Biomedical subjects

A Horsman

Publications and source records attributed to A Horsman.

At least 19 recordsLinked to original sources

PubMed1998

Primary breast abnormalities: selective pixel sampling on dynamic gadolinium-enhanced MR images.

PURPOSE: To evaluate a region-of-interest (ROI) analytic method that involves selective sampling of pixels within predetermined ranges of contrast material enhancement values ("thresholding") on magnetic resonance (MR) images of primary breast abnormalities. MATERIALS AND METHODS: Dynamic gadolinium-enhanced MR images were obtained in 105 women. ROIs were drawn to outline the full extent of lesions. Relative signal intensity increase was determined on a pixel-by-pixel basis on 1- and 2-minute postcontrast images, as was the maximum relative signal intensity increase. Thresholding was used to analyze each ROI, with the upper boundary defined by the highest pixel value and lower boundaries of 0%-100%. RESULTS: Seventy-one invasive carcinomas and 37 benign lesions were analyzed. Narrower thresholding (i.e., larger percentage) resulted in an increase in all enhancement ratios (P < .0005). The enhancement ratio on 1-minute postcontrast images differed between benign lesions and carcinomas (P < .0005), but there were no significant differences in 2-minute and maximum ratios. Mean enhancement differences between benign and malignant lesions increased with narrower thresholding, but variability also increased linearly. Results of receiver operating characteristic analysis showed that thresholding did not affect the diagnostic usefulness of enhancement ratios. CONCLUSION: Contrary to current opinion, selective sampling of the most enhancing areas of breast abnormalities may not provide any diagnostic advantage over the use of easily drawn, lesion-encompassing ROIs.

Biopsy↗

PubMed1997

Unchanged basal ganglia N-acetylaspartate and glutamate in idiopathic Parkinson's disease measured by proton magnetic resonance spectroscopy.

The lentiform nucleus of five patients with idiopathic Parkinson's disease (IPD) was studied by quantitative magnetic resonance spectroscopy (MRS), both before and after administration of apomorphine, and the spectra were compared with those from a group of age-matched normal subjects. The concentrations of the three major metabolites, choline, creatine, and N-acetylaspartate (NAA), were quantified using tissue water content as an internal concentration reference. Glutamate concentration was assessed as the (glutamate + glutamine; GLX)/creatine peak area ratio. In normal subjects, the mean +/- SD concentrations of the the three metabolites were 2.4 +/- 0.4 mumol/g wet wt for choline, 11.5 +/- 0.8 mumol/g for creatine, and 14.7 +/- 2.8 mumol/g for NAA. The Glx/creatine ratio was 1.26 +/- 0.12. There was no significant difference in these parameters in the lentiform nucleus of patients with IPD either before or after apomorphine. The absence of detectable differences in IPD in this study implies that the changes in glutamate metabolism in the basal ganglia predicted by animal work are more subtle than those currently observable by MRS.

Aged↗

PubMed1997

Dynamic MR imaging of the breast combined with analysis of contrast agent kinetics in the differentiation of primary breast tumours.

OBJECTIVE: To assess dynamic Gd-DTPA-enhanced magnetic resonance (MR) imaging in the diagnosis of primary breast pathology, and to test the hypothesis that analysis of contrast agent kinetics increases specificity. METHODS: Forty-seven women underwent breast MR imaging using three-dimensional and dynamic spoiled gradient-recalled sequences. Image interpretation was based on the evaluation of lesion conspicuity, signal intensity, contour and enhancement pattern from the static acquisitions. Assessment of contrast kinetics was based on pixel-by-pixel analysis of the dynamic data. A two-compartment model described by three parameters (amplitude of uptake, exchange rate and washout rate), and a three-compartment model described by two parameters (permeability and exchange rate) were used. Regions of interest were drawn for all lesions found in the dynamic sections. Mean regional pixel values were calculated for each parameter and tested for diagnostic efficacy. RESULTS: Twenty-two malignant and 36 benign lesions were examined. Fibroadenomas accounted for 86% of the benign tumours. Image interpretation had a sensitivity of 0.95 and specificity of 0.86. The fat-suppressed post-contrast images permitted good visualization of the contour and matrix characteristics of fibroadenomas, but all non-fibroadenomatous benign lesions were classified as indeterminate or suspicious. Significant differences were found between benign and malignant lesions in the amplitude of uptake (P = 0.0008) and exchange rate (P < 0.00005) of the two-compartment model, and permeability (P=0.0001) and exchange rate (P < 0.00005) of the three-compartment model. However, image interpretation was superior to the isolated use of quantitative indices (P=0.02). The most discriminating parameters were the exchange rates of both models, with no significant difference between them. CONCLUSION: Assessment of lesion morphology is essential and probably sufficient for the differentiation of fibroadenomas from malignant tumours. However, specificity of conventional MR imaging may be much lower for other types of primary benign breast pathology. Analysis of Gd-DTPA kinetics improves the specificity obtained using simple enhancement measurements and can be used to produce parametric images that provide information about lesion heterogeneity, permeability and vascularity.

