摘要:

AbstractRenal artery MR angiography has now emerged as a safe, accurate approach to renal arteriography. A comprehensive examination, including both three‐dimensional (3D) dynamic gadolinium‐enhanced and 3D phase contrast MRA techniques, allows evaluation of both the aorta‐renal and splanchnic arterial anatomy as well as the hemodynamic significance of any stenoses identified. The 3D gadolinium‐enhanced MRA technique produces a contrast arteriogram but without risks of iodinated contrast or ionizing radiation. The 3D phase contrast technique is a flow‐based technique, which may show dephasing in the presence of hemodynamically significant stenoses. A comprehensive examination should also include T1‐ and T2‐weighted imaging for the assessment of potential neoplastic masses and the ubiquitous renal cysts. Through trial and error over the course of over a thousand examinations, this comprehensive approach to the MR evaluation of renal vascular patholog

ISSN:1053-1807    

DOI:10.1002/jmri.1880080302

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

年代:1998

数据来源: WILEY

摘要:

AbstractMagnetic resonance cholangiopancreatography (MRCP) has replaced direct cholangiography and pancreatography in many instances. Its complete noninvasiveness and flexibility are less onerous for patients. For the use of screening as well as scrutiny, MRCP has played an important role in diagnosing various pathologies in this field. The usefulness of MRCP is not limited to anatomical evaluations; it can also yield physiologic and functional information. From a cost‐performance basis, MRCP is undoubtedly superior to direct methods. Coupled with a cutting‐edge MR system, MRCP has the potential to limit the use of invasive transpapillary and percutaneous methods merely to interventional purposes. In the near future, the emergence of interventional MR scanners will make MRCP even more competitive, and the replacement will be accelera

ISSN:1053-1807    

DOI:10.1002/jmri.1880080303

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

年代:1998

数据来源: WILEY

摘要:

AbstractConventional MRI (cMRI) has shown that brain abnormalities without clinical stroke can manifest in patients with sickle cell disease (SCD). We used quantitative MRI (qMRI) and psychometric testing to determine whether brain abnormalities can also be present in patients with SCD who appear normal on cMRI. Patients 4 years of age and older with no clinical evidence of stroke were stratified by cMRI as normal (n= 17) or abnormal (n= 13). Spin‐lattice relaxation time (T1) of gray and white matter structures was measured by the precise and accurate inversion recovery (PAIR) qMRI method. Patient cognitive ability was assessed with a standard psychometric instrument (WISC‐III or WISC‐R). In all 30 patients with SCD, qMRI T1 was lower than in 24 age‐ and race‐matched controls, in cortical gray matter (P<.0006) and caudate (P<.0009), as well as in the ratio of gray‐to‐white matter T1 (P<.008). In the 17 patients who were shown to be normal by cMRI, qMRI T1 was still lower than in controls, in both cortical gray matter (P<.02) and caudate (P<.004). Histograms of voxel T1 show that the proportion of voxels with T1 values intermediate between gray and white matter (ie, consistent with encephalomalacia) was 9% higher than controls in patients shown to be normal by cMRI (P<.05) and 15% higher than controls in patients shown to be abnormal by cMRI (P<.0005). The full scale intelligence quotient (FSIQ) of all patients with SCD was 75, compared to the FSIQ of 88 in a historical control group of patient siblings (P<.001). The FSIQ of patients shown to be normal by cMRI was 79, significantly lower than the FSIQ of patient siblings (P<.04). The FSIQ of 71 in patients shown to be abnormal by cMRI was significantly lower than both the patient siblings (P<.005) and the patients shown to be normal by cMRI (P<.04). Patients shown to be abnormal by cMRI scored lower than patients shown to be normal by cMRI, specifically on the subtests of vocabulary (P= .003) and information (P= .03). Cognitive impairment is thus significant, even in patients with SCD who were shown to be normal by cMRI, suggesting that cMRI may be insensitive to subtle neurologic damage that can be detected by qMRI. Because cognitive impairment can occur in children normal by cMRI, our findings imply that prophylactic therapy may be needed earlier in the course of SCD to mitigate neur

