MR Imaging of Congenital Heart Disease

MRI is useful for demonstrating the anatomy of various congenital cardiac lesions and plays an important role in the diagnosis of congenital cardiac lesions. Its large field of view and unlimited imaging planes enable the depiction of complex lesions, the complicated three-dimensional relations of the cardiac chambers and anomalies of the central pulmonary arteries, the systemic and pulmonary veins, and aorta. We describe the normal MR anatomy and MR imaging findings of a variety of congenital pathologies of the heart, in order to provide a better understanding and facilitate the interpretation of the MR features of various congenital heart diseases.

(31)P MR Spectroscopic Measurement of Intracellular pH in Normal Human Hearts

PURPOSE: To assess the usefulness of intracellular pH (pHi), calculated by determining the shift of a high-energy metabolite such as inorganic phosphate (Pi) or gamma-ATP after performing MRS with ECG-gated two-dimensional 31P CSI (chemical shift imaging), as a parameter for the overall state of the intracellular milieu. MATERIALS AND METHODS: Proton decoupled 31P CSI was performed on a 1.5-T scanner using a (1)H-(31)P dual-tuned surface coil. Cardiac MRS data were obtained from eight normal volunteers aged 24-32 years with no history of heart disease. From the spectra obtained from several regions of the heart, peak position and peak area were estimated. The metabolic ratios of alpha-, beta-, gamma-ATP, PCr, Pi, phosphodiester and diphosphoglycerate were calculated, and pHi was estimated from the chemical shift of Pi and gamma-ATP resonance. We then compared the data for the anterior myocardium with those previously published. RESULTS: The major phosphorous metabolites identified in these human hearts were as follows: PCr, at -0.1 to +0.1 ppm; three phosphate peaks from ATP, with a chemical shift centered at about -2.7 ppm (gamma-ATP), -7.8 ppm (alpha-ATP), and -16.3 ppm (beta-ATP); and phosphodiester (PDE) at 2-3 ppm, inorganic phosphate (Pi) at 4.5-5.4 ppm, and diphosphoglycerate (DPG) at 5.4-6.3 ppm. The PCr/beta-ATP ratio was 2.20+/-0.17 and the PDE/beta-ATP ratio, 1.04+/-0.09. pHi readings were 7.31+/-0.23 (calculated by the shift of Pi) and 6.81+/-0.20 (calculated by the shift of gamma-ATP). Pi/PCR was 0.539, a ratio higher than that mentioned in previously published reports. CONCLUSION: The measurement of intracelluar metabolism was affected by various kinds of factors. We believe, however, that pHi readings indicate the overall state of the cardiac intracelluar milieu. An unexpected pHi readings, seen at MRS, may reflect errors in the MR procedure itself and, or in the alanytical method.

Evaluation by Contrast-Enhanced MR Imaging of the Lateral Border Zone in Reperfused Myocardial Infarction in a Cat Model

OBJECTIVE: To identify and evaluate the lateral border zone by comparing the size and distribution of the abnormal signal area demonstrated by MR imaging with the infarct area revealed by pathological examination in a reperfused myocardial infarction cat model. MATERIALS AND METHODS: In eight cats, the left anterior descending coronary artery was occluded for 90 minutes, and this was followed by 90 minutes of reper-fusion. ECG-triggered breath-hold turbo spin-echo T2-weighted MR images were initially obtained along the short axis of the heart before the administration of contrast media. After the injection of Gadomer-17 and Gadophrin-2, contrast-enhanced T1-weighted MR images were obtained for three hours. The size of the abnormal signal area seen on each image was compared with that of the infarct area after TTC staining. To assess ultrastructural changes in the myocardium at the infarct area, lateral border zone and normal myocardium, electron microscopic examination was performed. RESULTS: The high signal area seen on T2-weighted images and the enhanced area seen on Gadomer-17-enhanced T1WI were larger than the enhanced area on Gadophrin-2-enhanced T1WI and the infarct area revealed by TTC staining; the difference was expressed as a percentage of the size of the total left ventricle mass (T2= 39.2 %; Gadomer-17 =37.25 % vs Gadophrin-2 = 29.6 %; TTC staining = 28.2 %; p < 0.05). The ultrastructural changes seen at the lateral border zone were compatible with reversible myocardial damage. CONCLUSION: In a reperfused myocardial infarction cat model, the presence and size of the lateral border zone can be determined by means of Gadomer-17- and Gadophrin-2-enhanced MR imaging.

MR Imaging of Congenital Heart Diseases in Adolescents and Adults

Echocardiography and catheterization angiography suffer certain limitations in the evaluation of congenital heart diseases in adults, though these are overcome by MRI, in which a wide field-of view, unlimited multiplanar imaging capability and three-dimensional contrast-enhanced MR angiography techniques are used. In adults, recently introduced fast imaging techniques provide cardiac MR images of sufficient quality and with less artifacts. Ventricular volume, ejection fraction, and vascular flow measurements, including pressure gradients and pulmonary-to-systemic flow ratio, can be calculated or obtained using fast cine MRI, phase-contrast MR flow-velocity mapping, and semiautomatic analysis software. MRI is superior to echocardiography in diagnosing partial anomalous pulmonary venous connection, unroofed coronary sinus, anomalies of the pulmonary arteries, aorta and systemic veins, complex heart diseases, and postsurgical sequelae. Biventricular function is reliably evaluated with cine MRI after repair of tetralogy of Fallot, and Senning's and Mustard's operations. MRI has an important and growing role in the morphologic and functional assessment of congenital heart diseases in adolescents and adults.

