Magnetic resonance evaluation of mitral stenosis

In order to study magnetic resonance (MR) abnormalities in mitral stenosis electrocardiogram (ECG)-gated MR imaging was performed with a 2.0 T MR system in 41 patients with mitral stenosis before catheterization. Mean transverse diameter of the left atrium was 8.9±1.4 cm and anteroposterior diameter was 5.1±1.0 cm, indicating significant enlargement. Homogeneous or inhomogeneous flow-related signals in ventricular diastole were detected in the left atrial cavity in 32 cases (78%), and in the atrial appendage in 35 cases (85%). In 21 patients having a mean wedge pulmonary arterial pressure higher than 20 mm Hg, 20 patients (95%) showed flow-related signals in ventricular diastole. Other MR findings were mitral valve doming in diastole, flow-related signal in the pulmonary artery during systole, and left atrial thrombi.     

二尖瓣狭窄合并左心房血栓患者的经皮二尖瓣球囊成形术

目的　评价经皮二尖瓣球囊成形术 (PBMV)治疗风湿性二尖瓣狭窄合并左心房血栓的临床疗效和安全性。方法　 2 7例风湿性二尖瓣狭窄合并左心房血栓患者进行PBMV ,19例食管超声心动图 (TEE)有左心房内新鲜血栓者术前经华法令抗凝治疗 3～ 6个月。结果　 2 7例风湿性二尖瓣狭窄合并左心房血栓患者进行PBMV均成功。 19例TEE有左心房内新鲜血栓者 ,PBMV术前经华法令抗凝治疗后 ,TEE复查示 9例左心房血栓消失 ,10例左心房内血栓明显缩小 ,机化为高强回声团块的陈旧性血栓 ;5例经胸心脏超声发现左心房陈旧性血栓 ,未行TEE也未予华法令治疗者 ,术中 1例发生脑栓塞。其余患者均无并发症发生。结论　对风湿性二尖瓣狭窄伴有心房纤维颤动患者 ,PBMV前应常规行TEE检查 ;二尖瓣狭窄伴左心房血栓者经充分抗凝治疗后行PBMV是安全可行的。     

Immediate postgadolinium spoiled gradient-echo MRI for evaluating the abdominal aorta in the setting of abdominal MR examination

To assess the reproducibility and image quality of immediate postgadolinium chelate spoiled gradient-echo MRI in demonstrating disease of the abdominal aorta. All patients (27 patients: 21 men, 6 women) with substantial disease of the abdominal aorta, who underwent abdominal MR examinations at 1.5 T between 1991 and 1995, were entered in the study. Patients were referred for evaluation of suspected aortic disease (14 patients) or other abdominal diseases (13 patients). Three experienced investigators manually measured luminal and external aortic wall diameters and rated image quality, definition of inner and outer walls, extent of disease, and presence of other abdominal abnormalities, in an independent fashion. A cardiovascular surgeon then rated all studies to determine whether clinical management could be based on the MR findings alone. There was 98 to 99% agreement in measurements of luminal and external wall diameter between the three investigators. Overall image quality was rated as good in 77.8 to 88.9% of patients. A total of 31 additional nonaortic abdominal abnormalities were detected by all observers. The cardiovascular surgeon rated 25 of 27 studies as adequate to determine clinical management based on MR findings alone. Immediate postgadolinium spoiled gradient-echo MRI is a reproducible technique for the demonstration of abdominal aortic disease and possesses good image quality. Advantages of this technique include simultaneous evaluation of other nonvascular diseases of the abdomen, short examination time, and easy implementation as part of routine abdominal MRI scanning protocol.     

Measurement of collateral blood flow in a porcine model of aortic coarctation by velocity-encoded cine MRI

The purpose of this study was to investigate the time course of development of collateral blood flow in an animal model of aortic coarctation. A juxtaductal aortic stenosis (model coarctation) was surgically created in five juvenile pigs. MRI was performed preoperatively, 1 to 2 days postoperatively, and 2 to 10 weeks postoperatively. Aortic blood flow was measured by velocity-encoded cine MR (VENC-MR). The percent change in aortic blood flow (ΔBF) from proximal to distal descending thoracic aorta was calculated, and a multiple-comparison paired t test used to assess changes in ΔBF over time. Invasive flow measurements were obtained in one animal before sacrifice using an ultrasonic probe. ΔBF preoperatively was ?2 ± 8% (mean ± SE). ΔBF increased to 32 ± 7% (mean ± SE, P = .022) 2 days postoperatively and 55 ± 19% (P = .032) 2 to 8 weeks postoperatively. Invasive measurements were in qualitative agreement with the VENC-MR data. VENC-MR is an accurate noninvasive method of measuring collateral blood flow in aortic coarctation. Recruitment and development of collateral flow pathways occur rapidly in an animal model.     

Effect of contrast dilution on contrast-enhanced MR angiography of the aorta and renal arteries

The aim of this study was to investigate the effect of gadolinium chelate dilution on vascular enhancement in contrast-enhanced two-dimensional (2D) MR subtraction angiography of aorta and renal arteries. Twenty patients were prospectively included. 2D subtraction MR angiography consisted of successive multisection breathhold GRE acquisitions of 16 s (2D FLASH, TR/TE 72/4, flip angle 60 degrees) obtained in the coronal plane before and after intravenous bolus administration of 0.1 mmol/kg BW gadolinium chelate. Patients underwent both diluted and undiluted gadolinium chelate administration in a random order. The data were studied both qualitatively and quantitatively on source and maximum intensity projection images. The length of renal arteries opacified was found not to differ significantly according to contrast dilution. The contrast enhancement percentage was not significantly modified according to the dilution used, but the time to peak enhancement was observed to be longer with the diluted contrast. Qualitatively, the best MR images were those obtained when undiluted contrast was injected first (chi2, P = 0.01). At a dosage of gadolinium chelate 0.1 mmol/kg BW, undiluted contrast 2D MR subtraction angiography seems to be more appropriate for studying diseases of the aorta and renal arteries than a similar diluted dose.     

