摘要:

AbstractMagnetic resonance imaging has achieved clinical importance and has become the primary tool in the investigation of head, spinal cord, pelvis, cancellous bone, pericaridium (with gating), gallbladder, lymph node masses, and very soon, in the evaluation of joints. In many areas, particularly with respiratory and ECG gating, this method promises to replace all other imaging modalities with the precision of information obtained. Today the exceptions are the alimentary tube and its mesentery, between the esophagus and rectum, and the peripheral lung.

ISSN:0740-3194    

DOI:10.1002/mrm.1910020402

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

年代:1985

数据来源: WILEY

摘要:

AbstractWhole‐body NMR imaging antennas (probes) are strongly affected by the inevitable magnetic and controllable dielectric losses. Using a convenient parallelepiped model, the magnetic losses are evaluated. By introducing the “ideal power gain,” the best possible antenna performance is delimited as a function of the frequency and the patient examined. By using a cylindrical model and introducing the “electrostatic quality factor” (EQF), the dielectric loss of any antenna can be estimated. With the help of the wideband field measurer described, a simple experimental arrangement, and the analysis developed, the performance of whole‐body NMR antennas can be compared and/or evaluated. An example is given for the application of this model at 6.4, 21, and 64 MHz for three typic

ISSN:0740-3194    

DOI:10.1002/mrm.1910020403

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

年代:1985

数据来源: WILEY

摘要:

AbstractSimple theoretical estimates of the average, maximum, and spatial variation of the radiofrequency power deposition (specific absorption rate) during hydrogen nuclear magnetic resonance imaging are deduced for homogeneous spheres and for cylinders of biological tissue with a uniformly penetrating linear rf field directed axially and transverse to the cylindrical axis. These are all simple scalar multiples of the expression for the cylinder in an axial field published earlier (Med. Phys.8, 510 (1981). Exact solutions for the power deposition in the cylinder with axial (Phys. Med. Biol.23, 630 (1978) and transversely directed rf field are also presented, and the spatial variation of power deposition in head and body models is examined. In the exact models, the specific absorption rates decrease rapidly and monotonically with decreasing radius despite local increases in rf field amplitude. Conversion factors are provided for calculating the power deposited by Gaussian and sinc‐modulated rf pulses used for slice selection in NMR imaging, relative to rectangular profiled pulses. Theoretical estimates are compared with direct measurements of the total power deposited in the bodies of nine adult males by a 63‐MHz body‐imaging system with transversely directed field, taking account of cable and NMR coil losses. The results for the average power deposition agree within about 20% for the exact model of the cylinder with axial field, when applied to the exposed torso volume enclosed by the rf coil. The average values predicted by the simple spherical and cylindrical models with axial fields, the exact cylindrical model with transverse field, and the simple truncated cylinder model with transverse field were about two to three times that measured, while the simple model consisting of an infinitely long cylinder with transverse field gave results about six times that measured. The surface power deposition measured by observing the incremental power as a function of external torso radius was comparable to the average value. This is consistent with the presence of a variable thickness peripheral adipose layer which does not substantially increase surface power deposition with increasing torso radius. The absence of highly localized intensity artifacts in 63‐MHz body images does not suggest anomalously intense power deposition at localized internal sites, although peak power is difficult to

ISSN:0740-3194    

DOI:10.1002/mrm.1910020404

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

年代:1985

数据来源: WILEY

摘要:

AbstractTo compare the specificity ofT1measurement for the diagnosis of prostatic carcinomain vivo, two groups of patients with clinically enlarged prostate glands have been imaged. One group comprising 25 patients was imaged at 1.7 MHz the other comprising 51 patients at 3.4 MHz.T1measurements together with the gross anatomical appearances of the prostate gland were observed and compared with the clinical and histologic diagnoses. At 1.7 MHz it was found that theT1measurement of carcinoma of the prostate and benign hypertrophy of the prostate fell into two distinct ranges with no overlap between the two conditions. Three false‐positive diagnoses of carcinoma were made in patients with prostatitis where theT1values fell in the upper part of the carcinoma range.T1measurement in the group studied at 3.4 MHz demonstrated no specific value for either condition and diagnosis of malignancy had to be made from the morphologic appearances of the gland. Morphologically benign hypertrophy appeared homogeneous while carcinoma appeared heterogeneous with small areas of increasedT1in the malignant part of the glan

