摘要:

AbstractThis study was designed to estimate the contribution of repositioning inaccuracies to measured intracranial lesion volumes in multiple sclerosis (MS). Five patients with MS were each scanned 10 times, using spin‐echo imaging (2,000/34/90), contiguous 5‐mm slices, and different scanning positions. The maximum displacements from baseline were ±4° (AP rotation) and 3 mm (slice offset). Lesion volume was measured twice for each scan using a semiautomated contour technique. Measured lesion volumes ranged from 4,328 mm3to 164,831 mm3. The mean intrarater coefficient of variation (CV) calculated for individual patients ranged from 1.1 to 4% (median, 1.7%). Using analysis of variance, the overall variance and CV due to altered scan position were greater than that due to rater error (repositioning CV 4.0%, intrarater CV 3.5%). The worst‐case difference between volumes in the same patient ranged from 8.9 to 32% (median, 9.9%). Both rater and repositioning errors were greater for smaller lesion volumes. The maximum potential error due to repositioning inaccuracies is of a similar magnitude to the 5 to 10% expected change in lesion volume over 1 year. This study justifies continued careful attention to accuracy in repositioning for serial MR studies in patients

ISSN:1053-1807    

DOI:10.1002/jmri.1880060502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractThe aim of the study was to compare the first‐passage profiles of dysprosium diethylenetriamine penta‐acetic acid bis(methylamide) (DTPA BMA) and the superparamagnetic iron oxide particles NSR 0430 in regions with severe and moderate cerebral ischemia. In seven rats subjected to middle cerebral artery occlusion, two dynamic MR perfusion imaging series were acquired after intravenous bolus injections of .5 mmol/kg dysprosium DTPA BMA and .06 mmolFe/kg iron oxide particles, respectively. The doses were chosen to obtain similar maximum signal change in normally perfused brain. The first‐passage profiles were compared in a region of interest (ROI) in the core area with severe ischemia and in a ROI in the penumbra area of moderate ischemia. The results were compared both as the calculated mean signal intensity versus time curves for all seven rats and statistically for an estimated mean transit time (MTT) after gamma variate fitting of the calculated concentration versus time curves. The first‐passage profiles for the two contrast agents were similar, both in the core area of severe ischemia and in the penumbra area of moderate ischemia. In this rat stroke model, dysprosium DTPA BMA and the superparamagnetic iron oxide particles NSR 0430 were found to be equally efficacious for the diagnosis of the perfusion deficit, but if safe for human investigations, iron oxide particles would have an advantage as equal susceptibility effect may be achieved with smaller injection

ISSN:1053-1807    

DOI:10.1002/jmri.1880060503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractImaging of activated brain areas based on changes of blood deoxyhemoglobin levels is now possible with MRI. Acetazolamide (ACZ) increases cerebral blood flow (CBF) without changing cerebral oxygen consumption; this results in signal changes observed in gradient echo MR images from the areas with an increase in CBF. We assessed signal changes after ACZ application in seven healthy subjects with a conventional 1.5‐T MRI scanner. The susceptibility‐sensitized three‐dimensional fast low‐angle shot (FLASH) sequence was used to visualize signal changes induced by ACZ. We analyzed anatomic localization of different ranges of detected signal changes. ACZ caused significant signal changes in the gray matter and at the edge of the cerebral cortex, the latter corresponding to draining surface veins. No significant differences were seen among different brain areas within the same slice. Using the maximum intensity projection technique, we were able to partially separate signal changes originating in draining veins from signal originating in the gray matter microvasculature. Signal changes from the microvessels reflect cerebrovascular reserve. Blood‐oxygen‐level‐dependent (BOLD) based MRI can evaluate CBF reserve with high spatial and temporal resolution. To assess cerebrovascular reserve, it is necessary to separate signal changes originating in large vessels from signal from brain mic

ISSN:1053-1807    

DOI:10.1002/jmri.1880060504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractCarotid artery atherosclerotic plaques (APs) can lead to brain ischemia, an event shown to correlate with both the degree of stenosis and the composition of the AP. Currently, accurate estimates of stenosis can be obtained by either x‐ray angiography or three‐dimensional time of‐flight (TOF) magnetic resonance angiography (MRA). Our purpose was to determine whether three‐dimensional TOF MRA images could also provide information on plaque location, morphology, and composition. Seven pre‐endarterectomy patients underwent three‐dimensional TOF MRA. After endarterectomy, plaque histology was evaluated. Three‐dimensional TOF MRA images contained sufficient soft tissue contrast to differentiate the plaques from the surrounding tissues in all cases. Estimation of plaque morphology had 80% correlation with histology. Finally, intraplaque hemorrhage and calcification were depicted as regions of moderately high and very low intensity, respectively. These preliminary results suggest that three‐dimensional TOF MRA may be useful in studying the development and progression of carotid

ISSN:1053-1807    

DOI:10.1002/jmri.1880060505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractPhase‐contrast magnetic resonance imaging (PC‐MRI) can be used to produce multiframe cine flow images of the coronary arteries. Accurate coronary flow measurement requires the elimination of respiratory motion artifacts using k‐space segmentation to acquire the data in a single breath‐hold. However, the duration of the breath‐hold is proportional to the number of cine frames. In the present study, the number of cine frames was varied and the accuracies of the coronary flow measurements were assessed using perivascular US. For the range of flows studied (2 ml/min to 147 ml/min), the correlation coefficients for PC‐MRI and US increased (.70–.98) and the limits of agreement improved (±45 ml · min−1to ± 10 ml · min−1) as the number of cine frames increased from one to six. The results suggest that the accuracy of breath‐hold cine PC‐MRI measurements of coronary artery flow improves as the number

