摘要:

AbstractIn chronic obstructive pulmonary disease (COPD), the development of pulmonary hypertension is common. This study was performed to assess the signs of right ventricular (RV) pressure overload and RV failure in COPD. In 8 COPD patients without primary cardiac disease, RV wall thickness, mass, and end‐diastolic volume were measured by cardiac‐triggered cine MRI. MR phase‐contrast velocity quantification was used to measure stroke volume and the patterns of flow into and out of the RV. Data of patients were tested versus those of a control group matched for age (n = 8). Results showed that the RV wall thickness was increased (.6 ± 0.1 vs 0.4 ± 0.1 cm,P<.001). RV mass was increased (67 ± 11 vs 57 ± 5 g,P<.005). RV stroke volume was decreased (57 ± 13 vs 71 ± 13 ml,P<.01), but RV ejection fraction was not different. In the main pulmonary artery flow, the quotient of acceleration time divided by ejection time was decreased (33 ± 5% vs 38 ± 4%,P<.05), which is indicative of pulmonary hypertension. In conclusion, this MRI protocol provides a tool to assess the effects of RV pressure overload in COPD before heart failure has be

ISSN:1053-1807    

DOI:10.1002/jmri.1880080502

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe goal of this study was to put together several techniques of image segmentation to provide a reliable assessment of the left ventricular mass with short‐axis cardiac MR images. No initial manual input was required for this process based on region growing, gradient detection, and adaptive thresholding. A comparison between actual mass and automatic assessment was implemented with 9 minipigs that underwent spin‐echo MR imaging. Fifteen normal volunteers were studied with a fast‐gradient‐echo sequence. The automatic segmentation was then controlled by three trained observers. Actual mass and automatic segmentation were strongly correlated (r= .97 withP<.01). For normal volunteers, the standard error of estimation of the automatic assessment (12 g) compared well with the average myocardial mass (120 ± 30 g) and the interobserver reproducibility of the manual assessment (9 g). These results allow the application of this method to the quantification of the left ventricular function and mass in clinical

ISSN:1053-1807    

DOI:10.1002/jmri.1880080503

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to s the value of MRI for measurement of pulmonary autograft diameters after transplantation to the aortic root in adults. Thirty‐eight adults underwent this operation. MRI and trans‐esophageal echocardiography (TEE) were performed in 30 and 27 patients, respectively, after a mean follow‐up period of 2.8 years. For internal validation of MRI, measurements at the diastolic short and long axes of the sinus level were used. Pulmonary autograft diameters were measured and compared with MRI and TEE at five different levels: the subannular region (1), an‐nulus (2), sinus (3), sinotubular junction (4), and the distal part of the autograft (5). The correlation coefficient (r2) between long‐ and short‐axis measurements for corresponding sinuses was .97. Diameters obtained with MRI were 1 to 3 mm larger than those obtained with TEE (P.3). Cine gradient echo MRI is an appropriate technique to evaluate pulmonary autograft diameters during follow‐up. Concordance with TEE was good, apart from a systematic differen

ISSN:1053-1807    

DOI:10.1002/jmri.1880080504

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

年代:1998

数据来源: WILEY

摘要:

AbstractAmong the ultrafast MRI techniques, the single‐shot fast spin‐echo sequence offers a robust alternative to echo planar imaging, essentially because of a much reduced sensitivity to B0inhomogeneity. This property is particularly appealing in situations in which B0in‐homogeneities can be severe and difficult to correct, such as in cardiac imaging. With single‐shot cardiac imaging, however, achieving high resolution over the necessarily large field of views without introducing back‐folding artifacts is problematic. One option is to use multishot sequences. However, then issues related to cardiac gating arise. Another solution is to use, optimized presaturation slabs with quadratic phase pulses generated by the Shinnar‐LeRoux algorithm. These can be set to reduce the field of view in the phase‐encoding direction, resulting in a reduction in the number of phase‐encoding steps. For instance, for a 1 × 2‐mm spatial resolution, over a rectangular, 250 × 125‐mm field of view, and using a half Fourier acquisition, an echo‐train length of only 40 is required. With a 4.5‐msec echo spacing, the total imaging time is ≈︁ 180 msec. The efficacy of this solution on phantoms and volunteers is demonstrated. Multislice short‐axis examinations of the whole heart, realized within a single short breath‐hold of ∼ 10 seconds, are shown. The possibility of investigating not only cardiac anatomy but also both contractility an

