Neil Chafetz

Lumbar spinal fusion. Assessment of functional stability with magnetic resonance imaging.

Segmental spinal instability was evaluated with magnetic resonance (MR) imaging, computed tomography (CT), and conventional radiography in 33 patients who had undergone surgical spinal fusion. In 16 of the 19 patients who had a diagnosis of solid fusion, the immobilized vertebral bodies demonstrated areas of high signal intensity on images with short repetition time (TR) and echo time (TE). The signal intensity of these areas was either less intense or normal on images with long TR and TE. In 10 of the 14 patients with segmental instability at the fusion site, subchondral vertebral bands of low signal intensity were shown on short TR/TE images, which demonstrated high signal intensity on long TR/TE images. All but two of the patients showed vertebral signal changes 12 or more months past fusion or onset of clinical symptoms. The vertebral MR signal intensity in solid lumbar fusions might be related to marrow composition changes resulting from decreased biomechanical stress, while the vertebral signal intensities in patients with unstable fusions might be related to reparative granulation tissue, inflammation, edema, and hyperemic changes. Magnetic resonance imaging appears to be unique in its assessment of functional fusion stability. Magnetic resonance may be most useful in patients symptomatic of fusion pseudarthrosis in whom conventional radiography and CT fail to demonstrate anatomic disruption.

Three-dimensional computed tomography and multiplanar reformations in the assessment of pseudarthrosis in posterior lumbar fusion patients

Three-dimensional (3-D) surface reconstructions and multiplanar computed tomography (CT) reformations were obtained in 30 patients with clinically suspected spinal fusion pseudarthrosis. The imaging studies were blind-reviewed and the results were compared with the clinical and surgical findings. Sagittal, planar, and curved coronal two-dimensional (2-D) reformations were more useful in the detection of bony nonunion than were axial CT scans, as the latter required more extensive analysis. Three-dimensional surface “cuts” adequately demonstrated pseudarthrosis in most cases. In some instances, however, segmentation artifacts created artifactual clefts or implied solidity, which contrasted with the interpretation of the 2-D Images. Sagittal 3-D cuts were helpful in demonstrating bony central and lateral stenosis. Three-dimensional surface reconstructions demonstrated superficial clefts and outlined the complex anatomy of the spinal fusions, thus facilitating pre- and intraoperative planning. The amount of bone stock available for pseudarthrosis repair at the fusion site and the need for additional harvesting of bone from the iliac crest also could be assessed easily. 3-D CT proved to be useful as an adjunctive imaging method in the evaluation of posterior lumbar fusion patients suspected of pseudarthrosis.

Stereophotogrammetry of the Lumbar Spine: A Technique for the Detection of Pseudarthrosis

A computer-assisted photogrammetric method for the detection of pseudarthrosis following spinal fusion is described. This radiologic method is quantitative and noninvasive and requires a minimum of clinician time. Results of tests with a phantom specimen are presented. Preliminary indications are that the method may prove to be a useful adjunct to the clinician in monitoring the postoperative course of patients requiring fusion procedures.

Three-dimensional CT and MR imaging in congenital dislocation of the hip: clinical and technical considerations.

Three-dimensional (3D) CT and 3D magnetic resonance (MR) imaging were performed in four patients with congential dysplasia of the hip. Two patients were studied by 3D CT and two by 3D MR. Prior to volume segmentation, two-dimensional (2D) MR image preprocessing was used to correct for nonuniform signal intensity distribution from local variations in field strength and coil response. An unsharp mask of the original MR scan was computed by extreme blurring of the image to suppress the details of the object. The unsharp mask was divided into the image on a pixel-by-pixel basis. For improved object contrast first and second echo images were combined in a 1:2 ratio. To add an additional feature for volume segmentation, 2D MR image homogeneity was computed based on 3 x 3 pixel neighborhoods. Volume segmentation was performed using one feature for CT, i.e., attenuation range, and two features for MR, i.e., signal intensity and image homogeneity range. Three dimensional CT and 3D MR demonstrated the 3D relationships of femoral heads and acetabula. Three-dimensional CT was limited to patients who had ossified femoral heads, whereas 3D MR demonstrated the cartilaginous femoral head. The extent of acetabular coverage on which the mode of therapy is based was shown. Three-dimensional MR permitted imaging without gonadal irradiation. The 2D MR image preprocessing described here should provide even better results in objects with greater contrast, i.e., nonosseous structures, and those of larger size with relation to image degradation from partial volume effect.