ISSN:1053-1807    

DOI:10.1002/jmri.1880060506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractBoth benign and malignant breast lesions may exhibit intense contrast enhancement when imaged using gadolinium‐enhanced MRI. We propose a quantitative approach for fitting dynamic signal intensity (SI) data that may distinguish benign from malignant lesions. We studied 78 lesions in 75 women (18 malignancies, 16 fibroadenomas, and 44 other benign breast lesions) to determine the potential of this model for decreasing false‐positive MR results. Twenty‐eight lesions showed no enhancement; all were benign. One lesion showed a complex pattern not amenable to region‐of‐interest analysis and was considered a false positive. SI versus time data for the remaining 49 lesions were fit to the proposed model. We found that one parameter,M, the normalized slope of the SI enhancement profile evaluated at half the maximal signal intensity, seemed to be highly correlated with malignancy and offered improved discrimination between malignant and benign lesions compared to a previously published two‐point s

ISSN:1053-1807    

DOI:10.1002/jmri.1880060507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper describes two semiautomated methods of segmentation of breast tumors from dynamic MR images obtained subsequent to administration of gadopentate dimeglumine. The first method, based on temporal correlation, generates a similarity map from the dynamic scans in which the value of each pixel is determined by its temporal similarity to a reference region of interest. The second method uses multispectral analysis and generates a feature map from a scatterplot of pixel intensities in the pre‐ and postcontrast images. The segmentation methods were tested on malignant and benign breast lesions in 11 patients with a range of tumor volumes and percentage contrast enhancement. The accuracy of both segmentation techniques and reproducibility of the multispectral method were investigated. A comparison of the two methods established that the temporal correlation method was superior based on accuracy, extent of user interaction, and speed of segmentatio

ISSN:1053-1807    

DOI:10.1002/jmri.1880060508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractDynamic MR images of the passage of gadopentetate dimeglumine through the kidneys of normal rats are obtained using a dual gradient‐echo sequence. The amplitudes of gradient echoes are defined by local T1 and T2* values in the tissue. The ratio of these amplitudes, primarily defined by local T2*, can be used to differentiate between T1 and T2* effects. This is particularly important with regard to renal studies because, due to a highly inhomogeneous distribution of gadopentetate dimeglumine in the kidney, T2* shortening can impede MR data analysis. To study changes in the observed signal caused by gadopentetate dimeglumine, curves of MR renal intensity versus time were obtained in the cortex and medulla after administration of the contrast agent. Using T2* compensation, distinct temporal peaks were observed in the cortex and outer medulla, indicating a high concentration of gadopentetate dimeglumine in the vascular phase. The authors conclude that this technique can be a useful tool for studying renal function noninvasivel

ISSN:1053-1807    

DOI:10.1002/jmri.1880060509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractTo determine the value of MRI in temporomandibular joint (TMJ) disorders, the data of MRI‐proven anterior disc dislocation without reduction (ADWOR) were correlated with clinical history and clinical data. MRI demonstrated degenerative bony changes and a reduced sagittal diameter of the condyle, a variable degree of disc deformation, and a thinned bilaminar zone in each of the joints with ADWOR, which clearly differed from patients with anterior disc dislocation with reduction (ADWR) (P = .01) and normal disc position (NDP) (P<.001). Of 59 patients and 83 TMJs that had been investigated in a 2‐year period, as shown by MRI, 22 patients (27 TMJs) had ADWOR (32 %), 16 joints had NDP (19 %), and 40 patients had ADWR (49 %). In patients with ADWOR, the clinical history revealed pain in either of the joints and/or cervical or masticatory muscles in 25 (93%) joints. Clinical investigation revealed various abnormalities in 22 joints; five of those presented without any pathologic clinical finding. Mouth opening was unlimited in nine patients (47%), palpation of the muscles of mastication was painless in 13 patients (52%), and joint noises during mouth opening or closing were noted in 14 patients (56%). According to clinical histories, four patients were suspected to have become symptomatic only after dental treatment. ADWOR is difficult to diagnose with clinical methods alone. The indication for MRI evaluation of the TMJ should be extended for asymptomatic patients with a history of limitation in mouth opening and pathologic x‐ray morphology of the condyle. Because symptoms may arise after dental treatment in these patients, aggravation of internal derangement may be avoided by careful han

ISSN:1053-1807    

DOI:10.1002/jmri.1880060510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractA new algorithm is introduced for inversion recovery (IR) image reconstruction. The original complex image is modeled as a product of three factors: magnitude, polarity, and a smoothly changing phase factor. The simple binary polarity factor is first unified by a region‐growing spin reversal (RGSR) operation, allowing the phase factor to be extracted. Multiplying the complex conjugate of the phase factor with the original complex data yields the desired IR contrast. The RGSR process is repeated with multiple seeds distributed in the field of view (FOV), and the results are added together, enabling disconnected tissues in the FOV to be handled. The extracted phase factor is filtered to reduce noise and artifacts, without losing useful information. The method is fully automatic and has been used practically in a large number of clinical examinations. The algorithm may also be useful for phase correction in simple proton spectroscopic imagin

ISSN:1053-1807    

DOI:10.1002/jmri.1880060511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY