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H K Genant

Publications and source records attributed to H K Genant.

499 records · Page 28Linked to original sources
PubMedDate not supplied

Impact of marrow fat on accuracy of quantitative CT.

An assessment of the role of marrow fat as a source of error in single energy quantitative CT (SEQCT) measurements of the spine is presented. Fat-induced shifts and spreads in SEQCT findings are discriminated and quantified. Studies using chemical analysis have reported an average vertebral bone mineral (MIN) loss of approximately 1.3 mg/ml (0.9%) per year from a peak MIN of 150 mg/ml at age 30 years with a standard error of the estimate (SEE) of approximately 23 mg/ml [coefficient of variation (CV) = 20%]; intraosseous vertebral fat content increases by approximately 2.4 mg/ml (1.4%) per year from a fat density of 175 mg/ml at age 30 years with an SEE of approximately 87.5 mg/ml (CV = 36%). If one does not adjust for the average age-related fat change, SEQCT underestimates MIN and overestimates MIN loss by 10-30% (at a scanner setting of approximately 80 kVp). Application of correction procedures reduces the average underestimation to 1-3%. The impact of residual vertebral fat variability on the accuracy of MIN measurements accounts for only 12-24% of the total accuracy error of typically 10-15 mg/ml. The impact of fat changes between zero and twice the normal age-related rate on MIN loss measurements on individual patients and patient groups (treatment versus control) accounts for only 1-2% of the total precision error of typically 1.5-3 mg/ml. From 94 to 99% of the spread of SEQCT versus age data is caused by sources of variability other than fat. All fat-related errors are higher than the above estimates by a factor of approximately 1.5-2.5 when scanning at higher voltages of up to 130 kVp. Given the limited impact of fat variability, we conclude that for most clinical applications, MIN and bone loss measurements should use SEQCT. Adjustment for the average under/overestimation (by either explicitly correcting SEQCT findings or by comparing them with normative data obtained on a similar scanner), measuring at low voltages of approximately 80 kVp, and strict compliance to quality assurance procedures are highly recommended to achieve optimum accuracy.

Adipose Tissue↗
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

Significance of QCT bone mineral density and its standard deviation as parameters to evaluate osteoporosis.

OBJECTIVE: A study using quantitative CT (QCT) of the spine was carried out to determine whether the standard deviation (SD) of the bone mineral density (BMD) within a given region of interest (ROI) could be used as a parameter to evaluate osteoporosis. MATERIALS AND METHODS: A low dose single energy protocol was used. The elliptical ROIs inside the trabecular bone of the vertebral bodies T12-L3 were analyzed for four patient groups: Group 1, 52 healthy premenopausal women (age 41 +/- 2 years); group 2, 119 healthy early postmenopausal women (53 +/- 4 years); group 3, 45 postmenopausal relatively healthy women (age 65 +/- 5 years); group 4, 26 osteoporotic women (age 67 +/- 5 years). Average group mean BMD values and their coefficients of variation (CV = SD/BMD) were calculated. The t values, percent decrements, z-scores, and analysis of variance (ANOVA) served to compare capabilities of the BMD and the CV to discriminate groups pairwise using all possible group combinations. RESULTS: The use of z-scores and percent decrements gave ambivalent and mostly insignificant results. The CV performed better than BMD in separating group pairs (1,3), (1,4), (2,3), and (2,4), but BMD was superior for group pairs (1,2) and (3,4). Using SD as an independent variable in addition to age and BMD in the ANOVA did not significantly change r2 or the standard error of the estimate. The t test showed highly significant better discriminatory capabilities for BMD compared to CV> CONCLUSION: The results of our study did not indicate a significant potential of the BMD SD as measured in trabecular single energy low dose spinal QCT to improve the discriminatory capabilities of BMD for a separation of osteoporotic from nonosteoporotic subjects.

Adult↗
PubMedDate not supplied

Relationships between young modulus of elasticity, ash density, and MRI derived effective transverse relaxation T2* in tibial specimens.

