrey, RB (1983). CT in the evaluation of spine infection. Spine, 8, 358-364. Brant-Zawadski, M, Miller, EM & Federle, MP (1981). CT in the evaluation of spine trauma. American Journal of Roentgenology, 136, 369-375. Carrera, G F , Williams, AL & Haughton, VM (1980). Computed tomography in sciatica. Radiology, 137, 433-437. Daniels, DL, Grogan, JP, Johansen JG, Meyer, GA, Williams, AL & Haughton, VM (1984). Cervical radiculopathy: computed tomography and myelography compared. Radiology, 151, 109-113. Epstein, BS, Epstein, JA & Jones, MD (1977). Lumbar spinal stenosis. Radiological Clinics of North America, 15, 227-239. Gargano, FP (1980). Transverse axial tomography of the lumbar spine. In Radiographic Evaluation of the Spine: Current Advances with Emphasis on Computed Tomography, Ed. Post, MJD Masson Publishing, New York. Haughton, V,. Eldevik, O, Magnaes, B & Amundsen, P (1982). A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar discs. Radiology, 142, 103-110. Hellen, CA, Stanley, P, Lewis-Jones, B & Heller, RF (1983). Value of Xray examinations of the cervical spine. British Medical Journal, 287, 1276-1278. Moloney, TW & Rogers, DE (1979). Medical technology--a different view of the contentious debate over costs. New England Journalof Medicine, 309, 1413 1419. Raskin, S & Keating, J (1982). Recognition of lumbar disk disease: comparison of myelography and computed tomography. American Journal of Neuroradiology, 3, 215 221. Roub, LW & Drayer, BP (1979). Spinal computed tomography: limitations and applications. American Journal of Roentgenology, 133, 267-273. Taveras, JM & Wood EH (Eds) (1976). In VII Disease of spinal cord. Diagnostic Radiology, 2nd Edition. p. 1209. The Williams & Wilkins Company, Baltimore. Whalen, JP & Baiter, S (Eds) (1984). Imaging procedures and doses. In Radiation Risks in Medicallmaging. Year Book Medical Publishers, Chicago.
CT of the Spine: Are Plain Spine Radiographs Necessary? B. M. TRESS and W. S. C. HARE
The University of Melbourne, Department of Radiology, Victoria, Australia
This study was designed to determine whether plain radiographs added any information of clinical significance to the information provided by CT (computed tomography) and its standard digital radiographs in 100 patients presenting for C T of the lumbar spine and 46 patients presenting for cervical spine CT. In only three (3%) of the lumbar studies and two (4.3%) of the cervical studies did the plain radiographs add diagnostic information. The added diagnostic information did not affect patient management in all cases with indications other than trauma. Good quality oblique cervical spine digital radiographs were obtained in 10 cases simply by moving the tube and detectors to the 45 ° arid 135 ° azimuths. The evidence from this study suggests that when a CT examination of lumbar or cervical spines is planned on a high resolution CT scanner for indications other than trauma, a conventional plain radiographic examination can be omitted in the first instance.
Computed tomographic scans performed by modern high resolution CT scanners are preceded by a computed digital radiograph generated by the scanner. The digital radiograph is primarily used for prescribing the exact levels and extent of subsequent scans. The diagnostic quality of the digital radiograph has progressively improved as high resolution CT scanners have been developed. It has always been considered that plain radiographs are mandatory in any radiological evaluation of the spine. The purpose of this study was to determine whether plain radiographs added any information of clinical significance to the information provided by the digital radiographs and CT studies in patients presenting for CT examinations of cervical and lumbar spines.