ISSN:0740-3194    

DOI:10.1002/mrm.1910020405

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

年代:1985

数据来源: WILEY

摘要:

AbstractExisting models for the contrast between one tissue and another in NMR imaging have shown that there are regions of ambiguity particularly in spin‐echo sequences. This paper indicates that there are further problems due to variations in slice formation with tissue parameters, and that it is necessary to be very conservative in assessing the magnitude ofT1in any imaging system. The change in shape affects the appearance of images due, in essence, to adjustments in partial volume effects, with some of the contributions to the signal from lesions with longT1coming from different regions to those for normal tissue. A simple model for a slice is used because the actual form in a real imaging situation is the result of a number of factors which are usually not accurately enough know

ISSN:0740-3194    

DOI:10.1002/mrm.1910020406

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

年代:1985

数据来源: WILEY

摘要:

AbstractT2‐selective proton imaging at 10 MHz is based on a Carr‐Purcell‐Meiboom‐Gill pulse sequence with at least 36 echoes and 2τ ≃ 6 ms employing the projection reconstruction technique. The transverse magnetization decay of the volume elements is multiexponential composed of up to three monoexponentialT2components. TheT2values are arranged inT2histograms which are slice specific.T2windows are defined in theT2histogram and used for imaging and for selectingT2values which are assigned to proton classes and tissues. Tissue characterization is based on the visualization of differences inT2behavior. TheT2values are transformed into 256 gray levels or, by use of a red‐green‐blue lookup table, into a rainbow code. Two display techniques have been developed and implemented in the RWTH Aachen Magnetic Resonance Software System (RAMSES): (i) for nonselectiveT2imaging with secondaryT2selection and encoding of molecular classes on the basis ofT2values; (ii) forT2‐selective imaging by employing combined primary and secondaryT2selection and encoding particular tissues and variations therein. The tissues can be identified by selecting different classes of molecules, like water, lipids, and proteins, when shifting the primaryT2window on theT2axis o

ISSN:0740-3194    

DOI:10.1002/mrm.1910020407

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

年代:1985

数据来源: WILEY

摘要:

AbstractSeveral methods are available for the localization of high‐resolution spectra. When the sample is a human subject, it may be difficult to realize a viable experimental protocol because the size and geometry of the subject often conflict with efficient probe design. In this paper a spectroscopic localization method is described which is based on the method of rotating frame imaging. A novel surface‐coil probe has been developed so that this experiment can be performed on a large sample.31P spectra from the thorax of a human subject are presented in which signals from liver and intercostal muscle are resolved. These data demonstrate that spatially resolved spectra of metabolitesin vivomay be obtained in a time that is acceptable for patient examinat

ISSN:0740-3194    

DOI:10.1002/mrm.1910020408

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

年代:1985

数据来源: WILEY

摘要:

AbstractPhosphorus‐31 NMR spin‐lattice relaxation times and resonance linewidths of rat leg muscle, brain, and liver metabolitesin vivohave been examined at 1.9‐, 4.7‐, and 8.5‐ T static magnetic field strengths. The resonance linewidthsexpressed in ppmthat have been measured are independent of field strength. The spin‐lattice relaxation times of muscle and brain phosphorus metabolites decrease linearly with increasing field strength while those of liver are constant over the range of static fiel

ISSN:0740-3194    

DOI:10.1002/mrm.1910020409

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

年代:1985

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910020401

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

年代:1985

数据来源: WILEY