Detection and characterization of intracardiac thrombi on MR imaging

OBJECTIVE: The aim of our study was to compare the diagnostic accuracy achieved using different MR techniques with the diagnostic accuracy achieved using transthoracic and transesophageal echocardiography to detect intracardiac thrombi. MATERIALS AND METHODS: Twenty-four patients with known or suspected intracardiac thrombi were examined using MR imaging and echocardiography. All MR examinations were performed on a 1.5-T MR scanner using dark-blood-prepared half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences, fast imaging steady-state free precession (trueFISP) cine sequences, and inversion recovery gradient-echo fast low-angle-shot (inversion recovery turbo FLASH) sequences after injection of 0.2 mmol/kg of gadolinium diethylene triamine pentaacetic acid. RESULTS: MR imaging and echocardiography revealed 12 thrombi-two in the right atrium, one in the right ventricle, three in the left atrium, and six in the left ventricle. Compared with echocardiography, MR imaging revealed three additional thrombi in the left ventricle; these thrombi were confirmed at surgery. All 15 thrombi appeared as filling defects on early contrast-enhanced inversion recovery turbo FLASH MR images. Only seven thrombi were detected on HASTE images, and 10 thrombi were seen on trueFISP images. Four thrombi showed enhancement 10-20 min after contrast material injection and were characterized as organized clots. CONCLUSION: Contrast-enhanced inversion recovery turbo FLASH sequences were superior to dark-blood-prepared HASTE and trueFISP cine MR images in revealing intracardiac thrombi. Compared with transthoracic echocardiography, MR imaging was more sensitive for the detection of left ventricular thrombi. The characterization of thrombi may be used to predict the risk of embolism, which is higher for subacute clots than for organized thrombi.     

Imaging asynchronous mechanical activation of the paced heart with tagged MRI

A method for imaging the rapid temporal-spatial evolution of myocardial deformations in the paced heart is proposed. High time resolution-tagged MR images were obtained after stimulation of the myocardium with an MR-compatible pacing system. The images were analyzed to reconstruct dynamic models of local 3D strains over the entire left ventricle during systole. Normal canine hearts were studied in vivo with pacing sites on the right atrium, left ventricular free wall and right ventricular apex. This method clearly resolved local variations in myocardial contraction patterns caused by ventricular pacing. Potential applications are noninvasive determination of electrical conduction abnormalities and the evaluation of new pacing therapies.     

Cardiac first-pass and myocardial perfusion in normal subjects assessed by sub-second Gd-DTPA enhanced MR imaging

To evaluate first pass in the right ventricular (RV) and left ventricular (LV) cavities and myocardial perfusion, subsecond MR imaging was performed in seven normal subjects following intravenous bolus injection of Gd-DTPA. After the baseline scans, sequential ECG-triggered images were obtained every three to four RR intervals. The procedure consisted of an initial presaturation pulse (150 degrees), and the acquisition time for one image was approximately 500 ms with 64 phase-encoding steps. After bolus administration of Gd-DTPA (0.05 mmol/kg body wt), progressively increasing signal intensities were observed in the RV cavity, the LV cavity, and the myocardial wall. Gadolinium DTPA enhanced subsecond MR offers temporal information of the first transit in the cardiac chambers and may provide useful clinical reference data for assessment of myocardial perfusion in patients with coronary artery disease.     

Echocardiographic-like angled views of the heart by MR imaging

Cardiac magnetic resonance (MR) imaging has developed rapidly to rival echocardiography as a noninvasive imaging modality. Anatomic detail may exceed that currently available using echocardiography techniques, and the ability to image moving protons may compete with Doppler color flow mapping in detecting valvular diseases and shunts. Because of the considerable clinical experience with echocardiography, as angled MR imaging planes become available as standard software packages, it may be useful for MR cardiac imaging to use standard, accepted echocardiographic nomenclature and imaging planes. This article describes the principles used to obtain long and short axis MR images that are comparable with echocardiographic imaging planes. Diagrams and illustrations are provided to orient the viewer using nomenclature common to echocardiography. These views may eventually be useful for functional analysis of the left ventricle and for detection and evaluation of valvular heart disease and intracardiac shunts.     