Adult↗

PubMed1997

In vivo quantification of citrate concentration and water T2 relaxation time of the pathologic prostate gland using 1H MRS and MRI.

We have previously reported a striking correlation between water T2 relaxation time and citrate concentration in the normal prostate (Liney G.P.; Lowry M.; Turnbull L.W.; Manton D.J.; Knowles A.J.; Blackband S.J.; Horsman A. Proton MR T2 maps correlate with the citrate concentration in the prostate. NMR Biomed. 9:59-64; 1996). In this study we present data from similar studies of the pathologic gland. The findings support the hypothesis that measurement of both citrate concentration and water T2 relaxation time in vivo may aid the differentiation of prostatic carcinoma from benign disease and normal tissue.

Adenocarcinoma↗

PubMed1997

Magnetic resonance imaging of the uterus after endometrial resection.

OBJECTIVE: Despite the increasing popularity of endometrial resection for the treatment of menstrual problems, the long term sequelae of this procedure are poorly recognised. As diagnostic hysteroscopy following endometrial resection is frequently unrewarding and transvaginal ultrasound is incapable of detecting subtle changes in endometrial morphology, magnetic resonance imaging was employed to evaluate the uterus. DESIGN: Retrospective study of unselected post-operative women. METHODS: Fifty-nine women, of whom 22 were amenorrhoeic, were studied a mean number of 34 months after endometrial resection, using a 1.5 Tesla magnetic resonance imaging system with a pelvic phased array coil for signal reception. T2-weighted FSE images were acquired through the long and short uterine axis and volumetric assessment of each uterine layer performed using an ISG Allegro workstation. MAIN OUTCOME MEASURES: The location and volume of residual endometrium, the volume of junctional zone and myometrial tissue, and the presence of additional intrauterine and pelvic pathology were recorded. RESULTS: Residual endometrium was demonstrated in all except three amenorrhoeic women, with a similar mean volume present in menstruating and amenorrhoeic groups. Additional findings included adenomyosis, haematometra, fallopian tube dilatation and free intraperitoneal fluid. CONCLUSIONS: The majority of amenorrhoeic and all menstruating women have residual endometrium after endometrial resection. The lack of communication of islands of residual endometrium with the uterine cavity results in haematometra formation, fallopian tube dilatation and possibly free intraperitoneal fluid.

Adult↗

PubMed1997

Prediction of axillary lymph node status in invasive breast cancer with dynamic contrast-enhanced MR imaging.

PURPOSE: To determine if magnetic resonance (MR) imaging can be used to predict axillary lymph node status in patients with breast cancer. MATERIALS AND METHODS: Fifty-one women with primary invasive breast cancer underwent dynamic contrast material-enhanced MR imaging of the breast Region-of-interest (ROI) analysis was performed on parametric images obtained with kinetic modeling of the data. Large and automated ROIs were selected. Typical enhancement ratios that represented the relative increase in mean pixel signal intensity were calculated for each ROI. Stepwise logistic regression analysis was applied to identify prognostic factors of axillary node status. Receiver operating characteristic analysis was performed and a Brier score and calibration curve were calculated to assess the diagnostic efficacy and predictive capability of the logistic regression model. RESULTS: The maximum enhancement ratio of the automated ROI was found to be the strongest predictor of node status (P < .001). Patient age (P = .007) and ROI size (P = .045) were also significant predictor variables. The model showed good accuracy (area beneath the fitted binormal receiver operating characteristic curve [Az] = 0.90; Brier score, 0.133). In 12 (24%) of the patients, a less than 5% or greater than 95% probability of positive-node status was correctly identified. CONCLUSION: The suggested predictive model may decrease the need for surgical staging of the axilla in patients with breast cancer.

Adult↗

PubMed1997

Dynamic MR imaging of invasive breast cancer: correlation with tumour grade and other histological factors.