ISSN:1053-1807    

DOI:10.1002/jmri.1880080505

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe application of fast imaging is necessary to reduce the scanning time for cardiac volumetric MRI. Fast spiral, echo planar imaging (EPI), and fast low‐angle shot (FLASH) imaging are rapid MRI techniques that allow image acquisition within a fraction of a second. Performed as a multi‐shot technique, breath‐hold imaging with high temporal and spatial resolution is feasible. This study evaluated the accuracy of interleaved spiral, EPI, and FLASH imaging for measuring ventricular volume and mass at .5T. Breath‐hold short‐axis cines in parallel planes covering both ventricles were acquired in 16 volunteers with all three fast methods, as well as with conventional gradient‐echo imaging for comparison. All fast techniques showed good agreement with conventional imaging. Despite its lower temporal resolution, FLASH imaging yielded higher image quality than EPI and spiral, making FLASH more reliable and suggesting that at .5T, it is the method of choice for rapid cardiac volumet

ISSN:1053-1807    

DOI:10.1002/jmri.1880080506

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

年代:1998

数据来源: WILEY

摘要:

AbstractSimulation of MR images is a useful tool for offline sequence development and as an aid to understanding image formation. One particular application of simulation is MR tagging, which is used for tracking myocardial motion. Simple spatial‐domain methods cannot adequately represent effects common in these images, such as motion artifact and signal wrap. An existing frequency‐domain model is shown to be inappropriate for tagged images, and an extension based on the Bloch equations and Fourier shift theorem is described to correct this. Software incorporating the new model is used to generate ideal tag intensity profiles and to accurately simulate tagged images. The shifted k‐space patterns associated with tagged images, and their dependence on the order of the binomial tagging sequence, are explained. An application of the Fourier shift theorem is suggested that allows more rapid simulation of static tagged i

ISSN:1053-1807    

DOI:10.1002/jmri.1880080507

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

年代:1998

数据来源: WILEY

摘要:

AbstractFour rabbits in which atherosclerotic disease was induced by diet and balloon angioplasty underwent conventional angiography and MR angiography (MRA) using a black blood pulse sequence before and 10 minutes after the iv injection of a macromolecular contrast agent, NC 100283 (1.0 mmol/kg), a dysprosium diethylenetriaminepentaacetic acid hexamethylenediamine copolymer (Dy‐DTPA polymer). Intraluminal signal intensity, apparent wall thickness, and lumen size measurements of the aorta and proximal common iliac arteries on precontract MRA images were compared with postcontrast images. Aortic lumen diameter measurements on the precontrast and postcontrast MRA studies were compared with lumen diameters from conventional angiograms. Intraluminal signal intensity decreased on postcontrast MRA images compared with precontrast images, with an average loss of signal equal to 29% (P<.05). Apparent wall thickness decreased by 24% (P<.05). Lumen diameter and area were generally larger (average of 15% and 33%, respectively) on postcontrast MRA images than on precontrast images. Aortic lumen diameter measurements from postcontrast MRA agreed closely (95% confidence interval of the mean difference was −.2 to .3 mm), and precontrast MRA images tended to underestimate aortic lumen diameter (95% confidence interval of the mean difference was .3 to .8 mm) compared with conventional angiography. Postcontrast MRA with NC 100283, a macromolecular Dy‐DTPA contrast agent, provides more accurate assessment of aortic lumen diameter than precontrast MRA, using conventional angiography as the standard refe