ISSN:1053-1807    

DOI:10.1002/jmri.1880080304

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

年代:1998

数据来源: WILEY

摘要:

AbstractWe describe a fast double inversion recovery (DIR) imaging sequence that effectively attenuates signal from both white matter and cerebrospinal fluid (CSF). The pulse sequence uses a novel inversion/excitation scheme and fast spin‐echo readout to maximize scan efficiency. The white matter/CSF suppressed images can be acquired from the entire brain in ∼6 minutes. Evaluation of the fast DIR sequence on patients with multiple sclerosis (MS) demonstrates high lesion conspicu

ISSN:1053-1807    

DOI:10.1002/jmri.1880080305

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe purpose of this work was to develop a method for determining the T1satand magnetization transfer (MT) rate constants by analyzing the slice‐select flip angle dependent MT behavior of normal white and gray matter. The technique uses a high MT power, three‐dimensional (3D) gradient‐recalled echo (GRE) sequence, with a well chosen MT pulse frequency offset, such that the experimental conditions closely satisfy requisite assumptions for invoking a first order rate process for MT. Integral to this method is that the T1satand MT ratio values are obtained under explicitly identical MT saturation conditions. The T1satof white matter was found to be approximately 300 msec, and the MT rate constant was approximately 2.0 sec−1. The T1satof gray matter was approximately 500 msec, and the MT rate constant was 1.1 sec−1. We also found a strong dependence of the MT rate constant on the slice‐select flip angle used for the imaging sequence, independent of the MT saturation parameters. Strongly T1‐weighted imaging sequences can result in the underestimation of the MT rate constant by 50%. Practical technical suggestions for quantitative MT experiments

ISSN:1053-1807    

DOI:10.1002/jmri.1880080306

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

年代:1998

数据来源: WILEY

摘要:

AbstractDisordered lingual function is a common clinical attribute of patients with oropharyngeal dysphagia. To determine physiologic patterns of lingual tissue motion during swallowing, we imaged the actively deforming tongue during water bolus swallows with sequential single‐slice sagittal orientation echo‐planar imaging. At rest, with the bolus contained in the oral cavity before swallow initiation, the tongue displayed a characteristic curved configuration consisting of a convex surface (anterior to the bolus) in continuity with a concave surface (containing the bolus) and a posterior‐located convex surface (comprising the tongue base). With swallow initiation, the previously deformed tongue underwent rapid biphasic displacement: (a) superior displacement of the anterior tongue and deepening of the midposterior‐located bolus‐containing concavity, resulting in a laterally beveled surface encompassing the bolus; and (b) retrograde displacement of the configured tissue, resulting in clearance of the bolus from the oral cavity to the oropharynx. These findings indicate that deglutitive tongue action can be depicted by echo‐planar imaging as a series of deformative surface modifications, which are related to the activity of intrinsic and extrinsic ling

ISSN:1053-1807    

DOI:10.1002/jmri.1880080307

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

年代:1998

数据来源: WILEY

摘要:

AbstractA macromolecular MR contrast medium (MMCM) designed to permit histochemical staining and specific tissue localization, albumin‐(biotin)10‐(Gd‐DTPA)25 (Bio‐Alb‐Gd), was used in a rat model of reperfused myocardial infarction to confirm the presence and distribution of microvascular hyperpermeability. T1‐weighted spin‐echo images were acquired before and after administration of Bio‐Alb‐Gd. An avidin‐biotin‐complex (ABC) stain, specific for the biotinylated MR contrast medium, was used to define the MMCM distribution and to detect any regional change in micro‐vascular permeability related to infarction. Immediately after Bio‐Alb‐Gd administration, the infarcted region was enhanced, with greatest signal intensity noted at the rim and less at the center. There was a gradual increase in signal intensity of the initially hypointense central region. The steady increase in signal intensity of the central region suggested convection transport of MMCM through the interstitial space and its influx into cellular compartment after leakage from the vascular compartment. Histologic findings confirmed regional microvascular hyperpermeability corresponding to the site of infarction and a predominant rim distribution of the MMCM. Bio‐Alb‐Gd was identified at high microscopic power in the intravascular, interstitial, and intracellular spaces at the periphery of reperfused infarcted myocardium. Bio‐Alb‐Gd can be used as an MR contrast medium in reperfused infarcted myocardium to confirm the existence and to localize altered microvascular permeability to macromolecules. Bio‐Alb‐Gd contrast technique removes all the ambiguity between the distribution of the MR or other imaging contrast agent and the distribution of t

ISSN:1053-1807    

DOI:10.1002/jmri.1880080308

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

年代:1998

数据来源: WILEY

摘要:

AbstractMotion of the coronary arteries during the heart cycle can result in image blurring and inaccurate flow quantification by MR. This condition applies particularly for longer acquisition windows that are typical of breath‐hold coronary flow measurements. To determine the sensitivity of the technique to in‐plane motion of different coronary arteries, the temporal variation in coronary position was measured in a plane perpendicular to the proximal portion of the vessel. The results indicated the presence of substantial displacement of the coronary arteries within the cardiac cycle, with a magnitude of motion approximately twice as large for the right as for the left coronary arteries. An estimation of the resulting vessel blurring was calculated, showing that the duration of the acquisition window for high spatial resolution coronary flow acquisitions should be less than 25 to 120 msec, depending on the specific coronary artery studied. In addition, these data specify optimal acquisition window placement for high resolution coronary angiogra

ISSN:1053-1807    

DOI:10.1002/jmri.1880080309

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

年代:1998

数据来源: WILEY

摘要:

AbstractReliable diagnosis and quantification of mitral regurgitation are important for patient management and for optimizing the time for surgery. Previous methods have often provided suboptimal results. The aim of this in vitro study was to evaluate MR phase‐velocity mapping in quantifying the mitral regurgitant volume (MRV) using a control volume (CV) method. A number of contiguous slices were acquired with all three velocity components measured. A CV was then selected, encompassing the regurgitant orifice. Mass conservation dictates that the net inflow into the CV should be equal to the regurgitant flow. Results showed that a CV, the boundary voxels of which excluded the region of flow acceleration and aliasing at the orifice, provided accurate measurements of the regurgitant flow. A smaller CV provided erroneous results because of flow acceleration and velocity aliasing close to the orifice. A large CV generally provided inaccurate results because of reduced velocity sensitivity far from the orifice. Aortic outflow, orifice shape, and valve geometry did not affect the accuracy of the CV measurements. The CV method is a promising approach to the problem of quantification of the MR

ISSN:1053-1807    

DOI:10.1002/jmri.1880080310

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

年代:1998

数据来源: WILEY

摘要:

AbstractPresaturation of fat signals by frequency‐selective radiofrequency (RF) pulses is often applied in MR angiography to improve the visualization of the blood vessels. Unfortunately, standard fat saturation methods might cause a considerable reduction of the blood signal in the measured slices. This effect is caused by an attenuation of blood magnetization in remote tissue regions with water protons showing a similar Larmor frequency as the fat protons in the recorded slice. The affected blood water protons subsequently flow into the recorded slice and provide low signal intensity. Suitable spatial‐spectral selective methods for slice‐selective fat saturation were developed to avoid this unwanted effect. A spatial‐spectral fat saturation technique was compared with a corresponding only spectrally selective approach. Both saturation techniques were included in a standard two‐dimensional (2D) cine sequence and applied in angiographic examinations of the thighs. The results indicate that spatial‐spectral saturation (acting slice selectively) leads to a clearly higher blood signal intensity in fat‐suppressed MR angiography compared with standard techniques, especially in measurements performed during the systolic phase of the

ISSN:1053-1807    

DOI:10.1002/jmri.1880080311

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

年代:1998

数据来源: WILEY