Magnetic resonance imaging of the heart: positioning and gradient angle selection for optimal imaging planes

Cardiac MRI: technical basis

Cardiac magnetic resonance (CMR) imaging is an effective method for noninvasively imaging the heart which in the last two decades impressively enhanced spatial and temporal resolution and imaging speed, broadening its spectrum of applications in cardiovascular disease. CMR imaging techniques are designed to noninvasively assess cardiovascular morphology, ventricular function, myocardial perfusion, tissue characterization, flow quantification and coronary artery disease. These intrinsic features yield CMR suitable for diagnosis, follow-up and longitudinal monitoring after treatment of cardiovascular diseases. The aim of this paper is to review the technical basis of CMR, from cardiac imaging planes to cardiac imaging sequences.

First Magnetic Resonance Managed by a Cardiology Department in the Spanish Public Healthcare System. Experience and Difficulties of an Innovative Model

Magnetic resonance (MR) is considered the gold standard in the assessment of myocardial morphology, function, perfusion, and viability. However, its main limitation is its scarce availability. In 2014, we installed the first MR scanner exclusively managed by a cardiology department within the publicly-funded Spanish healthcare system with the aim of improving patient-care, training and research in the department. In the time interval analyzed, July 2014 to May 2017, 3422 cardiac MR scans were performed (32minutes used per study; 96% with good quality; 75% with contrast media administration). The most prevalent clinical indications were cardiomyopathy (29%) and ischemic heart disease (12%). Twenty-five percent of studies were conducted in the context of research protocols. Follow-up studies predominated among outpatients, while pretherapeutic assessment was more common in hospitalized patients. The presumptive diagnosis was changed by cardiac MR scanning in up to 20% of patients investigated for ischemic heart disease. The installation and operative management of an MR scanner in our cardiology department has allowed us to integrate this technique into daily clinical practice, modify our clinical protocols, optimize access to this technology among cardiac patients, improve training, and conduct clinical research.

Oblique Views in Magnetic Resonance Imaging of the Heart by Combined Axial Rotations

Magnetic resonance imaging of the heart, and more specifically of the left ventricle (LV), is optimized by using oblique imaging planes adapted to the long and short axes of the LV, comparable to other imaging modalities in cardiology. We report a procedure to perform two chamber views, four chamber views and true short axis views by combinations of electronic axial rotations. The technique of selecting appropriate gradient angles is explained. Thus, there is no requirement for altering patient position in the imager, while individual anatomic variations are taken into account.

Non-Coronary Cardiac CT Imaging

Cardiac multidetector CT (MDCT) has moved from purely anatomic imaging, to assessment of cardiac function. Significant advances since the advent of multidetector CT now make it feasible to assess not only the coronary arteries, but also ejection fraction, ventricular volumes, myocardial mass and the presence of wall-motion abnormalities. Advances include improvements in EKG-gating, including improvements in temporal resolution, as well as the addition of delayed contrast-enhanced methods. Anatomic imaging has improved as well, with thinner collimation and better reconstruction methods. Three-dimensional software programs now permit excellent surface rendered displays and multiplanar reconstructions suitable as surgical and procedural "road maps."

Influence of positional and angular variation of automatically planned short-axis stacks on quantification of left ventricular dimensions and function with cardiovascular magnetic resonance

PURPOSE

To theoretically and experimentally investigate the influence of the automated cardiovascular magnetic resonance (CMR) scan planning pitfalls, namely inaccurate positioning and tilting of short-axis (SA) imaging planes, on quantification of the left ventricular (LV) dimensions and function.

MATERIALS AND METHODS

Eleven healthy subjects and eight patients underwent CMR. Manually and automatically planned SA sets were acquired. To obtain the quantitative measurements of LV function, one observer performed image analysis twice. The agreement between planning methods, as well as the decomposition of the total variation into interstudy and intraobserver components was measured.

RESULTS

The decomposition of the total variation showed that the interstudy factor accounts for 70-85% of the total variation, while the rest is due to the intraobserver factor. Moreover, the relative contribution of the interstudy factor remains independent from errors in slice positioning and small angular deviation of SA stacks from the optimal orientation. Good agreement between the theoretical and measured variability factors was observed.

CONCLUSION

Global LV function derived from the automatically planned CMR acquisitions yield accurate quantification of the human cardiovascular system. Inaccurate positioning and tilting of SA images does not affect the quantitative measurements of LV function. The computer-aided system for automated CMR has proven clinical applicability.

Accuracy of short-axis cardiac MRI automatically derived from scout acquisitions in free-breathing and breath-holding modes

To qualitatively assess the accuracy of automated cardiovascular magnetic resonance planning procedures devised from scout acquisitions in free-breathing and breath-holding modes, to quantitatively evaluate the accuracy of the derived left ventricular volumes, mass and function and compare these parameters with the ones obtained from the manually planned acquisitions. Ten healthy volunteers underwent cardiovascular MR (CMR) acquisitions for ventricular function assessment. Short-axis data sets of the left ventricle (LV) were manually planned and generated twice in an automatic fashion. Automated planning parameters were derived from gated scout acquisitions in free-breathing and breath-holding modes. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and left ventricular mass (LVM) were measured. The agreement between the manual and automatic planning methods, as well as the variability of the aforementioned measurements were assessed. The differences between two automated planning methods were also compared. The mean differences between the manual and automated CMR planning derived from gated scouts in free-breathing mode were 8.05 ml (EDV), 1.84 ml (ESV), 0.69% (EF), and 4.72 g (LVM). The comparison between manual and automated CMR planning derived from gated scouts in breath-holding mode yielded the following differences: 4.22 ml (EDV), 0.34 ml (ESV), 0.3% (EF), and -0.72 mg (LVM). The variability coefficients were 3.72 and 3.66 (EDV), 5.6 and 8.19 (ESV), 3.46 and 4.31 (EF), 6.49 and 5.20 (LVM) for the automated CMR planning methods derived from scouts in free-breathing and breath-holding modes, respectively. Automated CMR planning methods can provide accurate measurements of LV dimensions in normal subjects, and therefore may be utilized in the clinical environment to provide a cost-effective solution for functional assessment of the human cardiovascular system.

Apport de l’IRM dans l’exploration des anomalies cardiaques congénitales et des gros vaisseaux

Management of congenital heart diseases (CHD) frequently is a diagnostic challenge. MRI, as a complement to echocardiography, plays an important role in the non-invasive evaluation of these anomalies. MRI allows high resolution anatomical evaluation of these structures in multiple planes as well as functional evaluation. These features are helpful to further characterize extra-cardiac anomalies that may be difficult to assess at US and even angiography. MRI is thus a valuable imaging tool in the evaluation of CHD.

Determination of the left ventricular long-axis orientation from a single short-axis MR image: relation to BMI and age

Accurate determination of imaging planes in relation to the left ventricular (LV) long-axis orientation is important for anatomical and functional evaluation as well as for serial comparisons with cardiac magnetic resonance (CMR) imaging. Therefore, a fast and reliable method to test the accuracy of CMR imaging for measuring the orientation of the LV long-axis was developed and validated. In addition, the relationship between LV long-axis orientation and body mass index (BMI), gender and age was assessed. Two approaches were used, a long-axis approach (based on a manually defined vector) and a short-axis approach (based on a calculated vector). The concordance between the two approaches was assessed in 72 healthy volunteers. The accuracy and precision of MR imaging for measuring three-dimensional orientations were tested using a LV phantom. The mean difference between the long- and short-axis approaches for measuring the LV long-axis orientation in the study population was 0 +/- 3 degrees, 0 +/- 2 degrees, and -1 +/- 3 degrees in the frontal, transverse and sagittal plane, respectively. BMI and age were shown to influence LV long-axis orientation, especially in the frontal and sagittal planes. A significant difference in LV long-axis orientation in the frontal and sagittal planes was found between genders. The correlation coefficient between MR-measured phantom orientation and true phantom orientation was >0.98 in all three orthogonal planes. These observations suggest that a single LV short-axis MR image can be used for measuring LV long-axis orientation in patients with no cardiac disease.

How to plan and perform a cardiac MR imaging examination

Because of the enormous economic and social impact of cardiovascular disease in the United States there is a need for improved noninvasive diagnosis. Cardiac MR imaging isa versatile, comprehensive technique for assessing cardiac morphology and function. With an understanding of cardiac anatomy and physiology and MR imaging physical principles,cardiac MR imaging can be performed and can play an important role in patient management. This article provides the reader with a basic understanding of cardiac MR imaging and the practical applications required to perform cardiac MR imaging.

Performing cardiac MR imaging: an overview

Because of the enormous economic and social impact of cardiovascular disease in the United States, there is a need for improved noninvasive diagnosis. Cardiac MR imaging is a versatile, comprehensive technique for assessing cardiac morphology and function. With an understanding of cardiac anatomy and physiology as well as MR physical principles, cardiac MR imaging can be performed and play an important role in patient management.

Measurement of left ventricular dimensions and function in patients with dilated cardiomyopathy

Studies on medical therapy in heart failure are focused on changes of left ventricular (LV) dimensions and function. These changes may be small, requiring a large study group. We measured LV parameters (LV volumes, LV ejection fraction (LV-EF), and left ventricular mass (LVM)) with two-dimensional echocardiography (2D-echo) and magnetic resonance imaging (MRI) in 50 patients. Based on the difference between the measurements, we determined the variance of the results and calculated the sample sizes needed to detect changes of baseline values. For the calculated and measured parameters we found significant differences between the two techniques: LV-EF and LVM were higher in 2D-echo, and LV dimensions were comparable. The sample size to detect relevant changes from baseline with MRI was significantly (P < 0.01) smaller than in 2D-echo. We conclude that MRI is superior in clinical studies on left ventricular dimensional and functional changes, since measurements are more reproducible and the required sample size is substantially smaller, thereby reducing costs.

MRI of heart morphology. Comparison of nongradient echo sequences with single- and multislice acquisition

RATIONALE AND OBJECTIVES

A large variety of cardiac MRI sequences have been introduced for heart morphology evaluation. The aim of this study was to establish a practicable and robust examination protocol for standard high-field systems applying nongradient echo sequences with single- and multi-slice acquisition.

METHODS

Fifty-one patients received electrocardiogramgated MRI of the heart with "black-blood" preparation, comparing three single-slice and three multislice sequences with a T1-weighted turbo spin echo reference sequence. Demarcation of the left ventricular myocardium and cavity and the extent of flow and motion artifacts were assessed.

RESULTS

The myocardium and left ventricular cavity were depicted best with the single-slice T1- and T2-weighted turbo spin echo sequence. The nonbreath-hold multislice sequences produced marked artifacts and therefore were of poor diagnostic value. The TIRM haste sequence was best suited for fat suppression. The T2-weighted breath-hold single-shot sequence with half-Fourier imaging proved to be most appropriate for multislice imaging.

CONCLUSIONS

Sufficient depiction of heart morphology with comprehensive evaluation of signal changes can be achieved using nongradient spin echo and turbo spin echo sequences with breath-holding. For rational imaging of myocardial and heart chamber morphology, multislice and single-slice sequences should be combined.

MR imaging of adult patients with congenital heart disease

Although the incidence of congenital heart disease remains constant among newborns, improved medical and surgical techniques have dramatically prolonged life expectancy and produced a new, growing group of patients harboring these lesions: adults with congenital heart disease. Conventional imaging techniques in these patients may be limited because of patient size, chest configuration, or poor ventricular function. MR imaging provides a noninvasive means of directly demonstrating their developmental abnormalities and the sequelae of pathophysiologic changes caused by these lesions. Combined use of spin echo and gradient reversal echo acquisition techniques allows complete evaluation of cardiac morphology and function in these patients. An new medical and surgical therapies prolong the lives of these patients, the role of MR imaging for physiologic assessment and surgical planning will expand further.

Assessment of quantitative hypertrophy scores in hypertrophic cardiomyopathy: magnetic resonance imaging versus echocardiography

To compare the diagnostic value of spin-echo magnetic resonance (MR) imaging and transthoracic echocardiography in quantitative assessment of the extent of hypertrophy in patients with hypertrophic cardiomyopathy (HCM), we examined 52 consecutive patients with HCM. The Spirito-Maron and Wigle hypertrophy scores were calculated with wall thickness measurements obtained by both imaging modalities. MR imaging yielded complete assessment of anatomic features and allowed calculation of hypertrophy scores in 49 patients (94%). Adequate echocardiograms were obtained in 33 patients (63%) and correlated well with MR imaging for wall thickness measurements and for determination of the two hypertrophy scores (both r> 0.9). MR imaging provided additional information not available by echocardiography in 16 patients (31%). We conclude that the Spirito-Maron and Wigle hypertrophy scores correlated well between echocardiography and MR imaging. Because echocardiography was of insufficient quality for calculating adequate hypertrophy scores in 19 (37%) patients, MR imaging provided the most comprehensive diagnostic information in patients with HCM.

Detection of regional left ventricular asynchrony in obstructive hypertrophic cardiomyopathy by magnetic resonance imaging

Cine magnetic resonance imaging was used to analyze global and regional left ventricular function in seven patients with obstructive hypertrophic cardiomyopathy (HC) and 10 normal subjects. In patients with HC a 38% higher left ventricular mass index (106.4 +/- 20.2 gm/m2 vs 77.0 +/- 16.1 gm/m2, p < 0.005) associated with a lower end-diastolic volume index (44.9 +/- 8.9 ml/m2 vs 58.3 +/- 9.0 ml/m2, p < 0.005) resulted in an 85% higher mass-to-volume ratio (2.4 +/- 0.52 vs 1.3 +/- 0.57, p < 0.0005). Stroke volume did not differ significantly, whereas ejection fraction was higher (80.4% +/- 6.5% vs 65.4% +/- 7.2%, p < 0.0005) in patients with HC. Although early diastolic filling fraction was smaller in patients with HC (61.0% +/- 22.8% vs 68.4% +/- 14.6%), the difference did not reach significance because of substantial variability. In patients with HC (in contrast to normal subjects) the time to maximal wall thickening was shorter (p < 0.025) in the hypertrophied basal region of the ventricle (223 +/- 42 msec) than in the apical region (267 +/- 35 msec), reflecting asynchrony between these regions. Additionally, in patients with HC the standard deviation of the time to maximal wall thickening in the basal region was significantly higher when compared with that of normal subjects (40.0 +/- 24 msec vs 16.9 +/- 17 msec, p < 0.0005), reflecting asynchrony even within one region. Thus magnetic resonance imaging can detect regional left ventricular asynchrony, an important cause of impaired diastolic function, in patients with HC and normal global systolic function.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance imaging compared with angiography in the evaluation of intermediate-term result of coarctation balloon angioplasty

