Comparison of 1.5 Tesla and 0.35 Tesla field strength magnetic resonance imaging scans in the morphometric evaluation of the lumbar intervertebral foramina.

OBJECTIVE: To compare magnetic resonance imaging (MRI) scans obtained from 1.5 Tesla (T) MRI units with scans obtained from 0.35T MRI units in the morphometric evaluation of the lumbar intervertebral foramina (IVF). DESIGN: Three dimensions of lumbar IVFs were measured on a cadaveric lumbar spine by using Vernier calipers. The spine was embedded in gelatin to simulate soft tissue and scanned twice in a 1.5T MRI unit (3-mm and 5-mm slice thicknesses) and once in a 0.35T MRI unit (5-mm slice thickness). Measurements from the scans were made independently by three observers. The results obtained from the two units were compared to the actual IVF size (as measured by calipers) and to one another. RESULTS: The greatest superior-to-inferior distance had the strongest statistically significant correlation to the actual cadaver measurements for both the 0.35T and 1.5T imaging units [r = 0.986 (0.35T); r = 0.985 (1.5T at 3 mm) and r = 0.981 (1.5T at 5 mm); p < .0001 in all cases]. Mean differences and standard errors were minimal between measurements made from MRI scans of both 1.5T and 0.35T units and measurements made directly from the cadaveric spine. CONCLUSION: Both imaging units produced images that accurately depicted the actual size of the IVF. The MRI units of 0.35T field strength produced images of high morphometric accuracy. In addition, the potential for side effects and the operating costs are less with 0.35T units. Therefore, 0.35T MRI units may be a prudent choice as a clinical and research imaging tool in the evaluation of the lumbar IVF.

Postoperative fractures of lumbar articular facets: occult cause of radiculopathy.

Fracture of the inferior lumbar articular facets after laminectomy with facetectomy is a relatively common but unrecognized cause of radiculopathy. Although not all patients may be symptomatic from the fractures, some may have radiculopathy or back pain caused by displacement of the fracture fragment. In a series of 400 postoperative spinal computed tomographic (CT) scans, 25 patients were found who had fractures through the base of the inferior facets. Axial scans revealed no abnormality other than slight widening of the joint on the affected side. Sagittal views demonstrated a lucent defect similar to a pars interarticularis fracture, whereas coronal views showed the fracture at a different location in the base of the facet. Typically patients become symptomatic after a period of postsurgical well-being. A new pain pattern, local tenderness, pain on unusual movements, and relief with recumbency help suggest facet fracture versus recurrent disk herniation.

Multiplanar CT in the evaluation of degenerative spondylolisthesis. A review of 150 cases.

Degenerative spondylolisthesis (pseudospondylolisthesis) is a degenerative disorder of the intervertebral motion segment. It can be divided into two types: forward subluxation and backward subluxation. Forward subluxation is primarily a disease of the posterior joints and is found most commonly at L4/5. Retrolisthesis is a primary disorder of the disc space and is noted more commonly at L3/4. This paper reviews the CT findings in 150 patients with degenerative forward and backward subluxation. Proper evaluation of these disorders is extremely important because of the frequency of severe symptomatic spinal stenosis or foraminal encroachment.

CT evaluation of interbody fusion.

Reformatted computed tomography (CT) of the spine is very useful in the evaluation of patients who have previously been treated by lumbar or cervical interbody fusions. It allows incontrovertible evidence of failure of osseous fusion as well as defines the major causes of residual or recurrent symptoms. As CT methodology becomes a routine procedure, it will be the primary diagnostic aid in evaluating postoperative posterior lumbar interbody fusion (PLIF) patients.

Computed tomography of the spine: curved coronal reformations from serial images.

A new imaging format described here uses nonplanar reformations that follow the contour of curved structures intersected by a series of regularly spaced CT scans. The CT scanning procedure is described, and algorithmic details of this new format are presented. A standard set of reformatted images is suggested, and clinical examples are given to illustrate the diagnostic value of this new format.

CT multiplanar reconstruction in 253 cases of lumbar spondylolysis.

Two hundred fifty-three patients with lumbar pars interarticularis defects were studied by multiplanar high-resolution computed tomographic scanning (CT/MPR). Two hundred thirty patients had one or more pars defects at L5, 21 at L4, and two at L3. Within this group of patients, 21% had more than 5 mm of disk bulge or herniation, 34% had foraminal encroachment, and 34% had indentation on the neural canal from soft-tissue or bony callus formation.

Alar transverse process impingement of the L5 spinal nerve: the far-out syndrome.

This syndrome occurs in two types of patients: (1) the elderly person with degenerative scoliosis and (2) a somewhat younger adult population with isthmic spondylolisthesis and at least 20% slip. On plain radiograph, the Ferguson view (25 degrees caudocephalic) is best for visualizing the condition, however, CT is by far the best diagnostic tool. To show this far laterally, the "window" on the CT scanner must be opened wider than usual. Both coronal and parasagittal views will demonstrate the condition, but the coronal is the most valuable. Symptoms are classical spinal nerve compression. Usually it is the L5/S1 level that is involved, but other levels can be. At surgery, it is most important that nerve decompression be carried far enough laterally. This can mean sacrificing the lower half of the pedicle and the entire transverse process. Part of the body of S1 and of the sacral ala can be removed if the surgeon prefers. Because so much bone is removed, instability is a factor to be seriously considered. How to decompress adequately and still maintain stability often poses a most difficult problem.

Rheumatoid cervical myelopathy: evaluation by computerized tomography with multiplanar reconstruction.