Magnetization transfer contrast in MR imaging of the heart

The use of magnetization transfer contrast (MTC) in short-echo-time (TE) cardiac magnetic resonance (MR) imaging was evaluated. For most cardiac MR imaging protocols, either long TE and short repetition time or exogenous intravascular agents are used for generating contrast between the ventricular wall and cavity as well as detecting pathologic conditions of the ventricular wall. The major problem with long-TE images is that the motion of the heart degrades the spatial resolution of the image during the TE period. However, MTC is generated by an off-resonance irradiation during the interpulse delay period that is relatively insensitive to motion artifacts. Short-TE (5-15 msec) gradient-recalled echo sequences were used for imaging the heart with and without MTC. These studies revealed that MTC can be used to greatly improve the contrast between the myocardial wall and blood chamber in short-TE images and may provide useful parameters for tissue characterization in pathologic cardiac muscle.     

Pre-operative evaluation with MR in tetralogy of fallot and pulmonary atresia with ventricular septal defect

Purpose: To assess whether MR imaging could replace angiography in pre-operative evaluation of patients with tetralogy of Fallot and pulmonary atresia with ventricular septal defect (VSD), especially since the surgical correction was done earlier than was previously the rule.Material and Methods: Fourteen patients with tetralogy of Fallot (n=10) or pulmonary atresia with VSD (n=4), mean age 7.5±4.4 months, were evaluated with angiocardiography and MR before definitive surgical correction.Results: There was good diagnostic agreement between the two modalities when evaluating right ventricular outflow obstruction; 86% for valvular and 93% for supravalvular stenosis, but the agreement was somewhat lower for the subvalvular obstruction (57%). Surgery findings, however, were in favour of MR in 5 patients concerning the subvalvular right ventricular outflow tract obstruction. MR images identified all stenoses in the right and left pulmonary arteries, but overlooked one stenosis in the main pulmonary artery. MR could evaluate patency in all palliative shunts.Conclusion: Even in this young age group, MR imaging offers a good alternative to angiocardiography for the pre-operative evaluation of the right ventricular outflow tract, the main pulmonary artery and the proximal right and left pulmonary arteries, before definitive surgical correction of tetralogy of Fallot and pulmonary atresia with VSD.     

Optimal use of contrast medium in contrast enhanced MR imaging of the heart

With the recent development of fast MR imaging techniques, the diagnostic value of contrast enhanced MR imaging of the heart has been substantially improved. Since no tissue-specific contrast medium is available for clinical cardiac MR imaging at this point, both the early and late dynamics of extracellular MR contrast medium should be carefully evaluated for assessing the multiple aspects of cardiac function, including myocardial blood flow, myocardial, viability, and left ventricular function. Myocardial blood flow can be assessed by monitoring the first-pass passage of MR contrast medium. Quantitative assessments of arterial input function and output function in the regional myocardium can provide more accurate detection of altered myocardial blood flow in patients with coronary artery disease. Excellent contrast between infarcted myocardium and normal tissue can be obtained with delayed contrast enhanced MR imaging. Myocardial infarction, including small subendocardial infarction and chronic scar, is demonstrated as an area of "hyperenhancement" on delayed enhanced MR images, while the signal from normal myocardium is nearly null. This review paper describes the optimal dose and injection rate of MR contrast material for functional cardiac MR imaging studies. In addition, practical suggestions for obtaining good cardiac MR images and interpreting contrast enhanced MR images are given and are explained in detail.     

Forty-millisecond MR imaging of the abdomen at 2.0 T

The ability of an ultrafast magnetic resonance (MR) imaging technique to provide abdominal MR images free of motion artifacts was studied. Individual T2-weighted transverse MR images were acquired in as little as 40 msec on a whole-body system operating at 2.0 T. Clinical evaluation was undertaken with fat-suppressed images in which only protons of water molecules contributed to image signal intensity. The ultrafast MR images were compared with conventional MR images obtained at 0.6 T. In 22 patients and two healthy volunteers, ultrafast MR images were of diagnostic quality and free of motion artifacts. Images obtained at an echo time (TE) of 30 msec (imaging time, 40 msec) had liver signal-to-noise ratios of 56.3 +/- 22.6 (n = 19). Because of a smaller data matrix, ultrafast MR images had soft-tissue interfaces that were less sharp than those of the highest-quality conventional MR images in which no motion artifacts were present. However, ultrafast MR images demonstrated high T2-dependent soft-tissue contrast, and pathologic and normal anatomies were readily detected with both imaging techniques. This ultrafast imaging technique has significant promise in whole-body MR imaging, in which motion artifacts often degrade image quality.     

