摘要:

AbstractFamiliarity with the morphologic changes in the prostate and seminal vesicles (SV) after pelvic irradiation is important to the correct interpretation of follow‐up magnetic resonance (MR) studies. A retrospective study of 38 patients with prostatic or other pelvic tumors treated with radiation showed that 31.6% had a normal prostatic zonal pattern (peripheral zone hyper‐intense to central gland) on T2‐weighted images, and 7.9% showed reversal of the zonal pattern; among the rest, the entire gland was diffusely isointense to fat in 42.1%, hypointense to fat in 10.5%, and hyperintense to fat in 7.9%. Sixty‐three percent of the SV had a normal appearance, 21% had fewer tubules but normal signal intensity (SI), 8% had diffuse loss of SI (hypointense to fat), and 8% were hypointense to muscle. Quantitative measurements of SI of the prostate and SV demonstrated a statistically significant lower mean value for the irradiated patients relative to 10 control patients. A decrease in the size of both the prostate and SV was observed in 33% of patients with baseline studies. Use of additional treatment modalities in patients with prostatic carcinoma appeared to correlate with increased likelihood of developing abnormal changes. The authors conclude that in the irradiated patient, the prostate and SV can develop several patterns of SI abnormalities; in particular, diffuse low SI in the prostate and SV should establish radiation fibrosis as an important differential diagnosis to c

ISSN:1053-1807    

DOI:10.1002/jmri.1880010502

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe goal of this study was to determine the accuracy, the reproducibility, and some of the tissue determinants of image‐based myocardial T2 measurements. Image‐based T2 calculations for the free walls of the right ventricle (RV) and left ventricle (LV), in vitro T2 determination (at 0.47 T), and water, fat, and collagen content analyses were performed in ex vivo hog hearts. T2 values of the RV and LV free walls were also determined from spin‐echo images of 14 healthy human subjects. Preliminary reproducibility studies were performed with 10 sets of images acquired from a single subject. For both in vitro and image‐based T2 values of hog hearts, RV T2 was significantly longer than LV T2. Water content was the only tissue factor to significantly correlate with in vitro and image‐based T2 values. For the 14 human subjects studied, image‐based T2 values calculated from the first‐ and third‐echo images demonstrated a significant difference between LV and RV. The difference was not significant when the first‐ and second‐echo images were used. Image‐based T2 measurements of a single subject showed a coefficient of variation of 6.8% for the LV and 9.1% for the RV. The authors conclude that image‐based T2 measurements of normal myocardium can be made with sufficient precision to identify differences of the magnitude of those found between RV and LV T2 values. Image‐based T2 values of myocardium may provide useful data to

ISSN:1053-1807    

DOI:10.1002/jmri.1880010503

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

年代:1991

数据来源: WILEY

摘要:

AbstractExtensions to a previously described three‐point Dixon magnetic resonance imaging technique are presented that use alternative water/fat phase‐encoding strategies. The technique is generalized to phase encoding of (−θ,0,θ) or (0,θ,2θ) radians, and the signal‐to‐noise ratio (S/N) performance is evaluated. It was found that a θ of 2π/3 radians has optimal S/N but that a θ of π radians is a good compromise and that phase encoding of (O,π, 2π) radians offer an advantage over the previous method, which used (−π, O, π) increments, in that a T2′ (intravoxel susceptibility dephasing) image may be obtained in addition to the usual water, fat, and B0images. A new four‐point method with phase encoding of (O, π, 2π, 3π) radians that can also provide a measure of the spectral width of the fat resonance is suggested. The disadvantages of the method are the extra imagi

ISSN:1053-1807    

DOI:10.1002/jmri.1880010504

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

年代:1991

数据来源: WILEY

摘要:

AbstractA new pulse sequence that increases the number of sections that can be acquired with a T2‐weighted multisection imaging prescription is presented. The sequence achieves a higher efficiency in section acquisition per unit time by interleaving excitation and data collection for up to three separate sections during the long TE (⩾ 80 msec) of a T2‐weighted spin‐echo pulse sequence. The necessary modifications of the section‐select and readout gradient waveforms for the implementation of TE‐interleaved (TEI) sequences, with and without flow compensation, are described. Secondary‐ and stimulated‐echo artifacts are present on some TEI images, but these can be controlled with appropriate spoiler gradients. The signal‐to‐noise ratio for contiguous sections is slightly reduced compared with that of a standard multisection pulse sequence. These observations indicate that the effects of radio‐frequency section interference are enhance

ISSN:1053-1807    

DOI:10.1002/jmri.1880010505

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

年代:1991

数据来源: WILEY

摘要:

AbstractNovel image processing and computer graphics techniques were developed to create three‐dimensional (3D) models of vasculature from magnetic resonance (MR) angiographic images of the head or neck. Region growing was used to produce a mask that isolated the vascular signal in the MR angiographic data. The masked images were subjected to gradient‐shaded volume rendering to create 3D views of the vasculature. The computer‐derived model of intracranial vasculature was then merged with a 3D model of brain parenchyma derived from a set of MR images. The combined display of vascular and gyral anatomy may be useful for neurosurgical pla

ISSN:1053-1807    

DOI:10.1002/jmri.1880010506

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

年代:1991

数据来源: WILEY

摘要:

