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A Horsman

Publications and source records attributed to A Horsman.

86 records · Page 5Linked to original sources
PubMed1975

The measurement of sequential changes in cortical bone geometry.

A method is described whereby the sequential changes occurring in the thickness of the cortices of the metacarpal shafts may be observed. The method utilizes pairs of hand radiographs from which the total bone width and medullary width of the 2nd, 3rd and 4th metacarpals are determined in duplicate using needle-tipped Vernier calipers. The errors are discussed and the precision of the method is shown to compare very favourably with the precision of the most recent densitometric techniques. The rate of loss of bone in post-menopausal women is evaluated, and is shown to be dependent upon the number of years elapsed since the menopause.

Adult↗
PubMedDate not supplied

Comparison of conventional single echo and multi-echo sequences with a fast spin-echo sequence for quantitative T2 mapping: application to the prostate.

The accuracy of water T2 maps generated from a fast spin-echo (FSE) sequence was compared with data obtained by conventional single and multi-echo spin-echo pulse sequences using a commercial gel phantom. Spatially localized stimulated echo acquisition mode (STEAM) proton spectroscopy was also used to confirm the reported water T2 values of the gels contained in the phantom. The FSE sequence was shown to be superior in accuracy to both the single and multi-echo spin echo sequences and comparable to STEAM, producing results that were within 10% of known values. The effectiveness of the FSE sequence was further demonstrated by generating T2 maps of the normal and diseased prostate in clinically acceptable imaging times, resulting in comparable T2 values to those obtained using STEAM. Accurate quantitative T2 maps can be produced with the FSE sequence.

Carcinoma↗
PubMedDate not supplied

Microvessel density of invasive breast cancer assessed by dynamic Gd-DTPA enhanced MRI.

It has been postulated that the rapid enhancement demonstrated by breast carcinomas after administration of contrast media is a direct result of tumor angiogenesis. However, to date, little quantitative data have been published to support this view. A retrospective study has been undertaken to compare dynamic contrast-enhanced data obtained from 40 patients with microvessel density (MVD) evaluated in specimens immunohistochemically stained with a factor VIII related antigen. The dynamic data were analyzed quantitatively using both simple indices of enhancement and a two-compartment kinetic model. A moderate but significant correlation was demonstrated between initial enhancement and MVD, and this correlation strengthened when node-positive tumors were considered in isolation (r = .77, P < .0005). However, the data showed considerable variability. The enhancement characteristics of the tumors could not be explained solely by their MVD; therefore, MRI cannot be used to predict MVD in vivo. Further work is required to address the exact relationship between contrast-enhanced MRI and tumor angiogenesis.

Adult↗
PubMedDate not supplied

Dynamic MRI of invasive breast cancer: assessment of three region-of-interest analysis methods.

PURPOSE: In this study, three region-of-interest (ROI) analysis methods based on operator-defined and semiautomated sampling of pharmacokinetic breast maps of contrast uptake are described. The observer variability and impact of the methods on the estimated enhancement characteristics of invasive cancer are also presented. METHOD: Fifty-four women with invasive breast cancer underwent dynamic Gd-DTPA-enhanced MRI. ROIs were drawn by two observers on parametric images obtained from compartmental modeling of the dynamic data. Three methods were used: (a) An irregular ROI was drawn to include as much of the enhancing part of the tumor as possible (large ROI); (b) a 12 pixel circular ROI was placed at the most rapidly enhancing part of the large region (small ROI); and (c) a computer algorithm interrogated the large region pixel by pixel using a 9 pixel square mask and selected the region with the highest mean parameter value (semiautomated ROI). RESULTS: Significant observer variability and bias were found in the enhancement measurements using the large ROI method. There was no observer bias associated with the other methods, but the variability of the small ROI method was substantial. An almost perfect observer agreement was achieved using the semiautomated method. The small and semiautomated ROI methods produced significantly higher enhancement ratios than the large ROI method, especially in grade III carcinomas. CONCLUSION: Variability is inherent in subjective ROI analysis, but the semiautomated method of ROI selection and sampling of parameter images of the breast is an efficient and reliable alternative that may allow better standardization of the MR technique.

Adult↗
PubMedDate not supplied

Peripheral enhancement and spatial contrast uptake heterogeneity of primary breast tumours: quantitative assessment with dynamic MRI.

PURPOSE: The purpose of our study was to determine if quantitative analysis of peripheral enhancement and spatial contrast uptake heterogeneity is useful in the characterisation of abnormalities seen at breast MRI. METHOD: Ninety-one women underwent dynamic gadolinium-enhanced breast MRI. Regions of interest were processed by a parallel thinning algorithm to define central and peripheral subregions of lesions. Peripheral enhancement was quantified at every time point of the dynamic sequence as a signal difference-to-noise ratio. Moreover, a radiologist assessed the images for the presence of peripheral enhancement and classified the regional and subregional time-intensity profiles of each lesion. RESULTS: Sixty-four invasive carcinomas and 30 benign lesions were analysed. Significant differences were found between benign and malignant lesions in peripheral enhancement as determined from the dynamic images (p = 0.0002; sensitivity, 0.34; specificity, 1.00) in time-intensity profiles (p < 0.000005; sensitivity, 0.67; specificity, 0.93) and in peripheral percentage signal changes at 1 min postcontrast (p = 0.001). There was a much higher relative signal increase centrally than peripherally (p < 0.0005), but peripheral signal changes had greater diagnostic value than central ones (Az = 0.72 vs. 0.63; p = 0.02). Carcinomas showed higher peripheral enhancement than benign lesions (p = 0.001). Peripheral enhancement reached maximum diagnostic value at 4 min postcontrast (Az = 0.80) and performed best as a highly sensitive but moderately specific diagnostic index. CONCLUSION: Quantification of peripheral enhancement is diagnostically useful and offers insight into the enhancement mechanisms encountered in breast MRI. Primary breast tumours show substantial spatial contrast uptake heterogeneity. Lesion differentiation based on percentage signal changes is improved by restricting sampling to the periphery of tumours.

Adult↗
PubMedDate not supplied

Effect of temporal resolution on the diagnostic efficacy of contrast-enhanced MRI in the conservatively treated breast.

PURPOSE: Our goal was to assess the effect of image acquisition rate on the diagnostic efficacy of contrast-enhanced MRI in the conservatively treated breast. METHOD: Sixty-seven women, treated with breast-conserving surgery and radiotherapy for early-stage breast cancer, were imaged at 1.5 T using a dynamic contrast-enhanced sequence with a temporal resolution of 12 s. Enhancement was recorded over time for the dominant lesion in each patient. Data were subsequently removed to simulate various acquisition rates and the enhancement indexes of benign and malignant lesions were compared. RESULTS: Seventeen patients had confirmed local recurrence and 50 remained disease-free. There were significant differences in the enhancement indexes of benign and malignant lesions 24-264 s after contrast agent administration. Acquisition rate had a negligible effect upon diagnostic efficacy. CONCLUSION: Two image data sets collected before contrast agent administration and between 1.5 and 3.5 min afterward may be sufficient to differentiate recurrent and benign disease.

Adult↗