A left atrial pseudomass: Potential pitfall at thoracic MR imaging

We frequently observed a nodular soft-tissue structure in the region of the left atrium anterior to the orifice of the left inferior pulmonary vein on MR scans of the chest. To assess its morphologic characteristics and appearance, chest MR scans obtained in 49 patients were reviewed. ECG-gated conventional spin-echo T1-weighted and fast spin-echo (FSE) T2-weighted sequences were used. The location, morphology, and appearance of this soft-tissue structure was evaluated by two radiologists during one consensus reading. The psendomass in the region of the left atrium was identified on the T1-weighted images in 25 of 49 patients. The structure was also identified on FSE T2-weighted images in 6 of these patients. On the T1-weighted images, its appearance was either linear (54%) or nodular (46%). In conclusion, a nodular soft-tissue mass anterior to the orifice of the left inferior pulmonary vein into the left atrium is a frequent finding on chest MR scans and should not be confused with an intra-atrial mass. Careful evaluation of the regional anatomy identifies this structure as extraluminal and helps to avoid misinterpretation of an intracardiac mass.     

Measurement of stroke volume and cardiac output within a single breath hold with echo-planar MR imaging

The measurement of cardiac output and ejection fraction is useful in the treatment of diverse cardiac and cardiopulmonary disease states. Although several techniques are available for accurate measurement of left ventricular parameters, assessment of the right ventricle is less well represented. No single method is overwhelmingly superior, each having different strengths and weaknesses. In the present study, the applicability of an echo-planar magnetic resonance (MR) imaging method in which a complete volumetric measurement of the right and left ventricles may be obtained during 12 heartbeats is demonstrated. This rapidity permits imaging during a 15-second breath hold. The authors show in 12 volunteers that breath-hold echo-planar volume measurements of both ventricles were consistent with results obtained with conventional MR imaging methods.     

MR相位对比法和形态体积分析法评价心室功能的比较研究

目的探讨相位对比法MR和形态体积分析法MR成像技术在评价心室功能中的临床应用价值。方法应用相位对比法MR(phasecontrastmagneticresonanceimaging,PCMRI)和形态体积分析法电影MRI(stereologicalcinemagneticresonanceimaging,SCMRI)分别对12例健康成年人和46例心脏病患者进行检查。首先应用SCMRI行心脏左、右室短轴电影成像,分别描记左、右室心内、外膜界面,测出左右心室舒张末期容量(EDV)、收缩末期容量(ESV)、每搏输出量(SV)、射血分数(EF)等指标;再应用PCMRI和流量分析软件分别在主动脉瓣上和肺动脉瓣上水平测得1个心动周期内的前向血流,获得SV值,并将2种方法的测量结果进行比较;同时对正常志愿者与患者组、正常志愿者组左、右两侧心室,以及PCMRI法在主动脉瓣上和肺动脉瓣上水平测得的左右心室SV均值进行比较。结果(1)PCMRI与SCMRI法所测正常志愿者左、右心室的SV相关良好,相关系数分别为090和087,2种方法测得的SV均值差异无统计学意义(P>005)。(2)患者组2种MRI测量方法所得左室SV的相关系数为085,SV均值比较差异无统计学意义(P>005),应用PCMRI法在主动脉瓣上水平测得正常人与患者组的SV均值,差异有统计学意义(P<005)。结论PCMRI与SCMRI法相比,对心室每搏输出量(SV)测量准确,相关性好,重复性高,加     

Prospectively gated cardiac CT. Preliminary results in normal and postinfarction animal models

Cardiac motion introduces significant artifacts into standard CT images obtained through the heart. A newly developed prospectively gated CT system produced 87 gated scan sets in ten normal and infarcted dogs. Each cycle can provide up to 24 37-70 msec composite images of one transverse slice, equally spaced in time through the cardiac cycle. Eight to 12 2-second scans, obtained during a constant infusion of contrast, were required to collect the data for each gated set. The left and right ventricular myocardium was clearly seen, regions of myocardial infarction were identified, and atrial and ventricular filling and emptying were visualized. In areas of infarction, wall thickness was unchanged from diastole to systole. In addition to improved resolution, a gated CT series evaluation of wall motion abnormalities may provide a better means of locating myocardial infarction than the ungated CT image.     

CT of intracardiac and intrapericardial masses

Computed tomographic (CT) equipment capable of high-resolution, rapid-sequence scanning allows detection of intracardiac and intrapericardial masses. Two patients with intrapericardial masses (pheochromocytoma, organized hematoma) and three patients with intracardiac masses (right ventricular rhabdomyosarcoma, right atrial metastasis, and left atrial thrombus) are presented. CT is the imaging method of choice for displaying pericardial masses directly and may be superior to echocardiography and angiocardiography in the detection of ventricular thrombi. In patients with cardiac tumors, CT evaluates extent of disease including invasion of contiguous vessels and pulmonary metastases better than echocardiography. Dynamic scanning after bolus intravenous injection of contrast material is recommended for the evaluation of patients with suspected masses involving the heart or pericardium.     