Value of Cardiac MR Imaging for the Diagnosis of Arrhythmogenic Right Ventricular Dysplasia:Comparison of Clinical and MR Imaging Diagnostic Grades

PURPOSE: To evaluate the usefulness of cardiac MRI in the diagnosis of clinically suspected arrhythmogenic right ventricular dysplasia (ARVD). MATERIALS AND METHODS: Between February 1991 and January 1999, 15 patients [M:F=13:2, aged 2 -60 (mean, 37 -7) years] with clinically suspected ventricular arrhythmia due to unknown causes underwent MR imaging. Using a CP body array coil and the single slice breath hold technique, ECG-gated T1-weighted images were obtained. In all patients, these were acquired transaxially from the diaphragm to the aortic arch and along the true short and long axis, and in two, coronal images were obtained. On the basis of clinical and MRI diagnostic criteria, ARVD was classified as one of four types. The significance of differences in diagnostic grades between clinical and MRI criteria was determined using Wilcoxon's signed rank test. RESULTS: According to both clinical and MRI criteria, it was highly probable that three of the 15 patients had ARVD. In eleven, both sets of criteria indicated the same diagnostic grade. Wilcoxon's signed rank test indicated no significant differences in diagnostic grades between clinical and MRI criteria (p > 0.05). CONCLUSION: For the diagnosis or exclusion of ARVD, MR imaging is a useful modality.

Value of Cardiac MR Imaging for the Diagnosis of Arrhythmogenic Right Ventricular Dysplasia:Comparison of Clinical and MR Imaging Diagnostic Grades

PURPOSE: To evaluate the usefulness of cardiac MRI in the diagnosis of clinically suspected arrhythmogenic right ventricular dysplasia (ARVD). MATERIALS AND METHODS: Between February 1991 and January 1999, 15 patients [M:F=13:2, aged 2 -60 (mean, 37 -7) years] with clinically suspected ventricular arrhythmia due to unknown causes underwent MR imaging. Using a CP body array coil and the single slice breath hold technique, ECG-gated T1-weighted images were obtained. In all patients, these were acquired transaxially from the diaphragm to the aortic arch and along the true short and long axis, and in two, coronal images were obtained. On the basis of clinical and MRI diagnostic criteria, ARVD was classified as one of four types. The significance of differences in diagnostic grades between clinical and MRI criteria was determined using Wilcoxon's signed rank test. RESULTS: According to both clinical and MRI criteria, it was highly probable that three of the 15 patients had ARVD. In eleven, both sets of criteria indicated the same diagnostic grade. Wilcoxon's signed rank test indicated no significant differences in diagnostic grades between clinical and MRI criteria (p > 0.05). CONCLUSION: For the diagnosis or exclusion of ARVD, MR imaging is a useful modality.

The Role of MR Imaging in Determination of Atrial Situs in Congenital Heart Disease with Situs Ambiguus

PURPOSE: to assess the role of MR imaging in determining of the atrial situs in complicated congenital heart disease with situs ambiguus. MATERIALS AND METHODS: In order to classify the situs, the morphology of atrial appendages, on bronchial length ratio, the superior-inferior relation of the pulmonary artery (PA) and main bronchi on each side, and splenic abnormality were evaluated by MR imaging in 22 patients (12 boys and 10 girls), and the results were compared. RESULTS: In all patients, the superior-inferior relation of the PA and main bronchi tended to lateralize, and in one, bronchial length ratio was not consistent with the relation between the PA and bronchus. Bronchial and atrial situs, as determined by appendage morphology, were consistent in ten of 13 right isomerism patients, and in only three of nine of these with left isomerism. All 13 right isomerism patients, classified by the relation of the PA and main bronchi, showed asplenia, whereas eight of nine of these with left isomerism had polysplenia. CONCLUSION: In the assessment of atrial situs by MR imaging, the positional relation of a bronchus and the PA, bronchial length ratio, and splenic abnormality are constant and reliable. The accuracy of classification of situs on the basis of atrial appendage morphology is, however, limited.

Computer-Assited Instruction : MR Imaging of Congenital Heart Disease

PURPOSE: To develop a software program for computer-assisted instruction on MR imaging of congenital heart disease for medical students and residents to achieve repetitive and effective self-learning. MATERIALS AND METHODS: We used a film scanner(Scan Maker 35t) and IBM-PC(486 DX-2, 60 MHz) for acquisition and storage of image data. The accessories attached to the main processor were CD-ROM drive(Sony), sound card(Sound blaster-Pro), and speaker. We used software of Adobe Photoshop(v 3.0) and Paint Shop-Pro(v 3.0) for preprocessing image data, and Paint brush from Microsoft Windows 3.1 for labelling. The language used for programming was Visual basic(v 3.0)from Microsoft Corporation. RESULTS: We developed a software program for computer-assisted instruction on MR imaging of congenital heart disease as an effective educational tool.