femoral Prosthesis Subsidence in Asymptomatic Patients : a Stereophotogrammetric Assessment

A radiographic stereophotogrammetric technique (SPG) was used to evaluate quantitatively the presence of early femoral prosthesis subsidence after total hip arthroplasty (THA). This paper focuses on the measurement of subsidence in 12 patients who remained asymptomatic during the first two years after surgery. Only one of these had SPG estimated subsidence in excess of one millimeter at any timepoint. These findings are consistent with the conclusion that early postoperative subsidence is not a common finding among asymptomatic THA patients.

Neuromuscular thermography of the lumbar spine with CT correlation.

Fifteen asymptomatic volunteers and 19 patients with current CT (GE 8800 CT/T) scans demonstrating either thecal sac contour distortion or nerve root displacement from disc rupture or spinal stenosis of the L4-L5 or L5-S1 levels judged to be at least moderate in severity underwent lumbar thermography. All patients were studied with an infrared telethermographic unit (AGA model 720M) employing the technical standards recommended by the Academy of Neuromuscular Thermography. The thermographic exams were interpreted independently and in a blind fashion by two radiologists. Of the 15 exams of symptomatic patients, six were interpreted as positive and consistent with nerve fiber irritation. Of the 19 exams of patients with demonstrated CT abnormalities, all had positive thermograms for nerve fiber irritation (specificity 60%, sensitivity 100%). It is concluded that lumbar thermography is a sensitive examination for detecting those patients who will demonstrate lumbar spinal CT abnormalities and should play an important role in the diagnostic screening of low-back pain syndrome patients.

Magnetic Resonance Imaging: Skeletal Applications

It has been assumed that magnetic resonance imaging (MRI) would have limited utility in visualizing bones, due to the lack of hydrogen atoms in cortical bone. Nonetheless, that same lack makes it possible to clearly distinguish cortical bone from soft tissue and from marrow. Thus, roles are described for magnetic resonance imaging in depicting bone and soft tissue tumors, the spine (including the spinal cord and vertebral discs), and appendicular soft tissue, as well as the detection of avascular necrosis in the hip.

Establishing Quantitative Within-Subject Confidence Limits For Clinical Stereoroentgenographs

It is now quite clear that under ideal conditions, discrete points can be located on x-ray films with standard deviations of less than 50 i. However, under routine clinical conditions, such considerations as individual variation in anatomy, movement of the subject between exposures, and variations in image quality combine to produce considerable reductions in the confidence which can be placed in quantitative assessments made from stereoroentgenographic films. This paper discusses some considerations involved in designing mathematical models in such a way as to optimize the use of imperfect data in answering specific clinical questions.

Stereoroentgenographic System With Portable Calibration Cage For Use In Clinical Medicine

For the past five years, we have been accumulating information on the performance of a stereoroentgenographic system developed for use in clinical medicine and first reported at the NATO Symposium on the Application of Human Biostereometrics. This system represents an adaptation of normal case coplanar stereometry and involves the use of a single emitter which is displaced in a controlled fashion between exposures. The system has been used primarily for the detection of applicance loosening and settling following the placement of total hip protheses and also for the detection of pseudorthosis following lumbo-sacral fusion. One major goal has been the development of a data acquisition and analysis system suitable for general hospital use which can be operated by technicians without specialized photogrammetric training. This report will focus on system design and on the delineation of technical problems encountered during routine clinical use of the system.