Time‐resolved spin‐labeled balanced steady‐state free precession cineangiography for visualizing intracardiac shunt: technical considerations and clinical feasibility

A time‐resolved spin‐labeled cineangiographic MRI technique for visualizing blood flow in the heart and defects of the atrial septum is described. The method utilizes a spin labeling preparation and a time‐resolved balanced steady‐state free precession imaging readout that enhances blood in the left atrium or right atrium and suppresses background signal through inversion recovery. Four volunteer studies and 10 patient studies were performed at 1.5 T to characterize the signal properties and to test the clinical feasibility of depicting atrial septal defects. In volunteers, the spin‐labeled cineangiographic method depicted intracardiac blood flow patterns and demarcated the intact atrial septum. Peak target to adjacent atrial chamber contrast‐to‐noise ratios of 84 and 94 were obtained 758 and 689 ms postlabeling; 50% of peak contrast‐to‐noise ratio was maintained for 803 and 599 ms in the left atrium and right atrium, respectively. In all patients with an atrial septal defect, the spin‐labeled cineangiographic method demonstrated left‐to‐right flow and maintained good morphological assessment of surrounding cardiac structures. Right‐to‐left flow was seen in three patients. In conclusion, the spin‐labeled cineangiographic method displayed favorable signal properties in volunteers and demonstrated shunting in patients with atrial septal defects. The technique is expected to be a viable alternative to the few techniques available for visualizing blood flow in the heart. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Primary intracardiac tumors in magnetic resonance imaging

Fifteen patients suspected of having 18 intracardiac masses by two-dimensional echocardiography underwent MR imaging. In MR imaging, intracardiac masses were evaluated on both short TE (TE = 20-35 msec) and long TE (TE = 50-80 msec) spin echo sequences, and were differentiated from myocardium or papillary muscle. Three masses were excluded (they were papillary muscle) by MR imaging, and three were additionally found in patients with tuberous sclerosis. Fifteen masses were found by both echocardiography and MR imaging, one of which was stagnant blood. Cine MR imaging was needed to differentiate between thrombus and stagnant blood. MR imaging is useful for the evaluation of intracardiac masses. It is recommended in addition to echocardiography when cardiac tumors are suspected, especially in patients with tuberous sclerosis.     

Mitral stenosis: evaluation with MR imaging after percutaneous balloon valvuloplasty

To evaluate the pathoanatomic findings of mitral valve stenosis and changes after percutaneous balloon valvuloplasty (PBV), magnetic resonance (MR) imaging was performed in 23 patients. The patients were imaged with a 2.0-T system within 1 week before and 3-10 days after PBV. The angle of the interatrial septum was measured on the transverse image to facilitate a successful transseptal puncture. On MR images, the mean transverse and anteroposterior diameters of the left atrium at the level of the aortic root in the ventricular diastolic phase decreased significantly after PBV. Areas of flow-related intraluminal signal intensity detected in the left atrial cavity of 17 patients (74%) before the procedure disappeared in 15 patients after the procedure. Other MR imaging findings after PBV were the disappearance of intraluminal signal intensity in the pulmonary artery, normal curvature of the interatrial and interventricular septa, and pericardial effusion as a complication. MR imaging was thought to provide useful information before and after PBV in patients with mitral stenosis.     

Myocardial infarct size quantification by MR imaging early after coronary artery occlusion in dogs

The feasibility of using magnetic resonance (MR) imaging to estimate myocardial infarct size was explored in an in vitro model using only the inherent differences in contrast between infarcted and noninfarcted myocardium. Eight dogs underwent coronary occlusion; their hearts were removed 6 hours later. Estimates of T2 for normal and infarcted myocardium were derived from MR images. Infarct size was quantified anatomically using triphenyltetrazolium-chloride (TTC) staining and compared with MR estimates. The T2 values derived from the images clearly discriminated between infarcted (126 +/- 22 msec) and normal myocardium (88 +/- 10 msec, P less than .05), providing images with good contrast between normal and infarcted myocardium. Comparable differences in T2 values were also noted from spectrometric determinations. Estimates of infarct size by MR imaging compared well with TTC estimates (r = 0.98) over a wide range of infarct sizes from 3% to 29% of the left ventricular mass. These results suggest the potential for in vivo quantification of infarct size based on the inherent contrast difference between infarcted and normal myocardium.     