Between July 1986 and December 1990, 24 consecutive adult patients with native coarctation of the aorta underwent balloon dilatation. Their ages ranged from 15 to 55 (mean 25) years. Dissection of the aorta developed in one patient. The remaining 23 patients were restudied by catheterization and magnetic resonance imaging (MRI) 8 to 60 (mean 21) months after dilatation. Both studies were performed between 1 and 180 (mean 40) days of each other. The diameter of the aorta at the site of previous coarctation was measured on angiogram and MRI by two independent observers. The data were compared by means of linear regression analysis. The gradient across the previous coarctation site ranged from 0 to 20 (mean 7 +/- 7.3) mm Hg. The diameter of the aorta at the site of previous coarctation measured on angiogram was 13.7 +/- 3.7 mm and on MRI it measured 13.5 +/- 3.7 mm, with excellent correlation (r = 0.96, SEE = 0.92, p < 0.001). Two patients had small aneurysms 2 cm in diameter demonstrated by angiography and MRI, and two patients developed restenosis, diagnosed correctly by both cardiac catheterization and MRI. This study demonstrates that MRI provides excellent visualization of the anatomy of the aorta and is a good noninvasive method for follow-up of patients undergoing balloon coarctation angioplasty.

Variation in left ventricular regional wall stress with cine magnetic resonance imaging: normal subjects versus dilated cardiomyopathy

We measured the variation of end-systolic wall stress and its relation to regional ejection fraction in short-axis planes through the left ventricle in normal subjects and in patients with dilated cardiomyopathy (DCM) by cine magnetic resonance imaging. There was a gradual increase in end-systolic wall stress but a gradual decrease in ejection fraction from apex to base in normal subjects (14 +/- 6 to 52 +/- 15 kdyne/cm2, 78% +/- 12% to 62% +/- 8%) and in patients with DCM (49 +/- 28 to 130 +/- 30 kdyne/cm2, 40 +/- 18 to 23% +/- 9%). The end-systolic wall stress in patients with DCM was higher than in normal subjects at every level (p < 0.01). We conclude that there is a variation in end-systolic wall stress in both normal subjects and patients with DCM with regional ejection fraction inversely related to regional end-systolic wall stress.

Evaluation of cor pulmonale on a modified short-axis section of the heart by magnetic resonance imaging

Magnetic resonance imaging (MRI) of a modified short-axis section of the heart, in 36 patients with chronic pulmonary diseases, consisting of 19 patients with pulmonary hypertension (PH group; mean pulmonary arterial pressure > or = 20 mm Hg) and 17 patients without pulmonary hypertension (non-PH group) was evaluated to study the configuration of the right ventricle. Parameters of right ventricular hypertrophy, including right ventricular wall thickness (RVWT) and the ratio of RVWT to left ventricular posterior wall thickness (RVWT/LVPWT), with this method were significantly larger in the PH group than in the non-PH group (p < 0.01). RVWT and RVWT/LVPWT correlated well with mean pulmonary arterial pressure (r = 0.90, p < 0.001 and r = 0.89, p < 0.001), total pulmonary resistance (TPR; r = 0.88, p < 0.001 and r = 0.85, p < 0.001), and pulmonary arteriolar resistance (PAR; r = 0.83, p < 0.001 and r = 0.81, p < 0.001). This method of setting a patient in a supine position and slicing with single-oblique sections may seem overly simple compared with Dinsmore's double-oblique short-axis section of the heart, but it is more convenient in practice. These results suggest that a modified short-axis section of the heart by MRI provides valid clinical configurational information concerning the right ventricle on which to base a noninvasive diagnosis of cor pulmonale.