The purpose of this study was to explore the association between dynamic MR enhancement characteristics and histopathological prognostic factors of invasive breast cancer. 53 women with primary invasive breast cancer underwent dynamic contrast enhanced breast MRI. Region of interest (ROI) analysis was performed on synthetic images obtained by kinetic modelling of the dynamic data. Operator-defined, large ROIs and computer-defined, 9-pixel ROIs were selected for each tumour. The relative increase in mean ROI pixel intensity was expressed in the form of enhancement ratios. Univariate and multivariate analyses were performed to explore the association of these ratios with standard histological factors, including tumour size, histopathological classification, histological grade, the presence of extensive in situ component and lymphovascular invasion, multifocal disease, and axillary lymph node status. All enhancement ratios showed significant differences between node-positive and node-negative tumours (max. p = 0.002). However, automated ROI ratios showed less overlap between node-positive and node-negative carcinomas than did large ROI ratios. A strongly significant association was observed between all automated ROI enhancement ratios and histological tumour grade (max. p = 0.001). Based on stepwise multiple regression analysis, node status and histological grade were the only histopathological factors with a significant independent effect on the enhancement characteristics. In summary, there is a strong association between dynamic MR characteristics and two important prognostic markers of invasive breast cancer, namely axillary node status and histological grade. This may allow MRI to be used in pre-operative predictions of tumour behaviour and biological activity.

Adult↗

PubMed1996

Proton MR T2 maps correlate with the citrate concentration in the prostate.

A significant correlation between water T2 relaxation time and citrate concentration in the normal prostate is demonstrated using spatially localized spectroscopy and water T2 maps. These data imply that MR images may be used to infer the concentration of citrate at high spatial resolution. Preliminary results in patients demonstrate that this relationship is maintained in benign prostatic hyperplasia (BPH) and prostatic carcinoma. The determination of citrate concentration and water T2 may aid the differentiation of prostate carcinoma from BPH and normal tissue.

Adult↗

PubMed1996

Quantification of citrate concentration in the prostate by proton magnetic resonance spectroscopy: zonal and age-related differences.

A commercial phased-array multicoil was used to acquire water-suppressed localized proton spectra of the two major anatomical regions of the prostate. The signal-to-noise ratio and spectral resolution allowed identification of peaks from choline and creatine, as well as a major peak from citrate. Quantification of the citrate peak using experimentally determined relaxation parameters with tissue water as an internal concentration reference revealed a marked variability between different volunteers. Nevertheless, in each case, the citrate concentration was up to fourfold greater in the peripheral zone than in the central gland. Furthermore, the difference in citrate concentration between these two regions was positively correlated with the subjects age. The results indicate a consistent difference in cellular function between the major anatomical regions within the prostate and may have important consequences for the application of magnetic resonance spectroscopy to the diagnosis of prostatic pathology.

Adult↗

PubMed1996

Tumour volume determination from MR images by morphological segmentation.

Accurate tumour volume measurement from MR images requires some form of objective image segmentation, and therefore a certain degree of automation. Manual methods of separating data according to the various tissue types which they are thought to represent are inherently prone to operator subjectivity and can be very time consuming. A segmentation procedure based on morphological edge detection and region growing has been implemented and tested on a phantom of known adjustable volume. Comparisons have been made with a traditional data thresholding procedure for the determination of tumour volumes on a set of patients with intracerebral glioma. The two methods are shown to give similar results, with the morphological segmentation procedure having the advantages of being automated and faster.

Brain Neoplasms↗

PubMed1996

Improved peripheral MR angiography with temperature regulation in healthy patients.

Peripheral magnetic resonance (MR) angiography was performed in eight volunteers, with a temperature-controlled water blanket. After warming of the right foot, unobserved vessels became conspicuous in all patients: Average increase in signal intensity was nearly twofold in the major artery and vein depicted. A similar improvement was observed in an examination in one patient with diabetes. Peripheral MR angiography performed after warming provided additional diagnostic information.

Adult↗

PubMed1996

Maturation effects on the NMR microimaging characteristics of single neurons.

We have used an isolated neuronal preparation of single Aplysia californica L7 cells to study the effects of development on the nuclear magnetic resonance (NMR) characteristics, T2 spin-spin relaxation rate (RT2) and apparent diffusion coefficient (D), of intracellular water within the nuclear and cytoplasmic compartments. These studies demonstrate a significant correlation of animal weight, but not age, with RT2. On the other hand, D was not significantly different as a function of either age or weight in single L7 neurons. Demonstration of maturation dependence in single cells is important in understanding the cellular origins of developmental effects on NMR characteristics in cell assemblies such as brain.