Acute myocardial ischemia: MR imaging with Mn-TP

Cardiac-gated magnetic resonance (MR) imaging was performed in rats to determine the effects of manganese ethylenediaminetetraphosphonate (TP). Ten normal rats received Mn-TP in a dose of 50 mumol/kg through a tail-vein injection. Spin-echo MR images were obtained before and every 10 minutes after Mn-TP injection for 1 hour. Cardiac signal intensity (SI) increased more than 70% after Mn-TP injection and remained nearly unchanged 1 hour after injection. Myocardial T1 was 517 +/- 49 msec in eight control rats and 282 +/- 61 msec (P less than .001) in six rats 81 +/- 0 minutes after injection. Nine rats underwent occlusion of the left anterior descending coronary artery prior to MR imaging. Images were obtained before and 15, 30, and 60 minutes after Mn-TP injection. In normal myocardium, SI increased up to 82% and remained elevated for 1 hour. In ischemic myocardium, SI rose 11%, leading to a marked contrast between the two tissue zones. T1 was also different in the two regions: In normal tissue, it was 206 msec +/- 54; in ischemic tissue, 338 +/- 82 (P less than .001). With T1-weighted MR imaging, Mn-TP showed a potential for delineating the jeopardized area after acute myocardial ischemia.     

Cardiovascular applications of magnetic resonance imaging and phosphorus-31 spectroscopy.

Recent advances in cardiovascular applications of magnetic resonance (MR) imaging and phosphorus-31 spectroscopy are reported. MR velocity mapping is a valuable adjunct to conventional imaging techniques, providing information on flow velocities as well as on absolute blood flow volume in the aorta and pulmonary arteries. Recently, ultrafast MR techniques have become available to evaluate myocardial perfusion with the aid of MR contrast agents as perfusion marker. Dynamic MR imaging is a powerful tool to assess cardiac function and ventricular mass. In particular, right ventricular function and mass can be evaluated with great accuracy, contributing to improved assessment of the significance of disease processes which may affect the right heart. The role of phosphorus-31 spectroscopy of the heart is expanding for the evaluation of ischemic myocardial disease and cardiomyopathies. The phosphocreatine to adenosine triphosphate ratio appears to be a marker of disease in patients with cardiac hypertrophy. In conclusion, MR imaging and phosphorus-31 spectroscopy is gaining widespread acceptance for evaluation of many cardiovascular disease processes.     

Sequential MRI and CT monitoring in cryosurgery--an experimental study in rats

Cryosurgery is one of treatments of cancer, such as carcinomas of the face, oral cavity, prostate, breast, rectum and liver. But the method of cryosurgery seemed to be not yet completely established. The most important problem in this procedure is to define the extent of the cryolesion. But the trial with MRI and CT has not been reported. The purpose of this study is to investigate whether the image diagnosis such as Magnetic Resonance (MR) and CT is useful for the determination of the region during and after cryosurgery. The animal experiments were performed using 13 Wistar rats with inoculated Walker 256 cancer on both sides of femoral regions subcutaneously in the concentration of 1 million cells. After 7 days, cryosurgery was done by contacting for 15 sec with the absorbent cotton ball dipped in liquid nitrogen to the surface of right femoral tumor 3 to 6 times. The left side of tumor was intact. MRI was performed with a 0.1 Tesla ASAHI MR Mark-J and CT images were obtained using GE 9800. From the freezing to thawing, LF image (Low Flip Angle gradient echo image of Tr = 100 msec, Te = 18 msec, 60 degrees of flip angle) of MR and plain CT were taken every one minute. After thawing is over, SE image of Tr = 1500 msec, Te = 90 msec, IR images of Tr = 1200 msec, Td = 400 msec, and plain and contrast enhanced CT were carried out. Two and 7 days after cryosurgery, LF, SE and IR images of MR and CT with and without contrast medium were obtained with corresponding pathological examinations. The frozen cryolesion was of no signal intensity on the LF MR image and hypodensity on plain CT. Identification of cryolesion became possible during the cryosurgery. The cryolesion immediately after thawing showed higher intensity on the SE and LF images and hypodensity on enhanced CT. Therefore, the extent of cryosurgery can be diagnosed easily by these methods during and immediately after cryosurgery. In the follow-up studies after cryosurgery, the histological changes such as necrosis or tissue reaction were well represented by MRI and enhanced CT, but insufficiently by plain CT. From these experimental results, it may be concluded that MRI and CT are useful for monitoring the process of cryosurgery during and after the procedure.