were performed routinely prior to the CT study (Fig. 1). These were not magnified, no oblique projections were performed and the normal windows for the digital radiograph (window width 500, window level 200-300) were not varied. All the scans and digital radiographs were performed upon a GE 9800 CT scanner. The indications for the CT studies are shown in Tables 1 and 2. The findings of the digital radiograph and the CT studies were separately tabulated by the staff radiologist on duty for CT at the time of the examination. The plain film series was then evaluated. The number of cases in which the plain film series provided the same information as the digital radiograph, more information than the digital radiograph and more information than the digital radiograph and CT study combined was noted. Oblique digital radiographs were obtained of 10 patients presenting for cervical spinal CT by simply moving the tube and detectors to the 45 ° and 135° azimuths (or positions). The images were enlarged for hard copying (Fig. 2). Contrast and density were varied using the window width and level controls to allow adequate demonstration of the lower cervical spine and cervico-dorsal junction (Fig. 3). RESULTS The digital radiograph alone provided as much diagnostic information as the lumbosacral spine series in 91% of cases. In 9% of cases the digital radiographs provided
MATERIALS AND METHODS The patient sample consisted of 100 consecutive patients who had plain lumbosacral spine radiography performed before presenting for lumbar spinal CT and 46 patients who had a cervical spine series before presenting for cervical spine CT. The majority of the cervical spine referrals were from private practice physicians outside the hospital. The lumbosacral spine series consisted of a minimum of two antero-posterior and two lateral spine radiographs, including the entire lumbar and sacral regions. The minimal cervical spine series consisted of an antero-posterior, lateral and two oblique plain radiographs. Antero-posterior and lateral digital radiographs Correspondence to: Professor B. M. Tress, The University of Melbourne, Department of Radiology, The Royal Melbourne Hospital, 3050 Victoria, Australia.
(a)
(b)
Fig. 1 - Patient with residual ependymoma after laminectomy at L3 and L4 levels. Lateral (a) and antero-posterior (b) digital radiographs, clearly demonstrating laminectomy and scalloped posterior margins of L3 and L4.
318
CLINICALRADIOLOGY
Table 1 - Indications for CT of lumbar spine
Indication
Number
Sciatica Claudication of cauda equina Back pain Probable metastases Trauma Osteomyelitis Total
(%)
54 17 10 9 7 3
54 17 10 9 7 3
100
100
Table 2 - Indications for CT of cervical spine
Indication
Number
(%)
Spondylotic cord compression Trauma Radiculopathy Other
19 13 11 3
42 28 24 6
Total
46
100
less information than the lumbosacral spine series, even in retrospect. These cases included lesions such as congenitally absent pedicle, laminectomy and pars defects. However, in only 3 % of cases did the digital radiographs and CT scans together fail to show abnormalities demonstrated by the lumbosacral spine radiographs (Tables 3 and 4). In one case the lumbar spine series showed that there were five lumbar type discs instead of six because hypoplastic ribs had not been detected on the digital radiograph. Single cases of slight retrolisthesis and spondylolisthesis were not detected by digital radiography and CT scan. In only 37% of cases did the routine digital radiograph provide as much diagnostic information as the cervical spine series. The majority of the abnormalities detected by the cervical spine series consisted of osteophytic encroachment on the lower cervical spinal canal or intervertebral foramina. However, in only two cases, or 4.3%, did the plain cervical spine series provide more diagnostic information than the digital radiograph and CT combined. In one case a lateral mass fracture was not detected by CT, but CT had demonstrated a prolapsed disc. In the other case of a patient with a fractured odontoid process, the CV series showed that there was considerable mobility at the fracture site. In none of the non-trauma cases in which the plain radiographs showed more diagnostic information than CT and digital radiography was patient management changed. In each of the 10 cases in which oblique digital radiographs were performed the intervertebral foramina as far as and including the cervico-thoracic junction were clearly demonstrated (Fig. 2). In addition variation of the window widths and levels frequently enabled the cervicodorsal junction to be demonstrated in the lateral projection (Fig. 3).