Age Factors↗

PubMed1996

Observer variability in the interpretation of contrast enhanced MRI of the breast.

The purpose of this study was to determine observer variability in the interpretation of contrast enhanced breast MRI and to evaluate its effect on the detection and differentiation of breast cancer. 57 women underwent breast MRI using spin echo and dynamic spoiled gradient-recalled sequences. Images were independently reviewed by three radiologists, two experienced and one newly trained in breast MRI interpretation. One of the experienced readers reviewed all examinations twice. Interpretation was based on lesion conspicuity, signal intensity, contour and enhancement pattern. Contrast uptake was assessed using region of interest (ROI) analysis of the dynamic images and calculation of a maximum enhancement index. Sensitivity and specificity in the diagnosis of malignancy irrespective of disease extent, and in the diagnosis of multifocal malignancy were estimated. 113 lesions were reported. Kappa coefficient estimations showed only a moderate agreement between the two experienced readers in rating morphological characteristics; the agreement between the newly trained reader and the experienced readers was even worse. Moreover, there was significant interobserver and intraobserver variation in the enhancement index measurements. Weighted kappa values indicated good agreement between the experienced readers in lesion and overall interpretation, excellent intraobserver agreement, but substantial disagreement between the newly trained reader and both experienced readers. All readers showed good sensitivity in cancer detection, but specificity was substantially lower. There is significant observer variability and a substantial learning curve in the interpretation of breast MRI, and variability in the ROI analysis of dynamic data. Further efforts to improve the reliability of ROI analysis and image interpretation are needed to help MRI realise its full potential in the clinical management of breast cancer.

Adult↗

PubMed1995

NMR microscopy of single neurons using spin echo and line narrowed 2DFT imaging.

NMR microimages of single neural cells were acquired at 500 MHz using a conventional spin echo pulse sequence and a line-narrowing sequence that eliminates susceptibility effects. The data show that any contribution to the measured T2 relaxation rate arising from diffusion in local field inhomogeneities using spin echo sequences at high fields and high spatial resolution is relatively small. We conclude that the measured T2 difference between the nucleus and cytoplasm in these cells represents primarily a true T2 relaxation effect arising from the interactions of water with macromolecules in the two compartments and does not result from microsusceptibility differences. These observations have implications regarding water compartmentation in single cells and the interpretation of the MR characteristics of tissues in vivo.

Animals↗

PubMed1995

Determination of proton metabolite concentrations and relaxation parameters in normal human brain and intracranial tumours.

Quantitative proton spectroscopic studies were performed on 39 volunteers and 16 patients with intracranial tumours. Estimates of T2 were obtained in white matter, grey matter, cerebellum, astrocytomas and meningiomas; T1 was determined in white matter only. White matter values of T2 for trimethylamines, creatine and N-acetyl aspartate (NAA) were 309 +/- 84, 195 +/- 41 and 369 +/- 124 ms, respectively (mean +/- SD, n = 20). Metabolite concentrations in white matter were 2.0 +/- 0.4 mumol/g wet weight for trimethylamines, 7.3 +/- 1.1 for creatine and 11.4 +/- 1.4 for NAA. The mean concentrations of creatine and NAA in grey matter and all of three metabolites in cerebellum were greater than those in white matter. Tumour spectra were characterized by increased trimethylamines, reduced creatine and NAA and occasionally the presence of lactate. Meningiomas were further characterized by the presence of alanine. The mean T2 and concentration of trimethylamines in tumours was significantly greater than in normal brain. Creatine and NAA concentrations were decreased in all tumours. The longer T2 of trimethylamines and presence of alanine in meningiomas indicate that important differences exist in membrane and glucose metabolism within these tumours when compared to either astrocytomas or normal brain tissue.

Aspartic Acid↗

PubMed1995

A modified imaging sequence for accurate T2 measurements using NMR microscopy.

A modified spin-echo pulse sequence is described that enables accurate T2 measurements to be made in NMR microimaging experiments. The modified sequence eliminates cumulative diffusion losses that lead to an underestimation of the T2 relaxation time using conventional spin-echo pulse sequences. The approach is theoretically justified and confirmed in comparative experiments on phantoms.

Humans↗

PubMed1995

Dynamic gradient-echo and fat-suppressed spin-echo contrast-enhanced MRI of the breast.

