Biomedical subjects

P Steiger

Publications and source records attributed to P Steiger.

45 records · Page 3Linked to original sources

PubMed1987

[Magnetic resonance tomography in the determination of the functional stability of posterolateral lumbar spondylodeses].

MR tomography was used to assess functional lumbar stability in 30 patients with posterolateral fusions. The vertebral bodies of 9 of the 12 patients with unstable lumbar fusions presented with areas of decreased signal intensity on T1- and intermediately weighted images, which increased on T2-weighting. The vertebrae of 15 of the 18 patients with stable fusions demonstrated zones of increased signal intensity on T1- and intermediately weighted images, which were less intense or invisible on T2-weighing. Surgical correlation was available in 11 of the 30 patients studied. Hyperemia and inflammation appear to be responsible for the abnormal signal intensities in the patients with stable fusions, whereas an increase in adipose marrow due to decreased biomechanical stress is thought to account for the atypical signal intensities in the vertebral bodies of the patients with stable fusions. MR tomography seems to be a potential method for evaluating functional lumbar fusion stability. MR tomography may be particularly helpful in those patients with multiple back surgeries and possible instability, recurrent disc herniation, or postoperative fibrosis. MR is recommended in the patient, who appears clinically unstable, whose radiographs and CT, however, do not demonstrate fusion failure.

Adult↗

PubMedDate not supplied

Overlap detection and contour-tracking algorithms for critical organs--application to kidney.

An auto-contouring technique has been developed for critical structures on transverse Computer Tomographic (CT) images with one or two overlap regions where object and background have similar CT values. In this technique, those regions are identified and skipped during contour tracking. The contours thus obtained are discontinuous which are corrected afterwards by suitable interpolations. The overlap detection criterion is never satisfied in a nonoverlapping environment and the contour, in this case, is essentially tracked on the basis of CT value threshold alone. The entire process can be initiated by minimal operator intervention. The method has been successfully tested for kidneys and several examples are furnished. The success and concomitant limitations of this technique are also discussed.

Algorithms↗

PubMedDate not supplied

[Three-dimensional computerized tomography of diseases of the bones and joints].

Three-dimensional CT (3-DCT) surface reconstructions were generated in 157 patients with various disorders of the musculoskeletal system. Whereas generating the 3-D display of ligaments, tendons, intervertebral discs and nerve roots was difficult and time-consuming, the comprehension of complex abnormalities of bony structures was easier than with two-dimensional CT. 3-DCT was particularly useful in the preoperative planning of hip and spine surgeries while it also simplified the intraoperative orientation. 3-DCT proved to be a useful diagnostic method supplementing axial computed tomography.

Bone Diseases↗

PubMedDate not supplied

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 congenital 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., nonosseus structures, and those of larger size with relation to image degradation from partial volume effect.

Child↗

PubMedDate not supplied

Precise determination of paraspinous musculature by quantitative CT.

The ability to quantify muscular size has important implications in monitoring the effects of muscle disorders, in assessing the efficacy of interventions aimed at abbreviating muscle atrophy, and in examining the association between muscle and bone as a correlate of osteoporosis. We have developed an autocontouring technique for the precise determination of paraspinous musculature that can be implemented as an adjunct to our current CT method of spinal trabecular densitometry without additional scanning time or radiation exposure. Using two distinct patient groups, we evaluated the validity of this technique by assessing intra- and interobserver variability. Using the average coefficient of variation (CV) as an estimate of precision, we found intraobserver variability to be essentially equivalent whether evaluated in young, healthy men (0.69%) or in older, mildly osteoporotic women (0.74%). When the muscle evaluations of two observers were compared, the variability was somewhat higher, 1.81 and 1.83% in older and younger subjects, respectively. We scanned an additional 10 subjects twice, with intermediate repositioning, and found the reproducibility (CV) of determining paraspinous muscle area to be 0.97%. Given this estimated high level of precision, we derived the approximate magnitude of change in muscle size that could be observed using two-point measurements in time. Small average changes, on the order of 1-2%, could be detected using small groups of subjects (10-20/group). Moreover, we found that, even in the individual patient, relatively small changes (3-6%) could be detected given our low imprecision estimate. We believe this quantitative approach holds promise for monitoring muscle changes in vivo as well as for rigorously exploring the relationship between muscle and bone.

Adult↗

PubMedDate not supplied

Quantification of knee joint fluid volume by MR imaging and CT using three-dimensional data processing.