ISSN:1053-1807    

DOI:10.1002/jmri.1880080508

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to assess the diagnostic value of two‐dimensional (2D) MR subtraction angiography of lower extremities in patients with symptomatic peripheral arterial occlusive disease with conventional angiography as the standard of reference. Twenty patients were prospectively included. 2D subtraction MR angiography (MRA) consisted of multisection gradient‐recalled echo (GRE) acquisitions with the shortest TE available on our machine (4 msec), obtained in the coronal plane before and after intravenous bolus administration of gadolinium chelate. MR images were reconstructed after subtraction with a maximum‐pixel‐intensity‐projection (MIP) algorithm. MRA was performed in all cases 1–4 days before diagnostic angiography. In a prospective blinded analysis, the number and location of significant (ie,>50%) stenoses and occlusions were evaluated for each vascular segment. Sensitivity and specificity were used to evaluate MRA data. Significant stenoses (38 of 46, 83%) and occlusions (66 of 67, 99%) seen at conventional angiography were identified with MRA. The sensitivity and specificity of MRA for determination of stenoses>50% or occlusions was 100% and 97%, respectively. The location and extent of stenoses and/or occlusions on MRA and angiograms were well correlated (kappa values,r= .73,P<.05). Contrast 2D MR subtraction angiography, by providing comparable information to that of conventional angiography, is well suited to evaluate the presence and severity of atherosclerotic lesions of the

ISSN:1053-1807    

DOI:10.1002/jmri.1880080509

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

年代:1998

数据来源: WILEY

摘要:

AbstractIn this study, our purpose was to compare the high‐resolution contrast‐material‐enhanced three‐dimensional subtraction MR angiography with conventional angiography for occlusive disease in the pelvic and lower extremity arteries. A three‐dimensional fast‐imaging with steady precession (FISP) sequence with a 256 × 512 matrix was obtained on 1.5T MR unit using a phased array coil. Twenty patients with arteriosclerotic obstructive disease underwent subtraction dynamic contrast‐enhanced MR angiography. In 15 patients, three regions (pelvis, upper knee, and lower knee) were sequentially obtained after repeated injection of gadolinium‐diethylenetriamine pentaacetic acid (Gd‐DTPA). In the other five patients, one region was imaged (total of 50 examinations); a maximum‐intensity projection (MIP) algorithm was used for subtracted images. All patients also underwent conventional angiography. Angiographic images were divided into several anatomical segments. Three blinded radiologists independently graded a total of 50 anatomic segments with stenotic or obstructive diseases and 90 segments without disease. Subtracted images allowed resolution of small branch vessels in all examinations, although misregistration was seen in eight examinations of five patients. All arteries larger than 1 mm in diameter were visualized on subtracted images. For detection of significant stenosis (>50%), MR angiography had 96% sensitivity and 83% specificity. The correlation coefficient of degree of agreement between MR angiography and conventional angiography was .92. Stenotic vessels tended to be overestimated. We conclude that high‐resolution dynamic contrast‐enhanced three‐dimensional MR angiography is capable of depicting small vessel anatomy of the pelvis and lower extremities. Sequential MR angiography of different regions was feasible by repeated injection of Gd‐DTPA and subtraction. This technique is highly sensitive in detecting lesions, but stenosi

ISSN:1053-1807    

DOI:10.1002/jmri.1880080510

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to compare small and ultrasmall superparamagnetic iron oxide particles (SPIO and USPIO, respectively) as MR contrast agents for the evaluation of focal hepatic disease. In two different patient groups (SPIO [n = 53], USPIO [n = 27]), with focal liver disease (metastases, hepatocellular carcinoma [HCC], hepatocellular adenoma [HCA], and focal nodular hyperplasia [FNH]), spin‐echo T1‐ and T2‐weighted images (T1WI, T2WI) were obtained at 1.0T, before and after intravenous contrast administration. The percentage signal‐to‐noise ratio (SNR) change and lesion‐to‐liver contrast (LLC) were measured and statistically compared. The liver decreased in signal intensity (SI) after SPIO administration (−28%) and increased after USPIO administration (+16%) on T1WI. On T2WI, the liver decreased in SI on postcontrast images with both agents (−78% SPIO, −73% USPIO). This difference was not statistically significantly different (P⩽ .07). Both SPIO and USPIO provided>500% improvement in LLC on T2WI. On T1WI, LLC was increased in metastases (120%) and HCC (325%) with SPIO. Post‐USPIO, LLC was increased on T1WI only in metastases (>500%). Both SPIO and USPIO show excellent hepatic uptake, presumed secondary to reticuloendothelial activity, based on the degree of %SI change seen in the liver after administration of contrast on T2WI. However, USPIO preparations exhibit blood pool activity that may aid in further characterization of focal liver lesions, as is evidenced by their greater T1 effect in the liver and in s

ISSN:1053-1807    

DOI:10.1002/jmri.1880080511

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

年代:1998

数据来源: WILEY