Characterization of acute myocardial infarction by magnetic resonance imaging

The T2-weighted spin-echo technique is currently the most frequently used magnetic resonance imaging (MRI) method to visualize acute myocardial infarction. However, image quality is often degraded by ghost artifacts from blood flow, and respiratory and cardiac contractile motion. To enhance the usefulness of this technique for detailed characterization of infarction, a velocity-compensated spin-echo pulse sequence was tested by imaging a flow phantom, 6 normal subjects and 17 patients with acute myocardial infarction. After preliminary studies were performed in 7 patients to determine optimal imaging parameters, a standardized imaging protocol was used in the next 10. The location of myocardial infarction identified by the electrocardiogram and coronary anatomy was correctly identified in 10 of 10 patients. Distribution of the injury within the left ventricle was clearly visualized, and showed that patients often had a mixture of transmural and nontransmural injury. Heterogenous distribution of signal intensity within the infarction suggested the presence of hemorrhage. Papillary muscle involvement was readily apparent. Signal intensity of the infarction (brightest segment) was increased by 89 +/- 31% compared with the mean of the remote segments. The myocardial/skeletal muscle ratio was significantly (p less than 0.001) increased for the infarction segments compared with that for remote myocardium, allowing quantitative analysis of segmental signal intensity. The MRI wall motion study obtained as part of this protocol demonstrated wall thickening in 58% of the infarction segments and in 6 of 10 patients. This finding suggested the presence of reversibly injured myocardium. In conclusion, the results demonstrate the potential of MRI for detailed tissue characterization after acute myocardial infarction.

Application of cine nuclear magnetic resonance imaging for sequential evaluation of response to angiotensin-converting enzyme inhibitor therapy in dilated cardiomyopathy

Cine nuclear magnetic resonance (NMR) imaging was used to serially measure cardiovascular function in 17 patients with New York Heart Association class II or III heart failure and left ventricular ejection fraction less than or equal to 45% who were treated for 3 months with benazepril hydrochloride, a new angiotensin-converting enzyme inhibitor, while continuing treatment with diuretic agents and digoxin. Interobserver reproducibilities for ejection fraction (r = 0.94, SEE 3.3%), end-systolic volume (r = 0.98, SEE 10.6 ml), end-diastolic volume (r = 0.99, SEE 8.29 ml), end-systolic mass (r = 0.96, SEE 15.4 g), end-systolic wall stress (r = 0.91, SEE 10 dynes.s.cm-5) and end-systolic stress/volume ratio (r = 0.85, SEE 0.13) demonstrated applicability of cine NMR imaging for the serial assessment of cardiovascular function in response to pharmacologic interventions in patients with heart failure. During 12 weeks of treatment with benazepril, ejection fraction increased progressively from 29.7 +/- 2.2% (mean +/- SEM) to 36 +/- 2.2% (p less than 0.05), end-diastolic volume decreased from 166 +/- 14 to 158 +/- 12 ml (p = NS), end-systolic volume decreased from 118 +/- 12 to 106 +/- 11 ml (p less than 0.05), left ventricular mass decreased from 235 +/- 13 to 220 +/- 12 g (p less than 0.05), end-systolic wall stress decreased 29% from 90 +/- 5 to 64 +/- 5 dynes.s.cm-5 (p less than 0.05), end-systolic pressure decreased from 92.6 +/- 3.7 to 78.8 +/- 5.3 (p less than 0.05) and end-systolic stress/volume ratio, a load-independent index of contractility, decreased from 0.83 +/- 0.05 to 0.67 +/- 0.06 (p less than 0.05), demonstrating that improved ejection fraction is due to afterload reduction.

Measurement of right ventricular mass in normal and dilated cardiomyopathic ventricles using cine magnetic resonance imaging

The accurate quantification of right ventricular (RV) mass has eluded conventional imaging modalities. Accordingly, cine magnetic resonance imaging was used for quantification of RV as well as left ventricular (LV) mass in 10 normal subjects and in 10 patients with dilated cardiomyopathy with an LV ejection fraction less than 0.40. Hearts were imaged with 10 mm thick short-axis slices from apex to base with a short echo delay time of 5 ms. Each slice was partitioned into 3 sections: RV free wall, ventricular septum and LV free wall, for calculation of end-diastolic and end-systolic mass and LV:RV free wall ratio. RV end-diastolic mass in normal subjects was 45 +/- 8 g, which was similar to the values determined in previously published postmortem studies, mean 46 g (range 23 to 68). The value determined in patients with dilated cardiomyopathy was higher (50 +/- 11 g), but this difference was not significant. LV:RV free wall ratio in cardiomyopathy (3.6 +/- 1.0) was greater than in normal subjects (2.4 +/- 0.3), because of the greater LV free wall mass in dilated cardiomyopathy, where LV free wall end-diastolic mass was 173 +/- 40 g vs 107.1 +/- 19.9 g in normal subjects (p less than 0.05). RV mass measurements had 6.4 +/- 3.6% interobserver and 7.3 +/- 6.1% intraobserver variability. There were no significant differences between end-diastolic and end-systolic mass measurements. Thus, cine magnetic resonance imaging can reproducibly calculate RV mass. The values in normal subjects correspond to previously reported postmortem values for a population without heart disease.