A noninvasive, quantitative technique to estimate joint fluid volume using three-dimensional (3D) processing of magnetic resonance (MR) imaging and CT data was evaluated. The mean accuracy error of this 3D approach with MR imaging, performed on five fresh cadaver knees, was -2.4 +/- 5.1% SD when volume estimates were based on heavily T2-weighted transverse images. A considerably higher mean accuracy error of -12.5 +/- 16.9% SD was found when the 3D approach with CT was used (four fresh cadaver knees), probably because of the small attenuation differences between articular soft-tissue structures and joint fluid. A mean precision error of 4.9 +/- 2.3% SD was found when two radiologists independently evaluated in vivo MR imaging studies of 12 knees with joint effusion. Because of the low CT accuracy, no in vivo studies were performed using CT. Thus, this preliminary study shows that quantification of joint fluid volume with 3D data processing offers more accuracy with MR imaging than with CT. The 3D approach with MR imaging provides a potential tool for clinical studies.

Humans↗

PubMedDate not supplied

Electrically-stimulated muscle hypertrophy in paraplegia: assessment by quantitative CT.

To identify the magnitude of muscle hypertrophy following electrically stimulated exercise in paraplegic subjects, we used quantitative CT (QCT) of the midthigh prior to and following 6 weeks of bicycle ergometry. Three patients who had suffered acute spinal cord injury were examined in this pilot investigation. Average absolute changes in muscle cross-sectional area by QCT were determined to be 10.6 cm2 (p = 0.042) at a distal site located 100 mm above the tibial plateau and 18.8 cm2 (p = 0.019) at a more proximal site (175 mm). Expressed as a percentage increase, these changes were likewise found to be significant. When the total thigh musculature was segmented into anterior and posterior regions, significant increases were observed only among the anterior muscle groups at both the distal and the proximal sites. Muscle hypertrophy as determined by standard anthropometric techniques at 200 mm above the patella was not found to be significant. We conclude that QCT is a valuable technique for discerning changes in muscle size during fitness training and that, in our population, it was capable of differentiating specific muscle compartment hypertrophy secondary to electrical stimulation.

Adult↗

PubMedDate not supplied

Factors influencing long-term in vivo reproducibility of QCT overtebral densitometry).

OBJECTIVE: We investigated the long-term in vivo reproducibility of quantitative CT (QCT) examinations that were conducted in conformity with a standard and well established methodology. MATERIALS AND METHODS: The long-term reproducibility in vivo of QCT vertebral densitometry was studied in 12 normal postmenopausal women (mean age 51 years), who underwent four to five examinations over the same 2 year period. RESULTS: One group of six patients demonstrated good reproducibility with a coefficient of variation (CV) of bone mineral density (BMD) of < 2.4% and were considered "good cases." The other group of six patients showed poor reproducibility with a CV of BMD of > 3.2% and were considered "problem cases." A statistical study of the technical parameters of the QCT examination was performed to determine and correct for the factors that are correlated with reproducibility errors. Analyzing uncalibrated variations in Hounsfield numbers, we found that the surrounding soft tissues such as muscle, aorta, liver, and fat were correlated in both the good and the problem cases. However, only in the good cases did we find that the Hounsfield numbers of the vertebral bodies correlated strongly with the soft tissues and with parameters characteristic of the calibration regression line. CONCLUSION: Essentially, the calibration procedure appeared to fail in some examinations of the problem cases, causing poor long-term reproducibility. This calibration failure may be related to positioning of the subject in the gantry and to variations in electrical parameters of the X-ray tube. A CV > 1% between the four slopes of calibration for the individual vertebrae measured at the same visit may indicate calibration problems and may suggest the need for repeat scanning.

Aortography↗

PubMedDate not supplied

Three-dimensional digital displays in congenital dislocation of the hip: preliminary experience.

Four patients with congenital dislocation of the hip (CDH) were studied on a research basis with three-dimensional computed tomography (3-D CT) or, alternatively, with three-dimensional magnetic resonance imaging (3-D MR). 3-D CT and 3-D MR proved useful in demonstrating the extent of anterior and posterior acetabular coverage. 3-D CT was limited to patients greater than 6 months of age with ossified femoral heads. 3-D MR, in contrast to 3-D CT, demonstrated the cartilaginous femoral head in children less than 6 months of age, while avoiding gonadal irradiation. Both 3-D CT and 3-D MR appear promising in confirming the diagnosis and facilitating the choice of treatment modality in the child with complicated CDH.

Child, Preschool↗