PURPOSE: To evaluate heavily T2-weighted, dynamic contrast-enhanced and fat-suppressed magnetic resonance imaging (MRI) of the breast in comparison with conventional imaging and fine needle aspiration cytology (FNAC). PATIENTS AND METHODS: Fifty patients with surgically/pathologically proven breast disease were examined pre-operatively by MRI. The majority, 45 patients, had invasive carcinoma. T1-weighted spin-echo, T2-weighted fast spin-echo (with chemical-shift-selective fat-suppression in 20 cases), rapid dynamic contrast-enhanced gradient-echo and post-contrast fat-suppressed T1-weighted images were obtained. Signal intensity changes during dynamic scanning were assessed qualitatively and quantitatively. Comparison was made with the results of X-ray mammography, ultrasound and fine needle aspiration cytology. RESULTS: Unenhanced MRI was inadequate for determining the location, extent or nature of most lesions even when fat-suppressed T2-weighted images were obtained. Following contrast injection, there was significantly greater enhancement of invasive carcinomas than normal parenchyma. Invasive carcinomas of ductal and lobular subtypes did not differ significantly in their enhancement profiles. Prominent enhancement of the lesion periphery, which was a feature in 33 out of 50 cases (the majority of which were invasive carcinomas) was not due to central tumour necrosis. In four cases, invasive carcinomas which were clearly visible on early dynamic scans could not be identified on post-contrast fat-suppressed images. Lesions that were more numerous or extensive than had been recognised clinically or mammographically were revealed by MRI in 14 patients, though MRI was no more specific than conventional assessment. Invasion of the chest wall was accurately predicted by MRI in three cases. There was excellent correlation between tumour size shown by MRI and histopathology. FNAC was accurate in predicting the final histological diagnosis except in those cases where samples were unsatisfactory. CONCLUSIONS: Contrast-enhanced MRI appears useful in the assessment of suspected malignant breast masses, especially in younger women with predominantly glandular breast tissue. Specificity is no better than FNAC but tumour extent and multifocality are more accurately disclosed than by conventional imaging techniques. Contrast-enhanced chemical-shift-selective fat-suppressed images are sub-optimal in a small proportion of cases (particularly where lesions are located posteriorly) and some benign breast disease may appear misleadingly conspicuous on such images. Morphological features and quantification of lesion enhancement during dynamic scanning presently offer only limited prospects for discrimination between various pathologies. Heavily T2-weighted sequences appear of marginal value.

Adolescent↗

PubMed1995

Dynamic contrast-enhanced magnetic resonance imaging of the breast combined with pharmacokinetic analysis of gadolinium-DTPA uptake in the diagnosis of local recurrence of early stage breast carcinoma.

RATIONALE AND OBJECTIVES: This study was designed to assess the efficacy of dynamic contrast-enhanced magnetic resonance imaging (MRI) of the breast combined with pharmacokinetic analysis of gadolinium (Gd)-DTPA uptake in the diagnosis of local recurrence of early stage breast carcinoma. METHODS: Fifty women treated with breast-conserving surgery and radiotherapy underwent breast MRI. Dynamic magnetic resonance data obtained at four preselected slice locations were analyzed to examine Gd-DTPA uptake based on a pharmacokinetic model using three parameters: wash-in rate, wash-out rate, and amplitude of uptake. Synthetic images were produced from the above parameters and their derivatives--maximum uptake and reciprocal of half the time to maximum. For each region of interest (ROI), median parameter values were calculated. The mean pixel signal intensity of each ROI was plotted against time, and an enhancement index was determined. RESULTS: Sixty ROIs were selected: 49 lesions were benign, and 11, malignant. Significant differences between benign and malignant lesions were found for the enhancement index (P < 0.0001), maximum uptake (P < 0.0001), amplitude of uptake (P < 0.0001), wash-in rate (P = 0.03), wash-out rate (P = 0.01), and the reciprocal of half the time to maximum (P = 0.0005). The respective sensitivities and specificities were as follows: for the enhancement index, 1.00 and 0.96; for maximum uptake, 1.00 and 0.96; for amplitude of uptake, 0.91 and 0.94; for wash-in rate 0.82 and 0.47; for wash-out rate 0.91 and 0.59; and for the reciprocal of half the time to maximum, 1.00 and 0.51. CONCLUSIONS: Dynamic scanning proved essential for the detection and differential diagnosis of local tumor recurrence. Pharmacokinetic analysis of Gd-DTPA uptake can be used to produce parametric images that retain the spatial resolution of the original images while providing additional information about lesion permeability and vascularity, and helping to avoid the observer variability associated with ROI analysis.

Adult↗