Future diagnostic methods. A brief look at new technologies and their potential application to equine diagnosis

We live in an age in which highly sophisticated computerized equipment and imaging methods are becoming increasingly available. Demand from clients requires that we as veterinary professionals keep our eyes on the future potential of these technologies for diagnosis and treatment. This article briefly reviews some of the techniques that are just around the corner for the progressive equine practitioner.

Application of interlaced orientation slices in orthogonal planes for system characterization and as a basis for standardized brain sections in multiple-oblique positions

Interlaced acquisition of orthogonal spin-echo orientation slices yields saturated intersection lines, which are available for a system characterization (spatial distortions, slice thickness, chemical shift displacement). Additionally, these scout images contain complete information for a transformation of the gradient coordinate system into the oblique coordinate system of the patient, bearing standardized planes for improved image interpretation and quantitative examinations.

Quantitation of acute myocardial infarct size by nuclear magnetic resonance imaging

Nuclear magnetic resonance (NMR) imaging has shown potential in the detection and characterization of acute myocardial infarction in humans. This study was performed to evaluate the capability of NMR imaging in the measurement of infarct size in patients with recent myocardial infarction. Electrocardiographic (ECG)-gated spin-echo NMR imaging was performed in 26 patients a mean of 9 +/- 3 days (range 5 to 20) after infarction. The imaging technique used provided single-slice, spin-echo (time to echo [TE] = 60 ms) images of the left ventricle in its true short axis, allowing direct correlation of NMR infarct location and size with the region of severe hypokinesia on left ventriculography. In all 20 patients with complete NMR studies, infarct location was correctly identified by using specific, objective criteria. The correlation between the mean infarct volume (29 +/- 11 ml) and the quantitated left ventricular hypokinetic segment (7.5 +/- 4.0 cm) was good (r = 0.84, p = 0.0002), suggesting that NMR imaging of the heart may have a role in the noninvasive assessment of myocardial infarct size in patients.

The value of cine nuclear magnetic resonance imaging for assessing regional ventricular function

Previous nuclear magnetic resonance (NMR) imaging studies to assess left ventricular function have used multiple axial planes, which are compromised by partial volume effects and are time consuming to acquire and analyze. Accordingly, an imaging approach using cine NMR and planes aligned with the true cardiac axes of the left ventricle was developed in views comparable with left ventricular cineangiography. Cine NMR imaging was used to assess regional wall motion and was validated by comparison with biplane left ventricular cineangiography. Fifty-nine patients underwent cineangiographic and NMR studies within 72 h. A poor quality NMR study precluded analysis in 4. leaving a study group of 55 patients (mean age 58 +/- 12: 17 women). Cine NMR movie loops were acquired in two long-axis planes: 1) right anterior oblique plane, parallel to the septum, and 2) four chamber orthogonal plane, perpendicular to the septum (this view is comparable to the angiographic left anterior oblique view). To assess regional wall motion, the left ventricle in both cine NMR and cineangiographic images was divided into five segments and graded on a five point grading scale from 3 for normal through 0 for akinesia and -1 for dyskinesia. Regional wall thickening was used qualitatively to aid in the analysis of wall motion. For the 275 segments compared in the right anterior oblique view, agreement was within one grade in 263 (95.6%) of 275 segments, whereas absolute agreement was observed in 171 (62%) of 275 segments. In the left anterior oblique view, of 200 segments evaluated, agreement within one grade was achieved in 184 segments (92%) and agreement was complete in 132 (66%).(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance imaging of the heart: current status

The favorable technical capabilities of magnetic resonance imaging (MRI) make it well suited for delineating the heart and great vessels. The clinical applications of cardiac MRI have gradually expanded in the past several years. Currently, the most important applications use the modality to provide detailed morphologic information, especially about surgical lesions of the heart. Particularly noteworthy have been applications of MRI in preoperative assessment of patients with certain types of congenital heart disease, cardiac masses, and lesions of the great vessels. Other roles for the modality such as in functional cardiac imaging and nuclear magnetic resonance spectroscopy remain attractive, but these have not yet entered the domain of routine clinical practice.

Retrospective cardiac gating: a review of technical aspects and future directions

The advent of short TR gradient-echo imaging has made it possible to acquire cine images of the heart with conventional whole body MRI scanners. In this paper, technical details of the data collection and image reconstruction process for cine MRI using retrospective cardiac gating are presented. Specifically, the following issues are discussed: data sorting and interpolation; time resolution; motion compensation and phase information; the type of steady state sequence including optimal flip angle; respiratory motion and correction; and the potential of 3D imaging.