DISCUSSION CT of the lumbar spine is generally considered to be the examination of choice for the investigation of suspected disc prolapse (Raskin and Keating, 1982; Haughton et al.,
1982; Carrera et al., 1980) and spinal stenosis (Carrera et al., 1980; Epstein et al., 1977) and provides additional information in the evaluation of trauma (Brant-Zawadski et al., 1981), suspected metastases (Roub and Drayer, 1979) and osteomyelitis (Brant-Zawadski et al., 1983). In
patients with prolapsed intervertebral disc, plain radio. graphs may be normal, or show reduced disc spaces and osteophytes, but these are non-specific findings (Taveras and Wood, 1976). Plain radiography is notoriously inaccurate in the diagnosis of spinal stenosis (Gargano, !980). The radiation dose for a four film LSV series is of the order of 24 mGy maximum skin dose, 0.8 mGy mean active bone marrow dose and the dose to the gonads is approximately 2.18 mGy males and 7.21 mGy females (Whalen and Balter, 1984). The radiation dose from digital radiography is 1-2.5 mGy (General Electric, Milwaukee). Antero-posterior (A-P) and lateral digital radiographs are an integral part of the standard CT examination. Therefore, the radiation attributable to them is not additional to that of the CT scan procedure. If oblique digital radiographs are performed, the additional radiation is of the order of 2 mGy. The routine digital radiograph of the cervical spine was not as successful as that of the lumbar spine in determining abnormalities seen by plain radiography. This was due to the small size of cervical vertebrae relative to lumbar vertebrae, and to the inability of the patients in the supine position to depress their shoulders sufficiently to provide an adequate lateral digital radiograph of the lower cervical spine. In the present study the A-P and lateral digital radiographs were used for prescribing scan levels rather than for diagnosis and they were not enlarged in the hard copies. With minimal effort and time the quality of the digital radiography can be improved significantly. In fact all of the usual angulations used in conventional spinal plain radiography can be obtained automatically without moving the patient. These requirements, particularly in the cervical region, would be expected to overcome most of the deficiencies in digital radiography manifest in the present study. It should also be noted that because the digital radiographs and CT scans were evaluated before the plain film series in every case, this study is biased in favour of the plain film series. The inability of the A-P and lateral digital radiographs in the present study to demonstrate the lower cervical vertebrae adequately is probably not of importance in those patients presenting with a clinical diagnosis of cervical spondylosis. In a prospective, blinded trial the degree of spondylosis in patients presenting with a clinical diagnosis of cervical spondylosis when compared with an age and sex matched control group presenting for barium swallow was similar, with no statistically significant difference in degree of spondylosis between the two groups (Hellen et al., 1983). The CT scans in our study much more accurately depicted the dimensions of the spinal canal and the intervertebral foramina than did plain radiography, a CT feature previously noted by Roub and Drayer (1979). We also confirmed that high resolution cervical spinal CT can differentiate between soft disc herniation and spondylotic nerve root compression in patients presenting with cervical radiculopathy (Daniels et al., 1984). This potentially can dictate in which patients discectomy via the anterior approach (Cloward's procedure) should be performed and in which cases foraminotomy will suffice. In our small cervical spine series, no surgery was considered necessary. However,
CT OF THE SPINE
plain CT is of little use in the evaluation of cervical rnyelopathy due to spondylotic compression or multiple disc prolapses as scans through the lower cervical spine are often degraded by artefacts derived from the inclusion of the shoulders in the field of view. Myelography or magnetic resonance imaging (MRI) are more appropriate in this clinical context. In this study the number of patients referred from private practice clinicians for evaluation of presumed spondylotic cord compression reflected lack of consultation and indicated the need for more direct advice by the radiologist as to the limitations of a plain CT examination. Even though cervical and lumbar spine X-rays showed some abnormalities not demonstrated by CT and its standard digital radiograph, management of the nontrauma cases was not altered by the extra diagnostic information. This may in part reflect some inappropriate indications for radiological examination. The radiation dose from plain radiographs of the cervical spine is of the order of 6.4 mGy maximum skin dose and 0.08 mGy to the bone marrow (Whalen and Baiter, 1984). The geometry of third generation scanners is particularly conducive to the production of high quality digital radiographs, in that all the detectors are utilised in the production of the image. Only that portion of the 360 ° detector ring subtended by the fan beam of fourth generation scanners contributes to the digital radiograph, with resultant degradation of spatial resolution and increased noise. The cost of conventional plain cervical and lumbosacral radiography adds a significant financial burden to that of the CT scan. Moloney and Rogers (1979) found that it was the 'small ticket' radiological examinations rather than CT which contributed far more to the cost of radiological examinations in the United States. The evidence from this study suggests that when a CT
319
(b)
(c) Fig. 2 Cervical digital radiographs. (a) Antero-posterior. (b) Lateral. (c) 45 °. Oblique, clearly demonstrating intervertebral foramina.