AbstractThree magnetic resonance (MR) imaging techniques (T1‐weighted, T2‐weighted, and T1‐weighted gadopentetate dimeglumine—enhanced) were compared in 32 consecutive MR imaging studies of 26 patients with suspected musculoskeletal masses. T2‐weighted images were superior to T1‐weighted enhanced images with respect to detection and definition of lesions in 12% of cases (n = 4) and were equal in 88% of cases (n = 28). T2‐weighted images were also superior to T1‐weighted images in 38% of cases (n = 12). In no cases were T1‐weighted enhanced images superior to T2‐weighted images. In two cases, T1‐weighted images were superior to both T1‐weighted enhanced and T2‐weighted images. The authors conclude that gadopentetate dimeglumine did not provide much value in lesion detection above that obtained with T2‐weighted images. They also conclude that T1‐weighted images were occasionally superior to T1‐weighted enhanced images and T2‐weighted images because of loss of definition bet

ISSN:1053-1807    

DOI:10.1002/jmri.1880010507

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

年代:1991

数据来源: WILEY

摘要:

AbstractA dosimetry study of acute tissue damage induced by interstitial application of the neodymium‐yttrium‐aluminum‐garnet (Nd:YAG) laser was performed with magnetic resonance (MR) imaging. The MR appearance of the lesion was correlated with gross and histopathologic findings. Seventy‐six lesions were induced in rabbit muscle with laser power outputs of 5–20 W and exposure times of 20–600 seconds. MR imaging was performed immediately after laser exposure. T2‐weighted spin‐echo images clearly showed the acute thermal injuries caused by laser energy deposition and correlated best with histopathologic findings. These images showed three distinct layers, corresponding to central ablation, coagulative necrosis, and interstitial edema, respectively, in the pathologic findings. Lesion diameters measured on MR images showed a linear correlation with those in gross sections. Lesion volume increased not only with increasing total energy delivered but with increasing power output for a fixed total energy delivered. MR imaging is an accurate modality for dosimetry studies of laser‐indu

ISSN:1053-1807    

DOI:10.1002/jmri.1880010508

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe authors investigated the application of three‐dimensional (3D) magnetization‐prepared rapid gradient‐echo (MP‐RAGE) imaging to the acquisition of small (32 × 128 × 256) T1‐weighted 3D data sets with imaging times of approximately 1 minute. A theoretical model was used to study the contrast behavior of brain tissue. On the basis of these theoretical results, 3D MP‐RAGE sequences were implemented on a 1.5‐T whole‐body imager. Thirty‐two‐section 3D data sets demonstrating good signal‐to‐noise ratios and resolution and strong T1‐weighted contrast were obtained in 1 minute. Compared with standard short TR/TE spin‐echo sequences with the same imaging times and comparable sequence parameters, the 3D MP‐RAGE sequence delivered increases of more than 50% in the white matter/gray matter signal difference‐to‐noise and white matter signal‐to‐noise ratios, and provided almost twice as many sections. These sequences may find a clinical role in 3D scout imaging and screening and in

ISSN:1053-1807    

DOI:10.1002/jmri.1880010509

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe relationship between magnetic field gradient waveform moments and the motion sensitivity of magnetic resonance imaging was explored analytically and by computer simulation. The analysis and simulations revealed several key points. In general, waveform time moments define sensitivity to the time derivatives of position of moving material only at a single time point: the time about which the moments are computed. A Taylor series description of instantaneous position is expanded about this same time point to compute the phase acquired due to specific derivatives of position. A moment is proportional to phase sensitivity to a particular derivative of position throughout the waveform only when sensitivity to all lower‐order derivatives is zero. Under restricted conditions of waveform symmetry and motion characteristics, the phase due to motion may be expressed in terms of the average value of a derivative of position over the duration of the waveform. The choice of the moment center, or point of expansion, adds a degree of freedom that may be used advantageously in the design of motion‐compensating and motion phase‐encoding gradient waveforms. These results facilitate a more complete understanding of the effects of motion through a magnetic field gra

ISSN:1053-1807    

DOI:10.1002/jmri.1880010510

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

年代:1991

数据来源: WILEY

摘要:

AbstractBetween 1980 and 1990, 150 patients with cervicofacial vascular malformations were studied at the authors' institution with computed tomography, plain radiography, and angiography. Since 1989, 34 of these patients have also undergone magnetic resonance (MR) imaging. Capillary‐venous hemangiomas seem to be the best indication for the adjunctive use of MR imaging. The venous pouches, characteristic of this type of lesion, cause elevated signal intensity, well seen on the T2‐weighted images. Excellent fat and muscle differentiation with MR imaging allows appreciation of the depth of extension of these lesions and their delimitation from normal tissue. Arteriovenous malformations (AVMs) are characterized by serpentine signal voids, indicative of the high flow rate of these lesions. Delimitation of the AVM nidus in the midst of the afferent and efferent dilated vessels is often difficult. Study of immature angiomas with MR imaging should be restricted to lesions in specific locations (eg, orbital, laryngeal). Lymphatic malformations showed either tissular or cystic signal intensity changes. MR imaging does not replace other studies but represents an important complementary study for the delineation and diagnosis of deep extensions of vascular malformations, allowing better planning of ther

ISSN:1053-1807    

DOI:10.1002/jmri.1880010511

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

年代:1991

数据来源: WILEY