Accessory mitral valve tissue causing left ventricular outflow tract obstruction in D-transposition of the great arteries

Two patients with D-transposition of the great arteries (D-TGA) were found to have an unusual form of left ventricular outflow tract obstruction. Both had ball-like accessory mitral valve tissue that partially occluded the outflow tract. In one patient there was an intact septum, while in the other there were ventricular septal defects. The appearances have been described previously, although not in D-TGA. Recognition of accessory mitral valve tissue may allow resection of the tissue at the time of repair of the transposition complex.     

Dynamic gadolinium-enhanced three-dimensional abdominal MR arteriography

The abdominal aorta and renal, visceral, and iliac arteries were evaluated in 16 patients with three-dimensional Fourier transform imaging enhanced with gadopentetate dimeglumine. By imaging dynamically during the arterial phase of a 5-minute injection (0.2 mmol/kg), highly significant (P < .0001) preferential arterial enhancement (signal-to-noise ratio ± standard deviation, 10 ± 0.9), with minimal enhancement of the inferior vena cava (5.1 ± 1.4) or background tissues (fat, 4.3 ± 0.7; muscle, 2.4 ± 0.5), was achieved in every patient. In six patients with angiographic and/or surgical correlation, 10 of 10 stenoses and two of two occlusions were correctly identified. No inplane saturation or pulsatility artifact was identified in any of the 16 patients. In conclusion, dynamic imaging during the injection of gadopentetate dimeglumine is a promising technique for evaluation of the abdominal aorta and branch vessels.     

Calculation of three-dimensional left ventricular strains from biplanar tagged MR images.

The noninvasive measurement of time-resolved three-dimensional (3D) strains throughout the myocardium could greatly improve the clinical evaluation of cardiac disease and the ability to mathematically model the heart. On the basis of orthogonal arrays of tagged magnetic resonance (MR) images taken at several times during systole, such strains can be determined, but only after heart motion through the image planes is taken into account. An iterative material point-tracking algorithm is presented to solve this problem. It is tested by means of mathematical models of the heart with cylindric and spherical geometries that undergo deformations and bulk motions. Errors introduced by point-tracking interpolation were found to be negligible compared with those due to marker identification on the images. In a human heart studied with this technique, the corrected radial strains at the left ventricular base were approximately 2.5 times the two-dimensional estimates derived from the fixed image planes. The authors conclude that material point tracking allows accurate, time-resolved 3D strains to be calculated from tagged MR images, and that prior correction for motion of the heart through image planes is necessary.     

The Significance of Perfusion Defect at Myocardial Perfusion MR Imaging in a Cat Model of Acute Reperfused Myocardial Infarction

Objective

To determine whether the size of a perfusion defect seen at myocardial perfusion MR imaging represents the extent of irreversibly damaged myocardium in acute reperfused myocardial infarction.

Materials and Methods

In nine cats, reperfused myocardial infarction was induced by occlusion of the left anterior descending coronary artery for 90 minutes and subsequent reperfusion for 90 minutes. At single-slice myocardial perfusion MR imaging at the midventricular level using a turbo-FLASH sequence, 60 short-axis images were sequentially obtained with every heart beat after bolus injection of gadomer-17. The size of the perfusion defect was measured and compared with both the corresponding unstained area seen at triphenyl tetrazolium chloride (TTC) staining and the hyperenhanced area seen at gadophrin-2-enhanced MR imaging performed in the same cat six hours after myocardial perfusion MR imaging.

Results

The sizes of perfusion defects seen at gadomer-17-enhanced perfusion MR imaging, unstained areas at TTC staining, and hyperenhanced areas at gadophrin-2-enhanced MR imaging were 20.4 ± 4.3%, 29.0 ± 9.7%, and 30.7 ± 10.6% of the left ventricular myocardium, respectively. The perfusion defects seen at myocardial perfusion MR imaging were significantly smaller than the unstained areas at TTC staining and hyperenhanced areas at gadophrin-2-enhanced MR imaging (p < .01). The sizes of both the perfusion defect at myocardial perfusion MR imaging and the hyperenhanced area at gadophrin-2-enhanced MR imaging correlated well with the sizes of unstained areas at TTC staining (r = .64, p = .062 and r = .70, p = .035, respectively).

Conclusion

In this cat model, the perfusion defect revealed by myocardial perfusion MR imaging underestimated the true size of acute reperfused myocardial infarction. The defect may represent a more severely damaged area of infarction and probably has prognostic significance.     

MR angiography of the foot and ankle

To better understand the use of magnetic resonance angiography (MRA) in evaluating peripheral vascular disease, the authors studied arteries in the foot and ankle. Twenty patients with arterial occlusive disease of the lower extremity were studied with two-dimensional time-of-flight MRA, and the results were compared with those of 10 conventional x-ray arteriograms, four digital subtraction arteriograms, and three intraoperative arteriograms. The studies were reviewed and rated by three radiologists blinded to the patients' clinical history. Also, the first 16 patients were examined with MRA before and after intravenous injection of gadopentetate dimeglumine. The mean confidence levels for the reviewers' interpretations of the MRA studies were significantly higher than those for the conventional arteriograms for the medial plantar, lateral plantar, and plantar arch arteries of the feet (P ≦ 0.005). Postcontrast MRA images were inferior to precontrast images because of overlapping of veins and arteries. Time-of-flight MRA without gadolinium can serve as a useful complementary study for evaluating patients with peripheral vascular disease in the foot and ankle.