Nuclear magnetic resonance imaging of acute myocardial infarction within 24 hours of chest pain onset

The present study was intended to establish the feasibility, safety and usefulness of conventional spin-echo nuclear magnetic resonance (NMR) imaging for the detection of acute myocardial infarction within 24 hours of the onset of chest pain. Monitoring facilities were established in the NMR imaging suite that provided the same level of reliability and safety found in a standard coronary care unit. An imaging protocol was developed that allowed the acquisition of a complete study in 30 minutes while providing useful information about mechanical function and myocardial tissue contrast. Eighteen postthrombolysis patients were imaged within 21 +/- 2 hours of chest pain onset. No patient developed recurrent chest pain or arrhythmias in the NMR imaging suite. Relatively T2-weighted spin-echo images (echo time = 60 ms; repetition time = heart rate) provided interpretable images in 16 patients. Fourteen normal subjects were imaged for comparison. Thirteen of 16 patients had an increase in signal intensity in the region of the infarction. Regional wall thickening was assessed using a floating endocardial centroid technique. Wall motion abnormalities detected by NMR corresponded to those noted by 2-dimensional echocardiography and contrast angiography. Sensitivity, specificity and accuracy for the detection of infarction were 93, 80 and 87%, respectively, when signal intensity and wall thickening abnormalities were combined. In summary, NMR imaging is feasible in patients with acute myocardial infarction within 24 hours of chest pain onset. The study can be conducted safely and it provides useful information about acute myocardial infarction.

Assessment of tissue iron overload by nuclear magnetic resonance imaging

PURPOSE

The ability of stored intracellular iron to enhance magnetic susceptibility forms the basis by which tissue iron can be detected by nuclear magnetic resonance (NMR) imaging. We used this technique to assess myocardial, spleen, and liver iron content in patients with known or suspected iron overload disorders.

PATIENTS AND METHODS

Spin echo NMR images were obtained in 30 patients; 20 had chronic anemias treated by multiple blood transfusions, five had idiopathic hemochromatosis, and five had non-hemochromatotic liver disease with elevated serum ferritin levels and no stainable iron on liver biopsy. The acquisition of oblique images through the short axis of the left ventricle permitted assessment of left ventricular function, while demonstrating the liver and spleen on the same image. Iron content was assessed using a signal intensity ratio of organ (spleen, liver, or myocardium) to skeletal muscle.

RESULTS

In patients with multiple blood transfusions, iron content was highest in liver, followed by the spleen. Significant iron overload was detected in the myocardium of only one patient. Left ventricular systolic wall thickening was normal in patients receiving multiple blood transfusions. Two patients with treated idiopathic hemochromatosis had normal signal intensity ratios, and three untreated patients had evidence of significant deposits of iron in the liver and spleen as indicated by a reduction in signal intensity ratios (0.2 +/- 0.01 and 0.9 +/- 0.01, respectively). Five patients with non-hemochromatotic liver disease and high serum ferritin levels had normal signal intensity ratios by NMR imaging.

CONCLUSION

NMR imaging is a useful method of detecting tissue iron and distinguishing disease due to iron overload. Myocardial iron deposition is a late event, occurring after accumulation of iron in the spleen and liver.

Estimation of the functional and anatomic extent of myocardial infarction using magnetic resonance imaging

This study assesses magnetic resonance (MR) imaging for the evaluation of both the functional and anatomic extent of damage to the left ventricle (LV) from myocardial infarction (MI). This was accomplished by blinded region-of-interest analysis of 36 MR examinations (orthogonal-transaxial, electrocardiographically-gated, multiphasic, single spin-echo) for determination of ejection fraction (EF) and relative MI volume (i.e., percent of total LV myocardial volume). Comparison of the results was then made with a measure of global residual LV function (i.e., score quotient or SQ) derived from segmental scoring of LV wall motion on a two-dimensional echocardiogram (Echo) and with an EF value from a left ventriculogram (LVG), both performed relatively concurrently with MR. Significant (p less than 0.01) overall correlations were noted between MR-EF and both Echo-SQ (r = 0.56) and LVG-EF (r = 0.78), and these relationships were relatively stronger when MI was located in the right coronary artery (RCA) than when it was found in the left anterior descending (LAD) distribution (e.g., MR-EF compared with LVG-EF: r = 0.87, p less than 0.05 for RCA; and r = 0.48, p = NS for LAD). The best expression of relative MI volume appeared to be based upon absolute volume of regionally-thinned LV wall multiplied by a correction factor for its residual contractility and then the addition of a volume correcting for the amount of regional wall thinning by necrosis (i.e., "total-Fxn" MI volume).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac function by magnetic resonance imaging