Rheumatoid cervical myelopathy was studied in 14 patients, clinically, radiographically and by computerized tomography with multiplanar reconstruction (CT/MPR). CT/MPR demonstrated significant unsuspected areas of compromise in 9 of the 14 patients, and altered the surgical procedure in 7 of these 9 patients. CT/MPR clearly identifies all levels of involvement including rotary subluxation. CT/MPR also allows assessment of the spinal nerve canal/foramen and the alignment of the foramina transversaria. CT/MPR is an essential addition to the evaluation of rheumatoid cervical myelopathy.

Stereotactic neurosurgery using 3-D image data from computed tomography.

During the last decade computer tomography (CT) scanners have provided images that show internal anatomy of unsurpassed resolution and that, since they are inherently digital, a format computer graphics software can easily process. By combining CT images, a specially designed head-mounted instrument, and the software to coordinate them, improved surgical accuracy can result for stereotactic surgery. Using the head-mounted frame and the interactive computer software described here, the entire stereotactic approach is transportable to computer systems of three major CT manufacturers. Neurosurgeons now have a tool that allows trajectory selection and probe placement entirely within the CT suite. Compared with conventional stereotaxis, the CT-aided approach offers increased accuracy, with a significant fluid contrast injection for finding reference points and the avoidance of important brain structures due to the direct visualization afforded with CT. Key interactive features are shown here that allow unrestricted views of anatomy in the area of surgical interest. For example, oblique views that are normal to the trajectory of neurosurgical instruments are extracted in real time during the surgical procedure. Standard sagittal (lateral) and coronal (frontal) image planes are also shown integrated with the interactive technique. The surgical procedure is outlined and details of the pattern recognition technique for image-to-frame registration are presented. Test, phantom, and patient results are given.

Extracting oblique planes from serial CT sections.

Although geometric principles describing planes oblique to an orthogonal image data set are well understood, no implementation has been offered for their practical specification, extraction, and display in a clinical environment. Fast image generation and ease of user specification-requisite credentials for successful clinical implementations-are handicapped by the large volume of data to process. Other difficulties further complicate an interactive solution. Once oblique planes are generated, their orientation is often difficult to perceive without visual cues that aid their registration with standard image formats. In addition, Moire patterns introduced by digital aliasing often currupt resultant views. In this paper, techniques are outlined for simplifying oblique plane specification, a methodology is presented for image construction, and an interactive approach is illustrated to register images for such general view planes. Finally, digital aliasing of oblique planes is discussed, and a solution is given for this application.

Multiplanar computerized tomography in the normal spine and in the diagnosis of spinal stenosis. A gross anatomic-computerized tomographic correlation.

The limitations of current diagnostic tools, including myelography, in localizing the anatomic lesion in spinal stenosis are well recognized. The purpose of this study is to investigate whether computerized tomography can more effectively define the normal and abnormal osseous structures compromising the boundaries of the spinal canal, nerve root canal, and intervertebral foramen. This study is a pathologic-radiographic correlation between CT scans and sections of spine specimens that were so scanned. The tomographic images investigated were multiplanar, that is, simultaneously presenting transverse, coronal, and sagittal images. Spine specimens were chosen to show how the technique applies to the normal spine, as wel as to selected specimens with spinal stenosis. The role of the discs and apophyseal joints in shaping the intervertebral foramina and lateral recesses is emphasized in both normal and abnormal specimens. This study shows that computerized tomography can precisely localize anatomic lesions and, by comparison of the image to the gross anatomic specimen, that it is a reliable portrayal of the anatomic fact.

CSF enhancement for computerized tomography.

Metrizamide cisternography, combined with hypocycloidal tomography, has been performed in 12 patients with possible posterior fossa or parasellar mass lesions with finely detailed images of the basal cisterns resulting. Computed tomography was performed in nine of these patients and produced exceptional images of the cisternal anatomy. The technique of cerebrospinal fluid enhancement may be efficacious in identifying small basal masses not shown with conventional computed tomography, and thus may form an important complement to enhancement by intravenous injection of contrast medium.

Rapid computer-aided radiographic calculation of total lung capacity (TLC).

Methods currently used for determining total lung capacity are either simple but inaccurate in the presence of airways disease (gas dilution) or accurate but not generally available (body plethysmography). The manual radiographic method is accurate both in normals and in patients with airways disease but is very tedious to use. The authors have developed a semi-automatic radiographic method utilizing a position transducer and a small computer which reduces the time for each determination from approximately 20 min. to 1 min. Agreement with manual calculations in 80 controls and 80 patients with airways disease is excellent (average correlation coefficient, 0.9872; average residual error, 2.65% or 156 ml).

1975 Memorial Award Paper. Image generation and display techniques for CT scan data. Thin transverse and reconstructed coronal and sagittal planes.

The various limitations to computerized axial tomographic (CT) interpretation are due in part to the 8-13 mm standard tissue plane thickness and in part to the absence of alternative planes of view, such as coronal or sagittal images. This paper describes a method for gathering multiple overlapped 8 mm transverse sections, subjecting these data to a deconvolution process, and then displaying thin (1 mm) transverse as well as reconstructed coronal and sagittal CT images. Verification of the deconvolution technique with phantom experiments is described. Application of the phantom results to human post mortem CT scan data illustrates this method's faithful reconstruction of coronal and sagittal tissue densities when correlated with actual specimen photographs of a sectioned brain. A special CT procedure, limited basal overlap scanning, is proposed for use on current first generation CT scanners without hardware modification.

Further investigation and initial clinical use of advanced CT display capability.

The AUR Memorial Award Paper (this issue, pp. 403-416) described a technique for providing thin transverse CT sections and for redisplaying this transverse CT data as coronal or sagittal anatomic planes. This paper presents additional experience with cadaver models and the results of initial applications of the method to data obtained from living patients. The technique potentially enhances the clinical usefulness of CT scanning by providing precise triangulation and resolution of normal and abnormal structures.