OBJECTIVE: It has been hypothesized that the MR relaxation time T2* of bone marrow present in the intertrabecular spaces may be related to the density of the trabecular network and may be a predictor of trabecular bone properties. MATERIALS AND METHODS: To derive a relationship between the marrow relaxation time T2* and biomechanical properties of trabecular bone, we studied two sets of trabecular bone specimens from human tibiae. The first set consisted of 12 specimens that were defatted and immersed in saline; the second set consisted of 18 specimens with marrow in the trabecular spaces. The MR studies were conducted on a 1.5 T imaging system. In the first set of specimens, a GE sequence (TR = 70 ms; TE = 5, 10, 15, 20, 25 ms) was used to obtain images in the axial plane. In the second set, a water suppression pulse was used prior to an asymmetric SE sequence (TR = 300 ms; TE = 4, 8, 12, 16, 20, 24 ms) to obtain images in the axial, coronal, and sagittal planes. The T2* of the intertrabecular saline of the marrow fat was calculated assuming a monoexponential decay. In both sets, the elastic moduli were measured in three orthogonal directions (superoinferior, anteroposterior, and mediolateral). The ash density was determined after the completion of the experiments. RESULTS: Our results indicate a moderate significant negative correlation between T2* and ash density or elastic modulus (E) in both sets of specimens. The correlation coefficients were slightly improved between the transverse relaxation rate 1/T2* and bone density or E. We found a good correlation between T2* and the reciprocal ash density (r = 0.88) and between T2* and the reciprocal elastic modulus 1/E (r = 0.87 to r = 0.95) in the first set, while in the second set the correlation remained moderate. With use of a multiple linear regression model (1/E = a x T2* + b x 1/T2* + n), the reciprocal elastic moduli 1/E were predicted to > 90% by T2* and 1/T2* in the first set of specimens. This finding was not replicated with the second set of specimens. In the second set of specimens, we found poor to moderate correlation coefficients between the T2* times in the three orthogonal planes (r = 0.45 to r = 0.71). CONCLUSION: Trabecular bone properties such as density and strength may potentially be assessed with quantitative MR techniques. However, especially for in vitro studies, specimen preparation, acquisition parameters, and specimen geometry may have a significant impact on the obtained results.

Bone Density↗
PubMedDate not supplied

Assessment of trabecular structure using high resolution CT images and texture analysis.

PURPOSE: Our goal was to use high resolution (HR) CT images combined with texture analysis to investigate the trabecular structure of human vertebral specimens and to compare these techniques with bone mineral density (BMD) in the prediction of bone strength. METHOD: HR CT images with a slice thickness of 1 mm were obtained of 28 bone cubes. Four different groups of texture analysis techniques were used to assess these images. In addition, quantitative CT (QCT) was performed and elastic modulus (EM) was determined biomechanically. RESULTS: R2 between EM and BMD was 0.78 (p < 0.01). R2 values for EM versus most of the texture measures were also significant. Texture measures in addition to measures of BMD in a multivariate regression model significantly increased R2 up to 0.87. CONCLUSION: In an experimental setting, texture parameters calculated using HR CT images correlated significantly with EM. Combining texture measures with BMD improved the prediction of EM significantly.

Adult↗
PubMedDate not supplied

Assessment of vertebral bone mineral density using volumetric quantitative CT.

PURPOSE: The purpose of this work was to determine the precision and diagnostic efficacy of bone mineral density (BMD) measures based on volumetric quantitative CT (QCT) of the spine. METHOD: Volumetric CT scans of L1 and L2 (GE-9800Q; 80 kVp, 140 mAs, 3 mm slices) were acquired in a cohort of 62 osteoporotic women (mean age 70.4 years, T(DXA hip or spine) < -2.5), of whom 20 had vertebral fractures and 42 were nonfractured control subjects. An image analysis technique delineated trabecular, cortical, and integral regions in reference to a vertebra-fixed coordinate system. We computed precision values and fracture control differences for these new regions and for single-slice QCT and dual X-ray absorptiometry (DXA) measures synthesized from the volumetric data. RESULTS: Volumetric trabecular BMD showed higher precision (1.3%) than the synthesized single-slice measures (2.1-2.8%). Volumetric and single-slice trabecular BMD showed equivalent decrements between fractured and nonfractured subjects (17-19%), with integral BMD showing smaller and less significant differences (7-8%). CONCLUSION: Volumetric and single-slice QCT techniques are equivalent for vertebral fracture risk estimation, but volumetric techniques should be superior for monitoring therapy efficacy.

Absorptiometry, Photon↗
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↗
PubMedDate not supplied

Differentiation between postoperative scar and recurrent disk herniation: prospective comparison of MR, CT, and contrast-enhanced CT.

Twenty-five symptomatic postlumbar surgery patients had findings on lumbar spinal noncontrast CT that were equivocal for distinguishing recurrent disk herniation from postoperative epidural fibrosis (scar). Contrast-enhanced CT and lumbar MR imaging were performed to differentiate these two conditions. Of the 14 levels, surgically explored, the diagnosis of scar or recurrent disk herniation was correct with contrast-enhanced CT at 10 levels and with MR imaging at 11 levels. At the levels operated on less than 2 years prior to MR imaging, scar more frequently demonstrated intermediate than low signal intensity. Scar older than 2 years most often showed low signal intensity. These preliminary findings suggest that MR may be useful in differentiating postoperative fibrosis from recurrent disk herniation in a significant proportion of patients whose unenhanced CT scans are equivocal.

Cicatrix↗
PubMedDate not supplied

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.

Hip Joint↗