Gated magnetic resonance imaging of the heart displays cardiac structures with excellent resolution. This ability should be useful for assessment of cardiac physiology where acquisition of systolic and diastolic images is required. In this study, left ventricular ejection fraction was determined in 50 patients from oblique long axis views of the left ventricle using the area length formula. Angulated views were obtained by electronic gradient angulation. For comparison, all patients had monoplane angiocardiography in the RAO position. Forty-five patients were also studied by radionuclide ventriculography. Ejection fractions determined by MRI and angiocardiography were closely correlated (r = 0.90). Correlation between MRI and radionuclide ventriculography was also acceptable (r = 0.79). In addition to global left ventricular function, MR images provide information about regional wall motion. In order to acquire a three-dimensional set of images at various phases of the cardiac cycle, shorter imaging times are mandatory. A new imaging technique with potential for functional studies uses low flip angles, short repetition times and gradient refocused echoes. Up to 40 images can be obtained within one cardiac cycle. When displayed in a looped fashion, visual assessment of cardiac motion, intracardiac blood flow, and systolic wall thickening is possible. Potential advantages of functional studies by MRI are the concomitant acquisition of anatomical information and the three dimensional frame of reference.

Magnetic resonance imaging of the heart compared with anatomic and ultrasonographic data

The authors present a correlation study between the anatomy of the heart and its appearance with magnetic resonance imaging (MRI) and ultrasonography (US). Six hearts were studied by MR, then sliced along the same planes. The results are presented and compared with the data obtained in volunteers by MRI and ultrasonography. The correlation between the MRI of isolated hearts and their anatomic slices is excellent, the thinnest anatomic details are reproduced. The use of double oblique slices provides incidences similar to those of ultrasonography. The same incidences can be obtained in vivo. The morphologic study of the heart by these imaging techniques is thus very precise, as well as the study of cardiac volumes.

Preoperative evaluation of the thoracic aorta using MRI and angiography

The ability of ECG-gated magnetic resonance imaging (MRI) to evaluate disease of the thoracic aorta compared with angiography was prospectively assessed in 28 patients. MRI identified abnormalities in all patients, with confirmation at operation in 22 (79%) and by angiography alone in all 28. In 20 of the patients, MRI correctly diagnosed 20 of 21 aneurysms of the thoracic aorta (6 dissecting, 4 saccular, 10 fusiform), but 1 surgically proven fusiform aneurysm was categorized as an enlarged aortic dissection based on both MRI and angiographic findings. One dissection and 1 fusiform aneurysm were shown by MRI only. Coarctation of the aorta was identified in 4 patients. Ascending aortic enlargement and left ventricular hypertrophy were identified by MRI in 4 patients with aortic stenosis. In 7 patients (25%), MRI provided additional important information not shown by angiography and in 1 patient, the MRI findings resulted in a change in the surgical approach. In 14 of 28 patients (50%), angiography was necessary for definitive preoperative evaluation of the aortic valve, the coronary arteries, or the brachiocephalic vessels. MRI was a useful noninvasive supplement to angiography for the preoperative assessment of thoracic aortic disease.

Quantitation of cardiac dimensions from ECG-synchronized MRI studies

The ability to measure the heart is useful for evaluation of a wide variety of conditions. Magnetic resonance imaging (MRI) has a number of characteristics that make it potentially one of the best methods for obtaining cardiac measurements, in particular its ability to produce uniformly high-quality images in any desired plane. It is important that techniques for measurement be standardized so that methods are reproducible from patient to patient, allowing normal standards to be established, and from examination to examination in the same patient, so that serial measurements accurately reflect change in cardiac status.

Correlation between magnetic resonance imaging of the heart and cardiac anatomy

An understanding of anatomy forms the cornerstone for accurate interpretations of pathologic alterations. In this article, we present cardiac magnetic resonance images and the corresponding sections of normal hearts obtained at autopsy and cut in planes parallel and perpendicular to the ventricular septum in addition to the standard anatomic orthogonal planes (coronal, sagittal, and transverse). This correlation demonstrates the ability of magnetic resonance imaging to display cardiac anatomy accurately and noninvasively. Because magnetic resonance imaging provides excellent contrast between flowing blood and cardiac walls and has the capacity to provide direct images in multiple planes without inherent difficulties, this procedure has advantages over other currently available imaging techniques.

Techniques of non-orthogonal magnetic resonance imaging and its clinical application

A technique to obtain non-orthogonal magnetic resonance (MR) images in the body has been developed using a simple three-dimensional model (3-DM). Images were obtained with multiple non-orthogonal planes, without subjecting patients to uncomfortable oblique positions. Eighty-two patients were studied using non-orthogonal planes. Euler angle determinations (EAD) were developed for different anatomical locations as well as for multiple clinical situations. One or all three Euler angles were changed using the EAD to define any plane of orientation relative to reference orthogonal frame. In a series of 12 patients for postoperative evaluation of Mustard and Senning procedure, the demonstration of anastomotic site was superior with angled coronal planes when compared to the routine coronal views in 83% of the studies. With the use of EAD, acquisition time for non-orthogonal planes can be reduced. 3-DM aids in the understanding of the Euler angles and leads to multiple non-orthogonal planes.