(a)
examination of lumbar or cervical spines is planned on a high resolution CT scanner for most indications other than trauma, a conventional plain examination can be omitted in the first instance. In adopting this policy radiologists are encouraged to optimise the quality of the initial digital radiography ('scout views') by obtaining oblique views and refining the hard copy display by magnification and optimal window setting.
CLINICAL RADIOLOGY
320
Table 3 - Lumbosacral spine radiograph findings not detected by CT and digital radiographs
Finding
Number
% of tOtal
Transitional thoraclumbar vertebra Slight retrolisthesis Slight spondylolisthesis
1 1 1
1 1 1
Total
3
3
Table 4 - Cervical spine radiograph findings not detected by CT and digital radiography
Findings
Number
% of Total
Lateral mass fracture Mobility at odontoid fracture site
1 1
2.15 2.14
Total
2
4.3
References
(a)
(b) Fig. 3 - Lateral cervical computed radiographs. (a) Standard window width and level. (b) Increased window level to demonstrate cervicothoracic junction.
Brant-Zawadski, M, Burke, VD & Jeffrey, RB (1983). CT in the evaluation of spine infection. Spine, 8, 358-364. Brant-Zawadski, M, Miller, EM & Federle, MP (1981). CT in the evaluation of spine trauma. American Journal of Roentgenology, 136, 369-375. Carrera, G F , Williams, AL & Haughton, VM (1980). Computed tomography in sciatica. Radiology, 137, 433-437. Daniels, DL, Grogan, JP, Johansen JG, Meyer, GA, Williams, AL & Haughton, VM (1984). Cervical radiculopathy: computed tomography and myelography compared. Radiology, 151, 109-113. Epstein, BS, Epstein, JA & Jones, MD (1977). Lumbar spinal stenosis. Radiological Clinics of North America, 15, 227-239. Gargano, FP (1980). Transverse axial tomography of the lumbar spine. In Radiographic Evaluation of the Spine: Current Advances with Emphasis on Computed Tomography, Ed. Post, MJD Masson Publishing, New York. Haughton, V,. Eldevik, O, Magnaes, B & Amundsen, P (1982). A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar discs. Radiology, 142, 103-110. Hellen, CA, Stanley, P, Lewis-Jones, B & Heller, RF (1983). Value of Xray examinations of the cervical spine. British Medical Journal, 287, 1276-1278. Moloney, TW & Rogers, DE (1979). Medical technology--a different view of the contentious debate over costs. New England Journalof Medicine, 309, 1413 1419. Raskin, S & Keating, J (1982). Recognition of lumbar disk disease: comparison of myelography and computed tomography. American Journal of Neuroradiology, 3, 215 221. Roub, LW & Drayer, BP (1979). Spinal computed tomography: limitations and applications. American Journal of Roentgenology, 133, 267-273. Taveras, JM & Wood EH (Eds) (1976). In VII Disease of spinal cord. Diagnostic Radiology, 2nd Edition. p. 1209. The Williams & Wilkins Company, Baltimore. Whalen, JP & Baiter, S (Eds) (1984). Imaging procedures and doses. In Radiation Risks in Medicallmaging. Year Book Medical Publishers, Chicago.